WO2011072214A2

WO2011072214A2 - System and method for detecting the presence of liquid using confined out-of-plane acoustic modes

Info

Publication number: WO2011072214A2
Application number: PCT/US2010/059873
Authority: WO
Inventors: Terence J. Knowles; Kenneth A. Albrecht; Charles F. Bremigan Iii
Original assignee: Illinois Tool Works Inc.
Priority date: 2009-12-11
Filing date: 2010-12-10
Publication date: 2011-06-16
Also published as: WO2011072214A3

Abstract

An acoustic wave switch assembly (30) includes a substrate (36) having contact and mounting surfaces, wherein the contact surface (32) is opposite the mounting surface (20), a mesa (38) defining an acoustic wave cavity formed in the substrate, wherein the mesa gradually thins radially outward to a thinned moat (40) that surrounds the mesa, and a transducer (44) secured to the mounting surface of the substrate. The transducer is configured to generate a trapped acoustic wave within the acoustic wave cavity.

Description

SYSTEM AND METHOD FOR DETECTING THE PRESENCE OF LIQUID USING CONFINED OUT-OF-PLANE ACOUSTIC MODES

RELATED APPLICATIONS

[0001] This application relates to and claims priority benefits from U.S. Provisional Patent Application No. 61/285,877 entitled "System and Method for Detecting the Presence of Liquid Using Confined Out-of-Plane Acoustic Modes," filed December 11, 2009, which is hereby incorporated by reference in its entirety.

FIELD OF EMBODIMENTS OF THE INVENTION

[0002] Embodiments of the present invention generally relate to acoustic wave switches, and, more particularly, to a system and method for detecting the presence of liquid through an acoustic wave switch.

BACKGROUND

[0003] Acoustic wave switches are described and shown, for example, in United States Patent No. 7,106,310, entitled "Acoustic Wave Touch Actuated Switch," and United States Patent No. 7,265,746, entitled "Acoustic Wave Touch Detection Circuit and Method," both of which are hereby incorporated by reference in their entireties. In general, an acoustic wave switch includes a substrate having an acoustic wave/resonant cavity and a transducer that is configured to generate a trapped acoustic wave within the acoustic wave cavity.

[0004] United States Patent No. 7,027,943, entitled "Acoustic Wave Ice and Water Detector" (the "'943 patent"), which is also hereby incorporated by reference in its entirety, discloses an acoustic wave sensor that utilizes one or more acoustic waves trapped in an acoustic wave cavity to detect the presence of one or more substances on a surface of the acoustic wave cavity. To detect the presence of liquid, a trapped torsional acoustic wave is used. The sensor includes a number of transducers adjacent the acoustic wave cavity where a controller drives different sets of the transducers to generate different acoustic waves. SUMMARY OF EMBODIMENTS OF THE INVENTION

[0005] Certain embodiments of the present invention provide an acoustic wave switch assembly that includes a substrate, a mesa, and a transducer. The substrate has contact and mounting surfaces. The contact surface is opposite the mounting surface.

[0006] The mesa defines an acoustic wave cavity formed in the substrate. The mesa gradually thins radially outward from a center to a thinned moat that surrounds the mesa.

[0007] The transducer is secured to the mounting surface of the substrate. The transducer is configured to generate a trapped acoustic wave within the acoustic wave cavity. The transducer may be a compressional wave transducer configured to generate the trapped acoustic wave as a compressional out-of-plane wave.

[0008] In an embodiment, the transducer may be secured to an acoustic mass that is secured to a mounting surface of the substrate. The acoustic mass is of sufficient size and material to ensure that the transducer is configured to generate a trapped acoustic wave within the acoustic wave cavity. The transducer may be a compressional wave transducer configured to generate the trapped acoustic wave as a compressional out-of- plane wave.

[0009] In an embodiment, the transducer may be positioned between the substrate and the acoustic mass. Alternatively, the acoustic mass may be secured to the exposed top of the transducer such that it is securely positioned between the substrate and the transducer.

[0010] The assembly may also include a raised ridge surrounding the thinned moat. The raised ridge may be thicker than the mesa, which is, in turn, thicker than the moat.

[0011] Certain embodiments of the present invention provide an acoustic wave switch assembly that includes a substrate, a mesa defining an acoustic wave cavity formed in the substrate, a thinned moat that surrounds the mesa, and a raised ridge that surrounds the thinned moat. The mesa gradually thins radially away from a center toward the thinned moat.

[0012] Certain embodiments of the present invention provide an acoustic wave switch assembly that includes a substrate, a mesa defining an acoustic wave cavity formed in said substrate, wherein the mesa gradually thins radially away from a center toward a thinned moat that surrounds the mesa, a raised ridge that surrounds the thinned moat, wherein the raised ridge is thicker than the mesa, which is thicker than the thinned moat, and a compressional wave transducer secured to a mounting surface of the substrate. The transducer is configured to generate a trapped compressional acoustic wave within the acoustic wave cavity.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

[0013] Figure 1 illustrates an isometric, partial cross-sectional view of an acoustic wave switch.

[0014] Figure 2 illustrates a front view of an acoustic wave switch, according to an embodiment of the present invention.

[0015] Figure 3 illustrates a simplified cross-sectional view of an acoustic wave switch through line 3-3 of Figure 2, according to an embodiment of the present invention.

[0016] Figure 4 illustrates a cross-sectional view of an acoustic wave switch through line 3-3 of Figure 2, according to an embodiment of the present invention.

[0017] Figure 5 illustrates a cross-sectional view of an acoustic wave switch, according to an embodiment of the present invention.

[0018] Figure 6 illustrates a cross-sectional view of an acoustic wave switch, according to an embodiment of the present invention.

[0019] Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of "including" and "comprising" and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items and equivalents thereof.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0020] Figure 1 illustrates an isometric, partial cross-sectional view of an acoustic wave switch 10. The acoustic wave switch 10 includes an associated acoustic wave/resonant cavity 12 that extends through the thickness b_s of a substrate 14. The substrate 14 may be formed of metal, plastic, glass, ceramic, or the like that is capable of supporting a resonant acoustic wave.

[0021] The resonant cavity 12 is formed in the substrate 14 such that the mass per unit surface area of the resonant cavity 12 is greater than the mass per unit surface area of the substrate 14 adjacent the resonant cavity 12. In one embodiment, the mass per unit area of the substrate 14 in the switch region is increased to form the resonant cavity 12 by forming a thin plateau or mesa 16 on a surface of the substrate 14 that is parallel to the plane of the substrate 14 and/or a contact surface 18. The mesa 16 may be formed on a back surface 20 of the substrate 14 opposite the contact surface 18 of the resonant cavity 12. Alternatively, the mesa 16 may be formed on the contact surface 18.

[0022] A transducer 22, such as a piezoelectric transducer, is mounted on a surface 24 of the resonant cavity 12 to generate an acoustic wave that is substantially trapped or localized within the resonant cavity 12. Although the transducer 22 is shown as being mounted on the mesa 16, if the mesa 16 is formed on the contact surface 18 of the substrate 14, the transducer 22 may be mounted directly on the substrate surface of the resonant cavity 12 opposite the mesa 16. The transducer 22 is electrically connected to a sensing circuit 26 or separate processing unit. [0023] The acoustic wave switch 10 may use any type of acoustic wave capable of being substantially trapped in the resonant cavity 12. For simplicity, the acoustic wave switch 10 is described using a shear wave in a direction that is in the plane of the substrate 14, wherein the shear wave energy extends in a direction perpendicular to the plane of the substrate 14, that is, through the thickness of the substrate 14.

[0024] Because the fundamental or zeroth order mode of a horizontally polarized shear wave may not be substantially trapped, higher order shear wave modes are used in accordance with embodiments of the present invention. It should be appreciated that because the acoustic wave used is trapped, the wave is a standing wave. A standing wave has a number of advantages over an acoustic wave that propagates or travels along a path in a substrate. For example, propagating waves are not confined to the main path of propagation but can diffract off of the main path complicating touch detection. This is opposed to a standing wave that, by its nature, is confined to the area of a particular resonant cavity 12. Because the acoustic wave is confined, touch detection is easily accomplished. Further, the wave energy of a propagating wave is not stored at any location along the path. Once a propagating wave passes a point along the path, the wave is gone, thereby making timing and control critical for touch detection with propagating waves. There are no timing or control issues with a standing wave because the wave energy is stored in the resonant cavity 12. Moreover, a propagating wave is not a resonating wave. As such, the wave energy decays as it travels. A standing wave is resonant so that the wave is reinforced and prolonged. As a result, the standing wave has a much greater amplitude than a wave that is not confined. The operation of the acoustic wave switch 10 is further described in United States Patent No. 7,106,310, entitled "Acoustic Wave Touch Actuated Switch" (the "'310 patent").

[0025] The acoustic wave switch 10 provides a system and method of detecting pressure and movement with respect to the contact surface 18 of the acoustic wave switch 10, using acoustic wave energy that employs trapped energy concepts to create a localized mechanical resonator, or resonant cavity 12. The '310 patent discloses an acoustic wave switch that includes a substrate with an acoustic wave/resonant cavity formed therein such that the mass per unit area of the acoustic cavity is greater than the mass per unit area of the substrate adjacent the acoustic cavity. A transducer is mounted on the acoustic cavity for generating an acoustic wave that is substantially trapped in the cavity. Contact on the contact surface 18 of the acoustic wave cavity absorbs acoustic wave energy and produces a detectable change in the impedance of the transducer. Moreover, as contact occurs, the resonant frequency changes, which may be detected by the sensing circuit 26 and/or processing unit which is electrically connected to the transducer.

[0026] The acoustic wave switch 10 has a high Q (the ratio of the stored energy to lost or dissipated energy over a complete cycle) so as to enable contact to be detected by extremely simple, low-cost circuitry. The acoustic wave switch 10 is rugged, explosion proof, operates in the presence of liquids and other contaminants, and has a low power consumption.

[0027] The acoustic wave switch 10 may be connected to an extremely simple touch detection or sensing circuit, such as shown and described in the '310 patent. For example, the transducer 22 may be coupled to a multiplexer that sequentially couples the transducer 22 and its associated acoustic wave switch 10 to an oscillator, as discussed in the '310 patent. A touch on the contact surface 18 may be detected through a detected change in impedance, as described in the '310 patent. A change in impedance is detected as soon as contact is made with the contact surface 18.

[0028] Optionally, contact on the contact surface 18 may be detected by measuring the decay time of the acoustic wave within the resonant cavity 12. United States Patent No. 7,265,746, entitled "Acoustic Wave Touch Detection Circuit and Method" (the "'746 patent"), describes a controller that detects a sensed event such as a touch on an acoustic wave switch/sensor based on the decay time. The trapped acoustic wave within the acoustic wave/resonant cavity acts to "ring" the acoustic wave/resonant cavity. That is, as a voltage is applied to the transducer, the transducer operates to resonate the resonant cavity. [0029] As described in the '746 patent, the sensing circuit 26 is operatively connected to the acoustic wave switch 10 may include a controller that drives the transducer 22 to generate a resonant acoustic wave in the resonant cavity 12 during a first portion of a sampling cycle. In a second portion of the sampling cycle, the controller monitors the time that it takes for the acoustic wave signal from the transducer 22 to decay to a predetermined level. Based on the decay time, the controller detects a sensed event, such as contact on the contact surface 18.

[0030] As noted above, United States Patent No. 7,027,943, entitled "Acoustic Wave Ice and Water Detector" (the "'943 patent"), discloses an acoustic wave sensor that utilizes one or more acoustic waves trapped in an acoustic wave cavity to detect the presence of one or more substances on a surface of the acoustic wave cavity. To detect the presence of liquid, a trapped torsional acoustic wave is used.

[0031] Out-of-plane acoustic mode displacements are desirable for detecting the presence of liquid, because the amplitudes of the out-of-plane acoustic modes are generally more sensitive to the presence of liquids than shear modes. However, out-of- plane acoustic modes generally do not exhibit waveguide cut-off phenomena, and therefore may not be trapped by way of a cut-off. That is, before development of embodiments of the acoustic wave switch described below, out-of-plane acoustic waves were difficult to trap within a resonant cavity.

[0032] Embodiments of the present invention have been developed to provide an acoustic wave switch that uses out-of-plane acoustic modes to detect the presence of liquid. It has been found that an acoustic wave switch having a mesa that is creased or clamped around its periphery to form a thinned area is capable of trapping out-of-plane acoustic waves within the mesa.

[0033] Figure 2 illustrates a front view of an acoustic wave switch 30, according to an embodiment of the present invention. The acoustic wave switch 30 includes a contact surface 32 connected to a support post 34, which may be threaded. The support post 34 is configured to be secured into a reciprocal opening of a panel (not shown), or the like, onto or into which the acoustic wave switch 30 is positioned.

[0034] Figure 3 illustrates a simplified cross-sectional view of the acoustic wave switch 30 through line 3-3 of Figure 2, according to an embodiment of the present invention. The contact surface 32 of the acoustic wave switch 30 is formed from a substrate 36 having a mesa 38, which defines an acoustic wave cavity. A thinned periphery or moat 40 is formed around the mesa 38. The moat 40 may be formed through creasing or clamping, for example. The moat 40 is, in turn, surrounded by a raised circumferential ridge 42, which may be thicker than the mesa 38, as shown in Figure 3. The substrate 36 may be formed of metal, such as stainless steel, plastic, or any other material that is capable of trapping an acoustic wave within the mesa 38.

[0035] A compressional transducer 44 is secured underneath the mesa 38 and is configured to excite the acoustic wave cavity defined by the mesa 38, thereby resulting in out-of-plane acoustic mode displacement, which is confined to the face 46 of the mesa 38.

[0036] Unlike the acoustic wave switch 10, which includes a raised mesa 16 on the substrate 14, the acoustic wave switch 30 includes a mesa 38 surrounded by the thinned circumferential moat 40, which is, in turn, surrounded by the raised circumferential ridge 42. As shown in Figure 3, the mesa 38 gradually thins from the center X of the switch 30 radially outward. Thus, the center of the mesa 38 is the thickest portion of the mesa 38, while the thickness gradually decreases radially outward toward the moat 40.

[0037] The moat 40 is the thinnest portion of the contact surface 32. The thickness of the contact surface 32 increases from the moat 40 radially outward to the circumferential ridge 42. As shown, the circumferential ridge 42 may be thicker than the mesa 38. The ridge 42 may be an upright wall that surrounds the moat 40.

[0038] It has been found that the thinned moat 40 provides out-of-plane acoustic mode displacements when the transducer 44 is excited to produce acoustic waves within the mesa 38. The out-of-plane acoustic mode displacements are particularly useful in detecting the presence of liquid because the amplitudes of the modes are generally more sensitive to the presence of liquids, as compared to shear modes.

[0039] The thinned moat 40 causes the contact face 46 to act as a diaphragm. Excitation of the acoustic wave cavity defined by the mesa 38 with the compressional mode transducer 44 creates displacement modes that do not extend beyond the moat 40 into the circumferential ridge 42. That is, the waves do not pass into the circumferential ridge 42. Instead, the thinned moat 40 acts to trap the out-of-plane acoustic waves to the face 46 of the mesa 38.

[0040] The configuration of the mesa 38, with its gradual thinning into the moat 40, and the circumferential ridge 42, which acts to block the waves from entering therein, confines the out-of-plane acoustic mode waves to the mesa 38. This configuration may operate as a membrane with radial symmetry, similar to drumstick contact surfaces of a steel drum. In essence, the moat 40 may be a creased area that causes the out-of-plane acoustic waves to be trapped within the mesa 38. Because of the gradual thinning from the mesa 38 to the moat 40, the contact face 46 acts as a clamped plate or diaphragm. It has also been found that the gradual thinning toward the moat 40 is not overly sensitive to bubble formation, which could otherwise lead to liquid detection errors.

[0041] Confinement of the out-of-plane waves to the face 46 is generally desired because otherwise the body of the switch itself could be acoustically active and cause the signal amplitude to drastically diminish due to mounting in a fluid-containing vessel.

[0042] Figure 4 illustrates a cross-sectional view of the acoustic wave switch 30 through line 3-3 of Figure 2, according to an embodiment of the present invention. The switch 30 may also include a printed circuit board 48, which may control operation of the acoustic wave switch 30. A connection pin 50 connects the compressional transducer 44 to the printed circuit board 48. Additionally, a ground pin 52 may abut into an underside of the substrate 36 and connect to the printed circuit board 48.

[0043] Figure 5 illustrates a cross-sectional view of the acoustic wave switch 30, according to an embodiment of the present invention. In this embodiment, a mass 60, such as a stud, post, block, or the like, is secured to an underside of the transducer 44 (on the side of the transducer 44 that is not contacting the substrate 36). The mass 60 may be formed from a melted hemisphere of solder that is positioned on the underside of the transducer 44. The mass 60 may be formed of ferrous and/or non-ferrous materials. It has been found that the mass 60, which may weigh approximately 0.065 - 0.8 grams, for example, dramatically improves resonance within the mesa 38.

[0044] Figure 6 illustrates a cross-sectional view of the acoustic wave switch 30, according to an embodiment of the present invention. In this embodiment, the mass 60, such as a stud, post, block, or the like, is secured between the transducer 44 and the substrate 36. The mass 60 is positioned on top of the transducer 44 and to an underside of the substrate 36. In general, the embodiment shown in Figure 6 is similar to the embodiment shown in Figure 5, except that the mass 60 is positioned between the transducer 44 and the substrate 36 in Figure 6, as opposed to the transducer 44 being positioned between the mass 60 and the substrate 36, as shown in Figure 5.

[0045] Referring to Figures 5 and 6, the inertia of the mass 60 may cause the out-of-plane displacement on the face 46 to increase, and to increase the tensile and compressional attributes of the transducer 44. In any event, it has been found through empirical experimentation that adding the mass 60 to the underside of the transducer 44, or between the transducer 44 and the substrate 36, dramatically improves the response of the acoustic wave switch 30.

[0046] Thus, embodiments of the present invention provide an acoustic wave switch that is configured to efficiently detect the presence of liquid. Embodiments of the present invention provide an acoustic wave switch that uses out-of-plane acoustic modes to detect the presence of liquid. The thinned periphery or moat that surrounds the mesa acts to trap the out-of-plane acoustic mode waves within the mesa 38. As noted above, out-of-plane acoustic mode waves are more sensitive to the presence of liquid than shear modes.

[0047] While various spatial and directional terms, such as top, bottom, lower, mid, lateral, horizontal, vertical, front and the like may used to describe embodiments of the present invention, it is understood that such terms are merely used with respect to the orientations shown in the drawings. The orientations may be inverted, rotated, or otherwise changed, such that an upper portion is a lower portion, and vice versa, horizontal becomes vertical, and the like.

[0048] Variations and modifications of the foregoing are within the scope of the present invention. It is understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention. The claims are to be construed to include alternative embodiments to the extent permitted by the prior art.

[0049] Various features of the invention are set forth in the following claims.

Claims

1. An acoustic wave switch assembly comprising:

a substrate having contact and mounting surfaces, wherein the contact surface is opposite the mounting surface;

a mesa defining an acoustic wave cavity formed in said substrate, wherein said mesa gradually thins radially outward to a thinned moat that surrounds said mesa; and a transducer secured to said mounting surface of said substrate, said transducer configured to generate a trapped acoustic wave within said acoustic wave cavity.

2. The acoustic wave switch assembly of claim 1, further comprising a raised ridge surrounding said thinned moat.

3. The acoustic wave switch assembly of claim 2, wherein said raised ridge is thicker than said mesa, and wherein said mesa is thicker than said thinned moat.

4. The acoustic wave switch assembly of claim 1, wherein said transducer is a compressional wave transducer configured to generate the trapped acoustic wave as a compressional out-of-plane wave.

5. The acoustic wave switch assembly of claim 1, further comprising a mass secured to an exposed surface of said transducer.

6. The acoustic wave switch assembly of claim 5, wherein said mass is formed from one or more of ferrous, non-ferrous materials, or of melted solder.

7. An acoustic wave switch assembly comprising:

a mesa defining an acoustic wave cavity formed in said substrate;

a thinned moat that surrounds said mesa; and

a raised ridge that surrounds said thinned moat.

8. The acoustic wave switch of claim 7, further comprising a transducer secured to said mounting surface of said substrate, said transducer configured to generate a trapped acoustic wave within said acoustic wave cavity.

9. The acoustic wave switch of claim 7, wherein said mesa gradually thins radially away from a center toward said thinned moat.

11. The acoustic wave switch assembly of claim 7, wherein said raised ridge is thicker than said mesa, and wherein said mesa is thicker than said thinned moat.

12. The acoustic wave switch assembly of claim 8, wherein said transducer is a compressional wave transducer configured to generate the trapped acoustic wave as a compressional out-of-plane wave.

13. The acoustic wave switch assembly of claim 7, further comprising a mass secured to an exposed surface of said transducer.

14. The acoustic wave switch assembly of claim 13, wherein said mass is formed of one or more of ferrous or non-ferrous materials, or melted solder.

15. An acoustic wave switch assembly comprising:

a mesa defining an acoustic wave cavity formed in said substrate, wherein said mesa gradually thins radially away from a center toward a thinned moat that surrounds said mesa;

a raised ridge that surrounds said thinned moat, wherein said raised ridge is thicker than said mesa, and wherein said mesa is thicker than said thinned moat; and

a compressional wave transducer secured to said mounting surface of said substrate, said transducer configured to generate a trapped compressional acoustic wave within said acoustic wave cavity.

16. The acoustic wave switch assembly of claim 15, further comprising a mass secured to an exposed surface of said transducer.

17. The acoustic wave switch assembly of claim 15, wherein said mass is formed of one or more of ferrous or non-ferrous materials, or melted solder.