A PZT Based Material for Bimorph Type Transducers and a New Optical Method to Evaluate the Bimorph Performance

The displacement devices using piezoceramic sensors play an important role in many fields. Soft type piezoelectric materials used for such sensors are more appealing because of their lower coercive field, relatively low modulus of elasticity, high electromechanical coupling factors and piezoelectric strain coefficients. We designed a PZT type material doped with niobium and nickel to increase the strain coefficient and still retaining a high coupling coefficient. The chemical formula was Pb0.97Ba0.08Nb0.03Ni0.06Zr0.46Ti0.40O3. The main piezoelectric parameters were: d33=680 pm/V, d31=-235 pm/V, kp=0.64 and k31=0.42. A unimorph transducer was made from a thin sheet of such a piezoceramic material, tightly bonded on a thin optically polished glass plate and mounted as a cantilever. The performance of this transducer was evaluated by means of a new optical method which makes use of the Moiré deflectometry and provides high precision. The method is rather simply and consists mainly in the following: the Moiré fringes rotate when the bimorph bends under the influence of the electric field and by measuring the rotating angle of the fringes one can easily determine the bimorph curvature and the free end displacement.