Bridging the gap of impedance mismatch between air and solid materials

Resonant impedance matching layers for air-coupled ultrasonic applications in the range 0.4-2 MHz are presented. Their special properties make it possible to attach them easily to the surface of a piezoelectric transducer and/or to cover over the material under test. A detailed study of the properties of porous materials to produce matching layers as well as the efficiency of them is presented.