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.

KRS-5 optical fibers capable of transmitting high-power CO 2 laser beam

Abstract: Polycrystalline KRS-5 optical fibers were experimentally demonstrated to have high-power transmission capabilities for a cw CO2 laser beam. A typical sample of fibers provided by extrusion, 1 mm in diameter and 0.87 m in length, carried a laser power of 68 W to its output end and was found to remain free from damage at an incoming laser intensity up to 30 kW/cm2.

Application of the acousto-optic effect to pressure measurements in ultrasound fields in water using a laser vibrometer

Abstract: A non-intrusive measuring technique, applied to sensing and measuring acoustic waves at ultrasonic frequencies is considered. The method is optically based and so does not interfere with the ultrasound field. The measurement procedure relies on the acousto-optic effect, that is the change in refractive index which occurs with changing pressure in the ultrasound field. This change in refractive index is detected through the change in the path length of a laser beam propagating through the region of interest. Typically these changes are small corresponding to a physical change of the order of 10−6 m. Fourier analysis is used to separate the component of the signal corresponding to the pressure variation from background noise and vibrations which can be dominant. Application of the technique is illustrated for an underwater ultrasound transducer. Measurements are made using the optical technique and compared to measurements taken with a hydrophone. The effectiveness of the optical measuring technique is discussed. It is shown that the laser vibrometer produces a good estimation of the mean beam pressure provided an estimation of the beam width is available, a restriction which is often satisfied; and the acoustic field can be assumed to be approximately constant across the beam.

Effect of Die-Bonding Process on MEMS Device Performance: System-Level Modeling and Experimental Verification

Abstract: This paper presents a distributed nodal method (DNM) for compact modeling of the package-device interaction of microelectromechanical systems (MEMS). MEMS devices have movable structures that are sensitive to structural stresses and easily influenced by package structures and environmental parameters. Hence, it is necessary to include the packaged behavior of MEMS into a compact simulation tool with acceptable precision. The conventional nodal method is therefore modified to achieve this purpose. A node with distributed nodal quantities is defined to describe the distributed interactions among the device, package, and environmental temperature. Based on the definition, the related processes of element partition, nodal matrix formation, and element assembly have been demonstrated. The case of a die-bonded microbridge has been used as an example, since the microbridge is not only a typical MEMS structure but also is influenced easily by structural stresses. The DNM model is validated first by a finite-element method (FEM) simulation, then by two individual experiments, including the measurement of die warpage using a digital image correlation system and the detection of shifted natural frequencies of surface-micromachined bridges using a laser Doppler vibrometer system, both after die bonding. The FEM and test results agree with those evaluated by the model with a relative error of less than 10%. Stress alleviation of the test structure has been unintentionally achieved by die bonding, leading to relative shifts of 12%-26% and 19%-26% of the first and third natural frequencies of the microbridges. The packaged behavior also exhibits an evident distributed feature along the die surface as expected. Although, at current stage, the application of the DNM is still limited to static domain, it shows potential in developing hierarchical models of MEMS devices including the package.

Laser heterodyne system

Abstract: A laser heterodyne system is disclosed wherein received reflections of a beam of coherent light are amplified in a laser. The amplified received reflections are heterodyned with the light produced by the laser and the resulting beat frequency is detected using a photodetector. A controller, responsive to the beat frequency, controls, in one case, the frequency of a transmitting laser, and hence the frequency of the received light, and, in another case, the frequency of the light produced by the amplifying laser so that, in either case, the difference between the frequency of the received light and the frequency of the light produced by the amplifying laser is adjusted to maximize the amplification of the received light by the amlifying laser prior to detection by the photodetector.

An experimental comparison of the head/disk interface dynamics in 51/4- and 8-inch disk drives

Abstract: A laser Doppler vibrometer is used to measure the head/disk interface dynamics in computer disk drives. The stability of the head under steady operating conditions is compared between a 5/14-inch and two different 8-inch "Winchester" drives. In the larger drives, high-frequency vibrations (between 5 and 10 kHz) are detected on the slider which are not present in the smaller drive. These vibrations have amplitudes on the order of magnitude of the head/disk spacing and are related to the rolling and pitching modes of the slider. The vibrations of the disk, suspension, and actuator arm are also investigated and correlated with the results obtained on the slider.