Laser Doppler Vibrometer Without Directional Ambiguity Using Rectangular Phase Grating

The two-phase detection method for directional discrimination in laser Doppler measurements is discussed.The diffraction efficiency of a sin- gle period rectangular phase grating is analysed and a kind of back-scattered laser Doppler vibrometer without directional ambiguity using the single peri- od rectangular phase grating as the beam-combiner described.The principles of this kind of vibrometer are explained in detail,and some experimental re- sults are given.In this kind of vibrometer,the rectangular phase grating, without the zero diffracted order and even orders,is used to eliminate use- less stray light and to combine the useful signal light.Differential electronics is employed to reject signal noise.Therefore,the signal-to-noise ratio of Doppler signals and the measurement accuracy of the instrument are im- proved and the range of application is expanded.

New Type of 2-D Laser Doppler Vibrometer

The fundamentals and method of 2 D laser Doppler vibrometer are introduced.The factors influencing the measuring accuracy are analyzed. Moreover, the circuit for signal processing is designed. The vibrating amplitude and frequency of 2 D vibration in wider range can be measured simultaneously in non contact means,the measuring results are accurate.

All-fiber pulsed laser Doppler vibrometer development based on time-domain chopping techniques

A 1550 nm all-fiber pulsed laser Doppler vibrometer (LDV) based on time-domain chopping techniques is developed to overcome demodulation failures caused by multipath interference. The system adopts an adjustable configuration on pulse duration and pulse repetition frequency according to the distance. An experiment is carried out at a 25 m standoff with pulse duration of 80 ns, single pulse energy of 0.4 nJ, and pulse repetition frequency of 1 MHz. A waveform and spectrogram of the demodulated voice show that the pulsed LDV system has a good performance in long-range voice listening.

Middle ear reconstruction estimated by recurrence plot technique

Middle ear surgery techniques have enabled to improve hearing destroyed by a disease. Despite huge improvement in instrumentation and techniques the results of hearing improvement surgery are still difficult to predict. This paper presents the results of vibrations measurements in a human middle ear obtained at the Medical University of Lublin. Vibrations of the stapes in the case of the intact ossicular chain, after cement incus rebuilding and incus interpositions are compared each other. In this aim a new approach of ossicles vibrations observation is introduced in order to complete information obtained from classical approach which bases on the transfer function. Measurements of ossicular chain vibrations are performed on fresh human temporal bone specimen using the laser doppler vibrometer. Next, after classical research, the extended analysis with the recurrence plots technique is performed.

Analytical Identification of Magnetic Faults Induced by Material Properties and Mechanical Tolerance in PM Synchronous Motor

This paper presents an analytical model suitable for analyzing Permanent Magnet Synchronous motors. The difference between mass eccentricity and magnet eccentricity is described. The full derived vibration mathematical model incorporates both the electrical domain and mechanical domain. The shaft bending force, mass eccentricity exciting force, aerodynamic exciting force, and unbalanced-Magnet-Pull (UMP) are introduced in this three-dimensional motor model. The relative displacement between rotor and stator is calculated in order to avoid rotor to stator rub. The experiments were conducted with Laser Vibrometer for verifying the analysis results. The measurement results prove the effectiveness of the proposed analytic method.

Mechanical Impedance of Cerebral Material

The tentative variation of the mechanical impedance, of a cylindrical sample of cerebral material, has been achieved by Vibrometer Laser according to the frequency. The studied matter is supposed homogeneous, isotropic and stationary. A multilayered mechanical model has been associated to the studied sample to simulate its vibration. The theoretical expression of mechanical impedance has been determined while taking the mechanical/electric analogy as a basis. A good adjustment of theoretical model parameters permitted us to have a good agreement theory/experience of the mechanical impedance variation according to the sample vibration frequency.

Non-contact Acoustic Contour Imaging Method Using Phase Difference in Extremely Shallow Underground

Buried object which exists at extremely shallow underground can be detected by using an acoustic vibration and a SLDV （scanning laser Doppler vibrometer）. Non-contact acoustic exploration can be realized by using air coupled sound. It was confirmed that discovery and the identification of a buried thing were possible using the OFR method （optimum frequency range method）. However, in this method, only the amplitude of the vibration speed spectrum is used and did not use the phase information. Therefore a new imaging method is proposed that used the phase information of the vibration speed spectrum. From the experimental results, the possibility of the outline extraction by using the phase difference between each scan point is confirmed. As a future task, the phase difference image will become clearer by changing the scan point density and long duration time of emitted wave.

New speckle pattern interferometry for precise in situ deformation measurements

A new electronic speckle pattern interferometry method is proposed to realize in situ deformation measurements.The feature of the method is the combination of a high-speed camera and multiple laser Doppler vibrometers(LDVs)for synchronous measurements.The high-speed camera is used to record and select effective interferograms,while the LDVs are used to measure the rigid body displacement caused by vibrations.A series of effective interferograms with known shifted phase values are obtained to calculate the deformation phase.The experimental results show that the method performs well in measuring static and dynamic deformations with high accuracy in vibrating environments.

Research Activities Arising From the University of Kent

In this paper the author describes research and development activities in the field of optical sensing undertaken since his time within the Applied Optics Group at the University of Kent. The main topics covered are laser vibrometry and optical range-finding techniques. The author also gives a summary of his research at University of Kent, covering 1982-1985.

Novel sensing techniques for full-scale testing of civil structures

Performing full-scale structural testing is an important methodology for researchers and engineers in the civil engineering industry.Full scale testing helps the researchers understand civil infrastructures'loading scenarios,behaviors,and health conditions.It helps the engineers verify,polish,and simplify the structural design and analysis theories.To conduct a full-scale structural testing,sensors are used for data acquisitions.To help structural researchers and engineers get familiar with sensing technologies and select the most effective sensors,this study reviewed and categorized new sensing techniques for full-scale structural testing applications.The researchers of this study categorized sensors used for civil-infrastructure testing into traditional contact sensors and remote sensors based upon their application methodologies,and into cabled sensors and wireless sensors based upon their data communication strategies.The detailed descriptions of wireless sensors and remote sensing techniques and their on-site full-scale applications are presented.

Sparse Reconstruction and Damage Imaging Method Based on Uniform Sparse Sampling

The full wavefield detection method based on guided waves can efficiently detect and locate damages relying on the collection of large amounts of wavefield data.The acquisition process by scanning laser Doppler vibrometer(SLDV)is generally time-consuming,which is limited by Nyquist sampling theorem.To reduce the acquisition time,full wavefield data can be reconstructed from a small number of random sampling point signals combining with compressed sensing.However,the random sampling point signals need to be obtained by adding additional components to the SLDV system or offline processing.Because the random sparse sampling is difficult to achieve via the SLDV system,a new uniform sparse sampling strategy is proposed in this paper.By using the uniform sparse sampling coordinates instead of the random spatial sampling point coordinates,sparse sampling can be applied to SLDV without adding additional components or offline processing.The simulation and experimental results show that the proposed strategy can reduce the measurement locations required for accurate signal recovery to less than 90%of the Nyquist sampling grid,and the damage location error is within the minimum half wavelength.Compared with the conventional jittered sampling strategy,the proposed sampling strategy can directly reduce the sampling time of the SLDV system by more than 90%without adding additional components and achieve the same accuracy of guided wavefield reconstruction and damage location as the jittered sampling strategy.The research results can greatly improve the efficiency of damage detection technology based on wavefield analysis.