Resonance anti-reflection for ultrasonic density measurement

An ultrasonic method for measuring the density of liquids with a solid layer separating a reference fluid and a test fluid is presented. By adjusting the signal frequency according to the thickness of the layer, waves reflected at the first and at the second boundary of the layer interfere destructively. Thus, the layer appears to vanish for the incident waves. The resulting echo signal depends only on the acoustic impedances of the reference fluid and the test fluid and so the density of interest can be extracted. Transient and steady state parts of the echo signal yield data for the reference measurement. Phase shift evaluation is used to eliminate impedance ambiguities.