Abstract:
A bioultrasonic spectroscopy system and method for studies of ultrasonic tissue characterization in the VHF and UHF ranges were recently developed. Bulk linear acoustic properties of velocity, attenuation coefficient, impedance, and density can be determined in an ultrasonic transmission line in which the specimen is sandwiched between two SiO[inf 2]-buffer rods, having ZnO-film ultrasonic transducers on their outer ends, and with distilled water employed as the reference medium. An extensive study of the linear and nonlinear acoustic propagation behavior of liquids/tissues at these high frequencies has been initiated. In this paper, nonlinear wave propagation in the system of SiO[inf 2]/water specimen/SiO[inf 2] in the frequency range of the fundamental from 100 to 200 MHz is discussed theoretically and empirically for an input fundamental-frequency ultrasonic power of about 1 mW. A new method of measuring the nonlinearity parameter of liquids is proposed, taking notice that the sign of the nonlinearity parameter of SiO[inf 2] is different from that in liquids. The nonlinearity parameter is determined by measuring the distance between two rods at which the second-harmonic-component output of the receiving transducer becomes zero, with reference to the nonlinearity parameter of SiO[inf 2].