Ultrasonic transducer power output by modulated radiation pressure

TLDR

The apparatus combines the superior features of earlier radiation‑pressure‑based methods. The system measures transducer sound power by modulating the input at a low frequency, detecting the resulting force on a target mounted on an electromagnetic armature, and calibrating the force–current relationship with direct current and dead weights while sweeping the carrier frequency from 0.1 to 15 MHz. The technique yields absolute power measurements, shows encouraging agreement with other methods, and produces characteristic curves for both normal and defective transducers.

Abstract

We have set up and are using an apparatus for the measurement of total sound power output of a piezoelectric transducer radiating into water. This apparatus combines the better features of previously used methods which depend on radiation pressure. The input is modulated at a low frequency and the output power is intercepted by a target which experiences a force at the modulation frequency. The target is mounted on the armature of an electromagnetic receiver provided with an independent coil through which a current at the modulation frequency is adjusted in amplitude and phase, either manually or automatically by feedback, to arrest the motion of the armature. When the armature is stationary the force depends only on the current, and the apparatus can be calibrated using direct current and dead weights. It is thus absolute. In practice, the carrier frequency is swept over any part of the range 0.1–15 MHz while a recording of power output versus frequency is made. The results of comparisons made with those of other mehtods are encouraging. Examples of curves from normal and defective transducers are shown.