Laser Doppler Interferometer Research Articles

Characterisation of steels with microdefects using a laser interferometry technique

Low microdefect level is essential for ensuring the performance of material. Early detection of microdefect areas allows the estimation of the residual life of constructions and prevents catastrophic failures of components. Ultrasound laser interferometry provides a unique inspection method that enables the study and visualisation of the processes of elastic wave interaction with microdefects embedded in solids, in a non-contact way. In the present paper, the distribution of acoustic fields on the surface of the metal disks obtained was investigated with the use of a laser Doppler interferometer. Specimens containing micropores, cut from the bent section of a steam pipeline that had been subjected to long-term operation at a heat-electric generating station, were used for the studies. Various methods of data digital processing have been applied to trace changes in ultrasound beam energy distribution and geometrical parameters of ultrasound beam projection in case of the presence of microdefects.

Magnetic Phase Transition and Elastic Properties of α-Mn at Low Temperature

Elastic and anelastic properties of polycryatalline α-Mn at low temperature have been studied using electromagnetic acoustic resonance (EMAR) and resonance ultrasound spectroscopy coupled with a laser Doppler interferometer (RUS/Laser). α-Mn showed low Poisson's ratio both in the paramagnetic state at 290 K and in the anti-ferromagnetic state at 4 K. The acoustic Debye temperature was 479 K, showing good consistency with the previous work. Around the magnetic transition temperature (TN=98 K), remarkable changes in Poisson's ratio and internal friction are identified, indicating strong magnetic acoustic interaction at the transition temperature.

Atomically resolved dynamic force microscopy operating at 4.7MHz

We demonstrate atomically resolved frequency modulation dynamic force microscopy operating at 4.7MHz using the third flexural mode of a silicon cantilever. A high spring constant due to the higher mode realized stable imaging with an amplitude of 2Å, which was calculated to be a favorable value for high-resolution imaging. Although excessive stiffness decreases the sensitivity of the detection, a stable imaging was realized with a low noise heterodyne laser Doppler interferometer and a narrow bandwidth feedback circuit. An atomically resolved constant frequency shift images of the Si(111)-7×7 were obtained with the exposed and terminated dangling bonds at the tip apex.

Extraction of Signals from White and Colored Noise Using the Discrete Wavelet Transform

Methods based on wavelet analysis are used to study longitudinal elastic waves propagating in aluminum single crystals in the [111] and [001] directions at frequencies of 5 and 10 MHz. Results of the wavelet filtering of responses of the laser Doppler interferometer to these acoustic signals are reported. The efficiency of filtering the time dependencies of the interferometer response in the presence of white and colored noise is studied. Recommendations concerning the choice of the filtering parameters are given.

High-pressure phase transition of mullite under shock compression

Hugoniot measurements have been performed on mullite polycrystals in the pressure range up to 80GPa by using a two-stage light-gas gun and a Doppler laser interferometer. The Hugoniot elastic limit is determined to be 16.1±2.2GPa. The Hugoniot data show that the phase transition occurs at 30.4±3.6GPa. Comparison of the Hugoniot data with calculated theoretical Hugoniots suggests that the high-pressure phase transition of mullite is its disproportionation to corundum and stishovite. The mixed phase region is between 30 and 70GPa. It is indicated that this phase transition is very sluggish.

The effect of three-wave interference in laser Doppler vibrometry

In a laser Doppler interferometer, besides the probe and reference beams, a third coherent light wave, caused by spurious reflection, may hit the detector. Interference effects between regular and unwanted waves, which are dependent on the actual intensity ratios, contribute to the generation of the electrical output signal. A mathematical analysis predicts the appearance of ripple and spikes riding on the demodulated signal due to distorted modulation of the Doppler signal. These effects are verified by experiments, demonstrating the dependence of distortions on given optical conditions.

A gap capacitance method for slider flying height measurement in near-field optical disk drives

In order to overcome the diffraction limit of conventional optical disk drives, and substantially increase data storage capacity and density, near-field optical disk drives remain to be realized. The slider of a flying pickup head in a near-field optical disk drive has to fly at a stable spacing above the disk surface. To sense the slider flying height, a gap capacitance method is developed in this study to measure capacitance variation between the pickup head and disk surface. The capacitance varying with the flying height is modulated by a Colpitts oscillator. Subsequent demodulation accounts for height variation of the flying pickup head. Measurement results of this method are verified by using a laser Doppler interferometer.

Human middle ear transfer function measured by double laser interferometry system.

Simultaneous measurements of vibrations on the stapes footplate, incudostapedial (IS) joint, and tympanic membrane (TM) can be made in both normal and drained cochleae, and the stapes displacement transfer function (S-DTF) and TM displacement transfer function (TM-DTF) are derived. A single laser Doppler interferometer previously has been used for measuring movement of the stapes or TM in temporal bones. However, there may be a limitation to optimally describing acoustic-mechanical transmission when the interferometer and temporal bone are moved frequently during experimental recordings. Simultaneous measurements of vibrations of the TM and stapes footplate, or TM and IS joint may reveal different acoustic-mechanical characteristics of the middle ear. Dual laser interferometers simultaneously measured vibrations of the TM, IS joint, and stapes in 10 temporal bones with both intact and drained cochleae. From these measurements, the middle ear transfer function was expressed as the S-DTF, TM-DTF, and displacement transmission ratio (DTR). Simultaneous displacements of the TM, IS joint, and stapes footplate induced by sound pressure in the ear canal were recorded in both amplitude and phase. The middle ear transfer functions in terms of displacement ratio confirmed published single interferometer data but provided new information from drained cochlea. Stapes and TM displacement transfer functions were determined using dual interferometry, provided accurate amplitude and phase relationships from stapes footplate, IS joint, and TM, with new data from drained and normal cochlea.

Resonance Ultrasound Spectroscopy for Measuring Elastic Constants of Thin Films

We show an advanced technique for measuring elastic constants Cij of thin films deposited on substrates. Thin films often show anisotropy between the in-plane and out-of-plane directions because of their columnar structure, residual stress, texture, and incohesive bond. Then, thin films show macroscopically transverse isotropy and have five independent Cij. All the film Cij affect free-vibration resonance frequencies of the film/substrate layered specimen. Therefore, measuring the resonance frequencies permits us to determine the thin-film Cij with the other known parameters. In order to yield reliable Cij of thin films, we have to measure the resonance frequencies with sufficient accuracy and identify vibration modes of the measured resonance frequencies. We overcome these problems by developing a tripod and using a laser-Doppler interferometer, respectively. We applied the present technique to a copper thin film. Measured Cij are smaller than those of bulk and show elastic anisotropy. We attribute these features to the incohesive bond regions.

712 共振/レーザー法による薄膜の弾性定数測定と内部組織のマイクロメカニックス評価(GS-3 超音波計測)

We originally develop a measurement method for determining anisotropic elastic constants of thin films on substrates. It uses free-vibration resonance frequencies of a film/substrate rectangular parallelepiped specimen, which depend on dimensions, mass density and elastic constants of the film and substrate; film's elastic constants are inversely determined from the resonance frequencies. We measure the resonance frequencies with a high accuracy using a piezoelectric tripod transducer, consisting of needle-type transducers for generation and detection of vibration. Detected resonance peaks are identified by measuring the displacement distribution on the vibrating surface using laser-Doppler interferometer. We applied this method to copper and CVD diamond thin films. Their elastic constants show elastic anisotropy between the in-plane and out-of-plane directions. We attribute it to incohesive bonds at grain boundaries. This view is supported by micromechanics calculations.

Complete mode identification for resonance ultrasound spectroscopy

This study is devoted to deducing exact elastic constants of an anisotropic solid material without using any advance information on the elastic constants by incorporating a displacement-distribution measurement into resonant ultrasound spectroscopy (RUS). The usual RUS method measures free-vibration resonance frequencies of a solid and compares them with calculations to find the most suitable set of elastic constants by an inverse calculation. This comparison requires mode identification for the measured resonance frequencies, which has been difficult and never been free from ambiguity. This study then adopts a laser-Doppler interferometer to measure the displacement-distribution patterns on a surface of the vibrating specimen mounted on pinducers; comparison of the measured displacement distributions with those computed permits us to correctly identify the measured resonance frequencies, leading to unmistakable determination of elastic constants. Because the displacement patterns are hardly affected by the elastic constants, an exact answer is surely obtained even when unreasonable elastic constants are used as initial guesses at the beginning of the inverse calculation. The usefulness of the present technique is demonstrated with an aluminum alloy and a langasite crystal.

Investigating Distributed Sensor/Point Actuator Testbeds by Using Differential Laser Doppler Interferometer

The design principles, optical cone gurations, and capabilities of a newly developed advanced vibrometer/interferometer device called AVID are presented. The fundamental principles of this metrology instrument that enables it to have a dc to 20-MHz bandwidth and nanometer resolution are also detailed. The applicability of using laminated one-dimensional piezoelectric plates as testbeds to study some of the fundamental characteristics of piezoelectric actuators and sensors is also examined. Taking advantages of the linear and angular displacement/velocity measurement modes of the vibrometer/interferometer, the performance of distributed piezoelectric sensors, which can measure bending angle and bending displacement at any point of the testbed, is characterized. In addition, the corresponding piezoelectric actuator that can exert bending moment on the testbed is also evaluated. The hysteresis effect and feedback vibration control potential of both piezoelectric polymer polyvinylidene e uoride (PVF2) and piezoelectric ceramic lead, zirconate, and titarate (PZT) are investigated by using a bimorph cone guration testbed. Experimental results show that PVF 2 acts more linearly than PZT during sensing. Furthermore, the ine uence of the driving sources on the piezoelectric actuators can be verie ed experimentally. It can be shown that driving PZT by using a current source will have a less severe hysteresis effect than driving it with a traditional voltage source.

Evaluation of eardrum laser doppler interferometry as a diagnostic tool.

Laser Doppler interferometry (LDI) of the eardrum allows noncontact optical analysis of its vibrations in response to sound. Although LDI has been widely used in research, it has not yet been introduced into clinical practice as an adjunctive test for otological workup. The aim of this study was to evaluate LDI as a diagnostic tool in the clinical sphere. Prospective. A measurement system was developed based on a commercially available scanning He-Ne laser Doppler interferometer. The study included 129 eardrums of 79 subjects that were divided into 3 groups: 1) normal subjects and 2) patients with sensorineural and 3) conductive hearing loss (HL). All the patients suffering from conductive HL underwent ossiculoplasty, which allowed confirmation of the final diagnosis, and patients were assigned accordingly to the subgroups malleus fixation, incus luxation, and stapes fixation. The modified LDI system allowed bilateral evaluation of a subject within 30 minutes. No significant difference between normal subjects and patients having sensorineural HL were found. However, it was possible to distinguish between normal subjects and patients with conductive HL. Furthermore, the system had the ability to differentiate between various middle ear diseases. These groups differed statistically significantly in terms of manubrium vibration amplitude and resonance frequency. In malleus fixation significant differences in tympanic membrane movement patterns were found. Our LDI is applicable in clinical otological practice and serves as a valuable addition to the routine audiological investigations for preoperative evaluation of the mobility and integrity of the ossicular chain.

F-0803 耳小骨靭帯硬化耳の振動特性 : 有限要素法による解析(S43-1 生体現象に対する計算力学的アプローチ)(S43 生体力学シミュレーション)

The middle ear plays an important role in auditory mechanics, transmitting sound signals efficiently from the ear canal to the cochlea. If ligaments, which support ossicles, become fixed, conductive hearing loss occurs. A diagnosis of these fixations of the ligaments is difficult. Especially, as the anterior malleal ligament (AML) is a tiny ligament, its fixation is often overlooked. In this study, the effect of the AML fixation on the middle-ear vibration was analyzed by using a finite-element model of the middle ear and by measuring vibrations of temporal bones with a laser Doppler interferometer. Then, based on our findings, a diagnostic method for detecting the AML fixation was suggested.

Investigating distributed sensor/point actuator testbeds by using differential laser Doppler interferometer

Investigating distributed sensor/point actuator testbeds by using differential laser Doppler interferometer

The field and frequency dependence of the strain and polarisation in piezoelectric and electrostrictive ceramics

A laser Doppler interferometer system has been used to measure the strains of ferroelectric ceramics. The strains and polarisation of piezoelectric and electrostrictive ceramics have been investigated as a function of electric fields up to 4 MV/m in the frequency range from 0.01 Hz up to 1 kHz. The field and frequency dependence of the appropriate material constants have been calculated. Results on a range of piezoelectric PZT and electrostrictive PMN-PT ceramic materials are presented.

Ductile damage of tantalum under spalling effects. Experimental and metallurgical analysis

In this paper, we examine the experimental and metallurgical features of ductile damage of some high purity tantalum under dynamic uniaxial strain loading. This particular sollicitation is obtained by performing plate impact experiments using a single stage light gas gun. Such spall tests are performed in the 5 GPa - 12 GPa range of shock pressures for a 1.5 μs pulse duration. On the one hand, free surface velocity has been measured by means of a Doppler Laser Interferometer in order to quantify the spall stress levels as a function of shock pressure. Theses results are compared to those of litterature and we found a good agreement. On the other hand, tests with soft recovery of shocked samples have been achieved for metallurgical analyses. These ones allow us to better understand the different stages of nucleation, growth and coalescence of microvoids. The advanced analysis performed in this work quantifies the size, shape and evolution of microvoids, which give us precise informations to propose well defined hypotheses fo further modelling of damage phenomena for tantalum.

Experimental investigations of the use of cartilage in tympanic membrane reconstruction.

Temporalis fascia, perichondrium, and cartilage are commonly used for reconstruction of the tympanic membrane in middle ear surgery. Cartilage grafts offer the advantage of higher mechanical stability, particularly in cases of chronic tubal dysfunction, adhesive processes, or total defects of the tympanic membrane, in contrast to fascia and perichondrium, which presumably offer better acoustic quality. The purpose of this study was to determine the acoustic transfer characteristics of cartilage of varying thickness and its mechanical deformation when exposed to fluctuations in atmospheric pressure. Ten pairs of cartilage specimens from the cavum conchae and the tragus were obtained from fresh human cadavers. Young's modulus was determined by mechanical tension tests and statistically evaluated using the t test. The acoustic transfer characteristics of an additional 10 specimens were measured by a laser Doppler Interferometer after stimulation with white noise in an external auditory canal--tympanic membrane model. Mechanical stability was determined by measuring displacement of the cartilage using static pressure loads of < or = 4 kPa. Young's modulus determinations for conchal and tragal cartilage were 3.4 N/mm2 and 2.8 N/mm2, respectively, but the difference was not significant. Acoustic testing showed a 5-dB higher vibration amplitude in the midfrequency range for conchal compared with tragal cartilage, but the difference was not significant. Reducing cartilage thickness led to an improvement of its acoustic transfer qualities, with a thickness < or = 500 microm resulting in an acceptable acoustic transfer loss compared with the tympanic membrane. Both conchal and tragal cartilage are useful for reconstruction of the tympanic membrane from the perspective of their acoustic properties. The acoustic transfer loss of cartilage can be reduced by decreasing its thickness. A thickness of 500 microm is regarded as a good compromise between sufficient mechanical stability and low acoustic transfer loss.

Improvement of ultrasonic testing of concrete by combining signal conditioning methods, scanning laser vibrometer and space averaging techniques

This paper deals with the combination of several techniques to improve the ultrasonic pulse echo testing of concrete elements when a laser doppler interferometer is used as the ultrasonic receiver. This techniques involves specially designed ultrasonic probes, a pulse compression technique, random speckle modulation and space time signal processing methods. The pulse echo technique is carried out by sending frequency modulated chirp signals and performing a cross-correlation between the received and the transmitted signals. In combination with the application of recently available ultrasonic concrete probes as transmitter, this leads to an improvement in the signal-to-noise ratio. A laser doppler interferometer, equipped with a random speckle modulator, is used as detector of the ultrasound. Finally, the data sets are processed with various methods, involving time signals of several space points. Examples are the space averaging and the synthetic aperture focusing technique (SAFT). The advantage of the suggested technique is demonstrated by practical measurements on a test specimen. The improvement in results as compared to standard laser interferometric measurements will increase the feasibility of laser interferometric detection for non-destructive testing in civil engineering.

Miniature piezoelectric actuators: design concept, fabrication and performance evaluation

Magnifying mechanisms, which include bimorph configurations, waveguides, resonance, mechanical levers etc, that can convert a large-force, small-displacement piezoelectric material to become a smaller-force, large-displacement actuator are examined in detail. Sputtering processes for zinc oxide and lead-zirconate-titanate films, which are important for fabricating miniature laminated piezoelectric actuators, are presented. A newly developed laser Doppler interferometer that is especially designed for evaluating the performance of miniature piezoelectric actuators is also described. The design concept, optimization process, fabrication techniques and evaluation approach for such things as a piezoelectric impact hammer, a resonant dual-dimensional piezoelectric scanner, a Langevin type ultrasonic motor and a high-precision piezoelectric positioning stage are also discussed.