WO2000016283A1

WO2000016283A1 - Generation of electrostatic voltage potentials for rfid/eas using piezoelectric crystals

Info

Publication number: WO2000016283A1
Application number: PCT/US1999/020801
Authority: WO
Inventors: Victor Vega; John Bernhard Hattick; Charles L. Zimnicki
Original assignee: Motorola Inc.
Priority date: 1998-09-11
Filing date: 1999-09-10
Publication date: 2000-03-23
Also published as: AU6245899A

Abstract

A contactless programmable electrostatic RFID system (100) comprises a reader/encoder (101) with an exciter (201) and a transceiver (102). Using the high quality 'Q' resonator circuit, high voltages can be efficiently produced to generate required electrostatic exciter signals. The combination of a high quality 'Q' piezoelectric element and a capacitor in series resonance is connected to switches with switching logic to cause the flow of alternating current through the resonator combination at the resonant frequency. The exciter (201) in this way converts a low voltage, low current DC input signal into a high voltage, lower current output signal using only the piezoelectric element and a capacitor. The low power consumption of this type of exciter facilitates a battery-operated implementation.

Description

GENERATION OF ELECTROSTATIC VOLTAGE POTENTIALS FOR RFID/EAS USING PIEZOELECTRIC CRYSTALS

Field of the Invention The invention generally relates to radio frequency identification

(RFID) technology, and more particularly relates to contactless programmable electrostatic RFID technology.

Background of the Invention Radio frequency identification (RFID) technology allows identification data to be transferred remotely which provides a significant advantage in identifying persons, articles, parcels, and others. In general, to access identification data stored in a RFID transceiver (also referred to as a tag or a transponder) remotely, a RFID reader/encoder generates an energy field to activate the RFID transceiver and subsequently to retrieve data stored in the transceiver unit from a distance. The data retrieved is then processed by a host computer system to identify the person or article that is associated with the transceiver. While a transceiver that derives its power from the energy field is known as a passive transceiver, a transceiver that has its own power source is known as an active transceiver. RFID technology has found a wide range of applications including tracking, access control, theft prevention, security, etc.

For some applications, RFID technology is more preferable than magnetic strip technology, which also finds applications in a few of the areas above. The reason is systems employing RFID technology can store a lot more information than magnetic stripe technology. Magnetic stripe technology as commonly deployed has very limited memory capability. Moreover, magnetic stripe technology requires relatively high maintenance (e.g., heads cleaning). Furthermore, magnetic stripe technology is prone to moisture damages, dust damages, magnetic field damages, etc.

RFID technology should be distinguished from radio identification (Radio ID) technology that uses ordinary radio waves, or more precisely far field electromagnetic (EM) waves that are also known as radiation waves. Far field means the distance between the transceiver and reader is great compared to the wavelength of the EM carrier signal used. An example of Radio ID technology is the identify friend or foe (IFF) systems used with military aircraft. Far field EM waves have a field strength that varies inversely with the distance involved. In contrast, conventional RFID technology is based upon inductive coupling utilizing magnetic field waves. Conventional RFID technology operates in the near field where the operating distance is far less than one wavelength of the EM field. Unlike far field radio waves, the magnetic field strength is approximately proportional to the inverse cube of the distance from the source. In inductance-based RFID technology, an electromagnetic field is generated for use both as a power source for the transceiver and for transferring data and clock information between the reader/encoder and transceiver. Magnetic fields are generated by causing an alternating current to flow in coils that typically have multiple turns. Generally, these coils are wire wound or etched metal. This adversely impacts the costs, manufacturability, and packaging flexibility of inductance-based RFID technology. Due to the prohibitive costs and relatively high degree of manufacturing difficulty, electromagnetic RFID technology is not practical in high volume/low cost disposable applications. The bulky packaging, which is typical for electromagnetic RFID technology, further limits its application to those where thickness is not of primary importance.

For applications that require extended operating range and high sensitivity, high potential exciter circuits are typically required for electronic article surveillance (EAS) and RFID readers. In general, these conventional high voltage exciter circuits are designed using tuned inductors and capacitors that typically require expensive toroids and low- loss Litz wire. As a result, the conventional high voltage potential exciter circuits are expensive and bulky. Moreover, the conventional exciter circuits are also very inefficient in terms of the voltage they can generate. Furthermore, the magnetic fields created by conventional high-voltage potential exciter circuits may be undesirable for various reasons. Thus, a need exists for an inexpensive and compact apparatus, system, and method to generate high-voltage for RFID and EAS exciter signals efficiently without the associated magnetic fields.

Additionally, an EAS system is designed to prevent article thefts and is widely used in retail stores as well as libraries. An EAS system is typically implemented using magnetic stripe technology wherein a magnetic stripe is inserted into or attached to an article. Operationally, an EAS reader/detector constantly transmits a radio frequency (RF) activation signal. When the magnetic stripe receives the RF activation signal, it becomes activated and sends back the stored information. Accordingly, unless the magnetic stripe has been removed from the article or deactivated by the attendant, it triggers the reader/detector to sound an alarm, which alerts the attendant of a potential theft. In designing an EAS system, operating range and responsiveness (i.e., read time) are the two primary considerations. Operating range is important to accommodate the vast differences in sizes of parcels, baggage, etc. Operating responsiveness is important because a person attempting to illegally remove an article from a secured area will not likely pause when passing through the sensing area of the surveillance system to allow the EAS system time to read the surveillance tag. While magnetic stripe based EAS systems provide adequate read time and operating range, the stored authorization information can be erased if the magnetic stripe is subject to external magnetic fields. Hence, magnetic stripe based EAS systems are limited in their applications. Conventional RFID systems are too expensive, bulky, and limited in operating range to be used in EAS applications. Moreover, conventional RFID systems generally have a relatively low quality (hereinafter 'Q') factor (e.g., in the 10's) and therefore low detection sensitivity. Accordingly, conventional RFID systems are currently not suitable for EAS applications. Furthermore, due to the amount of data information transfer involved, the read time of conventional RFID systems is also not suitable for EAS applications.

Thus, a need also exists for a RFID apparatus, system, and method having the operating range, responsiveness, robustness, and sensitivity required for EAS applications that is also inexpensive, compact, and easy to implement.

Brief Description of the Drawings

FIG. 1 is a diagram illustrating a typical RFID system implementing the present invention.

FIG. 2 is a block diagram of an RFID reader illustrated in FIG. 1. FIG. 3 is a block diagram of the transceiver illustrated in FIG. 1. FIG. 4 is a block diagram of the analog interface module in the transceiver illustrated in FIG. 3.

FIG. 5 depicts a signal waveform from the reader (in write mode) illustrated in FIG. 2.

FIG. 6 depicts a signal waveform from the transceiver illustrated in FIG. 3.

FIG. 7 is a diagram of the exciter circuit illustrated in FIG. 2. FIG. 8 is a diagram of the resonator circuit illustrated in FIG. 7. FIG. 9A is a diagram of the amplitude modulator illustrated in FIG. 7. FIG. 9B is a schematic diagram of the damping circuit 902 illustrated in FIG. 9A.

FIG. 10 is a block diagram of an EAS reader implementing the present invention.

FIG. 11 is a block diagram of exciter 1001 illustrated in FIG. 10. FIG. 12 is a block diagram of an RFID/EAS reader for providing RFID and EAS functionality.

FIG. 13 is a block diagram of the RFID/EAS reader illustrated in FIG. 1.

FIG. 14 is a diagram of the detector circuit illustrated in FIG. 13 using a series resonance circuit. FIG. 15 is a diagram of an alternate detector circuit illustrated in

FIG. 13 using a series resonant circuit.

FIG. 16 is a diagram of the detector circuit illustrated in FIG. 13 using a parallel resonance circuit. FIG. 17 is a block diagram of an electrostatic EAS reader implementing the present invention.

Detailed Description of the Preferred Embodiments In the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. Well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present invention. While the following detailed description of the present invention describes its application to passive transceivers (i.e., without its own power source), it is to be appreciated that the present invention is also applicable to active transceivers (i.e., with its own power source). A first aspect of the detailed description of the electrostatic radio frequency identification (RFID) system invented by the applicant is provided below. An advantage of the first aspect of this invention is an improvement in the detection range between reader and transceiver by using an exciter that has a piezoelectric-based resonator circuit with a high quality factor 'Q' to generate a high voltage potential. This exciter circuit is also used for theft prevention or electronic article surveillance (EAS) as an additional benefit of a RFID system used for merchandising. Disposable transceivers are attached to merchandise and removed or deactivated at its purchase. A customer walking past the reader with an intact transceiver causes the transceiver to send its carrier signal. This signal is detected over an extended range and is used to trigger an alarm. As an alternate embodiment, an electrostatic EAS system implementing the present invention is also described below.

An advantage of this invention is to provide an enhanced EAS operating range for the electrostatic RFID/EAS system (i.e., between a reader and a transceiver) by having a high quality 'Q' resonator circuit in the exciter of the reader. This resonator circuit is used to generate a high voltage signal to activate RFID/EAS transceivers. The high quality 'Q' resonator circuit and the high voltage signal generated enhance the EAS operating range. Disposable transceivers are attached to merchandise and removed or deactivated at its purchase. An article in proximity of the reader with an enabled transceiver is interrogated. In turn, the enabled transceiver sends a data carrier signal. This signal is detected over an extended range and is used to trigger an alert. In short, the RFID/EAS reader can function in both RFID mode and EAS mode. In RFID mode, data information stored in the transceiver's memory is sent to the reader. In EAS mode, an alarm signal is sent to the reader. As an alternate embodiment, an electrostatic EAS system implementing the present invention for providing an enhanced EAS operating range is also described below. The present invention relates to an enhanced range electrostatic

RFID system 100, as depicted in FIG. 1 , comprising a reader/encoder 101 A (reader) a transceiver 102 and an optional host computer 103. Reader 101 A acts similar to a base station for transceivers 102. In one embodiment, the reader may also be connected to host computer 103, which may store a database. Alternatively, the reader 101 A may be connected to an audio alarm or a visual alarm (e.g., light emitting diodes (LED)) which are not illustrated in FIG. 1. The contactless data transfer is based on radio-frequency electric (electrostatic) fields rather than on electromagnetic fields for substantial cost and size advantages. FIG. 2 depicts an exemplary reader 101 A which is operated by an optional processor 204 connected to the optional host computer 103 storing a database and an external alarm 1004A for indicating an alarm condition. Processor 204 may be a microprocessor, microcomputer or other microcontroller device. Processor 204 initiates write (data programming) or read (query) operations to transceiver 102 by first causing exciter 201 to generate an electrostatic field between two conductive plates (electrodes), exciter electrode 205 and another which may be grounded in a monopole configuration of reader. The electrostatic field allows exciter signals to be transmitted to power and activate transceiver 102. Generating an electrostatic field between two floating electrodes is called "dipole operation". Conversely, generating an electrostatic field between an electrode and a virtual ground electrode is called "monopole operation". A virtual ground means a low impedance capacitive coupling at the operating frequency to ground. Other parts of reader 101 A include receiver 202 that receives electrostatic read data signals from transceiver 102 via receiver electrodes 206. An electrostatic read data signal received is then sent to demodulator 203 that demodulates the signal before passing it on to processor 204. In general, transceiver 102 transmits a read signal to reader 101 A in response to an exciter signal from reader 101. In other words, data transfer between reader 101 A and transceiver 102 is established through capacitive coupling between the reader electrodes and the transceiver electrodes with the air space in between forming the dielectric medium. In the preferred embodiment, the exciter signal transmitted from reader 101 A has an exciter (carrier) frequency of 125 kHz. Conversely, the read signal received from transceiver 102 has a carrier frequency of 62.5 kHz. It should be clear to a person of ordinary skill in the art that other carrier frequencies can also be used. The exciter frequency is used as a master clock signal for transceiver 102. Transceiver 102 generates a derivative, through division or multiplication, of the master clock signal for use in its operations such as writing data into its electrically erasable memory, if applicable, and retrieving data from it for communication back to reader 101. In so doing, communication is facilitated. FIG. 3 is a block diagram of transceiver 102. The transceiver 102 includes an analog interface module 301 , a bitrate generator 303, a write decoder 304, an optional charge pump 305, an input register 306, a controller 307, a mode register 308, a modulator 309, a memory 310, and electrodes 314 and 316. Transceiver 102 is usually implemented on a silicon chip. Electrodes 314 and 316 receive electrostatic exciter signals from reader 101 A and send electrostatic read signals back to reader 101. Electrodes 314 and 316 are coupled to the analog interface module at nodes 312 and 313. In this manner all signals received or transmitted by transceiver 102 pass through analog interface module 301. For optimum electrostatic performance, it is desirable to minimize the parasitic capacitance between electrodes 314 and 316. In one embodiment, the capacitance is kept to a minimum (e.g., 5pF or less). Internal bypass capacitance is provided in analog interface module 301 to serve as power storage. Controller 307 can deactivate transceiver 102 as needed. Controller 307 may a simple control circuit made of discreet logic components on a printed circuit board or an integrated circuit. The deactivation of modulator 309 results in the deactivation of transceiver 102 as a whole which is desirable, for example, when authorization is granted to allow a package or_ merchandise to be removed from a secured area implementing an EAS system. Controller 307 controls the functionality of transceiver 102 in conjunction with analog interface module 301. Controller 307 is coupled to nearly all components of transceiver 102 except for the electrodes and pads.

Memory 310 may be a non-volatile memory such as an electronically erasable programmable read only memory (EEPROM) that retains its information when power is cut off. If an EEPROM is used, charge pump 305 may be required in order to boost the voltage of the transceiver power supply in order to write data into the EEPROM. In RFID mode, controller 307 reads data information stored in memory 310 and sends the data information to the analog interface module 301 for communicating over transceiver electrodes 314 and 316. In EAS mode, only an alarm signal is sent to analog interface module 301 for communicating over electrodes 314 and 316.

Input register 306 temporarily stores information that is to be written into memory 310 because it takes time for charge pump 305 to achieve the required voltage. In any case, storing data into input register 306 allows controller 307 to also process other tasks for transceiver 102 while waiting for charge pump 305.

Mode register 308 reads configuration information for transceiver 102 from memory 310 and provides this to controller 307.

Write decoder 304 analyzes a data sequence being received by transceiver 102 and determines whether the transceiver can go into a write mode or whether it needs to remain in a read mode.

Modulator 309 prepares data read from memory 310 for transmission by transceiver 102. Modulator 309 encodes and modulates the data read from memory 310. When in proximity of reader 101 , transceiver 102 first receives the exciter signal. In the preferred embodiment, the exciter signal generated by reader 101 A has an exciter frequency of 125 kHz. After receiving the exciter signal, the transceiver 102 derives a square wave based on the exciter signal at the exciter frequency, which is used as a master clock signal for the transceiver 102. In so doing, transmitted information received by transceiver 102 is synchronized with the clock signal. This obviates the need for generating a clock with a duplicate clock oscillator and also the need for synchronizing the data and clock using phase-locked loop techniques.

Bitrate generator 303 receives as input the clock signal having a frequency of 125 kHz from a clock extraction circuit (not shown). The clock extraction circuit derives a clock signal having a frequency of 125 kHz from the exciter signal that serves as a master clock signal for transceiver 102. Bitrate generator 303 generates the data transfer rate at which data is transferred from/to memory 310 via controller 307 during a read or write mode, respectively. Bitrate generator 303 derives its data transfer rate from the exciter frequency of 125 kHz. The data transfer rate is provided to controller 307. In the preferred embodiment, bitrate generator 303 can be programmed to operate at either 125 kHz/16 (7.81 kHz) or 125 kHz/32 (3.91 kHz). Modulator 309 modulates the data information retrieved from memory 310 in phase shift keying (PSK) at a second carrier frequency (e.g., 62.5 kHz). This modulated signal is communicated to reader 101 A via electrodes 314-316. FIG. 4 is a block diagram of analog interface module 301 that performs multiple functions when receiving and sending electrostatic signals. Analog interface module 301 performs the power supply management function for RFID/EAS transceiver 102. Analog interface module 301 extracts a power signal from an exciter signal received from electrodes 314 and 316. Additionally, it performs clock extraction in clock extraction circuit 403 in order to provide a clock signal (having a first carrier frequency (e.g., 125 kHz)) to the other components of transceiver 102. In RFID write mode, analog interface module 301 also receives a data stream from the exciter signal. Gap detector circuit 405 and write decoder 304 analyze the data stream received in order to determine if transceiver 102 should perform a read operation or a write operation and communicates the results of the analysis to controller 307.

FIG. 5 depicts a waveform write sequence W1 transmitted by exciter 201. The waveform is controlled and timed by processor 204. The first part is an undampened sinusoid having a carrier frequency F1 of 125 kHz. It is followed by a zero amplitude start gap, which indicates to the transceiver 102 that a write command sequence may follow. This sequence is composed of a pulse stream representing logic zeros and ones, separated by zero amplitude field gaps between data bits. In transceiver 102, exciter frequency F1 is divided by two, resulting in a transceiver carrier frequency F2 of 62.5 kHz for modulation back to the reader 101. It should be clear to a person of ordinary skill in the art that F2 can be derived from exciter frequency F1 through either division (in which case F2<F1) or multiplication (in which case F2>F1 ).

FIG. 6 illustrates a read waveform W2 with a carrier frequency F2 of 62.5 kHz. This frequency is amplitude modulated by modulator 309 to represent the data sequence retrieved from memory 310 for transmission back to reader 101 A via electrodes 314 and 316. FIG. 7 illustrates an exemplary embodiment of exciter circuit 201. In short, a high 'Q' resonator circuit allows exciter 201 to generate a high electrostatic field for generating the exciter signal so that the communication range is improved. As shown in FIG. 7, exciter circuit 201 comprises voltage supply circuit 701 , resonator circuit 702, amplitude modulator 703, and feedback circuit 704. Voltage supply circuit 701 generates a regulated voltage Vr that is used to power resonator circuit 702. Voltage supply circuit 701 receives as input the output of feedback circuit 704 which is used by voltage supply circuit 701 to determine whether to increase or decrease the amplitude of voltage Vr. In other words, feedback circuit 704 maintains the amplitude of the high-voltage carrier frequency signal in an amplitude range. In general resonator circuit 702, which has a high quality 'Q' factor, generates and amplifies a high- voltage carrier frequency signal in response to the regulated voltage Vr. The high-voltage signal generated by resonator circuit 702 is provided as input to feedback circuit 704 which rectifies the voltage signal and reduces its amplitude to a more manageable level before supplying it as a feedback control input voltage to voltage supply circuit 701. Without this feedback control feature, the extremely high Q piezoelectric element is subject to self-destruction as a result of the excess energy generated. Amplitude __ modulator 703 receives as inputs a data sequence from processor 204 and the high voltage signal from resonator circuit 702. The data sequence is used to amplitude modulate the high-voltage signal from resonator circuit 702. In RFID mode, processor 204 sends a data sequence that allows amplitude modulator 703 to output an undamped and continuous exciter signal to exciter electrode 205. Conversely, in EAS mode, processor 204 sends a data sequence that causes amplitude modulator 703 to output a pulsed exciter signal to exciter electrode 205. Such a pulsed signal has the gaps and pulses as described in FIG. 5. Reference is now made to FIG. 8 illustrating an exemplary embodiment of resonator circuit 702. At the heart of resonator circuit 702 is a series resonant tank which comprises high voltage capacitor 832 and high quality 'Q' piezoelectric element 830 (having a 'Q' of about 10,000- 40,000) to generate a high-voltage excitation signal. In other words, a high-voltage amplitude is generated at the carrier frequency. Piezoelectric element 830 may be a piezoelectric quartz crystal, a piezoelectric lithium niobate crystal, a piezoelectric ceramic resonator, or others. This resonant combination maximizes the voltage at node 842 that is the junction of capacitor 832 and piezoelectric element 830. Node 842 is connected to amplitude modulator 703 and feedback 704. Resonator circuit 702 is controlled by control voltage Vr that is provided by voltage supply circuit 701. Control voltage Vr is typically 5-12 V DC. Capacitor 832 and piezoelectric element 830 are the only high-voltage components in the resonator circuit. The two terminals of the piezoelectric element 830 are connected to nodes 840 and 842, respectively. Node 842 is in turn connected to a terminal of capacitor 832, a resistor 834, an amplitude modulator 703 and a feedback 704. The other terminal of capacitor 832 is connected to node 844. Other components of resonator circuit 702 include two P-channe! MOSFETs 851 and 852, each having a source, a gate, and a drain. P- channel MOSFETs 851 and 852 have their sources S1 , S2 connected to Vr (about 5 Volts) and their drains D1 , D2 connected to nodes 840 and 844, respectively. Resonator circuit 702 further includes two N-channel MOSFETs 853 and 854, each having a source, a gate, and a drain. N- channel MOSFETs 853 and 854 have their sources S3, S4 connected to ground and their drains D3, D4 connected to terminals 840 and 844, respectively. Node 846 is connected to resistor 834 and to capacitors 836 and 838. Capacitor 836 is in turn connected to switching logic circuit 860. Capacitor 838 is in turn connected to ground. Switching logic circuit 860 controls the gates of MOSFETs 851 and 854 directly and controls the gates of MOSFETs 852 and 853 via logic inverter 862. The combination of resistor 834 and capacitor 838 functions as a frequency sensor which is coupled back to the switching logic circuit 860 via capacitor 836. In this way, the feedback loop is closed for resonator circuit 702. The frequency of resonator circuit 702 is determined by piezoelectric element 830.

MOSFETs 851 , 852, 853 and 854 operate in switching mode with no bias current required. As such, MOSFETs 851-854 may be illustrated as switches in FIG. 8. Depending on the voltage at node 846, nodes 840 and 844 are at Vr and ground in state ST1 , respectively, or at ground and Vr in state ST2. In other words, the polarity at nodes 840 and 844 alternately switches between Vr and ground. In short, combination of MOSFETs 851-854, switching logic circuit 860, and logic inverter 862 combine to form a switching circuit.

As shown in FIG. 8, piezoelectric element 830, which has a 'Q' of about 10,000-40,000 is connected in series with capacitor 832 to form a series resonant circuit. Piezoelectric element 830 converts a voltage across its terminals and the related current flow into stress energy. When released, such stress energy creates a high voltage peak. The stress energy stored in the volume of the piezoelectric element 830 is the integral of voltage and current over the stress buildup time, which is related to the resonant frequency, up to a maximum energy density. Operationally, assume that initially both nodes 840 and 842 are at ground and node 844 is at Vr in state ST1. A change to state ST2 means that a voltage differential V_D is created across piezoelectric element 830. As a result, capacitor 832 is charged by the current flowing through piezoelectric element 830. As capacitor 832 charges up, voltage potential V_D decreases to zero and the mechanical stress within piezoelectric element 830 can no longer be sustained. The stress energy is converted into a high voltage at the resonant frequency. With one side of piezoelectric element 830 anchored to Vr or ground, this large voltage pushes the potential of node 842 to a high peak voltage. The current created by the voltage across resistor 834 helps charge up capacitor 838. Due to the polarity switching discussed earlier, capacitor 838 is then charged to the opposite polarity. In effect, a saw tooth voltage signal is created across capacitor 838. Capacitor 836 helps provide this saw tooth voltage signal to switching logic circuit 860 thereby closing the feedback loop. When the saw tooth voltage signal reaches its peak and starts reversing its direction, switching logic circuit 860 then applies Vr to node 844 and ground to node 840 through the action of switching MOSFETs 851-854 thereby reversing the voltage across nodes 840 and 844. This polarity switch results in a large opposite polarity voltage peak on electrode 205 on which a high voltage (e.g., 2 kV peak-to-peak) relative to ground can be produced. Thus, a high voltage is produced in response to the input voltage Vr. Resistor 834 and capacitors 836 and 838 combine to act as a frequency sensing circuit to detect the completion of every half cycle for the saw tooth voltage signal having a carrier frequency derived from node 842 for switching logic circuit 860 thereby closing the feedback loop for the resonant switching frequency. At the completion of each half cycle, switching logic circuit 860 reverse the voltage across nodes 840 and 844 as discussed earlier.

FIG. 9A illustrates an exemplary schematic diagram of amplitude modulator circuit 703 that is used in a monopole configuration. As shown in FIG. 9A, amplitude modulator circuit 703 comprises isolator circuit 901 and damping circuit 902. Isolator circuit 901 receives as input the high voltage signal from resonator circuit 702 and passes this high voltage signal through as its output. Isolator circuit 901 is used to isolate its input from its output such that, for example, when its output is driven to ground, its input is largely unaffected. In so doing, the rise and fall envelope of the high voltage signal is optimized. Damping circuit 902 is connected to the output of isolator circuit 901 and to ground. Essentially, damping circuit provides a variable load to exciter electrode 205 to dampen the voltage amplitude. Damping circuit 902 receives as input a data sequence from processor 204 that determines the level of dampening. Such transmitted signal may be used, for example, in a RFID write mode data sequence. Given the above description, the constructions of isolator circuit 901 and damping circuit 902 should be obvious to a person of ordinary skill in the art. For brevity and clarity, their construction is not further described.

FIG. 9B illustrates an exemplary embodiment of damping circuit 902 of amplitude modulator 703. Damping circuit 902 comprises diodes 911- 914 and N-channel MOSFET transistor 915. Diodes 911-914 are connected together to form a full wave rectifier circuit. Transistor 915, which functions as a switch, has a gate connected to node 215, a source/drain connected to the anode of diode 923 and the anode of diode 922, and a drain/source connected to the cathode of diode 921 and the cathode of diode 924. The anode of diode 924 is coupled to the cathode of diode 923 and one end of capacitor 926 while its opposite end is coupled to ground. Capacitor 926 allows AC signals to path to ground while DC is allowed to charge the capacitor. Depending on whether damping circuit 902 is used in RFID reader 101 A, EAS reader 101 B, or an RFID/EAS reader 101C, the gate of transistor 915 is coupled to processor 204 or controller 1105, respectively at node 1011. Isolator circuit 901 and electrode 205 are coupled to the node 905 joining the anode of diode 921 and the cathode of diode 922. In so doing, damping circuit 902 can be used to dampen (load modulate) the exciter signal at electrode 205. The second embodiment of the present invention involving an electrostatic EAS reader is now described. Reference is now made to FIG. 10 illustrating electrostatic EAS reader 101 B. As shown in FIG. 10, electrostatic EAS reader 101B comprises exciter 1001 , detector circuit 1002, alarm circuit 1003, alarm 1004B, exciter electrode 205, and detector electrode 1006. Exciter electrode 205 is coupled to exciter 1001. Detector electrode 1006 is coupled to detector circuit 1002. Operationally, exciter 1001 implements the circuits discussed in FIGS. 7-9 above with only a few minor modifications. The exciter 1001 generally generates an exciter signal for activating an electrostatic transceiver. Basically, the exciter signal provides operating power to the electrostatic transceiver in the form of electrostatic (electric) energy. In addition, the carrier frequency of the exciter signal provides clock information for the electrostatic transceiver. In the preferred embodiment, the electrostatic exciter signal has a carrier frequency of 125 kHz. The electrostatic exciter signal is transmitted to the electrostatic transceiver through exciter electrode 205. In response, the electrostatic transceiver sends back an alarm signal to indicate the presence of an enabled transceiver. FIG. 11 illustrates an exemplary exciter 1001 that is implemented in

EAS reader 101 B. As shown in FIG. 11 , except for controller 1105, exciter 1001 is substantially similar to exciter 201 described earlier. Accordingly, voltage supply circuit 701 , resonator circuit 702, and amplitude modulator 703 of exciter 1001 function substantially like their counterparts in exciter 201 and are therefore not further described. However, controller 1105 is needed in exciter 1001 to generate the data sequence used to amplitude modulate the voltage at exciter electrode 205 to generate a pulsed exciter signal for EAS application. Such a controller is needed because EAS reader 101 B does not require a processor, as does RFID reader 101 , which can be used to generate the data sequence. Controller 1105 may simply be a mono-stable vibrator with its construction being obvious to a person of ordinary skill in the art.

In general, detector 1002 detects an electrostatic alarm signal from an electrostatic EAS transceiver via detector electrode 1006. In the preferred embodiment, detector 1002 is designed to detect an alarm signal with a carrier frequency of one half the excitation frequency (62.5 kHz). Detection is made only if the amplitude of the received signal reaches a predetermined threshold voltage. This may be accomplished by the use of comparators or simple CMOS inverters or gates with certain RC elements delaying a rise in signal level at the desired data carrier frequency to distinguish or filter noise. In the preferred embodiment, the threshold voltage is adjustable to accommodate various sensitivities or operating ranges. When a detection of the alarm signal having a carrier frequency of 62.5 kHz is made, detector 1002 sends the alarm signal to alarm circuit 1003. Alarm circuit 1003 activates the desired alarm (e.g., audio, visual, etc.) to indicate that an article has been detected. Alarm circuit 1003 has an alarm reset signal to de-assert the drive signal when the alarm is to be deactivated. The alarm reset may be automatic (not shown) or manual, as shown.

Detector 1002 is coupled to detector electrode 1006 and alarm circuit 1003. Detector 1002 is used to receive any signal that may be sent at a data carrier frequency expected for transmission by an EAS transceiver. In the preferred embodiment, detector 1002 is designed to detect a signal with a carrier frequency of 62.5 kHz. Such a signal is transmitted by an EAS transceiver when it is activated unless transceiver 102 is deactivated or removed. Detection is made only if the amplitude of the received signal reaches a threshold voltage in order to reduce noise from causing false alarms. When a detection of a signal having a carrier frequency of 62.5 kHz is made, detector circuit 1002 signals the alarm circuit 1003 which can immediately alert a security person.

FIG. 12 illustrates the third embodiment of the present invention. FIG. 12 illustrates an RFID/EAS reader 101C having a combination of elements of the RFID reader 101 A and the EAS reader 101 B in order to support both RFID and EAS. RFID/EAS reader 101 C includes the exciter electrode 205 and the receiver/detector electrode 1206, receiver/detector 1202, and exciter 201 , demodulator 203, and the processor 204. Reader 101C may optionally have an alarm 1004A self contained within the unit, processor 204 may connect to an external alarm 1004A or the processor 204 may cause a host computer (not shown in FIG. 12) to generate an alarm when detection occurs. With the exception of the receiver/detector 1202, the components in the reader 101C were previously introduced with reference to readers 101 A or 101 B. Reader 101C may be programmed to provide EAS operation only, RFID operation only or combined RFID/EAS operation. This is accomplished by programming the processor to control the exciter 201 in the differing way for support of EAS, RFID, or RFID/EAS operation modes. For the support of EAS or RFID alone, the exciter 201 may be controlled to be a continuous waveform. For combined support of RFID/EAS mode, the exciter is controlled to generate the pulsed waveform where the pulses have a predetermined period that is less than that needed to allow the RFID transceivers from being activated through the power on reset cycle. As previously described, a RFID transceiver 102 may be able to support EAS functionality as well by activating and communicating an alarm even when the exciter pulsed waveform is transmitted. In which case, the exciter 201 would be controlled by the processor 204 to continuously emit an excitation signal thereby powering up the RFID device that can then issue an alarm. In short, the RFID/EAS reader can function in both RFID mode and EAS mode. In RFID mode, data information stored in the transceiver's memory may be sent to the reader 101 C if in the read range of the reader. In EAS mode, an alarm signal is sent to the reader. As an alternate embodiment, an electrostatic EAS system implementing the present invention for providing an enhanced EAS operating range is also described below. The receiver/detector 1202 is the unique component of the reader

101C. As its name indicates, the receiver/detector 1202 includes the functionality of the receiver 202 and the detector 1002 that are previously described in one receiver/detector 1202. Reader 101 A can operate in an EAS mode with a RFID/EAS transceiver programmed into EAS mode. However, because the detector has greater sensitivity to detect the data carrier signal, the combined receiver/detector 1202 has a greater detection range than reader 101 A. After detection of the transceiver 102, it may be brought into read range such that it the reader 101C can receive data from the RFID/EAS transceiver over its less sensitive receiver. In which case the exciter 201 can operate continuously to excite RFID transceivers regardless of any programming or in a pulsed mode fashion to avoid waking RFID/EAS transceivers programmed to avoid EAS mode and it may transmit data to an RFID transceiver expecting some data information in return. In the case of the combined receiver/detector 1202, the receiver and detector within the receiver/detector 1202 may share the same electrostatic electrode 1206. To combine a detector with a receiver, a comparator or other similar circuit for providing detection is inserted in the front end of the receiver elements after pre-filtering of any unwanted frequencies has taken place. Similar to the detector 1002, the receiver/detector 1202 is used to receive any signal that may be sent at a data carrier frequency expected for transmission by an EAS transceiver or RFID/EAS transceiver. In the preferred embodiment, receiver/detector 1202 is designed to detect a signal with a carrier frequency of 62.5 kHz. Such a signal is transmitted by an EAS transceiver when it is activated unless transceiver 102 is deactivated or removed. Detection is made only if the amplitude of the received signal reaches a threshold voltage in order to reduce noise from causing false alarms. When a detection of a signal having a carrier frequency of 62.5 kHz is made, receiver/detector circuit 1202 signals the alarm 1004A through the alarm circuit 1003 which can immediately alert a security person. Alternatively, the processor 204 could directly control the alarm 1004B or cause the host to indicate an alarm.

The receiver/detector 1202 includes the enhanced exciter 201 previously described with its improved amplitude modulator 703 and high quality 'Q' resonator circuit 702 for larger excitation distances and therefore larger alarm distances for an EAS transceiver or RFID/EAS transceiver.

Three embodiments of the first aspect of the present invention are thus described. The first embodiment involves a RFID reader. The exciter circuit of the RFID reader has a resonator circuit with a high quality factor 'Q' that generates a high voltage signal at the resonant frequency. The second embodiment involves an electrostatic EAS reader. The EAS reader also implements the same resonator circuit with a high quality factor 'Q' to generate a high voltage signal at the resonant frequency. The third embodiment involves an RFID/EAS reader having a combination of elements of the RFID reader and the EAS reader.

Advantages of the first aspect of the present invention are its low cost, ease of manufacturability, and packaging flexibility. Another advantage is the generation of high exciter voltage potentials with low DC voltage and low DC current sources (e.g., to generate an exciter voltage of 2 KV peak-to-peak with only 3-5 V DC and at less than 100 mA DC input). Yet another advantage is enhanced operating range without violating exceeding compliance regulations. Yet another advantage is power efficiency and portability, which allows for applications where power and space are premium and which allows for battery operated readers for programming and reading transceivers in the field, e.g., warehouse inventory management. Yet another advantage is an increased electrostatic transmission field strength from the reader without bulky, heavy and expensive high voltage L/C tank circuits which also require higher operating current. Yet another advantage is decreased component and assembly cost for the reader versus those using L/C tank circuits. Yet another advantage is an adjustable communications range by setting the electrostatic signal strength by adjusting the resonator supply voltage. Yet another advantage is an increased electrostatic transmission field strength without creating undesirable magnetic fields.

The following discussion addresses a second aspect of the present invention using the piezoelectric crystal for detection of RFID/EAS tags. The second aspect of the present invention can be used for theft prevention as an additional benefit of a RFID system already installed for merchandising. The reader includes a detector circuit for detecting the presence of a signal carrier frequency transmitted by the transceiver in response to a signal from the reader. The detector circuit comprises a piezoelectric resonator circuit that is coupled to a receiver electrode. The piezoelectric resonator circuit is employed for its high sensitivity characteristics due to its high quality factor 'Q' at resonance. The high sensitivity is used to detect EAS transceiver signals thereby setting an alarm. In an alternate embodiment, the reader also includes the ability to write to or read electrostatic RFID transceivers. In an example application, disposable transceivers are attached to merchandise and removed or deactivated at its purchase. A customer walking past the reader with an active EAS transceiver causes the transceiver to send its carrier signal. This signal is detected over an extended range and is used to trigger an alert. Since RFID systems are used already for inventory tracking of merchandise, the invention is a means for economical theft prevention.

A second aspect of the detailed description of the electrostatic RFID/EAS system invented by the applicant is provided below. An advantage of the second aspect of this invention is to provide an enhanced EAS detection range for the electrostatic RFID/EAS system (i.e., between the reader and the transceiver) by adding a detection circuit to the reader for detecting the transceiver signal carrier frequency. This detection circuit is used for theft prevention or EAS as an additional benefit of a RFID system used for merchandising. Disposable transceivers are attached to merchandise and removed or deactivated at its purchase. A customer walking past the reader with an intact transceiver causes the transceiver to send its signal carrier signal. This signal is detected over an extended range and is used to trigger an alert. In short, the RFID/EAS reader can function in both RFID mode and EAS mode. In RFID mode, data information stored in the transceiver's memory is sent to the reader. In EAS mode, an alarm signal is sent to the reader. As an alternate embodiment, an electrostatic EAS system implementing the present invention for providing an enhanced EAS detection range is also described below.

FIG. 13 depicts a detector circuit 1310 coupled to at least one of receiver electrodes 206 to receive a read signal transmitted by transceiver 102. Detector circuit 1310 is designed to detect a signal with a predetermined carrier frequency, e.g., 62.5 kHz. Such a signal is transmitted by transceiver 102 when it is activated unless transceiver 102 is deactivated or removed. Detection is made only if the amplitude of the received signal reaches a threshold voltage. In the preferred embodiment, the threshold voltage is adjustable to accommodate different operating ranges. When a detection of a signal having a carrier frequency of 62.5 kHz is made, detector circuit 1310 signals processor 204 which immediately alerts security personnel. Because an alert is made as soon as a signal having the predetermined carrier frequency is detected and no additional information transfer is required, the operating response is fast. Moreover, the operating range is improved since detector circuit 1310 is designed to be sensitive by using a high Q piezoelectric element. Furthermore, the electrostatic RFID system implemented in the present invention is not adversely effected by magnetic fields. Pads 312-313 are preferably located at opposite far ends of the silicon chip for optimum assembly to the electrodes.

FIG. 14 shows an embodiment of detector circuit 1310 which comprises resonator circuit 1410, resistor 1415, diode 1420, capacitor 1925, bleed resistor 1430, zener diode 1435, comparator 1440 and a DAC (digital-to-analog converter) 1445 connected to processor 204. Resonator circuit 1410 consists of capacitor 1450 and piezoelectric element 1455 with a high Q factor connected in series for operating in a series resonant mode. One terminal of capacitor 1450 is connected to receiver electrode 206 and one terminal of piezoelectric element 1455 is connected to grounded resistor 1415. Piezoelectric element 1455 is also connected to diode 1420. Piezoelectric element 1455 may be a piezoelectric quartz crystal, a piezoelectric lithium niobate crystal, a piezoelectric ceramic resonator, or other piezoelectric materials.

When an alarm signal is received at receiver electrode 206, it passes through capacitor 1450 and piezoelectric element 1455. When the signal frequency is outside of its resonant frequency, the impedance across resonator circuit 1410 is large and the voltage developed across resistor 1415 is minimal. However, at the resonant frequency, which is 62.5 kHz in the preferred embodiment, the impedance across resonator circuit 1410 is at a minimum thus maximizing the voltage across resistor 1415. Resonator circuit 1410 is capable of having Quality factors, Q's, in the

10,000's at the resonant frequency that results in substantial improvement in sensitivity thereby enhancing detection of EAS or RFID/EAS articles. In particular, diode 1420 rectifies the detected voltage signal by passing only positive half cycles of the signal to grounded capacitor 1425 that acts as a storage device. By itself, capacitor 1425 serves as a peak detector for the rectified voltage signal generated by diode 1420. However, when bleed resistor 1430 is used in combination with capacitor 1425, they act as an envelope detector circuit to track the rectified voltage signal and to reset the circuit when the signal goes to zero. The envelope detector circuit generates an envelope detector signal. Zener diode 1435 is used to govern the envelope detector signal to a desirable level. Comparator 1440 compares the envelope detector signal against a threshold signal Vth. If the envelope detector circuit reaches the threshold voltage, comparator 1440 changes its logic state to initiate an alarm condition. In so doing, detector circuit 1310 provides sensitive and adjustable detection of any signal having a predetermined carrier frequency, such as 62.5 kHz, from transceiver 102. In the preferred embodiment, voltage signal Vth is generated by DAC 1445 under software control by processor 204. As such, the detection range can be adjusted by varying, for example, the threshold voltage Vth. Because detector circuit 1310 immediately indicates to processor 204 when a threshold voltage is reached with no data transfer required, the responsiveness is quick. Alternatively, voltage signal Vth can be supplied by any variable voltage source. It is to be appreciated that, in accordance with the present invention, the first carrier frequency for exciter signals from exciter 201 and the second carrier frequency for a read signal from transceiver 102 are to be different.

In an alternative embodiment, detector circuit 1310 may further include an operational amplifier and a plurality of diodes in a full wave rectifier configuration coupled between resistor 1415 and diode 1420. In another alternative embodiment, detector circuit 1310 may employ a phase-locked loop circuit in place of piezoelectric element 1455 and capacitor 1450. It should be understood to one familiar in the art that the order of capacitor 1450 and piezoelectric element 1455 within resonator circuit 1410 may be reversed.

FIG. 15 shows an alternate embodiment of detector circuit 210". As shown in FIG. 15, the elements of detector circuit 210" have double-primed reference numbers to make them more identifiable with their corresponding counterparts in FIG. 14. The connections between capacitor 778", resistor 777", zener diode 779", and comparator 780" are similar to that described in FIG. 14. However, in FIG. 15, diode 770" is connected between piezoelectric element 774" and capacitor 772". The functions of the elements in detector circuit 210" (FIG. 7B) are substantially similar to that of the elements in detector circuit 210 (FIG. 7A) and are not further discussed. It should be understood to one familiar in the art that the order of capacitor 772" and piezoelectric element 774" within resonator circuit 771" may be reversed. FIG. 16 shows yet another alternate embodiment of detector circuit

210'. As shown in FIG. 16, the elements of detector circuit 210' have primed reference numbers to make them more identifiable with their corresponding counterparts in FIG. 14. The connections between capacitor 778', resistor 777', zener diode 779', and comparator 780' are similar to that described in FIG. 14. However, in FIG. 16, grounded capacitor 772' and piezoelectric element 774' are connected in parallel to electrode 206' and to diode 770'. The functions of the elements in detector circuit 210' (FIG. 8) are substantially similar to that of the elements in detector circuit 210 (FIG. 7A) and are not further discussed. The above discussion describes the first embodiment of the present invention, a combined electrostatic RFID/EAS reader. The second embodiment of the present invention involves an electrostatic EAS reader and is described next. Reference is now made to FIG. 17 illustrating electrostatic EAS reader 101 '. As shown in FIG. 17, electrostatic EAS reader 101' comprises exciter 901 , detector circuit 902, alarm circuit 903, exciter electrode 905, and receiver electrode 906. Exciter electrode 905 is coupled to exciter 901. Receiver electrode 906 is coupled to detector circuit 902. Operationally, exciter 901 generates a RF exciter signal for activating an electrostatic transceiver. Basically, the RF exciter signal provides operating power to the electrostatic transceiver in the form of electrostatic (electric) energy. In addition, the carrier frequency of the RF exciter signal provides clock information for the electrostatic transceiver. In the preferred embodiment, the electrostatic RF exciter signal has a carrier frequency of 125 kHz. The electrostatic RF exciter signal is transmitted to the electrostatic transceiver through exciter electrode 905. In response, the electrostatic transceiver sends back a RF alarm signal to indicate that the article may not be removed without authorization.

Detector circuit 902 can employ either the embodiment described above in FIG. 14, the embodiment described above in FIG. 15, or the embodiment described above in FIG. 16. For brevity and clarity, these descriptions are not repeated. In general, detector circuit 902 detects an electrostatic RF alarm signal from electrostatic EAS transceiver 102' via receiver electrode 906, detector circuit 902. Detector circuit 902 is designed to detect an alarm signal with a carrier frequency of 62.5 kHz. Detection is made only if the amplitude of the received signal reaches a threshold voltage. In the preferred embodiment, the threshold voltage is adjustable to accommodate different operating ranges. When a detection of the alarm signal having a carrier frequency of 62.5 kHz is made, detector circuit 902 sends the RF alarm signal to alarm circuit 903. Alarm circuit 903 generates the proper signal to drive the desired alarm type (e.g., audio, visual, etc.) to indicate that an article is being removed without authorization. Alarm circuit 903 has an alarm reset signal to deassert the drive signal when the alarm is to be deactivated. The alarm reset may be automatic (not shown) or manual, as shown. Because an alert is made as soon as a signal having the predetermined carrier frequency is detected and no additional information transfer is required, the operating response is fast. Moreover, the operating range is improved since detector circuit 902 is designed to be sensitive by using a high Q piezoelectric element. It should be known to one skilled in the art that detection of a RFID/EAS transceiver is similarly achieved.

Two embodiments of the second aspect of the present invention are thus described. The first embodiment involves a combined RFID/EAS reader. The RFID/EAS reader has a detector circuit that uses a high sensitivity or high 'Q' circuit to detect the carrier frequency of interest in response to an alarm signal from a transceiver. In addition, the RFID/EAS reader has a receiver to read the contents of the RFID transceiver and an transmitter to write to the RFID/EAS transceiver. The second embodiment involves an electrostatic EAS reader. The EAS reader also implements the same high sensitivity or high 'Q' circuit to detect the carrier frequency of interest in response to an alarm signal from a transceiver. However, it does not contain a reader to read the RFID contents.

Advantages of the second aspect of the present invention are its low costs, ease of manufacturability, and packaging flexibility. Another advantage is improved sensitivity in detecting an EAS alarm signal. Yet another advantage is the ability to detect either EAS or RFID/EAS transceivers. Yet another advantage is improved operating range without violating FCC regulations and EMI regulations. Yet another advantage of the invention is the use of a RFID system already installed for merchandising for the additional benefit of theft prevention. Yet another advantage is the ability to detect single-bit EAS transceivers. Yet another advantage is the ability to detect RFID/EAS transceivers, also used for multiple-bit, article identification. Yet another advantage is the minor addition of the detector circuit to the reader resulting in detection of a transceiver carrier frequency at an extended and an adjustable range. Yet another advantage is decreased component and assembly cost for detection circuit by the use of a piezoelectric element. Yet another advantage is improved sensitivity, sufficient robustness, and improved read time that are required for EAS applications. Yet another advantage is savings in reader power and weight, thus facilitating battery operated readers for programming, reading and detecting transceivers (tags) in the field, e.g. in warehouse inventory management and theft prevention. While the present invention has been described in particular embodiments, the present invention should not be construed as limited by such embodiments, but rather construed according to the below claims.

Claims

What is claimed is:CLAIMS

1. A reader for providing an enhanced operating range, the reader __ comprising: a processor for controlling operation of the reader; at least one first electrode; and an exciter coupled to the processor and the at least one first electrode, the exciter comprising: a resonator circuit having a high quality 'Q'; a voltage supply circuit coupled to the resonator circuit, the voltage supply circuit generating a regulated voltage; wherein the resonator circuit generating a high voltage carrier frequency signal having a carrier frequency in response to the regulated voltage; a feedback circuit coupled to the voltage supply circuit and the resonator circuit, the feedback circuit maintaining the high voltage carrier frequency signal in an amplitude range; and a modulator coupled to the resonator circuit, the at least one first electrode, and the processor, the modulator modulating a carrier frequency signal using a signal from the processor to generate an exciter signal; wherein the at least one first electrode generating a high electrostatic field for transmitting the exciter signal thereby improving a communication range.

2. The reader of claim 1 , wherein the processor is one of the following: a microprocessor for controlling the communication of an electrostatic read data signal, a controller for controlling the generation of the exciter signal.

3. The reader of claim 1 , wherein the modulator generates a continuous exciter signal in a radio frequency identification mode and a pulsed exciter signal in an electronic article surveillance mode.

4. The reader of claim 1 , further comprising: a receiver coupled to the processor; at least one second electrode coupled to the receiver, the receiver receiving an electrostatic read data signal from the at least one second electrode; and a demodulator coupled to the receiver and the processor, the demodulator receiving the electrostatic read data signal, the demodulator demodulating the electrostatic read data signal prior to sending it to the processor.

5. The reader of claim 1 or 4, further comprising a detector for detecting an electrostatic signal at a carrier frequency and indicating an alarm.

6. The reader of claim 4 or 5, wherein the modulator generates one of the following: a pulsed exciter signal in an electronic article surveillance (EAS) mode, a continuous exciter signal in a radio frequency identification (RFID) mode, a continuous exciter signal in a RFID mode and a pulsed exciter signal in an EAS mode.

7. The reader of claim 1 , wherein the resonator circuit comprises: a resonator comprising a piezoelectric element having a high quality 'Q' factor and a capacitor connected in series; a switching circuit coupled to the resonator, the switching circuit connected to the regulated voltage and GROUND; and a frequency sensing circuit coupled to the modulator, the feedback circuit, and the switching circuit, the frequency sensing circuit detecting when a half cycle of the carrier frequency is complete, after the half cycle is complete, the sensing circuit alerting the switching circuit; wherein in response to the frequency sensing circuit, the switching circuit alternately providing the resonator with opposite polarity voltages causing stress energy to build up in the resonator thereby generating the exciter signal having a high voltage amplitude at the carrier frequency.

8. The reader of claim 7, wherein the switching circuit comprising: a switching logic circuit connected to the frequency sensing circuit; an inverter connected to the switching circuit; a first P-channel MOSFET having a source, a gate, and a drain, the drain of the first P-channel MOSFET is connected to a terminal of the piezoelectric element, the gate of the first P-channel MOSFET is connected to the switching circuit; a second P-channel MOSFET having a source, a gate, and a drain, the source of the first P-channel MOSFET and the source of the second P- channel MOSFET connected to the regulated voltage, the drain of the second P-channel MOSFET is connected to the frequency sensing circuit, the gate of the second P-channel MOSFET is connected to the inverter; a third N-channel MOSFET having a source, a gate, and a drain, the drain of the third N-channel MOSFET is connected to the terminal of the piezoelectric element, the gate of the third N-channel MOSFET is connected to the inverter; and a fourth N-channel MOSFET having a source, a gate, and a drain, the source of the third N-channel MOSFET and the source of the fourth N- channel MOSFET connected to ground, the drain of the fourth N-channel MOSFET is connected to the frequency sensing circuit, the gate of the fourth N-channel MOSFET is connected to the switching circuit.

9. The reader of claim 8, wherein the piezoelectric element comprises at least one of the following: a piezoelectric quartz crystal, a piezoelectric lithium niobate crystal; a piezoelectric ceramic resonator.

10. A transceiver for use with a reader, the transceiver comprising: a plurality of electrodes for receiving an exciter signal and sending an alarm signal; an analog interface module coupled to the plurality of electrodes, the analog interface module extracting a power signal and a clock signal having a first carrier frequency from the exciter signal received by the plurality of electrodes, the analog interface module rectifying and regulating the exciter signal for use in activating the transceiver; a memory for storing data information; a modulator coupled to the memory, the modulator modulating data information stored in the memory with a second carrier frequency; and a controller coupled to the analog interface module and the memory, if a radio frequency identification mode is involved, the controller reading data information from the memory and sending the data information to the analog interface module for communicating over the plurality of electrodes, if an electronic article surveillance mode is involved, the controller sending the alarm signal to the analog interface module for communicating over the plurality of electrodes.

11. A method for maximizing a communication range of a reader, the steps comprising: generating a regulated voltage; generating a high voltage carrier frequency signal in response to the regulated voltage using a high quality factor 'Q' resonator circuit; maintaining the high voltage carrier frequency signal in an amplitude range using feedback; modulating the high voltage carrier frequency signal using a transmission command sequence to generate an exciter signal; and generating a high electrostatic field for transmitting the exciter signal thereby maximizing the communication range with a transceiver.

12. The method of claim 11 , wherein the step of generating the high voltage carrier frequency signal comprises: detecting and alerting when a half cycle of a carrier frequency is complete; and after the half cycle is complete, alternately providing the high quality 'Q' resonator circuit with opposite polarity voltages causing stress energy to build up in the high quality 'Q' resonator circuit thereby generating the exciter signal having a high voltage amplitude at the carrier frequency.

13. A reader having an enhanced operating range, the reader comprising: at least one first electrode; an exciter coupled to the at least one first electrode, the exciter comprising: a resonator circuit having a high quality 'Q'; a voltage supply circuit coupled the resonator circuit, the voltage supply circuit generating a regulated voltage; wherein the resonator circuit generating a high voltage carrier frequency signal having a carrier frequency in response to the regulated voltage; a feedback circuit coupled to the voltage supply circuit and the resonator circuit, the feedback circuit maintaining the high voltage carrier frequency signal in an amplitude range; a controller for generating a data sequence; a modulator coupled to the resonator circuit, the controller, and the at least one first electrode, the modulator modulating a carrier frequency signal using a data sequence from the controller to generate an exciter signal; wherein the at least one first electrode generating a high electrostatic field for transmitting the exciter signal thereby improving a communication range; at least one second electrode; and a detector circuit coupled to the at least one second electrode, the detector circuit detecting an alarm signal having a second carrier frequency for generating an alarm.

14. A reader for providing an enhanced detection range, the reader comprising: at least one first electrode; an exciter coupled to the at least one first electrode, the exciter generating and transmitting an exciter signal having a first carrier frequency over the at least one first electrode; at least one second electrode; and a detector circuit coupled to the at least one second electrode, the detector circuit detecting an alarm signal having a second carrier frequency, the detector circuit amplifying the alarm signal if the second carrier frequency is sensed.

15. The reader of claim 14, wherein the detector circuit comprises: a resonator circuit comprising a piezoelectric element having a high

Q factor, the piezoelectric element coupled to the at least one second electrode; the piezoelectric element passively amplifying the alarm signal detected across the at least one second electrode at resonant frequency; an envelope detector coupled to the piezoelectric element, the envelope detector generating an envelope detector signal; and a comparator receiving as inputs the envelope detector signal and a threshold signal, the comparator generating a signal when the envelope detector signal reaches the threshold signal.

16. The reader of claim 15, wherein the detector circuit further comprises a voltage source coupled to the comparator for generating the threshold signal.

17. The reader of claim 16, wherein the voltage source comprises a variable voltage source.

18. The reader claim 16, wherein the detector circuit further comprises a zener diode coupled in parallel to a second capacitor for governing the envelope detector signal to a desirable level.

19. The reader of claim 18, wherein the detector circuit further comprises an operational amplifier coupled to a plurality of diodes and the piezoelectric element.

20. The reader of claim 14 further comprising: a processor coupled to the exciter and to a host computer storing a database; and a receiver coupled to the at least one second electrode, the receiver receiving a radio frequency (RF) signal, the receiver demodulating the RF signal and passing it to the processor.

21. The reader of claim 15, wherein the piezoelectric element comprises one of the following: a piezoelectric ceramic resonator, a piezoelectric quartz crystal, a piezoelectric lithium niobate crystal.

22. The reader of claim 15, wherein the detector circuit comprises a phase-locked loop circuit.

23. A transponder for use with a reader comprising: a plurality of electrodes for receiving an exciter signal and transmitting an alarm signal; an analog interface module coupled to the plurality of electrodes, the analog interface module extracting a power signal and a clock signal having a first carrier frequency from the exciter signal received by the plurality of electrodes, the analog interface module rectifying and regulating the exciter signal for use in activating the transponder; a memory for storing data; a modulator coupled to the memory, the modulator modulating data information stored in the memory with a second carrier frequency; and a controller coupled to the analog interface module and the memory, if a radio frequency identification mode is involved, the controller reading data information from the memory and sending the data information to the analog interface module for transmitting over the third plurality of electrodes, if an electronic article surveillance mode is involved, the controller sending the alarm signal to the analog interface module for sending over the third plurality of electrodes.

24. A method for detecting an alarm signal having a carrier frequency comprising: electrostatically receiving the alarm signal; sensing the carrier frequency of the alarm signal; rectifying the alarm signal when the carrier frequency is sensed to generate a rectified signal; generating an envelope detector signal by tracking the rectified signal; generating a threshold signal; comparing the envelope detector signal to the threshold signal; and generating an alarm signal when the envelope detector signal reaches the threshold signal.

25. The method of claim 24 further comprising passively amplifying the alarm signal at a resonant frequency using a piezoelectric element.