Simple homodyne ultrasound interferometer for solid state physical acoustics

Ultrasonic pulse-echo technique is a valuable and non-destructive tool to explore elastic properties of materials. We propose a new instrument based on mass-produced microchips. In our design, the signal is processed by an AD8302 RF gain and phase detector (www.analog.com). Its phase output is linearly proportional to the phase difference between the exciting and response signals. The gain output is proportional to the log of the ratio of amplitudes of the received to the exciting signals. To exclude the non-linear fragments and to enable exploring large phase changes, we employ a parallel connection of two detectors, fed by in-phase and quadrature reference signals, respectively. The interferometer was tested by measuring the temperature dependences of both sound speed and attenuation in metallic glasses as well as in ferroelectric KTaNbO3 (KTN) single crystals. The instrument allows for exploring phase transitions with precision of ΔV/V ∼ 10−7 (V is ultrasound speed) in the broad dynamic range from −60 ...