Model-based method for improvements in the calibration of ultrasonic power measurements at low-power levels

Abstract

The measurement uncertainty in the calibration of ultrasonic power measurements at low-power levels was reduced by a model-based signal-processing method. The ultrasonic power measurement system is based on the radiation force balance method according to IEC 61161. Outputs of an electronic balance and the excitation voltage were simultaneously sampled and recorded. A computer-controlled coaxial switch that utilizes data lines of the parallel port of a desktop computer was used for power-on and power-off control. Power-on and power-off intervals were finely controlled by the desktop computer. The Electroacoustic radiation conductance, defined as the ratio of the ultrasonic power of a transducer and the square of the rf voltage at its input, was calculated from the recorded data. During data processing, a simple model for drifting and switching was proposed and a least-mean-squares algorithm was used to estimate parameters of the model. Good measurement reproducibility was also observed that resulted in the reduction of total measurement uncertainty.