Abstract – In the research of methods for evaluation and characterization of therapy ultrasound transducers that will be used in the hyperthermia applications, the measurement of some acoustic parameters is specially important. We have used a modified broadband through-transmission technique proposed by Ping He [1,3] for measuring acoustic dispersion and attenuation because it requires a minimum number of variables to be measured and eliminates the needs for measuring the speed of sound in the water and the trigger delays in data sampling. In addition it minimizes the uncertainty in determining the phase spectra. Unfortunately we have found some inconvenient aspects of this technique in our application. Keywords: Attenuation; Dispersion and Ultrasound. I. Introduction An understanding of the interaction of ultrasound with tissue medium in time and frequency domains and the ability to determine the waveform change in propagating ultrasound pulses should be valuable in the design of array transducers and in quantitative ultrasound characterization of tissue. Acoustic parameters related to ultrasound attenuation and dispersion determine material properties, that are of considerable importance in theoretical acoustics, nondestructive evaluation, and tissue ultrasonic characterization. [1-5] Many media, including soft tissues, have been observed to have an attenuation function, which increases with frequency and can be expressed by a power law function: y 0 ) ( (1) Where: : is angular frequency 0 : arbitrary real non negative constant y : arbitrary real non negative constant : has units of Np/m.[4] For most materials, the power law exponent y has values from 0 to 2, with the majority in the 2 1 y range. In medical ultrasound [15], for tissue absorption, y varies from 1 to 1.7. When a broadband ultrasound pulse passes through a layer of medium, the waveform of the pulse changes as a result of the attenuation and dispersion of the medium. As a result of it and taking information reported in [1], the higher frequency components of the pulse are attenuated more than the lower frequency components. After passing through the layer, the transmitted pulse is not just a scaled down version of the incident pulse, but it will have a different shape. Dispersion refers to the phenomenon that the phase velocity of a propagating wave also changes with frequency [2]. Since the magnitude of dispersion for most materials is very small, often less than 1% within the frequency range from 1 MHz to 10 MHz, minimizing measurement uncertainties is particularly important in such applications. Dispersion causes additional changes in the waveform of the propagating pulse because the wave components with different frequencies travel at different speeds. [2] Determination of dispersion using the above transmission method [1,3] requires the measurements of a reference velocity (usually the sound velocity in water), the thickness of the specimen, of the transmission coefficient at the water- specimen interface and the phase spectra of two transmitted ultrasound pulses. The purpose of this paper is to examine and evaluate the Ping He’s method from analyzing experimental results obtained in some materials and the possible implementation of these in a system that is currently in development which goal is to measure acoustic parameters within a phantom during ultrasonic hyperthermia treatments. II. Theory The most of methods that have been proposed for determining dispersion from the local attenuation [7-11], requires the measurement of the sound velocity in water and the trigger delays of the sampling window to the sample and the water, and have the disadvantage of the associated uncertainties by the thickness measurement that limited the accuracy of the dispersion measurement. On the other hand, the measurement of attenuation and dispersion using a broadband, through – transmission technique has been described by many authors [12-14]. In these cases the absolute phase velocity of the specimen at a number of frequencies must be determined; and the dispersion is then expressed as the change in phase velocity with frequency. Experimental Estimation of Acoustic Attenuation and Dispersion M. Vázquez 1 , L. Leija 1 , A. Vera 1 , A. Ramos 2 , E. Moreno 3 1 Department of Electrical Engineering, CINVESTAV-IPN, México D.F., México. 2 Department of Signals, Systems and Ultrasonic Technologies, C.S.I.C, Madrid, Spain. 3 Ultrasonic Center, ICIMAF. Calle 15 No 551 e/C y D Vedado, La Habana, Cuba. Phone (52) 5550613800 Ext. 6212 Fax (52) 5557477080 E-mail: mvazquez@cinvestav.mx 2nd International Conference on Electrical and Electronics Engineering (ICEEE) and XI Conference on Electrical Engineering (CIE 2005) Mexico City, Mexico. September 7-9, 2005 156 IEEE Catalog Number: 05EX1097 ISBN: 0-7803-9230-2 0-7803-9230-2/05/$20.00 ©2005 IEEE.