Acoustic pulse echo measurements at 200 MHz

We have carried out acoustic pulse echo measurement with 2‐nsec‐wide pulses. These are used to excite a zinc oxide layer deposited on a conically shaped sapphire buffer rod 2 mm in diameter at the tip of the cone. We have found that an easy way to make contact between the sapphire rod and a solid material under study is by means of a gold foil. We have measured the thickness of a nickel plating on aluminum of the order of 50 μm, and that of a 134‐μm‐thick glass slide to within 2%.