Influence of the Electrical Test Setup on the Voltage Gain Measurement of an Unloaded Rosen-Type Piezoelectric Transformer Vibrating in the First Three Modes

In recent years, Piezoelectric Transformers (PTs) have become a great success due to their excellent properties, especially in applications requiring high voltage. The Rosen-type PT is well known for this performance, as its voltage gain at the resonant frequency can reach few thousands. However, the high output impedance of this device can make an accurate electrical measurement of the output voltage difficult, hence the need to ensure good impedance matching along the measuring electrical test setup. For this purpose, two high impedance oscilloscope probes were successively added to the secondary side to further emulate the measurement chain and match the experiments as closely as possible with the developed 1D model. Accordingly, for an unloaded Rosen type piezoelectric transformer, made of hard ceramic (pz26) with corresponding dimensions 2L×w×t =25 mm×3 mm×2 mm and operating in the first three modes, the corresponding input impedances Zin were evaluated at 665 Ω - 225 Ω and 1974 Ω, while the output impedances Zout were evaluated at 19.2 MΩ - 15.4 MΩ, and 1.8 MΩ. A voltage gain of 164, 179 and 23 at frequencies of 69.4 kHz, 136 kHz and 204.6 kHz, respectively was successfully measured, with a precision of less than 5%. In addition, a detailed equivalent circuit of the transformer was built and all its lumped RLC components were experimentally identified using the Nyquist diagram showing, on the whole, a well-accepted agreement with the expected results.