GB2349465A - Thin film SAW strain gauge - Google Patents
Thin film SAW strain gauge Download PDFInfo
- Publication number
- GB2349465A GB2349465A GB9909652A GB9909652A GB2349465A GB 2349465 A GB2349465 A GB 2349465A GB 9909652 A GB9909652 A GB 9909652A GB 9909652 A GB9909652 A GB 9909652A GB 2349465 A GB2349465 A GB 2349465A
- Authority
- GB
- United Kingdom
- Prior art keywords
- substrate
- layer
- deposited
- arrays
- array
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
- 239000010409 thin film Substances 0.000 title description 9
- 239000000758 substrate Substances 0.000 claims abstract description 60
- 239000010410 layer Substances 0.000 claims abstract description 46
- 238000003491 array Methods 0.000 claims abstract description 19
- 239000000463 material Substances 0.000 claims abstract description 18
- 239000002356 single layer Substances 0.000 claims abstract description 4
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 claims description 10
- 238000000151 deposition Methods 0.000 claims description 6
- 230000008021 deposition Effects 0.000 claims description 6
- 238000000034 method Methods 0.000 claims description 5
- 239000010453 quartz Substances 0.000 claims description 5
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 5
- 239000011787 zinc oxide Substances 0.000 claims description 5
- 238000004544 sputter deposition Methods 0.000 claims description 4
- 238000012360 testing method Methods 0.000 claims description 4
- 230000008569 process Effects 0.000 claims description 3
- 150000004767 nitrides Chemical class 0.000 claims description 2
- 230000005284 excitation Effects 0.000 claims 2
- 229910017083 AlN Inorganic materials 0.000 claims 1
- PIGFYZPCRLYGLF-UHFFFAOYSA-N Aluminum nitride Chemical compound [Al]#N PIGFYZPCRLYGLF-UHFFFAOYSA-N 0.000 claims 1
- 239000002305 electric material Substances 0.000 description 3
- 238000005452 bending Methods 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 230000018109 developmental process Effects 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 229910000611 Zinc aluminium Inorganic materials 0.000 description 1
- 239000004411 aluminium Substances 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 230000003321 amplification Effects 0.000 description 1
- 238000009530 blood pressure measurement Methods 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000005672 electromagnetic field Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012806 monitoring device Methods 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 238000003199 nucleic acid amplification method Methods 0.000 description 1
- 229920003023 plastic Polymers 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 238000010897 surface acoustic wave method Methods 0.000 description 1
- 230000002277 temperature effect Effects 0.000 description 1
- 238000005303 weighing Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L1/00—Measuring force or stress, in general
- G01L1/16—Measuring force or stress, in general using properties of piezoelectric devices
- G01L1/162—Measuring force or stress, in general using properties of piezoelectric devices using piezoelectric resonators
- G01L1/165—Measuring force or stress, in general using properties of piezoelectric devices using piezoelectric resonators with acoustic surface waves
Landscapes
- Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- General Physics & Mathematics (AREA)
- Measuring Fluid Pressure (AREA)
- Piezo-Electric Or Mechanical Vibrators, Or Delay Or Filter Circuits (AREA)
Abstract
The strain gauge comprises one or more juxtaposed interdigitated electrode arrays 16,17 deposited as a thin layer onto a piezoelectric substrate 15 wherein the substrate is a flexible or rigid layer. Typically the substrate is in the form of a single layer of material of substantially uniform characteristics. Alternatively the substrate is formed from at least two layers each layer differing in some characteristic such as piezo electric behaviour. The, or at least one, array in the structure on the substrate may have a secondary layer deposited upon it. The secondary layer serves in the structure to passivate the surface of, or each, array on which it is deposited. Typically in the structure the secondary layer includes one or more interdigitated arrays as aforesaid and/or some other device for connection to an array either in the secondary layer or in some either layer in the structure. Radio means R may be provided to excite and interrogate the device.
Description
2349465 THIN FILM DEVICE This invention relates to a thin film device. In
particular it is concerned with a thin film device deposited on a substrate. 5 It is known to deposit a surface acoustic wave ('SAW') device made up of a layer in the form of an interdigitated array of electrodes deposited on a substrate of piezoelectric material. On introducing a signal into an input side of the array any subsequent deformation of the substrate material results in a deformation of the array which can be detected and measured by a corresponding change in an output signal from the output side of the array. By using such a device it is possible to measure strain to a much higher degree of accuracy than is possible with a conventional resistive strain gauge. The small size to which a SAW device, and any immediate envelope for it, can be manufactured ensures that the device does not intrude to any significant extent on a component with which the device is being used nor affect behaviour of the component. Furthermore the array in such a device can be interrogated remotely so reducing even further any physical intrusion by the SAW device into the working environment.
According to a first aspect of the present invention there is provided a device in the form of one or more structures, the or each structure comprising an interdigitated electrode array deposited as a thin layer onto a piezoelectric substrate wherein the substrate is a flexible or rigid layer.
According to a first preferred version of the first aspect of the present invention the substrate includes a material selected from the group comprising quartz, zinc oxide or aluminium. nitride. Typically the substrate is can be in the form of a single layer of material of substantially uniform characteristics.
2 According to a second preferred version of the first aspect of the present invention or of any preceding preferred version thereof the substrate is formed by a sputtering process of deposition which serves to provide for a particular alignment of the substrate material to optimise a piezoelectric characteristic of 5 the deposited material.
According to a third preferred version of the first aspect of the present invention or any preceding preferred version thereof the structure includes at least two juxtaposed interdigitated arrays deposited on the substrate. Typically the structure includes four juxtaposed interdigitated arrays deposited on a common substrate with interconnections between the arrays to enable the arrays in combination to serve as a bridge network.
According to a fourth preferred version of the first aspect of the present invention or any preceding preferred version thereof the, or at least one, array in the structure on the substrate has a secondary layer deposited upon it. Typically the secondary layer serves in the structure to passivate the surface of, or each, array on which it is deposited.
According to a preferred version of the fourth preferred version of the first aspect of the present invention the structure the secondary layer includes one or more interdigitated arrays as aforesaid and/or some other device for connection to an array either in the secondary layer or in some either layer in the structure.
According to a second aspect of the present invention there is provided a device according to the first aspect or any preferred version thereof with an encapsulating means which in combination with the substrate serve to enclose the, or all, the structures, incorporated in the device.
3 An exemplary embodiment of the invention will now be described with reference to the accompanying drawings for a torque measuring device for use in the automotive field, wherein: Figure 1 is of a shaft on which the device is mounted; and
Figure 2 is a block diagram of a system for driving the device shown in Figure 1.
FIGURES 1 AND 2 Shaft 11 rotating about longitudinal axis L in direction of arrow A serves to transmit torque from end 12 to end 13. The shaft 11 has mounted upon it a device 14 comprising a flexible thin film substrate 15 of quartz (an inherently piezo-electric material) bonded to the shaft. Prior to attachment to the shaft 11 device 14 was fabricated by means of a deposition on the substrate 15 of two thin film structures 16, 17 each being made up of a pair of inter- digitated electrodes typically, in the case of structure 16, a pair 18 made up of electrodes 19, 20. Each structure 16, 17 has an axis, respectively, axis 16A, 17A.
The substrate 15 is mounted on the shaft 11 so that axes 16A, 17A lie orthogonally relative to axis L of the shaft 11. The device 14 is housed within a metal envelope 18 (shown only in part) to isolate the structures 16, 17 and their associated components 16B, 17B mounted on, or by way of, the substrate 15. In this way the operating elements of the device 14 are isolated from the ambient atmosphere. In addition the use of a metallic housing 18 also serves to isolate the operating elements from stray electromagnetic fields in the vicinity of the shaft. The selected parts of the device 14 are chosen to provide for effective operation in an ambient working temperature range of between - 40 to 1250C
The components 16B, 17B are in the form of miniaturised radio wave handling devices to enable the SAW structures 16, 17 to be excited and interrogated using 4 a remotely mounted radio transmitter receiver R. This enables the device 14 to be mounted without a need for physical connections between the device and monitoring device. The device has an operating frequency of 20OMHz but alternative embodiments could be operated at a frequency in the Gigahertz 5 range.
Development work has established a device 14 can be provided which in packaged form has a plan area about 10mm square.
The substrate 15 is bonded to the shaft so as to effectively transmit strain from the shaft 11 into the structures 16, 17. The substrate 15 while being flexible must also be sufficiently rigid and of satisfactory surface finish to ensure that the structure 16,17 can be accurately deposited as a thin film upon, and adhere to, the substrate 15.
In order to minimise temperature effects the temperature coefficients and thermal mass of the structures 16, 17 are made as near identical as possible. In addition the axes 16A, 17A of the structures 16, 17 are symmetrically positioned on the substrate..
The above example refers to a substrate 15 of quartz that is to say an inherently piezoelectric material upon which the structures 16, 17 are deposited directly. Other piezo electric materials can be used. Alternatively a suitable base material can be used which is not inherently piezo electric with a suitable piezo electric material deposited upon it. Typically a layer of silicon can have a thin layer of zinc oxide deposited upon it and structures corresponding to structures 16, 17 deposited on the zinc oxide layer. Again with a multi-layered substrate the lowest layer, which is to be attached to the component under test, can be a plastics material rather than a ceramic one. The method of deposition to form the substrate can also be selected to enhance the characteristics required by the finished product. Typically sputtering can be used to deposit the substrate so as to achieve the piezo-electric function.
The desired characteristics of the device can be optimised by the method of deposition of the substrate, whether as a homogeneous layer or as a number of layers; by the surface finish of the substrate which is to receive the thin film interdigitated structures forming the SAW. 5 By making use of higher radio operating frequencies the size of the operating structures can be reduced with a consequent reduction in the overall size of the device and so in turn its cost.
The exemplary embodiment describes a basic SAW device involving a substrate having a pair of structures deposited upon it. Further developments are envisaged where more than two structures can be deposited on the substrate having a geometric relationship with each other. Typically a network can be provided on a given substrate incorporating four structure linked as a bridge for strain measurement.
A substrate can be used to support circuitry and other elements, including active elements, typically in the form of thin film layers. These can serve in the modification, amplification or in some other way modify an output from or an input to one or more of the structures. This could include temperature compensation. The deposited components could include transistors or other active modules.
The example refers to a substrate bearing two structures. However the use of layer technology would enable more than one layer of structures or other components to be carried by the substrate with connection extending among elements in a given layer or extending between elements in different layers.
The use of a SAW device of the proposed type provides for a sensitivity orders of magnitude greater than a conventional strain gauge. The use of relatively high radio frequency for exciting and interrogating the device provides for the 6 use of relatively small components and the ability to mount on the component under test a small and light object which will not act to influence the behaviour of the component.
The exemplary embodiment is sued to measure the torque of a rotating shaft. However the ability to measure accurately strain arising in a local area through the use of one or more devices according to the present invention enables it to be applied to a wide range of applications. Thus attachment of the device to a surface subject to deformation, such as by changes in pressure of a fluid, which should be taken to include air, contained by the surface, would enable the device to be used for pressure measurement or change. The invention can be used to measure strain arising from bending rather than twisting. The invention lends itself to readily providing a device of small size. For small magnitudes of strain the invention can provide for a device for measuring torque required to mix small volumes of liquid or measuring load to weigh bank notes. For large scale use a device can be provided for measuring torque transmitted by a jet engine drive shaft or ships propeller shaft. Further possible applications include tyre pressure monitoring, weighing functions, and measurement of force, bending, vibration and load.
7
Claims (5)
1 A device in the form of one or more structures, the or each structure comprising one or more juxtaposed interdigitated electrode arrays deposited as a thin layer onto a piezoelectric substrate wherein the substrate is a flexible or rigid layer.
2 A device as claimed in Claim 1 wherein the substrate is in the form of a single layer of material of substantially uniform characteristics
3 A device as claimed in Claim 1 wherein the substrate is formed from at least two layers each layer differing in some characteristic such as piezo electric behaviour.
4 A device as claimed in any preceding claim wherein the substrate is, or includes, a material selected from the group comprising quartz, zinc oxide or aluminium nitride.
A device as claimed in any preceding claim wherein the substrate is formed by a sputtering process of deposition which serves to provide for a particular alignment of the substrate material to optimise a piezoelectric characteristic of the deposited material.
6 A device as claimed in any preceding claim wherein the structure includes at least two juxtaposed interdigitated arrays deposited on the substrate.
7 A device as claimed in Claim 6 wherein the structure includes four juxtaposed interdigitated arrays deposited on a common substrate with interconnections between the arrays to enable the arrays in combination to serve as a bridge network.
8 8 A device as claimed in any preceding claim wherein the, or at least one array in the structure on the substrate has a secondary layer deposited upon it.
9 A device as claimed in Claim 6 wherein the secondary layer serves in the structure to passivate the surface of, or each, array on which it is deposited.
A device as claimed in Claim 6 wherein in the structure the secondary layer includes one or more interdigitated arrays as aforesaid and/or some other device for connection to an array either in the secondary layer or in some either layer in the structure.
11 A device as claimed in any preceding claim including an encapsulating means which in combination with the substrate serve to enclose the, or all, the structures, incorporated in the device.
12 A device as claimed in any preceding claim adapted for excitation and/or interrogation by radio means remote from the device.
13 A test component equipped with a device as claimed in any preceding claim.
14 A device as hereinbefore described with reference to the accompanying drawings.
9 Amendments to the claims have been filed as follows CLAIMS I An electronic device in the form of one or more structures characterised in that the, the or each structure comprises one or more juxtaposed interdigitated electrode arrays deposited as a thin layer onto a piezoelectric substrate wherein the substrate is a flexible or rigid layer. 2 A device as claimed in Claim 1 characterised in that the substrate is in the form of a single layer of material of substantially uniform characteristics 3 A device as claimed in Claim 1 characterised in that the substrate is formed from at least two layers each layer differing in some characteristic such as piezo electric behaviour. 4 A device as claimed in any preceding claim characterised in that the substrate is, or includes, a material selected from the group comprising quartz, zinc oxide or alurninium nitride.
5 A device as claimed in any preceding claim characterised in that the substrate is formed by a sputtering process of deposition which serves to provide for a particular alignment of the substrate material to optimise a piezoelectric characteristic of the deposited material. 6 A device as claimed in any preceding claim characterised in that the structure includes at least two juxtaposed interdigitated arrays deposited on the substrate. 7 A device as claimed in Claim 6 characterised in that the structure includes four juxtaposed interdigitated arrays deposited on a common substrate with interconnections between the arrays to enable the arrays in combination to serve as a bridge network.
(0 8 A device as claimed in any preceding claim characterised in that the, or at least one, array in the structure on the substrate has a secondary layer deposited upon it. 9 A device as claimed in Claim 6 characterised in that the secondary layer serves in the structure to passivate the surface of, or each, array on which it is deposited. 10 A device as claimed in Claim 6 characterised in that the secondary layer includes one or more interdigitated arrays as aforesaid and/or some other device for connection to an array either in the secondary layer or in some either layer in the structure. 11 A device as claimed in any preceding claim characterised by an encapsulating means which in combination with the substrate serve to enclose the, or all, the structures, incorporated in the device. 12 A device as claimed in any preceding claim characterised by being adapted for excitation and/or interrogation by radio means remote from the device. 13 A test component equipped with a device as claimed in any preceding claim. 14 A device as hereinbefore described with reference to the accompanying drawings.
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9909652A GB2349465A (en) | 1999-04-27 | 1999-04-27 | Thin film SAW strain gauge |
| PCT/GB2000/001437 WO2000065320A1 (en) | 1999-04-27 | 2000-04-26 | Thin film device |
| AU45802/00A AU4580200A (en) | 1999-04-27 | 2000-04-26 | Thin film device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9909652A GB2349465A (en) | 1999-04-27 | 1999-04-27 | Thin film SAW strain gauge |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9909652D0 GB9909652D0 (en) | 1999-06-23 |
| GB2349465A true GB2349465A (en) | 2000-11-01 |
Family
ID=10852339
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9909652A Withdrawn GB2349465A (en) | 1999-04-27 | 1999-04-27 | Thin film SAW strain gauge |
Country Status (3)
| Country | Link |
|---|---|
| AU (1) | AU4580200A (en) |
| GB (1) | GB2349465A (en) |
| WO (1) | WO2000065320A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8479590B2 (en) | 2010-11-18 | 2013-07-09 | Honeywell International Inc. | System for monitoring structural assets |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2889375B1 (en) | 2005-07-29 | 2008-02-15 | Temex Sas Soc Par Actions Simp | HYBRID RESONANT STRUCTURE |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3888115A (en) * | 1973-03-30 | 1975-06-10 | Texas Instruments Inc | Strain sensor |
| US4096740A (en) * | 1974-06-17 | 1978-06-27 | Rockwell International Corporation | Surface acoustic wave strain detector and gage |
| JPS60122303A (en) * | 1983-12-05 | 1985-06-29 | Agency Of Ind Science & Technol | Strain gauge |
| WO1991013832A2 (en) * | 1990-03-03 | 1991-09-19 | Anthony Lonsdale | Method and apparatus for measuring strain |
| GB2298486A (en) * | 1995-03-03 | 1996-09-04 | Era Patents Ltd | SAW displacement transducer having a moveable electrode |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5687913A (en) * | 1979-12-19 | 1981-07-17 | Matsushita Electric Ind Co Ltd | Surface elastic wave element |
| FR2553884B1 (en) * | 1983-10-25 | 1985-12-27 | Thomson Csf | SURFACE ELASTIC WAVE FORCE SENSOR |
| JPH036915A (en) * | 1989-06-02 | 1991-01-14 | Clarion Co Ltd | Surface acoustic wave convolver and convolution integration device using same |
| EP0475139A3 (en) * | 1990-09-04 | 1992-03-25 | Motorola, Inc. | Method and apparatus for saw device passivation |
| US5047363A (en) * | 1990-09-04 | 1991-09-10 | Motorola, Inc. | Method and apparatus for reducing heterostructure acoustic charge transport device saw drive power requirements |
| US5365770A (en) * | 1993-04-05 | 1994-11-22 | Ford Motor Company | Ultrasonic wave interferometers |
| WO1997009596A2 (en) * | 1995-09-04 | 1997-03-13 | Siemens Aktiengesellschaft | Process and sensor for detecting operational data on moving/rotating parts of a device, especially an electric motor |
-
1999
- 1999-04-27 GB GB9909652A patent/GB2349465A/en not_active Withdrawn
-
2000
- 2000-04-26 AU AU45802/00A patent/AU4580200A/en not_active Abandoned
- 2000-04-26 WO PCT/GB2000/001437 patent/WO2000065320A1/en not_active Ceased
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3888115A (en) * | 1973-03-30 | 1975-06-10 | Texas Instruments Inc | Strain sensor |
| US4096740A (en) * | 1974-06-17 | 1978-06-27 | Rockwell International Corporation | Surface acoustic wave strain detector and gage |
| JPS60122303A (en) * | 1983-12-05 | 1985-06-29 | Agency Of Ind Science & Technol | Strain gauge |
| WO1991013832A2 (en) * | 1990-03-03 | 1991-09-19 | Anthony Lonsdale | Method and apparatus for measuring strain |
| GB2298486A (en) * | 1995-03-03 | 1996-09-04 | Era Patents Ltd | SAW displacement transducer having a moveable electrode |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8479590B2 (en) | 2010-11-18 | 2013-07-09 | Honeywell International Inc. | System for monitoring structural assets |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9909652D0 (en) | 1999-06-23 |
| WO2000065320A1 (en) | 2000-11-02 |
| AU4580200A (en) | 2000-11-10 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |