Research On Measuring Method Of Piezoelectric Ceramic Ferroelectric Hysteresis Loop

Ferroelectric hysteresis loop is the important characteristic and one of criteria of piezoelectric ceramic with ferroelectricity.The important material parameters such as saturation polarization intensity P_s,residual polarization intensity P_r,coercive electric field E_c and dielectric loss etc.can be available by measuring the ferroelectric hysteresis loop of piezoelectric ceramic.Measurement method of ferroelectric hysteresis loop is the important part involved in ceramic measurement.Sawyer-Tower circuit is widely used in the measurement of ferroelectric hysteresis loop and low frequency AC high voltage generator is the key of the measurement of ferroelectric hysteresis loop.In this paper,low-frequency AC high-voltage generator is implemented by control the cascading of H-bridges base on cascaded multilevel inverter theory.The measurement of ferroelectric hysteresis loop is achieved using Sawyer-Tower circuit and virtual instrument technology developed on Lab VIEW.Firstly,The problem that MCU can’t do fast floating-point operations is solved and a control strategy for H-bridge cascaded multi-level inverter is established with cascaded multilevel inverter theory combining virtual instrument technology:the upper computer is responsible for calculation,and the MCU is responsible for control.H-bridge power module is designed base on multiple output technology of flyback converter.Secondly,the independent outputs of the module include DC 200V and DC 14V driving for arms of H-bridge are available.And optoelectronic isolation control is achieved by using optocoupler to drive arms of H-bridge.Then measurement and control circuit based on STC8A8K64D4 MCU and Sawyer-Tower circuit is designed.Finally,upper computer program developed on Lab VIEW communication with the MCU through USB to serial port.The SPWM control table from upper computer program is received and saved to Flash memory of the MCU.The cascading of 4 H-bridge based on the SPWM control table is controlled by the MCU to generate 1 Hz sinusoidal high voltage for Sawyer-Tower circuit.In the same time,measurement of the output of Sawyer-Tower circuit is carried out and data is sent to upper computer program.Upper computer program receives data from the MCU and the data is processed to draw ferroelectric hysteresis loop.Complete closed Ferroelectric hysteresis loop and initial polarization curve are available when two piezoelectric ceramics with thicknesses of 0.3mm and 0.5mm respectively,are measured by the ferroelectric hysteresis loop measurement system of this paper.Measure the same piezoelectric ceramic using commercial instrument HT66A and compare with the previous measurement results.The results indicate the success of the hysteresis loop measurement system developed in this paper.