Abstract:
A mechanical property testing device and method for reliably measuring strain and fatigue characteristics of material specimens is described. An input electrical signal is applied to create an electric field around a first piezoelectric member. The resultant deformation of the first piezoelectric member transfers a force to the specimen being tested which transfers a force to a second piezoelectric member causing deformation. The deformation of the second piezoelectric member generates an output electrical field which is measured. The stress state of the specimen is calculated from fundamental material constants and the measured output electrical field.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of pending U.S. Provisional Patent Application Ser. No. 61/073,080 filed on Jun. 17, 2008. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a device and method for testing materials, and more particularly, to a piezoelectric device for measuring the mechanical properties of materials. 
       BACKGROUND OF THE INVENTION 
       [0003]    Measurement of mechanical properties of microscale samples of material, such as thin films, is very difficult due to the small size of the material. The material properties of small structures and thin films cannot be easily related to the properties of bulk samples because of several reasons. Samples used for bulk mechanical testing generally have dimensions significantly greater than microstructural features, whereas in thin films, the geometrical and microstructural dimensions are on the same order of magnitude. Therefore, assumption of homogeneity and isotropy is not valid when obtaining the mechanical properties. Furthermore, different manufacturing techniques are used in fabricating small specimens and thin films resulting in different microstructure than bulk materials. In addition, because of comparable size of the structural dimensions and microstructural and defect dimensions, inelastic deformation mechanisms are far different from bulk specimens. 
         [0004]    Testing materials at scales smaller than a millimeter is a challenge due to limiting factors such as specimen gripping techniques, the application of small forces, and the ability to measure small strain values. Therefore, conventional instruments cannot be used to test these properties. A challenge for creating new microscale testing systems is the design of reliable loading and data capture methods. Regular strain gages are not applicable due to their large size, and strain measurement techniques such as capacitive gages and digital image correlation are either expensive, hard to use, or not accurate enough. In addition, digital imaging correlation is a slow and labor intensive process that is not practical for long term fatigue tests. 
         [0005]    The Measurement of mechanical properties of micro-scale samples is particularly challenging in fatigue testing of materials since load and displacement are both needed to be monitored for many cycles. The present invention is a device and method that addresses the need for applying load and measuring deformation at small scale as well as long term fatigue testing and reliable strain measurements on micro-scale samples. 
       SUMMARY OF THE INVENTION 
       [0006]    The disclosed device is designed to perform tension, or compression, or tension-compression cyclic testing of micro-scale specimens and thin stand alone films of materials. The objective is to facilitate measuring both strain and stress in the materials only by monitoring input and output electrical signals. The device consists of two piezoelectric members that are fabricated on both sides of the specimen in a frame. The input electrical signal induces some amount of deformation in the first piezoelectric material resulting in a force that is transferred to the material being tested. The test material deforms and at the same time transfers a force to the second piezoelectric member causing some amount of deformation in the second piezoelectric member which subsequently induces output signals that are measured. Knowing the fundamental material constants of the piezoelectric material, stresses and strains are calculated from the input and output electrical signals. 
         [0007]    Although the device and method were developed for micro-scale size specimens, it is clear to those skilled in the art that the device and method can be used to measure the material properties in macro-scale specimens. The principle is valid for any scale. In addition, this apparatus can be used to monitor the change in mechanical properties of many types of materials. The change in properties could be a secondary effect of a primary substance or process. For example, certain polymers change their stiffness when exposed to water or certain chemicals. This stiffness change can be measured and monitored using the disclosed apparatus and method. Therefore, chemical and biological sensors may be built based on the same principle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Understanding that drawings depict only certain preferred embodiments of the invention and are therefore not to be considered limiting of its scope, the preferred embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings. 
           [0009]      FIG. 1  is a drawing of the mechanical properties testing device. 
           [0010]      FIG. 2  is a diagram showing the crystallographic orientation of the piezoelectric membranes in one embodiment. 
           [0011]      FIGS. 3  is a diagram of one embodiment of the mechanical properties testing device for micro specimens. 
           [0012]      FIGS. 4   a - h  show the steps for preparing the mechanical properties testing device using MEMS processing technology. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0013]    In the following description, numerous specific details are provided for a thorough understanding of specific preferred embodiments. However, those skilled in the art will recognize that embodiments can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In some cases, well-known structures, materials, or operations are not shown or described in detail in order to avoid obscuring aspects of the preferred embodiments. Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in a variety of alternative embodiments. Thus, the following more detailed description of the embodiments of the present invention, as represented in the drawings, is not intended to limit the scope of the invention, but is merely representative of the various embodiments of the invention. 
         [0014]    One embodiment of the mechanical property testing device is shown in  FIG. 1 . A frame  11  provides a rigid structure that does not deform under the applied testing loads. The first piezoelectric member  12 , with a layer of nonconductive material  14  on each end, is positioned against one side of the frame  11 . The second piezoelectric member  13 , with a layer of nonconductive material  14  on each end, is positioned against the opposite side of the frame  11  such that the axis of the first piezoelectric member  12  and the second piezoelectric member  13  are colinear. The test specimen  15  is located between the first piezoelectric member  12  and the second piezoelectric member  13  such that the test specimen  15  is in contact with a layer of nonconductive material  14  on each end of both the first piezoelectric member  12  and the second piezoelectric member  13 . The layers of nonconductive material  14  confine the electric fields and currents to the piezoelectric material. The nonconductive material  14  is optional if the first piezoelectric member  12  and the second piezoelectric member  13  are in contact with nonconductive materials or are nonconductive themselves. 
         [0015]    The geometry of the first piezoelectric member  12  and the second piezoelectric member  13  can be circular rods, square rods, rectangular rods, or any other appropriate geometry. The first piezoelectric member  12  and the second piezoelectric member  13  can be selected from a variety of ceramic materials, polymers, manmade crystals, natural crystals, and other natural materials. The first piezoelectric member  12  and the second piezoelectric member  13  can be the same chemical composition but they do not necessarily have to be. A partial list of piezoelectric materials is presented in Table 1. Those skilled in the art will recognize other piezoelectric materials that can be used in the disclosed invention. 
         [0000]    
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Piezoelectric Materials 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 barium titanate 
                 lead titanate 
                 Lead zirconate titanate 
               
               
                   
                 potassium niobate 
                 lithium niobate 
                 lithium tantalite 
               
               
                   
                 sodium tungstate 
                 quartz 
                 polyvinylidene fluoride 
               
               
                   
                   
               
             
          
         
       
     
         [0016]    With continuing reference to  FIG. 1 , input conducting layers or plates  16  are located adjacent to the first piezoelectric member  12  such that when an input electrical signal is generated an electrical field is created between the input conducting plates  16 . These input conducting plates  16  can be in contact with the first piezoelectric member  12  or sufficiently close to generate an electric field around the first piezoelectric member  12 . The lengths of the input conducting plates  16  are slightly less than the length of the first piezoelectric member  12  such that they do not come in contact with the frame  11  or the test specimen  15 . 
         [0017]    Also shown in  FIG. 1  are the output conducting layers or plates  17  which are located alongside the second piezoelectric member  13 . The lengths of the output conducting plates  17  are slightly less than the lengths of the second piezoelectric member  13  such that they do not come in contact with the frame  11  or the test specimen  15 . The output electrical signal detected by the output conducting plates  17  are measured by standard techniques known to those skilled in the art. 
         [0018]    A standard test procedure begins with mounting the specimen between the first and second piezoelectric member. If the specimen is conductive, layers of non-conductive material are placed between the specimen and piezoelectric members. The specimen, piezoelectric members, and nonconductive layers are secured together by epoxy, or bonding or other known means to attach the materials together and create a co-linear structure which is secured within the frame. The input conducting plates are used to generate an electric field around the first piezoelectric member which induces a shape change in the first piezoelectric member. This shape change exerts a force on the specimen. Since the specimen is constrained against the second piezoelectric member, the applied force will cause the specimen to deform and induce a force on the second piezoelectric member. This force will be translated to deformation in the second piezoelectric member, thus producing an output electric signal that is picked up by the output conducting plates. Knowing the fundamental material constants of the piezoelectric material, stresses and strains are calculated from the input and output electrical signals. The magnitude of the applied electric field determines the applied load, or force exerted on the specimen. The electric field can be applied such that the specimen is in tension or compression or it can be cycled from one to the other, thus tension, or compression, or tension-compression cyclic testing can be performed. 
         [0019]    Both the first piezoelectric member and the second piezoelectric member are governed by the following equation, 
         [0000]    
       
      
       S=d,E+s 
       E 
       T  
      
     
         [0020]    where S is the strain of the material, E is the electric field applied, T is the stress in the material. The meaning of each material constant is given in the table below. 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 Symbol 
                 Description 
                 Unit 
               
               
                   
               
             
             
               
                 T 
                 Stress 
                 Pa 
               
               
                 S 
                 Strain 
                 m/m 
               
               
                 E 
                 Electric field 
                 V/m 
               
               
                 d 
                 Piezoelectric strain 
                 C/N 
               
               
                   
                 constant 
               
               
                 s 
                 Elastic compliance 
                 m 2 /N 
               
               
                   
               
             
          
         
       
     
         [0021]    The equations are expanded for one example material for clarity. LiNbO 3  properties are given blow: 
         [0000]    
       
         
           
             
               
                 
                   
                       
                   
                    
                   
                     d 
                     = 
                     
                       
                         [ 
                         
                           
                             
                               0 
                             
                             
                               0 
                             
                             
                               0 
                             
                             
                               0 
                             
                             
                               69.2 
                             
                             
                               
                                 - 
                                 20.8 
                               
                             
                           
                           
                             
                               
                                 - 
                                 20.8 
                               
                             
                             
                               20.8 
                             
                             
                               0 
                             
                             
                               69.2 
                             
                             
                               0 
                             
                             
                               0 
                             
                           
                           
                             
                               
                                 - 
                                 0.85 
                               
                             
                             
                               0 
                             
                             
                               6 
                             
                             
                               0 
                             
                             
                               0 
                             
                             
                               0 
                             
                           
                         
                         ] 
                       
                       × 
                       
                         10 
                         
                           - 
                           12 
                         
                       
                        
                       
                         C 
                         N 
                       
                     
                   
                 
               
               
                 2 
               
             
             
               
                 
                   
                     s 
                     E 
                   
                   = 
                   
                     
                       [ 
                       
                         
                           
                             5.831 
                           
                           
                             
                               - 
                               1.150 
                             
                           
                           
                             
                               - 
                               1.452 
                             
                           
                           
                             
                               - 
                               1.000 
                             
                           
                           
                             0 
                           
                           
                             0 
                           
                         
                         
                           
                             
                               - 
                               1.150 
                             
                           
                           
                             5.831 
                           
                           
                             1.452 
                           
                           
                             1.000 
                           
                           
                             0 
                           
                           
                             0 
                           
                         
                         
                           
                             
                               - 
                               1.452 
                             
                           
                           
                             1.452 
                           
                           
                             5.026 
                           
                           
                             0 
                           
                           
                             0 
                           
                           
                             0 
                           
                         
                         
                           
                             
                               - 
                               1.000 
                             
                           
                           
                             1.000 
                           
                           
                             0 
                           
                           
                             17.10 
                           
                           
                             0 
                           
                           
                             0 
                           
                         
                         
                           
                             0 
                           
                           
                             0 
                           
                           
                             0 
                           
                           
                             0 
                           
                           
                             17.10 
                           
                           
                             
                               - 
                               1.000 
                             
                           
                         
                         
                           
                             0 
                           
                           
                             0 
                           
                           
                             0 
                           
                           
                             0 
                           
                           
                             
                               - 
                               1.00 
                             
                           
                           
                             13.96 
                           
                         
                       
                       ] 
                     
                     × 
                     
                       10 
                       
                         - 
                         12 
                       
                     
                      
                     
                       
                         m 
                         2 
                       
                       N 
                     
                   
                 
               
               
                 3 
               
             
           
         
       
     
         [0022]    For the example shown in  FIG. 2 , where the first piezoelectric member  22  is oriented in the (001) crystal orientation (z) and the second piezoelectric member  23  is oriented in the (100) crystal orientation (x), and the electric field is applied in the z direction, the equations for the first piezoelectric member are: 
         [0000]    
       
         
           
             
               
                 
                   S 
                   = 
                   
                     
                       
                         [ 
                         
                           
                             
                               0 
                             
                             
                               
                                 - 
                                 20.8 
                               
                             
                             
                               
                                 - 
                                 0.85 
                               
                             
                           
                           
                             
                               0 
                             
                             
                               20.8 
                             
                             
                               0 
                             
                           
                           
                             
                               0 
                             
                             
                               0 
                             
                             
                               6 
                             
                           
                           
                             
                               0 
                             
                             
                               69.2 
                             
                             
                               0 
                             
                           
                           
                             
                               69.2 
                             
                             
                               0 
                             
                             
                               0 
                             
                           
                           
                             
                               
                                 - 
                                 20.8 
                               
                             
                             
                               0 
                             
                             
                               0 
                             
                           
                         
                         ] 
                       
                       [ 
                       
                           
                       
                        
                       
                         
                           
                             0 
                           
                         
                         
                           
                             0 
                           
                         
                         
                           
                             
                               E 
                               3 
                             
                           
                         
                       
                       ] 
                     
                     + 
                     
                         
                       
                         
                           [ 
                           
                               
                           
                            
                           
                             
                               
                                 5.831 
                               
                               
                                 
                                   - 
                                   1.150 
                                 
                               
                               
                                 
                                   - 
                                   1.452 
                                 
                               
                               
                                 
                                   - 
                                   1.000 
                                 
                               
                               
                                 0 
                               
                               
                                 0 
                               
                             
                             
                               
                                 
                                   - 
                                   1.150 
                                 
                               
                               
                                 5.831 
                               
                               
                                 1.452 
                               
                               
                                 1.000 
                               
                               
                                 0 
                               
                               
                                 0 
                               
                             
                             
                               
                                 
                                   - 
                                   1.452 
                                 
                               
                               
                                 1.452 
                               
                               
                                 5.026 
                               
                               
                                 0 
                               
                               
                                 0 
                               
                               
                                 0 
                               
                             
                             
                               
                                 
                                   - 
                                   1.000 
                                 
                               
                               
                                 1.000 
                               
                               
                                 0 
                               
                               
                                 17.10 
                               
                               
                                 0 
                               
                               
                                 0 
                               
                             
                             
                               
                                 0 
                               
                               
                                 0 
                               
                               
                                 0 
                               
                               
                                 0 
                               
                               
                                 17.10 
                               
                               
                                 
                                   - 
                                   1.000 
                                 
                               
                             
                             
                               
                                 0 
                               
                               
                                 0 
                               
                               
                                 0 
                               
                               
                                 0 
                               
                               
                                 
                                   - 
                                   1.00 
                                 
                               
                               
                                 13.96 
                               
                             
                           
                           ] 
                         
                          
                         
                           [ 
                           
                             
                               
                                 0 
                               
                             
                             
                               
                                 0 
                               
                             
                             
                               
                                 
                                   T 
                                   3 
                                 
                               
                             
                             
                               
                                 0 
                               
                             
                             
                               
                                 0 
                               
                             
                             
                               
                                 0 
                               
                             
                           
                           ] 
                         
                       
                     
                   
                 
               
               
                 4 
               
             
           
         
       
     
         [0023]    where E, T and S are in V/m, Pa, and μm/m respectively. 
         [0000]    
       
         
           
             
               
                 
                   S 
                   = 
                   
                     
                       [ 
                       
                         
                           
                             
                               
                                 - 
                                 0.85 
                               
                                
                               
                                 E 
                                 3 
                               
                             
                           
                         
                         
                           
                             0 
                           
                         
                         
                           
                             
                               6 
                                
                               
                                 E 
                                 3 
                               
                             
                           
                         
                         
                           
                             0 
                           
                         
                         
                           
                             0 
                           
                         
                         
                           
                             0 
                           
                         
                       
                       ] 
                     
                     + 
                     
                       [ 
                       
                         
                           
                             
                               
                                 - 
                                 1.452 
                               
                                
                               
                                 T 
                                 3 
                               
                             
                           
                         
                         
                           
                             
                               1.452 
                                
                               
                                 T 
                                 3 
                               
                             
                           
                         
                         
                           
                             
                               5.026 
                                
                               
                                 T 
                                 3 
                               
                             
                           
                         
                         
                           
                             0 
                           
                         
                         
                           
                             0 
                           
                         
                         
                           
                             0 
                           
                         
                       
                       ] 
                     
                   
                 
               
               
                 5 
               
             
           
         
       
     
         [0024]    In this equation E 3  is the input signal and is known. The equations for the second piezoelectric member then can be written as: 
         [0000]    
       
         
           
             
               
                 
                   S 
                   = 
                   
                     
                       
                         [ 
                         
                           
                             
                               0 
                             
                             
                               
                                 - 
                                 20.8 
                               
                             
                             
                               
                                 - 
                                 0.85 
                               
                             
                           
                           
                             
                               0 
                             
                             
                               20.8 
                             
                             
                               0 
                             
                           
                           
                             
                               0 
                             
                             
                               0 
                             
                             
                               6 
                             
                           
                           
                             
                               0 
                             
                             
                               69.2 
                             
                             
                               0 
                             
                           
                           
                             
                               69.2 
                             
                             
                               0 
                             
                             
                               0 
                             
                           
                           
                             
                               
                                 - 
                                 20.8 
                               
                             
                             
                               0 
                             
                             
                               0 
                             
                           
                         
                         ] 
                       
                       [ 
                       
                           
                       
                        
                       
                         
                           
                             
                               E 
                               1 
                             
                           
                         
                         
                           
                             
                               E 
                               2 
                             
                           
                         
                         
                           
                             
                               E 
                               3 
                             
                           
                         
                       
                       ] 
                     
                     + 
                     
                         
                       
                           
                       
                        
                       
                         
                           [ 
                           
                             
                               
                                 5.831 
                               
                               
                                 
                                   - 
                                   1.150 
                                 
                               
                               
                                 
                                   - 
                                   1.452 
                                 
                               
                               
                                 
                                   - 
                                   1.000 
                                 
                               
                               
                                 0 
                               
                               
                                 0 
                               
                             
                             
                               
                                 
                                   - 
                                   1.150 
                                 
                               
                               
                                 5.831 
                               
                               
                                 1.452 
                               
                               
                                 1.000 
                               
                               
                                 0 
                               
                               
                                 0 
                               
                             
                             
                               
                                 
                                   - 
                                   1.452 
                                 
                               
                               
                                 1.452 
                               
                               
                                 5.026 
                               
                               
                                 0 
                               
                               
                                 0 
                               
                               
                                 0 
                               
                             
                             
                               
                                 
                                   - 
                                   1.000 
                                 
                               
                               
                                 1.000 
                               
                               
                                 0 
                               
                               
                                 17.10 
                               
                               
                                 0 
                               
                               
                                 0 
                               
                             
                             
                               
                                 0 
                               
                               
                                 0 
                               
                               
                                 0 
                               
                               
                                 0 
                               
                               
                                 17.10 
                               
                               
                                 
                                   - 
                                   1.000 
                                 
                               
                             
                             
                               
                                 0 
                               
                               
                                 0 
                               
                               
                                 0 
                               
                               
                                 0 
                               
                               
                                 
                                   - 
                                   1.00 
                                 
                               
                               
                                 13.96 
                               
                             
                           
                           ] 
                         
                          
                         
                           [ 
                           
                             
                               
                                 
                                   T 
                                   1 
                                 
                               
                             
                             
                               
                                 0 
                               
                             
                             
                               
                                 0 
                               
                             
                             
                               
                                 0 
                               
                             
                             
                               
                                 0 
                               
                             
                             
                               
                                 0 
                               
                             
                           
                           ] 
                         
                       
                     
                   
                 
               
               
                 6 
               
             
           
         
       
     
         [0025]    In the second piezoelectric member there is only traction in the x direction. Simplifying these equations results in following equation: 
         [0000]    
       
         
           
             
               
                 
                   S 
                   = 
                   
                     [ 
                     
                       
                         
                           
                             
                               
                                 - 
                                 20.8 
                               
                                
                               
                                 E 
                                 2 
                               
                             
                             - 
                             
                               0.85 
                                
                               
                                 E 
                                 3 
                               
                             
                             + 
                             
                               5.831 
                                
                               
                                 T 
                                 1 
                               
                             
                           
                         
                       
                       
                         
                           
                             
                               20.8 
                                
                               
                                 E 
                                 2 
                               
                             
                             - 
                             
                               1.150 
                                
                               
                                 T 
                                 1 
                               
                             
                           
                         
                       
                       
                         
                           
                             
                               6 
                                
                               
                                 E 
                                 3 
                               
                             
                             - 
                             
                               1.452 
                                
                               
                                 T 
                                 1 
                               
                             
                           
                         
                       
                       
                         
                           
                             
                               69.2 
                                
                               
                                 E 
                                 2 
                               
                             
                             - 
                             
                               T 
                               1 
                             
                           
                         
                       
                       
                         
                           
                             69.2 
                              
                             
                               E 
                               1 
                             
                           
                         
                       
                       
                         
                           
                             
                               - 
                               20.8 
                             
                              
                             
                               E 
                               1 
                             
                           
                         
                       
                     
                     ] 
                   
                 
               
               
                 7 
               
             
           
         
       
     
         [0026]    If the characteristics of the second piezoelectric member are known, then by knowing the output signals, E 3 , the traction and strains can be calculated from equation 7. By knowing the traction which is the same and opposite direction of the traction in the first piezoelectric member, then the strain in the first piezoelectric member is known and therefore, the strain in the specimen can be calculated by deducting the strain in these two pieces. 
         [0027]    In another embodiment, the mechanical properties device is constructed for use in the measurement of mechanical properties of micro-size specimens as shown in  FIG. 3 . This micro machine facilitates measuring both strain and stress in the materials only by monitoring the input and output electrical signals. The machine consists of a first piezoelectric member  32  and a second piezoelectric member  33  fabricated on both sides of the specimen  35  and constrained in a frame  31 . In this embodiment, the specimen  35  is a conductive metallic material and therefore, layers of nonconductive material  34  are fabricated on both ends of the first piezoelectric member  32  and both ends of the second piezoelectric member  33 . These layers of nonconductive material  34  prevent the input electrical signal from disturbing the output electrical signal. The layers of non-conductive material  34  are rigid so that their deformation is negligible. These can be materials such as glass, quartz, alumina, or other appropriate materials. The layers of nonconductive material  34  may not be required if the piezoelectric members are made from nonconductive materials or if the specimen is nonconductive. Another configuration to reduce interactions between the input and output electric fields is to use piezoelectric materials with different chemical compositions for the first and second piezoelectric members or to change the crystal orientation of the two piezoelectric members with respect to each other. An input electrical signal is applied to the input conducting plates  36  adjacent to the first piezoelectric member  32 . This induces some deformation in the first piezoelectric member  32  which exerts a force on the specimen  35 . Since the specimen  35  is constrained on both sides, the specimen  35  is deformed and induces a force on the second piezoelectric member  33 . This force causes the second piezoelectric member  33  to deform and thus produce an output electrical signal which is detected by the output conducting plates  37 . Knowing the fundamental material constants of the piezoelectric materials, stresses and strains are calculated from the input and output electrical signals. 
         [0028]    One method for preparing the specimen and test device for micro scale applications involves jointly fabricating the specimen and test device together. This is done in a clean room using micro fabrication methods. The steps for micro fabricating the specimen and test device specimen are shown in  FIG. 4   a - h . In the first step,  FIG. 4   a , a frame  31  is created by etching a cavity in silicon or any other appropriate type of substrate using a micro-fabrication technique such as photolithography, or micro-machining, or other appropriate technique.  FIG. 4   b  shows the next step in which the specimen  35  (material to be tested) is deposited inside the frame  31 . The deposition can be done using different techniques such as stencil printing, CVD or PVD, sputtering, or other appropriate technique. The type of deposition depends on the material type and the feasibility and ease of fabrication technique. A photolithography and etching process then follows to remove four strips  38  of material as shown in  FIG. 4   c . These four strips  38  go completely through the thickness of the material to be tested  35 . The ends of these four strips  38  do not go completely to the frame  31 . Referring to  FIG. 4   d , the four strips  38  are then filled with copper or any electrical conductive material to form the input conducting plates  36  and output conducting plates  37  by a deposition technique such as stencil printing, CVD or PVD, sputtering or other appropriate technique. The type of deposition depends on the material type and the feasibility and ease of fabrication technique. The input conducting plates  36  do not necessarily need to be the same material as the output conducting plates  37 . The conducting plates can be positioned differently so the input electrical signal can be applied to induce deformation in different piezoelectric crystal orientations.  FIG. 4   e  shows the next step in which two cavities  39  are formed by removing the material between the input conducting plates  36  and removing the material between the output conducting plates  37  by etching or other appropriate method to form. This material is removed all the way to the frame  31 . Piezoelectric material is deposited in these cavities, as shown in  FIG. 4   f , by standard micro fabrication methods to form the first piezoelectric member  32  and the second piezoelectric member  33 . The material removal or etched from the previous step is such that in the region where the piezoelectric material is in contact with the frame, the piezoelectric material is chamfered. This allows the piezoelectric members to deform freely without constraints. The first piezoelectric member  32  does not necessarily need to be the same chemical composition as the second piezoelectric member  33 . The next step, shown in  FIG. 4   g , is the removal of the material between the conducting plates  36  and  37  and the frame  31  by standard micro fabrication methods. The specimen  35  remains as a thin film sandwiched between the first piezoelectric member  32  and the second piezoelectric member  33 .  FIG. 4   h  shows the final steps of securing an electrical connection  46  from the input electrical source to the input conducting plates  36  and an electrical connection  47  from the output conducting plates  37 . The back of the frame is etched to create a free standing beam, constrained by a frame  31 , with the specimen  35  sandwiched between the first piezoelectric member  32  and the second piezoelectric member  33 . 
         [0029]    It will be obvious to those having skill in the art that many modifications may be made to the details of the above described embodiments without departing from the underlying principles of the invention. For example, a micro scale fabrication method can involve securing the specimen between the piezoelectric members using epoxy, or other means of attachment, and then fabricating the frame and conducting plates. Other materials that change dimensions as a result of another type of applied field, such as magneto restrictive materials that change dimensions in the presence of magnetic fields, can be used in the disclosed invention.