GB2037988A - Pressure sensor - Google Patents
Pressure sensor Download PDFInfo
- Publication number
- GB2037988A GB2037988A GB7943332A GB7943332A GB2037988A GB 2037988 A GB2037988 A GB 2037988A GB 7943332 A GB7943332 A GB 7943332A GB 7943332 A GB7943332 A GB 7943332A GB 2037988 A GB2037988 A GB 2037988A
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- GB
- United Kingdom
- Prior art keywords
- sleeve
- substrate
- saw
- cavity
- vacuum
- 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.)
- Granted
Links
- 239000000758 substrate Substances 0.000 claims abstract description 68
- 238000010897 surface acoustic wave method Methods 0.000 claims abstract description 57
- 229910052751 metal Inorganic materials 0.000 claims abstract description 30
- 239000002184 metal Substances 0.000 claims abstract description 30
- 238000007789 sealing Methods 0.000 claims abstract description 13
- 239000012530 fluid Substances 0.000 claims abstract description 12
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 10
- 238000006073 displacement reaction Methods 0.000 claims description 6
- 238000002844 melting Methods 0.000 claims description 5
- 230000008018 melting Effects 0.000 claims description 5
- 229910052759 nickel Inorganic materials 0.000 claims description 5
- 239000012528 membrane Substances 0.000 claims 3
- 230000001351 cycling effect Effects 0.000 abstract description 5
- 239000000463 material Substances 0.000 description 15
- 239000010453 quartz Substances 0.000 description 9
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 9
- 229910000679 solder Inorganic materials 0.000 description 7
- 239000013078 crystal Substances 0.000 description 4
- 230000005489 elastic deformation Effects 0.000 description 4
- 239000004020 conductor Substances 0.000 description 3
- 230000013011 mating Effects 0.000 description 3
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 description 2
- 238000004891 communication Methods 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 2
- 239000010931 gold Substances 0.000 description 2
- 229910052737 gold Inorganic materials 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 230000010355 oscillation Effects 0.000 description 2
- 239000010409 thin film Substances 0.000 description 2
- WSMQKESQZFQMFW-UHFFFAOYSA-N 5-methyl-pyrazole-3-carboxylic acid Chemical compound CC1=CC(C(O)=O)=NN1 WSMQKESQZFQMFW-UHFFFAOYSA-N 0.000 description 1
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- 101000635799 Homo sapiens Run domain Beclin-1-interacting and cysteine-rich domain-containing protein Proteins 0.000 description 1
- 102100030852 Run domain Beclin-1-interacting and cysteine-rich domain-containing protein Human genes 0.000 description 1
- 230000001154 acute effect Effects 0.000 description 1
- 238000007792 addition Methods 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000010292 electrical insulation Methods 0.000 description 1
- 238000005538 encapsulation Methods 0.000 description 1
- 239000010408 film Substances 0.000 description 1
- 238000009501 film coating Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 229910052738 indium Inorganic materials 0.000 description 1
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 239000012212 insulator Substances 0.000 description 1
- 238000002955 isolation Methods 0.000 description 1
- LQBJWKCYZGMFEV-UHFFFAOYSA-N lead tin Chemical compound [Sn].[Pb] LQBJWKCYZGMFEV-UHFFFAOYSA-N 0.000 description 1
- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- NJPPVKZQTLUDBO-UHFFFAOYSA-N novaluron Chemical compound C1=C(Cl)C(OC(F)(F)C(OC(F)(F)F)F)=CC=C1NC(=O)NC(=O)C1=C(F)C=CC=C1F NJPPVKZQTLUDBO-UHFFFAOYSA-N 0.000 description 1
- 238000004806 packaging method and process Methods 0.000 description 1
- 238000007747 plating Methods 0.000 description 1
- 238000001552 radio frequency sputter deposition Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000011787 zinc oxide Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
- G01L9/0001—Transmitting or indicating the displacement of elastically deformable gauges by electric, electro-mechanical, magnetic or electro-magnetic means
- G01L9/0008—Transmitting or indicating the displacement of elastically deformable gauges by electric, electro-mechanical, magnetic or electro-magnetic means using vibrations
- G01L9/0022—Transmitting or indicating the displacement of elastically deformable gauges by electric, electro-mechanical, magnetic or electro-magnetic means using vibrations of a piezoelectric element
- G01L9/0025—Transmitting or indicating the displacement of elastically deformable gauges by electric, electro-mechanical, magnetic or electro-magnetic means using vibrations of a piezoelectric element with acoustic surface waves
Landscapes
- Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- General Physics & Mathematics (AREA)
- Measuring Fluid Pressure (AREA)
Abstract
A surface acoustic wave (SAW) pressure sensor 10 is mechanically supported within a vacuum sealing structure 32, 36 by a cylindrical metal sleeve 44 which isolates the SAW sensor substrate 11 from induced thermal strain resulting from temperature cycling of the structure, and which provides for a fluid conduit 48 through the vacuum environment from the sensor diaphragm to an orifice 50 formed through the wall of the structure. <IMAGE>
Description
SPECIFICATION
Surface acoustic wave (saw) pressure sensor structure
This invention relates to surface acoustic wave (SAW) pressure sensors, and more particularly to vacuum encapsulating structures therefore.
SAW pressure sensors are well known in the art, as reported in U.S. Patents 3 978 731 and 4 100 81 1. Briefly stated, SAW delay lines which include a planar substrate having two major surfaces with electro-acoustic transducers disposed in an active signal region on one of the surfaces are adapted to provide SAW pressure sensors by forming a flexible, deformable diaphragm in the active signal region. The diaphragm is formed between the surface of the substrate which includes the active signal region and a parallel surface provided by the end wall of an interior cylindrical cavity, or bore, formed in the second major surface.The cavity acts as a fluid conduit to the interior surface of the diaphragm for applied pressure signals which apply stress to the diaphragm causing it to deform and change the acoustic wave propagation characteristics in the active signal region of the substrate. By connecting the SAW delay lirie to an external oscillator the change in acoustic wave propagation velocity may be measured as a change in the frequency of oscillation, all of which is disclosed in the hereinbefore referenced patents.
When used as absolute pressure sensing devices, the SAW pressure sensors must be vacuum encapsulated to provide zero baron a
reference surface of the diaphragm (the active signal region surface) while permitting access to the opposite surface of the diaphragm (the interior surface formed by the cavity end wall) for the sensed pressure signals. The encapsulating structure must also permit external electrical
connection to the transducers of the delay line
and, ideally, must not induce thermal strain in the
SAW active signal region resulting from temperature cycling of the structure over the
operating temperature range of the sensor. The
requirement to prevent, or minimize induced
thermal strain presents difficulties when there are
different temperature coefficients of expansion
between the SAW substrate material and the
vacuum encapsulating material.The problem is
particularly acute when the SAW substrate itself
comprises piezoelectric material, such as quartz
which has anisotropic temperature coefficients of
expansion. One structure which satisfies all of the
requirements, especially that of minimizing
induced strain, is described in copending
application No. 79.31281, Serial No.2032214, wherein the vacuum structure is formed from the
same crystal material comprising the substrate,
which results in identical expansion characteristics
over temperature and which is electrically
insulative permitting a bond of the structure
directly across the transducer conductors. As a
result, the active signal region is maintained in a vacuum while the opposite surface of the diaphragm is readily accessible to the sensed pressure signals.There are many instances, however, where a metal vacuum structure would be preferred due to the operating environment.
While suitable metal packaging techniques are available for providing the electrical
interconnection to the transducers, the
combination of the dissimilar materials, i.e. metal
and crystal, results not only in induced strain in the
SAW sensor diaphragm but, for piezoelectric
substrates with an isotropic temperature
characteristics, the strain may become so severe
as to cause the rupture of the vacuum seal of the
structure to the substrate. At the present time this
provides a definite limitation on both the accuracy
and the maximum operating temperature range of
metal encapsulated SAW pressure sensors.
Objects of the present invention include
providing an encapsulating structure for
maintaining a SAW pressure sensor in a vacuum
environment over an extended temperature range
of operation and for isolating the SAW sensor
diaphragm from induced thermal strain resulting
from temperature cycling of the structure over the
same range of temperature.
According to one aspect of the present
invention, the SAW pressure sensor is supported
in a vacuum environment within a vacuum sealing
structure by a cylindrical metal sleeve which
displaces the sensor from a mounting wall of the
structure at a distance ten to twenty times greater than the value of the cylinder wall thickness, the
sleeve being disposed at one end in a vacuum
sealing relationship to the cavity opening in the
SAW substrate and being disposed at the other
end in a vacuum sealing relationship to an orifice
formed through the mounting wall of the
structure, the sleeve providing a fluid conduit for
external pressure signals through the vacuum
environment from the orifice to the interior surface
of the SAW diaphragm.According to another
aspect of the present invention the sleeve
diameter is at the minimum value required to
support the sensor over the operating range of
vibration frequencies. According to still another
aspect of the present invention the sleeve is
comprised of a metal having a temperature
coefficient of expansion which is intermediate to that of the anisotropic temperature coefficients of
a piezoelectric SAW substrate. In further accord with the last aspect, the sleeve comprises a metal
having good vacuum characteristics, including low vapor pressure, high melting point corrosion
resistance, is easily outgassed; may be machine formed, and which may be soldered, welded, or braized, such as nickel.
The vacuum encapsulating structure of the present invention provides a minimum vacuum of 10-6 torr over an extended temperature range on the order of 2000 C. The structure provides for isolation of the SAW substrate to minimize the induced strain into the substrate resulting from temperature cycling of the vacuum structure over the operating temperature range of the sensor.
These and other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of preferred embodiments thereof, as illustrated in the accompanying drawing.
Fig. 1 is a perspective view of a prior art SAW pressure sensor, as may be used in the present invention;
Fig. 2 is a simplified, sectioned side elevation view of the SAW sensor of Fig. 1,
Fig. 3 is a simplified illustration of one thermal expansion characteristic of the SAW pressure sensor structure of the present invention,
Fig. 4 is a simplified, sectioned side elevation view of one embodiment of a vacuum encapsulated SAW pressure sensor structure according to the present invention, and
Fig. 5 is a simplified, partial sectioned side elevation view of an alternative embodiment of the saw pressure sensor structure shown in Fig. 4.
Referring now-to Figs. 1 and 2, a SAW pressure sensor 10 on the type disclosed in U.S. Patent 4 1000 811 includes a planar substrate 11 having first and second major surfaces 12, 14. Pairs of electro-acoustic transducers 16, 18 are disposed on the first surface in the active signal region 1 9 which also includes the deformable diaphragm 20 formed in the substrate by a cylindrical cavity, or bore, 22 of diameter do. The thickness of the diaphragm is measured between the first surface
12 and the interior surface 24 formed in the substrate by the end wall of the cavity 22. The diaphragm 20 flexes in response to pressure on the surface 24 from a fluid presented into the cavity.
Typically, the substrate is comprised of piezoelectric material, although piezoelectric
material such as zinc oxide may be deposited in a form of a thin-film coating between the tranducers
16, 18 and the first surface 12. If piezoelectric, the substrate may comprise any of the known
piezoelectric materials including quartz, lithium
niobate or lithium tantalate. Of these quartz is the
most widely used because of its availability and
lower cost. The quartz has anisotropic temperature coefficient characteristics, the optic
or Z axis having a temperature coefficient of
expansion which is on the order of twice that in
either of the X or Y axes. The quartz substrate is
cut from a bulk quartz crystal in any one of a
number of known crystallographic orientations,
such as a Y-cut or a ST-cut wafer, depending on
the particular SAW device application.ForY-cut
quartz the 250C temperature coefficient of
expansion in the Z axis is on the order of
13.7 x 10 cm
cm OC and in the X axis, the axis of the SAW propagation
it is on the order of 7.5x1Oe cm
cm OC As a result of the anisotropic temperature characteristics the cylindrical cavity 22 deforms overthe operating range of temperatures in a generally elliptical fashion, as shown in Fig. 3.The illustration of Fig. 3 is exaggerated for teaching purposes to demonstrate the nature of the deformation, where a circle 26 represents the shape of the cavity at room temperature which deforms with increasing temperature to a geometry which is substantially elliptical as illustrated in phantom by the ellipsoid 28, the major axis of the ellipsoid being along the Z axis of the crystal wafer.
Referring now to Fig. 4, in a vacuum encapsulated SAW pressure sensor structure 30 according to the present invention, the SAW sensor 10 is encapsulated by a vacuum enclosure comprising a cover portion 32 adapted to enclose the sensor 10 within a chamber 34 formed by the cover 32 and a base portion 36. the cover and base are formed from vacuum type material, whether metal or glass, suitable for providing a minimum vacuum of 10-8 torr within the chamber 34. The cover is bonded to the base along the mating surface 37 with a vacuum seal, such as a solder seal, or weld. The cover 32 includes a small orifice 38 which allows evacuation of the chamber 34 following the bonding of the cover to the base, after which the orifice is closed off with a solder seal 39.
The electrical connections between the SAW transducers 1 6, 18 and the external oscillator circuits (not shown) are provided through electrical conductors 40 which are mounted through the base 36 with feed-thru insulators 41, of a type known in the art, which provide both electrical insulation of the conductor and a vacuum seal between the chamber 34 and the outside ambient. For a metal vacuum enclosure the base itself may be used as the return current path for the transducer and internal ground wires 42 may be provided between the SAW transducers and the base.
The SAW sensor 10 is sup-por-ted in the chamber by a cylindrical metal sleeve 44 which displaces the sensor substrate 11 at a distance, or height (hut) above the inside surface 46 of the base. The sleeve has a diameter (D) which is equal
to or less than the diameter of the cavity 22. The sleeve aperture 48 provides a fluid passage, or conduit, between the cavity and an orifice 50 formed through the wall of the base and accessible to an external source of pressure signals (not shown). In Fig. 4 the metal sleeve 44 is illustrated as a straight walled cylinder having a bearing surface 52 adapted to fit into a counterbore formed in the substrate 11 along thecircumference of the cavity opening of the substrate 11, and having a seating surface 54 adapted to fit into a similar type counterbore provided in the surface 46 along the circumference of the orifice 50. Each of the sleeve surfaces are bonded to their respective mating surfaces by a solder seal. In assembly of the structure the sleeve is first sealed to the substrate.
Following a step of RF sputtering thin-films of chrome and gold to the side wall of the counterbore, a plating of nickel is applied to the gold film and the bearing surface 52 is soldered in the counterbore with a lead tin solder having a melting point of approximately 2000 C. At a later step the seating surface is soldered to the base with a lower temperature indium solder having a
melting point temperature of 1 560C. Each of the solder bonds provide a vacuum seal of the substrate and base to the mating surfaces of the sleeve.
The metal sleeve comprises a vacuum type
metal having good vacuum characteristics, such as: low vapor pressure, high melting point, corrosion resistance, may be easily outgassed,
may be formed by machining, and may be soldered, welded, or brazed. To prevent the rupture of the vacuum seal between the sleeve and the substrate, the metal must also be of a type having a temperature coefficient of expansion which is compatible to that of the substrate.
For the piezoelectric material substrates having
anisoptropic temperature characteristics, the
metal should have a temperature coefficient
between those of the optic axis and the X and Y axes, such that in Fig. 3 a metal having a
compatible temperature coefficient provides for a
sleeve expansion from the solid circle 26 to the
dashed circle 60 while the cavity expands from
the circle 26 to the ellipsoid 28. The preferred
metal, as illustrated, expands less along the Z axis
than the substrate but more along the X axis,
providing an approximate mean expansion to that
of the two axes of the substrate.
The expansion of the sleeve beyond the substrate in the X axis, if permitted, would result in strain being induced into the substrate, and possibly fractures along the interior surface of the cavity. If, however, the metal sleeve deforms such that the cylinder walls yield to the restricted expansion of the sleeve along the substrate X axis, the sleeve will follow the elliptical distortion characteristic of the substrate cavity, reducing or even eliminating the induced strain and maintaining the integrity of the vacuum seal, Of course, the sleeve must exhibit an elastic deformation allowing restoration of the sleeve contour at room ambient along with the restoration of the cavity.Therefore, in addition-to the requirements that the sleeve be comprised of metal which is suitable for providing a vacuum seal, i.e. high vapor pressure, it must have a temperature coefficient which is compatible to that of the anisotropic characteristics of the quartz and must also exhibit an elastic deformation characteristic.One metal which satisfies all of these requirements is nickel which provides all of the requirements for a good vacuum material and has a 2 5 OC temperature coefficient of
12.6 x 10-6 cm
cm OC Nickel exhibits an inherent elastic deformation characteristic and through suitable sleeve geometry, including wall thickness, sleeve length, and sleeve diameter, the sleeve may be made to exhibit the deformation required to conform in concert with the quartz substrate over the operating temperature range of the sensor.
The deformation may be provided by selecting a length for the sleeve which ensures that the substrate 11 is displaced from the base interior surface 46 at a height (h1) which is ten times greater than the thickness of the cylinder walls 62, which are formed to a minimum dimension. The minimum wall thickness is selected with consideration given to: providing the sleeve structure with sufficient rigidity to prevent deformation of the sleeve cylindrical shape under a maximum pressure differential between sensed pressure and the zero psi of the chamber 34, and providing a vacuum tight seal over the same operating range of sensed pressures, i.e. that the cylinder walls do not become so thin as to exhibit a porosity which may provide for a vacuum leak.A minimum dimension for the cylinder wall thickness for a 3.45 bar sensor isin the-range of 5.08.10-3 to 7.62.10-3 cm. A more conservation, practical wall thickness for the same sensor is on the order of 12.7.10~3cm, which then establishes the height (h1) as 12.7.10~2cm. The additional length of the sleeve beyond that of the height dimension is selected to provide a suitable insertion length of the sleeve into each of the counterbores for the cavity 22 and orifice 50.
Establishing the 10:1 ratio between the height and the wall thickness provides the sleeve with sufficient elasticity to allow the bearing surface 52 and the adjacent top portion to deform in cooperation with the cavity, however, the dissimilar temperature coefficients still produce dimensional differences in expansion. The solder seal along the surface 52 exhibits sufficient elasticity to maintain the vacuum seal despite the slight dissimilarities in deformation. To provide the minimum displacement the sleeve diameter (D) is selected at the minimum value possible. This is limited by two constraints. The first constraint is the diameter of the cavity 22 since the outer diameter of the sleeve cannot be less than that of the opening of the cavity at the substrate surface.
As illustrated in Fig. 4, the cavity diameter is equal to that of the diaphragm since the diaphragm (20,
Fig. 1) is formed by boring the cavity into the substrate second surface. If alternative methods can be found to provide the required diaphragm diameter the diameter of the remaining part of the cavity, i.e. that part opening at the surface 24, can be narrower and still provide for fluid communication from the orifice 50 to the diaphragm surface 24, such that the sleeve diameter may be smaller than that of the diaphragm itself. The second constraint is that the sleeve must provide the required rigid support of the substrate mass. The substrate/sleeve mounting is in the nature of a pedestal which may vibrate under sensor operating conditions.If the vibration, or oscillation, is severe enough it may result in a tearing away of the substrate from the sleeve surface 52 resulting in a vacuum leak, or a break in the electrical connections provided to the
SAW transducers. A minimum diameter which satisfies the mechanical support requirements is on the order of one quarter of the maximum dimension of the rectangular substrate of Fig. 1. If a circular substrate is used the sleeve diameter is on the order of one quarter that of the substrate.
Since the diaphragm diameter is typically one half that of a circular substrate, or one half the maximum dimension of a rectangular substrate, the minimum diameter for the sleeve 44 is on the order of one half the diameter of the diaphragm.
In summary, the metal sleeve 44 has the characteristics of: (1) comprising a vacuum type metal having a temperature coefficient of expansion compatible with that of the anisotropic characteristics of the SAW substrate material, (2) has as an overall length to wall thickness which provides for displacement of the substrate from the enclosure base at a distance which is ten times greater than the wall thickness of the sleeve, and (3) and has a sleeve diameter which is equal to or less than the diameter of the diaphragm formed in the SAW substrate, and which has an optimum minimum diameter equal to one half that of the diaphragm. As long as these requirements are satisfied, the sleeve may have a slightly-altered geometry to satisfy alternative mounting
requirements of the sleeve to both the substrate and the orifice formed in the wall, such as the base 46, of the vacuum structure.
Referring now to Fig. 5, in an alternative embodiment the sleeve 44' includes a rim, or flange, 70 formed around the outer surface of the cylindrical wall. The rim provides a bearing surface 72 for supporting the substrate 11 at the hight (h,) above the surface 46 of the base 36. In this manner, the substrate 11 need not have the counterbore formed along the circumference of the cavity, which may be preferred. The sleeve 44' comprises the same material as that of the sleeve 44, having the same requirements of providing a vacuum seal and an elastic deformation characteristic such that the sleeve conforms to the deformation of the aperture over temperature. The sleeve provides for a similar fluid conduit 48 between the orifice 50 and the cavity 22 allowing for fluid communication between an external source of pressure signals and the surface 24 of the diaphragm formed in the substrate.The sleeve 44' also has a seating surface 74 which mates with a countersink in the base 36 of the enclosure.
In Fig. 5, the seating surface is provided by a shoulder portion 76 of the sleeve which permits both forenhanced mechanical strength of the sleeve at the seating surface and also for a
reduction in the diameter of the orifice 50 formed in the base. This allows for practical considerations in both providing the thin-walled sleeve with sufficient rigidity for handling, i.e. to prevent distortion of the sleeve during fabrication
which may result for sleeves having the minimum
wall thickness, and also for providing an opening
at the orifice which is compatible to standard size
pressure fittings, such that the orifice and/or
the interior wall of the shoulder 76 may be
threaded to an external fluid conduit.Since
the sleeves 44 and 44' each have temperature
coefficients which are compatible with the metal
enclosure there is no requirement that the sleeve
exhibit unusual deformation along the seating
surface. Any incidental differences in temperature
coefficients which may induce strain in the base
36 do not provide any induced strain in the
substrate. Therefore, the sleeve 44 shown in Fig. 4
may similarly be provided with the shoulder 76
illustrated for the sleeve 44' while the bearing
surface 52 of the sleeve 44 remains the same. The
vacuum encapsulated SAW pressure sensor
structure of the present invention provides for
both the tight vacuum encapsulation of the SAW
substrate to prevent the deterioration or change in
propagation velocity due to ambient
contamination while also providing the required
zero bar reference for an absolute pressure sensor
configuration.The use of the metal sleeve to
support the substrate at a displaced dimension
from the wall of the structural enclosure isolates
the SAW substrate from any induced strain
resulting from temperature cycling of the structure
over the temperature range of operation. The
sleeve geometry including length, wall thickness,
and diameter may be altered within the guidelines
recited hereinbefore to provide for higher
operating temperature ranges, such that a
minimum wall thickness in the range of 5.08.10-3
to 7.62.103cm for a sensor having a maximum
pressure differential of 3.45 bar must be increased to satisfy higher pressure differentials. For a 600
bar sensor, the minimum wall thickness is on the
order of 7.62.10-3 to 10.16.10~3cm with a typical
thickness on the order of 20.32.10~3cm. The
preferred material for the metal sleeve is nickel,
although any material having the requisite
characteristics described hereinbefore may be
used. Similarly, although the invention has been
shown and described with respect to illustrative embodiments thereof, it should be understood by - those skilled in the art that the foregoing and
various other changes, omissions and additions in
the form and detail thereof may be made therein
without departing from the spirit and the scope of
the invention.
Claims (6)
1. A vacuum encapsulated structure for a
surface acoustic wave (SAW) pressure sensor
structure, comprising:
a SAW pressure sensor including a SAW delay
line disposed in an active signal region of a first
one of two parallel major surfaces of a substrate,
said substrate having a deformable diaphragm
formed therein coextensive with said active signal
region, said diaphragm having a membrane
thickness determined by the relative displacement
of said first surface from a parallel interior surface defined by the end wall of a cylindrical cavity formed in the second major surface of said substrate, said cavity having a diameter definitive of the diameter of said deformable diaphragm;;
a vacuum sealing enclosure including a base portion and a cover portion joined to said base portion in a vacuum sealing relationship said base portion and cover portion being adapted to receive said SAW sensor in a vacuum chamber formed therebetween, said base portion including an orifice therethrough adapted for alignment with said cavity in said substrate; and
a cylindrical metal sleeve having a central aperture formed along the length thereof and joined in a vacuum sealing relationship at opposite ends thereof to said cavity and to said orifice, said sleeve providing mutually matching surfaces at each end in dependence on the outer diameter and wall thickness of said sleeve, said central aperture providing a fluid conduit for external pressure signals through said vacuum environment from said orifice to said cavity, said sleeve supporting said SAW pressure sensor in displacement from said base portion at a value which is from ten to twenty times greater than the wall thickness of said sleeve.
2. A vacuum encapsulated stucture for a surface acoustic wave (SAW) pressure sensor structure, comprising:
a SAW pressure sensor including a SAW delay line disposed in an active signal region on a first one of two parallel major surfaces of a substrate,
said substrate having a deformable diaphragm formed therein coextensive with said active signal region, said diaphragm having a membrane thickness determined by the relative displacement of said first surface' from a parallel interior surface
defined by the'wend wall of a cylindrical cavity formed in the second major surface of said substrate, said cavity having a diameter definitive of the diameter of said deformable diaphragm.
a vacuum sealing enclosure including a base portion and a cover portion joined to said base portion in a vacuum sealing relationship, said base portion and cover portion being adapted to receive said SAW sensor in a vacuum chamber formed therebetween, said base portion including an orifice therethrough adapted for alignment with said cavity in said substrate; and
a cylindrical metal sleeve having a central aperture formed along the length therof and joined in a vacuum sealing relationship at opposite ends thereof to said cavity and to said orifice, said sleeve providing mutually matching surfaces at each end in dependence on the outer diameter and wall thickness of said sleeve, said central aperture providing a fluid conduit for external pressure signals through said vacuum environment from said orifice to said cavity, said sleeve having a minimum outer diameter which is less than the diameter of said deformable diaphragm.
3. A vacuum encapsulated stucture for a surface acoustic wave (SAW) pressure sensor structure, comprising:
a SAW pressure sensor including a SAW delay line disposed in an active signal region on a first one of two parallel major surfaces of a substrate, said substrate having a deformable diaphragm formed therein coextensive with said active signal region, said diaphragm having a membrane thickness determined by the relative displacement of said first surface from a parallel interior surface defined buy the end wall of a cylindrical cavity formed in the second major surface of said substrate, said cavity having a diameter definitive of the diameter of said deformable diaphragm;;
a vacuum sealing enclosure including a base portion and a cover portion joined to said base portion in a vacuum sealing relationship, said base portion and cover portion being adapted to receive said SAW sensor in a vacuum chamber formed therebetween, said base portion including an orifice therethrough adapted for alignment with said cavity in said substrate; and
a cylindrical metal sleeve having a central aperture formed along the length thereof and joined in a vacuum sealing relationship at opposite ends thereof to said cavity and to said orifice, said sleeve providing mutually matching surfaces at each end in dependence on the outer diameter and wall thickness of said sleeve. said central aperture providing a fluid conduit for external pressure signals through said vacuum environment from said orifice to said-cavity, said sleeve being formed from a metal having a low vapor pressure and high melting point temperature.
4. The structure of claim 2, wherein said sleeve outer diameter is equal to one half the diameter of said deformable diaphragm.
5. The structure of claim 3, wherein said sleeve is formed from nickel.
6. A vacuum encapsulated stucture substantially as hereinbefore described with reference to and as illustrated in Fig. 3 to 5 of the drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US97254278A | 1978-12-22 | 1978-12-22 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2037988A true GB2037988A (en) | 1980-07-16 |
| GB2037988B GB2037988B (en) | 1983-03-02 |
Family
ID=25519783
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB7943332A Expired GB2037988B (en) | 1978-12-22 | 1979-12-17 | Pressure sensor |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS5598323A (en) |
| AU (1) | AU524762B2 (en) |
| CA (1) | CA1126975A (en) |
| DE (1) | DE2951469A1 (en) |
| FR (1) | FR2444936A1 (en) |
| GB (1) | GB2037988B (en) |
| IT (1) | IT1125925B (en) |
| SE (1) | SE7910311L (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB0329019D0 (en) | 2003-12-15 | 2004-01-14 | Imp College Innovations Ltd | Acoustic wave devices |
| JP4983176B2 (en) * | 2006-09-14 | 2012-07-25 | セイコーエプソン株式会社 | Manufacturing method of pressure sensor |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3697917A (en) * | 1971-08-02 | 1972-10-10 | Gen Electric | Semiconductor strain gage pressure transducer |
| GB1389610A (en) * | 1972-10-11 | 1975-04-03 | Marconi Co Ltd | Surfacewave devices |
| JPS52149992A (en) * | 1976-06-09 | 1977-12-13 | Hitachi Ltd | Pressure transducer |
| JPS5365089A (en) * | 1976-11-24 | 1978-06-10 | Toshiba Corp | Semiconductor pressure transducer |
| US4100811A (en) * | 1977-03-18 | 1978-07-18 | United Technologies Corporation | Differential surface acoustic wave transducer |
| US4216401A (en) * | 1978-12-22 | 1980-08-05 | United Technologies Corporation | Surface acoustic wave (SAW) pressure sensor structure |
-
1979
- 1979-12-11 CA CA341,637A patent/CA1126975A/en not_active Expired
- 1979-12-13 AU AU53797/79A patent/AU524762B2/en not_active Ceased
- 1979-12-14 SE SE7910311A patent/SE7910311L/en not_active Application Discontinuation
- 1979-12-17 GB GB7943332A patent/GB2037988B/en not_active Expired
- 1979-12-18 IT IT28110/79A patent/IT1125925B/en active
- 1979-12-20 DE DE19792951469 patent/DE2951469A1/en not_active Withdrawn
- 1979-12-21 JP JP16746779A patent/JPS5598323A/en active Granted
- 1979-12-24 FR FR7931570A patent/FR2444936A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5598323A (en) | 1980-07-26 |
| DE2951469A1 (en) | 1980-07-03 |
| IT1125925B (en) | 1986-05-14 |
| SE7910311L (en) | 1980-06-23 |
| IT7928110A0 (en) | 1979-12-18 |
| JPS6345049B2 (en) | 1988-09-07 |
| AU524762B2 (en) | 1982-09-30 |
| GB2037988B (en) | 1983-03-02 |
| CA1126975A (en) | 1982-07-06 |
| AU5379779A (en) | 1980-06-26 |
| FR2444936A1 (en) | 1980-07-18 |
| FR2444936B1 (en) | 1982-10-08 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19941217 |