Consideration of Radiation Impedance Calculation Methods for Cylindrical Array Sound Source

Abstract

In a phased array, the interval between the centers of the sound source elements which adjoin each other is set below half the wavelength in order to suppress the gratinglobe. At this interval, the array sound source can gain strong radiation power. The estimation of radiation impedance is important in the analysis of the radiation power. The Greenspon's method which is a radiation impedance calculation method of rectangular pistons on a cylinder is explained, and some defects of this method are clarified. For the evaluation of Greenspon's method, we introduce the combined Helmholtz integral equation formulation (CHIEF) method. The radiation impedance is calculated using both Greenspon's method and the CHIEF method, and the results are compared. On the basis of comparison of the radiation power measured while driving the cylindrical phased array with the theoretical value of radiation power determined using the caluculated value of radiation impedance, it is considered that Greenspon's method and the CHIEF method give accurate estimations.