Measuring the impedance of ultrasonic transducers

For ultrasonic transducers whose impedance is usually highly variable with frequency, impedance measurement is quite difficult. Cheap and easy devices which are currently available are not suitable for this purpose. Expensive scientific devices are known to be used; usually, they are designed for such measurements in a wide frequency band, from acoustic to microwave range. Simpler and cheaper devices with a narrower band are not commercially available. For hydroacoustic applications, the frequency range may be reduced to 1MHz or even 250 kHz in most cases. This article discusses the possibilities of building a simple and cheap automated system of measuring electric impedance of ultrasonic transducers used in hydroacoustics. The presented results are based on the concept of using a digital oscilloscope as the basic tool for measuring the impedance magnitude and phase. The results have been verified in the original measurement system.