Acoustic properties of alumina colloidal/polymer nano-composite film on silicon

Alumina colloidal/polymer composite films on silicon substrates have been successfully fabricated using the sol-gel method, in which the crystallite sizes of alumina are between 20 and 50 nm. The density and ultrasonic phase velocities in these films with different alumina ratios from 14% to 32% were measured at the desired operating frequency. We have proved that the density, acoustic phase velocities, and hence the acoustic impedance of the nanocomposite films increase with the alumina content, which gives us another option of tailoring the acoustic impedance of the nano-composite film for making the matching layer of high-frequency medical ultrasonic transducers.