Abstract: This paper describes a transducer that is intended for measuring the level of material in air. The elements connected longditudially in the array are used as the driving source and the high-order step-compensated flexural mode plate acts as the radiating face. The transducer works as both the sound projector and the echo receiver. It is characterized by high directivity,low mechanical Q and high sensitivity. A level measurement of coal in the coal bin bas been successfully made in the range of 20m.