Accurate velocity measurement of periodic striae of TiO₂- SiO₂ glasses by the line-focus-beam ultrasonic material- characterization system

The evaluation of periodic striae layers in TiO₂-SiO₂ ultra-low-expansion glasses, formed during production, is discussed through the measurement of leaky surface acoustic-wave (LSAW) velocities by the line-focus-beam (LFB) ultrasonic material-characterization system. The averaging effect associated with an LSAW propagation region interacting with periodic striae on a specimen surface was examined at 225 MHz, taking several specimens prepared with inclination angles of θ = 0,2, 5, 10, 20, and 90° to the plane of striae layers with a periodicity of 0.16mm. LSAW velocities corresponding to TiO₂ concentrations in the glass were properly measured for the specimens with θ less than 10°, and the perpendicular specimen (θ = 90°) was suitable for accurate determination of the striae periodicities for LSAW propagation perpendicular to the striae plane.