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 40 nm displacement (λ/200,000) using 40 kHz air-coupled ultrasonic waves has been achieved.

Nanometer-Order Resolution Displacement Measurement System by Air-Coupled Ultrasonic Wave Introducing Maximum Phase-Sensitivity Tuning

“…Multiple-Reference Waves [10][11][12] Figure 1 shows the principle of displacement measurement in the transmission mode. The transmitting transducer is placed face-to-face with the receiving transducer at the distance z.…”

“…To achieve a nanometer-order resolution, we have recently reported a phasedetection method for overcoming this limitation. 11) In this paper, we describe an improved displacementmeasurement system in which a maximum phase-sensitivity automatic tuning is introduced to our improved phasedetection method. 11) In this system, phase sensitivity is automatically tuned to the maximum with a feedback control of the phases of multiple-reference waves.…”

“…11) In this paper, we describe an improved displacementmeasurement system in which a maximum phase-sensitivity automatic tuning is introduced to our improved phasedetection method. 11) In this system, phase sensitivity is automatically tuned to the maximum with a feedback control of the phases of multiple-reference waves. The principle of the phase-detection method introducing multiple-reference waves, on which our previous system is based, will be explained first.…”

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.…”