A new characterization technique for lossy piezoceramic resonators

Piezoelectricity was discovered by the brothers Curie in 1880. They found that, in certain materials such as zincblende, tourmaline, can sugar, topaz and quartz, mechanical stresses were accompanied by the production of electric surface charges. The piezoelectric effect remained a curiosity until the early 1920s when it was utilized to realize crystal resonators for the stabilization of oscillators, thereby launching the field of frequency control. Piezoelectricity has found many applications as oscillators, filters, and sensors in televisions, cellular phones, radios, ultrasonic imaging, radar and signal processing to name just a few. Most of these applications use high Q single crystal materials such as quartz. These materials can become expensive as the application becomes more specialized. Piezoceramic materials can be used in these applications because it is less expensive, but the Q of the material is low and has very blunt characteristics as compared to quartz. This low Q and blunt resonance is connected to the loss in the material and makes it difficult to characterize the material and to get the maximum performance out of devices made from this material.; We have developed a new characterization technique for lossy piezoceramic material based on the use of complex frequencies to stimulate the devices complex resonant point. This technique enables us to find the frequency dependent attenuation constant, and the impedance at the complex resonant point. The material properties of piezoceramics can be described through the use of complex material constants. The solution of the acoustic wave equation leads to complex frequencies as the resonant points for a thickness excited resonator. This leads to the use of complex frequency excitation, which is an exponentially decaying sine wave. The Laplace transform of this type of signal has an imaginary part which is the frequency and the real part which is related to the attenuation of the device. So this type of signal is ideal to characterize lossy materials which can be described with complex material constants. Experimental results will be presented showcasing the complex frequency excitation technique. The attenuation constant calculations will be presented along with the variation of the impedance as a function of the attenuation constant. Modeling and simulation results using an equivalent circuit model will also be presented.