Improved phase-detection method using an air-coupled ultrasonic wave for a few-tens of nanometers displacement measurements

Abstract

To enhance the phase sensitivity of ultrasonic signals, phases of the multi-reference-wave are arranged around the maximum phase-sensitive region. The resolution of the phase detection is improved by magnifying the maximum sensitive phase detection outputs. A resolution of 40nm displacement (λ/200, 000) using 40kHz air-coupled ultrasonic waves has been achieved.