Ultrasonic Air Coupled Transducer Output Impedance Measurement Technique

Abstract

Estimation of the output impedance of ultrasonic transducers is required for electrical matching circuits design and for receiving amplifiers noise optimization. This paper presents a simple technique for transducer output impedance estimation using the same data acquisition system and signals that are conventionally used in non-destructive testing. A pair of ultrasonic transducers is used: one for transmission, one for reception. Received signal is recorded under low and high resistance load and transducer output impedance is then obtained from these two signals. Hence, this technique requires only one measurement channel and bias errors are low (no need for calibration). In addition, it is ground referenced and does not require the transducer to be removed from the positioning fixture. Experimental results obtained using different probing signals have been compared against conventional measurements obtained by an impedance analyser.

Ultrasonic Needle Hydrophone Calibration in Air by Parabolic Off-Axis Mirror Focused Beam Using Three-Transducer Reciprocity

“…where ρ and c are the density and the sound propagation velocity for the coupling media (air was used here), A is the active transducer surface area (obtained using transducer radius a), M is the reception sensitivity, V/Pa, S P is the transmission sensitivity, expressed as the ratio of the sound pressure on transducer surface p TX to driving current I TX , Pa/A. The input impedance Z in of the amplifier and the transducer impedance Z T were measured as per [27] and used to convert the voltage registered by the amplifier V in into an open circuit voltage [14]:…”

“…The amplitude and the phase of the registered current and voltage signals were estimated using the Sine Wave Correlation (SWC) technique [27], using the gated part of the signal (shown in red on Fig. 9).…”