Diagnostic ultrasound power meter

Ultrasound imaging is widely used in many branches of medicine. We propose a new design for a simple and accurate instrument to check ultrasound power levels of imaging equipment. Power meters currently available mostly rely on a force balance approach, balancing the radiation force exerted by an ultrasound wave on a reflector with a restoring force. The restoring force may be provided by an electronic feedback system. The meter we describe uses a simple implementation of a force balance using gravity as the restoring force. A flat hollow vane, sized to intercept and reflect an ultrasound beam incident upon it, is hung vertically in a water filled vessel from a pivot point. The transducer being tested is applied to a membrane window angled at 45/spl deg/ to the vertical, such that the ultrasound beam is incident on the vane from 45/spl deg/ above horizontal in the vertical plane, reflected at 45/spl deg/ below horizontal, and thereby a force exerted on the vane in the horizontal direction. This force rotates the vane slightly about the pivot. As the vane rotates it experiences an increasing balancing force due to gravity which counteracts the radiation force. The rotation or displacement of the vane is measured using a magnet and linear Hall effect sensor. By appropriate selection of vane mass and buoyancy, high sensitivity can be achieved. We have validated the device using a calibrated ultrasound source and demonstrated a linear output from 0 to 300 mW (r=0.999, p<0.001).