Noncontact measurement of vibration using airborne ultrasound

Abstract

A noncontact ultrasonic method for measuring the surface normal vibration of objects was studied. The instrument consists of a pair of 420 kHz ultrasonic air transducers. One is used to emit ultrasounds toward the moving surface, and the other receives the ultrasound reflected from the object under test. Two effects induce a phase modulation on the received signal. The first effect results from the variation of the round trip time interval tau required for the wavefront to go from the emitter to the moving surface and back to the receiver. This is the Doppler effect directly proportional to the surface displacement. The second effect results from the nonlinear parametric interactions of the ultrasonic beams (forward and backward) with the low frequency sound field emitted in the air by the vibrating surface. This latter phenomenon, which is a volume effect, is proportional to the velocity of the vibrating surface and increases with the distance between the transducers and the surface under test. The relative contribution of the Doppler and parametric effects are evaluated, and both have to be taken into account for ultrasonic interferometry in air.

Feasibility Study on a Noncontact Remote-Sensing Vibration Transducer Using RF Polarimetry

“…2) Remote-Sensing Transducers: A variety of technologies have been used to remotely measure vibrations including ultrasound [21], [22], magnetic fields [23], light strobes [24], [25], and digital cameras [26]. In addition, specific vibrometry applications could be found for each technology's unique strength or particular characteristic.…”

Application of Interferometry in Ultrasonic System for Vibration

“…There are many kinds of ultra harmonics of rectangular, therefore, the circuit without the steady-state operation mode can be called multi vibrator as self-excitation. [4], [5] As shown in the Fig.3., the circuit for ultrasonic transmitting consists of the circuit of NE555 time-based and the correlative circuit. The output of capacitor C 1 is unchanged.…”

“…The software extracted effectively characteristic value of the vibration signal. 4,5 The frequency of the excitation signal in the experiment was selected at 71.2Hz. The irregular original signal was provided in Fig.5.…”

A Highly Accurate Ultrasonic Measurement System for Tremor Using Binary Amplitude-Shift-Keying and Phase-Shift Method

“…However, the measurable vibration frequency range of an object decreases when the distance between the object and transducers increases. To overcome the drawback, Figuroa and Barbieri offered an ultrasonic ranging system based on the phase-shift method for structural vibration measurement [7][8][9][10]. However, the measurement resolution varies with the range of the displacements being measured.…”