A simple method to characterize the impedance of pyroelectric materials at ultra-low frequencies

Abstract

The purpose of this work is to demonstrate a new simple stand-alone method of characterizing the impedance of a pyroelectric cell. This method utilizes a pyroelectric single pole low-pass filter technique. Utilizing the properties of a pyroelectric single pole low-pass filter technique, a known input voltage is applied and using simple equations, capacitance Cp and resistance Rp at a frequency range of 1 mHz to 1 Hz can be calculated. For verification purposes, an LCR meter and an impedance analyzer were exploited at 10 and 100 Hz, respectively. Results showed that Rp values for two materials, lead zirconate titanate-5A and polyvinylidene difluoride, were within 8%, and Cp values were within 7.5%. In addition, to verify the importance of the impedance values in energy harvesting applications, output power was measured with varying impedance values. The optimal load resistances for polyvinylidene difluoride and lead zirconate titanate-5A were consistent with the measured pyroelectric impedance at the particular heat range with 10.9% and 1.4%, respectively. The pyroelectric single pole low-pass filter method presented here demonstrates that for pyroelectric materials the impedance depends on two major factors: (1) average working temperature and (2) the heating rate. Neglecting these two factors can result in inefficient and unpredictable behavior of pyroelectric materials when used in energy harvesting applications.