Method and apparatus for fabricating a pressure-wave sensor with a leveling support element

A method and an apparatus for fabricating a pressure-waveform sensor with a leveling support element. One embodiment provides a pressure-waveform sensor having a housing, a support element, and a piezoelectric element having a first end secured between the support element and the housing, and a second end in a cantilevered orientation. The support element and the piezoelectric element together form a plurality of support regions to level the piezoelectric element and relative to the housing. In some embodiments, the support element includes a ring having three slots spaced apart on one face of the ring, or one or more support regions formed with a shim having a thickness equal to a thickness of the piezoelectric device, or support regions that are integral to the support element. Another aspect provides a method for fabricating a pressure-waveform sensor. The method includes the steps of forming a housing structure with an inner lip, and supporting a cantilevered piezoelectric element with a support structure such that contact is made with the inner lip at a plurality of points in order to level the piezoelectric element relative to the inner lip.

FIELD OF THE INVENTION
 This invention relates to the field of medical sensors, and, more
 specifically, to a method and apparatus of sensing an arterial pulse
 pressure, and, in particular, the blood pressure waveform in the radial
 artery of the human body.
 BACKGROUND OF THE INVENTION
 Conventionally, blood pressure has been measured by one of four basic
 methods: invasive, oscillometric, auscultatory and tonometric. The
 invasive method, also known as an arterial-line method (or "A-line"),
 typically involves insertion of a needle or catheter into an artery. A
 transducer connected by a fluid column to the needle or catheter is used
 to determine exact arterial pressure. With proper instrumentation,
 systolic, diastolic, and mean arterial pressures may be determined, and a
 blood-pressure waveform may be recorded. This invasive method is difficult
 to set up, is expensive and time consuming, and involves a potential
 medical risk to the subject or patient (for example, formation of emboli
 or subsequent infection). Set up of the arterial-line method also poses
 technical problems. Resonance often occurs and causes significant errors.
 Also, if a blood clot forms on the end of the needle or catheter, or the
 end of the needle or catheter is located against an arterial wall, a large
 error may result. To eliminate or reduce these errors, the apparatus must
 be checked, flushed, and adjusted frequently. A skilled medical
 practitioner is required to insert a needle or catheter into the artery,
 which contributes to the expense of this method. Medical complications are
 also possible, such as infection, nerve and/or blood vessel damage.
 The other three traditional methods of measuring blood pressure arc
 non-invasive. The oscillometric method measures the amplitude of blood
 pressure oscillations in an inflated cuff. Typically, the cuff is placed
 around the left upper arm of the patient and then pressurized to different
 levels. Mean pressure is determined by sweeping the cuff pressure and
 determining the cuff pressure at the instant the peak amplitude occurs.
 Systolic and diastolic pressure is determined by cuff pressure when the
 pressure oscillation is at some predetermined ratio of peak amplitude.
 The auscultatory method also involves inflation of a cuff placed around the
 left upper arm of the patient. After inflation of the cuff to a point
 where circulation is stopped, the cuff is permitted to deflate. Systolic
 pressure is indicated when Korotkoff sounds begin to occur as the cuff is
 deflated. Diastolic pressure is indicated when the Korotkoff sounds become
 muffled or disappear.
 The fourth method used to determine arterial blood pressure has been
 tonometry. The tonometric method typically involves a transducer
 positioned over a superficial artery. The transducer may include an array
 of pressure-sensitive elements. A hold-down force is applied to the
 transducer in order to partially flatten the wall of the underlying artery
 without occluding the artery. Each of the pressure-sensitive elements in
 the array typically has at least one dimension smaller than the lumen of
 the underlying artery in which blood pressure is measured. The transducer
 is positioned such that at least one of the individual pressure sensitive
 elements is over at least a portion of the underlying artery. The output
 from one or more of the pressure-sensitive elements is selected for
 monitoring blood pressure. These tonometric systems either use an
 upper-arm cuff to calibrate blood-pressure values, or they measure a
 reference pressure directly from the wrist and correlate this with
 arterial pressure. However, when a patient moves, recalibration of the
 tonometric system is often required because the system may experience a
 change in electrical gains. Because the accuracy of such tonometric
 systems depends upon the accurate positioning of the individual pressure
 sensitive element over the underlying artery, placement of the transducer
 is critical. Consequently, placement of the transducer with these
 tonometric systems is time-consuming and prone to error. Also, expensive
 electro-mechanical systems guided by software/hardware computer approaches
 are often used to assist in maintaining transducer placement.
 The oscillometric, auscultatory and tonometric methods measure and detect
 blood pressure by sensing force or displacement caused by blood pressure
 pulses within the underlying artery that is compressed or flattened. The
 blood pressure is sensed by measuring forces exerted by blood pressure
 pulses in a direction perpendicular to the underlying artery. However,
 with these methods, the blood pressure pulse also exerts forces parallel
 to the underlying artery as the blood pressure pulses cross the edges of
 the sensor which is pressed against the skin overlying the underlying
 artery of the patient. In particular, with the oscillometric and the
 auscultatory methods, parallel forces are exerted on the edges or sides of
 the cuff. With the tonometric method, parallel forces are exerted on the
 edges of the transducer. These parallel forces exerted upon the sensor by
 the blood pressure pulses create a pressure gradient across the
 pressure-sensitive elements. This uneven pressure gradient creates at
 least two different pressures, one pressure at the edge of the
 pressure-sensitive element and a second pressure directly beneath the
 pressure sensitive element. As a result, the oscillometric, auscultatory
 and tonometric methods can produce inaccurate and inconsistent blood
 pressure measurements.
 Further, the oscillometric and auscultatory methods are directed at
 determining the systolic, diastolic, and/or mean blood pressure values,
 but are not suited to providing a calibrated waveform of the arterial
 pulse pressure.
 The traditional systolic-diastolic method for measuring blood pressure
 provides the physician with very limited clinical information about the
 patient's vascular health. In contrast, the HDI/PulseWave.TM. DO-2020
 system made by Hypertension Diagnostics, Inc., the assignee of the present
 invention, measures a blood pressure waveform produced by the beating
 heart that, it is believed, can be analyzed to provide an assessment of
 arterial elasticity. When the aortic valve closes after the heart has
 ejected its stroke volume of blood (the blood ejected during each heart
 beat), the decay or decrease of blood pressure within the arteries prior
 to the next heart beat forms a pressure curve or waveform which is
 indicative of arterial elasticity. Subtle changes in arterial elasticity
 introduce changes in the arterial system that are reflected in the
 arterial blood pressure waveform and research suggests that these changes
 in the function and structure of the arterial wall precede the development
 of coronary artery disease, or the premature stiffening of the small
 arteries which appears to be an early marker for cardiovascular disease.
 Incorporating the physiological phenomena associated with blood pressure
 waveforms, Drs. Jay N. Cohn and Stanley M. Finkelstein, Professors at the
 University of Minnesota in Minneapolis, developed in the early 1980's a
 method for determining a measure of elasticity in both large and small
 arteries. That technique involved an invasive procedure that placed a
 catheter connected to a pressure transducer into the patient's artery in
 order to obtain a blood pressure waveform that could be analyzed using a
 modified Windkessel model, a well-established electrical analog model
 which describes the pressure changes during the diastolic phase of the
 cardiac cycle in the circulatory system.
 This "blood pressure waveform" or "pulse contour" analysis method provided
 an independent assessment of the elasticity or flexibility of the large
 arteries which expand to briefly store blood ejected by the heart, and of
 the small arteries (arterioles) which produce oscillations or reflections
 in response to the blood pressure waveform generated during each heart
 beat.
 By assessing the elasticity of the arterial system, clinical investigators
 have been able to identify a reduction in arterial elasticity in patients
 without evidence of traditional risk factors, suggesting the early
 presence of vascular disease. Furthermore, clinical research data has
 demonstrated that individuals with heart failure, coronary artery disease,
 hypertension and diabetes typically exhibit a loss of arterial elasticity.
 These abnormal blood vessel changes often appear to precede overt signs of
 cardiovascular disease and the occurrence of a heart attack or stroke by
 many years. Clinical investigators have also demonstrated an age-related
 loss of elasticity of both the large and small arteries suggesting that
 premature stiffening of an individual's arteries is an apparent marker for
 the early onset of cardiovascular disease.
 There is a need to obtain, non-invasively, an accurate, repeatable
 blood-pressure waveform from the radial artery, in order to avoid the
 problems associated with invasive procedures such as those described
 above.
 In particular, a sensor approximately 1/2" in diameter and approximately
 1/2" in height has been found to provide good results. However, the
 construction of such a sensor is difficult due to its small size and need
 to be rigged, sealed, and accurate. Thus there is a need for an improved
 sensor structure and method.
 SUMMARY OF THE INVENTION
 The invention includes a method and an apparatus for fabricating a
 pressure-wave (also called pressure-waveform) sensor with an improved
 support element. The support element precisely levels a piezoelectric
 element relative to the sensor housing. In one embodiment, the sensor is
 used for sensing an arterial-pulse-pressure waveform.
 One embodiment provides a pressure-waveform sensor having a housing, a
 support element, and a piezoelectric element having a first end secured
 between the support element and the housing, and a second end in a
 cantilevered orientation. The support element and the piezoelectric
 element together form a plurality of support regions to level the
 piezoelectric element relative to the housing.
 In some embodiments of the pressure-waveform sensor, the support element
 includes a ring having three slots spaced apart on one face of the ring,
 and having the piezoelectric element mounted to a first one of the slots.
 In one such embodiment, the ring further includes leveler elements mounted
 in a second and a third of the three slots to provide two of the support
 regions.
 In one embodiment, one or more of the plurality of support regions are
 formed with a shim having a thickness equal to a thickness of the
 piezoelectric device. In some embodiments of the pressure-waveform sensor,
 the support element has a first face region for attaching to the first end
 of the piezoelectric element, and a second face region elevated and
 relative to the first face region to provide one or more of the plurality
 of support regions. In one such embodiment, the support regions of the
 second face region are integral to the support element.
 Another aspect of the present invention provides a method for fabricating a
 pressure-waveform sensor. The method includes the steps of forming a
 housing structure with an inner lip, and supporting a cantilevered
 piezoelectric element with a support structure such that contact is made
 with the inner lip at a plurality of regions in order to level the
 piezoelectric element relative to the inner lip.

DESCRIPTION OF THE PREFERRED EMBODIMENT
 In the following detailed description of the preferred embodiments,
 reference is made to the accompanying drawings which form a part hereof,
 and in which is shown by way of illustration, specific embodiments in
 which the invention may be practiced. It is to be understood that other
 embodiments may be utilized and structural changes may be made without
 departing from the scope of the present invention.
 When measuring the pressure waveform from the radial artery in the human
 arm, a sensor approximately 1/2" in diameter and approximately 1/2" in
 height has been found to provide good results. One such sensor is
 described in patent application Ser. No. 09/045,018 entitled "SENSOR AND
 METHOD FOR SENSING ARTERIAL PULSE PRESSURE" and is assigned to the
 assignee of the present invention, and is incorporated herein by
 reference. Moreover, co-pending application Ser. No. 09/045,449 entitled
 "APATUS AND METHOD FOR HOLDING AND POSITIONING AN ARTERIAL PULSE
 PRESSURE SENSOR" and 09/045,420 entitled "APATUS AND METHOD FOR BLOOD
 PRESSURE PULSE WAVEFORM CONTOUR ANALYSIS" show ways of using the present
 invention, and are also incorporated herein by reference.
 The invention described in this application is useful for many types of
 arterial-pulse-pressure sensing devices, including those having a
 piezoelectric element contained in a housing. The invention is useful with
 many mechanical configurations of leveling support elements.
 FIG. 1 shows a cross-section view of one embodiment of assembled arterial
 pulse pressure sensor 100. In the embodiment shown, arterial pulse
 pressure sensor 100 includes housing 110, diaphragm 120 which is welded to
 housing 110 (in one embodiment, laser welded), cover 130 which is screwed
 onto housing 110 and sealed using O-ring 140, cable adaptor 150 which is
 screwed to housing 110 and glued and sealed to signal/power cable 152 with
 epoxy, piezoelectric double-plate ceramic element (DPCE) 170 which is
 attached using epoxy between piezoelectric-element-holder ring 180 and
 shelf 112 of housing 110, and amplifier 190 which is mounted to
 piezoelectric-element-holder ring 180 (also generically called holder
 element 180, since other embodiments use a triangle, or a square, or a
 disc, or other suitable shape in place of the ring shown in this
 embodiment). Since one embodiment uses piezoelectric element 170, this
 embodiment is described as having first end 168 secured between
 piezoelectric element holder ring 180 and housing 110, and second end 169
 in a cantilevered orientation 171, and piezoelectric-element post 172
 attached to second end 169 of piezoelectric element 170. Contact point(s)
 177 is the area or areas wherein support element 400 (or alternative 500,
 600, 700, or 800) make mechanical (and optionally electrical) contact with
 inner lip 112 of housing 110. It is to be understood that other
 embodiments include single-plate ceramic piezoelectric elements or other
 types of pressure-sensing elements in place of DPCE 170, and will have a
 corresponding piezoelectric element holder ring 180 and post in some of
 those embodiments. The adjective term "DPCE" applies to those embodiments
 having a DPCE 170 sensing element, but not to other embodiments having
 other types of sensing elements.
 In one embodiment, a piezoelectric double-plate ceramic element (DPCE) that
 is 0.021 inches thick is cut to 0.180 inches long and 0.050 inches wide.
 The top surface forms one electrical contact (to which a wire is soldered,
 and the wire is then attached to amplifier 190), and the bottom surface
 forms the other electrical contact (which is made by contact to housing
 shoulder 112) once DPCE-holder ring 180 is secured using epoxy. In one
 embodiment, piezoelectric DPCE 170 is a ceramic piezoelectric block cut
 from a bulk plate or sheet of Bimorph.RTM. material (e.g., from a sheet of
 PZT-5A originally measuring 1.5 inches long by 0.75 inches wide by 0.021
 inches thick) available from Morgan Matroc, Inc., Electro Ceramics
 Division, Bedford, Ohio. Bimorph.RTM. is a registered tradename of Morgan
 Matroc, Inc., Electro Ceramics Division, for a double-plate ceramic
 element. The two thin plates are bonded together so they amplify their
 piezoelectric actions. A DPCE generates greater voltage when bent,
 deformed or displaced than does a single-plate ceramic element.
 In various embodiments, support element 400 (or alternative support
 elements 500, 600, 700, or 800) is formed as a ring 180 or triangle or a
 square or disc or other shape not shown, that is used to support
 piezoelectric element 170, and optionally, to support amplifier 190.
 Support element 400 provides a two-pronged purpose. First, support clement
 400 provides reliable acoustic and mechanical contact for piezoelectric
 element 170 and post 172 with diaphragm 120. Therefore, the displacement
 coupling of piezoelectric element 170 with diaphragm 120 via post 172 is
 more reliable with one or more support regions (alternatively embodied as
 feet, shims, raised bumps, balls, or other leveling elements located
 either on support element 400 or housing 110 such that piezoelectric
 element 170 is provided level support). Second, support element 400
 provides good electrical contact by leveling piezoelectric element 170
 relative to housing 110, that is, the lower face of the first end 168 of
 piezoelectric element 170 is reliably in level contact with shelf 112 of
 housing 110, thus resulting in a good electrical connection. In one
 embodiment, a conductive adhesive such as epoxy is used between first end
 168 of piezoelectric element 170 and shelf 112 of housing 110 to give
 better electrical contact. In other embodiments, no epoxy is used, such
 that the electrical contact is a mechanical butt joint.
 In one embodiment, housing 110, diaphragm 120, cover 130, cable adaptor
 150, and piezoelectric element holder ring 180 are medical-grade stainless
 steel (type 316L), in order to be durable and relatively inert for the
 intended use of skin-contact arterial pulse-pressure sensing. The
 piezoelectric element holder ring 180, in various embodiments, is made of
 stainless steel, plastic, ceramic or other suitable material and
 combinations thereof Deflection of diaphragm 120 causes piezoelectric
 element 170 to flex and thereby generate an electrical signal, which in
 turn is amplified and conditioned by amplifier 190 and coupled to
 signal/power cable 152 (also called input/output cable 152). Cable 152
 provides both delivery of input electrical power to amplifier 190, as well
 as receiving the output signal from amplifier 190, all using only two
 signal conductors (e.g., input/output wire 153, and ground 154). In one
 embodiment, diaphragm 120 is displacementally coupled to second end 169 of
 the piezoelectric element 170. In one such embodiment, this displacement
 coupling is achieved by epoxying post 172 to second end 169, and locating
 the other end against diaphragm 120. Diaphragm 120 forms an insulating
 connection and an electrical connection. Moreover, diaphragm 120 provides
 structural support and proper alignment of piezoelectric element 170 as
 piezoelectric element 170 is inserted into housing 110. In one embodiment,
 cable 152 is connected to a constant-current source by connector 159
 (e.g., a two-milliamp constant-current source), and amplifier 190 then
 provides a varying voltage (on the same signal wire that provides the
 constant current) linearly proportional to the pressure on diaphragm 120.
 An external circuit then receives and processes the arterial
 pulse-pressure waveform from the varying voltage. In some embodiments, the
 sensor 100 has amplifier 190 secured to a face of support element 400
 opposite to the piezoelectric element 170.
 Female threads 119 that are machined into the upper bore of housing 110
 mate with male threads 139 of cover 130. O-ring gasket 140 forms a seal
 between housing 110 and cover 130. (In another embodiment, an O-ring
 gasket is also provided to seal between housing 110 and cable adaptor 150.
 In one preferred embodiment though, a potting epoxy is used instead of an
 O-ring to seal between housing 110 and cable adaptor 150.) Female threads
 117 in the sidewall bore of housing 110 mate with male threads 157 of
 cable adaptor 150. In one embodiment, signal/power cable 152 is secured
 into the opening in cable adaptor 150 using epoxy, and cured in an oven at
 150.degree. F. for a minimum of 30 minutes. In one embodiment, holder ring
 180 has slot 184 through one wall of the top face, and slot 440 through
 two walls of the bottom face. One end of piezoelectric element 170 is
 located mostly within slot 440 (i.e., the bottom surface of piezoelectric
 element 170 extends slightly below the bottom surface of holder ring 180
 in order to make electrical and mechanical contact with shelf 112 of
 housing 110), but piezoelectric element 170 is electrically insulated from
 holder ring 180 by a layer of epoxy 179.
 FIG. 2 shows a side view of the leveling support element 400 for a
 piezoelectric element 170. The support element 400 and the piezoelectric
 element 170 together form a plurality of support regions 421, 441. As in
 FIG. 1, piezoelectric element holder ring 180 has a slot 184 through one
 wall on the top face of ring 180, and a slot 440 through one wall on the
 bottom face of ring 180. One end of piezoelectric element 170 is located
 mostly within slot 440 (i.e., the bottom surface of piezoelectric element
 170 as shown in FIG. 1 extends slightly below the bottom surface of
 piezoelectric element holder ring 180 in order to make electrical and
 mechanical contact with shelf 112 of housing 110), but piezoelectric
 element 170 is electrically insulated from piezoelectric element holder
 ring 180 by a layer of epoxy 179. Ring 180, in various embodiments, is
 made of stainless steel, plastic, ceramic or other suitable material
 and/or combinations thereof. In various embodiments post 172 is made of
 stainless steel, plastic, ceramic or other suitable material and/or
 combinations thereof.
 FIG. 3 is a cross-section view of one embodiment of prior art housing 110
 having diaphragm 120. In this embodiment, diaphragm 120 is a disc of
 medical-grade stainless steel (type 316L) having a diameter of 0.5 inches
 and a thickness of 0.006 inches. The thickness of diaphragm 120 is chosen
 to be thick enough to impart ruggedness and durability to arterial pulse
 pressure sensor 100, yet thin enough to provide the sensitivity and
 frequency response desired. In one embodiment, diaphragm 120 is
 laser-welded to the bottom surface of housing 110 across opening 111,
 using a pulsed NdYAG laser welder, with weld settings of: pulse
 rate--40/sec; pulse width--1; joules/pulse--0.3; and seconds/rev--5.5.
 Other types of welding such as Tungsten Inert Gas (TIG), may be used. A
 diaphragm welding pilot is used to hold the housing and a diaphragm
 welding heat sink is also used.
 FIG. 4A is an exploded isometric view of one embodiment of support element
 400 as a ring having two slots 420 and one slot 440 spaced apart on one
 face of ring 180, and having the piezoelectric element 170 with a post 172
 mounted to a first one of the slots 440. In one embodiment, the three
 slots (two slots 420 and slot 440) are spaced about 120 degrees from one
 another on the ring. In one such embodiment, the support element 400
 further includes wire leveler elements 410 mounted in a second slot 420
 and a third slot 420 of the three slots in order to provide support
 regions.
 FIG. 4B is a bottom view of leveling support element 400 for piezoelectric
 element 170. In the embodiment shown, support element 400 and
 piezoelectric element 170 together form a plurality of support regions
 421.
 FIG. 4C is an isometric view of assembled support element 400 as a ring
 having support regions 421. The wire leveler elements are embedded within
 epoxy in slots 420. The support element 400 has slot 184 through one of
 its walls. Slot 440 for the piezoelectric element 170 is opposite of
 support regions 421. Epoxy is inserted in slot 440 prior to machining a
 small slot within the epoxy for piezoelectric element 170, in order that
 an insulating layer 179 of epoxy electrically insulates piezoelectric
 element 170 from holder element 180.
 FIG. 4D is a side view of, support element 400 shown in FIG. 4C showing
 support regions 421 of support element 400.
 FIG. 5A is an isometric view of support element 500 and shim 560 atop its
 face. Shim 560 is thinner relative to piezoelectric element 170 because
 piezoelectric element sits atop ring 580. As used herein, the term shim
 can be flat, spherical, cylindrical or any other shape spacing element
 used to provide a leveling function. Also the present invention includes a
 raised feature integrally formed on another part such as feet in FIG. 6
 and a raised or elevated lip in FIG. 8. Ring 580 has epoxy 579 providing
 insulating and electrical contact. In some embodiments, support element
 500 is an alternative embodiment that can be substituted for support
 element 400 in the device shown in FIG. 1.
 FIG. 5B is a side view of support element 500 as shown in FIG. 5A. Each of
 the components are still visible from this view.
 FIG. 6 is an isometric view of support element 600 with integral support
 regions 450. In some embodiments, support element 600 is an alternative
 embodiment that can be substituted for support element 400 in the device
 shown in FIG. 1.
 FIG. 7A is an exploded isometric view of support element 700 includes a
 shim 460 having a thickness equal to a thickness of piezoelectric element
 170, atop its face. In some such embodiments, shim 460 is thinner than the
 thickness of piezoelectric clement 170, wherein piezoelectric element is
 recessed within slot 440. In some embodiments, shim 460 is equal in
 thickness to piezoelectric element 170, wherein both are mounted in
 relatively the same height on ring 180 and slot 440 has been eliminated.
 In some embodiments, shim 460 is thicker than piezoeletic element 170,
 wherein piezoelectric element 170 is seated in epoxy (thus providing an
 insulating spacer) on top of ring 180. In some embodiments, support
 element 700 is an alternative embodiment that can be substituted for
 support element 400 in the device shown in FIG. 1.
 FIG. 7B is a side view of support element 700 shown in FIG. 7A showing the
 support element 700 having a shim 460 atop its face.
 FIG. 7C is a top view of FIG. 7A showing support element 700 having a shim
 460 atop its face.
 FIG. 8A is an isometric view of support element 800 integrally formed with
 a raised region 470 having a thickness sufficient to level piezoelectric
 element 170. The support element 800 has slot 184 through one of its walls
 on the amplifier face and another slot 440 atop its face for the
 piezoelectric element. Slot 184 is 0.051 inches wide and 0.030 inches deep
 is machined in the upper surface, but only through one wall, as shown.
 Slot 184 is used as a reference during machining and assembly operations.
 In some embodiments of the pressure-waveform sensor 100, the support
 element 800 has a first face region (i.e., within slot 440) for attaching
 to the first end 168 of the piezoelectric element 170, and a second face
 region 470 elevated relative to the first face region 440 to provide one
 or more of the plurality of support regions 421. In one such embodiment,
 the support region or regions 421 of the second face region 470 are
 integral to the support element 800. In some embodiments, support element
 800 is an alternative embodiment that can be substituted for support
 element 400 in the device shown in FIG. 1.
 FIG. 8B is a side view of support element 800 shown in FIG. 8A.
 FIG. 8C is a top view of support element 800 shown in FIG. 8C.
 FIG. 9 is a flowchart detailing a method 900 for fabricating a
 pressure-waveform sensor (e.g., sensor 100). The method includes the steps
 of forming 910 a housing structure 110 with an inner lip 112, and
 supporting 920 a cantilevered piezoelectric element 170 with a support
 structure 400 such that contact is made with the inner lip 112 at a
 plurality of regions in order to level the piezoelectric element 170
 relative to the inner lip 112. Some embodiments of method 900 further
 includes a step of mounting 930 an amplifier 190 to a face of the support
 structure 400.
 FIG. 10 is a flowchart detailing a method 1100 for constructing a
 pressure-waveform sensor leveler support element (e.g., elements 400, 500,
 600, 700, or 800). The method includes a step 1110 of constructing support
 element in a shape to provide support regions, a step 1120 of mounting a
 cantilevered piezoelectric element in a first one of the slots. In some
 such embodiments, the method further includes a step 1130 of mounting
 leveler elements in one or more slots to provide one or more support
 regions. In some embodiments, the method further includes a step 1140 of
 forming the support regions as integral to the support element.
 In some embodiments, the method includes a step 1150 of positioning the
 support regions of the support element and the piezoelectric element to be
 coplanar; and
 In some embodiments the method includes a step 1160 of extending a post
 from the piezoelectric element to beyond the support regions to contact a
 diaphragm.
 In some embodiments, sensor 100 further includes a configuration where
 support regions 421 of the support element 400 and piezoelectric element
 170 are coplanar. In other embodiments, sensor 100 further includes post
 172 secured to cantilevered piezoelectric element 170. In addition, post
 172 extends below the plane of support regions 421.
 Except for the leveling features of support elements (400, 500, 600, 700,
 and 800) and other features described herein, other aspects of various
 embodiments of sensor 100 are made according to the description and
 instructions in patent application Ser. No. 09/045,018 entitled "SENSOR
 AND METHOD FOR SENSING ARTERIAL PULSE PRESSURE" mentioned above.
 Conclusion
 Described above is a method and an apparatus for fabricating a
 pressure-waveform sensor with a support element 400.
 One embodiment provides a pressure-waveform sensor 100 having a housing
 110, a support element 400 (or, in other embodiments, support element 500,
 600, 700 or 800) and a piezoelectric element 170 having a first end 168
 secured between the support element 400 and the housing 110, and a second
 end 169 in a cantilevered orientation 171. The support element 400 and the
 piezoelectric element 170 together provide a plurality of support regions
 421, 441 to level the piezoelectric element 170 and the support element
 400 relative to the housing 110.
 In one embodiment, one or more of the plurality of support regions 421 are
 formed with a shim 460 having a thickness equal to a thickness of the
 piezoelectric element 170. In some such embodiments, a diaphragm 120 is
 displacementally coupled to the second end 169 of the piezoelectric
 element 170.
 In some embodiments of the pressure-waveform sensor 100, the support
 element 400 includes a ring 180 having two slots 420 and one slot 440
 spaced apart on one face of the ring, and having the piezoelectric element
 170 mounted to a first one of the slots 440. In one such embodiment, the
 ring 400 further includes one or more wire leveler elements 410 mounted in
 a second slot 420 and a third slot 420 of the three slots to provide two
 of the support regions. In one such embodiment, the support regions are
 421 are formed using shims having a thickness equal to the piezoelectric
 element 170 and/or a sufficient thickness to level the piezoelectric
 element 170 relative to the housing 110.
 In some embodiments of the pressure-waveform sensor 100, the support
 element 400 has a first face region 440 for attaching to the first end 168
 of the piezoelectric element 170, and a second face region 470 elevated
 relative to the first face region 440 to provide one or more of the
 plurality of support regions 421. In one such embodiment, the support
 region or regions 421 of the second face region 470 are integral to the
 support element 400.
 In some embodiments, the sensor 100 further includes a configuration where
 the support regions of the support element 400 and the piezoelectric
 element 170 are coplanar. In other embodiments, the sensor 100 further
 includes a post 172 secured to the cantilevered piezoelectric element 170.
 In addition, the post 172 extends below the plane of the support region
 421.
 In some embodiments, the sensor 100 further includes an amplifier 190
 secured to a face of support element 400 opposite to the piezoelectric
 element 170.
 Another aspect of the present invention provides a method 900 for
 fabricating a pressure-waveform sensor. The method includes the steps of
 forming 910 a housing structure 110 with an inner lip 112, and supporting
 920 a cantilevered piezoelectric element 170 with a support element 400
 such that contact is made with the inner lip 112 at a plurality of points
 in order to level the piezoelectric element 170 relative to the inner lip
 112.
 Some embodiments of method 900 further includes a step 930 of mounting an
 amplifier 190 to a face of the support structure 400. In other
 embodiments, the method further includes a step 940 of forming a shim
 having sufficient thickness to level the piezoelectric device relative to
 the housing structure 110.
 Another aspect of the present invention provides a method 1100 for
 fabricating a pressure-waveform leveler support element 400500700 or 800.
 The method includes a step 1110 of constructing support element in a shape
 to provide support regions, a step 1120 of mounting a cantilevered
 piezoelectric element in a first one of the slots. In some such
 embodiments, the method further includes a step 1130 of mounting leveler
 elements in one or more slots to provide one or more support regions. In
 some embodiments, the method further includes a step 1140 of forming the
 support regions as integral to the support element.
 In some embodiments, the method includes a step 1150 of positioning the
 support element and the piezoelectric element to be coplanar relative to
 the housing structure.
 In some embodiments, the method includes a step 1150 of positioning the
 support regions of the support element and the piezoelectric element to be
 coplanar; and
 In some embodiments the method includes a step 1160 of extending a post
 from the piezoelectric element to beyond the support regions to contact a
 diaphragm.
 In various embodiments, support element 400 is made of stainless steel,
 plastic or ceramic. Stainless steel is a conductor (and in some such
 embodiments, an insulating layer 179 is used (see FIG. 1), whereas plastic
 and ceramic are electrical insulators (and in those embodiments, layer 179
 is not needed).
 In one embodiment of support element 400, a slot 184 is machined into one
 face of ring 180, and slot 440 and two slots 420 (e.g., three identical
 slots spaced 120 degrees from one another) machined into the opposing face
 of ring 180. The three slots are filled with epoxy 179. Three identical
 smaller and shallower slots are then machined into the epoxy (in one
 embodiment, slot 184 is used to register, align, and center the smaller
 slots in the epoxy to the center of the slots 420 and 440). Element 170 is
 epoxied into slot 440, and spacers 410 are epoxied into the slots 420. If
 a defect is discovered in the epoxy of slot 440, then one of the slots 420
 (which are identical to the desired slot 440) is instead used for holding
 cantilevered piezoelectric element 170, and the spacer 410 is epoxied to
 slot 440 (since defects that affect piezoelectric element 170 may not
 degrade the function of a spacer 410. In one embodiment, the assembled
 support element 400 is then inserted into housing 110, and then conductive
 epoxy is placed into slot 184 on top of a ground wire from amplifier 190,
 thus electrically grounding (connecting) support element 400 to housing
 110 and to the ground wire from amplifier 190 (with no epoxy between
 piezoelectric element 170 and shelf 112, which are electrically coupled by
 contact).
 It is to be understood that the above description is intended to be
 illustrative, and not restrictive. Although numerous characteristics and
 advantages of various embodiments of the present invention have been set
 forth in the foregoing description, together with details of the structure
 and function of various embodiments, many other embodiments and changes to
 details will be apparent to those of skill in the art upon reviewing the
 above description. The scope of the invention should, therefore, be
 determined with reference to the appended claims, along with the full
 scope of equivalents to which such claims are entitled.