WO2001077633A1 - Surface acoustic wave type strain sensor - Google Patents

Surface acoustic wave type strain sensor Download PDF

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Publication number
WO2001077633A1
WO2001077633A1 PCT/GB2000/002178 GB0002178W WO0177633A1 WO 2001077633 A1 WO2001077633 A1 WO 2001077633A1 GB 0002178 W GB0002178 W GB 0002178W WO 0177633 A1 WO0177633 A1 WO 0177633A1
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WO
WIPO (PCT)
Prior art keywords
substrate
lid
strain sensor
sensor according
strain
Prior art date
Application number
PCT/GB2000/002178
Other languages
French (fr)
Inventor
Crofton John Brierley
Giles Humpston
Original Assignee
Marconi Optical Components Limited
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Marconi Optical Components Limited filed Critical Marconi Optical Components Limited
Priority to AU5095100A priority Critical patent/AU5095100A/en
Publication of WO2001077633A1 publication Critical patent/WO2001077633A1/en

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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

Definitions

  • This invention relates to a strain sensor and more especially to a strain sensor based on
  • SAW surface acoustic wave
  • SAW devices work on the principle of converting an AC electrical signal to an acoustic wave using a piezoelectric material.
  • the acoustic wave propagates as a surface wave in the piezoelectric material, or other solid material to which the piezoelectric material is attached, and is then converted back into an electrical signal by a transducer on the surface of the piezoelectric material.
  • the transducer comprises a suitable electrode pattern such as sets of interdigitated electrodes.
  • SAW devices display a characteristic resonant frequency which is a function of their electrode spacing and the phase velocity of the medium in which the wave propagates.
  • the SAW is very sensitive to changes at the surface of the material in which it is travelling and very low levels of contamination can significantly affect the properties of the acoustic wave. Furthermore changes in the gaseous atmosphere at the surface such as humidity, pressure or gas composition can affect the characteristics of the surface wave. For this reason it is known to hermetically encapsulate the SAW device in a gaseous or evacuated environment. Typically this involves fixing the SAW device to a base portion of the package using adhesive or solder and then sealing a lid onto the base to enclose the device. Often the electrical connections to the device are made using pins which pass through the base portion of the package.
  • One suggested application of SAW devices is for sensing tensile or compressive strain (that is the elongation or contraction divided by the original length).
  • a strain sensor comprises: a substrate made of piezoelectric material or having a layer of piezoelectric material upon a first surface thereof; an electrode arrangement on the piezoelectric material forming in combination therewith a surface acoustic wave device and characterised by a lid bonded around its periphery to said first surface of the substrate, such that in combination with the first surface it defines a volume enclosing the surface acoustic wave device. Since at least one face of the substrate in which the SAW travels is fully accessible this enables the sensor to be directly coupled to the source of the strain.
  • the sensor can be mounted with the face of the substrate remote from the face having the electrode arrangement in
  • the lid is configured to be smaller than the substrate such that opposite edges of the first surface of the substrate are exposed.
  • the sensor can be subjected to strain by clamping these exposed edges in suitable mounts and effecting relative movement between the mounts.
  • a particular advantage of such an arrangement is that the sensor is less prone to hysteresis since the strain does not pass through the bond between the enclosure and substrate.
  • the lid is made of a material having substantially the same coefficient of thermal expansion as that of the substrate. Furthermore the lid is preferably bonded to the substrate by a material having a coefficient of thermal expansion which is substantially the same as that of the substrate and lid. In a preferred embodiment the substrate and/or lid comprise single crystal quartz.
  • the piezoelectric material comprises lithium niobate (LiNbO ⁇ or lithium tantolate (LiTaO 3 ).
  • the strain sensor further comprises electrically conducting tracks on the first surface connected to the electrode arrangement and extending through the junction between the substrate and lid to the outside of the lid. This allows electrical connection to the sensor.
  • the strain sensor of the present invention enables a selected atmosphere to be provided around the SAW device.
  • the volume between the lid and substrate is evacuated or filled with a selected gas or liquid.
  • Figure 1 is a schematic perspective partial cutaway representation of a strain sensor in accordance with the invention.
  • Figure 2 is a representation of the strain sensor of Figure 1 mounted to an object to measure flexural strain.
  • a strain sensor 2 which comprises a substrate 4 of single crystal quartz which is cut in the ST direction.
  • the substrate 4 is rectangular and of dimensions 9mm by 7mm and 0.25mm - 0.5mm in thickness.
  • an electrode arrangement 6 which in conjunction with the substrate comprises a SAW device.
  • the SAW device comprises a single port resonator which is configured to have a resonant frequency of operation of approximately 200MHz.
  • the electrode arrangement comprises three sections 6a-6c of interdigitated electrodes.
  • the centre section 6b constitutes the SAW transducer which is used to both generate and measure the SAW.
  • the sections 6a and 6b which flank the transducer section 6b acts as reflectors of the SAW. It will be appreciated that other forms of resonators and electrode structures can be used.
  • the contact pads 10 are located adjacent opposite edges of the substrate and are used for connecting the sensor to external drive/measuring circuitry.
  • the electrode arrangement 6a-6c, tracks 8 and contacts 10 comprise aluminium which is evaporated or sputtered onto the substrate.
  • the contact pads 10, which are exposed to the atmosphere, are preferably further coated in gold.
  • a lid or enclosure 12 is bonded around its periphery to the substrate 4 by a seam or seal 14 of epoxy resin.
  • the lid 12 comprises a sheet of single quartz crystal cut in the ST orientation and is of approximately a quarter of a millimetre thickness.
  • the epoxy seal 14 is arranged to have a thickness of between 5 and 500 microns such that a sealed volume is defined over the electrode arrangement 6 between the first surface 5 of the substrate 4 and the underside of the lid 12.
  • the lid 12 has dimensions which are smaller than that of the substrate such that the contact pads 10 are located outside of the seam 14 and are therefore accessible when the lid 12 is mounted to the substrate. Additionally opposite ends 18, 20 of the substrate are accessible.
  • the lid 12 is made of the same material as the substrate 4 to reduce any likelihood of differential thermal expansion of the two parts, the lid 12 can alternatively be made of a different material having substantially the same coefficient of thermal expansion as that of the substrate 4.
  • the lid material should additionally be impervious to gas.
  • Other forms of sealant can be used though it should be impervious to gas to ensure that a gas tight volume is provided around the SAW device.
  • the sealant has a coefficient of thermal expansion which is substantially the same as that of the substrate 4 and lid 12 to limit the effects of
  • the underside 15 of the substrate is mechanically coupled (using for example adhesive) to an object in which strain is to be sensed.
  • Electrical connections 17 to the SAW device are made via the contact pads 10.
  • the object is subjected to tensile or compressive strain in the direction indicated by the double headed arrow 'A' this causes a corresponding expansion or contraction of the substrate 4 which in turn causes a change in the spacing between electrodes of the interdigitated electrode arrangement 6a-6c.
  • This change in spacing results in a change in the resonant frequency of the SAW device which is detected by external circuitry using the connections 17.
  • a particular advantage of the strain sensor of the present invention is that the underside 15 of the substrate 4 upon which the SAW device is formed is free of any encumbrances which enables direct mechanical coupling of the device to the source of strain.
  • this shows an alternative method of mounting the strain sensor 2 for measuring flexural strain in an object 16.
  • Opposite edges 18, 20 of the substrate 4 are clamped or otherwise bonded into respective mounting blocks 22, 24 which are themselves mechanically coupled to the object 16.
  • the object 16 and sensor 2 are shown in an exaggerated state of flexural strain.
  • a particular advantage of this arrangement is that the sensor 2 is less prone to hysteresis since the strain does not pass through the bond 14 between the lid 12 and substrate 4.
  • the substrate can comprise any bulk piezoelectric crystalline material or can comprise a non-piezoelectric material with a thin film of piezoelectric, such as lithium niobate
  • LiNbO 3 lithium tantolate
  • LiTaO 3 lithium tantolate
  • the SAW device can be of any known design such as a double port resonator or delay line. Whilst a rectangular substrate has been described it could be of any shape. For ease of fabrication however it is preferably a simple geometric shape such as a square, triangle or diamond since such shapes can be readily and economically cut, or scribed from a wafer.
  • the overall dimensions of the strain sensor are largely constrained by the transducer (electrode arrangement 6a-6c) size and the substrate area necessary to allow sealing of the lid and external electrical connection. It is envisaged that considerably smaller devices could be fabricated.
  • the frequency of operation of the strain sensor will be determined by the intended application and can consequently be anywhere in the kHz region through to GHz frequencies. Higher frequency devices will generally have smaller dimensions.
  • the seal material can be any of a wide variety of sealing mediums which have a liquid phase allowing the material to wet the surfaces of the lid and substrate.
  • the seal is a metal alloy (solder or braze) and the substrate and lid include areas of wettable material that can be wetted by the molten alloy. With such an arrangement a non-electrically conducting dielectric material is provided between the electrical connecting tracks on the surface of the substrate and the wettable areas to prevent electrical shorting of the tracks by the seal.
  • the sealant is made of a glass frit capable of wetting both the substrate surface, metal tracks or dielectric coated metal tracks and the lid.
  • the thickness of the sealant chosen depends on the volume of the cavity that is required for the SAW to be sealed within.
  • the metals that are used to form the SAW transducer and electrical connections can be of any suitably electrically conductive medium.
  • the electrical link between the device and its external contact pads can be of any design capable of conducting the required AC signal, such as a non-contact capacitive link.
  • One or more of the electrical connections to the SAW device could be provided on the underside of the substrate or printed on the surface of the lid and electrical connection to these connections could be by a non- contact process.
  • the strain sensor of the present invention can be readily used in the measurement of strain since the bottom surface of the substrate is free of encumbrances and can therefore be readily and directly attached to a source of strain, which is transferred through the substrate material of the SAW surface. Whilst the present application has been described in relation to the measurement of strain it will be appreciated that the strain sensor can also be used to measure torque, pressure or any other physical parameter which results in a strain being applied to the sensor. For example in the case
  • the lid of the device can be attached to another surface to keep the lid rigid.
  • a selected atmosphere can be provided within the cavity of the sensor, such as a gaseous environment, a vacuum or liquid.

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  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • General Physics & Mathematics (AREA)
  • Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)

Abstract

A strain sensor (2) comprises: a substrate (4) made of piezoelectric material or having a layer of piezoelectric material upon a first surface (5) thereof and an electrode arrangement (6a-6c) on the piezoelectric material forming in combination therewith a surface acoustic wave device. A lid (12) is bonded around its periphery to said first surface (5) of the substrate, such that in combination with the first surface (5) it defines a volume fully enclosing the surface acoustic wave device. The sensor (2) is mounted to an object (16) in which strain is to be measured by mechanically coupling the face (15) of the substrate which is remote from the first surface (5) and which is free of encumbrances to the object. Preferably the lid (12) and substrate (4) are made of the same material, such as single crystal quartz, or from materials having coefficients of thermal expansion which are substantially the same.

Description

SURFACE ACOUSTIC WAVE TYPE STRAIN SENSOR
This invention relates to a strain sensor and more especially to a strain sensor based on
a surface acoustic wave (SAW) device.
SAW devices work on the principle of converting an AC electrical signal to an acoustic wave using a piezoelectric material. The acoustic wave propagates as a surface wave in the piezoelectric material, or other solid material to which the piezoelectric material is attached, and is then converted back into an electrical signal by a transducer on the surface of the piezoelectric material. Typically the transducer comprises a suitable electrode pattern such as sets of interdigitated electrodes. SAW devices display a characteristic resonant frequency which is a function of their electrode spacing and the phase velocity of the medium in which the wave propagates.
The SAW is very sensitive to changes at the surface of the material in which it is travelling and very low levels of contamination can significantly affect the properties of the acoustic wave. Furthermore changes in the gaseous atmosphere at the surface such as humidity, pressure or gas composition can affect the characteristics of the surface wave. For this reason it is known to hermetically encapsulate the SAW device in a gaseous or evacuated environment. Typically this involves fixing the SAW device to a base portion of the package using adhesive or solder and then sealing a lid onto the base to enclose the device. Often the electrical connections to the device are made using pins which pass through the base portion of the package. One suggested application of SAW devices is for sensing tensile or compressive strain (that is the elongation or contraction divided by the original length). When the surface of the SAW device is subjected to tensile or compressive strain this modifies the spacing between the interdigitated electrodes of the transducer which modifies the resonant frequency of the device. Measuring the change in resonant frequency gives a measure of the applied strain. To accurately measure strain using a SAW device requires the surface of the device where the SAW is generated to be in as close proximity to the source of the strain as possible. Where the SAW device comprises a piezoelectric crystal it would be desirable to mechanically couple the crystal directly to the source of the strain. However as described above SAW devices are hermetically packaged making it impossible to directly couple the crystal in this way.
A need exists therefore for a robust strain sensor which can be readily attached to an object in which strain is to be sensed. The present invention has arisen in an endeavour to provide a SAW strain sensor which at least in part overcomes the limitations of the known arrangements.
According to the present invention a strain sensor comprises: a substrate made of piezoelectric material or having a layer of piezoelectric material upon a first surface thereof; an electrode arrangement on the piezoelectric material forming in combination therewith a surface acoustic wave device and characterised by a lid bonded around its periphery to said first surface of the substrate, such that in combination with the first surface it defines a volume enclosing the surface acoustic wave device. Since at least one face of the substrate in which the SAW travels is fully accessible this enables the sensor to be directly coupled to the source of the strain. The sensor can be mounted with the face of the substrate remote from the face having the electrode arrangement in
mechanical contact with the object in which strain is to be measured. Preferably the lid is configured to be smaller than the substrate such that opposite edges of the first surface of the substrate are exposed. With such an arrangement the sensor can be subjected to strain by clamping these exposed edges in suitable mounts and effecting relative movement between the mounts. A particular advantage of such an arrangement is that the sensor is less prone to hysteresis since the strain does not pass through the bond between the enclosure and substrate.
Advantageously the lid is made of a material having substantially the same coefficient of thermal expansion as that of the substrate. Furthermore the lid is preferably bonded to the substrate by a material having a coefficient of thermal expansion which is substantially the same as that of the substrate and lid. In a preferred embodiment the substrate and/or lid comprise single crystal quartz.
Preferably the piezoelectric material comprises lithium niobate (LiNbO ^ or lithium tantolate (LiTaO3).
Advantageously the strain sensor further comprises electrically conducting tracks on the first surface connected to the electrode arrangement and extending through the junction between the substrate and lid to the outside of the lid. This allows electrical connection to the sensor. The strain sensor of the present invention enables a selected atmosphere to be provided around the SAW device. Preferably the volume between the lid and substrate is evacuated or filled with a selected gas or liquid.
A strain sensor in accordance with the invention will now be described by way of example only with reference to the accompanying drawings in which:
Figure 1 is a schematic perspective partial cutaway representation of a strain sensor in accordance with the invention and
Figure 2 is a representation of the strain sensor of Figure 1 mounted to an object to measure flexural strain.
Referring to Figure 1 there is shown a strain sensor 2 which comprises a substrate 4 of single crystal quartz which is cut in the ST direction. The substrate 4 is rectangular and of dimensions 9mm by 7mm and 0.25mm - 0.5mm in thickness. Upon an upper surface 5 of the substrate 4 there is provided in a known manner an electrode arrangement 6 which in conjunction with the substrate comprises a SAW device. In the embodiment illustrated the SAW device comprises a single port resonator which is configured to have a resonant frequency of operation of approximately 200MHz. As illustrated the electrode arrangement comprises three sections 6a-6c of interdigitated electrodes. The centre section 6b constitutes the SAW transducer which is used to both generate and measure the SAW. The sections 6a and 6b which flank the transducer section 6b acts as reflectors of the SAW. It will be appreciated that other forms of resonators and electrode structures can be used.
Extending from, and electrically connected to, the transducer electrode arrangement 6b are two electrically conducting tracks 8 which terminate in a respective contact pad 10. The contact pads 10 are located adjacent opposite edges of the substrate and are used for connecting the sensor to external drive/measuring circuitry. The electrode arrangement 6a-6c, tracks 8 and contacts 10 comprise aluminium which is evaporated or sputtered onto the substrate. The contact pads 10, which are exposed to the atmosphere, are preferably further coated in gold.
A lid or enclosure 12 is bonded around its periphery to the substrate 4 by a seam or seal 14 of epoxy resin. The lid 12 comprises a sheet of single quartz crystal cut in the ST orientation and is of approximately a quarter of a millimetre thickness. The epoxy seal 14 is arranged to have a thickness of between 5 and 500 microns such that a sealed volume is defined over the electrode arrangement 6 between the first surface 5 of the substrate 4 and the underside of the lid 12. The lid 12 has dimensions which are smaller than that of the substrate such that the contact pads 10 are located outside of the seam 14 and are therefore accessible when the lid 12 is mounted to the substrate. Additionally opposite ends 18, 20 of the substrate are accessible.
Whilst it is preferable that the lid 12 is made of the same material as the substrate 4 to reduce any likelihood of differential thermal expansion of the two parts, the lid 12 can alternatively be made of a different material having substantially the same coefficient of thermal expansion as that of the substrate 4. The lid material should additionally be impervious to gas. Other forms of sealant can be used though it should be impervious to gas to ensure that a gas tight volume is provided around the SAW device. Furthermore it is preferable that the sealant has a coefficient of thermal expansion which is substantially the same as that of the substrate 4 and lid 12 to limit the effects of
differential thermal expansion.
In operation the underside 15 of the substrate, that is the face opposite the first face 5, is mechanically coupled (using for example adhesive) to an object in which strain is to be sensed. Electrical connections 17 to the SAW device are made via the contact pads 10. When the object is subjected to tensile or compressive strain in the direction indicated by the double headed arrow 'A' this causes a corresponding expansion or contraction of the substrate 4 which in turn causes a change in the spacing between electrodes of the interdigitated electrode arrangement 6a-6c. This change in spacing results in a change in the resonant frequency of the SAW device which is detected by external circuitry using the connections 17. A particular advantage of the strain sensor of the present invention is that the underside 15 of the substrate 4 upon which the SAW device is formed is free of any encumbrances which enables direct mechanical coupling of the device to the source of strain.
Referring to Figure 2 this shows an alternative method of mounting the strain sensor 2 for measuring flexural strain in an object 16. Opposite edges 18, 20 of the substrate 4 are clamped or otherwise bonded into respective mounting blocks 22, 24 which are themselves mechanically coupled to the object 16. For the purpose of illustration the object 16 and sensor 2 are shown in an exaggerated state of flexural strain. A particular advantage of this arrangement is that the sensor 2 is less prone to hysteresis since the strain does not pass through the bond 14 between the lid 12 and substrate 4.
It will be appreciated by those skilled in the art that modifications can be made to the embodiment described which are within the scope of the invention. For example the substrate can comprise any bulk piezoelectric crystalline material or can comprise a non-piezoelectric material with a thin film of piezoelectric, such as lithium niobate
(LiNbO3)or lithium tantolate (LiTaO3), deposited on its surface. Clearly the dimensions of the substrate, lid or seal can be tailored for a given application.
The SAW device can be of any known design such as a double port resonator or delay line. Whilst a rectangular substrate has been described it could be of any shape. For ease of fabrication however it is preferably a simple geometric shape such as a square, triangle or diamond since such shapes can be readily and economically cut, or scribed from a wafer.
The overall dimensions of the strain sensor are largely constrained by the transducer (electrode arrangement 6a-6c) size and the substrate area necessary to allow sealing of the lid and external electrical connection. It is envisaged that considerably smaller devices could be fabricated.
The frequency of operation of the strain sensor will be determined by the intended application and can consequently be anywhere in the kHz region through to GHz frequencies. Higher frequency devices will generally have smaller dimensions. The seal material can be any of a wide variety of sealing mediums which have a liquid phase allowing the material to wet the surfaces of the lid and substrate. In alternative embodiments the seal is a metal alloy (solder or braze) and the substrate and lid include areas of wettable material that can be wetted by the molten alloy. With such an arrangement a non-electrically conducting dielectric material is provided between the electrical connecting tracks on the surface of the substrate and the wettable areas to prevent electrical shorting of the tracks by the seal. In yet a further embodiment the sealant is made of a glass frit capable of wetting both the substrate surface, metal tracks or dielectric coated metal tracks and the lid. The thickness of the sealant chosen depends on the volume of the cavity that is required for the SAW to be sealed within.
The metals that are used to form the SAW transducer and electrical connections can be of any suitably electrically conductive medium. The electrical link between the device and its external contact pads can be of any design capable of conducting the required AC signal, such as a non-contact capacitive link. One or more of the electrical connections to the SAW device could be provided on the underside of the substrate or printed on the surface of the lid and electrical connection to these connections could be by a non- contact process.
The strain sensor of the present invention can be readily used in the measurement of strain since the bottom surface of the substrate is free of encumbrances and can therefore be readily and directly attached to a source of strain, which is transferred through the substrate material of the SAW surface. Whilst the present application has been described in relation to the measurement of strain it will be appreciated that the strain sensor can also be used to measure torque, pressure or any other physical parameter which results in a strain being applied to the sensor. For example in the case
of pressure sensing the underside of the substrate is not attached to another object such that changes in the ambient pressure will result in a difference in pressure between the inside and outside of the cavity. Depending on the relative stiffness of the substrate and lid this will be translated into a strain on the SAW device. In this configuration the lid of the device can be attached to another surface to keep the lid rigid.
It will be appreciated that a selected atmosphere can be provided within the cavity of the sensor, such as a gaseous environment, a vacuum or liquid.

Claims

1. A strain sensor (2) comprising: a substrate (4) made of piezoelectric material or having a layer of piezoelectric material upon a first surface (5) thereof; an electrode arrangement (6a-6c) on the piezoelectric material forming in combination therewith a surface acoustic wave device and characterised by a lid (12) bonded around its periphery to said first surface (5) of the substrate(4), such that in combination with the first surface(5) it defines a volume fully enclosing the surface acoustic wave device.
2. A strain sensor according to Claim 1 in which the lid (12) is configured to be smaller than the substrate (4) such that opposite edges (18,20) of the first surface (5) of the substrate (4) are exposed.
3. A strain sensor according to Claim 1 or Claim 2 in which the lid (12) is made of material having substantially the same coefficient of thermal expansion as that of the substrate (4).
4. A strain sensor according to Claim 3 in which the lid (12) is bonded to the
substrate (4) by a material having a coefficient of thermal expansion substantially the same as that of the substrate and lid.
5. A strain sensor according to any preceding claim in which the substrate (4) and/or lid (12) comprises single crystal quartz.
6. A strain sensor according to any preceding claim in which the piezoelectric
material comprises lithium niobate.
7. A strain sensor according to any one of Claims 1 to 5 in which the piezoelectric material comprises lithium tantolate.
8. A strain sensor according to any preceding claim and further comprising electrically conducting tracks (8) on the first surface (5) connected to the electrode arrangement (6b) and extending through the junction between the substrate (4) and lid (12) to the outside of the lid.
9. A strain sensor according to any preceding claim in which the volume between the lid and substrate is evacuated.
10. A strain sensor according to any preceding claim in which the volume between
the lid and substrate is filled with a selected gas or liquid.
PCT/GB2000/002178 2000-04-12 2000-06-06 Surface acoustic wave type strain sensor WO2001077633A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU5095100A AU5095100A (en) 2000-04-12 2000-06-06 Surface acoustic wave type strain sensor

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0008839.3 2000-04-12
GB0008839A GB2361318A (en) 2000-04-12 2000-04-12 A surface acoustic wave strain sensor

Publications (1)

Publication Number Publication Date
WO2001077633A1 true WO2001077633A1 (en) 2001-10-18

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WO2006059822A1 (en) * 2004-12-04 2006-06-08 Mdt Co., Ltd. Power-free/wireless sensor based on surface acoustic wave with energy collecting type
KR100693222B1 (en) * 2006-04-28 2007-03-12 주식회사 엠디티 Saw transponder for sensing pressure
KR100763020B1 (en) * 2005-02-28 2007-10-02 주식회사 엠디티 SAW based passive radio sensig system using piezoelectric power and wireless power transmission
JP2017075955A (en) * 2016-11-28 2017-04-20 セイコーエプソン株式会社 Force detecting device and robot
US11499545B2 (en) 2019-07-19 2022-11-15 General Electric Company Systems and methods for piston rod monitoring

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WO2003081195A1 (en) 2002-03-21 2003-10-02 Transense Technologies Plc Pressure monitor incorporating saw device
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Publication number Priority date Publication date Assignee Title
WO2006059822A1 (en) * 2004-12-04 2006-06-08 Mdt Co., Ltd. Power-free/wireless sensor based on surface acoustic wave with energy collecting type
KR100600807B1 (en) 2004-12-04 2006-07-18 주식회사 엠디티 SAW based passive radio sensors using energy gatherer
JP2008522184A (en) * 2004-12-04 2008-06-26 エムディーティー カンパニー リミテッド Energy-collecting surface acoustic wave-based no-power / wireless sensor
JP4856652B2 (en) * 2004-12-04 2012-01-18 エムディーティー カンパニー リミテッド Energy-collecting surface acoustic wave-based no-power / wireless sensor
KR100763020B1 (en) * 2005-02-28 2007-10-02 주식회사 엠디티 SAW based passive radio sensig system using piezoelectric power and wireless power transmission
KR100693222B1 (en) * 2006-04-28 2007-03-12 주식회사 엠디티 Saw transponder for sensing pressure
JP2017075955A (en) * 2016-11-28 2017-04-20 セイコーエプソン株式会社 Force detecting device and robot
US11499545B2 (en) 2019-07-19 2022-11-15 General Electric Company Systems and methods for piston rod monitoring

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