Jy. Wu et Kk. Shung, MULTIFREQUENCY TRANSDUCER ASSEMBLY FOR NONLINEAR ULTRASONIC MEASUREMENTS, The Journal of the Acoustical Society of America, 93(4), 1993, pp. 2231-2234
This letter provides more detail on a multi-frequency transducer assem
bly used in our nonlinear image enhancement experiments [J. Acoust. So
c. Am. 88, 2852 (1990)]. In these experiments, high-intensity ultrason
ic waves were launched into the medium and second harmonic signals or
the sum-frequency signals were detected. Therefore, a transducer assem
bly was needed to operate at two different frequencies separated appro
ximately by an octave. The signals in the lower frequency band were mu
ch stronger than the nonlinear signals in the higher band which were t
he signals of interest. The signals in both bands are coaxial and the
much weaker signals in the higher band had to be extracted from the st
ronger background. The heart of the transducer assembly was an acousti
c beam separator. The principle of the beam separator was based on the
total transmission of the acoustic waves through a thin isotropic sol
id layer in a fluid medium. The beam separator served both functions o
f beam relocation and acoustic filtering. The filtering was accomplish
ed by using both the total transmission phenomenon and the Fabry-Perot
interference phenomenon.