Laser Doppler Interferometer Research Articles

Laser Doppler Interferometry as a receiver of the ultrasonic waves: An experimental study on Gosford sandstone

The change of ultrasonic velocities and displacement on the core scale for the isotropic Gosford sandstone was studied using the Laser Doppler Interferometry (LDI) method. We observed that the P- and S-wave velocities and the corresponding surface displacement of the sample consist of multiple wavelets at the core scale. Ultrasonic wave velocity experiments usually measure the average wavelet recorded by two transducers (source and receiver). The recorded travel velocity varies as a function of the material’s elastic properties; therefore, knowing the components of the averaged wavelet can be used to understand such behaviour in detail. LDI had been used to measure particle displacement for decades however its accuracy to measure precise ultrasonic velocity has not been studied in details. We designed an experiment to study the averaging wavelets by its components using LDI on isotropic Gosford sandstone to study the displacement pattern and the accuracy of the velocity recorded by LDI in porous media. By changing the monitoring system from a receiving transducer (which normally are 5 to 20 mm in diameter) to a laser beam receiver (diameter of about 0.2 mm) on the same surface area enables us to scan the behaviour of transmitted wave at much higher spatial resolution at different zones on the surface of the sample. A Laser Doppler Interferometer, as a receiver, benefits this experimental study over piezoelectric transducers because, (a) A much smaller area of measurement than the wavelength is covered, (b) it records the full particle-velocity wave field and displacement vector, and (c) strain in ultrasonic wave can be directly measured. This study plotted the displacement field within the boundaries of the source transducer and outer orbit of the transducer zone to show the effect of energy distribution when the wave passed through the porous media. We compared the displacement rate for the sample on the nanometre scale and observed that the averaging of the recorded wavelets by LDI show a resemblance to the waveform recorded by a pair of conventional transducers in terms of the velocity and waveform features. This verifies the accuracy of the component’s wavelets and validity of such an experimental approach for future studies of ultrasonic measurements (velocity and displacement) at grain scale for porous media by LDI.

Characterization of Ultrasonic Transducer Response Using Laser Doppler Interferometer in kHz-Range for Civil Engineering Applications

Characterization of Ultrasonic Transducer Response Using Laser Doppler Interferometer in kHz-Range for Civil Engineering Applications

Lateral resolution limit of laser Doppler vibrometer microscopes for the measurement of surface acoustic waves

The lateral or transverse resolution of single-point interferometers for vibration measurement is especially critical for microelectromechanical systems (MEMS) vibrating up to the gigahertz range. In this regime, the acoustic wavelengths are typically in the range of the size of the laser focus. Thus, a successful vibration measurement requires distinct knowledge about the lateral resolution limit and its dependencies with instrumentation parameters. In this paper, we derive an analytic approximation formula, which allows for estimation of the systematic measurement deviation of the vibration amplitude and, thus, a definition of the lateral resolution limit of single-point interferometers for vibration measurement. Further, a compensation and an optimum numerical aperture are proposed the reduce the measurement deviation. For this, the model includes a laser-interferometer microscope of Mach-Zehnder type with Gaussian laser beams considering the Gouy effect and wavefront curvature. As a measurement scenario, an unidirectional surface acoustic wave (SAW) is regarded. The theoretic findings have been validated in the experiment with a representative vibration measurement on a SAW filter at 433,{mathrm {MHz}} with our heterodyne laser-Doppler interferometer with offset-locked semiconductor lasers. The provided formulas help instrument designers and users to choose suitable instrument parameters, especially the numerical aperture of the utilized microscope objective.

A compact photoelectric measurement system for harmonic vibrating table

A compact measurement system for harmonic vibration based on photoelectric array is proposed. Cooperating with a planar reflective mirror, which is fixed on the measured vibrating table, the photoelectric array outputs a vibration-sensitive signal. Theoretical model and simulation are discussed for the optical sensor. A frequency-tracking algorithm is proposed to realize effective measurement of vibration amplitude and frequency. Experiments are carried out on a precision vibrating table at different vibrating frequencies and different drive voltages, and reasonable results are achieved. Finally, taking the vibration with maximum amplitude as an example, the measurement results by laser Doppler interferometer are a frequency of 10 Hz and an amplitude of 72.25 μm, the measurement results by the optical sensor are a frequency of 10 Hz and an amplitude of 72.05 μm. Theoretical and experimental results show the feasibility of this system in harmonic vibration parameter measurements.

The Structure Design and Analysis of a Parallel Kinematic Mechanism Based on Abbe’s Principle

The purpose of this study is to design and analysis of a parallel kinematic mechanism based on Abbe’s principle can be applied to the 3D-coordinate measuring machine. In this study is the design and analysis of the parallel kinematic mechanism, which includes the mechanism design of linear drive rod mechanism and displacement sensing position coaxial, and the intersection of the three linear drive rod mechanisms are located at the contact probe. Therefore, the design of this study improves the displacement of the linear drive rod and Abbe error resulted from the angle variation of the displacement sensor. Furthermore, the mechanism performance has been verified experimentally. Through precision tests of the machine by a laser Doppler interferometer, the linear drive rod mechanism positioning precisions are within 1μm.

Shock Wave Properties of Inert and Chemically Active Porous Media

Shock wave properties of porous specimens made on the basis of matrices composed of inert and chemically active media (silicon rubber and emulsion, which is an aqueous solution of ammonium nitrate with mineral oil and emulsifier) are studied. The porosity of the specimens is generated by using a filler composed of glass microspheres. The wave velocity profiles are measured by a VISAR laser Doppler interferometer. It is shown that the shock compressibility of porous silicon rubber at pressures below 0.1 GPa displays an anomalous behavior, resulting in smearing of the compression pulse front propagating over the specimen. In the emulsion matrices without microspheres, there are no noticeable chemical transformations up to the pressure of 15 GPa. Addition of microspheres drastically decreases the threshold of chemical reaction initiation and leads to the formation of a steady detonation wave.

Research note: the effect of strain amplitude produced by ultrasonic waves on its velocity

ABSTRACTThe effect of the amplitude of ultrasonic waves propagating through a sample is not often taken into account in laboratory experiments. However, ultrasonic waves can produce relatively large strain inside the sample, and thus change the properties of the sample. To investigate the effect of strain amplitude on the P‐wave velocity, a series of ultrasonic wave propagation experiments were carried out on three different media. All measurements were performed at 1 MHz central frequency and at the strain levels inside propagating waves of ∼3.0 × 10−6 to 6.0 × 10−5 without applying confining pressure to the sample. Strains in the waves were measured by a laser Doppler interferometer upon wave arrival on a free surface of the sample. The ultrasonic velocities were measured by a pair of P‐wave transducers located at the same measuring point as the laser beam of the LDI. The effect of strain on P‐wave velocity varied for different material. The P‐wave velocity was calculated using both a first arrival and a first maximum peak at different applied voltage. The P‐wave velocity remained unchanged for a pure elastic medium (aluminium); however, the velocity increased continuously with the increasing of the strain for polymethylmethacrylate and Gosford sandstone. For Gosford sandstone, velocity increases up to 0.8% with strain increase from 7.0 × 10−6 to 2.0 × 10−5. This effect of velocity increase with the strain induced by an ultrasonic wave can be explained by the in‐elasticity of both the polymethylmethacrylate and Gosford sandstone samples.

Optimal modification of tooth flank form error considering measurement and compensation of cutter geometric errors for spiral bevel and hypoid gears

In design and manufacturing for the spiral bevel and hypoid gear, the cutter geometric errors (CGEs) is one of main factors affecting tooth flan flank form error. To get an accurate and effective modification of tooth flank form error, a novel optimization and operation approach is proposed by correlating with measurement and compensation of CGEs. Firstly, an accurate modification model with optimal machine settings is developed as a nonlinear least square problem. Where, a small number of machine settings are selected as unknown optimal design variable by sensitivity analysis method. Then, CGEs are defined and their influences on the tooth flank form error are investigated for synthesis and analysis of the accurate higher-order modification. Finally, the optimal modification with small number of machine settings is performed based on measurement of the Doppler Laser interferometer MCV2002 following ISO 230-2(1997) standard and numerical control (NC) compensation of CGEs. In additional to the optimal design parameters is set to improve computational efficiency, the Levenberg–Marquardat (L–M) algorithm with trust-region strategy is applied to solve for the new machine settings with modification variations. A numerical application to a real case is designed to identify the validity of the proposed methodology.

Torsional Piezoelectric Strain in Monocrystalline Paratellurite

Crystals of the 422 symmetry class exhibit interesting piezoelectric behavior, as their piezoelectric tensor has only a single non-zero coefficient, d123 = d14: such unique behavior has the potential to enable novel gyroscopic sensors and high-precision torsional MEMS actuators. Although alpha-phase tellurium dioxide (paratellurite, alpha-TeO2) is one of the few materials belonging to this symmetry class, this material has been primarily studied for its interesting optical properties. Indeed, a large uncertainty in the piezoelectric coefficient of paratellurite exists, with d123 measurements on single crystals ranging from 8.13 pC/N to 14.58 pC/N; this large uncertainty results from the difficulty in using conventional piezoelectric characterization techniques on paratellurite, and impedes adoption of this extraordinary material. The present study characterizes the piezoelectric behavior of this interesting material using two independent techniques, (1) a three dimensional laser Doppler interferometer system, and (2) electrochemical impedance spectroscopy (EIS). The experimental results are analyzed using numerical simulations for dynamic excitation conditions over a frequency range of 20 Hz to 200 kHz.

Laser Doppler velocimetry using a modified computer mouse

A computer mouse has been modified for use as a low-cost laser Doppler interferometer and used to measure the two-component fluid velocity of a flowing soap film. The mouse sensor contains two vertical cavity surface emitting lasers, photodiodes, and signal processing hardware integrated into a single package, approximately 1 cm2 in size, and interfaces to a host computer via a standard USB port. Using the principle of self-mixing interferometry, whereby laser light re-enters the laser cavity after being scattered from a moving target, the Doppler shift and velocity of scatterers dispersed in the flow are measured. Observations of the boundary layer in a turbulent soap film channel flow demonstrate the capabilities of the sensor.

LEAD-FREE BNT PIEZOELECTRIC THIN FILMS BY SOL-GEL METHOD.

The objective of this work is to synthesize lead-free piezoelectric thin films by the Sol-Gel method:bismuth sodium titanate (Bi0.5Na0.5TiO3 or BNT).BNT films were annealed with the rapid thermal process (RTP).The film treated at 700°C is dense and well crystallized in the perovskite phase. The first results of electricalcharacterizations showed promising dielectric, ferroelectric and piezoelectric performance. At 12 kHz, thedielectric constant and losses are 430 and 0.07, respectively. Ferroelectric hysteresis measurements indicated aremanent polarization of 10μC/cm2, associated with a coercive field of 70 kV/cm. The piezoelectric properties ofBNT films were studied with a laser Doppler interferometer: a piezoelectric coefficient (d33effmax) of 42 pm/V was measured.

Joint inversion of P-, and S-wave travel times for characterisation of anisotropic materials using laser Doppler interferometry measurements

SUMMARY We used laser Doppler interferometer for measuring the displacement on the sample surface. These measurements allow us to clearly separate different wave types, whose picked travel times are used for estimation of VTI anisotropy parameters. One of the observations in this study is the very strong amplitude of critically refracted SP wave at the measurement surface. We confirmed the characteristics of this wave by numerical modelling. We used this wave to improve the estimates of the anisotropy. The observed strong amplitude of this wave can have strong implications for the interpretation of ultrasonic

Laser Doppler Interferometry (LDI) to obtain full stiffness tensor: A case study on a deformation zone in Sweden

Estimation of elastic anisotropy, which is usually caused by rock fabrics and mineral orientations, has an important role in exploration seismology and a better understanding of crustal seismic reflections. If not properly taken care of during data processing steps, it leads to wrong interpretation and/or distorted seismic image. In this work, a state-of-the-art under the development Laser Doppler Interferometer (LDI) device is used to measure phase velocities on the surface of rock samples from a major poly-phase crustal scale deformation zone (Osterbybruk Deformation Zone) in the Bergslagen region of eastern Sweden. Then, a general inversion code is deployed to invert the measured phase velocities to obtain full elastic stiffness tensors of two samples from the deformation zone. At the end, results are used to correct for the anisotropy effects using three dimensionless Tsvankin's parameters and a non-hyperbolic moveout equation. The resulting stacked section shows partial reflection improvement of the deformation zone compared with the traditional isotropic processing approach. This illustrates that rock anisotropy contributes to the generation of the reflections from the deformation zones in the study area although they do not show significant density contrast with their surrounding rocks.

Review on Acoustic Transducers for Resonant Ultrasound Spectroscopy

Determination of elastic constants using resonant ultrasound spectroscopy requires transducers that can measure resonance frequencies accurately and identify the vibrational mode of each resonance frequency. We developed three transducers, namely an electromagnetic acoustic transducer, a tripod piezoelectric transducer coupled with a laser Doppler interferometer, and an antenna transmission transducer, for use with various materials and in different measurement circumstances. Their capability in resonant ultrasound spectroscopy and their applications are described.

J0430104 プラズマ溶射CoNiCrAlYの内部摩擦の組織依存性([J043-01]厚膜形成技術と厚膜の機械特性評価(1),機械材料・材料加工部門)

Microstructure dependence of elastic modulus and internal friction of APSed CoNiCrAlY was investigated using resonance ultrasound spectroscopy. The freestanding coatings with different spraying powder sizes are prepared. Further, the annealed coatings were prepared. The specimens were oscillated using a transducer, and the resonance frequencies and modes were determined using a laser Doppler interferometer. As a result, it was found internal friction was decreased and Young's modulus was increased by thermal treatment because of sintering. On the other hand, the internal friction did not change depending on the spraying powder size. The Young's modulus was increased with a decrease of spraying powder size because of high oxidization.

Dynamic force calibration by impact excitation

Introduce a method of dynamic force calibration by impact excitation. An analysis of the 200kN standard dynamic force calibration equipment at NIM is presented. The heavy hammer and the force transducer under test are brought to collision, and the impact force is measured by laser-Doppler interferometer. Traceability of force is realized by the determination of mass and acceleration. Two experiments were introduced and a typical example of impact process was performed.

Subsonic jet pressure fluctuation characterization by tomographic laser interferometry

This paper describes the application of a nonconventional experimental technique based on optical interferometry for the characterization of aeroacoustic sources. The specific test case studied is a turbulent subsonic jet. Traditional experimental methods exploited for the measurement of aerodynamic velocity fields are laser Doppler anemometer and particle image velocimetry which have an important drawback due to the fact that they can measure only if the flow is seeded with tracer particles. The technique proposed, by exploiting a laser Doppler interferometer and a tomographic algorithm for 3D field reconstruction, overcomes the problem of the flow seeding since it allows directly measuring the flow pressure fluctuation due to the flow turbulence. A laser Doppler interferometer indeed is sensitive to the density oscillation within the medium traversed by the laser beam even though it integrates the density oscillation along the entire path traveled by the laser. Consequently, the 3D distribution of the flow density fluctuation can be recovered only by exploiting a tomographic reconstruction algorithm applied to several projections. Finally, the flow pressure fluctuation can be inferred from the flow density measured, which comprehends both the aerodynamic pressure related to the turbulence and the sound pressure due to the propagation of the acoustic waves into the far field. In relation to the test case studied in this paper, e.g., the turbulent subsonic jet, the method allows a complete aeroacoustic characterization of the flow field since it measures both the aerodynamic “cause” of the noise, such as the vortex shedding, and the acoustic “effect” of it, i.e., the sound propagation in the 3D space. The performances and the uncertainty have been evaluated and discussed, and the technique has been experimentally validated.

Microsecond ramp compression of a metallic liner driven by a 5 MA current on the SPHINX machine using a dynamic load current multiplier pulse shaping

SPHINX is a 6 MA, 1-μs Linear Transformer Driver (LTD) operated by the CEA Gramat (France) and primarily used for imploding Z-pinch loads for radiation effects studies. Among the options that are currently being evaluated to improve the generator performances are an upgrade to a 20 MA, 1-μs LTD machine and various power amplification schemes, including a compact Dynamic Load Current Multiplier (DLCM). A method for performing magnetic ramp compression experiments, without modifying the generator operation scheme, was developed using the DLCM to shape the initial current pulse in order to obtain the desired load current profile. In this paper, we discuss the overall configuration that was selected for these experiments, including the choice of a coaxial cylindrical geometry for the load and its return current electrode. We present both 3-D Magneto-hydrodynamic and 1D Lagrangian hydrodynamic simulations which helped guide the design of the experimental configuration. Initial results obtained over a set of experiments on an aluminium cylindrical liner, ramp-compressed to a peak pressure of 23 GPa, are presented and analyzed. Details of the electrical and laser Doppler interferometer setups used to monitor and diagnose the ramp compression experiments are provided. In particular, the configuration used to field both homodyne and heterodyne velocimetry diagnostics in the reduced access available within the liner's interior is described. Current profiles measured at various critical locations across the system, particularly the load current, enabled a comprehensive tracking of the current circulation and demonstrate adequate pulse shaping by the DLCM. The liner inner free surface velocity measurements obtained from the heterodyne velocimeter agree with the hydrocode results obtained using the measured load current as the input. An extensive hydrodynamic analysis is carried out to examine information such as pressure and particle velocity history profiles or magnetic diffusion across the liner. The potential of the technique in terms of applications and achievable ramp pressure levels lies in the prospects for improving the DLCM efficiency through the use of a closing switch (currently under development), reducing the load dimensions and optimizing the diagnostics.

Non linear dynamics of mechanosensory flight control in flies

In most animals, rhythmic motion is governed by central pattern generators (CPGs) - neural circuits that generate periodic patterned output. Sensory input to the CPG is not necessary to maintain the periodic neural activity, but is known to strongly influence it. For example, proprioceptive afferent input may entrain the neural CPG rhythm to the mechanical resonance frequency of a limb [1]. CPGs have been shown to govern the locomotor rhythms in vertebrates as well as in insects. A CPG governing the flight rhythm, however, has not been identified in flies, which are known for their remarkable flight maneuverability. In flies, the wingbeat rhythm is generated myogenically by stretch-activated power muscles and hence is not directly controlled by neural input. It is therefore unclear if the insights gained for proprioceptive feedback in CPG-based motor systems [1] likewise apply to flight control in flies. In our study, we investigated if and how proprioceptive feedback influences the rhythm of the myogenic wing beat oscillator. We concentrated on mechanosensory input from the halteres - specialized „gyroscopic sensory organs of flies. The halteres are known to activate the motor neurons of miniscule steering muscles, which in turn modulate the motion of the wings. In our experiments [2], tethered flying fruit flies (Drosophila melanogaster) were vibrated by a piezoelectric actuator to stimulate the haltere mechanosensory pathways. We used a laser Doppler interferometer to measure the vibrations of the tether resulting from the superposition of the piezo-delivered stimulus and the fly's wing beat. We determined the phase relationship between the wing motion and the mechanical stimulus in each wing stroke and applied an automated synchrogram analysis [3] to detect entrainment and higher-order synchronization. The flies synchronized with the stimulus for specific ranges of stimulus amplitude and frequency, revealing the characteristic Arnol'd tongues of a forced limit cycle oscillator. Our analysis shows that the steering muscles (activated by proprioceptive input) act as a mechanical forcing of the central power muscle oscillator. We propose that the mechanical forcing of a myogenic limit cycle oscillator permits flies to avoid the comparatively slow control based on a neural central pattern generator. In the entrainment study described above, flies were attached to tethers with high resonance frequency and damping coefficient. While experimenting with tethers of varying mechanical properties, however, we observed that the fly's behavior was significantly influenced by the properties of the tether. To systematically explore this influence for a given fly, we altered the tether's resonance frequency by clamping the tether at a different point in each distinct flight test. In these experiments, no piezo stimulus was applied. Yet, when the tether resonance frequency was comparable to the wing beat frequency, the forces from the fly lead to large cumulative motion of the tether and activation of the haltere mechanosensors. The fly therefore received delayed feedback dependent on its previous activity. This lead to a variety of observed dynamical regimes, including the locking of the wing beat frequency to the tether resonance frequency when their initial difference was sufficiently small (similar to limb entrainment in [1]). We were able to reproduce most of the observed dynamical features in a simplified mathematical model of two mutually coupled oscillators: a phase-reduced nonlinear oscillator representing the wing beat and a linear oscillator representing the tether dynamics.

High-speed impact test using an inertial mass and an optical interferometer

A high-speed impact testing method for evaluating mechanical properties of materials is proposed using an inertial mass and a dual beat-frequencies laser Doppler interferometer (DB-LDI). In this method, an inertial mass levitated using an aerostatic linear bearing is made to collide with the material being tested at a high initial velocity. During the collision, the velocity of the mass, which is even higher than the critical velocity (±0.56 m/s) defined by the frequency difference of the Zeeman laser, is accurately measured using the DB-LDI. The position, acceleration, and impact force of the mass are calculated from the measured velocity. Using the proposed method, the mechanical properties of a visco-elastic material under a high-speed impact loading condition can be accurately evaluated.