Abstract:
A beam-type sensor capable of measuring displacement or acceleration includes a thin, flexible sheet of piezoresponsive material defining broad sides and a proximal end. In order to optimize boundary conditions, the proximal end of the sheet is supported by a clamp that provides a “clean” transition between support and no-support. Electrical connections to conductors associated with the broad sides are integrated into the clamp. In one embodiment, two sheets of piezoelectric material are connected electrically in parallel. In another embodiment, two sheets of piezoelectric material are connected electrically in series.

Description:
This application claims the priority of Provisional Application No. 60/350,553, filed Jan. 22, 2002. 

   FIELD OF THE INVENTION 
   The invention relates to piezoresponsive sensors, and more particularly to cantilevered piezoresponsive sensors with particular mechanical support boundary conditions and electrical interconnections. 
   BACKGROUND OF THE INVENTION 
   Certain semi-crystalline polymers, such as polarized fluoropolymer polyvinylidene fluoride (PVDF) are known to have piezoresponsive properties, which may include piezoelectric response. For this reason, PVDF has been used in various sensors to produce a voltage as a function of force or displacement. Depending upon the structure of a sensor using a piezoresponsive material, and its orientation and the manner of deformation of the piezoresponsive material, a useful response may be developed at electrodes located at various regions of the piezoresponsive material. For example, electrical connections can be made to conductive polymer, metallized foil, or conductive paint laminates or sandwiches containing the piezoresponsive material. The signal produced by such a piezoresponsive material may be in the form of a change in electrical resistance, in the generation of a charge, or the generation of a voltage. 
   Polymer resin piezoelectric materials are particularly useful because the polymers can be embodied as sensing elements which are both flexible and elastic, and develop a sense signal representing resiliently biased deformation when subjected to force. In the case of PVDF piezoelectric polymer, the sensing element is advantageously embodied as a thin strip. The piezoelectric element is oriented so that the strip is deflected, as by compression or stretching (tension) by the applied force, and two or more electrical contacts are made with the material, so that a voltage signal is produced in response to the force. The voltage is produced because deformation of the polymer material changes the relative positions of charges in the polymer chain or in the semi-crystalline lattice structure. Such sensing elements are useful over a range of frequencies, ranging from near-zero frequencies associated with direct current, up to ultrasound frequencies associated with alternating current. In addition to the sensing of forces, acceleration and displacement, such piezoresponsive sensors can be used in other contexts, such as for the sensing of changes in temperature, or for operation as a switch for generating a trigger signal for operation of a MOSFET or CMOS circuit. 
   A multi-mode accelerometer is described in U.S. Pat. No. 5,452,612. Another accelerometer is described in U.S. Pat. No. 6,252,335. A rate-responsive pacemaker including an accelerometer-based physical activity sensor is described in U.S. Pat. No. 5,833,713. U.S. Pat. No. 6,252,335 describes a beam accelerometer. 
   Low-cost cantilever beam type shock sensors are commercially available, as for example the Measurement Specialties Inc. LDTX and LDTM series. Incorporation of these devices into useful products requires the product designer to develop secure and reliable cantilever-clamped/free region boundary conditions so that the conditions at the mechanical boundary between the supported and the free portions of the beam can be predicted and maintained constant from unit to unit. When the electrical response of a piezoresponsive sensor in response to a particular mechanical stimulus may be insufficient, it may be desirable to concatenate together multiple sensors. The concatenation of two or more piezoresponsive sensors into a single unit additionally implicates the problems of achieving the proper electrical interconnections among the individual sensors. Additional problems associated with the design of piezoresponsive sensors lie in the temperature sensitivity of the piezoelectric materials, which may be damaged by overheating attributable to soldering of the electrical connections of the sensor unit to a utilization device. Improved devices are desired. 
   SUMMARY OF THE INVENTION 
   Thus, a sensor according to an aspect of the invention comprises a first sheet of piezoresponsive material defining first and second broad sides, and also defining, in registry on the first and second broad sides, first, second and third nonoverlapping regions. A first sheet of electrical conductor extends over, and is in contact with, the first broad side of the first sheet of piezoresponsive material in the second and third regions of the first broad side and does not extend over, or contact, the first broad side in the first region. A second sheet of electrical conductor extends over, and is in contact with, the second broad side of the first sheet of piezoresponsive material in the first and second regions of, and does not extend over, or contact, the second broad side of the first sheet of piezoresponsive material in the third region. As a result, or whereby, that second region of the first sheet of piezoresponsive material lying between the second regions of the second and third sheets of conductive material, when strained or flexed, produces a sensor response, which may be a voltage, between the second and third sheets of electrical conductor. The sensor also includes first and second electrically conductive means making contact with the first and second sheets of electrical conductor, for making signals from the first sheet of piezoresponsive material available as a sensor signal. 
   In a variant of this aspect of the invention, the sensor further comprises a third sheet of electrical conductor extending over, and in contact with, the first broad side of the first sheet of piezoelectric material in the first region, and not extending over or in contact with the first broad side of the first sheet of piezoelectric material in the second and third regions, the first and third sheets of electrical conductor being electrically isolated from each other. 
   In yet another variant of this aspect of the invention, the sensor further comprises at least one plated-through hole extending through the first sheet of piezoresponsive material in the first region, for making electrical connection between the second and third sheets of electrical conductor. In such an arrangement, the first and second electrically conductive means make electrical contact with the second sheet of electrical conductor through the plated-through hole. 
   When used at frequencies below the resonant frequency of the beam structure, a piezoresponsive sensor in accordance with embodiments of the present invention can operate as an accelerometer, providing an electrical response which may be linearly related to the acceleration of the beam support in a direction normal to the upper surface of the beam. When operated at a frequency above the resonant frequency of the beam structure, the sensor operates as a displacement transducer, providing an electrical response which may be linearly related to the displacement of the beam support. When operated below resonance, the sensor provides an electrical response which may be linearly related to the displacement of the tip of the beam relative to the beam support structure. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1   a  is a simplified perspective or isometric view of a sensor assembly according to an aspect of the invention, including a piezoresponsive assembly,  FIG. 1   b  is a simplified exploded perspective or isometric view of the structure of  FIG. 1   a ,  FIG. 1   c  is a side cross-sectional view of the sensor assembly of  FIG. 1   a ,  FIG. 1   d  is a plan view of the structure of  FIG. 1   a ,  FIG. 1   e  is a simplified, exploded, perspective or isometric view of the piezoresponsive assembly of  FIG. 1   a ,  FIG. 1   f  is a representation of the longitudinal extent of the various constituents of the piezoresponsive assembly of  FIG. 1   e ,  FIGS. 1   g ,  1   h ,  1   i , and  1   j  are plan views of some conductors of the piezoresponsive assembly of  FIG. 1   e , and  FIG. 1   k  is a plan view of the piezoelectric assembly of  FIG. 1   a , with conceptual partitions into three regions; 
       FIG. 2  is a simplified cross-sectional representation, corresponding in general to  FIG. 1   c , of an embodiment of the invention in which the piezoresponsive assembly is oriented orthogonal to the support pins. 
       FIGS. 3A and 3B  show embodiments wherein conductive electrode layers may be applied only in a specific region of the piezoelectrically active surface of a piezoelectric layer in order to increase sensitivity of the output signal. 
       FIG. 3C  illustrates a side view of a cantilever beam sensor structure having a force F applied to the tip of the beam;  FIG. 3D  is a graphical illustration of the stress on the beam, with the stress level decreasing linearly with beam length based on tip force;  FIG. 3E  is a graphical illustration of the output of piezoresponsive material showing the output varying linearly with stress on the beam;  FIG. 3F  provides a graphical illustration of the total output signal S as the average output over the active electrode region covered for the case illustrated in  FIGS. 3A and 3B ;  FIG. 3G  provides a graphical illustration of the total output signal S′ as the average output over the active electrode region covered for the case illustrated in  FIG. 3H ;  FIG. 3H  shows a cantilever beam structure wherein the upper and lower electrode layers define an active electrode region that covers substantially the entire area of the piezoelectric layer. 
       FIG. 4  illustrates an embodiment of the invention wherein two piezoelectric layers are electrically connected in series. 
   

   DESCRIPTION OF THE INVENTION 
   In  FIGS. 1   a  and  1   b , the sensor  100  includes a sheet or sheet assembly  110  of piezoresponsive material defining proximal  110 P and distal  110 R ends, with various conductors for making electrical connection between the sheet piezoresponsive material and the outside world. In  FIGS. 1   a  and  1   b , sheet assembly  110  is connected at a proximal end  110   l  to a structure designated generally as  120 , which includes a printed-circuit assembly designated generally as  130  and also includes an electrical connection arrangement designated generally as  180 . Sheet assembly  110  is supported at and near its proximal end or side  110 P by printed-circuit assembly  130 . Printed-circuit (pc) assembly  130  includes upper and lower pc boards  130   u  and  130   l , respectively, which are fastened together, with the piezoresponsive sheet assembly  110  clamped therebetween. 
   As mentioned, piezoresponsive assembly  110  of  FIGS. 1   a  and  1   b  is supported at one end by printed-circuit assembly  130 . That end  110 R of piezoresponsive assembly  130  which is remote from printed-circuit assembly  130  supports a weight or mass designated generally as  150  in a cantilever manner. Any movement of the sensor  100  in the direction of double-headed arrow  199  will tend to bend the piezoresponsive assembly  110 . It may be advantageous to have mass  150  made from a magnetically permeable material or to be magnetic. 
   Ring mass  150  of  FIGS. 1   a  and  1   b  is bipartite, with a first portion  150   u  on the upper side of the piezoresponsive assembly  110 , and a second portion  150   l  on the lower side. Each part  150   u  and  150  defines a through aperture  150   ua  and  150   la , respectively, to aid in fastening the weight to the remote end  110 R of the piezoresponsive assembly  110 . A rivet, eyelet or screw arrangement illustrated as  150   r  extends through the apertures  150   ua  and  150   la  of the weight, and through an aperture  110   wa  in the piezoresponsive assembly  110 . 
   The near end (as illustrated in  FIG. 1   b ) of sheet  110  defines a pair of apertures  110   aa  and  110   ab . Electrical connection arrangement  180  of  FIGS. 1   a  and  1   b  includes bent pins  180   a  and  180   b , which provide both physical support of sensor  100  and electrical terminals at which the sensed signal can be received. As shown in  FIGS. 1   a  and  1   b , the pins extend a predetermined distance in a plane perpendicular to the plane of the assembly before bending at bend  180   be  such that distal portions  180   ad ,  180   bd  of the pins lie in a plane parallel to the plane of the assembly. In this manner, the bent pins may be mounted to a vertical surface for sensing horizontal accelerations. Alternatively, straight pins that extend from the assembly only in the plane perpendicular thereto are also contemplated, for example, for mounting onto a horizontal surface for sensing vertical accelerations. Upper printed circuit board  130   u  defines apertures  130   uaa  and  130   uab  registered with apertures  130   laa  and  130   lab , respectively, of lower printed circuit board  130   l , and also registered with apertures  110   aa  and  110   ab , respectively, in sheet  110 . Each of pins  180   a  and  180   b  includes a flange  180   af  and  180   bf , respectively, which are intended to bear on the underside of printed circuit board  130   l , with a remote portion  180   ar ,  180   br  of pins  180   a ,  180   b , respectively, projecting through an aperture  110   a ,  110   b . Remote portions  180   ar  and  18   br  of pins  180   a  and  180   b , respectively, are dimensioned to project at least part-way through apertures in the juxtaposed printed-circuit boards  130 . More particularly, remote end  180   ar  of pin  180   a  projects at least partway through registered apertures  130   laa ,  110   aa , and  130   uaa , and remote end  180   br  of pin  180  projects at least part-way through registered apertures  130   lab ,  110   ab , and  130   uab . It should be noted that the sensed signal may be in the form of a change in resistance or in the form of a voltage or charge. When bent pins  180   a  and  180   b  are inserted into an underlying printed-circuit board (not illustrated) the sensor  100  projects “vertically” from the underlying printed-circuit board. 
   Two elements  182   a  and  182   b  are illustrated on the upper surface of printed-circuit board  130   u  of  FIG. 1   a . Reference to the cross-section of  FIG. 1   c  reveals that these elements are the visible portions of fasteners which, together with portions of pins  180 , hold the printed-circuit boards  130   u ,  130   l  together. Fasteners  182   a  and  182   b  may be screws threaded into appropriately threaded apertures (not illustrated) in the remote ends  180   ar ,  180   br  of pins  180   a  and  180   b , respectively, or they may be the peened-over remote ends of the pins themselves, so they may be considered to be the ends of rivets. In the cross-section of  FIG. 1   c , the fastener  182   b  can be seen to be a screw. 
     FIG. 1   d  is a plan view of the structure illustrated in  FIGS. 1   a ,  1   b , and  1   c , showing some dimensions in millimeters, and also illustrating some artwork which may be placed on the visible portion of the piezoresponsive assembly  110 . 
     FIG. 1   e  illustrates the composition of sheet assembly  110  of piezoresponsive material. In  FIG. 1   e , sheet of piezoresponsive material  110  is a flexible generally rectangular structure including a support sheet  210  of flexible material located near the center of the structure. Support sheet  210  is mechanically coupled to the piezoresponsive material for aiding in support thereof and for providing a neutral flexural axis for the overall assembly such that average length extensional stress through the thickness of the piezoresponsive layer resulting from flexure of the tip has enhanced magnitude. In a particular embodiment of the invention, support sheet  210  is of a polymer material, such as MYLAR, but it may be any flexible material, such as a metal. Support sheet  210  as illustrated has an upper surface  210   us  and a lower surface  210   ls . The near end of support sheet  210  defines apertures  210   aa  and  210   ab , which are located at positions corresponding to the locations of apertures  110   aa  and  110   ab  of  FIG. 1   b . The far end of support sheet  210  defines an aperture  210   wa  at a location corresponding to the location of aperture  110   wa  of  FIG. 1   b . The layers  214  and  217  immediately above and below support sheet  210  are layers of adhesive material. The upper layer  214  of adhesive material affixes to the upper surface  210   us  of support sheet  210  a first or upper composite sheet, designated generally as  212 . Similarly, the lower adhesive layer  217  of adhesive material affixes to the lower surface  210   ls  of support sheet  210  a second or lower composite sheet, designated generally as  216 . Each of composite sheets  212  and  216  is itself a composite of a layer or sheet of piezoresponsive material such as piezoelectric PVDF with a conductive layer in contact with each broad surface. Thus, upper composite sheet  212  includes a piezoresponsive sheet  222  defining a broad upper surface  222   us  and a broad lower surface  222   ls , and lower composite sheet  216  includes a piezoresponsive sheet  226  defining broad upper and lower sufaces  226   us  and  226   ls , respectively, with a conductive layer in contact with each broad surface. 
   As illustrated in  FIG. 1   e , upper piezoresponsive sheet  222  of composite sheet  212  defines near-end apertures  222   aa  and  222   ab  and far-end aperture  222   wa , all registered with corresponding apertures of flexible support sheet  210 , for like purposes. The upper surface  222   us  of piezoresponsive sheet  222  is in contact with a patterened layer or film  201 / 202  of electrical conductor, and the lower surface  222   ls  of piezoresponsive sheet  222  is similarly in contact with a patterned layer or film  203  of conductor. In order to describe the regions of the upper and lower surfaces of piezoresponsive sheet  222  to which the portions of the patterned conductor are applied, reference is made to  FIG. 1   k .  FIG. 1   k  represents a plan view of piezoresponsive sheet  222  of  FIG. 1   e , partitioned into three nonoverlapping regions  11 ,  12 , and  13  by first and second mutually orthogonal dash lines  88  and  89 . These regions  11 ,  12 , and  13  may be considered to extend through the sheet, so that corresponding regions are registered on both upper and lower sides of piezoresponsive sheet  222 . 
     FIG. 1   g  illustrates in plan view a possible layout of conductive layer  201 / 202  of  FIG. 1   e . In  FIG. 1   e , upper surface  222   us  of piezoresponsive sheet  222  is overlain in region  11  by a patterned conductor layer or film portion  201 , and in regions  12  and  13  by a contiguous patterned conductor  202 . Patterned conductive layer or film portions (sheets)  201  and  202  are not in direct electrical contact with each other. Lower surface  222   ls  of piezoresponsive sheet  222  is “underlain” by conductive layer or film (sheet)  203 . Thus, conductive sheet  203  of  FIG. 1   e  underlies, and is in contact with, the lower surface  222   ls  of piezoresponsive sheet  222  in regions  11  and  12 .  FIG. 1   h  illustrates in plan view one possible layout of conductive sheet  203  of  FIG. 1   e . Electrically conductive sheets  201 ,  202 , and  203  define apertures at locations corresponding to the apertures of piezoresponsive sheet  222 . 
   It will be noted that the presence of printed circuit board  130  of  FIGS. 1   a  and  1   b  clamps a portion of the composite assembly  110  in a region roughly corresponding to regions  11  and  13  of  FIG. 1   k , preventing any bending of the composite sheet in this region. Since the composite sheet cannot bend in this region in response to bending moments attributable to the mass  150 , no piezoresponsive voltages (hereinafter “piezoelectric voltages”) can appear between the top and bottom (upper surface  222   us , lower surface  222   ls ) of piezoelectric sheet  222  of  FIG. 1   e  in regions  11  and  13 . Thus, bending of composite arrangement  110  in use does not produce any voltage on conductive region  201  in region  11  relative to that portion of conductor  202  lying in region  11 . In effect, conductor  201  is a mere conductive pad, available for making contact with a conductor (not illustrated) of the printed circuit board  130   u  of  FIG. 1   b . However, electrical conductors  202  and  203  of  FIG. 1   e  lie on opposite sides of piezoelectric sheet  222  in a region in which bending can occur, and respond electrically. In a piezoresistive material, the resistance will change between those portions of conductive sheets  202  and  203  which overlie/underlie the same portion of the piezoresponsive sheet  222  when the sheet is flexed. In the case of piezoelectric material, an electrical voltage will appear between conductive sheets  202  and  203  in response to flexure. It should be noted that conductive sheet  203  does not extend as far toward remote end  110 R as does sheet  203 , to thereby assure that flexure of the piezoresponsive sheet  110  of  FIGS. 1   a  and  1   b  attributable to anomalies associated with the presence of aperture  110   wa  do not affect the linearity or reproducibility of the sensor. 
   It will be noted that conductive sheet  203  is located within the interior of the structure of piezoresponsive assembly  110 , while sheet  202  lies near the outer portion. In order to provide for convenient electrical connection to inner layer  223  of conductor, a set of registered apertures  201   apl ,  222   apl , and  203   apl are defined through layers  201 ,  222 , and  203 , respectively, and plated through to provide electrical connection between conductive layer  203  and outer layer  201 . As mentioned, conductive layer  201  is not responsive to flexure, so its presence simply provides a convenient connection pad for electrical access to conductor layer  203 . When piezoresponsive assembly  110  is flexed, the electrical response attributable to piezoresponsive sheet  222  is felt “between” (in the electrical sense of the word, rather than in the mechanical or position sense of the word) the accessible portions of conductors  201  and  202 . More particularly, when assembly  110  is piezoelectric and is flexed in a particular direction, which for example may be “down at the remote end,” a voltage is felt which is arbitrarily defined as positive (+) on conductor  201  (and  203 ) and negative (−) on conductor  202 . 
   As illustrated in  FIG. 1   e , lower piezoresponsive sheet  226  of composite sheet  216  defines near-end apertures  226   aa  and  226   ab  and far-end aperture  226   wa , all registered with corresponding apertures of flexible support sheet  210  and with corresponding apertures associated with piezoresponsive sheet  212 , for like purposes. The upper surface  226   us  of piezoresponsive sheet  226  is in contact with a patterned layer or film  205  of electrical conductor, and the lower surface  226   ls  of piezoresponsive sheet  226  is similarly in contact with a patterned layer or film  206 / 207  of conductor.  FIGS. 1   i  and  1   j  represent plan views of a possible layout of the conductor sheets  205  and  206 / 207 . The regions of the upper and lower surfaces of piezoresponsive sheet  226  to which portions of the patterned conductors  205  and  206 / 207  are applied are the same regions  11 ,  12 , and  13  referred to in conjunction with  FIG. 1   k , and discussed in conjunction with conductor regions  201 ,  202 , and  203 . In addition, the regions  11 ,  12 , and  13  associated with conductors  205 ,  206 , and  207  are in registry with the regions  11 ,  12 , and  13  associated with conductors  201 ,  202 , and  203 . 
   In  FIG. 1   e , upper surface  226   us  of piezoresponsive sheet  226  is overlain in regions  11  and  12  by a patterned conductor layer or film portion (sheet)  205 . Lower surface  226   ls  of piezoresponsive sheet  226  is “underlain” by conductive layer or film portions (sheets)  206  and  207 . Patterned conductive layer or film portions (sheets)  206  and  207  are not in direct electrical contact with each other. Thus, conductive sheet  206  underlies, and is in contact with, lower surface  226   ls  of piezoresponsive sheet  226  in region  11 , and conductive sheet  207  of  FIG. 1   e  underlies, and is in contact with, the lower surface  226   ls  of piezoresponsive sheet  226  in regions  12  and  13 . Electrically conductive sheets  205 ,  206 , and  207  define apertures at locations corresponding to the apertures of piezoresponsive sheet  226 . 
   As mentioned, the presence of printed circuit board  130  of  FIGS. 1   a  and  1   b  clamps a portion of the composite assembly  110  in a region roughly corresponding to regions  11  and  13  of  FIG. 1   k , preventing any bending of the composite sheet in this region. Thus, bending of composite arrangement  110  in normal use does not produce any voltage on conductive region  206  in region  11  relative to that portion of conductor  205  lying in region  11 . In effect, conductor  206  is a mere conductive pad, available for making contact with a conductor (not illustrated) of the printed circuit board  130   u  of  FIG. 1   b . However, electrical conductors  205  and  206  of  FIG. 1   e  lie on opposite sides of piezoelectric sheet  226  in a region in which bending can occur, and respond electrically. It should be noted that conductive sheet  205  does not extend as far toward remote end  110 R as does sheet  207 , for the same reasons given above in regard to conductors  202  and  203 . 
   It will be noted that conductive sheet  205  is located within the interior of the structure of piezoresponsive assembly  110 , while sheet  207  lies near the outer portion. In order to provide for convenient electrical connection to inner conductor layer  205 , a set of registered apertures  205   apl ,  226   apl , and  206   apl are defined through layers  205 ,  226 , and  206 , respectively, and plated through to provide electrical connection between conductive layer  205  and outer conductive layer  206 . When piezoresponsive assembly  110  is flexed, the electrical response attributable to piezoresponsive sheet  226  is felt “between” (in the electrical sense of the word) the accessible portions of conductors  206  and  207 . More particularly, when assembly  110  is piezoelectric and is flexed in a particular direction, which for example may be “down at the remote end,” a voltage is felt which, using the same standard applied to sheet  222 , is defined as positive (+) on conductor  205  (and  206 ) and negative (−) on conductor  207 . 
   Piezoresponsive assemblies  212  and  216  of  FIG. 1   e  are bonded by adhesive layers  214  and  217  to upper and lower surfaces  210   us  and  210   ls , respectively, of support sheet  210 . An upper cover or coating illustrated as  220   u  overlies the upper surface of upper conductor sheet  202  at least in region  12 , and a lower cover or coating  220   l  “overlies” the lower surface of lower conductor sheet  207 , at least in region  12 . Regions  11  and  12  may be left uncoated to facilitate electrical connections to the various metal portions, if desired. 
     FIG. 1   f  is a simplified representation of the longitudinal extent of the various layers and sheets of piezoresponsive assembly  110  of  FIGS. 1   a ,  1   b , and  1   e , showing some of the same elements as are shown in  FIG. 1   e  in a quasi-cross-sectional view. 
   Referring once more to  FIGS. 1   a  and  1   b , note that the remote ends  180   ar  and  180   br  of the electrical connection pins extend through apertures  110   aa  and  110   ab  of the piezoresponsive assembly  110 . The flanges  180   af  and  180   bf  make physical and electrical contact with the lower surface of the piezoelectric assembly  110 , and the fasteners (rivets, eyelets or screws)  182   a  and  182   b  make contact with the upper surface. That being so, fastener  182   a  of pin  180   a  of  FIG. 1   c  makes contact with conductor  201  of  FIG. 1   e , and flange  180   af  of pin  180   a  makes contact with conductor  206  of  FIG. 1   e . Similarly, fastener  182   b  of pin  180   b  of  FIG. 1   c  makes contact with conductor  202  of  FIG. 1   e , and flange  180   bf  makes contact with conductor  207  of  FIG. 1   e . Since conductor  201  of  FIG. 1   e  makes electrical contact with conductor  203 , pin  182   a  makes contact with conductor  203  by way of conductor  201 . Since conductor sheet or layer  206  of  FIG. 1   e  makes electrical contact with electrical sheet  205  by way of plated-through aperture  226   apl , pin  180   a  also makes contact with sheet  205 . Thus, pin  180   a  is in electrical contact with lower conductor sheet  203  of piezoresponsive subassembly  212  of  FIG. 1   e  and with upper conductor sheet  205  of piezoresponsive subassembly  216 . Similarly, pin  180   b  is in electrical contact with upper conductor sheet  202  of  FIG. 1   e  of piezoelectric subassembly  212  and with lower conductor sheet  207  of piezoresponsive subassembly  216 . 
   The fastening together of piezoresponsive subassemblies  212  and  216  of  FIG. 1   e  by means of support sheet  210  and adhesive layers  214  and  217  means that the piezoresponsive sheets  222  and  226  undergo stresses of opposite polarity when the tip of the structure  110 R is flexed. For example, when the tip  110 R of piezoresponsive assembly  110  is flexed downward, the piezoresponsive sheet  222  undergoes tensile stress whereas piezoresponsive sheet  226  undergoes compressive stress. In order to provide voltage of the same polarity from piezoelectric sheets  212  and  226  at the pins  180  in response to flexure of the piezoresponsive assembly  110 , the polarities of the piezoelectric sheets  212  and  226  are reversed, by “turning over” or reversing from top to bottom one of the piezoelectric sheets  212 ,  226 . Assuming that the polarization of piezoelectric sheet  222  is positive (+) on its upper surface  222   us  and negative (−) on its lower surface in conventional notation, so that the charge or voltage on upper conductor sheet  202  is + and on lower conductive sheet  203  is −, then piezoelectric sheet  226  is oriented so that its upper surface  226   us  and conductive sheet  205  are negative (−) and the lower surface  226   ls  and conductive sheet  207  are positive (+). With this polarity adjustment, pin  180   a  is connected to both the negative conductors  203  and  205 , and pin  180   b  is connected to both positive conductors  202  and  207 . The charge available from this arrangement is twice that available from a single layer of piezoelectric material. 
     FIG. 4  illustrates an embodiment similar to that described in  FIG. 1E , but wherein two piezoelectric layers are electrically connected in series with piezoelectric polarities arranged such that a deflection of the free end of the substrate causes addition of the electrical output from the two piezoelectric layers in a manner that enables an electric potential Vcc to be produced between the outermost electrode of each piezoelectric layer. As illustrated in exploded view in  FIG. 4 , the assembly  400  comprises an upper composite layer comprising a piezoresponsive layer  422  having an upper surface  422   u  on which is disposed a patterned electrode layer  402 , and lower surface  422   l  on which is disposed patterned electrode layer  403 . Piezoresponsive layer  422  includes apertures  422   aa ,  422   ab , and  422   ac  disposed at a near end and aperture  422   wa  at a far end. In like fashion, a lower composite layer comprises a second piezoelectric layer  426  sandwiched between patterned electrode layers  205  and  207 , with apertures  426   a ,  426   b ,  426   c  and  426   wa , respectively registered with layer  422  apertures  422   aa ,  422   ab ,  422   ac  and  422   wa . Support sheet  410  is disposed between the upper and lower composite layers. Support sheet  410  has an upper surface  410   u  on which is disposed a z-axis electrically conductive adhesive layer  409 , and lower surface  410   l  on which is disposed z-axis conductive adhesive layer  408 . Sheet  410 , along with conductive adhesive layers  408  and  409  each have corresponding apertures registered with apertures  422   aa ,  422   ab ,  422   ac  and  422   wa  of layer  422  (and thus with layer  426 ). Sheet  410  further includes electrically conductive pad  412  disposed on the upper and lower surfaces of sheet  410  about aperture  410   ac  and electrically connected through aperture  410   ac . The adhesive layers thus affix the upper and lower composite layers to one another via the support sheet  410 , thereby providing a single composite structure. 
   As illustrated in  FIG. 4 , the assembly is partitioned into four nonoverlapping regions  11 ,  12 ,  13  and  14 . The patterned electrode layers  402  and  403  define overlapping portion  12  and non-overlapping portions  11  and  14  for piezoresponsive layer  422 . Electrode layer  402  includes aperture  402   aa  registered with piezoresponsive layer aperture  422   aa , while electrode layer  403  includes aperture  403   ac  registered with piezoresponsive layer aperture  422   ac . Patterned electrode layers  405  and  407  define overlapping portion  12  and non-overlapping portions  13  and  14  for piezoresponsive layer  426 . Electrode layer  405  includes aperture  405   ac  registered with piezoresponsive layer aperture  426   ac , while electrode layer  407  includes aperture  407   ab  registered with piezoresponsive layer aperture  426   ab . Conductive pad  412  formed in region  14  is thus in electrical communication with electrodes  403  and  405 . The clamping member (not shown) is coupled to the near end of the assembly in a manner analogous to that previously described. 
     FIG. 2  is a simplified cross-sectional representation, corresponding in general to  FIG. 1   c , of an embodiment of the invention in which the piezoresponsive assembly is oriented orthogonal to the support pins, or in other words in parallel with the broad surface of the underlying printed-circuit board (not illustrated). In  FIG. 2 , elements corresponding to those of  FIG. 1   c  are designated by like reference numerals, and are not further discussed. Instead of the bent pin  180   b  and flange  180   bf  of  FIG. 1   c , the arrangement of  FIG. 2  has a straight pin  280   b  projecting from a support  280   bs . The upper end of support  280   bs  of  FIG. 2  presents about the same diameter and configuration to the printed-circuit boards  130  as does the flange portion  180   bf  of pin  180   b . Consequently, all the same advantages accrue as are discussed in relation to the sensor  100 , with the sole difference being that the orientation of the plane of the piezoresponsive assembly  110  is parallel with the plane of the underlying printed-circuit board rather than vertical. 
   It will be appreciated that sensors according to the various aspects of the invention may be suitable for use in measurement of displacement of the weighted, distal, or tip end relative to the base or support end in a direction normal or orthogonal to the major surface of the piezoresponsive assembly, and can therefore respond to acceleration or to displacement of the base relative to the distal end or to displacement of the distal end relative to the base. 
   It will also be appreciated that the configuration of the conductive layers  202  and  207  is such that the conductors tend to enclose the remainder of the piezoresponsive assembly  110 , and provide a measure of electrostatic shielding thereto. 
   Other embodiments of the invention will be apparent to those skilled in the art. For example, as shown in  FIG. 3A , a conductive electrode layer on one or more sides of the piezoelectric layers may be applied only in a specific region of the piezoelectrically active surface of the piezoelectric layer in order to increase sensitivity of the output signal. That is, at least one of the electrode layers is applied only in a region of the piezoelectrically active surface that is substantially less than the total active surface, such that the overlapping portions of the two electrode layers is substantially small compared to the overall surface of the piezoelectric layer. For example, applying conductive electrode layer  202  only to a specific, narrow region AA of piezoelectric layer  222  near the cantilever boundary condition of the support structure (and applying corresponding conductive electrode layer  203  to region AAL of the lower surface of piezoelectric layer  222  overlapping region AA operates to substantially increase the output of the active region. Note that, as shown in  FIGS. 3A and 3B , the active electrode region is the area defined by the overlap of electrode layers on both the top and bottom surfaces of the piezoelectric layer. Thus, the active electrode area is the same for  FIGS. 3A and 3B . 
     FIG. 3C  illustrates a side view of the cantilever beam sensor structure having a force F applied to the tip of the beam.  FIG. 3D  is a graphical illustration of the relevant stress on the beam, with the stress level decreasing linearly with beam length based on tip force.  FIG. 3E  is a graphical illustration of the output of the piezoresponsive material and shows the output varying linearly with stress on the beam.  FIG. 3F  provides a graphical illustration of the total output signal S as the average output over the active electrode region covered for the case illustrated in  FIGS. 3A and 3B . As shown, the electrodes cover only a small portion of the active piezoresponsive region. In contrast,  FIG. 3G  provides a graphical illustration of the total output signal S′ as the average output over the active electrode region covered for the case illustrated in  FIG. 3H , wherein the upper and lower electrode layers define an active electrode region that covers substantially the entire area of the piezoelectric layer. 
   Furthermore, while there has been shown a single mass positioned at the end of the beam structure, it is also contemplated to add one or more additional masses to increase sensor output. It is further contemplated that the overall device will function simply as the result of the “self loading” of the mass of the piezoresponsive material and the support beams without the need for any additional mass. All such variations and modifications are intended to be within the scope of the appended claims.