Fabrication and characterization of silica aerogel films for air-coupled piezoelectric transducers in the megahertz range

New materials and designs are needed for efficient air-coupling of piezoelectric transducers in the megahertz range. In this sense, a new type of matching layer has been essayed and is presented here. They are made of two quarter-wavelength (λ/4) layers (both at 3 MHz): a silica aerogel film (0.015 Mrayl) and a polymer sheet. The aerogel film was directly produced on the polymer sheet and it was characterized by scanning electron microscopy. The matching layer was attached to a PZ-27 piezoceramic (3 MHz), the electrical impedance was both measured and theoretically calculated. The pitch-catch response of transducers (3 MHz) that could be produced with this technology was theoretically calculated.