ACCURATE MEASUREMENT OF COEFFICIENTS IN A FERROELECTRIC CERAMIC

In the IRE Standards, or resonance-antiresonance, method for determining coefficients in a ferroelectric ceramic, one measures as a function of frequency the absolute value of the admittance of electroded samples. This process destroys all phase information. Without phase information, three potential sources of error can affect the measured coefficient values. 1) The testing signal can easily pass the threshold of nonlinearity in the material without the notice; this effect can lead to erroneously high values for the piezoelectric coefficient. 2) Any scatter of values in the dielectric constant due to inhomogeneity or frequency dependence is directly reflected in the apparent piezoelectric coefficients. 3) Piezoelectric phase angles, which may perturb the apparent piezoelectric coefficient by several percent, are completely ignored. In addition to these three drawbacks, the IRE Standards technique is not applicable in the case of weak resonances (i.e., resonances with the figure of merit M less than 3), or in cases where the antiresonance is marred by nearby spurious responses. An alternative measurement technique described here preserves phase information and eliminates most error due to the above three sources. It is applicable to weak resonances where M is as small as 0.1. Additionally, it may even be used sometimes when spurious satellite resonances occur near the main resonance. This alternative technique requires measurements of the half-power frequencies, and of the complex admittance at resonance or Measurements on a total of five sample geometries are needed for determining all the electroelastic coefficients. To illustrate the new the complete set of coefficients are evaluated for two typical ferroelectric-ceramic compositions. © 1969 IEEE. All rights reserved.