A theoretical assessment of a thermal technique to measure acoustic power radiated by ultrasound transducers.
The parameters affecting the temperature rise in an insonified absorber are studied computationally. Finite-element and analytical solutions are obtained for the transient energy equation in a cylindrical absorber. When the ultrasound beam radius is less than the radius of the absorber, the temperature field is seen to be considerably more complex than when the absorber cross section is uniformly heated. Circumstances in which power predictions based upon uniform heating would result in appreciable error are identified. The rise time required to achieve equilibrium is studied as a function of operational parameters, including absorber geometry and thermal properties as well as ultrasound beamwidth and frequency. The rise time is seen to increase approximately as the square of the absorber length, while optimized temperature rise increases linearly with absorber length, demonstrating a tradeoff in ultrasound power determination via equilibrium temperature measurements: longer lengths produce higher sensitivity, but also longer times before measurements can be made. A transient technique that may bypass this tradeoff is suggested.
Myers
Matthew R
MR
Center for Devices and Radiological Health, US Food and Drug Administration, Rockville, MD 20852, USA. mrm@cdrh.fda.gov
Herman
Bruce A
BA
D002138:Calibration; D003198:Computer Simulation; D019544:Equipment Failure Analysis / Q000379:methods*; D008962:Models, Theoretical; D012680:Sensitivity and Specificity; D013696:Temperature; D014159:Transducers; D014465:Ultrasonics