Abstract
A method is proposed for estimating the acoustic power output of ultrasound transducers using a two-port model with electrical impedance measurements made in three different propagation media. When evaluated for two high-intensity focused ultrasound transducers at centre frequencies between 0.50 and 3.19 MHz, the resulting power estimates exceeded acoustic estimates by 4.5–21.8%. The method was shown to be valid for drive levels producing up to 20 MPa in water and should therefore be appropriate for many HIFU (high-intensity focused ultrasound) applications, with the primary advantage of employing relatively low-cost, non-specialist materials and instrumentation.
Highlights
The measurement of transducer acoustic output is necessary for deriving safety indices for diagnostic ultrasound transducers; for a review, see [1]
Calculating the total power dissipation from electrical impedance measurements may provide an upper limit to the acoustic power output, under the assumption that all electrical power going into the transducer is converted to acoustic power
Electrical impedance measurements were made with two high-intensity focused ultrasound (HIFU) transducers loaded in turn with three distinct fluid media
Summary
The measurement of transducer acoustic output is necessary for deriving safety indices for diagnostic ultrasound transducers; for a review, see [1]. Parameters defining safety (peak rarefaction pressure, spatial-peak temporal-average intensity, temporal-average acoustic power) are determined usually by using either a hydrophone measurement system (for pressure and intensity measurement and sometimes for acoustic power calculations) or a radiation force balance (for acoustic power measurement) [1,3]. There are several drawbacks for using hydrophone systems, such as the difficulty in measuring high pressures (they generally do not withstand high pressures and/or long pulses) and the time for the setup of field scans required for power calculation. Measurements using a radiation force balance are much more time efficient; the specific-purpose devices are relatively expensive (7–24k USD) and unobtainable by many laboratories and institutes with a limited budget. A clinician may test the performance of a transducer over time without requiring access to expensive equipment.
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