Transducer radiation pattern modification

Abstract

Ultrasonic transducers were used to simulate radiation patterns of an electromagnetic cavity-backed slot antenna when mounted on a flat ground plane as well as by itself in free space. A 12-in. spherical transducer excited in radial mode was selected to provide essentially isotropic coverage generated by the antenna. The radiation coverage of this transducer was significantly distorted, when mounted on a flat surface just like the antenna. This distortion was caused by both the presence of the plane in the near field as well as due to reflection of the energy from the lower half of the spherical transducer by the plane surface, resulting in the interference or distorted pattern. Then the plane surface immediately underneath the spherical transducer was treated with a synthetic rubber adhesive, “Miracle Seal,” and the resulting surface was randomly shaped in order to diffuse the incident ultrasonic radiation; thus, utilizing our background in scattering, and reverberation of sound, was used in a reverse fashion in order to obtain a very smooth isotropic pattern. The resulting pattern did not contain any sharp nulls which were reduced to less than forty percent of the original number and were significantly attenuated (in decibels) by 75% on the average.