SAW transduction in electrostrictive substrates

Using electrostrictive materials for surface acoustic wave (SAW) device substrates allows for electronic control of the frequency response of the device. Centrosymmetric materials will not be piezoelectric, but by applying a static DC biasing electric field, a peizoelectric response can be induced in the substrate. If this bias field is spatially varying, then the induced piezoelectric response will also be spatially varying. In fact, since the piezoelectric response is controlled by the DC biasing electric field, changing the bias distribution will change the response of the filter. This allows for a real-time electronically programmable SAW device. The constitutive relations for pure electrostrictive materials are manipulated to show this induced piezoelectric response under an applied electric bias field. Normal mode theory is used to obtain the response of SAW devices in which a spatially varying piezoelectric response is established. The result is similar to that for standard piezoelectric theory except that the pertinent variable now becomes the spatially varying piezoelectric response. Experimental results for several spatially varying piezoelectric patterns are presented.