|University of Illinois at Urbana-Champaign | Department of Electrical and Computer Engineering | Department of Bioengineering
Department of Statistics | Coordinated Science Laboratory | Beckman Institute | Food Science and Human Nutrition | Division of Nutritional Sciences | College of Engineering
|Friday, January 18th, 2019|
Transducer Beam Characteristics
In the Bioacoustics Research Laboratory, spherically-focused, high-frequency transducers are used in our investigations. Because the transducer is an integral part of any acoustic data acquisition and imaging system, it is imperative to have accurate information on its spatial and temporal acoustic field characteristics. These characteristics include:
Spatial acoustic field characteristics:
Temporal acoustic field characteristics in the focal region:
To obtain the acoustic pulse-echo field characteristics, a 38 µm tungsten wire target oriented normal to the sound beam direction is scanned in a rectangular grid pattern in a tank filled with filtered, degassed water. The grid spacings are a half or a quarter of the acoustic wavelength, depending on the estimated center frequency of the transducer and the estimated total length of the scan. The spatial field distribution is obtained by taking the pulse intensity integral of each received waveform. The pulse intensity integral is defined as the time integral of the intensity of a pulse taken over the time in which the acoustic pressure is nonzero. Beamwidth, depth of focus and focal length at true focus are determined from a spatial contour map of the pulse intensity integral. Center frequency, bandwidth, fractional bandwidth, and pulse duration are determined from the RF signal at the true focal point.
Why is this all necessary when the transducer comes with specifications from the manufacturer? Most likely, the system used to test the transducer at the factory is not the same system being used in the laboratory. The transmit-receive spatial and temporal acoustic field characteristics have been found to vary with the excitation system used. Also, over the life of the transducer, its characteristics or performance may change, e.g. deterioration of electrical connections. Thus the measurement of acoustic field characteristics should be done when the transducer is new from the factory, and periodically thereafter to ensure accuracy.
For more information on the acoustic field measurement technique:
K. Raum and W. D. O'Brien, Jr. Pulse-Echo Field Distribution Measurement
Technique of High-Frequency Ultrasound Sources. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 44, 810-815, 1997.
K. Raum and W. D. O'Brien, Jr. Pulse-Echo Field Distribution Measurement Technique for High-Frequency Ultrasound Sources. Proceedings of the 1997 IEEE Ultrasonics Symposium, pp 1747-1750, 1997.
Additional contributions that deal with ultrasound exposure are as follows:
F. Dunn, A. J. Averbuch and W. D. O'Brien, Jr. A Primary Method for the Determination of Ultrasonic Intensity with Elastic Sphere Radiometer. Acustica, 38, 58-61, 1977.
R. C. Preston, D. R. Bacon, S. S. Corbett III, G. R. Harris, P. A. Lewin, J. A. MacGregor, W. D. O'Brien, Jr. and T. L. Szabo. Interlaboratory Comparison of Hydrophone Calibrations. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 35, 206-213, 1988.
C. M. W. Daft, T. A. Siddiqi, D. W. Fitting, R. A. Meyer and W. D. O'Brien, Jr. In-Vivo Fetal Exposimetry. IEEE Transaction on Ultrasonics, Ferroelectrics, and Frequency Control 37, 500-505, 1990.
N. B. Smith, C. V. Vorhees, R. A. Meyer and W. D. O'Brien, Jr. An Automated Ultrasonic Exposure System to Assess the Effects of In Utero Diagnostic Ultrasound. Proceedings of the 1990 IEEE Ultrasonics Symposium, pp. 1385-1388, 1990.
J. A. Jensen, D. R. Gandhi and W. D. O'Brien, Jr. Ultrasound Fields in an Attenuating Medium. Proceedings of the 1993 IEEE Ultrasonics Symposium, pp 943-946, 1993.
D. R. Gandhi and W. D. O'Brien, Jr. Nonlinear Acoustic Wave Propagation in Tissue. Proceedings of the 1993 IEEE Ultrasonics Symposium, pp 939-942, 1993.
A. Goldstein, D. R. Gandhi and W. D. O'Brien, Jr. Diffraction Phenomena with Co-Axial Plane Piston Transducers. Proceedings of the 1994 IEEE Ultrasonics Symposium, pp 1757-1760,1994.
D. Swiney and W. D. O'Brien, Jr. Human Fetal Diagnostic Ultrasound Exposimetry System. Proceedings of the 1996 IEEE Ultrasonics Symposium, pp 1167-1169, 1996.
A. Goldstein, D. R. Gandhi and W. D. O'Brien, Jr. Diffraction Effects in
Hydrophone Measurements. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 45, 972-979, 1998.
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|Bioacoustics Research Lab.|