Laser Doppler vibrometer

About: Laser Doppler vibrometer is a research topic. Over the lifetime, 6319 publications have been published within this topic receiving 76068 citations.

Eye-safe, single-frequency pulsed all-fiber laser for Doppler wind lidar

Abstract: A single-frequency pulsed erbium-doped fiber (EDF) laser with master-oscillator power-amplifier configuration at 1 533 nm is developed. A short-cavity, erbium-doped phosphate glass fiber laser is utilized as a seeder laser with a linewidth of 5 kHz and power of 40 mW. The seeder laser is modulated to be a pulse laser with a repetition rate of 10 kHz and pulse duration of 500 ns. The amplifier consists of two pre-amplifiers and one main amplifier. The detailed characteristics of the spectrum and linewidth of the amplifiers are presented. A pulse energy of 116 1J and a linewidth of 1.1 MHz are obtained. This laser can be a candidate transmitter for an all-fiber Doppler wind lidar in the boundary layer.

Investigation of Slider Vibrations Due to Contact With a Smooth Disk Surface

Abstract: The dynamic behavior of pico sliders is investigated during slider-disk contacts as a function of velocity, pitch angle, crown height, and lubricant thickness using laser Doppler vibrometry and acoustic emission sensors Analog and digital filtering methods are applied to distinguish air bearing and slider body resonances from frequencies related to disk runout, load beam design, and gimbal structure Sliders with high pitch angle and small crown were found to exhibit smaller vibration amplitudes after slider-disk contacts than sliders with low pitch angle or large crown The lubricant thickness of the disk was found to affect both the glide avalanche height of the disk and the dynamic behavior of the slider The results show that roll and pitch frequencies of the air bearing increase with decreasing disk velocity

Continuous and Damped Vibration Detection Based on Fiber Diversity Detection Sensor by Rayleigh Backscattering

Abstract: An optical fiber vibration sensor based on a polarization diversity scheme has been developed to study structural vibration properties under external disturbance. The polarization diversity scheme has improved signal-to-noise ratio (SNR) by over 13 dB with capability of detection frequency of sub-hertz to tens of kilo- hertz. The minimum dynamic strain we have detected is 3 nepsiv, and the SNR of the sensor is >37 dB without any averaging. For the first time, Rayleigh backscattering has been utilized to detect continuous and damped vibration generated by a piezo fiber stretcher and vibrating cantilever with a frequency range of sub-hertz to 16 kHz. We also use this sensor and polarization analyzer to characterize the polarization state change and phase shift of the piezo fiber stretcher in transmission and Rayleigh backscattering up to kilohertz frequency, both results agrees quantitatively.

Heterodyned self-mixing laser diode vibrometer

Abstract: This patent describes a new method for remotely measuring vibration of an object based on laser Doppler vibrometry. The method combines an external two-pass frequency shifting technique with self-mixed, heterodyne detection to provide a compact measurement system that requires only three optical components. A standard diode laser package, consisting of a laser and a monitor photodiode, is used to emit light and detect the scattered signal, a lens is used to collimate the light, and an external modulator is used to shift the optical frequency. The diode laser may be used with or without temperature stabilization. The unique design permits the measurement of objects from a range of long distances without the need for focusing or alignment. Measurements made with the system are characterized by high signal-to-noise ratio, wide dynamic range, and simple alignment.

2-D steering and propelling of acoustic bubble-powered microswimmers

Abstract: This paper describes bi-directional (linear and rotational) propelling and 2-D steering of acoustic bubble-powered microswimmers that are achieved in a centimeter-scale pool (beyond chip level scale). The core structure of a microswimmer is a microtube with one end open in which a gaseous bubble is trapped. The swimmer is propelled by microstreaming flows that are generated when the trapped bubble is oscillated by an external acoustic wave. The bubble oscillation and thus propelling force are highly dependent on the frequency of the acoustic wave and the bubble length. This dependence is experimentally studied by measuring the resonance behaviors of the testing pool and bubble using a laser Doppler vibrometer (LDV) and by evaluating the generated streaming flows. The key idea in the present 2-D steering is to utilize this dependence. Multiple bubbles with different lengths are mounted on a single microswimmer with a variety of arrangements. By controlling the frequency of the acoustic wave, only frequency-matched bubbles can strongly oscillate and generate strong propulsion. By arranging multiple bubbles of different lengths in parallel but with their openings opposite and switching the frequency of the acoustic wave, bi-directionally linear propelling motions are successfully achieved. The propelling forces are calculated by a CFD analysis using the Ansys Fluent® package. For bi-directional rotations, a similar method but with diagonal arrangement of bubbles on a rectangular swimmer is also applied. The rotation can be easily reversed when the frequency of the acoustic wave is switched. For 2-D steering, short bubbles are aligned perpendicular to long bubbles. It is successfully demonstrated that the microswimmer navigates through a T-junction channel under full control with and without carrying a payload. During the navigation, the frequency is the main control input to select and resonate targeted bubbles. All of these operations are achieved by a single piezoelectric actuator.