Measurement of the vibrational isolation characteristics of an underwater transducer element mount by laser vibrometery

For the purpose of vibration isolation, underwater transducer elements are often mounted on a constrained layer base plate. The mass of the constraining plate in conjunction with the compliance of the damping layer adds an additional degree of freedom to the axial response of the element at low frequencies. A laser vibrometery system is used to measure the vibrational characteristics of the element and its isolation mount. This technique eliminates erroneous results caused by the added mass of an accelerometer. Three element configurations are studied—the transducer directly glued to the base plate, the transducer mounted with a syntactic foam isolation ring, and the transducer with the isolation ring supported by a constrained layer damped base plate. The ratio of the output voltage of the transducer to the velocity of the base is reported for each configuration in frequency ranges from 70 Hz to 16 kHz. The experimental results are compared to an analytic model.