Measurement of vibration distribution on focusing source using a thin rod reflector

Utilizing the concept of time reversal and the transmitter-receiver reciprocity, the distribution of the vibration amplitude and phase is estimated for a focusing source without using a hydrophone. When a tone burst wave is radiated in water, the sound wave reflected from the top of a thin rod is detected with the concave source itself. Scanning the reflector surface in the plane normal to the acoustic axis, two-dimensional data of the amplitude and phase of the output voltage are stored and then the calculations of square root and time reversal are executed for the data. Comparing with the case detecting the sound with a needle type hydrophone set at the same position as the reflector, the advantage and disadvantage of the present method are discussed taking a piezoelectric concave source with a star-shape electrode for instance. The experiment is also carried out for the high-frequency concave-source with an aperture radius of 4 mm which is too small to measure with an ordinary hydrophone.