Accurate Electrical Properties Research Articles

The effect of simulation strategies on prediction of power deposition in the tissue around electronic implants during magnetic resonance imaging

Numerical simulations are increasingly employed in safety assessment of high-field magnetic resonance imaging (MRI) in patients with conductive medical implants such as those with deep brain stimulation (DBS) devices. Performing numerical simulations with realistic patient models and implant geometry is the preferred method as it provides the most accurate results; however, in many cases such an approach is infeasible due to limitation of computational resources. The difficulties in reconstructing realistic patient and device models and obtaining accurate electrical properties of tissue have compelled researchers to adopt compromises, either to exceedingly simplify implant structure and geometry, or the complexity of the body model. This study examines the effect of variations in anatomical details of the human body model and implant geometry on predicted values of specific absorption rate (SAR) values during MRI in a patient with a DBS implant. We used a patient-derived model of a fully implanted DBS implant and performed numerical simulations to calculate the maximum SAR during MRI at 1.5T (64 MHz) and 3T (127 MHz). We then assessed the effect of uncertainties in dielectric properties of tissue, complexity of body model, truncation of body/DBS model, and DBS lead geometry on SAR. Our results showed that 40% variation in the conductivity of individual tissues in a heterogeneous body model caused a peak of 7% variation in maximum SAR value at 64 MHz, and 10.6% variation in SAR at 127 MHz. SAR predictions from a homogeneous body model with a conductivity range of could cover the full range of SAR variations predicted by the heterogeneous body model. Truncation of body model below the implanted pulse generator changed the predicted SAR by 16% at 1.5T and 32% at 3T while saving 250% and 148% in computational time and memory allocation, respectively. In contrast, variation in DBS lead geometry significantly changed the SAR by up to 51% at 64 MHz and 67% at 127 MHz. These results suggest that the error introduced by simplifying the implant’s geometry could negate the benefit of using a realistic body model, should such model be used at the expense of oversimplifying implant geometry.

Magnetic Resonance-Electrical Properties Tomography by Directly Solving Maxwell’s Curl Equations

Magnetic Resonance-Electrical Properties Tomography (MR-EPT) is a method to reconstruct the electrical properties (EPs) of bio-tissues from the measured radiofrequency (RF) field in Magnetic Resonance Imaging (MRI). Current MR-EPT approaches reconstruct the EP profile by solving a second-order partial differential wave equation problem, which is sensitive to noise and can induce large reconstruction artefacts near tissue boundaries and areas with inaccurate field measurements. In this paper, a novel MR-EPT approach is proposed, which is based on a direct solution to Maxwell’s curl equations. The distribution of EPs is calculated by iteratively fitting the RF field calculated by the finite-difference-time-domain (FDTD) technique to the measured values. To solve the time-consuming problem of the iterative fitting, a graphics processing unit (GPU) is used to accelerate the FDTD technique to process the field calculation kernel. The new EPT method was evaluated by investigating a numerical head phantom, and it was found that EP values can be accurately calculated and were relatively insensitive to simulated RF field errors. The feasibility of the proposed method was further validated using phantom-based experimental data collected from a 9.4 Tesla (T) Magnetic Resonance Imaging (MRI) system. The results also indicated that more accurate EP values could be reconstructed from the new method compared with conventional methods. Moreover, even in the absence of phase information of the RF field, the proposed approach is still capable of offering robust EPT solutions, thus having improved practicality for potential clinical applications.

Precise Electrical Characterization of LEDs with Wide-Band Material

The accurate electrical properties of semiconductor GaN based blue Light-Emitting Diodes (LED) with Multiple-Quantum Well (MQW) structure and GaAsP based red LED, were measured by single Capacitance-Voltage (C-V) method and single Current-Voltage (I-V) method at large forward bias. After comparing the experimental results, we found that the apparent capacitance Cp of GaN based blue LED and GaAsP based red LED measured by C-V method display obviously negative value at large forward bias and low frequency, which is in conflict with the well known Shockley's p-n junction theory and model. Besides, the precise Characterization of apparent capacitance Cp and apparent conductance Gp is obtained.

Non-destructive testing of hardened cement specimens at microwave frequencies using a simple free-space method

In this research paper, we show microwave reflection and transmission properties measured from various sides of hardened mortar and concrete specimens with different water-to-cement ratios. These properties are important in predicting/measuring accurate electrical properties of cement-based materials which can eventually be utilized in structural health monitoring, public safety, and propagation-related research. Measurements are carried out by a simple and relatively inexpensive non-destructive free-space set-up with its newly developed calibration technique at X-band (8–12 GHz) during 3–36 months after samples’ preparation. A new approach (relative difference approach) is introduced for transmission properties to predict the state and degree of hydration inside specimens. It is shown that concrete specimens will complete the hydration sooner than mortar specimens with the same water-to-cement ratio ( w/ c) ratio due to heavy aggregates. In addition, among the specimens, while the concrete specimen with a higher w/ c ratio will exhibit faster hydration during approximately 3–6.1 months, the mortar specimen with a lower w/ c ratio will display rapid hydration during approximately 6.1–30 months. Besides, it is demonstrated that the magnitude of transmission properties for the top (or bottom) is less than those for the right (or left) side due to the effect of gravels and sand particles in specimens. Measurement results indicate that a varying electrical property depending on height should be used for cement-based materials in the predicting the channel properties in propagation-related researches.

An ab initio study of vibrational corrections to the electrical properties of ethylene

Accurate SCF and MP2 quartic property hypersurfaces have been computed for the energy, quadrupole moment and polarizability tensor of ethylene to obtain zero-point vibrational corrections to the properties. Coupled with accurate electrical properties computed at a high level correlated r e geometry, using a range of correlated methods, especially BD and BD(T), along with a number of purpose-built polarized basis sets, definitive estimates have been made of these properties that incorporate the effects of vibrational averaging. The effect of deuterium substitution on the properties was investigated, and the frequency dependence of the polarizability tensor was studied also. Careful attention has been paid to a critical comparison between these theoretical estimates and experimental measurements, and agreement between the two is shown to be exceptionally good. In particular, it is possible to resolve the disagreement between recent theoretical calculations and experimental measurements of the Cotton–Mouton constant. The results focus attention on both the general utility of the present method, and the necessity to allow for the effects of zero-point vibrational averaging when comparing theory with experiment, or even when comparing different theoretical results with one another using experiment as a benchmark.

An ab initio study of vibrational corrections to the electrical properties of ethane

SCF quartic property hypersurfaces have been computed for the energy, quadrupole moment and polarizability tensor of ethane via finite differences of analytical derivatives to obtain zeropoint vibrational corrections to the properties. Coupled with accurate electrical properties computed at a correlated r e geometry, using a range of correlated methods, especially BD and BD(T), excellent estimates of these properties have been obtained that incorporate the effects of vibrational averaging. The effect of deuterium substitution on the properties has been investigated, including the first known theoretical prediction of the dipole moment of CH3CD3, and the frequency dependence of the polarizability tensor and Rayleigh depolarization ratio have been examined. Careful attention has been paid to a critical comparison between these theoretical estimates and experimental measurements. Although the vibrational corrections are limited to SCF theory, and basis sets not as extensive as used in some studies of this kind, nevertheless the results can be compared quantitatively with experiment, and the agreement is found to be excellent. The results underline the necessity to allow for the effects of zero-point vibrational averaging when comparing theory with experiment, and suggest a viable approach for studies on larger molecules.

An ab initio study of vibrational corrections to the electrical properties of the fluoromethanes: CH3F, CH2F2, CHF3 and CF4

Accurate SCF and MP2 quartic property hypersurfaces have been computed for the energy, dipole moments, quadrupole moments and polarizability tensors of the fluorinated methanes CF4, CHF3, CH2F2 and CH3F, to establish accurate values of zero-point vibrational corrections to the properties. Using a consistent set of re geometries from density functional theory, these ZPVCs are coupled with accurate electrical properties computed using a range of correlated methods, especially BD and BD(T), and a number of purpose-built polarized basis sets, to obtain near definitive estimates of these properties that incorporate the effects of vibrational averaging. Careful attention has been paid to a critical comparison between these theoretical estimates and experimental measurements, and agreement between the two is shown to be exceptionally good. In particular, it is clear that in many instances more precise experimental results would be required in order to discriminate between different correlated results, or between the present results and those which may be obtained with larger basis sets. The work highlights the necessity to allow for the effects of zero-point vibrational averaging when comparing theory with experiment, or even when comparing different theoretical results with one another using experiment as a benchmark. It also points to the need for further precise experimental measurements of some of these properties.

Size Effect of the Dielectric Properties in Bismuth-Based Layer- Structured Ferroelectric Films

Bismuth-based-layer-structured ferroelectric films have been formed epitaxially on Nb-doped SrTiO3 substrates by pulsed laser deposition (PLD). These films show an atomically smooth surface with a wide terrace of 100 nm–200 nm, as observed by atomic force microscopy (AFM) which is ideal for measuring such properties. Crystal growth apparently changes from the step-flow mode to the island-state mode according to the number of perovskite layers sandwiched by bismuth oxide layers. Additionally, the dielectric constant of the three film types, that is Bi2VO5.5 (n=1), Bi3TiNbO9 (n=2), and Bi4Ti3O12 (n=3) decreases proportionally with decreasing film thickness. It is considered that the size effect plays an important role in determining dielectric properties. Bismuth-layered ferroelectric films, with their atomically flat surfaces and accurate electrical properties, are an ideal material for applications in semiconductor devices.

Accurate ab initio study of acetylene Vibrational and rotational corrections to electrical properties

Accurate ab initio SCF and MP2 quartic property (hyper)surfaces have been computed for the energy, quadrupole moment, Θ, polarizability, α, and polarizability anisotropy, Δα, of acetylene (HCCH) with the properties expanded in a Taylor series of the dimensionless normal coordinates, qi , about the potential energy minimum. Applying the contact transformation expressions for the expectation value of a property in an arbitrary rotational-vibrational state, we obtain both zero-point vibrational corrections (ZPVCs) to the properties and predictions of the properties in excited rotational-vibrational states. A numerical least-squares method was utilized for the calculation of the required derivatives. We have also computed accurate electrical properties at the experimental re geometry in order to provide definitive estimates of Θ, α and Δα for acetylene that incorporate both vibrational and rotational effects. A wide range of electron-correlation methods were utilized for this purpose including QCISD(T), BD and BD(T), coupled with a range of large augmented triple-zeta basis sets. Special attention was paid to the quadrupole moment, Θ, as there has been substantial interest and controversy in the experimental determination of this quantity. Where possible we have critically compared theory and experiment, the outcome highlighting the utility of the present method and the general necessity for the inclusion of vibrational corrections with accurate theoretical predictions of electrical properties.

Accurateab initiostudy of acetylene Vibrational and rotational corrections to electrical properties

Accurate ab initio SCF and MP2 quartic property (hyper)surfaces have been computed for the energy, quadrupole moment, Θ, polarizability, α, and polarizability anisotropy, Δα, of acetylene (HCCH) with the properties expanded in a Taylor series of the dimensionless normal coordinates, qi , about the potential energy minimum. Applying the contact transformation expressions for the expectation value of a property in an arbitrary rotational-vibrational state, we obtain both zero-point vibrational corrections (ZPVCs) to the properties and predictions of the properties in excited rotational-vibrational states. A numerical least-squares method was utilized for the calculation of the required derivatives. We have also computed accurate electrical properties at the experimental re geometry in order to provide definitive estimates of Θ, α and Δα for acetylene that incorporate both vibrational and rotational effects. A wide range of electron-correlation methods were utilized for this purpose including QCISD(T), BD and BD(T), coupled with a range of large augmented triple-zeta basis sets. Special attention was paid to the quadrupole moment, Θ, as there has been substantial interest and controversy in the experimental determination of this quantity. Where possible we have critically compared theory and experiment, the outcome highlighting the utility of the present method and the general necessity for the inclusion of vibrational corrections with accurate theoretical predictions of electrical properties.