Ultra-high distance resolution using phase information of 40 kHz air-coupled ultrasonic wave

An ultra-high distance resolution of a pinhole-based low-frequency air-coupled ultrasonic system beyond the diffraction limit is described. The high phase sensitivity of 40 kHz air-coupled ultrasonic wave signals is obtained when a distance between the pinhole and an object is small. Distance resolution of λ/900 000 (10 nm) with noncontact has been achieved using phase information of narrowband continuous ultrasonic waves.