Dumiload: A Variable-Radiation-Impedance Simulator

A wide range of radiation load impedances for a transducer element has been created by a laboratory device. This range included all the radiation impedances that exist for any of the transducers of a large planar array of over 400 elements. The device is called DUMILOAD, which is a contraction of DUmmy Mechanical Impedance LOAD. The DUMILOAD consists of a transducer terminated with an electrical impedance. A purely passive electrical impedance is sufficient to create positive radiation resistances. The DUMILOAD transducer is cemented face to face with a test transducer. The radiation impedance of the test transducer is controlled by adjusting the electrical impedance terminating the load transducer. The DUMILOAD is an existing research tool and has been of great value for high power transducer testing at NEL. The procedures necessary to create a desired radiation impedance are presented and a simple but precise method for measuring directly the radiation impedance achieved is described.