Extension of Thin Wire Techniques in the FDTD Method for Debye Media

Kuklin, Dmitry

doi:10.2528/pierm16081804

Cited by 15 publications

(4 citation statements)

References 18 publications

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“…The considered model implant was a straight wire (

300 mm

length, core: one‐dimensional wire as perfect electric conductor 93 ; insulated [relative permittivity

{italicε}_{normalr} = 3

] except for

10 mm

at the distal tip) that was oriented parallel to the

z

‐axis and that touched the spinal cord at coordinates

x = 0 mm, y = - 106 mm, z = - 130 mm

relative to the isocenter. In a simple cable model, the implant's electrical properties would correspond to a physical wire with an inner conductor of

0.83 mm

diameter 94 (see the supporting information A). The voxel mesh had an isotropic resolution of

2 mm

.…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Towards an integrated radiofrequency safety concept for implant carriers in MRI based on sensor‐equipped implants and parallel transmission

et al. 2023

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To protect implant carriers in MRI from excessive radiofrequency (RF) heating it has previously been suggested to assess that hazard via sensors on the implant. Other work recommended parallel transmission (pTx) to actively mitigate implant‐related heating. Here, both ideas are integrated into one comprehensive safety concept where native pTx safety (without implant) is ensured by state‐of‐the‐art field simulations and the implant‐specific hazard is quantified in situ using physical sensors. The concept is demonstrated by electromagnetic simulations performed on a human voxel model with a simplified spinal‐cord implant in an eight‐channel pTx body coil at 3T. To integrate implant and native safety, the sensor signal must be calibrated in terms of an established safety metric (e.g., specific absorption rate [SAR]). Virtual experiments show that E‐field and implant‐current sensors are well suited for this purpose, while temperature sensors require some caution, and B1 probes are inadequate. Based on an implant sensor matrix bold-italicQnormals, constructed in situ from sensor readings, and precomputed native SAR limits, a vector space of safe RF excitations is determined where both global (native) and local (implant‐related) safety requirements are satisfied. Within this safe‐excitation subspace, the solution with the best image quality in terms of B1+ magnitude and homogeneity is then found by a straightforward optimization algorithm. In the investigated example, the optimized pTx shim provides a 3‐fold higher meanB1+ magnitude compared with circularly polarized excitation for a maximum implant‐related temperature increase ∆Timp≤1K. To date, sensor‐equipped implants interfaced to a pTx scanner exist as demonstrator items in research labs, but commercial devices are not yet within sight. This paper aims to demonstrate the significant benefits of such an approach and how this could impact implant‐related RF safety in MRI. Today, the responsibility for safe implant scanning lies with the implant manufacturer and the MRI operator; within the sensor concept, the MRI manufacturer would assume much of the operator's current responsibility.

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“…The considered model implant was a straight wire (

300 mm

length, core: one‐dimensional wire as perfect electric conductor 93 ; insulated [relative permittivity

{italicε}_{normalr} = 3

] except for

10 mm

at the distal tip) that was oriented parallel to the

z

‐axis and that touched the spinal cord at coordinates

x = 0 mm, y = - 106 mm, z = - 130 mm

relative to the isocenter. In a simple cable model, the implant's electrical properties would correspond to a physical wire with an inner conductor of

0.83 mm

diameter 94 (see the supporting information A). The voxel mesh had an isotropic resolution of

2 mm

.…”

Section: Methodsmentioning

confidence: 99%

“…x ¼ 0 mm,y ¼ À106 mm, z ¼ À130 mm relative to the isocenter. In a simple cable model, the implant's electrical properties would correspond to a physical wire with an inner conductor of 0:83 mm diameter 94 (see the supporting information A). The voxel mesh had an isotropic resolution of 2 mm.…”

Section: Field Calculations (Figurementioning

confidence: 99%

Towards an integrated radiofrequency safety concept for implant carriers in MRI based on sensor‐equipped implants and parallel transmission

et al. 2023

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“…The frequency-dependent soil properties are modeled with the Debye relaxation model using auxiliary differential equation method [9,13,14]. The n-term Debye function expansion:…”

Section: Fdtd Modelmentioning

confidence: 99%

Numerical Analysis of Electromagnetic Coupling Effects in Measurements of Frequency Dependent Soil Electrical Properties

Kuklin¹

2019

PIER M

Self Cite

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Recent studies show that the frequency dependent soil properties can significantly influence transient grounding resistance and, subsequently, lightning protection and reliability of the electrical grid. However, these properties require further research: for example, it is not clear what factors (apart from the low-frequency resistivity) should be taken into consideration to determine accurately the properties for a particular soil (without conducting laborious measurements). Additional experimental data are needed.When measurements are conducted, the electromagnetic coupling between circuits can cause significant measurement error at frequencies about several MHz. In order to estimate this error, it is convenient to use a calculation method, as in this case, it is possible to set particular frequency dependent properties for the ground and compare those with the calculated ones (using an electrode array).In the article, the electromagnetic coupling error is examined for several commonly used electrode arrays using the finite difference time domain method. This method allows simulating wires with infinite length, which is important for modeling pole-dipole and pole-pole arrays. Its drawback for this type of calculations, however, that it is relatively time-consuming. It was found that among the considered array configurations the error is smallest for the dipole-dipole arrays with the perpendicular allocation of the measurement wires and the pole-dipole array. By increasing the distance between particular parts of measurement wires, one can significantly reduce the error for some other arrays.

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“…Additionally, another limitation of PEC wire model is its ability to model only thick wires. Implementing a thin-wire model in the FDTD like [40], [41] would enable modelling of the wire with more realistic thickness.…”

Section: B Array Design and Modellingmentioning

confidence: 99%

Design and Modelling of an Enclosed Array of Square Spiral Antennas for Microwave Tomography

Subotic¹,

Pjevalica²,

Palfi³

2017

ElAEE

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Microwave tomography is a microwave imaging method in which the resolution is not limited by wavelength, but rather by measurement noise and modelling errors. Inversion algorithm is used for obtaining an image from the measured scattered waves. Performance improvement of the inversion algorithm is introduced by approximately modelled antennas as a point, line or plane source. Such modelling of antennas introduces modelling errors. Antenna array in the unshielded measurement chamber will pick up external interference, as well as backscattering of array's own radiation. Multipath occurring in measurement chamber has a large impact on the measurement performance. The wave propagated through the air and reflected from the chamber walls could mask a weaker wave scattered by the object under imaging. Also, a larger number of the antennas improves inversion and gives a more accurate image. This paper proposes a novel design of enclosed measurement antenna array for microwave tomography. To obtain an accurate and efficient antenna model in 3D FDTD, a square spiral wire antenna is used in this design. A metal shield protects the process of measurement from external interference and backscattering. Between the antenna array and the metal shield an absorption wall is introduced, which decreases multipath and partially prevents signal masking. Square spiral wire antennas are overlapped and packed, giving a larger number of antennas in the same space. Enclosed antenna array is modelled in 3D FDTD. Proposed antenna array is compared with solutions found in literature. Comparison is done using metrics relevant for antenna array measurement in microwave tomography.

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Extension of Thin Wire Techniques in the FDTD Method for Debye Media

Cited by 15 publications

References 18 publications

Towards an integrated radiofrequency safety concept for implant carriers in MRI based on sensor‐equipped implants and parallel transmission

Towards an integrated radiofrequency safety concept for implant carriers in MRI based on sensor‐equipped implants and parallel transmission

Numerical Analysis of Electromagnetic Coupling Effects in Measurements of Frequency Dependent Soil Electrical Properties

Design and Modelling of an Enclosed Array of Square Spiral Antennas for Microwave Tomography

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