Precise Displacement Measurements Using Phase Information of 40 kHz Ultrasonic Waves in Pinhole-Based Air-Coupled Ultrasonic System

Abstract

Noncontact precise displacement measurements, including surface profiling, were demonstrated using the phase information of narrow-band 40 kHz continuous waves (wavelength λ=9 mm) in a pinhole-based air-coupled ultrasonic system beyond the diffraction limit. Real-time displacement measurements with a distance resolution of λ/900,000 (10 nm) were accomplished using a highly sensitive phase variation when the distance between the pinhole and the surface of an object was in the range from approximately 5 to 10 µm. To extend the working distance of our system while maintaining a high resolution, an automatic distance control system was constructed and introduced in our system. Using this advanced system, a surface topographical profile of 16 µm height was successfully measured, while maintaining maximum phase sensitivity. These results demonstrate the usefulness of our system when applied to noncontact precise displacement measurements.

Temperature Dependence of Parametric Phenomenon in Airborne Ultrasound for Temperature Measurement

“…We defined p 00 as p 00 ¼ 2&cU; thus, the amplitude of the ultrasound p 0 becomes jp 00 sinðk 0 =2ÞðR À zÞj in eq. (7). U (m/s) is the amplitude of particle velocity on the surface of the piston.…”

“…Sound probes have been used to measure many physical factors such as temperature, [1][2][3][4][5][6] displacement, 7) distance, 8,9) velocity, [10][11][12][13] surface roughness, 14) and position, 15,16) and for adaptation to communication techniques 17,18) and special devices. 19) Since acoustic methods of measurement have attractive features such as being noncontact, nondestructive, and causing little disturbance on a measured field.…”

Air-coupled ultrasonic time-of-flight measurement system using amplitude-modulated and phase inverted driving signal for accurate distance measurements

“…In the distance measurements, a signalto-noise ratio (SNR) of ultrasonic wave signals is decreased by a large attenuation of ultrasound in air and a huge acoustic-impedance mismatch between the transmitter and air. To obtain sufficient amplitude of the ultrasonic wave signals, a narrow-band transducer [1,2,3] has been essential and widely used. However, narrow-band transducers generate an ultrasonic wave with a broad envelope.…”

“…If a sharp envelope can be realized using the narrow-band transducers, then an accuracy of the TOF measurement will be improved with the high sensitivity. When the TOF measurement has accuracy better than a half of the wave period of the ultrasonic wave, the TOF measurement can be combined with the phase-detection (PD) measurement [1,2,3]. This combination [4,5,6,7] enables us to extend the measurable range with high measurement accuracy.…”

Direction-Variable Beam by Decentered Annular Array Sound Source with Rounded Width of Elements

“…In metrology, imaging, and communication, the application of acoustic probes is widely studied. [1][2][3][4][5] In order to obtain an output with high accuracy, it is desirable that a sound beam with a small width be used. Generally, the width of sound beams radiated in the propagating space increases due to diffraction.…”