Disc piezoelectric ceramic transformers

In this contribution, we present our study on the discshaped and homogeneously poled piezoelectric ceramics transformers working in various planar-extensional vibration modes. Transformers are designed with electrodes divided into wedge, axisymmetrical ring-dot, moonie, Smile or Jin-Jiang segments. Electrodes are designed on one side of the transformer; opposite side is fully electroded. A set of transformers with different electrode pattern has been prepared from hard PZT ceramics (type APC841, diameter 20mm, thickness 0.8mm). Transformation ratio, efficiency, input and output impedance were measured for low-power signal. Transformer efficiency and transformation ratio were measured as a function of frequency and impedance load in the secondary circuit. Parameters were further measured for the fundamental and second resonance. Optimum impedance for the maximum efficiency has been found. Maximum efficiency and no-load transformation ratio can reach almost 100% and 52 for the fundamental resonance of ring-dot transformers and 98% and 67 for the second resonance of wedge 2 segment transformers. Maximum impedance was reached at optimum impedance, which is in the range from 500 Ω to 10k Ω depending on the electrode pattern and size. Fundamental vibration mode and its overtones were further studied using frequency modulated digital holographic interferometry. Normal displacement distribution on the transformer surface was visualized. The shape of vibration mode was influenced by the mechanical clamping of the transformer during its operation. Operating shapes were also simulated by the finite element method. Complementary information has been obtained by the infrared camera visualization of surface temperature profile at higher driving power.