Stroboscopic Holographic Interferometry Research Articles

Numerical Determination of Natural Frequencies and Modes of the Vibrations of a Thick-Walled Cylindrical Shell

The dynamic characteristics of a thick-walled cylindrical shell are determined numerically using the finite-element method implemented with licensed FEMAR software. The natural frequencies and modes are compared with those obtained earlier experimentally by the method of stroboscopic holographic interferometry. Frequency coefficients demonstrating how the natural frequency depends on the physical and mechanical parameters of the material are determined.

Natural Frequencies and Modes of Noncircular Cylindrical Shells with Variable Thickness

The dynamic characteristics of thin cylindrical isotropic shells with variable thickness are determined using numerical and experimental approaches. Numerical calculations are performed by the finite-element method with FEMAR software. In experimental study, stroboscopic holographic interferometry is used which makes it possible to observe interferential patterns of vibrations of the shell surface in real time. The results obtained by two different methods are compared

Visualization of thin CFRP plates modal shapes by time averaged pulse stroboscopic digital holographic interferometry

Visualization of thin CFRP plates modal shapes by time averaged pulse stroboscopic digital holographic interferometry

Three-dimensional vibrometry of the human eardrum with stroboscopic lensless digital holography.

The eardrum or tympanic membrane (TM) transforms acoustic energy at the ear canal into mechanical motions of the ossicles. The acousto-mechanical transformer behavior of the TM is determined by its shape, three-dimensional (3-D) motion, and mechanical properties. We have developed an optoelectronic holographic system to measure the shape and 3-D sound-induced displacements of the TM. The shape of the TM is measured with dual-wavelength holographic contouring using a tunable near IR laser source with a central wavelength of 780 nm. 3-D components of sound-induced displacements of the TM are measured with the method of multiple sensitivity vectors using stroboscopic holographic interferometry. To accurately obtain sensitivity vectors, a new technique is developed and used in which the sensitivity vectors are obtained from the images of a specular sphere that is being illuminated from different directions. Shape and 3-D acoustically induced displacement components of cadaveric human TMs at several excitation frequencies are measured at more than one million points on its surface. A numerical rotation matrix is used to rotate the original Euclidean coordinate of the measuring system in order to obtain in-plane and out-of-plane motion components. Results show that in-plane components of motion are much smaller (<20%) than the out-of-plane motions’ components.

Investigation on Fracture Behaviour of Turbine Blades Under Self‐Exciting Modes

Abstract: This paper investigates the failure mechanisms of turbine blades occurring during similar conditions of turbine operation. Optical techniques are utilised to identify critical frequencies that may be the cause of blade fractures. For that purpose, time average, stroboscopic holographic interferometry and holographic moiré are utilised to record vibration patterns. Strain maps are computed from stroboscopic and holographic moiré patterns. Stress distributions are computed under the assumption of linear elasticity. It is found that stress trajectories deduced from holographic measurements match well with the initial trajectories of crack observed for the in‐service broken specimens. This fact allows the excitation modes causing blade fractures to be identified. Finite element analyses carried out on models corrected in view of the experimentally observed vibration modes provide the values of stress causing fracture initiation. The paper discusses the failure mechanisms of the blades on the basis the experimental evidence and finite elements results. The observed failure modes seem to be a form of the principal normal stress fracture criterion. An argument based on damage accumulation explains the observed behaviour. Further evidence on failure mechanisms is gathered from scanning electron microscope images of the fractured specimens.

Separate recording of rationally related vibration frequencies using digital stroboscopic holographic interferometry

A method for separate recording of rationally related vibration frequencies is presented. To record and measure the mode shape of vibrations, a synchronized stroboscopic CCD camera is used. Synchronization and control of the camera acquisition for recording stroboscopic holographic sequence has been realized. The phase for different states of the object vibration is calculated using the Fourier-transform method. Experimental results are presented, and the advantages and disadvantages of the proposed method are discussed.

Optoelectronic holographic otoscope for measurement of nano-displacements in tympanic membranes

Current methodologies for characterizing tympanic membrane (TM) motion are usually limited to either average acoustic estimates (admittance or reflectance) or single-point mobility measurements, neither of which suffices to characterize the detailed mechanical response of the TM to sound. Furthermore, while acoustic and single-point measurements may aid in diagnosing some middle-ear disorders, they are not always useful. Measurements of the motion of the entire TM surface can provide more information than these other techniques and may be superior for diagnosing pathology. We present advances in our development of a new compact optoelectronic holographic otoscope (OEHO) system for full field-of-view characterization of nanometer-scale sound-induced displacements of the TM surface at video rates. The OEHO system consists of a fiber optic subsystem, a compact otoscope head, and a high-speed image processing computer with advanced software for recording and processing holographic images coupled to a computer-controlled sound-stimulation and recording system. A prototype OEHO system is in use in a medical research environment to address basic science questions regarding TM function. The prototype provides real-time observation of sound-induced TM displacement patterns over a broad frequency range. Representative time-averaged and stroboscopic holographic interferometry results in animals and human cadaver samples are shown, and their potential utility is discussed.

Measuring metal plate vibrations by digital stroboscopic holographic interferometry of focused images

A method for digital stroboscopic holographic interferometry of focused images for measuring points of displacements of a metal plate vibrating at a resonant frequency is considered. Unlike classical holographic interferometry, in this method, the measurement process does not include the process of interferogram obtaining, recording, and interpretation.

209 実時間ストロボホログラフィー干渉法による水中超音波音圧分布の測定(GS-10 計測)

209 実時間ストロボホログラフィー干渉法による水中超音波音圧分布の測定(GS-10 計測)

Holographic real-time imaging of standing waves in gases

Stroboscopic holographic interferometry has been developed at an advanced undergraduate level allowing real-time imaging of standing sound waves in gas filled, closed tube resonators. A heterodyne Mach–Zehnder interferometer was first built by students to show the feasibility of interferometric detection of sound waves in a small cell. In the subsequent holographic study, the laser irradiance is modulated by an acousto-optic cell at frequencies near that of the standing wave, and a video camera records the fringe motion due to sound pressure changes. Fractional fringe shifts are observed for an air filled cell, and multiple fringe shifts are imaged for the case of freon. Sound reflections from the cell ends are easily observed, with nonsinusoidal waveforms dominating at high intensities due to superposition of resonator harmonics.

Stroboscopic holographic interferometry: measurements of vector components of a vibration

The interpretation of time-averaged holographic fringes recorded with a vibrating object presents problems when the direction of the motion is not known or when points on the object are moving in two or three dimensions. Measurements on additional holograms with properly chosen directions of the sensitivity vector are then required to evaluate the vibration amplitude. However, reduction of the data, even along a single line, is laborious and subject to errors. This paper describes a computerized system which uses stroboscopic illumination in conjunction with digital phase-shifting techniques to evaluate the magnitude and direction of the surface displacements at a uniformly spaced array of points covering the vibrating object. These values are used along with data on the shape of the object to calculate the in-plane and out-of-plane components of the vibration at these points. The operation of the system is illustrated with some results obtained with a compressor blade from a jet engine. Measurements of the surface displacements at different epochs of the vibration cycle permit a detailed analysis of complex vibrations.

Thermal waves visualized by holographic interferometry

The propagation of long thermal waves induced in thin aluminum plates by a slowly modulated heat source was investigated by stroboscopic holographic interferometry. The effect of different modulation frequencies on the visualization of such waves is shown. Experimental results confirm analytical thermoelastic predictions. The application of long thermal waves to holographic nondestructive testing is demonstrated.

Stroboscopic holographic interferometry: Application of digital techniques

Stroboscopic holographic interferometry is a very powerful tool for study of vibrating objects. It is shown how its capabilities can be extended by applying digital techniques to make real-time measurements of the optical path differences at a uniformly spaced array of points covering the interference pattern. Areas vibrating in antiphase can be identified clearly, and a three-dimensional displacement map of the surface of the object can be generated.

Modes and waves in a cochlear model

A simplified model hydroelastic system having many features in common with the cochlea is studied theoretically and experimentally. The system consists of a slender rigid tube filled with a viscous incompressible fluid. The tube is divided lengthwise into two chambers (scala vestibuli, scala tympani) by an interior surface, part of which is rigid and part elastic. The elastic portion is an isotropic plate having variable width and is clamped on its edges. The system is driven by a sinusoidal input at the stapes end. The mechanical model is 24 times life size and dynamical similarity is maintained. Wave patterns in the plate are measured using time-averaged and stroboscopic holographic interferometry. At low frequency (corresponding to less than 500 cycles/s in the cochlea) the response can be adequately predicted by a one dimensional theory. The waves are a combination of travelling and standing waves. The traveling component is solely a dissipative effect. Discrete resonances are readily observed in the low frequency range.

Stroboscopic holographic interferometry of vibration with space-variant phase

A method employing pulsed illumination for the holographic analysis of vibration with space-variant phase is described. Superimposition of two stroboscopically recorded interference patterns to get the amplitude and the phase of vibration at the intersections of fringes is suggested. Contour maps of these two quantities over the entire object surface can then be prepared by interpolation. Detailed solutions are presented for single and double frequency vibrations.

Real-time holographic interferometry: a system

A complete photographic system for performing real-time holographic interferometry is described. The holograms are recorded on an experimental film that permits rapid, dry, in-place processing in a specially designed chamber. The expose-process-view cycle is fully automated so that real-time interferograms can be produced with ease. The features of the system pertinent to holography are discussed and examples of real-time stroboscopic holographic interferometry are shown.

Quadruple-Exposure Technique in Stroboscopic Holographic Interferometry

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text K. N. Chopra and G. S Bhatnagar, "Quadruple-Exposure Technique in Stroboscopic Holographic Interferometry," Appl. Opt. 13, 2468-2470 (1974) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Stroboscopic holographic interferometry of vibration simultaneously in two sinusoidal modes

A stroboscopic technique is suggested to perform the analysis of vibration with two sinusoidal mode combinations. The approach permits analysis of the vibration amplitude due to each mode without disturbance of the amplitude of the other mode.

Recording linearity in triple-exposure stroboscopic holographic interferometry

Effective beam intensity ratio is evaluated and discussed for the case of triple-exposure stroboscopic holographic interferometry.

A direct approach to reduce recording time in stroboscopic holographic interferometry

A direct method to reduce the recording time during the pulsed illumination in stroboscopic holographic interferometry is suggested. The technique involves increasing the recording time while the object is in static position and decreasing the recording time during the pulsed illumination accordingly while the object is vibrating. The approach is applied to double-exposure and triple-exposure cases of stroboscopic holographic interferometry, where it is found that considerable reduction in the recording time is possible.