WO2001073389A1

WO2001073389A1 - Sensor for non-contacting detection via modulation of electromagnetic signal through by measurement entity controlled mechanical resonance

Info

Publication number: WO2001073389A1
Application number: PCT/SE1999/001000
Authority: WO
Inventors: Carl Tyrén
Original assignee: Tyren Carl
Priority date: 1998-05-26
Filing date: 1999-06-08
Publication date: 2001-10-04
Also published as: SE9801892D0; WO2001073389A8; SE513392C2; SE9801892L

Abstract

A method for contactless detection of preferably mechanic measuring quantities such as torque, force or pressure, characterised in that a measuring quantity actuates a mechanic resonance in a string shaped element and that said resonance is excited by naturally appearing vibrations or movements in the vicinity of the sensor. The sensor is radiated with for instance microwave energy and a modulation of the microwave signal caused by the mechanic oscillation of the string element of the sensor. The distance between the sensor and the microwave transceiver can be > 10 m.

Description

Sensor for Non-Contacting Detection Via Modulation of Electromagnetic signal Through by Measurement Entity Controlled MechaninaJ Jesnnanr .

Contactless detection of mechanical quantities with the use of a cheap and robust sensing technique is at the present stage a neglected area. One example is the measuring of torque and tyre pressure on vehicles so as to improve safety, performance and environmental consideration.

The Invention

It is a fact that a microwave signal can be amplitude modulated by a mechanically oscillating object in the signal path between a transmitter and a receiver. Experiments have shown that an approximately 10 cm long guitar string in mechanical oscillation at 150 Hz will introduce an obvious amplitude modulation of a 1 ,3 GHz microwave signal. If the mechanical tension of the guitar string is changed to make the string oscillate at 230 Hz instead the amplitude modulation of the HF-signal will follow the change. The distance between the microwave antenna and the guitar string was in the above mentioned example approximately 5 m and the microwave power was approximately 100 mW.

If a plurality but frequency separated mechanical resonances are made to oscillate at the same time, for instance by playing a chord on a guitar all these frequencies appear at the same time in the spectrum of the amplitude modulated HF signal. These physical effects form a basis for a contactless and simultaneous detection of a plurality of sensors of the same or different measuring quantities.

A prior art and commercially available pressure sensor operates according to a so called "vibrating string" principle. By a trivial mechanical arrangement the pressure to measured is transformed into a corresponding mechanical tension in a string that is excited at its resonance frequency. The measuring of this resonance frequency is made locally within the cover of the pressure sensor, for instance by an induction technique. By combining a mechanical HF modulation and the prior art "vibrating string" pressure sensor principle a new pressure sensor for remote detection can be designed, that is (Fig. 1) a sensor comprising:

a pressure sensing element (such as a membrane bellows) that is connected to a mechanical resonance element, the frequency thereof thus being controlled (such as a guitar string),

a mechanical excitation signal for exciting the mechanical resonance oscillation (such as vibrations from the road surface and the motor vehicle in the tire pressure sensor application, and

a radio transceiver including an amplitude demodulator and subsequent signal transformation from AM to pressure.

An identical method can be used also for measuring the torque (Fig. 2). A string element is provided between two locations along a main tension line on the axle, the torque of which is to be measured. The string is arranged clear from the axle surface so that it can be brought into resonance oscillation - for instance by naturally occurring vibrations in the axle or by a strike excitation from the rotation of the axle.

The string is mechanically biased so as to increase or decrease its resonance frequency depending on tensile stress or compressive stress along a selected line of elongation. By arranging a plurality of strings on the same axle in different elongation directions and tuned to different frequency bands (by giving them different length, biasing level, load from weight, etc.) the complete mechanical strain condition of the axle can be detected without contact and at a considerable distance. By using an element, the mechanical shape thereof changing in dependence of its temperature, and by connecting it for the control of a mechanical resonance frequency in accordance with the above described method also a telemetric temperature sensor can be designed in accordance with the above described new principle.

Measuring and monitoring mechanical vibrations is a considerable technical field. In this area the new radio technique provides a great variety of possibilities. A vibrating object can be irradiated directly with electromagnetic signals and the modulation produced by the mechanical motion can be analysed. As an alternative for instance antenna like wire elements can be arranged on a vibrating structure in specifically interesting measuring points. An acoustic signal setting a simple membrane to oscillate will provide in accordance with the new principle a microphone function per se.

With regard to string instruments, again as an example a guitar, there is provided a new method for a transform from a mechanical/acoustic to an electric signal for further processing and distribution in sound-signal systems. In for instance applications involving torque and tire pressure measuring a further effect can be used for the purpose of improving the detecting reliability and to obtain further information such as the rotation speed and angular motion. When the oscillating string in the sensor is made also to rotate the antenna aspect with regard to transmitting/receiving antennas of the detecting system will be changed, which will result in a superposition modulation of the total strength in the electromagnetic signal from the oscillating string. This will mean that the spectral line from the string in the amplitude modulated spectrum of the HF signal, the position of the frequency thereof corresponding to a specific tire pressure or torque, now will vary in strength depending on the rotation of the sensor. As a result also information about for instance the rotation speed and angular motion of the tire. This information can be used to discriminate tire signals originating from the associated car (which normally all are rotationally synchronised) from signals originating from other vehicles that are provided with the same type of measuring system for tire pressure measuring and that are close by. A further development and analysis of the new principle described above and the use of it in a measuring system is of course possible and is considered within the scope of the present invention.

Claims

1. A method for detecting a measuring quantity, characterised in that said measuring quantity actuates a mechanical oscillating movement that is detected as a modulation of an electromagnetic wave propagation.

2. A method according to claim 1, characterised in that said measuring quantity actuates a mechanical resonance frequency.

3. A method according to claim 1, characterised in that said mechanical oscillating movement is excited by mechanic energy available in the immediate vicinity.

4. A method according to claim 1 and claim 2, characterised in that said measuring quantity is a gas or liquid pressure.

5. A method according to claim 1 and claim 2, characterised in that said measuring quantity is a torque.

6. A method according to claim 1 and claim 2, characterised in that said measuring quantity is a temperature.

7. A method according to claim 1 and claim 2, characterised in that a plurality of measuring quantities are detected simultaneously by having non-coincident resonance frequencies actuated thereby.

8. A method according to claim 1, characterised in that a variation of intensity, of the mechanic oscillating movement related to a electromagnetic wave propagation that appears in connection with a rotation of the rotating element, is used to detect said rotation.

9. A method according to claim 1 and claim 8, c h a ra c t e ri s e d in that variations of intensity are used to associate a plurality of rotating sensors.

10. A device according to claim 1 , 2 and 3, c o m p r i s i n g:

A a device for transforming a measuring quantity into a mechanic movement,

B a string formed element that is provided to effect a transversal resonance oscillation, a longitudinal biasing being controlled by A,

C a device connecting A and B to a mechanic power source for exciting said resonance oscillation and

D a device for transmitting and receiving an electromagnetic wave propagation and for detecting a modulation of the wave propagation and for computing said measuring quantity from said modulation.