The Design Of First And Second Order Combined Sensors

A combined sensor is described as a directional receiver. Many quantities of an acoustic field can be simultaneously measured at a point using the combined sensor. New ideas for solving underwater acoustic problems are provided using those obtained amplitude and phase information. Because of potential and important value of engineering application, technology corresponding to the combined sensor is paid many attentions by underwater acoustic association during last about decade.This paper shows how the finite-difference approximation can be utilized to estimate of the pressure gradient and second order gradient, and analyses some of the errors that occur when finite-differences are used. The error analysis leads to the recommendation that the second order sensor be realized with moving-coil velocity senor or accelerometers and a pressure sensor at the origin. This will eliminate the gradient estimation error and significantly reduce the second order gradient estimation error, since the second order gradient of the pressure can now be estimated by first order finite-difference approximation.This paper discusses two schemes of combined sensors design. And the practical structures of prototypes are presented. They can be rigidly mounted on the underwater structures to measure the acoustic pressure, acoustic particle velocity or acceleration and the spatial gradient of the velocity or acceleration of an acoustic field at a collocated point. Thus, it may eliminate some problems brought by the spring suspension of co-oscillating acoustic vector sensor. At last, performance measurement results of the prototypes are given.