Low-pressure measurement using an ultrasonic sensor II

Pressure dependence of ultrasonic signals transmitted through an area evacuated over the range of 13 Pa to atmospheric pressure was found to show a linear relationship in a log-log plot, in which a bend appears at around 103-104 Pa. The cause of the bend was not clear. A treatment including the absorption of ultrasonic waves into the medium in the evacuated area was applied to the analysis. A least squares fitting of the equation obtained to the experimental results showed good agreement, and the absorption coefficient obtained from the fitting parameters gave a reasonable value.