A sensor capable of operating in a harsh environment may be exposed to high temperatures, vibrations, ionizing radiation, and/or chemical exposure. A high-temperature gas turbine is one example of a harsh environment. The measurement of temperature, pressure, fuel flow, and rotor speed is vital in assessing or monitoring the state of high-temperature gas turbines. High cycle fatigue (HCF), caused by pressure fluctuations in the air flow across the turbine blades and vanes, is the primary source of component failure in gas turbines. The ability to locally measure pressure fluctuations can provide insight to significantly reduce HCF. For this application, as well as others, there is a need for sensors that can survive in such a harsh environment yet provide accurate measurements.
Embodiments of the present invention include methods and apparatuses for measuring static and dynamic pressure in harsh environments. In certain embodiments, the sensors take the form of a passive wireless microelectromechanical system (MEMS) capacitive-type pressure sensor that operates using radio frequency electromagnetic radiation.
In one embodiment, the method includes providing a microelectromechanical system (MEMS) sensor with a diaphragm, which deflects either downward or upward in response to a corresponding applied pressure difference across the diaphragm. Furthermore, a conductive ground plane under the diaphragm and a conductive antenna under the ground plane form a capacitive element. An incident electromagnetic wave interacts with the antenna under the ground plane on the MEMS sensor in such a way that a portion of the incident electromagnetic wave is reflected back providing information about the deflection of the diaphragm and hence the applied pressure to the MEMS sensor. Methods of embodiments of the present invention can be used for static (e.g., time invariant) or dynamic (e.g., varies with time) measurements of pressure.
The MEMS sensor can include a structurally rigid handle that is attached to the diaphragm in the periphery of an air cavity separating the handle from the diaphragm. Furthermore, a ground plane may be formed under the diaphragm, and an antenna may be formed under the handle. The placement of the antenna and ground plane may vary in location such as to provide a desired capacitance change for pressure measurement. The air gap between the handle and diaphragm allows the diaphragm to displace by an applied pressure yielding a change in capacitance. A vent channel and hole may be formed for dynamic pressure measurement, while the vent channel and/or hole may be excluded for static pressure measurement. The pressure applied to the MEMS sensor is determined based on magnitude and/or phase characteristics of the reflected electromagnetic waves. The sensor is designed to have a corresponding electrical resonant frequency such that as the diaphragm deflects in response to an applied pressure, the electrical resonant frequency shifts, which results in direct measurement of the applied pressure. Sensors according to certain embodiments of the present invention can be applied in applications such as high-temperature gas turbines, where conventional sensors are unable to operate.
In another embodiment, a passive wireless pressure sensor may be constructed of materials designed to operate in harsh environments. A handle and a diaphragm, for example, can be formed with sapphire. The ground plane and antenna elements, on the other hand, can be formed with platinum. It is desirable to have sufficient electrical isolation between the ground plane and antenna elements so that they behave like a capacitor. Furthermore, the material chosen for the handle and diaphragm should have electrical isolation across the desired operating temperature range of the MEMS sensor. Sapphire has a high melting temperature of 2030° C. and is known to have excellent electrical, mechanical, and optical properties. Platinum has a high melting temperature of 1768° C. and has a low power-law creep with sapphire.
A waveguide can be provided to guide the electromagnetic waves to and from the MEMS sensor. The transmitter and receiver electronics are located on the frontend of the electromagnetic waveguide, while the sensor is placed at the backend of the electromagnetic waveguide. The electromagnetic waveguide also makes it physically realizable for interaction with the sensor while in a high-temperature gas turbine due to the fact that electromagnetic waves are unable to penetrate through conductive walls. The electromagnetic waveguide should also be constructed of high-temperature compatible materials. The electromagnetic waves are in the radio frequency range of interest. The electromagnetic waveguide allows the transmitter and receiver electronics to interact with the passive wireless pressure sensor.
Sensors of certain embodiments of the present invention may be passive (e.g., no internal energy sources such as batteries are required) and wireless (e.g., no wires are directly attached to the MEMS sensor). The sensor can also be constructed of high temperature compatible materials, such as sapphire for the handle and diaphragm and platinum for the ground plane and antenna elements. The antenna can be a planar type such as a patch antenna. Furthermore, the antenna element can include a slot or some other defect in the antenna or ground plane for introducing circular polarization to the antenna element. The antenna may use circular polarization for providing increased contrast between the MEMS sensor and any existing background.
Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
Embodiments of the present invention include methods, apparatuses, and theory for measuring static and dynamic pressure in harsh environments. This is described further in the publication by J. E. Rogers, Y.-K. Yoon, M. Sheplak, and J. W. Judy, “A Passive Wireless Microelectromechanical Pressure Sensor for Harsh Environments,” Journal of Microelectromechanical Systems, vol. 27, no. 1, February 2018, which is hereby incorporated by reference in its entirety. Certain embodiments can take the form of a microelectromechanical system (MEMS) capacitive-type passive wireless pressure sensor that operates using radio frequency electromagnetic radiation.
Pressure sensors of certain embodiments of the present invention can be both passive (e.g., no local internal energy sources) and wireless (e.g., no wired local interface electronics). The passive wireless sensor can electrically operate, for example, at Ku-band frequencies around 15 GHz (e.g., 2 cm wavelength in free-space). The passive wireless sensor can operate in the far-field, as opposed to existing pressure sensors that are inductively coupled in the near-field. The separation distance between the transmitter/receiver and the MEMS sensor in the inductively coupled near-field affects the sensor's behavior, while in the far-field this is not the case.
The passive wireless dynamic pressure sensor transduces acoustic fluctuations (e.g., dynamic pressure) into mechanical vibrations of a diaphragm. The mechanical vibrations are further transduced to a frequency shift of an electrical resonator. The pressure sensor can reside at the backend of an electromagnetic waveguide for sensor interaction. An electromagnetic wave (preferably with power at some Ku-band frequency in the vicinity of 15 GHz) is transmitted from the frontend of the electromagnetic waveguide to the backend where it interacts with the sensor. The power loss through the waveguide is related to the length and attenuation of the electromagnetic waveguide at the desired operating frequency. Using these techniques, embodiments of the present invention can take static or dynamic pressure measurements both passively and wirelessly.
Passive wireless pressure sensors of certain embodiments of the present invention can be designed to operate at temperatures in excess of 1000° C. The sensors can operate in the far-field at Ku-band frequencies around 15 GHz. A passive wireless dynamic pressure sensor 10 of certain embodiments of the present invention can include a reflective patch antenna 13 with a slot 18 under a circular diaphragm 11, as shown in
The diaphragm 11 of the passive wireless dynamic pressure sensor is designed to deflect in response to an applied pressure. The patch antenna 13 and the ground plane 12 have the air gap 15, which forms a capacitor. There is also an inductance associated with the antenna 13 and the ground plane 12 such that the pressure sensor has a nominal (e.g., no deflection) electrical resonant frequency. The electrical resonant frequency changes as a function of the capacitance change of the pressure sensor. An increase in the applied pressure to the diaphragm, for example, increases the capacitance and decreases the electrical resonant frequency. The change in the electrical resonant frequency is directly related to the applied pressure by the equivalent sensitivity of the pressure sensor.
An incident electromagnetic wave (e.g., incident RF) from a transmitter interacts with the patch antenna 13 and capacitive element such that a portion of the incident electromagnetic wave is reflected or backscattered (e.g., reflected RF) to a receiver. Note that the transmitter that transmits the incident electromagnetic wave and the receiver that receives the reflected electromagnetic wave are not shown in
The strength of the reflected electromagnetic wave is a function of the capacitive gap 15 as well as the physical area of the antenna 13. The relationship is illustrated in more details in the Sensor Modeling and Analysis section below. The wireless sensing of certain embodiments of the present invention can be considered a combination of RF backscattering and radar.
A passive wireless dynamic pressure sensor can include a deformable diaphragm 21 with an electrically conductive ground plane 22 under the diaphragm 21, as shown in
The patch antenna of certain embodiments of the present invention can be circularly polarized. Patch antennas are inherently linearly polarized, however they can be made to be circularly polarized by a few techniques, such as that shown in
From a material construction standpoint, high-temperature dynamic pressure sensors of certain embodiments of the present invention can include a sapphire-based diaphragm with handle and a platinum-based slot antenna with ground plane. Sapphire has a high melting temperature of 2030° C. and is known to have excellent electrical, mechanical, and optical properties. Platinum has a high melting temperature of 1768° C. and has a low power-law creep with sapphire. Laser machining of sapphire can be cost prohibitive as well as time consuming. The addition of an inner layer between the two sapphire dies can functionally serve to create an air gap and vent channel. A high-temperature compatible metal such as titanium can be deposited at a controlled rate to form the inner layer and for precise definition of the air gap. The low resistivity of the metal does not interfere with the electrical performance of the sensor as the high resistivity of the sapphire electrically isolates the antenna and ground plane.
The packaging of the passive wireless dynamic pressure sensor can consist of two conductive plates 101 and 102 in
An electromagnetic waveguide with two channels can be designed to interact with the dynamic pressure sensor. The two channels can be two perpendicular rectangular channels constructed side by side for transmitting electromagnetic waves in one direction and receiving electromagnetic waves in a perpendicular direction. The receive electromagnetic waveguide is perpendicular to the transmit such that there is minimal unwanted signal transmission from the transmitter to the receiver. The passive wireless pressure sensor may be circularly polarized to reflect a portion of the transmitted electromagnetic waves through the receive electromagnetic waveguide.
An exemplary electromagnetic waveguide 1110 is pictured in
The subject invention includes, but is not limited to, the following exemplified embodiments.
A static or dynamic pressure sensor for harsh environments comprising: a diaphragm; a waveguide operably connected to the diaphragm; and an electromagnetic wave producing and receiving (e.g., sensing) device attached to the waveguide (opposite the diaphragm).
The sensor of Embodiment 1, further comprising a handle connected between the diaphragm and the waveguide.
The sensor of any of Embodiments 1 to 2, wherein the waveguide transmits radio frequency waves.
The sensor of any of Embodiments 1 to 3, wherein the electromagnetic wave producing and receiving device produces and receives radio frequency waves (e.g., from 1 to 100 GHz and more preferably from 10 to 20 GHz).
The sensor of any of Embodiments 1 to 4, further comprising a ground plane formed on either the diaphragm or the handle.
The sensor of any of Embodiments 1 to 5, further comprising an antenna formed on either the handle or the diaphragm.
The sensor of any of Embodiments 1 to 6, further comprising a dielectric gap between the diaphragm and the handle (e.g., filled with air, or a gas or liquid).
The sensor of any of Embodiments 1 to 7, wherein the antenna is a planar antenna (e.g., patch antenna) with or without a defect in the antenna or ground plane (e.g., slot).
The sensor of any of Embodiments 1 to 8, wherein the ground plane and/or antenna are comprised of a high-temperature compatible electrically conductive material (e.g., platinum). The ground plane and/or antenna may also be comprised of one or more of the following materials: titanium, chromium, iridium, tungsten, etc.
The sensor of any of Embodiments 1 to 9, wherein the sensor is suitable for operating in an acoustic frequency ranging from 20 Hz to 100 kHz.
The sensor of any of Embodiments 1 to 10, wherein the diaphragm and/or handle are comprised of a high-temperature compatible material (e.g., sapphire). The diaphragm may also be one or more of the following materials: aluminum nitride, silicon carbide, silicon nitride, diamond, etc.
The sensor of any of Embodiments 1 to 11, wherein waveguide is comprised of a high-temperature compatible electrically conductive material.
The sensor of any of Embodiments 1 to 12, further comprising a vent structure that acoustically connects the dielectric gap with the outside environment. The vent structure, for example, may be a serpentine vent.
The sensor of any of Embodiments 1 to 13, further comprising one or more plates for securing the sensor to the waveguide. Two plates, for example, one or both with a recess to accommodate the sensor for simultaneously interacting with a high-temperature environment and an electromagnetic waveguide.
The sensor of any of Embodiments 1 to 14, wherein the diameter of the antenna is between 0.5 and 20 mm and more preferably between 2 and 8 mm.
The sensor of any of Embodiments 1 to 15, wherein the diameter of the diaphragm is between 0.5 and 20 mm and more preferably between 2 and 8 mm.
The sensor of any of Embodiments 1 to 16, wherein the sensor utilizes a combination of RF backscattering and radar to measure diaphragm displacement.
A method for taking pressure measurements in harsh environments comprising: providing a microelectromechanical system (MEMS) including a diaphragm; transmitting electromagnetic waves toward the MEMS; receiving the electromagnetic waves as they are reflected off the MEMS; and determining diaphragm position or pressure applied to the diaphragm using measurements obtained from the reflected waves. The diaphragm position or the applied pressure can be determined based at least on the calibration of the MEMS device.
The method of Embodiment 101, further comprising providing a waveguide to channel or guide the electromagnetic waves.
The method of any of Embodiments 101 to 102, wherein the electromagnetic waves are radio frequency waves.
The method of any of Embodiments 101 to 103, wherein the MEMS further includes a handle that is bonded to the diaphragm.
The method of any of Embodiments 101 to 104, wherein the MEMS further includes a ground plane which may be formed on either the diaphragm or the handle.
The method of any of Embodiments 101 to 105, wherein the MEMS further includes an antenna which may be formed on either the handle or diaphragm.
The method of any of Embodiments 101 to 106, wherein the MEMS further includes a vent structure for dynamic pressure measurement.
The method of any of Embodiments 101 to 107, wherein the MEMS further includes a dielectric gap between the diaphragm and the handle.
The method of any of Embodiments 101 to 108, wherein the position of the diaphragm is obtained based on magnitude and/or phase shifts of the electromagnetic waves.
The method of any of Embodiments 101 to 109, wherein the sensor utilizes a combination of RF backscattering and radar to measure diaphragm displacement.
Acousto-Mechanical Lumped Element Model
The acousto-mechanical portion of the dynamic pressure sensor can be modeled as a lumped element model (LEM) just beyond the first mechanical resonance. The acoustomechanical LEM assumes there is no relationship between spatial variations (e.g., displacement along diaphragm) and temporal variations (i.e., time). In the mechanical domain elements are treated as a point load at a single location, whereas in the acoustic domain elements are treated as an integrated load across some area. The acousto-mechanical LEM of the dynamic pressure sensor is shown in
The fractional change in the electrical resonant frequency of the dynamic pressure sensor due to temperature is
where α is the coefficient of thermal expansion (CTE) of the slot antenna, γ is the thermal coefficient of dielectric constant of the handle, and ΔT is the change in temperature from room temperature.
The dynamic pressure sensor transduces an applied pressure p to the diaphragm into a displacement w(p). The quasi-static displacement of a uniformly loaded circular diaphragm is
where p is the applied pressure, a is the radius of the diaphragm, D is the flexural rigidity of the diaphragm, and r is the radial distance from the center of the diaphragm. The maximum deflection of the diaphragm at the center where r=0 is ωpk=pa4/64D.
The flexural rigidity of the diaphragm is related to the Young's modulus E, the thickness h, and the Poisson's ratio v of the diaphragm as D=Eh3/12(1−v2). The acoustic compliance of the diaphragm is the ratio of the displaced volume of the circular diaphragm ΔV to the uniformly loaded applied pressure or
The mechanical sensitivity of the diaphragm Sm is equivalent to the acoustic compliance of the diaphragm Cda. The acoustic mass of the circular diaphragm is determined by equating the lumped kinetic energy of the diaphragm to the total kinetic energy such that
where ρA is the area density of the diaphragm.
The radiation mass is an additional mass term caused by fluid particles that oscillate with the diaphragm given as
where ρo is the density of the fluidic medium (e.g., air).
The quality factor of the diaphragm related to air damping Qair, thermoelastic damping Qtherm, support losses Qsup, and surface losses Qsurf is given as Q−1=Qair−1+Qtherm−1+Qsup−1+Qsurf−1.
The damping ratio ξ=½Q is experimentally determined due to the difficulty in isolating the many forms of damping. The acoustic resistance associated with damping of the diaphragm is
The acoustic compliance of the cavity is
where V is the volume of the cavity and co is the isoentropic speed of sound.
The acoustic compliance of the cavity is inherently low for MEMS, resulting in an effect known as cavity stiffening. The effect of cavity stiffening is sensitivity loss. The acoustomechanical sensitivity of the dynamic pressure sensor due to cavity stiffening is
The acoustic mass of the cavity is
The acoustic resistance of the vent structure for a rectangular cross-section is
where μ is the dynamic viscosity of the fluidic medium (e.g., air), Leff is the effective length of the vent, wv is the width of the vent channel, and is the depth of the vent channel.
The acoustic bandwidth of the dynamic pressure sensor is related to the cut-off frequency fa,o∝1/√{square root over (C)}ca and cut-on frequency fa,co∝1/Rva of the pressure sensor as Δfa=fa,o−fa,co.
Electrical Lumped Element Model
The electrical portion of the dynamic pressure sensor can be modeled as a LEM under the assumption that the diameter of the patch antenna 2b is much less than the electrical operating wavelength λ=c/f√{square root over (εeff)}. The radius of a circular patch antenna is related to the electrical operating wavelength as b=1.841λ/2π, which makes it physically unrealizable to fulfill the assumption that 2b<<λ. The transmission line and cavity models were developed to represent microstrip antennas. The transmission line model is a distributed element model with an input impedance that varies with the width of the patch Was tan βW, whereas the cavity model is a LEM assuming the patch antenna behaves like a narrow-band resonator (i.e., lossy cavity). The cavity model has boundary conditions such that an incident electric field on the surface of the patch is constrained to {circumflex over (z)}×[{right arrow over (E)}r+{right arrow over (E)}i]=Zs[{circumflex over (z)}×{right arrow over (J)}s] and is considered appropriate for describing the scattering behavior of a patch antenna. The electrical LEM of the dynamic pressure sensor is shown in
The input impedance of the first resonant mode of the cavity is described as a parallel RLC circuit with
The nominal capacitance between the slot antenna and ground plane for an unloaded diaphragm is related to the capacitance of the handle C1=εoεrA/m and the air gap capacitance C2=εoA/ωo as Co=C1∥C2. The nominal capacitance for an unloaded diaphragm is expanded to
where εo is the permittivity of free-space, A is the area of the circular patch antenna, d=wo+m is the nominal distance between the antenna and ground plane, εr is the relative permittivity of the handle, wo is the nominal air gap between the ground plane and the handle, and m is the handle thickness.
The area of the circular patch antenna A=πb2 does not account for fringe effects along the periphery of the antenna. The effective antenna radius accounting for the fringe fields is
where εeff is the effective permittivity of the antenna.
The nominal electrical resonant frequency is related to the nominal capacitance C0 and the inductance Lo as fo=½π√{square root over (LoCo)}. The electrical resonant frequency is also related to the electrical operating wavelength as fo=c/λ√{square root over (εeff)}. The inductance of the circular patch antenna is derived as
where μ0 is the magnetic permeability of free-space.
The capacitance between the slot antenna and ground plane for a uniformly applied load is
where g=wo−w (p, r) is the displaced air gap due to loading.
The electrical quality factor Qe is related to the radiation quality factor Qr, surface wave quality factor Qsw, dielectric quality factor Qd, and conductor quality factor Qc as Qe−1=Qr−1+Qsw−1+Qd−1+Qc−1. The losses associated with surface waves, dielectric, and conductor are generally low compared to the radiation losses such that Qe=Qr. The electrical quality factor for the dynamic pressure sensor is then
where Rrad is the radiation resistance of the antenna and Zo is the impedance of free-space.
The expression in (15) agrees with Balanis' assessment of microstrip patch antennas using a volumetric relationship that determined Q∝√{square root over (εeff)}. The electrical sensitivity of the dynamic pressure sensor is
The sensitivity of the dynamic pressure sensor relates the acousto-mechanical and electrical sensitivities as
The dynamic range of the dynamic pressure sensor is
where pmax is the maximum pressure to the sensor that yields a linear response and pmin is the minimum detectable pressure.
The antenna reflection coefficient for the circular patch antenna describes a band-pass response of the RCS as
where Rp is the parallel resistance of the antenna.
The antenna reflection coefficient is bounded such that 0≤|Γa|≤1 and at electrical resonance reduces to Γa=Rp/(Rrad+Rp). The structural mode RCS of the antenna also contributes to the scattered power. The structural mode RCS of the circular patch antenna in the optical region (i.e., L>>λ) is σs=4π3b4/λ2. The structural mode RCS below the optical region can be more accurately determined using a numerically determined correction factor F. For simplification, the structural reflection coefficient for the circular patch antenna in the far-field is
where RA and RB are chosen to correspond to the numerically determined structural RCS of the antenna.
The insertion loss relating the power received to the power transmitted at the frontend of the electromagnetic waveguide due to the sensor affixed to the backend of the electromagnetic waveguide is
where η1=e−2al and η2=e−2al are the transmit and receive path power losses in the electromagnetic waveguide.
Sensor Polarization
A circular patch antenna intrinsically has scattering behavior identical to the incident electromagnetic wave. The effect of an incident linearly polarized E-field, for example, is a scattered linearly polarized E-field. The issue with observing the scattered E-field in the same direction as the incident E-field is there is a decrease in contrast between the background and the sensor. The addition of a slot to a circular patch antenna will induce circular polarization in the antenna. Circular polarization allows observation of the incident E-field in a perpendicular direction to the incident E-field, which increases contrast between the sensor and the background.
The scattering parameters relate some incident E-field Eij to a resultant scattered E-field Eri as aij=,Eri/Eij with magnitude and phase aij=|aij|ejθ
The far-field RCS in vertical (v) and horizontal (h) directions are related to the scattered and incident E-fields as
A circular patch antenna is intrinsically reciprocal and therefore has equivalent cross-polarization RCS parameters (i.e., σhv=σvh). Furthermore, a circularly polarized patch antenna has equivalent RCS parameters in both axes (e.g., σvv=σhv). The composite scattered E-field in phasor form with vertical and horizontal components is
Er(t)=ĥEhrejωt+{circumflex over (v)}Evrej(ωt+δ), (24)
where δ is the phase difference between the E-fields.
A circularly polarized electromagnetic wave has equal power in both the horizontal and vertical directions and an axial ratio of AR=1. It is quite difficult in practice to achieve circular polarization. It is typically the case that an axial ratio of AR>1 is attainable such that the polarization is slightly elliptical.
Several prototypes including a demonstration pressure sensor with a silicon diaphragm and a high temperature pressure sensor with a sapphire diaphragm were constructed to prove the concepts of certain embodiments of the present invention. Although certain parameters (including dimensions) and materials are discussed in the following examples, they are not to be construed as limiting embodiments of the present invention, as many of the parameters were chosen to accommodate commercially available parts. In practice, embodiments of the present invention can be custom fabricated to achieve precise performance characteristics and alternative configurations.
A greater understanding of the embodiments of the present invention and of its many advantages may be had from the following examples, given by way of illustration. The following examples are illustrative of some of the methods, applications, embodiments and variants of the present invention. They are, of course, not to be considered as limiting the invention. Numerous changes and modifications can be made with respect to the embodiments of the invention.
In
Optimization of the diaphragm was performed using commercially available software. The demonstration sensor was designed such that two diaphragm sizes (e.g., 7.6 mm and 6.4 mm) satisfy corresponding pressure requirements (e.g., 3 kPa and 6 kPa) for a pre-determined maximum displacement of 13.5 μm. The optimized design parameters for the demonstration sensor are given in Table I.
A set of proof-of-concept static and dynamic pressure sensors are fabricated to validate the ability to do passive wireless pressure sensing. The proof-of-concept pressure sensors are fabricated with silicon due to its low-cost, mature machinability, and good mechanical properties for MEMS. Borofloat® 33 is selected for the handle of the proof-of-concept pressure sensors due to its low-cost and compatibility with microfabrication processes. A silicon-on-insulator (SOI) wafer with a 475 μm thick silicon backside, 0.5 μm thick oxide, and 50 μm thick device layer and a 270 μm thick Borofloat® 33 wafer are used for fabrication of the proof-of-concept pressure sensors. The proof-of-concept pressure sensors are fabricated at the University of Florida's Nanoscale Research Facility (NRF) in a class 100 clean room using common microfabrication processes. The proof-of-concept pressure sensors have a silicon diaphragm and Borofloat® 33 handle.
As shown in the fabrication process of
Both the static and dynamic proof-of-concept pressure sensors with 5.6, 5.7, and 5.8 mm antenna diameters are characterized to validate the ability to measure static pressure and dynamic pressure, respectively. The measured data is summarized in Table II. Additionally, the change in the electrical resonant frequency as a function of the applied pressure at 1 kHz for a dynamic pressure sensor with a 5.6 mm antenna diameter is shown in
A high-temperature pressure sensor is constructed of materials that are able to operate at temperatures in excess of 1000° C. The diaphragm, handle, and structural body, for example, are constructed of sapphire and the capacitive element including the antenna and ground plane are constructed of platinum. A set of 10 mm×10 mm A-plane sapphire die with 50 μm and 200 μm thicknesses are selected for fabrication of the high-temperature pressure sensor's diaphragm and handle, respectively. Laser machining of sapphire has been successfully accomplished; however, laser machining can be cost prohibitive as well as time consuming. The fabrication process as shown in
The first processing step is to define a ground plane on the diaphragm and an antenna on the handle by sputter depositing and patterning 300 nm of chrome for a lift-off process. Next, 10 nm of titanium followed by 150 nm of platinum are sputter deposited. The antenna and ground plane are then defined by performing a lift-off. The second processing step is to define the cavity and vent channel by sputter depositing and patterning 2.5 μm of titanium. The third processing step is to attach the two sapphire die using an alumina adhesive.
The high-temperature dynamic pressure sensor is characterized. The average change in the electrical resonant frequency for the high-temperature pressure sensor is 92 kHz, which corresponds to a minimum detectable frequency of 130 kHz. The nominal electrical resonant frequency of the high-temperature dynamic pressure sensor with a 3.8 mm antenna diameter is measured as 14.784 GHz. The change in the electrical resonant frequency as a function of the applied pressure at 1 kHz for the high-temperature dynamic pressure sensor is shown in
The electrical resonant frequency will change as a function of temperature as described in equation (1). The high-temperature pressure sensor has a platinum-based antenna and ground plane with a CTE of 9 ppm/° C. and a sapphire handle with a thermal coefficient of dielectric constant of 230 ppm/° C. The predicted electrical resonant frequency as a function of temperature is shown in
It should be understood that the examples and embodiments described herein are for illustrative purposes only. Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
This patent application claims priority to Provisional Application Ser. No. 62/522,830, filed Jun. 21, 2017 which is incorporated herein by reference in its entirety.
This invention was made with government support under Grant No. DE-FE0012370 awarded by Department of Energy. The government has certain rights in the invention.
Number | Name | Date | Kind |
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7444878 | Pepples | Nov 2008 | B1 |
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WO-2018197128 | Nov 2018 | WO |
Entry |
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English translation of Mayer (WO2018197128) description, accessed from patentscope.wipo.int Mar. 31, 2020. |
English translation of Mayer (WO2018197128) claims, accessed from patentscope.wipo.int Mar. 31, 2020. |
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20180372563 A1 | Dec 2018 | US |
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62522830 | Jun 2017 | US |