The overall goal of this resonance ultrasonic spectroscopy method, is to measure a complete set of material constants and their temperature dependence for a piezoelectric material using only one sample. The Impedance Method defined in the piezoelectric standards of the institute of electrical and electronic engineers, require 5 to 7 samples of different geometries in order to measure the complete set of material constant for piezoelectric material. The main advantage of the resonance ultrasonic spectroscopy technique is that the full tensor properties can be obtained from one sample, avoiding inconsistency caused by sample to sample variations.
Data acquired from this method, enable people to simulate the performance of electromechanical devices and to quantify the performance degradation at higher temperatures using finer element method. First, glue a rectangular parallel pipe to PZT-4 ceramic sample to the bottom surface of a metal rod using a very thin layer of wax by heating the rod and sample to about 60 degrees Celsius. After cooling to room temperature, tightly fit the rod into a metal cylinder with a larger outer diameter so that the bottom surface of the cylinder and sample can be polished together to guarantee the flatness of the sample surface Wet a plexiglass plate with tap water, and sprinkle 6 micron aluminum oxide powder onto the wet surface.
Place the sample holder with the sample glued to it onto the plexiglass plate, and make a circular motion to grind the sample service flat. Then wash the plexiglass plate, and sample holder, thoroughly with tap water. Following this, sprinkle 3 Micron aluminum oxide powder onto the wet plexiglass plate and repeat the grinding to smoothen the sample surface.
Wash the glass plate and sample holder clean with tap water. Lift the sample off of the holder by heating the assembly to about 60 degrees Celsius to melt the wax. When finished, remove the remaining wax from the sample surface with acetone.
Connect a 15 megahertz longitudinal wave transducer and a digital oscilloscope to a pulcer reciever. Next, place the transducer onto the sample surface along the X direction with some coupling grease in between. Press the curser key on the control panel of the digital oscilloscope.
Then, press the side menu button V bars, and rotate the general purpose knob to move one cursor line to the highest peak of the first echo signal. At this point, press the Select key, and rotate the general purpose knob to move the other cursor line to the corresponding peak in the second echo signal. Read the numerical value at the place marked with an up triangle on the screen, which is the roundtrip time of flight of the longitudinal wave pulse along the X-axis.
Connect an impedance analyzer to a control computer, and turn both on. Then, insert the sample in the fixture connected to the analyzer and place the whole assembly into a temperature chamber. After closing the temperature chamber, press the key Meas on the impedance analyzer panel, and select CP-D.
Next, set the chamber to 20 degrees Celsius, using the control computer. Open the spreadsheet software and read the capacitance data. Then, save the results into a file.
Following this, change the chamber temperature by pressing the up key on the impedance analyzer panel. Repeat the previous step for each temperature increment, after the chamber temperature becomes stable. At this point, place the sample in between the transmitting and receiving transducers of the resonance ultrasound spectroscopy system, with contacts only at the opposite corners of the sample.
Run the control interface of the dynamic resonance system by double clicking on the software file DRS.exe. Set the start frequency, the stop frequency, and the total number of data points to be collected. Measure the resonance spectrum of the sample in this frequency range at room temperature, and save the spectrum into a file.
Place the sample inbetween the transmitting and receiving transducers that are already in the furnace, with contacts only at the opposite corners of the sample. Following this, run the resonance ultrasound spectroscopy system measuring software and measure the resonance frequencies of the sample. Then, save the results into a file.
Increase the temperature of the sample with a temperature step of 5 degrees Celsius. Repeat the previous step, until the desired temperature is reached. For the PZT-4 ceramic sample the elastic constants C11E, C33E, and C44E, increase with the temperature.
While the elastic constant C12E and C13E are nearly independent of temperature in the range of 20 to 120 degrees Celsius. On the other hand, the piezoelectric constants E33, E31, and E15 are strongly temperature dependent. The measured dialectric constants and the predicted ones calculated based on the full set of material constants obtained by this method show excellent agreement.
The piezoelectric constants D15 and D33 calculated using one set of formulas and the values calculated using another set of formulas also show good agreement. These results confirm that the full set material constants obtained for the PZT-4 ceramic sample, are highly self-consistent for the temperature range from 20 to 120 degrees Celsius. This RUS technique allows us to measure the full tensor properties at elevated temperatures with self-consistency, which paved the way for researchers in the field of device simulation to explore the possibility of predicting the real performance of electromechanical devices particularly to predict the performance degradation with heater generation during operation.
After watching this video, you should have a good understanding of how to perform resonance ultrasonic spectroscopy measurements at elevated temperatures. The key is to acquire a reliable set of constants at room temperature and then deroute the full tensor property at the high temperatures based on the room temperature data.
