RESUMO
This paper presents an ultrasonic method for measuring the mass density of liquids with a solid layer separating a reference fluid and a test fluid. By adjusting the frequency of the exciting signal according to the thickness of the layer, it is possible to generate destructive interference of the waves reflected at the first and second boundary of the layer. Thus, the layer appears to vanish for the incident waves. In the steady state the resulting echo signal depends only on the acoustic impedances of the reference fluid and the test fluid and the density of interest can be extracted. Short- and long-term drifts of the electronics and the ultrasonic transducer (implied) are eliminated by using the well-known pulse-echo technique, with additional frontwave detection. The method presented here is a first step in developing an ultrasonic mass flow meter.
