Showing papers on "Laser Doppler vibrometer published in 2004"

Single virus particle mass detection using microresonators with nanoscale thickness

Abstract: In this letter, we present the microfabrication and application of arrays of silicon cantilever beams as microresonator sensors with nanoscale thickness to detect the mass of individual virus particles. The dimensions of the fabricated cantilever beams were in the range of 4–5 μm in length, 1–2 μm in width and 20–30 nm in thickness. The virus particles we used in the study were vaccinia virus, which is a member of the Poxviridae family and forms the basis of the smallpox vaccine. The frequency spectra of the cantilever beams, due to thermal and ambient noise, were measured using a laser Doppler vibrometer under ambient conditions. The change in resonant frequency as a function of the virus particle mass binding on the cantilever beam surface forms the basis of the detection scheme. We have demonstrated the detection of a single vaccinia virus particle with an average mass of 9.5 fg. These devices can be very useful as components of biosensors for the detection of airborne virus particles.

Structural health monitoring using scanning laser vibrometry: II. Lamb waves for damage detection

Abstract: Guided ultrasonic waves have shown great potential for structural health monitoring. Various types of transducer can be used for actuating and sensing of these waves. This includes non-contact approaches such as optical/laser techniques. Classical laser methods usually involve high energy interferometers. The paper demonstrates that a commercial laser vibrometer, designed for vibration/modal analysis, can be used for crack detection in metallic structures. The study involves a simple fatigue test in order to initiate and grow a crack. Lamb waves generated by one bonded piezoceramic transducer were sensed using a multi-point scanning laser vibrometer. The results demonstrate the potential of laser vibrometry for simple, rapid and robust detection of fatigue cracks in metallic structures.

Self-mixing laser diode velocimetry: application to vibration and velocity measurement

Abstract: A review of recent experimental and theoretical results concerning laser diode self-mixing velocimetry is presented, showing that this technique can be deployed to measure velocity and vibration of solid targets with an extremely simple optical setup. This technique reduces optical alignment problems and achieves results comparable to those obtained by the conventional laser Doppler velocimetry (LDV) approach. It is demonstrated that the self-mixing signal can be processed to recover the target velocity and vibration by applying the same analysis method used for LDV. An optimal signal processing method is then proposed to recover the target velocity with good accuracy, also in the presence of relevant speckle disturbance. Application to the measurement of sub-micron vibrations is also demonstrated, using a self-mixing vibrometer instrument capable of 5-nm accuracy. As an example, the characterization of response and hysteresis of piezoceramic transducers (PZTs) is carried out. These results illustrate the effectiveness of the self-mixing technique in the field of laser velocimetry, opening the way to new applications where compactness and low cost of the measuring apparatus are essential.

Detection of bacterial cells and antibodies using surface micromachined thin silicon cantilever resonators

Abstract: This article describes a surface micromachined cantilever beam-based resonator for biological sensing applications. The study used a novel microfabrication technique of merged epitaxial lateral overgrowth (MELO) and chemical mechanical polishing (CMP) to fabricate thin, low stress, single-crystal silicon cantilever beams. The vibration spectra of the cantilever beams, excited by thermal and ambient noise, was measured in air using a Dimension 3100 Series scanning probe microscope (SPM), and in certain cases, a Polytec MSV300 laser Doppler vibrometer. The sensors were used to detect the mass of Listeria innocua bacteria by applying increasing concentration of bacteria suspension on the same cantilever beams and measuring the resonant frequency changes in air. Cantilever beams were also used to detect the mass of proteins such as Bovine Serum Albumin (BSA) and antibodies for Listeria that were attached to the cantilever’s surfaces by physical adsorption; following which they were used to capture and detect ...

Laser irradiation apparatus, laser irradiation method and method for manufacturing semiconductor device

Abstract: It is an object of the present invention to provide a laser irradiation apparatus which can form a linear beam spot with a short optical path length, form a linear beam spot being long in a long-side direction, and reduce displacement of a condensing point at opposite ends in a direction of its line. In a laser irradiation apparatus having an optical system for shaping a laser beam emitted from a laser oscillator into a linear beam spot having a long-side direction and a short-side direction, the optical system includes a long-side direction condensing cylindrical lens disposed between a first short-side direction condensing cylindrical lens and a second short-side direction condensing cylindrical lens. Displacement of a position of a homogeneous plane is generated by the long-side direction condensing cylindrical lens so that a distance from the homogeneous plane to the second short-side direction condensing cylindrical lens is constant not depending on a field angle.

Laser-based method and system for memory link processing with picosecond lasers

Abstract: A laser-based method of removing a target link structure of a circuit fabricated on a substrate includes generating a pulsed laser output at a pre-determined wavelength less than an absorption edge of the substrate. The laser output includes at least one pulse having a pulse duration in the range of about 10 picoseconds to less than 1 nanosecond, the pulse duration being within a thermal laser processing range. The method also includes delivering and focusing the laser output onto the target link structure. The focused laser output has sufficient power density at a location within the target structure to reduce the reflectivity of the target structure and efficiently couple the focused laser output into the target structure to remove the link without damaging the substrate.

Demonstration and characterization of PZT thin-film sensors and actuators for meso- and micro-structures

Abstract: Recent development of next-generation medical devices, such as endoscopes and hearing aids, call for PZT (lead zirconate titanate oxide) thin-film sensors and actuators with thickness in the range of 1–30 μm to enhance actuation strength and sensor sensitivity. Currently, sol–gel derived PZT films often have thickness less than 0.2 μm per coating. Moreover, thermal stresses in the films limit the crack-free area to less than 1 mm2. This paper has four specific goals. The first goal is to demonstrate an improved sol–gel process using rapid thermal annealing and a diluted sealant coating. The resulting thickness can reach 2 μm in three coatings with a crack-free area as large as 5 mm ×5 mm . The second goal is to characterize piezoelectric properties of the fabricated PZT films experimentally. The resulting piezoelectric constant d33 is 120 pC/N and the dielectric constant ranges from 200 to 400. The third goal is to demonstrate the use of the PZT thin film as a calibrated sensor. The specimen is a silicon cantilever ( 30 mm ×7.5 mm ×0.4 mm ) with a PZT thin film ( 4 mm ×4 mm ×1 μm ). Moreover, a tiny shaker excites the cantilever at the fixed end, and a charge amplifier detects the charge accumulated in the PZT film. In the meantime, a laser vibrometer measures the deflection of the cantilever at three points along the PZT film, from which the strain is calculated using Euler–Bernoulli beam theory. Comparison of the strain and the charge amplifier voltage determines the calibration constant of the PZT thin-film sensor. The last goal is to demonstrate the use of the PZT thin film as a powerful actuator through active vibration control. In experiments, a tiny bulk PZT patch is first glued to the silicon cantilever. A function generator drives the bulk PZT simulating a source of disturbance exciting the silicon cantilever. In the meantime, a laser Doppler vibrometer (LDV) measures velocity of the cantilever tip. With a phase shifter as the controller, the LDV measurement is fed back to the PZT thin-film actuator to actively control the cantilever vibration. To evaluate the effectiveness of the active vibration control, a spectrum analyzer measures the frequency response functions (FRF) from the bulk PZT voltage to the LDV response. Experimental results show that the simple active vibration control scheme can reduce resonance amplitude of the first bending mode by 66%.

Closed-loop-controlled vortex shedding and vibration of a flexibly supported square cylinder under different schemes

Abstract: Different schemes were experimentally investigated of the closed-loop control of vortex shedding from a spring-supported square cylinder in cross flow. The control action was implemented through the perturbation of one cylinder surface, which was generated by three piezoelectric ceramic actuators, embedded underneath the surface and controlled by a proportional-integral-derivative controller. Three control schemes were investigated using different feedback signals, including the turbulent flow signal measured by a hot wire, flow-induced structural oscillation signal obtained by a laser vibrometer, and a combination of both signals. An investigation was conducted at the resonance condition, when the vortex-shedding frequency coincided with the natural frequency of the fluid-structure system. The flow and structural vibration were measured using particle image velocimetry, laser-induced fluorescence flow visualization, a laser Doppler anemometer, and a laser vibrometer. It was observed that the control scheme based on the feedback of both flow and structural oscillation led to the almost complete destruction of the Karman vortex street and a reduction in the structural vibration, vortex shedding strength, and drag coefficient by 82%, 65%, and 35%, respectively, outperforming by far an open-loop control as well as the other two closed-loop schemes.

New approach for the measurement of damping properties of materials using the Oberst beam

Abstract: The Oberst method is widely used for the measurement of the mechanical properties of viscoelastic or damping materials. The application of this method, as described in the ASTM E756 standard, gives good results as long as the experimental set-up does not interfere with the system under test. The main difficulty is to avoid adding damping and mass to the beam owing to the excitation and response measurement. In this paper, a method is proposed to skirt those problems. The classical cantilever Oberst beam is replaced by a double sized free-free beam excited in its center. The analysis is based on a frequency response function measured between the imposed velocity at the center (measured with an accelerometer) and an arbitrary point on the beam (measured with a laser vibrometer). The composite beam (base beam + material) properties are first extracted from the measurement by an optimization algorithm. Young’s modulus and structural damping coefficient of the material under test can be deduced using classical...

Structural Damage Assessment Using Vibration Modal Analysis

Abstract: Vibration techniques have been employed for detecting the presence and monitoring the progression of damage in structures Pinpointing the location of damage is a more complicated and elaborate task This paper presents modal analysis techniques for locating damage in a wooden wall structure by evaluating damage-sensitive parameters such as resonant pole shifts and mode shapes, residue and stiffness changes Artificial damage (simulating termite degradation) was created in one of the walls of a specially constructed room The wall was excited using an impact hammer and its frequency response measured using a laser vibrometer Resonant poles (plotted in the s-plane) were used for identifying modes that are sensitive to damage, since not all modes are equally affected by the presence of damage The damaged region was identified by visual comparison of the deformation mode shapes before and after damage The modal residue and stiffness changes were also quantified for a better representation of the damage lo

Comparison of stress field forming methods for vibro-acoustography

Abstract: Vibro-acoustography is a method that produces images of the acoustic response of a material to a localized harmonic motion generated by ultrasound radiation force. The low-frequency, oscillatory radiation force (e.g., 10 kHz) is produced by amplitude modulating a single ultrasound beam, or by interfering two beams of slightly different frequencies. Proper beam forming for the stress field of the probing ultrasound is very important because it determines the resolution of the imaging system. Three beam-forming geometries are studied: amplitude modulation, confocal, and x-focal. The amplitude of radiation force on a unit point target is calculated from the ultrasound energy density averaged over a short period of time. The profiles of radiation stress amplitude oil the focal plane and on the beam axis are derived. The theory is validated by experiments using a small sphere as a point target. A laser vibrometer is used to measure the velocity of the sphere, which is proportional to the radiation stress exerted on the target as the transducer is scanned over the focal plane or along the beam axis. The measured velocity profiles match the theory. The theory and experimental technique may be useful in future transducer design for vibro-acoustography.

Processing apparatus using laser beam

Abstract: A processing apparatus using a laser beam, which comprises holding means for holding a workpiece, and laser beam application means for irradiating the workpiece, held by the holding means, with a pulsed laser beam capable of passing through the workpiece, thereby deteriorating the workpiece. The laser beam application means includes pulsed laser beam oscillation means and transmitting/focusing means for transmitting and focusing the pulsed laser beam oscillated by the pulsed laser beam oscillation means. The transmitting/focusing means focuses the pulsed laser beam, with a time difference provided, to at least two focus points displaced in the optical axis direction.

Characterization and failure analysis of MEMS: high resolution optical investigation of small out-of-plane movements and fast vibrations

Abstract: A high resolution optical tool is required to investigate the mechanical behavior and failure modes of micro-electromechanical systems (MEMS). We report on the possibilities of a newly developed optical characterization tool for MEMS devices. Both slow movements and fast mechanical vibrations up to 15 MHz can be monitored. The instrument can perform an imaging operation for a complete image at once by employing laser TV holography, which is a large advantage over scanning laser Doppler vibrometers. For vibration measurements, this new, interference based instrument uses a beat frequency between object excitation and reference beam excitation. A normal CCD camera is used to obtain 3D images and movies of periodic mechanical motions of MEMS devices. Excitation can be by means of a PZT, or by using electronic excitation. We show that the instrument is a very useful tool for the characterization and failure analysis of MEMS devices.

Mass sensing with resonating ultra-thin silicon beams detected by a double-beam laser Doppler vibrometer

Abstract: This paper reports on mass sensing with 33 nm thick single-crystalline cantilevers by a double-beam laser Doppler vibrometer. The resonant frequency of an oscillating thin cantilever beam is very sensitive to a loaded mass. However, the drift of the resonance, due to gas adsorption and mechanical instability, limits the minimum detectable mass in general. Two cantilevers for sensing and its reference will compensate their influences. Two cantilevers were made to self-oscillate by electrostatic actuation at different resonant frequencies. A 10 pg sample (a particle of organosilicon monomer) was mounted at the end of one cantilever, and thermogravimetry of the sample using the two cantilevers was demonstrated. The cantilevers were heated up by a heater in vacuum, and the change in mass was detected from the change in resonant frequency. The exact temperature change can be estimated from the change in resonant frequency of one cantilever as a reference. The derivative of the frequency change, corresponding to desorbed mass, clearly shows a peak of mass desorption at about 270 °C.

Theoretical analysis and experimental measurement for resonant vibration of piezoceramic circular plates

Abstract: Based on the electroelastic theory for piezoelectric plates, the vibration characteristics of piezoceramic disks with free-boundary conditions are investigated in this work by theoretical analysis, numerical simulation, and experimental measurement. The resonance of thin piezoceramic disks is classified into three types of vibration modes: transverse, tangential, and radial extensional modes. All of these modes are investigated in detail. Two optical techniques, amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) and laser Doppler vibrometer (LDV), are used to validate the theoretical analysis. Because the clear fringe patterns are shown only at resonant frequencies, both the resonant frequencies and the corresponding mode shapes are obtained experimentally at the same time by the proposed AF-ESPI method. Good quality of the interferometric fringe patterns for both the transverse and extensional vibration mode shapes are demonstrated. The resonant frequencies of the piezoceramic disk also are measured by the conventional impedance analysis. Both theoretical and experimental results indicate that the transverse and tangential vibration modes cannot be measured by the impedance analysis, and only the resonant frequencies of extensional vibration modes can be obtained. Numerical calculations based on the finite element method also are performed, and the results are compared with the theoretical analysis and experimental measurements. It is shown that the finite element method (FEM) calculations and the experimental results agree fairly well for the resonant frequencies and mode shapes. The resonant frequencies and mode shapes predicted by theoretical analysis and calculated by finite element method are in good agreement, and the difference of resonant frequencies for both results with the thickness-to-diameter (h/D) ratios, ranging from 0.01 to 0.1, are presented.

Focusing an optical beam to two foci

Abstract: A Plate polarising beam splitter 22 splits an incident laser beam 21 to form a first laser beam 24 and a second laser beam 25. The first laser beam is optically modified using an arcuate reflector 23 so that the first laser beam has a different divergence or convergence from that of the second laser beam. The first laser beam 24 is focussed at a first focus 27 on an optical axis of a focussing lens 26 and the second laser beam is focussed at a second focus 28 on the optical axis for machining a workpiece. The apparatus is suitable for machining with the laser beams steered by a galvanometer scanner.

Nonperturbing measurements of spatially distributed underwater acoustic fields using a scanning laser Doppler vibrometer

Abstract: Localized changes in the density of water induced by the presence of an acoustic field cause perturbations in the localized refractive index. This relationship has given rise to a number of nonperturbing optical metrology techniques for recording measurement parameters from underwater acoustic fields. A method that has been recently developed involves the use of a Laser Doppler Vibrometer (LDV) targeted at a fixed, nonvibrating, plate through an underwater acoustic field. Measurements of the rate of change of optical pathlength along a line section enable the identification of the temporal and frequency characteristics of the acoustic wave front. This approach has been extended through the use of a scanning LDV, which facilitates the measurement of a range of spatially distributed parameters. A mathematical model is presented that relates the distribution of pressure amplitude and phase in a planar wave front with the rate of change of optical pathlength measured by the LDV along a specifically orientated laser line section. Measurements of a 1 MHz acoustic tone burst generated by a focused transducer are described and the results presented. Graphical depictions of the acoustic power and phase distribution recorded by the LDV are shown, together with images representing time history during the acoustic wave propagation.

Monitoring of a laser source with front and rear output photodetectors to determine frontal laser power and power changes over laser lifetime

Abstract: A power monitoring and correction to a desired power level of a laser or group of lasers utilizes two photodetectors which are employed to accurately determine the amount of output power from the front end or “customer” end of a laser or a plurality of such lasers. During power detection, which may be accomplished intermittently or continuously, the laser is modulated with a tone of low frequency modulation. One photodetector at the rear of the laser is employed to detect the DC value of the frequency tone, i.e., a value or number representative of the AC peak-to-peak swing, amplitude or modulation depth of the tone. Also, the rear photodetector may be employed to determine the optical modulation index (OMI). In either case, these values may be employed in a closed loop feedback system to adjust or otherwise calibrate the value of the low tone frequency relative to the total desired bias current applied to the laser. A front photodetector is employed to receive a portion of the total output of the laser, or of each laser, and the average output power of the laser, or of each laser, is determined from already knowing the optical modulation index (OMI) via the rear photodetector. Thus, by measuring and/or calibrating the laser OMI with the use of a rear photodetector, the average output power from the front end output can be unambiguously determined from detection of the AC peak-to-peak swing or amplitude of the low frequency tone received via the front photodetector.

Experimental demonstration of remote, passive acousto-optic sensing

Abstract: Passively detecting underwater sound from the air can allow aircraft and surface vessels to monitor the underwater acoustic environment. Experimental research into an optical hydrophone is being conducted for remote, aerial detection of underwater sound. A laser beam is directed onto the water surface to measure the velocity of the vibrations occurring as the underwater acoustic signal reaches the water surface. The acoustically generated surface vibrations modulate the phase of the laser beam. Sound detection occurs when the laser is reflected back towards the sensor. Therefore, laser alignment on the specularly reflecting water surface is critical. As the water surface moves, the laser beam is reflected away from the photodetector and no signal is obtained. One option to mitigate this problem is to continually steer the laser onto a spot on the water surface that provides a direct back-reflection. Results are presented from a laboratory test that investigates the feasibility of the acousto-optic sensor detection on hydrostatic and hydrodynamic surfaces using a laser Doppler vibrometer in combination with a laser-based, surface normal glint tracker for remotely detecting underwater sound. This paper outlines the acousto-optic sensor and tracker concepts and presents experimental results comparing sensor operation under various sea surface conditions.

Laser vibrometry meets laser speckle

Abstract: This paper begins with a review of the fundamental mechanism by which speckle noise is generated in Laser Vibrometry before describing a new numerical simulation of speckle behavior for prediction of noise level in a real measurement. The simulation data provides real insight into the phase and amplitude modulation of the Doppler signal as a result of speckle changes. The paper also includes experimental data looking at the influence of speckle noise in measurements on rotors with a selection of surface treatments and in scanning and tracking configurations.

Piezoelectric transducer surface vibration characterization using acoustic holography and laser vibrometry

Abstract: The acoustic pressure radiated by a piezoelectric source can be predicted based on the normal velocity distribution along the transducer surface. However, up to now, there have been no reliable direct methods of surface vibration measurement in liquids. The transducer vibration is frequently considered as being uniform (thickness mode), which may be incorrect due to the transducer structure (e.g., phased arrays) or due to excitation of Lamb waves in the piezoelectric plate in addition to the thickness vibration mode. A holographic method has been developed and experimentally used that enables reconstruction of the radiator vibration pattern. The method includes: measurement of wave amplitude and phase at different points of a plane and perpendicular to the acoustic axis at some distance from the source; theoretical time reversal of the waveform in each gridpoint; backpropagation of the field to the source using the Rayleigh integral. Vibration of piezoelectric transducers was also studied using a laser vibrometer. A special experimental and theoretical study was performed in order to show that this well-developed method gives wrong results when the transducer is in contact with the liquid, because of strong acousto-optic interaction in a condensed media. It is shown that, although the acoustic holographic approach has limited spatial resolution (of the order of a wavelength), it allows fairly exact prediction of the radiated field pattern.

High-frequency, silicon-based ultrasonic nozzles using multiple Fourier horns

Abstract: This paper presents the design, simulation, and characterization of microfabricated 0.5 MHz, silicon-based, ultrasonic nozzles. Each nozzle is made of a piezoelectric drive section and a silicon resonator consisting of multiple Fourier horns, each with half wavelength design and twice amplitude magnification. Results of finite element three-dimensional (3-D) simulation using a commercial program predicted existence of one resonant frequency of pure longitudinal vibration. Both impedance analysis and measurement of longitudinal vibration confirmed the simulation results with one pure longitudinal vibration mode at the resonant frequency in excellent agreement with the design value. Furthermore, at the resonant frequency, the measured longitudinal vibration amplitude sit the nozzle tip increases as the number of Fourier horns (n) increases in good agreement with the theoretical values of 2/sup n/. Using this design, very high vibration amplitude gain at the nozzle tip can be achieved with no reduction in the tip cross-sectional area for contact of liquid to be atomized. Therefore, the required electric drive power should be drastically reduced, decreasing the likelihood of transducer failure in ultrasonic atomization.