A piezoelectric beam actuator with a pure twisting response

We present for the first time ever, a piezoelectric beam actuator that can be directly driven in pure torsion. The beam actuator is designed with interdigitated electrodes (IDEs), on both its top and bottom surfaces. The IDEs are used for both poling and driving. When the IDEs are driven by a voltage with the same polarity as used for poling, they induce a combination of shear and expansion strains, close to the top and bottom surfaces. The expansion strains at the top and bottom surfaces are similar, and hence they produce no net bending. However, the shear strains at the top and bottom surfaces are in opposite directions, and they produce a pure twist. If the IDEs on the top and bottom surfaces are driven by the same voltage but in opposite polarity, then a pure bending response is produced. We experimentally demonstrate that the actuator can be driven in either pure torsion or in pure bending, with negligible cross-coupling.