Well-known Measurement Technique Research Articles

Vibration insensitive THz wave interferometry for characterizing optical phase shifter

Optic interferometry is a well-known measurement technique with high precision attained through the optical interference caused by the superposition of lightwaves. However, with fiber-optic interferometry, the phases of the lightwaves are susceptible to interference via the fiber fluctuation that is unavoidably induced by the environmental vibration, which makes the measurement result unstable and limits the usage scenarios of the interferometric installation. In this paper, a fiber-optic THz wave interferometer aiming for vibration isolation is presented. Due to the longer wavelength of the THz wave, the influence of optical fiber fluctuation on the phase noise is considerably suppressed. For verifying the feasibility of the fiber-optic THz wave interferometer, it is used here to measure the optical phase shift at a fiber-pigtailed thermo-optic phase shifter. The experimental results show that, compared with an all-fiber interferometer, the fiber-optic THz interferometer enables accurate measurement of an optical phase shift as well as an improved signal-to-noise ratio of interference with 6dB gain.

Hue-Based Gray Coding Method for Three-Dimensional Surface Measurement of Cutlery With Specular Reflection

Many measurement methods have been proposed for use in automated production. Existing methods for measuring three-dimensional surface height data operate by projecting fringe patterns onto a target object and capturing images of them. However, these methods do not work well for cutlery, such as table forks and spoons, because specular reflection causes exposure change on the cutlery surface. To overcome this difficulty, this paper presents a measurement method for cutlery with specular reflection. The proposed method is based on a well-known measurement technique, the gray coding method, which is robust to exposure change because the captured fringe patterns are handled by discretizing their values. Furthermore, the gray coding method is improved by introducing hue-channel information into the captured fringe patterns. The hue-channel information is more robust to exposure change than brightness, which is used in existing methods. Experimental results for real cutlery show that the proposed hue-based gray coding method enables more robust measurement than existing methods.

Doppler-shifted laser self-mixing interferometry for enhanced detection sensitivity

ABSTRACTLaser self-mixing interferometry (SMI) is a well-known measurement technique having been applied to the fields of geometrical quantities detection, medical treatment and industry manufacturing. Its detection sensitivity can be improved by frequency shifting towards the laser's relaxation oscillation frequency (ROF), which has always been implemented by a pair of acousto-optic modulators (AOM). This manuscript presents a novel method based on Doppler effect for frequency shifting, which is based on a rotating disk and has the advantages of convenient adjustment and low cost. The theoretical analysis in the form of Doppler shift and time-delayed rate equations is followed, and simulative and experimental results are included to prove its validity. To our knowledge, this technique has not been used in practice till now, and the proposed structure, with these advantages, can find significant applications in designing high performance SMI sensors, and can extend SMI measurement to more kinds of non-cooperative surfaces.

Full-field measurement with nanometric accuracy of 3D superficial displacements by digital profile correlation: A powerful tool for mechanics of materials

In recent decades, technological innovations have prompted the development of pioneering materials that attempt to satisfy new and forthcoming needs. The innovation in these materials is usually from their peculiar properties, which in many cases make them uniquely appropriate for a specific application. In this context, the development of innovative measurement techniques can provide more comprehensive understanding and knowledge of these materials' properties, often non-conventional and not easily retrieved by standard procedures. In order to obtain a full-field 3D displacement vector of a surface under investigation, the author proposes the combination of two well-known measurement techniques: the Confocal Microscopy (CM) and the two-dimensional Digital Image Correlation (2D-DIC). Specifically, CM has demonstrated its ability to successfully attain microscopic topography on a highly finished surface with sub-micrometric roughness, and such a technique could be used as a carrier to successfully apply the 2D-DIC algorithm. By this approach, it is not difficult to reach an accuracy of a few nanometers on the displacement measurement. The feasibility of the procedure proposed herein was demonstrated by two case studies: a tensile test of a Ni-alloy edge crack specimen, and a hardness test carried out on a thick AISI 1040 disk.

Multi-color magnetic nanoparticle imaging using magnetorelaxometry

Magnetorelaxometry (MRX) is a well-known measurement technique which allows the retrieval of magnetic nanoparticle (MNP) characteristics such as size distribution and clustering behavior. This technique also enables the non-invasive reconstruction of the spatial MNP distribution by solving an inverse problem, referred to as MRX imaging. Although MRX allows the imaging of a broad range of MNP types, little research has been done on imaging different MNP types simultaneously. Biomedical applications can benefit significantly from a measurement technique that allows the separation of the resulting measurement signal into its components originating from different MNP types. In this paper, we present a theoretical procedure and experimental validation to show the feasibility of MRX imaging in reconstructing multiple MNP types simultaneously. Because each particle type has its own characteristic MRX signal, it is possible to take this a priori information into account while solving the inverse problem. This way each particle type’s signal can be separated and its spatial distribution reconstructed. By assigning a unique color code and intensity to each particle type’s signal, an image can be obtained in which each spatial distribution is depicted in the resulting color and with the intensity measuring the amount of particles of that type, hence the name multi-color MNP imaging. The theoretical procedure is validated by reconstructing six phantoms, with different spatial arrangements of multiple MNP types, using MRX imaging. It is observed that MRX imaging easily allows up to four particle types to be separated simultaneously, meaning their quantitative spatial distributions can be obtained.

Non-contact on-machine measurement using a chromatic confocal probe for an ultra-precision turning machine

On-machine measurement (OMM) involves the interruption of the machining process and the subsequent measurement of the workpiece without its removal from the machining tool. Chromatic confocal sensing is a well-known measurement technique that is able to evaluate the position of a point on an object surface along the optical axis of the system with high accuracy. The present study integrates a chromatic confocal measurement probe with an ultra-precision diamond turning machine to achieve the non-contact OMM of machined components. The procedure for establishing the position of the rotary axis of the spindle based on dual standard spheres is first described in detail, and the relevant OMM procedure for machined components of different surface topographies is explained. Then, a 50-μm quartz step height standard is employed to investigate the linear measurement accuracy of the chromatic confocal probe. Finally, the measurement accuracy of the proposed OMM method is compared experimentally with that of the stylus method. The results show that the estimated form error value of the OMM method agrees well with the value obtained by the stylus method. The proposed OMM method feasibly achieves non-contact OMM with a nanometer-level accuracy for an ultra-precision turning machine and is capable of reconstructing the 3D surface topography of flat, spherical, and aspheric surfaces. After integrating the OMM method, the ultra-precision turning machine can realize the function of processing-measurement integration.

Use of Integrated Simulation and Experimentation to Quantify Impact Damage

The term damage can be generally defined as a change introduced into a system that affects its performance. Its identification and characterization is a valid help in deciding amongst continuing the operation or performing a repair or replacement of the system. A valid support to this decision is based on the use of well-known measurement techniques from Non-Destructive Testing and Evaluation (NDT&E). A well-established correlation between damage and features extracted from the measured data makes these techniques capable of providing information about the extent of the damage. However the prediction of the remaining useful life of a system by comparing full-filed measurements techniques and FEM analysis results is the challenge of an increasing number of research studies. The need of a guide for enumerating the extent of the damage has been the thrust to perform this work. A common methodology developed for both numerical and experimental studies will be presented. It consists of three main parts: proper selection of the parameter capable of describing the damage in a quantitative manner; several approaches to obtain results from measurement techniques and FEM analysis; and damage assessment making use of a quantitative comparison of FEM results only, full-field experimental results only, or comparison of FEM to experimental results. A different approach in damage assessment will be also presented making use of Zernike moment descriptors from which the severity of the damage is inferred. An example to illustrate the methodology will be shown.