GB2451861A - Surface acoustic wave based sensor in vented housing - Google Patents
Surface acoustic wave based sensor in vented housing Download PDFInfo
- Publication number
- GB2451861A GB2451861A GB0715886A GB0715886A GB2451861A GB 2451861 A GB2451861 A GB 2451861A GB 0715886 A GB0715886 A GB 0715886A GB 0715886 A GB0715886 A GB 0715886A GB 2451861 A GB2451861 A GB 2451861A
- Authority
- GB
- United Kingdom
- Prior art keywords
- lid
- substrate
- saw
- housing
- based sensor
- 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- Withdrawn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
- 238000010897 surface acoustic wave method Methods 0.000 title abstract 4
- 239000000758 substrate Substances 0.000 claims abstract description 38
- 239000000463 material Substances 0.000 claims abstract description 11
- 239000000428 dust Substances 0.000 claims abstract description 3
- 239000012530 fluid Substances 0.000 claims description 4
- 230000001133 acceleration Effects 0.000 abstract description 7
- 230000008859 change Effects 0.000 description 7
- 238000005259 measurement Methods 0.000 description 7
- 230000035945 sensitivity Effects 0.000 description 5
- 238000013022 venting Methods 0.000 description 4
- 239000000853 adhesive Substances 0.000 description 3
- 230000001070 adhesive effect Effects 0.000 description 3
- 229910000833 kovar Inorganic materials 0.000 description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 238000005452 bending Methods 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 229910001092 metal group alloy Inorganic materials 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 230000004044 response Effects 0.000 description 2
- 229910000990 Ni alloy Inorganic materials 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 229910010293 ceramic material Inorganic materials 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000005284 excitation Effects 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 238000012806 monitoring device Methods 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 239000010453 quartz Substances 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 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
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/22—Details, e.g. general constructional or apparatus details
- G01N29/32—Arrangements for suppressing undesired influences, e.g. temperature or pressure variations, compensating for signal noise
- G01N29/323—Arrangements for suppressing undesired influences, e.g. temperature or pressure variations, compensating for signal noise compensating for pressure or tension variations
Abstract
A surface acoustic wave (SAW) based sensor 1 comprises a base 2 and sides 3a which together form a shallow container or chamber, and a lid 5 which closes the container to form an aperture or chamber 6 therein. One or more substrates 7 are mounted in the aperture. SAW devices X, Y, Z are mounted on the substrate 7 so as to be responsive to changes in the strain field within the substrate. One side of the lid 5 is exposed to the environment surrounding the housing. A projection 10 formed on the lid 5 engages against the substrate 7 so as to transmit deflections in the lid 5 to the substrate 7. The container or chamber 4 is vented by means of holes 12 formed in the sides 3a such that there is no pressure differential across the lid 5. The holes are sized to prevent dust ingress, and may contain filters. The container may also be vented by forming the lid from a permeable material. The sensor may be adapted to measure force, acceleration or torque.
Description
VENTED SAW BASED SENSOR
This present invention relates to SAW based sensors for measurement of force, torque and acceleration.
SAW based sensors are known in the art for measurement of pressure, for example in our United Kingdom patent application GB-A-2352814. The SAW devices are mounted on a substrate which is disposed in a sealed package A i2_L...._t. __._ (uwAIrIIfig ictCicuv pui. u wgpiuw wi uuc suiiai pueu lu LL1 reference pressure and the other to the environment whose pressure is to be monitored, and has a dimple which engages the surface of the substrate.
Variations in pressure in the environment cause deflections of the diaphragm which are transmitted to the substrate through the dimple. This causes changes in the strain field within the substrate which results in a change in the characteristic frequency of the SAW devices. These changes in characteristic frequency can be monitored by interrogating the SAW devices and hence used to measure the pressure differential across the diaphragm.
According to the present invention there is provided a SAW based sensor comprising a housing having an internal aperture in which a substrate is mounted, at least one SAW device mounted on the substrate responsive to changes in the strain field within the substrate, and a lid extending at least partially across a side of the housing so as to have a side exposed to the environment surrounding the housing and having a projection formed thereon which engages against the substrate so as to transmit deflections in the lid, to the substrate, wherein the housing is vented such that there is no pressure differential across the lid.
A sensor in accordance with the invention has the advantage that the venting of the housing makes the or each SAW pressure insensitive, enabling simple and accurate measuring of other parameters such as force, torque or acceleration by use of suitable apparatus to take the lid responsive to the require parameter or parameters. For example, by virtue of the mass of the diapgrani, it will have some inertia and hence will deflect when accelerated.
The sensitivity can be improved by mounted a mass on the lid. Alternatively, a lever arm which is responsive to torque may be arrange with its end engaging against the lid, so as to deflect it in response to torque variations.
The aperture of the housing may be vented by provision of suitable holes in the housing to allow fluid in the surrounding environment, be it air, water or something else, to enter the aperture. Preferably, the holes are sized to prevent or substantially e1iminte the ingress of dirt, dust or the like into the aperture, which could interfere with the accurate operation of the device, Alternatively, some sort of filter may be used, extending across or even engaged in each hole, which prevents the passage of foreign bodies.
Alternatively, the lid may be formed of permeable material which allows the passage of fluid from the surrounding environment there-through, thereby ensuring pressure equalisation between the environment and the aperture.
in a preferred embodiment, three SAW resonator devices are mounted on the substrate each having a different resonant frequency. By analysis of the frequency shifts produced by distortion of the lid in one of the SAW devices a temperature compensated indication of the distortion of the SAW device and accordingly the displacement of the lid may be obtained, together with an indication of temperature of the SAW device. The three SAW devices maybe located on the same side of a common substrate or two rosy be located on one side of a common substrate and the other located on the opposite side of the common substrate. Alternatively, two individual substrates, one carrying two SAW devices (on the same or respective opposite sides thereof) and one carrying one SAW device may be provided, if more than one substrate is provided the arrangement should be such that one SAW device is subjected to strain from the deflection of the lid and two SAW devices are unstrained providing references for the measurements. The orientation of one of the unstrained SAW devices is preferably at a non-zero angle to the propagation direction of the other unstrained SAW device to provide unambiguous temperature information.
In the preferred embodiment of the invention the means remote from the edge of the frame for transmitting movement of the diaphragm to the SAW device comprises one or more bumps provided on the lid which can press on the substrate of a SAW device but which cannot exert a pulling force on the SAW device. The or each bump may be provided by a depression formed in the material of the lid or by means of a suitable member secured to the lid.
At least three SAW devices, one inclined with respect to at least one of the others, are required so that temperature can. be measured in addition to the other parameter (force, torque etc) Preferably, the lid acting as a diaphragm is a metal alloy, for example an iron, cobalt, nickel alloy. For example the lid may be of Kovar. The base is preferably of a metal alloy (for example Kovar) but may be of any suitable material, for example a ceramic material.
The invention will be better understood from the following description of preferred embodiments thereof, given by way of example only, reference being had to the accompanying drawings wherein: Figure 1 is a schematic sectional side view of a sensor of the invention; Figure 1A is a schematic top view of the sensor of Figure 1 with the lid removed; Figure 2 is a schematic view of an arrangement of the sensor of the invention for measuring force; Figure 3 is a schematic view of an arrangement of the sensor of the invention for measuring acceleration; and Figure 4 is a schematic view of an arrangement of the sensor of the invention for measuring torque.
Referring firstly to Figures 1 and IA, there is shown schematically a sensor package 1 comprising a base 2 and sides 3a which together form a shallow container 4. The container 4 may be formed of any suitable material, and in the preferred embodiment of the invention is formed of a metal material, for example ICovar. The container 4 has secured to the open end thereof a lid 5 having a major surface 5A acting as a diaphragm, the lidS closing the container 4 so as to form an internal chamber 6 therein. The lid may be of any suitable material, for example but not limited to Kovar.
The chamber is not sealed as in prior art systems but is instead vented so as to allow pressure equalisation across the lidS. In the illustrated embodiment this is achieved by provision of venting holes 12 in the side 3a of the container 4, although other venting systems may be used such as a permeable material for the lidS.
Mounted within the chamber 6 is a single substrate 7 which has formed thereon three SAW devices X, Y, Z, to provide a temperature compensated parameter (which hereinafter will be referred to as force but may be other none pressure based parameters such as torque or acceleration) and temperature mothtoring output The SAW devices may, for example, be SAW resonators having different resonant frequencies so that the changes in the resonant frequencies of the respective SAW devices may be determined using existing conventional SAW device interrogating technology.
The advantage of this arrangement is that the SAW devices X and Z can be located to remain unstrained and only the SAW device Y is strained when the lid is deformed. This considerably simplifies the process of sensor calibration and calculation of pressure and temperature from the results of frequency measurements.
Indeed, the measured difference between the two resonant frequencies, 1f -f depends only on temperature, not on the parameter deflecting the lid., so the value of the temperature can be immediately found from If -fj. Since both the devices X and Z are fabricated on the same substrate the frequency difference tf -f will depend on the temperature only in the case if the temperature characteristic of the device Z differs from that of the device X. In order to achieve such a differing temperature characteristic, the device Z is rotated relative to the device X at a certain angle as shown in Fig IA. The temperature sensitivity depends on the rotation angle. An angle is in the range of 10.300, in particular 16-20° has been found to achieve particularly good results. For example, and angle of 18° gives the sensitivity of approximately 2 kHz°C' for the ST-X cut quartz substrate.
The value of the parameter deflecting the lid can be found from the measured frequency difference IfA -fj. The sensitivity of If -fj to pressure usually also depends on temperature. Knowing this dependence from calibration data and having found the temperature from I -fJ allows full temperature compensation of the measured pressure to be achieved without a need of solving non-linear algebraic equations.
The substrate 7 is supported by the base 2 and for convenience may be secured to the base by means of a flexible adhesive. If adhesive is used to secure the substrate in position, the flexibility of the adhesive should be such that the respective end regions 8,9 of the substrate 7 are free to move as subslrate 7 is acted upon by a projection 10 formed integrally with or secured to the lid 5. Accordingly the end regions 8,9 will be substantially unstrained even when the central region is strained as a result of movement of the diaphragm.
The lid 5 is provided, in the centre of the major surface 5A, with a projection 10 formed by a dimple pressed in the material of the lid. The projection 10 is able to exert a downward force (as viewed in Fig 1B) at the centre of the substrate, but is unable to exert a force on ends 8,9.
Suitable antennae are provided for receiving an excitation signal for each of the SAW devices X, Y, Z and for transmitting a response signal from each of the SAW devices. The antennae may be located on the exterior of the container 4 in which case appropriate electrical connections must be provided extending through the material of the container 4. Alternatively, it may be possible to lay the antennae down as tracks on the interior surface of the container 4 or on suitable areas of the substrate 7 not occupied by the SAW devices themselves.
In use, a sensor package I as described above is used in a configuration in which changes in the measured parameter cause changes in the deflection of the lid 5. Since the chamber 6 is vented so there is no pressure differentia across the lid 5, any deflection of the lid 5 must as a result only of changes in the parameter to be measure and/or changes in temperature. Defection of the lid 5 will cause bending of the substrate 7 and accordingly a change in the resonant frequency of the central SAW device Y. The resonant frequency of the SAW devices may be determined by known techniques to calibrate the monitoring device.
If there is a change in parameter to be measured, this will result in a movement of the lid 5 acting as a diaphragm. An increase in parameter will result in movement of the diaphragm towards the base 2 and a reduction in parameter will cause a movement of the diaphragm away from the base 2.
Either change will result in a change in the bending of the substrate 7 with a resultant change in the resonant frequency of the central SAW device Y. By monitoring the changes in resonant frequency of the SAW devices an indication may be provided of the change in the parameter.
The embodiment of Figure 1 is particularly desirable in that one substrate 7 is provided and accordingly SAW devices may be provided on one surface only.
Figure 2 shows a practical configuration of the package for use in measuring force. The force to be measured is directly lid 5, suitable calibration being carried out to enable changes in the resonant frequency of the SAWs to be equated to actual force measurements. Changes in the applied force F causes variations in the deflection of the lid 5 which is transmitted to the substrate 7 through the projection 9, varying the strain field therein. This variation in the strain field in turn causes variations in the resonant frequency of the SAW Y which, is detected and converted into a force measurement.
Figure 3 shows a configuration for measuring acceleration. A mass such as a ball 20 is mounted on the lid above the projection 10 in order to increase the sensitivity. Due to the inertia of the ball 20, changes in acceleration will cause changes in the effective weight of the ball 20 which in turn will cause changes in the deflection of the lid 5. These are then detected by the SAW Y in exactly the same way as described above.
Figure 4 shows an apparatus for measuring torque using the sensor package 1. A lever ann 30 to which the torque to be measured is applied has a first end 31 pivotally mounted to a base and a second end 32 having a projection 33 thereon which engages against the lid 5. Variations in the torque valy the rotational position of the lever arm 30 which varies the load applied to the lid 5 through the projection 34 and hence the deflection of the lid 5. These variations in deflection of the lid are then detected and measured using the SAWs as previously described.
Although described in relation to the use of 3 SAWs, it wi]1 be understood that a single SAW may be used to take temperature uncompensated measurements, the important feature of the invention being the venting of the chamber to cBmi"te any pressure differential across the lid 5 and hence any variation in deflection of the lid 5 resulting from pressure variations.
Claims (6)
- SClaims 1. A SAW based sensor comprising a housing having an internal aperture in which a substrate is mounted, at least one SAW device mounted on the substrate responsive to changes in the strain field within the substrate, and a lid extending at least partially across a side of the housing so as to have a side exposed to the environment surrounding the housing and having a projection formed thereon which engages against the substrate so as to transmit deflections in the lid to the substrate, wherein the housing is vented such that there is no pressure differential across the lid.
- 2. A SAW based sensor according to claim 1, wherein the housing is be vented by provision of suitable holes in the housing to allow fluid in the surrounding environment to enter the housing.
- 3. A SAW based sensor according to claim 2, wherein the holes are sized to prevent or substantially eliminate the ingress of dirt, dust or the like into the aperture.
- 4. A SAW based sensor according to claim 2 or claim 3, wherein filter material is associated with each hole which prevents the passage of foreign bodies.
- 5. A SAW based sensor according to claim 1, wherein the lid may be formed of permeable material through which fluid from the surrounding environment may pass.
- 6. A SAW based sensor substantially as herein described with reference to the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB0715886A GB2451861A (en) | 2007-08-14 | 2007-08-14 | Surface acoustic wave based sensor in vented housing |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB0715886A GB2451861A (en) | 2007-08-14 | 2007-08-14 | Surface acoustic wave based sensor in vented housing |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB0715886D0 GB0715886D0 (en) | 2007-09-26 |
| GB2451861A true GB2451861A (en) | 2009-02-18 |
Family
ID=38566406
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB0715886A Withdrawn GB2451861A (en) | 2007-08-14 | 2007-08-14 | Surface acoustic wave based sensor in vented housing |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2451861A (en) |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2465977A (en) * | 2008-12-02 | 2010-06-09 | Transense Technologies Plc | Sensor package with connection pins in lid |
| DE102011106392A1 (en) | 2011-07-02 | 2013-01-03 | Ott-Jakob Spanntechnik Gmbh | Device for measuring force on a measuring body |
| EP2554962A1 (en) * | 2011-08-01 | 2013-02-06 | Honeywell Romania S.R.L. | Wireless saw differential strain gauge |
| AT13196U1 (en) * | 2012-07-11 | 2013-08-15 | Ctr Carinthian Tech Res Ag | sensor arrangement |
| CN108106757A (en) * | 2016-11-24 | 2018-06-01 | 精工爱普生株式会社 | Force detection sensor, force snesor, torque sensor and robot |
| US10005551B2 (en) | 2015-07-06 | 2018-06-26 | General Electric Company | Passive wireless sensors for rotary machines |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4265124A (en) * | 1979-06-04 | 1981-05-05 | Rockwell International Corporation | Remote acoustic wave sensors |
| US4317372A (en) * | 1979-03-09 | 1982-03-02 | Thomson-Csf | Surface acoustic wave pressure gauge |
| GB2372328A (en) * | 2000-10-10 | 2002-08-21 | Transense Technologies Plc | Pressure Monitor Incorporating SAW Device |
| GB2386684A (en) * | 2002-03-21 | 2003-09-24 | Transense Technologies Plc | Fluid pressure sensor with three SAW devices |
| JP2004150879A (en) * | 2002-10-29 | 2004-05-27 | Ulvac Japan Ltd | Cell for biosensor |
-
2007
- 2007-08-14 GB GB0715886A patent/GB2451861A/en not_active Withdrawn
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4317372A (en) * | 1979-03-09 | 1982-03-02 | Thomson-Csf | Surface acoustic wave pressure gauge |
| US4265124A (en) * | 1979-06-04 | 1981-05-05 | Rockwell International Corporation | Remote acoustic wave sensors |
| GB2372328A (en) * | 2000-10-10 | 2002-08-21 | Transense Technologies Plc | Pressure Monitor Incorporating SAW Device |
| GB2386684A (en) * | 2002-03-21 | 2003-09-24 | Transense Technologies Plc | Fluid pressure sensor with three SAW devices |
| JP2004150879A (en) * | 2002-10-29 | 2004-05-27 | Ulvac Japan Ltd | Cell for biosensor |
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2465977A (en) * | 2008-12-02 | 2010-06-09 | Transense Technologies Plc | Sensor package with connection pins in lid |
| DE102011106392A1 (en) | 2011-07-02 | 2013-01-03 | Ott-Jakob Spanntechnik Gmbh | Device for measuring force on a measuring body |
| EP2543978A1 (en) | 2011-07-02 | 2013-01-09 | Ott-Jakob Spanntechnik GmbH | Device for measuring force exerted on a measuring body |
| EP2554962A1 (en) * | 2011-08-01 | 2013-02-06 | Honeywell Romania S.R.L. | Wireless saw differential strain gauge |
| AT13196U1 (en) * | 2012-07-11 | 2013-08-15 | Ctr Carinthian Tech Res Ag | sensor arrangement |
| US10005551B2 (en) | 2015-07-06 | 2018-06-26 | General Electric Company | Passive wireless sensors for rotary machines |
| CN108106757A (en) * | 2016-11-24 | 2018-06-01 | 精工爱普生株式会社 | Force detection sensor, force snesor, torque sensor and robot |
| CN108106757B (en) * | 2016-11-24 | 2022-03-08 | 精工爱普生株式会社 | Force detection sensor, force sensor, torque sensor, and robot |
Also Published As
| Publication number | Publication date |
|---|---|
| GB0715886D0 (en) | 2007-09-26 |
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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) |