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.

Distributed vibration sensing and control of a piezoelectric laminated curved beam

Abstract: The distributed vibration sensing and control of a piezoelectric laminated curved beam are studied. The mathematical model of a curved beam with a distributed piezoelectric sensor and actuator is formulated first, followed by vibration analysis. This model provides estimates of the sensor signal, actuator-induced membrane force, and actuator-induced bending moment, as well as predicting the controlled damping ratio and dynamic response. The sensor sensitivity with various sensor thicknesses is studied and compared. The effectiveness of active damping controls is evaluated with respect to different beam thickness, and sensor/actuator thickness. Numerical examples are provided and simulation results are discussed.

Current state and trends of ensuring traceability for vibration and shock measurements

Abstract: Recent and current activities at the level of national metrology institutes (NMIs) towards ensuring traceability of vibration and shock measurements to the International System of Units are mainly twofold: (i) initiating and contributing to new international standardization projects, within the International Organization for Standardization, ISO TC 108, to specify upgraded or new standard methods for the vibration and shock calibration of transducers; and (ii) improving the metrological base by developing upgraded or new standard equipment (e.g. national measurement standards) in compliance with up-to-date standard methods. Laser interferometry, which is the preferred primary vibration calibration method at NMI level, has been further developed at the Physikalisch-Technische Bundesanstalt (PTB) in recent years as a uniform methodology and technique for the primary measurement of translational motion quantities (e.g. acceleration) and rotational motion quantities (e.g. angular acceleration) at sinusoidal, shock-shaped and other, user-defined time histories. A traceability chain has been defined and developed which realizes and disseminates the units of the respective physical quantities at such time-dependencies which reproduce as closely as possible, during calibration of any transducer (e.g. accelerometer) or measuring instrument (e.g. laser vibrometer), the conditions of use after calibration (i.e. shock measurement in the peak acceleration range 1000 m/s2 to 50000 m/s2). A general account is given of the state of the art in transducer calibration, and an ensemble is presented of six national measurement standards (example from the PTB) with comparison results verifying the lowest measurement uncertainty achieved so far. From a survey of past comparisons, conclusions are drawn for key comparisons in the field of vibration and shock. Recommendations for future work areas are made.

Frequency stabilization for two-mode laser

Abstract: Frequency stabilization is disclosed for a two-mode laser, such as a Zeemanaser. The emission frequency of the laser is servo-stabilized to the center of the atomic gain curve to provide a stable laser reference frequency that is independant of time and enviromental operating conditions. Stabilization in a longitudinal-field Zeeman laser is achieved by utilizing the mode-pulling effect which makes the frequency difference between the two circular polarization components have a parabolic dependence on the optical frequency of the laser. The detected intermode beat frequency from the laser is subjected to digital phase-sensitive, drift-free integration, utilizing a reversible counter, to provide a cumulative count with a rate of increase corresponding to the displacement of the average wavelength from the atomic center wavelength and an analog error-correction signal is generated therefrom which is coupled to the laser. The error-correction signal is processed and coupled to the piezoelectric crystal which controls the emission frequency of the laser for fast laser frequency correction control, and may be also processed and coupled to the heater coil on the laser for thermally providing slow frequency correctional control.

Method for mobile survey of road surface

Abstract: A road surface illuminated by sunlight is scanned with a laser beam at right angles to the direction of travel, the intensity of the laser beam being intensity modulated with a predetermined frequency; laser beams reflected from the road surface are received and optically filtered to filter out light having frequencies outside that of the laser beam The optically filtered laser beam strikes a plurality of beam position sensing elements from which respective electrical signals are derived The resulting electrical signals are then multiplexed and electrically band-pass filtered wherein the center frequency of the band-pass filtering coincides with the frequency at which the laser beam is intensity modulated

Means for controlling the power output of laser diodes in a ROS system

Abstract: The present invention provides a means and method for efficiently and automatically monitoring and adjusting the power output of either a single or a dual beam laser diode array used to provide the scanning beams in a ROS system. Collimated light outputs from a collimator lens assembly following either a single or dual beam laser are reflected along an optical path to impinge on one or two photodiodes positioned so as to intercept the reflected light. The photodiode output is proportional to the power output of the laser diode associated with the photodiode. In one multi-beam embodiment, polarization of the laser diode output is controlled so as to ensure that only outputs from an associated laser diode is sensed by an associated photodiode. In another embodiment, a half wave plate is used to rotate the polarization of one of the laser diodes.