Showing papers on "Laser Doppler vibrometer published in 2007"

Clinical utility of laser-Doppler vibrometer measurements in live normal and pathologic human ears.

Abstract: The laser-Doppler vibrometer (LDV) is a research tool that can be used to quickly measure the sound-induced velocity of the tympanic membrane near the umbo (the inferior tip of the malleus) in live human subjects and patients. In this manuscript we demonstrate the LDV to be a sensitive and selective tool for the diagnosis and differentiation of various ossicular disorders in patients with intact tympanic membranes and aerated middle ears. Patients with partial or total ossicular interruption or malleus fixation are readily separated from normal-hearing subjects with the LDV. The combination of LDV measurements and air-bone gap can distinguish patients with fixed stapes from those with normal ears. LDV measurements can also help differentiate air-bone gaps produced by ossicular pathologies from those associated with pathologies of inner-ear sound conduction such as a superior semicircular canal dehiscence.

A waveform design method for high-speed inkjet printing based on self-sensing measurement

Abstract: A high-speed waveform design method for piezo inkjet printing is proposed. This method uses the pressure wave information inside the ink dispenser. The pressure wave inside the inkjet dispenser can be effectively measured from the piezo current because the piezo has the self-sensing capability. The measured pressure wave was compared with the dispenser vibration measured by the laser Doppler vibrometer. For high-speed inkjet printing, a two-pulse waveform was designed based on the measured pressure wave to effectively suppress the residual pressure wave after jetting.

Squeeze-film damping in the free molecular regime: model validation and measurement on a MEMS

Abstract: Squeeze-film damping (SFD) is important in MEMS oscillators because it determines the quality factor of the oscillators. Published models for predicting SFD gave widely different results in the free-molecule regime, where the distance traveled by gas molecules between collisions in free space is much larger than the thickness of the squeezed gas film. The work presented here provides new experimental data for validating SFD models in that regime. The case studied here is where a rigid plate oscillates vertically while staying parallel to the substrate. The test device was an almost rectangular microplate supported by beam springs. The structure was excited by shaking the base. The velocities of numerous points on the plate and of the substrate were measured with a laser Doppler vibrometer and a microscope. An experimental modal analysis curve-fit the multiple frequency response functions to give the damping ratios. The test structure was contained in a vacuum chamber with air pressures controlled to provide a five-order-of-magnitude range of Knudsen numbers. The damping ratios from the measurements are compared with predictions from various published models. The measured damping ratios are close to predictions from models that are based on the Reynolds equation and take into account the inertia of the gas.

Estimation of tissue’s elasticity with surface wave speed

Abstract: The mechanical response of tissues to external forces has gained considerable interest in medical diagnosis. One approach to imaging tissue elastic properties is to apply an external force on the surface of the body. Another approach is to generate a localized force inside the tissue with the radiation force of ultrasound. In this paper, a new method is developed to estimate tissue’s elasticity based on surface wave speed measurement. The theory of surface wave speed is developed for estimating tissue’s elasticity. Experiments are carried out on a tissue-mimicking ultrasound phantom. An amplitude modulated ultrasound signal of a few hundred hertz is used to generate a localized force in the phantom. The surface wave fields are measured with a laser vibrometer. It shows that the surface wave speed can be used for inversely estimating tissue’s elastic properties based on tissue’s surface measurement.

Development of Deformable Mirror Composed of Piezoelectric Thin Films for Adaptive Optics

Abstract: In this paper, we report a piezoelectric deformable mirror composed of piezoelectric thin films for low-voltage adaptive optics (AO). A 2-mum-thick piezoelectric Pb(Zr,Ti)O3 (PZT) film was deposited on a Pt-coated silicon-on-insulator (SOI) substrate, and a diaphragm structure of 15 mm in diameter was fabricated by etching a Si handle wafer. A 19-element unimorph actuator array was produced on the PZT films with an Al reflective layer over the backside of the diaphragm. Measurements of the displacement profile using a laser Doppler vibrometer demonstrated that a large displacement of approximately 1 mum was obtained by applying a voltage of 10 Vpp on one actuator. To examine the application feasibility of the deformable mirror to AO, we reproduced low-order Zernike modes by calculating the voltage on each individual electrode using an influence function matrix. The measurements demonstrated that the deformable mirror could produce the Zernike modes up to the seventh term. Considering the low-voltage actuation as well as the capability for miniaturization of the electrode size, deformable mirrors (DMs) actuated by PZT films are desirable for low-cost AO

Compact and robust laser system for rubidium laser cooling based on the frequency doubling of a fiber bench at 1560 nm

Abstract: We propose a new compact and reliable laser system for rubidium laser cooling in onboard experiments like atomic clocks or atomic inertial sensors The system is based on the frequency doubling of a telecom fiber bench at 1560 nm Fiber components at 1560 nm allow us to generate the repumping laser and to control dynamically the power and the frequency of the 780 nm laser With this laser system, we obtain a magneto-optical trap of 85Rb even in the presence of mechanical vibrations and strong thermal variations (12 °C in 30 min)

Measurement of absolute flow velocity vector using dual-angle, delay-encoded Doppler optical coherence tomography.

Abstract: Single-beam laser Doppler measurements of flow velocity are only sensitive to the velocity component parallel to the optical axis. We describe a simple modification to a standard Doppler optical coherence tomography (OCT) system using a single sample beam that provides velocity information from multiple angles within the beam. By introducing a glass plate midway into the OCT beam path, the sample beam is divided into several components, each with a different group delay and each providing a separate interferogram with its own effective Doppler angle. By combining the Doppler shift measured in each of these component interferograms, the flow velocity vector is fully determined.

Frequency jitter and spectral width of an injection-seeded Q-switched Nd:YAG laser for a Doppler wind lidar

Abstract: The design of a 50 Hz single longitudinal mode, diode-pumped and frequency-tripled Nd:YAG master oscillator power amplifier is described, and the first measurements of output parameters are presented. The laser oscillator is injection-seeded by a tuneable monolithic Nd:YAG ring laser and frequency stabilized by minimising the Q-switch build-up time. The laser system will be an integral part of an airborne instrument demonstrator for a first satellite based Doppler wind lidar to measure vertical profiles of one component of the atmospheric wind vector. This paper focuses on the investigation of the frequency jitter and the linewidth of the laser, which are measured on a pulse-to-pulse basis. For this purpose a compact, high accuracy beat frequency monitoring system has been developed at DLR. By operating the amplifier stage at half the repetition rate (50 Hz) of the oscillator, we could reduce the frequency stability from 10 MHz (rms) to 1.3 MHz (rms) (over a 14 s period). We have determined a mean linewidth of 15 MHz (FWHM) at 1064 nm. These measured laser parameters enable wind velocity measurements in the atmosphere (0–15 km) at an accuracy of 1 to 2 m/s.

Dynamics-based Damage Detection of Composite Laminated Beams using Contact and Noncontact Measurement Systems

Abstract: A reliable and effective damage detection technique is one of the significant tools to maintain the safety and integrity of structures. A dynamic response offers viable information for the identification of damage in the structures. However, the performance of such dynamics-based damage detection depends on the quality of measured data and the effectiveness of data processing algorithms. In this article, the experimentally measured data of two sensor systems, i.e., a surface-bonded piezoelectric sensor system and a noncontact scanning laser vibrometer (SLV) system, are studied, and their effectiveness in damage identification of composite laminated beams is compared. Three dynamics-based damage detection algorithms are evaluated using the data acquired from these two measurement systems. The curvature mode shape is selected as a parameter to locate damage due to its sensitivity. The piezoelectric sensors directly acquire the curvature mode shapes of the structures, while the SLV measures the displacement ...

Measurement and analysis of rolling tire vibrations

Abstract: This paper presents the measurement and analysis of rolling tire vibrations due to road impact excitations, such as from cobbled roads, junctions between concrete road surface plates, railroad crossings. Vibrations of the tire surface due to road impact excitations cause noise radiation in the frequency band typically below 500 Hz. Tire vibration measurements with a laser Doppler vibrometer are performed on a test set-up based on a tire-on-tire principle which allows highly repetitive and controllable impact excitation tests under various realistic operating conditions. The influence on the measured velocity of random noise, cross sensitivity and alignment errors is discussed. An operational modal analysis technique is applied on sequential vibration measurements to characterise the dynamic behaviour of the rolling tire. Comparison between the operational modal parameters of the rolling tire and the modal parameters of the non-rolling tire allows an assessment of the changes in dynamic behaviour due to rolling.

Direct visualization of surface acoustic waves along substrates using smoke particles

Abstract: Smoke particles (SPs) are used to directly visualize surface acoustic waves (SAWs) propagating on a 128°-rotated Y-cut X-propagating lithium niobate (LiNbO3) substrate. By electrically exciting a SAW device in a compartment filled with SP, the SP were found to collect along the regions where the SAW propagates on the substrate. The results of the experiments show that SPs are deposited adjacent to regions of large vibration amplitude and form a clear pattern corresponding to the surface wave profile on the substrate. Through an analysis of the SAW-induced acoustic streaming in the air adjacent to the substrate and the surface acceleration measured with a laser Doppler vibrometer, we postulate that the large transverse surface accelerations due to the SAW ejects SP from the surface and carries them aloft to relatively quiescent regions nearby via acoustic streaming. Offering finer detail than fine powders common in Chladni figures [E. Chladni, Entdeckungen uber die Theorie des Klanges (Weidmanns, Erben und...

Laser display device

Abstract: Provided is a laser display device. The laser display device may include at least one light source configured to emit at least one laser beam, at least one scanning unit configured to perform a scanning with the at least one laser beam, and an image forming unit configured to generate excitation light and scattering light by receiving the at least one laser beam from the scanning unit to form an image.

Bidirectional operation and gyroscopic properties of passively mode-locked Nd:YVO4 ring laser

Abstract: A simple LD-end-pumped, passively mode-locked Nd:YVO4 ring laser with bidirectional outputs was demonstrated, and the gyroscopic properties of the ring laser was studied. The laser was continuous wave mode-locked by use of a semiconductor saturable absorber mirror (SESAM), and both clockwise and counter-clockwise outputs are stable laser pulse trains with pulse duration of 64 ps. The continuous wave mode-locking was obtained under pump power as low as 540 mW. The average output power is 50 mW for the counter-clockwise laser and 52mW for the clockwise laser under pump power of 1378 mW. The whole slope efficiency of the ring laser is about 9.4%. The two output pulse trains of the ring laser were combined to study its gyroscopic properties. The beat frequency of the pulsed solid-state laser gyro versus the rotation rates follows the Sagnac formula. The laser gyro has a large dead band of 6-8 dec/s, which was believed to be caused by the long pulse duration and the colliding of the opposite pulses on the SESAM.

Multipoint laser vibrometer for modal analysis

Abstract: Experimental modal analysis of multifrequency vibration requires a measurement system with appropriate temporal and spatial resolution to recover the mode shapes. To fully understand the vibration it is necessary to be able to measure not only the vibration amplitude but also the vibration phase. We describe a multipoint laser vibrometer that is capable of high spatial and temporal resolution with simultaneous measurement of 256 points along a line at up to 80 kHz. The multipoint vibrometer is demonstrated by recovering modal vibration data from a simple test object subject to transient excitation. A practical application is presented in which the vibrometer is used to measure vibration on a squealing rotating disk brake.

Characterisation of PZT thin film micro-actuators using a silicon micro-force sensor.

Abstract: This paper reports on the measurements of displacement and blocking force of piezoelectric micro-cantilevers. The free displacement was studied using a surface profiler and a laser vibrometer. The experimental data were compared with an analytical model which showed that the PZT thin film has a Young's modulus of 110 GPa and a piezoelectric coefficient d 31,f of 30 pC/N. The blocking force was investigated by means of a micro-machined silicon force sensor based on the silicon piezoresistive effect. The generated force was detected by measuring a change in voltage within a piezoresistors bridge. The sensor was calibrated using a commercial nano-indenter as a force and displacement standard. Application of the method showed that a 700 μm long micro-cantilever showed a maximum displacement of 800 nm and a blocking force of 0.1 mN at an actuation voltage of 5 V, within experimental error of the theoretical predictions based on the known piezoelectric and elastic properties of the PZT film.

Human Life Signs Detection Using High-Sensitivity Pulsed Laser Vibrometer

Abstract: We demonstrate experimentally the detection, in a remote and noncontact manner, of human life signs using a high-sensitivity pulsed laser vibrometer. The high surface displacement detection sensitivity of the photo-electromotive-force (photo-EMF) pulsed laser vibrometer, combined with its tolerance to the presence and moderate temporal variations of optical speckles in the light beams, allows the detection of human heartbeats, breathing, and gross physical movement from essentially any part of a human subject's surface, even in the presence of clothing, all the while without limiting the interrogation points to specific locations like the chest and carotid areas. In contrast to conventional Michelson interferometer-based laser vibrometers, the photo-EMF pulsed laser vibrometer (PPLV) does not require the use of retroreflective tapes or special electronic filtering to retrieve vividly the biological subject's life signs. Experimental results demonstrating the detection of life signs from various parts of biological subjects' bodies, with or without the coverage of clothing are presented. We also demonstrate the monitoring of a human subject's heart movements by interrogating the back of his/her hand. Results from using PPLV to determine extremity blood circulation at various levels of proximal occluding pressures are also presented.

Laser vibrometry and impedance characterization of piezoelectric microcantilevers

Abstract: This paper gives a precise insight into the frequency response of self-actuating cantilevers, extended to high-order modes An original approach is presented, based on a mixed experimental scheme regarding both impedance and laser Doppler interferometry measurements, performed with an impedance analyser and a vibrometer, respectively, and supported by some computational analysis as well The experimental results obtained by the two different techniques agree reasonably well, as for the location of the resonances in the spectrum is concerned However, certain particular modes, torsionally shaped and detected by the vibrometer, show no impedance change due to symmetry reasons A computational model has been successfully employed and utilized to shed some light on this phenomenon The model demonstrates that the induced reaction charge redistribution cancels out only for those particular torsional modes featuring an anti-symmetrical nature; as a consequence, no impedance change is to be expected in the resonances This explanation perfectly fits the impedance measurements carried out, including the missing torsional modesCorrections were made to this article on 10 April 2007 The greyscale figures were replaced with colour versions

Characterization of a bimorph deformable mirror using stroboscopic phase-shifting interferometry

Abstract: The static and dynamic characteristics of a bimorph deformable mirror (DM) for use in an adaptive optics system are described. The DM is a 35-actuator device composed of two disks of lead magnesium niobate (PMN), an electrostrictive ceramic that produces a mechanical strain in response to an imposed electric field. A custom stroboscopic phase-shifting interferometer was developed to measure the deformation of the mirror in response to applied voltage. The ability of the mirror to replicate optical aberrations described by the Zernike polynomials was tested as a measure of the mirror's static performance. The natural frequencies of the DM were measured up to 20 kHz using both stroboscopic interferometry as well as a commercial laser Doppler vibrometer (LDV). Interferometric measurements of the DM surface profile were analyzed by fitting the surface with mode-shapes predicted using classical plate theory for an elastically supported disk. The measured natural frequencies were found to be in good agreement with the predictions of the theoretical model.

Methods and systems for generating pulse trains for material processing

Abstract: Systems and methods generate laser pulse trains for material processing. In one embodiment, stable laser pulse trains at high repetition rates are generated from a continuous wave (CW) or quasi-CW laser beams. One or more laser pulses in the laser pulse train may be shaped to control energy delivered to a target material. In another embodiment, multiple laser beams are distributed to multiple processing heads from a single laser pulse, CW laser beam, or quasi-CW laser beam. In one such embodiment, a single optical deflector distributes multiple laser beams among respective processing heads.

A silicon straight tube fluid density sensor

Abstract: In this paper, a new and simple silicon straight tube is tested as a fluid density sensor. The tube structure has a hexagonal cross section. The fabrication process consists of anisotropic silicon etching and silicon fusion bonding. A tube structure with a length of 2.65 cm was tested. The sample volume is 9.3 μL. The first three modes of vibrations were investigated with a laser Doppler vibrometer for air and five liquid mixtures. The fluid density sensitivity of each mode was measured and the average was −256 ± 6 ppm (kg m−3)−1 around the density of water. The density of an unknown fluid can be continuously monitored using this sensor by measuring the resonance frequency of one of the vibration modes and extracting the density from the calibration curves.

Laser beam irradiation apparatus and laser working machine

Abstract: A laser beam irradiation apparatus includes an oscillation unit, an acousto-optic deflection unit for deflecting a laser beam oscillated by the oscillation unit, a condenser for condensing the deflected laser beam, and a control unit. The control unit determines an actual output power of the laser beam based on a light reception signal received from laser beam output detection means in response to a control signal for controlling a deflection angle adjustment unit of the deflection unit. Then, the control unit arithmetically operates the ratio of an actual output power corresponding to the control signal with reference to the lowest value of the actual output power. Further, the control unit arithmetically operates a correction value corresponding to the ratio of the actual output power to produce a control map and controls the output adjustment unit based on the control map.

Confocal microscope apparatus

Abstract: A confocal microscope apparatus comprises a first optical scanning system which obtains a scan image of a sample using a laser beam from a first laser light source, a second optical scanning system which scans specific regions of a sample with a laser beam from a second laser light source that is different from the first laser light source, thereby causing a particular phenomenon, and a beam diameter varying mechanism which can change the beam diameter of the laser beam of at least one of the first optical scanning system and the second optical scanning system With this configuration, the apparatus further comprises an excitation light intensity distribution calculator which calculates and stores the excitation light intensity distribution along a depth direction on the sample surface from the beam diameter of the laser beam output from the beam diameter varying mechanism

Piezoelectric Optical Micro Scanner with Built-in Torsion Sensors

Abstract: The present study describes the design, fabrication and demonstration of the piezoelectric optical micro scanners (piezoelectric scanners) with built-in torsion sensors. We have developed the piezoelectric scanners with piezoelectric torsion sensors utilizing Pb(Zr,Ti)O3 (PZT) thin films. A mirror (1 ×1 mm2) is supported by hinges, and the hinges are connected to resonators. The torsion sensors are formed on the hinges, which detect the rotation of the mirror through the direct piezoelectric effect of the PZT thin films. The micro scanners were fabricated from a multilayer of Pt/Ti/PZT/Pt/Ti/SiO2 deposited on a silicon-on-insulator wafer using microelectromechanical systems bulk micromachining. The output voltage and phase of the torsion sensor showed the resonant peak compatible with the data measured by a laser Doppler vibrometer. The gain of the torsion sensor was measured to be 0.0012. We compared the scanning angle of the reflected light and output voltage of the torsion sensor as a function of the voltage applied to the resonators. The torsion sensor showed a nonlinear increase in the output voltage, which is in good agreement with that in the scanning angle.

Laser beam machining system

Abstract: A laser beam machining system including a chuck table for holding a work, and a laser beam irradiation unit for irradiating the work held on the chuck table with a laser beam, wherein the laser beam irradiation unit includes: a pulsed laser beam oscillator for oscillating a pulsed laser beam; a condenser for condensing the pulsed laser beam oscillated from the pulsed laser beam oscillator; a laser beam scanning unit disposed between the pulsed laser beam oscillator and the condenser and operative to deflect the pulsed laser beam to be inputted to the condenser; and a laser beam reshaping unit which ids disposed between the pulsed laser beam oscillator and the laser beam scanning unit and by which the energy distribution of the pulsed laser beam oscillated from the pulsed laser beam oscillator is reshaped into a top hat shape.

Young's Modulus Measurements in Standard IC CMOS Processes Using MEMS Test Structures

Abstract: This letter1 presents a method to measure the Young's moduli of individual thin-film layers in a commercial integrated circuit (IC) foundry process. The method is based on measuring the resonance frequency of an array of micromachined cantilevers and using the presented optimization analysis to determine the elastic modulus of each layer. Arrays of cantilever test structures were fabricated in a commercial CMOS IC process and were released using XeF2 as a postprocessing etch. A piezoelectric transducer placed under the test chip was used to excite the cantilevers to resonance, and the resonance frequency was measured using a laser Doppler vibrometer. It is reported that excellent agreement for values of Young's modulus is observed for cantilevers between 200 and 400 mum in length, with average standard deviation being 4.07 GPa.

A Self-Mixing Laser Sensor Design With an Extended Kalman Filter for Optimal Online Structural Analysis and Damping Evaluation

Abstract: We have developed a new algorithm based on the extended Kalman filter in order to improve the resolution of a self-mixing (SM) optical displacement sensor This noncontact sensor, which provides vibration measurement with a very high accuracy, can be used for online quality control, for example, measuring the damping of excited mechanical structures This SM sensor subject to weak feedback has been tested in comparison with a commercial vibrometer in order to measure the frequency response function (FRF) of a plate with a passive damping to be characterized, and to show the efficiency of a damping treatment