A versatile force balance for ultrasound power measurement

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Abstract
The passing decades have witnessed many designs of instrument for measuring the radiated power output from ultrasound equipment, both in the low power, diagnostic range and in the higher power range as used in therapy, for example. Criteria to be considered during design, encompass the following: high sensitivity/resolution- to microwatts; power handling to tens of watts; simplicity of use and calibration; quick response time; stability of readings and zero; the need for a frequency-independent linear response; ability to accept all current sizes of transducer; portability and ruggedness. The criteria must be accommodated in a single instrument. This paper starts with a brief review of but some of the previous designs, and identifies a fundamental problem with many. The instrument here described hopefully eliminates this problem and essentially meets the above criteria. Using the force-balance principle, the instrument has a 70 mm diameter reflecting target, plus a concentric absorber, in a water-filled chamber. The maximum sensitivity is 1 mW FSD, resolution better than 50 mu W and a maximum power capability of 10 W. The instrument is very portable, weighing only 3 kg.
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