Performance of sputtered SiO2 film as acoustic antireflection coating at sapphire/water interface

The effect of sputtered SiO2 films as an acoustic antireflection coating for matching the large acoustic discontinuity at the sapphire/water interface is experimentally and theoretically investigated in a frequency range of 200 to 1100 MHz. By the introduction of SiO2 films, the transmission loss of more than 9 dB at the interface is reduced to less than 1 dB at a quarter-wavelength frequency of SiO2 film with high reproducibility.