Distance measuring device, and coordinate input apparatus utilizing the same

摘要

A distance measuring device is capable, even utilizing the Lamb wave with velocity fluctuating from device to device, of easily setting an approximate wave velocity and of effecting precise distance calculation even with such approximate wave velocity. There is employed a system of measuring the thickness d of the wave transmitting plate, then determining the group velocity Vg of the Lamb wave from the measured thickness, then determining the phase velocity Vp of the Lamb wave from the plate thickness d and the frequency f of the Lamb wave, and deriving the distance from Vg, Vp and the arrival delay time of the Lamb wave.