We characterize the observed phase and amplitude of acoustic birefringence
data collected with an electromagnetic acoustic transducer. Our characteriz
ation models are extended versions of an idealized model for acoustic biref
ringence. In the extended models, angle-dependent terms account for observe
d variability in phase and amplitude which is not predicted by the idealize
d theory. Possible sources of this extra variability include material inhom
ogeneity and angle-dependent sensor gain. The adjustable parameters in the
model are determined by minimizing the sum of the squared phase residuals p
lus the sum of the squared amplitude residuals. To facilitate convergence,
we determine the model parameters by fitting the extended models sequential
ly according to model complexity. Ten experimental data sets were collected
from the same sample. We estimate the mean value of each model parameter a
nd its associated standard error. For each extended model, we estimate the
mean phase delay between the fast and slow modes. We also estimate the mean
rotation angle of the pure-mode polarization directions (relative to a ref
erence coordinate system in the specimen). From run to run, we observed pha
se data drift. However, the difference between the phases of the slow and f
ast modes did not follow this drift.