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The traditional pressure sensors are mostly based on piezoresistive, piezoelectric effect, and strain gauge, which are easily affected by ambient temperature. The structure of some sensors is rather complex to effectively acquire the signal or measure distribution force. Therefore, a pressure sensor based on the planar coil and elastic element was designed to solve this problem. The newly designed sensor has a spiral planar coil made by a printed circuit board and a polydimethylsiloxane (PDMS) thin film as the elastic element. The conductive layer is attached on the upper surface of PDMS to realise the eddy current effect. Meanwhile, a simulation model was established to find the relationship between deformation displacement and the pressure of the elastic element. By generating the experimental curves of the deformation displacement of the elastic element and the output frequency of the eddy current sensor, the pressure measurement on the surface of the elastic element can be identified. The preliminary experimental results showed that the eddy current pressure sensor based on the plane coil has good linearity and repeatability, and it can realise large area distributed pressure measurement, which is also suitable for accurate measurement of distribution force. [ABSTRACT FROM AUTHOR]

With the wide application of the high-speed electrical machine with the active magnetic bearings (AMBs), improving the dynamic response and the resolution of the displacement sensor for AMBs becomes an actual challenge for industrial development. This paper proposes a self-differential eddy current displacement sensor (ECDS) for radial AMBs system. The phase advance network method was utilized to improve the dynamic characteristic for the sensor based on the equivalent transfer function model. The reason of the sensor-to-sensor crosstalk was analyzed in detail to provide a theoretical basis for improving the resolution of the sensor. First, the operating principle of the ECDS was analyzed in detail. Second, the miniaturization design was presented: the two symmetrical probe coils were used as the working inductors in the Hartley oscillation circuit to form a self-differential structure to simplify the measuring circuit observably, and suppress the common mode interference. Third, the dynamic characteristic of the sensor and the sensor-to-sensor crosstalk was described and compensated. Finally, a series of experiments was carried out to test the sensor performance. The experimental results showed that the ECDS with the features of the minimum circuit, the wide bandwidth, and the high resolution can greatly improve the controllability of the AMBs system. [ABSTRACT FROM AUTHOR]

Purpose Magnetic permeability variations of ferromagnetic materials under elastic stress offer the potential to monitor tension based on the inverse magnetostrictive effect. The purpose of this paper is to propose an innovative self-inductance tension eddy current sensor to detect tension.Design/methodology/approach The effectiveness of conventional elasto-magnetic (EM) sensor is limited during signal detection, due to its complex sensor structure, which includes excitation and induction coils. In this paper, a novel self-inductance tension eddy current sensor using a single coil is presented.Findings The output signal was analyzed through oscilloscope in the frequency domain and via self-developed data logger in the time domain. Experimental results show the existence of a linear relationship between voltage across the sensor and tension. The sensor sensitivity is dependent on operating conditions, such as current and frequency of the input signal.Practical implications The self-inductance sensor has great potential for replacing conventional EM sensor due to its low cost, simple structure, high precision and good repeatability in tension detection.Originality/value A spilt sleeve structure provides a higher permeability path to magnetic field lines than a non-sleeve structure, thus reducing the loss of magnetic field. The self-developed data logger improves sensitivity and signal-to-noise ratio of sensor. The novel sensor, as a replacement of the EM sensor, can easily and accurately monitor the tension force. [ABSTRACT FROM AUTHOR]

The thickness of anti-corrosive layer coated in the inner surface of steel oil containers is very important to prevent the containers from corrosion. To make the measurement accurate, some effective means are needed, especially for the eddy current sensor inclining or deviating over the curved inner surface of the containers. By using an electromagnetic field simulation method with high accuracy, the distorted signals and the measure precision of lift-off were analyzed. Then, some correction measures were proposed according to the characteristics of testing signals due to the sensor's inclination or deviation. Simulation results confirmed their effectiveness for enhancing the measure precision. The conclusions can give an effective theoretical guide to the centering and verticality controlling of the sensor in practice. [ABSTRACT FROM AUTHOR]

Eddy current testing is quite a popular non-contact and cost-effective method for nondestructive evaluation of product quality and structural integrity. Excitation frequency is one of the key performance factors for defect characterization. In the literature, there are many interesting papers dealing with wide spectral content and optimal frequency in terms of detection sensitivity. However, research activity on frequency optimization with respect to characterization performances is lacking. In this paper, an investigation into optimum excitation frequency has been conducted to enhance surface defect classification performance. The influences of excitation frequency for a group of defects were revealed in terms of detection sensitivity, contrast between defect features, and classification accuracy using kernel principal component analysis (KPCA) and a support vector machine (SVM). It is observed that probe signals are the most sensitive on the whole for a group of defects when excitation frequency is set near the frequency at which maximum probe signals are retrieved for the largest defect. After the use of KPCA, the margins between the defect features are optimum from the perspective of the SVM, which adopts optimal hyperplanes for structure risk minimization. As a result, the best classification accuracy is obtained. The main contribution is that the influences of excitation frequency on defect characterization are interpreted, and experiment-based procedures are proposed to determine the optimal excitation frequency for a group of defects rather than a single defect with respect to optimal characterization performances. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents a new complete approach for Tool Condition Monitoring (TCM) in milling. The aim is the early detection of small damages so that catastrophic tool failures are prevented. A versatile in-process monitoring system is introduced for reliability concerns. The tool condition is determined by estimates of the radial eccentricity of the teeth. An adequate criterion is proposed combining mechanical model of milling and angular approach. Then, a new solution is proposed for the estimate of cutting force using eddy current sensors implemented close to spindle nose. Signals are analysed in the angular domain, notably by synchronous averaging technique. Phase shifts induced by changes of machining direction are compensated. Results are compared with cutting forces measured with a dynamometer table. The proposed method is implemented in an industrial case of pocket machining operation. One of the cutting edges has been slightly damaged during the machining, as shown by a direct measurement of the tool. A control chart is established with the estimates of cutter eccentricity obtained during the machining from the eddy current sensors signals. Efficiency and reliability of the method is demonstrated by a successful detection of the damage. [Copyright &y& Elsevier]

Abstract: Measurement of nano-scale copper film thickness is of great importance in the semiconductor industry. The eddy current method is used for the purpose due to its non-destructive and fast dynamic response features. In this paper, an equivalent circuit model is used to get the relationship between the measurement sensitivity and sensor parameters. It is found that the internal resistance of an eddy current sensor plays a primary role in the improvement of the measurement sensitivity beside of the Q factor of the sensor. A simple experimental setup is established and a series of Cu films with the thicknesses ranging from 20nm to 350nm are prepared as test samples. Test results indicate that the sensitivity of an optimized sensor made of a lower resistant multi-wire Cu line has better sensitivity than that wound with a higher resistant single Cu wire under large lift-off. [Copyright &y& Elsevier]

The anti-corrosive coating in pipeline and oil tanker is taken as a crucial component in petroleum industry and needs a robust NDE tool to evaluate its thickness. For the thick coating on the curved steel bases of various sizes, the eddy current sensor's evaluation capability for thick coating and the influence of the test-piece sizes on the evaluation precision are two key problems had to be solved. Taking into account the dimension effect of the sensor on signals, a wide-range sensor was designed and applied to the coating evaluation. The relationship between coil responses and liftoff was investigated and a NDE strategy based on a polynomial coefficient database was proposed to cope with the influence of test-piece sizes. Its applicability was verified by simulation results. [ABSTRACT FROM AUTHOR]

Abstract: Analytical solutions for the inductance can be easily obtained for coils with rectangular cross sections having multiple turns realizing a homogeneous current distribution. These models have at least six parameters and do not consider the self-capacitance of the coil. The inner magnetic field is partially included, so that the accuracy of the static impedance is limited especially at higher frequencies. Even at lower frequencies, reference measurements without target are generally needed for self-calibration. By direct evaluation of the magnetic vector potential at the contour of the coil wire, a coil inductance model with a simpler mathematical structure can be obtained, which allows a consideration of the self-capacitance and the inner inductance. This avoids the need for reference measurements and the influence of distance, conductivity and permeability can be easier quantified. Inductance calculation requires 250ms on a standard personal computer for 100 frequencies resulting in a deviation of at most 5% for the static inductance. This is a good result with respect to the low impedances in the μΩ range, which are generally hard to measure. The proposed model represents a good basis for models of multiple turns with a precisely defined geometry including the self-capacitance effects. [Copyright &y& Elsevier]

Abstract: The 500MWe sodium cooled prototype fast breeder reactor (PFBR) presently under advanced stage of construction has two diverse and independent shut-down systems. Each shutdown system comprises of independent sensing systems, control logic and drive mechanisms. The drive mechanism belonging to the first shutdown system is used for controlling reactor power and also for shutting down the reactor. It is known as control and safety drive rod mechanism (CSRDM). The mechanism belonging to the second shutdown system is used only for shutting down the reactor and is called diverse safety rod drive mechanism (DSRDM). CSRDM has potentiometer which is used to determine the position of the control and safety rod (CSR). The free fall time of control and safety rod can also be measured with the help of the potentiometer. Constraint of putting similar type of instrument in DSRDM has prohibited position detection of DSR as well as measurement of free fall time of diverse safety rod (DSR). However center has embarked on development of three different techniques to detect the position and free fall time of DSR. These techniques are Kalman filtering technique using neutronic signal to detect position of DSR, measurement of acoustic signal which is produced when DSR hits the dashpot and the eddy current based technique. Description of development of eddy current based sensor to detect position and free fall time of DSR is the main aim of this paper. The sensor consists of five coils which are inductively coupled. The change in position of DSR causes change in inductance of the coil and hence voltage induced in the coil. The measurement of coil voltage reveals the position of the DSR. Sodium testing of the sensor has been carried out on a 1:1 model of the sensor. The performance of the sensor at various temperatures and frequencies has been studied and found satisfactory. The sodium testing has shown encouraging results and have proven the feasibility of using such a sensor for the reactor application. The piston of the DSR is made of modified 9Cr–1Mo magnetic steel. A sensor winding is placed around the dashpot, the inductance of the winding changes when the DSR is deposited in the dashpot. Transformer coupling between two windings is then used to measure the inductance change of the sensor winding to facilitate non-contact measurement. The winding configuration has been chosen such that the signal can be picked-up even when there is misalignment between the coils due to thermal and radiation induced dimensional changes. [Copyright &y& Elsevier]

In order to provide a contactless measurement technique to examine products during the fabrication process, a modular design of an eddy current micro sensor was developed and fabricated in thin-film technology. The sensor consists of two parts, a single-turn excitation coil and an anisotropic magneto-resistance (AMR) sensor. The AMR sensor detects the change of the magnetic field induced in a sample by the excitation coil. Initial investigations were conducted to prove the capability of the completed eddy current micro sensor. A defect was created on the surface of a Cu probe. The electrical output signal of the AMR sensor was subsequently compared to optical measurements of the surface profile of the crack. There is a high correlation between the optical measurements and to those of the eddy current micro sensor. [ABSTRACT FROM AUTHOR]

For decades, vibration and oil analysis have usually been used to detect early bearing faults and track their progression over time. Progress has been seen in condition monitoring through vibration analysis of rolling element bearings using improved sensors and advanced signal processing techniques. In this paper, the authors investigate the use of air-coupled ultrasound and eddy current sensors as diagnostic tools for the detection of bearing faults. A series of experiments was carried out in a laboratory environment: localized defects with different sizes were created intentionally on the test bearing components simulating evolving cracks or other related faults. The resulting data for a constant bearing speed and load have shown that both sensors are capable of detecting different types of defects located on the bearing components. The data from the air-coupled ultrasound and eddy current sensors were also compared with those obtained from an accelerometer. The test method and the processing technique are described and the spectra of the different signals are analyzed and discussed. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a new flexible eddy current sensor array and its measurement system that used for conformable proximity sensing, for instance, the gap between curved surfaces. The sensor probe, designed to consist of a forked coils array and a long flat cable, is manufactured on a thin flexible substrate by the flexible printed circuit board (FPCB) technology. The probe is very thin and flexible, so that it can conform to the surface geometries of the measured objects. Time division multiplexing (TDM) technology has been introduced to scan and sample all the sensing elements. Some reforms are also implemented to the conventional LC oscillator to solve the problem of the coils having a low Q-factor. Experimental results show that, to a steel target, the measurement accuracy of the sensor system can reach ±0.5% for a 2mm full scale. The practice for real-time inspection of the small gaps between large curved surfaces is also considered. [Copyright &y& Elsevier]

Abstract: Increasing demands on re-enforced concrete constructions (e.g. bridges) require long-term multi-sensor monitoring techniques. For failure prediction of components the continuous monitoring of force and stress in reinforced concrete components is required. Coils can detect very small stress variations in ferromagnetic steels due to the magneto-elastic effect. Their main advantage over strain gauges is the ability of a medium-free measurement. Environmental and real construction conditions led to a sensor arrangement with six individual eddy current coils. These coils were arranged around a strand wire and are also in direct contact with the material under testing. Due to changing magnetostriction coefficients of different structural steels an impedance calibration is necessary [D. Jiles, Introduction to Magnetism and Magnetic Materials, Chapman and Hall, London, 1991]. [Copyright &y& Elsevier]

Joint replacement surgeries have enabled motion for millions of people suffering from arthritis or grave injuries. However, over 10% of these surgeries are revision surgeries. We have first analyzed the data from the worldwide orthopedic registers and concluded that the micromotion of orthopedic implants is the major reason for revisions. Then, we propose the use of inductive eddy current sensors for in vivo micromotion detection of the order of tens of μ m. To design and evaluate its characteristics, we have developed efficient strategies for the accurate numerical simulation of eddy current sensors implanted in the human body. We present the response of the eddy current sensor as a function of its frequency and position based on the robust curve fit analysis. Sensitivity and Sensitivity Range parameters are defined for the present context and are evaluated. The proposed sensors are fabricated and tested in the bovine leg. [ABSTRACT FROM AUTHOR]