Laser Doppler Vibrometry Method Research Articles

Analysis of frequency response sensor of MEMS gyroscope in vacuum chamber

This article presents a study of the frequency response of a MEMS gyroscope in a vacuum chamber. On the basis of experimental studies by the method of laser Doppler vibrometry, the dependences of the amplitude of oscillations of the inertial mass in the vertical plane at various pressures are obtained. The bandwidth of the MEMS sensor was also measured.As a result of the experiments, the damping factors were determined to compose a more complete mathematical model and for more accurate finite element modeling in ANSYS, and refined parameters of the electrostatic drive and the amplitude of oscillations along the axis of the drive were obtained. These studies will be useful for determining the residual degree of vacuum in the case for further frequency tuning of the device.

Handheld laser-fiber vibrometry probe for assessing auditory ossicles displacement.

.Significance: Measurements of auditory ossicles displacement are commonly carried out by means of laser-Doppler vibrometry (LDV), which is considered to be a gold standard. The limitation of the LDV method, especially for in vivo measurements, is the necessity to expose an object in a straight line to a laser beam operating from a distance. An alternative to this approach is the use of a handheld laser-fiber vibrometry probe (HLFVP) with a curved tip.Aim: We evaluate the feasibility of an HLFVP with a curved tip for measuring sound-induced displacement of the auditory ossicles.Approach: A handheld vibrometer probe guiding the laser beam with a fiber-optic cable was used for displacement measurements of the incus body and the posterior crus of the stapes. Tonal stimuli at frequencies of 0.5, 1, 2, and 4 kHz were presented by means of an insert earphone positioned in the outer ear canal. The probe was fixed at the measurement site using a tripod or hand-held by one of the two surgeons.Results: The measurements were carried out on six fresh temporal bones. Multivariate analysis of variance showed statistically significant differences for stimulus frequency (, , and ), bone (, , and ), and measurement site (, , and ) in the absence of statistically significant differences for the probe fixation method (, , and ). Standard deviations of the means were 6.9, 2.6, 1.9, and for frequency, bone, site, and fixation, respectively. Ear transfer functions were found to be consistent with literature data.Conclusions: The feasibility of applying HLFVP to measure the displacement of auditory ossicles has been confirmed. HLFVP offers the possibility of carrying out measurements at various angles; however, this needs to be standardized taking into account anatomical limitations and surgical convenience.

Facial Muscle Activity: High-Sensitivity Noncontact Measurement Using Laser Doppler Vibrometry

Facial expression is regulated by facial muscles and it is an important communication modality, generally held to convey signs of emotion, stress, pain, and social engagement. The assessment of facial expression has a role in a variety of scientific areas, as well as applied situations, including affective computing, marketing, and clinical evaluation, and is now an area of intensive development using computerized image processing approaches. Assessment has conventionally involved the analysis of facial images by trained coders, relying on the parsing of facial movements into standardized elemental actions. Direct measurement of the electromyographic (EMG) activity from the engaged muscles offers theoretical advantages, especially in terms of sensitivity, but involves burdensome procedures, including application of electrodes. In this article, we describe an alternative measurement method for the direct assessment from facial muscles using the noncontact technique of laser Doppler vibrometry (LDV). The application of LDV to measuring muscle activity relies on the detection of the small lateral muscle vibration signals that accompany contraction along the longitudinal axis. The sensitivity of the LDV method was demonstrated in a study involving a posed facial expression that is generally associated with the emotion of disgust. Ascending sequences of expression strength were anchored by a condition entailing imagery of a disgusting odor while avoiding visible facial expression. LDV signals were shown to compare favorably with the simultaneous EMG, in disclosing signs of activation even at levels that were not sufficient to produce visible facial actions.

Chladni Figures in Modal Analysis of a Double-Panel Structure.

Analysis of the structural vibration, under the sound excitation is an important part of the quality assurance during the design process of devices. One of the most commonly used method is Laser Doppler Vibrometry (LDV). However, under the rapid fluctuations of temperature, structural resonances are shifted into the other frequencies. In such situation LDV method may be inconvenient, due to the scanning time. In this paper the authors proposed Chladni figures to modal analysis of the double-panel structure, excited by the loudspeaker enclosed inside the casing with a rigid frame. Double-panel structure has been proven to be particularly useful for noise and vibration reduction applications. Vision images, obtained during the experiments are converted to binary patterns, using GLCM matrix, and compared with simulations performed in ANSYS.

Noncontact Sensing of Facial Muscle Activity Using Laser Doppler Vibrometry: Time Domain Data Analysis

Movements of the facial muscles offer a promising avenue for assessing stress, fatigue and emotion, and appear useful for a number of applied and clinical purposes. This paper describes a novel application of laser Doppler vibrometry (LDV) as a noncontact method for assessing facial myographic activity. The principle of the LDV method involves detection of the minute vibrations of contracting muscles, associated with the activation of individual motor units. Data were obtained from 11 participants who received 15-20 min of training before the measurement acquisitions. Participants produced several standardized facial expressions involving activation of the upper face (lowering and raising the eyebrows) and the lower face (raising the upper lip, stretching the lip corners, and clenching the jaw). The associated muscle vibratory activity was assessed using the LDV method, within context of the simultaneous electromyogram (EMG). A separate condition entailed study of the jaw muscle signals during repetitive chewing. The temporal, spatial and measurement sensitivity aspects were studied in separate tests; the present report focuses on the temporal aspects of the response, in comparison to the onsets and offsets of the simultaneous EMG and gross facial surface displacement. The LDV signals were obtained from a site overlying the principal involved muscle for the various movements. Results showed that LDV myographic signals (LDV-MMG) could be recorded from all facial muscles studied, although they were relatively small from the muscles of the upper face. LDV-MMG signals were especially prominent at times of contraction onset and offset, indicating that the method may be particularly useful for the study of dynamic activity as would be associated with brief changes in facial expression. The LDV-MMG signals generally were found to lead the onset of the EMG signal by about 100 ms, and to lag the offset of the EMG signal by about 200 ms. The LDV-MMG response associated with chewing was associated in time with the EMG and displacement signs of chewing, but were generally more polyphasic in form. The findings generally support the potential use of the LDV method as a non-contact and non-obtrusive method for assessing activity of the facial muscles.

Chemical expansion of praseodymium-cerium oxide films at high temperatures by laser doppler vibrometry

The chemical expansion of Pr0.1Ce0.9O2−δ (PCO) films was determined as function of oxygen activity at 720 °C by laser Doppler vibrometry (LDV) in combination with previously reported chemical capacitance studies that provided relevant oxygen nonstoichiometry δ data. The LDV method enabled detection of nanometer displacements, provided that displacement frequencies were above 1 Hz. The PCO films were deposited on yttrium stabilized zirconia (YSZ) substrates operated in the electrochemical oxygen pump mode at 720 °C to periodically adjust the oxygen activity within the PCO film. The potential across the YSZ was varied between 0 and 0.3 V, corresponding to oxygen partial pressures of about 0.2 bar and 10−7 bar, respectively. The electrochemically induced expansion/contraction of the PCO film was observed to induce deflection in both film and substrate, as clearly demonstrated by scanning the sample surface by the LDV. A maximum displacement of about 18 nm at the center of the substrate plate was found during application of a periodic 1 Hz pumping voltage. A much lower displacement, on the order of 1 nm, was obtained when a pin-type sample support was applied, characteristic of chemical expansion of the film itself. These data were used to discuss correlations with similar recent data obtained by monitoring displacements of the PCO/YSZ sandwich structure with the aid of a specially modified nanoindenter.

Investigations of the transverse vibration characteristics of piezoceramic circular plates with V-notches

This article pertains to experimental validation of the study presented in a previous paper by the same authors , in which the transverse vibration characteristics of piezoceramic circular plates with V-notches were investigated theoretically using Ritz’s method incorporating defined equivalent constants. For experimental measurement, two optical methods – amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) and laser Doppler vibrometry (LDV) – were employed to conceptualize the analytical results. The AF-ESPI method demonstrates the advantages of combining high fringe sensitivity and noise reduction, which are achieved using the time-averaged and subtraction electronic speckle pattern interferometry methods, respectively. Both vibration mode shapes and resonant frequencies of V-notched piezoceramic plates were obtained using the AF-ESPI method; in addition, the resonant frequencies were also determined quickly using the LDV method. By varying the corner angles and notch–depth ratios, various types of piezoceramic plate (V-notched, sectorial, semicircular, segmented, and sharp-notched) were used for experimental measurements. Numerical calculations were performed using the finite element method, and the results were compared with the experimental measurements and theoretical predictions. It was shown that the resonant frequencies and mode shapes obtained using the two experimental methods agreed fairly closely with the theoretical and numerical results.

Cardiorespiratory interactions: Noncontact assessment using laser Doppler vibrometry.

The application of a noncontact physiological recording technique, based on the method of laser Doppler vibrometry (LDV), is described. The effectiveness of the LDV method as a physiological recording modality lies in the ability to detect very small movements of the skin, associated with internal mechanophysiological activities. The method is validated for a range of cardiovascular variables, extracted from the contour of the carotid pulse waveform as a function of phase of the respiration cycle. Data were obtained from 32 young healthy participants, while resting and breathing spontaneously. Individual beats were assigned to four segments, corresponding with inspiration and expiration peaks and transitional periods. Measures relating to cardiac and vascular dynamics are shown to agree with the pattern of effects seen in the substantial body of literature based on human and animal experiments, and with selected signals recorded simultaneously with conventional sensors. These effects include changes in heart rate, systolic time intervals, and stroke volume. There was also some evidence for vascular adjustments over the respiration cycle. The effectiveness of custom algorithmic approaches for extracting the key signal features was confirmed. The advantages of the LDV method are discussed in terms of the metrological properties and utility in psychophysiological research. Although used here within a suite of conventional sensors and electrodes, the LDV method can be used on a stand-alone, noncontact basis, with no requirement for skin preparation, and can be used in harsh environments including the MR scanner.

High sensitivity non-contact method for dynamic quantification of elastic waves and strains in transparent media

This paper presents time resolved quantitative evaluation of elastic stress waves in solid media by utilising an adaptation of the well-established laser Doppler vibrometry method. We show that the introduction of elastic stress waves in a transparent medium gives rise to detectable and quantifiable changes in the refractive index, which is proportional to stress. The method is tested for mechanical excitation at frequencies from 10 to 25kHz in an acrylic bar. This refractometric quantification can measure internal strains as low as 1×10−11. Additionally, finite element analysis is conducted to gauge the validity of the results. In the presented work an acrylic bar is used, this method however should be applicable to any transparent solid.

Laser Doppler vibrometry measurement of the mechanical myogram

Contracting muscles show complex dimensional changes that include lateral expansion. Because this expansion process is intrinsically vibrational, driven by repetitive actions of multiple motor units, it can be sensed and quantified using the method of Laser Doppler Vibrometry (LDV). LDV has a number of advantages over more traditional mechanical methods based on microphones and accelerometers. The LDV mechanical myogram from a small hand muscle (the first dorsal interosseous) was studied under conditions of elastic loading applied to the tip of the abducted index finger. The LDV signal was shown to be related systematically to the level of force production, and to compare favorably with conventional methods for sensing the mechanical and electrical aspects of muscle contraction.

NUMERICAL AND EXPERIMENTAL STUDIES ON THE STRUCTURE-BORNE NOISE CONTROL OF A RESIDENTIAL KITCHEN HOOD

and optimize both existing and new designs. Improving the design of the residential kitchen hood requires in-depth knowledge of the structure. In particular, the dynamic behaviour of the structure during the working period needs to be studied carefully during the design stage. A tool for predicting the structure-borne noise behaviour would save a considerable amount of time, reduce the number of prototypes that need to be built, and decrease the development costs. This paper concentrates on reducing the noise generated from the vibrating structure of a residential kitchen hood by using both numerical and experimental methods. Normal modes of the structure were identified, and the results agree well with the finite-element model. To validate the finite element model, an operational deflectionshape analysis of the structure was performed by using the laser Doppler vibrometry method. This study presents the finite element model and the experimental results of a kitchen hood. This study shows that the contribution of structure-borne noise from the vibrating panels to the overall kitchen hood noise levels is significant, especially at low frequencies. Thus, panel vibration is a critical design consideration for end users because of its relationship to noise and comfort.

Effects of acousto-optic diffraction in the acoustic frequency range on the laser Doppler vibrometry method in air

The effect of acousto-optic diffraction on the transmitted laser signal light path in the laser Doppler vibrometry (LDV) method has been a known concern to measurement accuracy. To further understand and quantify the LDV accuracy implications, for the in-air case, an experimental study was performed in a high-intensity sound field within the acoustic frequency range (less than 20 kHz). Results of the study showed that acousto-optic diffraction has minimal impact on the accuracy of LDV measurements for the in-air case in sound-fields less than 20 kHz. Follow-on work investigating the effect of measurements in water is proposed. It is hypothesized that the higher refractive index of water will exacerbate the impact of the acousto-optic effect on the accuracy of LDV measurements. Previous work in the field in the megahertz frequency region has shown this. However, within the acoustic frequency range, the accuracy implications remain unknown.

Hidden State Models for Noncontact Measurements of the Carotid Pulse Using a Laser Doppler Vibrometer

The method of laser Doppler vibrometry (LDV) is used to sense movements of the skin overlying the carotid artery. When pointed at the skin overlying the carotid artery, the mechanical movements of the skin disclose physiological activity relating to the blood pressure pulse over the cardiac cycle. In this paper, signal modeling is addressed, with close attention to the underlying physiology. Segments of the LDV signal corresponding to single heartbeats, called LDV pulses, are extracted. Hidden Markov models (HMMs) are used to capture the dynamics of the LDV pulses from beat to beat based on pulse morphology; under resting conditions these dynamics are primarily due to respiration-related effects. LDV pulses are classified according to state, by computing the optimal state path through the data using trained HMMs. HMM state dynamics are examined within the context of respiratory effort using strain gauges placed around the abdomen. This study presented here provides a graphical model approach to modeling the dependence of the LDV pulse on latent states.

Transient thermo-mechanical analysis of smart power switches by a laser Doppler vibrometer and numerical simulations

In the paper, application of a laser Doppler vibrometry (LDV) technique for the surface thermal expansion measurement of the semiconductor power devices is presented. As the LDV method can provide a signal directly proportional to the velocity of the surface deformation even for step inputs, the study of a thermal deformation transient process has been accomplished. The time dependence of surface out-of-plane displacement was obtained by integration of the measured velocity time dependences for several discrete surface points. The LDV results of transient performance were confronted with those simulated by the finite-element method. Such a numerical/experimental analysis has been carried out on a composite multilayer structure of a smart power switch device operating under short circuit conditions. A good quantitative coincidence was achieved between thermo-mechanical modelling and LDV measurements.

Dynamic analysis of silicon micromachined double-rotor scanning mirror

The use of MEMS-based technologies for producing scanning mirrors enables its batch production with a consequent increase in the throughput and a decrease in the manufacturing costs per device. However, the use of Silicon as a structural material could introduce non-linearities in the device behavior due to the variation of its mechanical properties according to the crystalline orientation. The orthotropic properties when taken into account in the finite element model of the device could enhance the accuracy in the design of micromachined scanning mirrors. The model used in this paper does not take into account the orthotropic behavior, however, satisfactory results were obtained. To validate the finite element model, a modal analysis of the device was performed using the Laser Doppler Vibrometry method. The normal modes of the structure were identified and the results agree well with the finite element model. This work presents the FE model and experimental modal analysis results of a Silicon micromachined double-rotor scanning mirror.

Thermo-mechanical characterization of micromachined GaAs-based thermal converter using contactless optical methods

Design and construction of GaAs-based micromachined thermal converter device consisting of a high electron mobility transistor (as a microwave heater) and a thin film resistor (as a temperature sensor), integrated on 1 μm thick polyimide fixed GaAs/AlGaAs island structure are introduced. The influence of thermal residual stresses as well as device temperature variations on membrane-like multilayer structure are discussed. A noninvasive and contactless optical methods such as laser confocal microscopy, laser Doppler vibrometry (LDV) and thin layer interferometry are applied to analyze experimentally the thermo-mechanical properties of the micromachined device. LDV method is used to evaluate the device temperature time constant ( τ c ∼1.5 ms) and nano-deformations induced by the temperature changes at any point of device. A confocal microscope is chosen to analyse the 3D deformation profiles of the device at different temperature-induced stress states. The device deformation changes (∼3 μm) induced by power dissipation of 9.5 mW (temperature increase of 395 K) are found to be negligible with respect to the dimensions of the polyimide fixed island structure (160 μm × 120 μm).The optical characterization methods are proved to be a useful tool in design of new thermally based MEMS devices.

Measuring the motions in the human middle ear by Laser Doppler Vibrometry

For the detection of tiny motions which are caused by the tympanic membrane under normal hearing conditions, the touch-free method of Laser Doppler Vibrometry was used. Spectra containing information about the motions of the middle ear bones were recorded within 1 min when the umbo was chosen as the detection point and acoustic stimulation was performed via white noise excitation. It was observed that these spectra correlate to middle ear diseases, which had been artificially induced by manipulations in the chain of the middle ear bones in human temporal bones. The dosimetry of the applied laser radiation was found to be harmless to the tympanic membrane, which opened the way for successful in vivo measurements.