We describe frequency noise measurements for an optical frequency comb by using a delayed self-heterodyne method with a Michelson-type fiber-optic delay line interferometer without a low-noise reference laser. We measured the frequency noise power spectral densities (PSDs) for free-running and frequency-stabilized comb modes and estimated the uncertainties of the measurement results. For example, for

Substrate deformation affects the behaviour of many cell types, including bone, skeletal muscle and endothelial cells. Nowadays, in vitro tests are widely employed to study the mechanotransduction induced by substrate deformation. The aim of in vitro systems is to properly reproduce the mechanical stimuli sensed by the tissue in the cellular microenvironment. Accurate strain measurement and control

Because of uneven temperature distributions, machine tools can generate thermal errors, which significantly contribute to machining errors. Previous research has shown that thermal volumetric errors can be directly measured using optical methods or indirectly calculated using error mapping methods. However, these methods are limited to or restricted by specific working conditions. Therefore, our study

Near-field imaging based on an electromagnetic sensor has been widely used for nondestructive detection. An approach to detect the near-surface defects in pipeline coatings and dielectric pipelines is proposed. Based on the characteristics of resonant frequency shifts, a novel method using artificial neural network (ANN) is established to quantitatively evaluate circular-section shape defects in pipes

The quantitative measurement of acoustic properties is indispensable for many applications. The realization of devices for the evaluation of acoustic properties with higher accuracy and lower error is of great importance. Moreover, the ability to obtain the high-frequency acoustic characteristics of materials is also highly desirable. In this research, the pulse echo method is applied to measure a

Although the original short-time Fourier-transform-based synchrosqueezing transform (FSST) and its second-order transform (FSST2) can effectively improve the readability of quasi-stationary signal and time-varying signal, respectively, the weak components of time–frequency representation are often submerged easily by noises and large-amplitude instantaneous frequencies (IFs). Moreover, aerospace engines

In the field of optical microscopy, height valuations, or calibrations, are critical to ensure accuracy and traceability. Height assessment, however, may be controversial, particularly for measurements on large steps or narrow grooves. Thus, standard setting and instrument operations are essential. In this paper, the limited energy lost (LEL) method, which is a Chinese solution, and the well-known

A probe optical fiber hydrogen sensor based on an in-fiber Fabry–Pérot interferometer (FPI) is proposed and experimentally demonstrated. The interferometer consists of a micro-cavity which is filled with thermosensitive liquid and lateral surface coated with hydrogen-sensitive material of Pt-loaded WO 3 . When the sensor is exposed to the hydrogen environment, the refractive index of the liquid in

In recent years, an increasing number of reported studies and technological applications have relied on controlling the wetting behavior at the solid–liquid interface. In order to study wetting behavior, the contact angle based on the sessile droplet method and the surface tension using the pendant droplet method are the most widely used metrics, which are conventionally obtained using a goniometer

Rat electrocardiography (ECG) is frequently used in biomedical research as a model for exploring heart function in a wide variety of experimental conditions. Subcutaneous ECG is a common approach to record rat heart rhythm using implanted needle electrodes to sense the rat ECG signals with the animal under deep anesthesia. However, such an invasive measurement could cause inconvenience due to cumbersome

This paper proposes a new approach for processing measured data from active Infra Red (IR) thermography, where a soft sensing algorithm is exploited for in depth defect reconstruction. This is achieved by propagating the information gathered at the wall surface to the inner layers. Correlating the experimental 2D measurements to a Finite Element (FE) model of the tested specimen it is possible to update

Multi-scale entropy (MSE) is a widely recognized feature extraction approach to mechanical fault diagnosis, for it can effectively estimate the complexity of nonlinear time series. For MSE algorithm, due to the sensitivity of entropy estimation on series length, the scale factors are often required to be limited to a small range. Nevertheless, in the existing MSE methods, the scale factors can only

The dynamic characteristics of a probing system directly affect the accuracy of dynamic measuring results and should be investigated comprehensively. Many methods can be used to identify the dynamic model of a probe. However, the uncertainty evaluation for the identified probe model remains a problem. A method based on signal transmission chain analysis is proposed in this paper to evaluate the uncertainties

Velocity updating typically involves integration of the transformed specific force and gravity Coriolis velocity increments. If the angular rate and specific force vectors maintain fixed directions relative to a frame, updating the velocity in that frame will be straightforward. In practice, the coning angular rate and sculling specific force vectors cause a calculation error in velocity updating on

Roadside trees are a vital component of urban greenery and play an important role in intelligent transportation and environmental protection. Quickly and efficiently identifying the spatial distribution of roadside trees is key to providing basic data for urban management and conservation decisions. In this study, we researched the potential of data fusing the Gaofen-2 (GF-2) satellite imagery rich

With the increasing number of long span bridges, real-time, accurate and continuous monitoring of their safety is important at present. This study investigates the combination of a global navigation satellite system (GNSS) and accelerometer for monitoring dynamic and semi-static characteristics of bridge structures. A field experiment was conducted with the integration of a GNSS and accelerometer.

This paper reports on the comparison of two Josephson arbitrary waveform synthesizers for frequencies up to 500 kHz. Both independent pulse-driven Josephson arrays produce a 10 mV RMS sinusoidal voltage. They are alternately connected to an analog-to-digital converter which serves as a transfer standard. The setup is capable to of synthesizing quantum-based waveforms using two different pulse-bias

The fast kurtogram is one of the most commonly applied methods for detecting rolling element bearing faults, and has been proven to be to be effective in most cases. However, the shortcomings of the kurtosis index limit the robustness and universality of the method, in that the kurtosis index is sensitive to single impulses with large amplitudes, and the segmentation of the spectrum is not adaptive

Non-zero temperature gradients in temperature-sensitive paint (TSP) cause the apparent temperature (the temperature measured by the TSP) to correspond to the temperature somewhere inside the TSP, which does not equal the top surface temperature. Treating the apparent temperature as the average temperature across the TSP layer is not always accurate, especially when there is a large temperature gradient

Several spurious effects are known to degrade the performance of phase-only spatial light modulators. We introduce a comprehensive model that takes into account the major ones: curvature of the back panel, pixel crosstalk and the internal Fabry–Perot cavity. To estimate the model parameters with high accuracy, we generate blazed grating patterns and acquire the intensity response curves of the first

The measurements of size distribution of small particles (e.g. dusts, droplets, bubbles, etc) are critical for a broad range of applications in environmental science, public health, industrial manufacturing, etc. Laser diffraction (LD), a widely used method for such applications, depends on model-based inversion with underlying assumptions on particle properties. Furthermore, the presence of sampling

Surgery remains one of the key treatment options for tumour removal, and surgeons primarily rely on eye and touch to assess the boundary between healthy and cancerous tissue with no cellular information as guidance. There is therefore a need for a device or instrument that can be used by the surgeon in real-time during the surgical procedure to ensure as many of the cancerous cells and as few of the

An optical chopper is described that has comparable performance to commercially available units. The new chopper is built within the frame of a hard disk drive, and uses the existing motor and its disk for operation. The rotation speed is measured using a photo-interrupter and is adjusted with a microcontroller. Chopping frequencies from 150 Hz to 1650 Hz with phase jitter less than 0.38 degrees per

Evaporation plays a central but largely invisible role in the moisture dynamics of buildings and urban microenvironments. Local evaporation rates control water flux and material damage, and are altered by climate change. While potential evaporation (PE) (or potential evapotranspiration (PET)) can be estimated on the large-scale, there are few if any methods of making local PE measurements. We describe

Large components docking is an important step in industrial manufacturing. During the docking process, the relative pose of joining components needs real-time and accurate acquisition. Existing methods rely on expensive and complex optical instruments. Photogrammetry has the advantages of low cost and fast measurement speed, but its measurement accuracy decreases sharply along with the increase of

Due to limitations in the generalisation ability of currently proposed improved variational mode decomposition (VMD) methods, it is hard to precisely and efficiently discern signal characteristics from different power systems. Meanwhile, it is difficult to separate non-order noise sources in current studies. To address this issue, a novel scheme is proposed based on parameter-adaptive VMD and partial

Object segmentation is a common task in bin-picking. Region-growing-based methods have been proven to be applicable for ordinary tasks, but they are not suitable for closely adjacent and stacked scenes. In this paper, we propose an inward-region-growing-based accurate partitioning method for bin-picking. A boundary bud generation algorithm is proposed for detecting the boundary initial points of closely

During the calibration of an aerodynamic probe, the correlation between the present representative flow quantities of the fluid and the measurand is determined. Thus, a large number, sometimes several thousands, of different calibration points are set and measured, making this a very time-consuming process. The differences in the calibration data of similar constructed probes are very small. With the

Welding of high-strength steels can result in large tensile strains as the base metal and filler material cool from their molten state. To combat these large tensile strains, low-transformation-temperature (LTT) metal fillers have been proposed. These fillers undergo a martensitic phase transformation at a lower temperature which can ultimately reduce the tensile strain or can even introduce compressive

We describe here an artifact that may affect to magneto-optical Kerr measurements. When paramagnetic sample holders (SH) with non-negligible susceptibilities are used, the inhomogeneity of the applied magnetic field can induce forces and torques on it, shifting the reflected beam, and altering its intensity at the photodetector. The effect is even and can be avoided using low susceptibility paramagnetic

This study reports on a dual-port, side-incident microwave probe dedicated to the non-destructive inspection of metal pipes. Two types of side-incident probes (LJ and JL) are proposed to emit TM 01 - and TM 02 -mode microwaves into the pipe under test, and each type of probe has two ports used to inspect in two opposite directions. Numerical simulations are conducted to study the dimensional parameters

The present paper concerns the oxide layer thickness determination of oxidized metals in the case where an optical interference phenomenon occurs due to multiple reflections inside the oxide layer. The paper focuses on anodized titanium but can be extended to the layer thickness determination of any material composed of a non-absorbing layer over an absorbing substrate. It establishes theoretical formulae

In this study, we investigated an annular flexible eddy current array sensor for quantitative monitoring of cracks in ferromagnetic steels under varying loads and temperatures. First, the sensor was designed to monitor the length of cracks in ferromagnetic materials. Using numerical simulations, the effects of permeability, lift-off distance, and conductivity on the response of the sensor were studied

In this paper, a novel approach is proposed to calibrate an underwater fisheye camera with the multi-frequency heterodyne technique based on the light field. First, an underwater fisheye camera imaging model based on the light field is established to demonstrate the multiple refractions of light in underwater propagation and the extraordinary imaging characteristics of the fisheye lens, which shows

Infrared thermography has been successfully adopted in the field of flow diagnostics over the last decades. Detecting the laminar–turbulent boundary layer transition through variations in the convective heat transfer is one of the primary applications due to its impact on the aerodynamic performance. Recent developments in fast–response infrared cameras allow unsteady measurement of fast–moving surfaces

The vibration signal of roller bearings contains important information, but the strong background noise makes fault diagnosis difficult. In this paper, inspired by the idea of a block-matching 3D algorithm, using local and nonlocal correlation of vibration signal, a patch-matching 2D (PM2D) denoising method is proposed for the first time to suppress noise in vibration signals. The proposed denoising

In this paper, the usefulness of planar Particle Image Velocimetry (PIV) measurements to determine the volumetric flow rate from a rectangular or round jet exit is assessed. Both two-component PIV (2C–PIV) and through-plane three-component (3C) stereo PIV (SPIV) data sets were acquired at the exit of a turbulent, rectangular nozzle and a round nozzle with Reynolds numbers between 10 000 and 100 000

The feasibility of a new design and measurement concept of a combined optical and x-ray interferometer (COXI) is demonstrated here. Mechanical noise in the x-ray interferometer can be cancelled efficiently with fast and synchronous detection of the optical interferometer phase and x-ray counts. The scan-length requirement of the decadic step method of conventional COXI setups is reduced by more than

Precise web tension measurement is critical for web handling and process control in roll-to-roll (R2R) manufacturing systems. Calculating web tension by using out-of-plane vibration measurement offers a contactless solution to tension measurement during the R2R process, which is suitable for situations where contacting web tension measurement sensors cannot be applied. In this paper, a real-time prediction

The particle/droplet image analysis (PDIA) technique is often used for droplet sizing in sprays. Successful use of PDIA for drop size measurement in sprays mandates careful calibration, and determination of the depth of field (DOF) for particles of different size classes. This is typically done with a calibration target that has circles etched on it. In the present study, a calibration experiment was

A camera in an underwater stereo vision system conforms to a multi-layer refraction model, and the perspective projection camera model is invalid. Because the imaging light is refracted, the corresponding pixel does not conform to the traditional polar constraint, and the stereo matching methods must conduct a two-dimensional search. In this paper, a standard expression is proposed to reduce the search

A generalizedcalibration technique for model errors is proposed for uniform linear arrays. Being different from the existing calibration methods, this technique constructs covariance matrices for two adjacent sampling periods, from a reference source with a known location, and then estimates the model errors from the difference between these matrices and an equation formed by using the MUSIC null space

Due to large noise, severe multi-path errors and the frequent rise and fall of satellites caused by propagation obstacles and mirror materials widespread in urban canyons with low-cost receivers produced with low-power design and restricted computing resources, the positioning accuracy in urban canyons with normal RTK has been heavily reduced with these large biased observations and discontinuous tracking

We address the problem of extracting the position and the Euler angles of an underground object from measurements of the magnetic field above that object. The traditional Euler inversion positioning method requires us to make use of the high-order magnetic gradient tensor system and extract the second-order tensor data, but at the same time it will increase the sensitivity to errors and measurement

The main features of the Calibration Curve Computing (CCC) Software, a tool for regression analysis developed at the INRIM, the Italian National Metrology Institute, are described in this paper. The first release of the software tool, version 1.3, has been available on the INRIM website for free download since 2015. It was developed under a Matlab environment and distributed as an executable file.

The existence of abrupt change points in mechanical equipment degradation leads to inaccuracies in the prediction of its residual life. We propose a real-time residual life prediction method based on kernel density estimation (KDE) considering the influence of abrupt change points. First, a non-parametric cumulative sum method is used to detect abrupt change points in the degradation process. Then

In order to counteract the adverse effects of biases in direct inertial navigation system/global navigation satellite system integration, a novel robust partly strong tracking consider state-dependent Riccati equation filter (PSTCSDREF) algorithm is proposed. A nonlinear ‘consider’ approach is utilized to incorporate bias statistics into a state estimation error covariance of the state-dependent Riccati

This work focuses on the void fraction measurement of gas–liquid two-phase flow by a 12-electrode contactless resistivity array sensor. Such a sensor, which can realize different excitation patterns, is developed here. Five different excitation patterns (with 1, 2, 3, 4 or 5 electrodes) and three two-phase distributions (bubble flow, stratified flow and annular flow) are investigated. Two data processing

Particulate matter emission from the combustion of fossil fuels is a major concern due to its harmful effects on human health and impact on engine performance. Measurement of the smoke point of these fuels is a key issue in order to assess the tendency of fuels to generate particulate matter. Although certain commercial devices for measuring the smoke point are available, they are very expensive and

Microelectromechanical systems (MEMS) are widely used in the navigation field due to their low cost and easy integration. Its low positioning accuracy restricts its expansion into the high-end navigation field. To improve the performance of MEMS inertial devices, this paper proposes a nested Kalman fusion (NKF) for MEMS gyroscope array data fusion applied to the virtual gyroscope. First, the algorithm

This paper presents a method for the simultaneous reconstruction of temperature and soot volume fraction distributions in axisymmetric flames. In the proposed method, the radiation temperature and emissivity are determined using a multi-wavelength method. Then, based on the decomposition of the emissivity, the soot volume fraction distribution is reconstructed. Accordingly, the temperature distribution

Color image indices used to characterize surface roughness are more sensitive than grayscale images or spectral indices owing to the rich information contained in color images. In this paper, a method for measuring grinding surface roughness grinding based on the singular value entropy of the color image quaternion matrix is proposed. Color images captured at different levels of surface roughness are

There are some commonly-used optimization techniques for the analysis of measured data in spectroscopic Mueller matrix ellipsometry (MME) used, for example, to calculate the layer thicknesses of samples under test. Concentrating on the metrological aspects of MME, we identified a non-optimal treatment of depolarization in all these techniques. We therefore recently developed an improved optimization

We report a neutron beam polarization P = [99.9982 ± 0.0024]%, which means an improvement of two orders of magnitude compared to known values. Actually, one can assume this neutron beam to be 100% polarized, because due to the special beam guidance the overlap of spin-up neutrons and spin-down neutrons could be suppressed down to 1.2 × 10 −12 [rel. units]. These values are about four orders of magnitude

Tomographic background-oriented schlieren (BOS) is used to measure three-dimensional instantaneous density fields in turbulent flows. Density gradients are related to the refractive index through the Gladstone-Dale relation. Based on path-integrated apparent displacements in a background pattern from path variations in light rays travelling through the flow, a tomographic reconstruction of the three-dimensional

The Shannon entropy measure, applied to the time frequency distribution of a signal, is a reliable indicator to quantitatively analyze the health status of a rolling element bearing. Usually, however, conventional time frequency representations rely on the selection of the best scale of a base function in order to deal with the noise components present in a vibration signal. In this context, the time

The early detection of blade icing is gaining increasing attention due to its importance in guaranteeing wind turbine safety and operation efficiency. In this study, a wind turbine icing fault detection method based on discriminative feature learning is proposed. First, a stacked autoencoder (SAE) is trained to generate representations, which utilizes a large amount of normal operating data, as well

Microfluidic devices present new opportunities for a wide range of applicationsin which the temperature control of nanoliter droplets is required. Due to the inherent size of the employed miniature volumes, several challenges exist, related to temperature measurements. In this work, we present a non-contact and label-free dielectric-based temperature measurement technique. A capacitive sensor transduces

Conventional intelligent diagnostic models are built on the foundation that the training data and testing data are recorded under the same operating conditions, which neglects the fact that the operating condition of the rotating machinery usually varies. The feature distribution of the recorded data under one set of operating conditions may be inconsistent with the feature distribution of the data

In contact resonance force microscopy and related dynamic atomic force microscopy methods, an accurate description of the real-time cantilever dynamics is essential to the mapping of local material properties, such as viscoelasticity, piezo response, and chemical composition. Stiffness and damping variations of the tip-sample contact result in variations in the cantilever’s resonance frequency and