Magnetic Induction Tomography System Research Articles

Development and evaluation of a slurry density measurement system based on Applied Current-Magnetic Induction Tomography (AC-MIT)

Slurries are an important part of many industrial processes such as food processing, mineral and dredging industries. In this study, an Applied Current Magnetic Induction Tomography (AC-MIT) system was developed for measuring solid mass concentration of slurry in pipeline. The proposed AC-MIT system has two annular electrodes as transmitter sensors and 16 coils as receiver sensors. Performance of developed AC-MIT system was evaluated at five levels of salinity (7.5, 10, 12.5, 15 and 17.5 gr/lit of NaCl) and five levels of temperature (19, 24, 29, 34 and 39 °C). Some evaluation parameters such as; standard deviation (SD) and root mean square error (RMSE) were used to assess the system performance. Analysis of variance (ANOVA) is conducted to investigate the effect of temperature and salinity on the system performance. Multivariate regression method was assessed in order to predict the performance of AC-MIT system at different levels of temperature and salinity of the carrier phase as well as different solid mass concentrations. The ANOVA results showed that change in the temperature and salinity levels of the carrier phase did not have a significant effect on system performance (p > 0.05). Also there is a good correlation (R2 in the range of 0.98–0.99) for the measured solid mass concentration in both manual sampling method and AC-MIT system. This result is confirmed by the multivariate regression assessments as well as.

Numerical simulations of magnetic induction tomography system based on a 3D head model

Magnetic induction tomography (MIT) has been proposed as a novel, non-invasive, and non-contact technique for diagnosing brain injuries. The design of the hardware system of MIT is a challenging research area. In this study, we constructed a 16-coil MIT simulation model with an actual cranio-cerebral anatomical structure in COMSOL. We analysed the factors which influence the MIT signal by constructing different types of haemorrhagic stroke models. In addition, the safety of MIT devices was evaluated in detail using the specific absorption rate. The results show that the phase noise of the hardware data acquisition system should be less than 0.001° for the detection of a small peripheral haemorrhage with 5 mL. The result of the specific absorption rate shows that the security of MIT equipment should not be overlooked, and we need to establish a trade-off between signal intensity and device security. This study can provide data to support additional improvements in the performance of hardware systems in the future.

Sensitivity Analysis of Circular and Helmet Coil Arrays in Magnetic Induction Tomography for Stroke Detection.

Magnetic induction tomography (MIT) is harmless and contactless technique for measuring the conductivity of the biological tissue. MIT could be used for initial diagnosis and continuous monitoring of stroke. Different kinds of coil arrays have been proposed for MIT systems. Previous research results using a circular 16-channel MIT model reported difficulties with detection and measurement of small bioelectric signals. For stroke imaging, a system with a higher sensitivity is required. We aim to improve the sensitivity by increasing the number of coils and placing them closer to the head. In this paper, a helmet type coil array with 31 coils is introduced. For simplicity, the head is modelled as a sphere with white matter as a material. The stroke is simulated as a single inclusion with blood and assigned different sizes and positions. Sensitivity distribution and target response of the stroke were evaluated for the helmet model and compared with the circular MIT system. The simulations and analysis were performed at 10 MHz frequency with different coil pairs. Results from comparison of the two MIT models show that the Helmet coil array provides better spatial sensitivity, which has been estimated to be more than 20 times higher than the circular model. Further, when all coils are taken in account, the recorded sensitivity improvement was in the range of 13-90-fold.

Magnetic Induction Tomography Using Multi-Channel Phase-Domain Transceiver for Structural Health Monitoring

This article aims to develop a miniaturized magnetic induction tomography (MIT) system with a multi-channel phase-domain transceiver integrated circuit (IC). MIT is an imaging technique using phase shift between a primary magnetic field and induced field caused by the conductivity of a target object. Due to the weak strength of time-varying magnetic field, it is difficult to differentiate the magnetic field interaction. In particular, if the conductivity of the target object is low, the induced field is too small to identify the phase difference. The magnetic dipole model is applied to modeling the MIT system and analyzing performance. The model offers an effective means to analyze and visualize magnetic field interaction in multi-channel by the sum of magnetic dipoles. Then, a multi-channel MIT detection device is developed to include the phase-domain transceiver for automatic high-resolution phase measurement and wireless connectivity, achieving enhanced power efficiency and miniaturization. Finally, the multi-channel MIT system is applied to identify the various sizes of cracks on carbon fiber rods. The sensitivity of the system is analyzed by imaging the cracks by multi-channel measurement. The results show that the multi-channel MIT system can be successfully miniaturized and perform the nondestructive test (NDT).

Simulation of Single Channel Magnetic Induction Tomography for Meningitis Detection By Using COMSOL Multiphysics

Meningitis is a inflammation of the meninges and the most common central nervous system (CNS) due to bacterial infection. Numbers of children who have bacterial meningitis are still high in recent 15 years regardless of the availability of newer antibiotics and preventive strategies. This research focuses on simulation using COMSOL Multiphysics on the design and development of magnetic induction tomography (MIT) system that emphasizes on a single channel rotatable of brain tissue imaging. The purpose of this simulation is to test the capability of the developed MIT system in detecting the change in conductivity and to identify the suitable transmitter-receiver pair and the optimum frequency based on phase shift measurement technique for detecting the conductivity property distribution of brain tissues. The obtained result verified that the performance of the square coil with 12 number of turns (5Tx-12Rx) with 10MHz frequency has been identified as the suitable transmitter-receiver pair and the optimum frequency for detecting the conductivity property distribution of brain tissues.

A Study of Magnetic Induction Tomography (MIT) for Calcium Oxalate Renal Screening

Nephrolithiasis is a process of stone formation in the kidney by crystallization. The increasing prevalence of nephrolithiasis from time to time had sought an alternative from the conventional imaging techniques that is invasive, radiative, and non-rapid usage. This paper enclosed a design simulation study of Magnetic Induction Tomography (MIT) system using COMSOL Multiphysics for renal imaging. MIT is a soft field tomography and non-contact imaging modality which can project the passive electromagnetic properties (conductivity, permittivity and permeability) under the principle of electromagnetic induction. In this research also, 8 copper trans-receiver coils were employed in the MIT system and fixed by the insulation belt. Meanwhile, geometric set-up of renal organ was set to imitate the transverse section of human renal. In the methodology, sensor performance analyses were done using frequency ranging from 50 kHz to 2 MHz of the MIT system on radii of calcium oxalate in renal. The sensor response and pattern is discussed in this paper.

Multi-Frequency Magnetic Induction Tomography System and Algorithm for Imaging Metallic Objects.

Magnetic induction tomography (MIT) is largely focused on applications in biomedical and industrial process engineering. MIT has a great potential for imaging metallic samples; however, there are fewer developments directed toward the testing and monitoring of metal components. Eddy-current non-destructive testing is well established, showing that corrosion, fatigue and mechanical loading are detectable in metals. Applying the same principles to MIT would provide a useful imaging tool for determining the condition of metal components. A compact MIT instrument is described, including the design aspects and system performance characterisation, assessing dynamic range and signal quality. The image rendering ability is assessed using both external and internal object inclusions. A multi-frequency MIT system has similar capabilities as transient based pulsed eddy current instruments. The forward model for frequency swap multi-frequency is solved, using a computationally efficient numerical modelling with the edge-based finite elements method. The image reconstruction for spectral imaging is done by adaptation of a spectrally correlative base algorithm, providing whole spectrum data for the conductivity or permeability.

Non-contact detection of single-cell lead-acid battery electrodes’ defects through conductivity reconstruction by magnetic induction tomography

The change of electrodes’ conductivity is a crucial parameter during battery aging process, non-contact detection of battery electrodes’ defects through conductivity reconstruction is an innovative technology. In this paper, the magnetic induction tomography (MIT) was applied to reconstruct the conductivity of electrodes, the simplified battery models with complete and broken electrodes were chosen as target A and target Brespectively, and an eight-channel MIT system was designed to measure the change of mutual induced voltage. A method of computing the forward problem called ‘A·E’ was adopted to compute the coefficient matrix for the forward problem and the frequency 12.665kHz was chosen as the excitation frequency. Based on the conductivity reconstruction images, relative errors of reconstructed conductivity and objective function, ‘A·E’ method exhibited advantages in terms of computation time and accuracy compared to coefficient sensitivity method with the simulation data. In order to test the accuracy of ‘A·E’ method, data measured by MIT system was applied in the inverse problem with four regularization parameter selection methods. L-curve criterion and generalized cross-validation criterion identified defects successfully as they were more sensitive to the change of conductivity.

Exploratory Designing a Magnetic Induction Tomography Sensor Coil Circuit for Agarwood

Magnetic induction tomography (MIT) is an imaging modality focused on tracing the transmission of electrical conductivity within the body. This technique used to image electromagnetic properties of an object by using the eddy current effect. This paper explains the primary analog transceiver circuit of MIT. This is a surrogate design of the analog system in the electronic components for pattern recognition and conditioning. This MIT system operating with a single excitation signal frequency at 10MHz. The input voltage received by the receiver sensor would become the circuit input which contained information. The four stages process in the receiver circuit successfully captured the signal from the transmitter. These subsystems have their functions and can be put into effect in many ways. Therefore, the circuit was used to be reliable at agarwood samples. The approach transceiver circuit were successful and functional for MIT coil sensing. The input voltage feedback depending on the conductivity of the samples. As the dielectric properties of samples are high, the input voltage at the receiver also high. Therefore, 10MHz can use for agriculture while this range of frequency is usually used in biomedical applications. Series – parallel circuit gives a greater induction factor and therefore more induced voltage for the load of the receiver.

A Modular Magnetic Induction Tomography System for Low-Conductivity Medium Imaging

Due to the noncontact, nonradiative, and low-cost features, magnetic induction tomography (MIT) is highly applicable in conductive medium imaging. To meet the demands of low-conductivity medium imaging in industrial and biomedical applications, a portable, flexible, and extensible MIT system with high-phase detection precision is proposed. The proposed system is designed with different modules. Therefore, it is flexible to extend and meet different applications. The sensor modules can be used as both the excitation and the detection. The detected signal is directly demodulated at the sensor end, which avoids the external interference that may be introduced into the transmission of the detected signal. A phase demodulation part is designed which can achieve 0.0068° phase detection precision. Furthermore, the designed system does not need to rely on other instruments to realize the signal generation and demodulation, which makes the MIT system independent and portable in the practical application. The sensing coils have high consistency, and the signal-to-noise ratio (SNR) of the demodulated signal is over 60 dB. To illustrate the performance of the system, the capability of reconstructing low-conductivity saline solutions is studied. The images of conductivity distribution are obtained using the Tikhonov regularization method. The minimum detectable volume of saline solution is 10 mL, with a spatial resolution of 16.6%. The minimum detectable conductivity is 0.1 S/m, and the maximum detectable depth is 40 mm. The reconstructed results indicate the feasibility of low-conductivity medium imaging in the industrial and biomedical applications by the proposed MIT system.

Solution of 2D MIT Forward Problem by Considering Skin and Proximity Effects in Coils

Previous studies on the forward problem of magnetic induction tomography (MIT) have used simplified Maxwell's equations which assume a constant and position-independent total current density (TCD) inside the coils (ignoring skin effect). Moreover, they assume that TCD is independent of relative position of the coils (ignoring proximity effect). This article presents an improved finite element (FE) modeling for the two-dimensional (2D) forward problem of MIT by incorporating skin and proximity effects in the exciter and sensor coils. Consideration of skin and proximity effects requires the use of a position-dependent TCD in Maxwell's equations inside the coil domain. The FE method implementation of the improved forward method is validated with a simple analytical test problem. To evaluate the performance of the improved method in possible medical and industrial applications with low conductivity regions, a 16 coils 2D MIT system is modeled and the FE method is employed to solve the forward problem using a synthetic phantom. Results show the difference between the real parts of induced voltages obtained from the early and improved method falls into the range which is meaningful in terms of achievable conductivity contrast from the improved one. This discrepancy can generate considerable errors in image reconstruction. By considering skin and proximity effects, the improved method generates lower voltages in the coils suggesting the use of more precise hardware to detect inclusion. Findings show the importance and necessity of using improved method for modeling 2D MIT coils especially at low conductivity applications where measured signals are inherently weak.

Small Scale Non-Invasive Imaging Using Magnetic Induction Tomography - Hardware Desig

This study is conducted to preliminary image the conductivity profile through the development of small scale non-invasive Magnetic Induction Tomography (MIT) system. It is proved that the Magnetic Induction Tomography interested in mapping the passive electrical properties of materials; conductivity (σ), permittivity (e) and permeability (µ) in both process and medical tomography. The system is realized by designing the functional ferrite-core coil sensors, electronic measurements circuits for excitation and receiving coil, data acquisition system for transferring the data to the PC and suitable image reconstruction algorithm for providing the conductivity distributions measurement. The important characteristic for excitation coil is the one that can maintain the stability the optimum sine wave frequency ranging from 400 kHz up to 10 MHz. The sine waves are fed to the excitation coil through the application of high current amplifier component respectively. In the experiments, the copper phantom represent as high conductivity material were placed into the region of interest. The initial 16 channel MIT consists of 8 excitation coil and 8 receiving coil stacked alternately. On the receiving circuit, the major problem is the weak secondary signal perturbation sensed by the receiving coil has been improved by placing the variable amplifier on each receiver. The enhancement of conductivity profile imaging has been made by using a common Linear Back Projection (LBP) algorithm. The measurement was done on single and dual arrangement of copper phantom aligns in random coordinate so that the sensitivity of the excitation and receiving coil sensor can be experimentally observed. The imaging’s results show that the hardware’s and algorithm used was capable to process the data captured at the receiver. The results obtained can be useful for further improvement and research towards magnetic induction tomography.

Design of a scanning magnetic induction phase measurement system for respiratory monitoring.

The commonly used respiratory monitoring methods in clinical medicine are chest belt or ventilators, which are not easy to carry and cumbersome to operate. In order to solve this problem, a low-cost and portable magnetic induction phase detection system for respiratory monitoring is proposed. In this study, a magnetic induction tomography system for respiration detection is established, and the phase sensitivity of the system to conductive object is evaluated through a series of experiments. At the same time, phantom experiments are carried out to simulate the respiratory process, and the phase monitoring indicators are collected to describe different respiratory states. The experimental results show that the phase detection results are consistent with the changes in the respiratory cycle. The signal-to-noise ratio of the system is 79 dB. It proves the feasibility of using magnetic induction phase measurement in respiratory monitoring and provides a new detection method of respiratory monitoring.

In situ steel solidification imaging in continuous casting using magnetic induction tomography

The solidification process in continuous casting is a critical part of steel production. The speed and quality of the solidification process determines the quality of the final product. Computational fluid dynamics (CFD) simulations are often used to describe the process and to design its control system but, so far, there has been no tool that provides an online measurement of the solidification front of hot steel during the continuous casting process. This paper presents a novel magnetic induction tomography (MIT) solution, developed in the EU-funded SHELL-THICK project, to work in a real casting setting and to provide a real-time and reliable measurement of the shell thickness in a cross section of the strand. The new MIT system was installed at the end of the secondary cooling chamber of a casting unit and tested over several days in a real production process. MIT is able to create an internal map of the electrical conductivity of hot steel deep inside the billet. The image of electrical conductivity is then converted to a temperature profile that allows the measurement of the solid, mushy and liquid layers. In this study, such a conversion is done by synchronizing in one time step the MIT measurement and the thermal map generated with the actual process parameters available at that time. The MIT results were then compared with the results obtained with the CFD and thermal modelling of the industrial process. This is the first time in situ monitoring of the interior structure has been carried out during a real continuous casting.

Coupled Multi-Resolution WMF-FEM to Solve the Forward Problem in Magnetic Induction Tomography Technology

Magnetic Induction Tomography (MIT), is a promising modality used for non-invasive imaging. However, there are some critical limitations in the MIT technique, including the forward problem. In this study, a coupled multi-resolution method combining Wavelet-based Mech Free (WMF) method and Finite Element Method (FEM), short for WMF-FEM method, is proposed to solve the MIT forward problem. Results show that using the WMF-FEM method could successfully solve the mesh coordinates dependence problem in FEM, apply boundary condition in the WMF method, and increase MIT approximations. Simulations show improved results compared to the standard FEM and WFM method. The proposed coupled multi-resolution WMF-FEM method could be used in the MIT technique to solve the forward problem. The contribution of this paper is a simulated MIT system whose performance is closely predicted by mathematical models. The derivation of the simulation equations of the coupled WMF-FEM method is shown. This new approach to the forward problem in MIT has shown an increase in the accuracy in MIT approximations.

Sector sensor array technique for high conductivity materials imaging in magnetic induction tomography

BackgroundMagnetic induction tomography (MIT) is a tomographic imaging technique, which has potential applications in security, industry, and medicine. Typically, sensors form a closed structure around the object. However, the measurement cannot be achieved using a closed sensor array in the process of severe brain trauma nursing and the neurosurgery operation.ResultsThe new sector sensor array magnetic induction tomography (SMIT) system is developed to realize real-time monitoring in the treatment of the brain. The functions of the drive coil and the sensor coil are separated in this system. The detection sensitivity of the imaging region boundary is analyzed through simulation. The sensor array locates on the high detection-sensitivity area, and the low sensitivity detection area is reserved for operation and clinical equipment. The sensor array received the energy of the signal accounts for reach 90% of the total energy. The integrity measuring data are obtained using a rotating scan in the system. In the experiment, we analyze the effects that system parameters have on the quality of imaging, for example, the scan step size, the number of sensors, the coverage angle of the sensor array and the scan angle. The experiment result provides a reference for the SMIT system design under a particular condition. In the complete measurement, the SMIT system reconstructs the images of center goal and margin goal, and the actual images have high peak signal-to-noise ratio.ConclusionsThe SMIT system can rebuild the conductivity distribution of the imaging region using incomplete space. In rotation measurement, the system provides a working place for clinical care. The flexible design of the system based on the experiment result makes the different treatment for brain injury own matched SMIT equipment.

Practical Current Distribution Measurement Systems for Lead Cells

In this paper, the current distribution of an experimental lead cell is estimated using two methods and the results are compared. Noninvasive measurements are obtained using our magnetic tomography system, consisting of an array of magnetic sensors and a solver algorithm that is specially adapted for application to lead cells. Verification of this magnetic tomography system is achieved by comparing the results with data from a new invasive measurement instrument also reported in this paper. This new instrument is an array of ferrous cored current transducers submerged in the cell electrolyte, providing a direct spatially and temporally resolved measurement of the ionic current in a lead cell. Comparisons between the techniques and data are drawn. The new flowthrough internal sensor array has been designed specifically for this application and represents an improvement over a similar system reported in the literature. In addition, some auxiliary features of the experimental setup are designed to enable useful magnetic measurements to be taken by minimizing the complexity of the setup, and therefore the complexity of the models needed to interpret the data. Example results are presented for a typical automotive lead cell operating at a low state of charge and in a fatigued condition, to demonstrate the ability of both measurement systems to produce spatially and temporally resolved images of current distribution. The methods are evaluated, and the future work is recommended.

Design of a Magnetic Induction Tomography System by Gradiometer Coils for Conductive Fluid Imaging

Magnetic induction tomography (MIT) is a non-intrusive and non-invasive method that can image the cross-sectional conductivity distribution inside the object without contact. Target applications are conductive fluid testing in biomedical or industrial processes. The gradiometer coil is used as the front-end sensor of the proposed MIT system. As demonstrated through theoretical analysis and numerical simulation, the phase sensitivity to the conductivity of the gradiometer is greatly enhanced by eliminating the primary voltage with differential coils. The sensitivity is tunable by the residual voltage. The experimental test illustrates that 2 °/(Sm -1 ) sensitivity can be achieved at 10 MHz. The eight-channel MIT system MIT hardware is based on a dual-channel data acquisition board PCI-5122 at 100-MS/S sample rate per channel and a waveform generator PCI-5412 as the 10-MHz excitation source. One frame of data contains 64 phase measurements, and each is calculated with the built-in fast Fourier transform (FFT) function on LabVIEW. With full-period sampling and averaging, the sensor array can achieve less than 5-m° phase noise. The system yields good long-term stability with a phase drift less than 20 m° over 4 h. We use a FEM model to solve the forward problem and then reconstruct the 2D images by a one-step Laplacian regularization algorithm. The experimental phantom tests show that the system is capable of imaging the conductivity distribution and also indicate that the images' quality becomes better by tuning an appropriate regularization coefficient.

Magnetic Induction Tomography Using Magnetic Dipole and Lumped Parameter Model

This paper presents a novel approach to analyze the magnetic field of magnetic induction tomography (MIT) using magnetic dipoles and a lumped parameter model. The MIT is a next-generation medical imaging technique that can identify the conductivity of target objects and construct images. It is noninvasive and can be compact in design and, thus, used as a portable instrument. However, it still exhibits inferior performance due to the nonlinearity, low signal-to-noise ratio of the magnetic field, and ill-posed inverse problem. To overcome such difficulties, the magnetic field of the MIT system is first modeled using magnetic dipoles and a lumped parameter. In particular, the extended distributed multipole (eDMP) model is proposed to analyze the system, using magnetic dipoles. The method can dramatically reduce the computational efforts and improve the ill-posed condition. Hence, the forward and inverse problems of MIT are solved using the eDMP method. The modeling method can be validated by comparing with experiments, varying the modeling parameters. Finally, the image can be reconstructed, and then, the position and shape of the object can be characterized to develop the MIT.

Resolving the sign conflict problem for hp–hexahedral Nédélec elements with application to eddy current problems

The eddy current approximation of Maxwell’s equations is relevant for Magnetic Induction Tomography (MIT), which is a practical system for the detection of conducting inclusions from measurements of mutual inductance with both industrial and clinical applications. An MIT system produces a conductivity image from the measured fields by solving an inverse problem computationally. This is typically an iterative process, which requires the forward solution of a Maxwell’s equations for the electromagnetic fields in and around conducting bodies at each iteration. As the (conductivity) images are typically described by voxels, a hexahedral finite element grid is preferable for the forward solver. Low order Nédélec (edge element) discretisations are generally applied, but these require dense meshes to ensure that skin effects are properly captured. On the other hand, hp–Nédélec finite elements can ensure the skin effects in conducting components are accurately captured, without the need for dense meshes and, therefore, offer possible advantages for MIT. Unfortunately, the hierarchic nature of hp–Nédélec basis functions introduces edge and face parameterisations leading to sign conflict issues when enforcing tangential continuity between elements. This work describes a procedure for addressing this issue on general conforming hexahedral meshes and an implementation of a hierarchic hp–Nédélec finite element basis within the deal.II finite element library. The resulting software is used to simulate Maxwell forward problems, including those set on multiply connected domains, to demonstrate its potential as an MIT forward solver.