Experimental investigation of electrostrictive polarization biased direct apparent piezoelectric properties in polyurethane elastomer under quasistatic conditions

Polyurethane elastomer was recently discovered to demonstrate a very high f ield induced electrostrictive response. In this work an experimental setup, consisting of an electric circuit and a mechanical system, was designed an d constructed for the measurement of the electrostrictive polarization bias ed apparent piezoelectric response of polyurethane elastomers in a direct p iezoelectric effect under quasistatic conditions. The electric circuit desi gn allows the application of a direct current (dc) bias electric field to t he sample and the possibility of picking up the generated quasistatic elect rical signal separately. The mechanical system provides the function of a v ibration source from which the stress and strain of the sample can be measu red. Therefore, such effective piezoelectric properties as d(31) and k(31) can be measured. The electromechanical coupling coefficient was derived by two different methods. One was from the deduction based on the piezoelectri c equations. The other was from the calculation based on the basic definiti on of the electromechanical coupling coefficient (i.e., through the exact m easurement of input mechanical energy and output electric energy). In the l atter case, the internal resistance of the sample and the de bias blocking capacitor were found to be the critical factors for precision determination of the total electrical energy output. The different approaches led to clo se agreement. The effective d(31) can be 184 pC/N under a 25 MV/m bias elec tric field in a 30-mu m thick sample, which is much higher than that of typ ical piezoelectric polymers. (C) 1999 John Wiley & Sons, Inc.