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Radiation (waves) exerts a force on objects which reflect or absorb it. The effect can be used to measure the power of an ultrasonic beam by directing it on to a reflector coupled to a force measuring device. The forces involved are very small (0.135 mg/mW) and so the measurement device must be extremely sensitive. There are various designs, including a reflector suspended by fine wires which moves in response to the ultrasound radiation in a water bath, a reflector made in the form of a float which is pushed downwards, or the reflector may be the face of a strain gauge pressure transducer. Such devices would be found in the physics or electronics laboratory for calibrating or testing the output of ultrasonic devices.
Content and Design Copyright 2000 Dr. Malcolm C Brown. See Title Page for more details