Measurement of spectral response of ultrasonic probes. Effect of diffraction, lens, and transmitter/receiver circuit

Many phenomena may alter the measured spectral response of a probe. Obvious ones are transmitter pulse spectrum or hydrophone sensitivity. Less obvious is the diffraction effect due to finite aperture and lens. If measurements are not made at the geometrical focal point, but at the maximum pressure point, an alteration of the spectrum is observed. Spectrum is also altered by lens absorption, especially for high frequency probes. Finally, the electrical part of the system, including cable, matching circuit, transmitter and receiver, may greatly modify the measured spectrum. This paper shows how these phenomena can be taken into account and illustrates their importance in practical examples of 1D probes