Calculation Of Absorption Rate Research Articles

A novel prediction for conjugated heat and mass transfer in falling film and membrane during LiBr absorption

The present investigation is intended to develop an understanding of how the vapor pressure and inlet temperature of the solution affect the absorption rate, which is helpful for the design of absorption heat pump systems. Many conjugated heat and mass transfer processes in falling film and membrane during lithium bromide (LiBr) absorption have not been well addressed. This paper proposes combining the meshless Radial Basis Function (RBF) and Discontinuous Galerkin (DG) methods to solve the conjugated heat and mass transfer in falling film and membrane-based absorption problems. The derivatives in the transverse direction are discretized using the RBF method. Owing to the parabolic nature of the governing equations, the DG methods can be used to discretize the derivatives in the streamwise direction. The efficacy of the proposed method is shown by comparing its results with analytical solutions and experimental data available in the literature. Furthermore, the proposed method is used to evaluate the analytical solutions of the heat and mass transfer problem in a membrane-based absorber. The previous published works simplified the problem to obtain the analytical solutions by providing the mean temperature and concentration values as the boundary conditions at the membrane-solution interface. The comparison of the RBF-DG method and the analytical solutions reveals that there are minor changes in temperature and local concentration values along the streamwise direction, but the profiles and trends are relatively similar across the film. A comparison of mass absorption rate calculations shows that RBF-DG and analytical solutions are compatible. The advantage of the numerical method is that various types of boundary conditions can be handled easily without any simplifications. Moreover, the numerical results of the proposed method are compared with experimental data, and they present good agreement. As a results, the absorption rate of falling film and membrane becomes capable of being accurately predicted.

A Compact Dual-Band Implantable Antenna for Wireless Biotelemetry in Arteriovenous Grafts

Arteriovenous grafts (AVGs) are indispensable life-saving implants for chronic kidney disease (CKD) patients undergoing hemodialysis. However, AVGs will often fail due to postoperative complications such as cellular accumulation termed restenosis, blood clots, and infections, which are dominant causes of morbidity and mortality. A new generation of hemodialysis implants equipped with biosensors and multi-band antennas for wireless power and telemetry systems that can detect specific pathological parameters and report AVGs’ patency would be transformative for CKD. Our study proposes a compact dual-band implantable antenna for hemodialysis monitoring applications. It operates in 1.4 GHz and 2.45 GHz for wireless power transfer and biotelemetry purposes. The miniaturized antenna with a current size of 5 × 5 × 0.635 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> exhibits wide bandwidth (300 MHz at 1.4 GHz band and 380 MHz at 2.45 GHz band), along with good impedance matching at two resonance frequencies. In addition, simulations are performed separately in a three-layer homogenous phantom and a realistic human body model. Measurements of the proposed antenna are evaluated in minced pork. The measured results of the fabricated antenna prototype are closely harmonized with the simulation ones, and the effect of different proportions of fat tissue in pork mince was analyzed, to verify the sensitivity of the antenna to the contacting medium. The specific absorption rate (SAR) and link budget calculation are also analyzed. Finally, the wireless biotelemetry function of the proposed antenna is realized and visualized by adopting a pair of nRF24L01 wireless transceivers, and sustainable and stable wireless data transmission characteristics are shown at a high data rate of 2 Mbps with up to 20 cm transmission distance.

Energy Harvesting Rectenna Using High-Gain Triple-Band Antenna for Powering Internet-of-Things (IoT) Devices in a Smart Office

A new rectenna that can be utilized for sending/receiving data and scavenging radio frequency (RF) waves for linking and powering the Internet-of-Things (IoT) devices is proposed. The rectenna has three operating frequency bands; the lower frequency band is used for energy harvesting, and the other two frequency bands are assigned for data communication. It comprises a stacked four-layer antenna integrated with a voltage doubler rectifier. The antenna consists of a driven element, a planar reflector, and a planar director composed of a periodic structure of a square patch with a hexagonal slot in its center. The measurement results show that the proposed antenna covers 1.86–2.65, 2.84–3.64, and 5.34–6 GHz with an impedance bandwidth of 35%, 24.7%, and 11.64%, respectively. The antenna exhibits a high measured gain of 8.1, 8.9, and 9 dBi at 2.3, 3.5, and 5.7 GHz, respectively. The Industrial, Scientific and Medical (ISM) 2.45-GHz frequency band is selected for energy harvesting. Moreover, specific absorption rate (SAR) calculations are done for the antenna using the Hugo model to ensure lower absorption operation. The proposed antenna provides acceptable values of SAR; the values are under the safety standard limits for RF exposure. Then, a rectifier circuit is designed, fabricated, and tested separately. Finally, the rectifier is integrated with the proposed enhanced-gain antenna to produce a rectenna system. The rectenna presents a power conversion efficiency (PCE) of 69.7% and a dc output voltage of 1.9 V at an input power of 2 dBm. The PCE of the proposed rectenna is over 50% at a range of input power from −6.5 to 4.7 dBm.

An investigation into the dependence of virtual observation point‐based specific absorption rate calculation complexity on number of channels

An investigation into the dependence of virtual observation point‐based specific absorption rate calculation complexity on number of channels

An investigation into the dependence of virtual observation point-based specific absorption rate calculation complexity on number of channels.

This study aims to find a relation between the number of channels and the computational burden for specific absorption rate (SAR) calculation using virtual observation point-based SAR compression. Eleven different arrays of rectangular loops covering a cylinder of fixed size around the head of an anatomically correct voxel model were simulated. The resulting Q-matrices were compressed with 2 different compression algorithms, with the overestimation fixed to a certain fraction of worst-case SAR, median SAR, or minimum SAR. The latter 2 were calculated from 1e6 normalized random excitation vectors. The number of virtual observation points increased with the number of channels to the power of 2.3-3.7, depending on the compression algorithm when holding the relative error fixed. Together with the increase in the size of the Q-matrices (and therefore the size of the virtual observation points), the total increase in computational burden with the number of channels was to the power of 4.3-5.7. The computational cost emphasizes the need to use the best possible compression algorithms when moving to high channel counts.

Specific Absorption Rate (SAR) Calculations in the Abdomen of the Human Body Caused by Smartphone at Various Tilt Angles: A Consideration of the 1950MHz Band

Specific Absorption Rate (SAR) Calculations in the Abdomen of the Human Body Caused by Smartphone at Various Tilt Angles: A Consideration of the 1950MHz Band

Tailoring defects and nanocrystal transformation for optimal heating power in bimagnetic CoyFe1-yO@CoxFe3-xO4 particles.

The effects of cobalt incorporation in spherical heterostructured iron oxide nanocrystals (NCs) of sub-critical size have been explored by colloidal chemistry methods. Synchrotron X-ray total scattering methods suggest that cobalt (Co) substitution in rock salt iron oxide NCs tends to remedy their vacant iron sites, offering a higher degree of resistance to oxidative conversion. Self-passivation still creates a spinel-like shell, but with a higher volume fraction of the rock salt Co-containing phase in the core. The higher divalent metal stoichiometry in the rock salt phase, with increasing Co content, results in a population of unoccupied tetrahedral metal sites in the spinel part, likely through oxidative shell creation, involving an ordered defect-clustering mechanism, directly correlated to core stabilization. To shed light on the effects of Co-substitution and atomic-scale defects (vacant sites), Monte Carlo simulations suggest that the designed NCs, with desirable, enhanced magnetic properties (cf. exchange bias and coercivity), are developed with magnetocrystalline anisotropy which increases due to a relatively low content of Co ions in the lattice. The growth of optimally performing candidates combines also a strongly exchange-coupled system, secured through a high volumetric ratio rock salt phase, interfaced by a not so defective spinel shell. In view of these requirements, specific absorption rate (SAR) calculations demonstrate that the rock salt core sufficiently protected from oxidation and the heterostructure preserved over time, play a key role in magnetically mediated heating efficacies, for potential use of such NCs in magnetic hyperthermia applications.

Carbothermal treated ferrite nanoparticles with improved magnetic heating efficiency and T1-MRI performance

Ferrite nanoparticle based T1-magnetic resonance imaging (T1-MRI) guided magnetic hyperthermia is a promising method for accurate tumor treatment. In previous studies, ultra-small sized ferrite nanoparticles were required to achieve excellent T1-MRI performance. However, an ultra-small size is usually accompanied by weak magnetization, resulting in a low magnetic heating efficiency, which is insufficient for magnetic hyperthermia. Therefore, ferrite nanoparticles with high magnetic heating efficiency and excellent T1-MRI performance capabilities are still highly desired. Here, oxygen vacancies are introduced in Mn0.6Zn0.4Al0.2Fe1.8O4 ferrite nanoparticles by applying carbothermal treatments. As oxygen vacancy concentrations increase, the intrinsic loss power increases up to 2.55 nH m2/kg, which is 33% higher than that of Fe3O4 nanoparticles used in magnetic hyperthermia. Specific absorption rate (SAR) calculations indicate that the predominant heat generation mechanism changes from hysteresis loss and relaxation loss to eddy current loss owing to conductivity enhancement by carbothermal treatments. The eddy current loss accounts for 70.6% of the total SAR, and plays a crucial role in increasing magnetic heating efficiency. In addition, Mn0.6Zn0.4Al0.2Fe1.8O4 ferrite nanoparticles with oxygen vacancies exhibit a significantly high r1 value of 9.69 mM−1 s−1 and a low r2/r1 ratio of 1.6 on a 3.0 T scanner. This is because oxygen vacancies naturally exhibit oxygen affinity in water molecules. The findings of this study could serve as a methodological reference of preparing ferrite nanoparticles for T1-MRI guided magnetic hyperthermia.

Wearable Magnetoinductive Waveguide for Low-Loss Wireless Body Area Networks

A novel approach of wearable magnetoinductive waveguide (MIW) is introduced for wireless body area network (WBAN) communications that brings forward significant advances over state-of-the-art. The MIW consists of series of electrically small resonant loops worn upon the human body to support magnetoinductive waves (MI waves) for low-loss/low-power WBANs. Compared to previous approaches, the proposed MIW exhibits 63 dB lower loss, translating conventional power levels of mW down to μW or nW. In this work, we introduce the operating principle of MIW WBAN through underlying theory and dispersion diagrams. The proof-of-concept numerical and experimental results are reported for frequency bands centered around 40.4 and 80.7 MHz for a cylindrical human limb and are found to be in excellent agreement. Design guidelines are extensively discussed to accommodate several possible scenarios (frequency selection, gap between the loops, number of loops, and loop radius) along with practical considerations including loop tilts, anatomical limbs, limb movements, unequal loop gaps, and loop failure. Specific absorption rate (SAR) calculations confirm that this technology is highly safe for human use. A bit error rate (BER) analysis further demonstrates that the MIW can form a high-quality communication channel for WBAN. Overall, the reported approach unveils a new possibility of low-loss and seamless WBANs.

A MINIATURE IMPLANTED ANTENNA FOR UHF RFID APPLICATIONS

In this paper, the design of a miniature antenna dedicated to be implanted in a small animal and intended to work in the European UHF RFID (865–868 MHz) band is presented. One of the goals of this work is the miniaturization of the radiating element while preserving its efficiency to allow a reliable communication between an external interrogating reader and the implanted device. The radiating element is a small rectangular loop antenna associated with a dipole allowing impedance matching. The antenna has dimensions of 2.4mm × 25.4mm × 0.5mm and integrates an Impinj Monza 4 chip presenting an impedance of 5.5−j74Ohms at 868 MHz. The antenna is designed and optimized by using the ANSYS HFSS software. The obtained results show a simulated radiation efficiency of 0.7% and simulated total gain of −17.5 dBi. A prototype is realized, and RSSI measurements have demonstrated the possibility of reliable wireless communications between the implanted antenna and an external reader. In addition, Specific Absorption Rate (SAR) calculation indicates that this implanted antenna meets the required safety regulations

Miniaturized quad-band coplanar-fed monopole antenna for tablet computers

PurposeThis paper aims to present the design of a compact quad-band coplanar-fed monopole antenna for tablet computer applications.Design/methodology/approachThe antenna has the smallest size of 26 × 14 mm and supports GSM, Wi-Fi, WIMAX and Bluetooth. The proposed antenna consists of a coplanar fed main radiator, c-shaped stubs and parasitic meandered stub. The inverted c-shaped stubs enhance the bandwidth of upper frequencies. The resonance at 2.4 GHz is individually controlled by the coupled meandered stub.FindingsThe percentage bandwidth in the four operating bands are 8.7/4.12/27.8/13.3%. Furthermore, the antenna is integrated with the mock-up ground plane and specific absorption rate (SAR) calculations are performed. The estimated SAR is less than 1.6 W/kg for a 1 g body tissue. The gain and efficiency of the antenna are 3.56/4.37/4.97/6 dBi and 82.4/85/97.1/89.3%, respectively. The measured impedance and radiation characteristics of the fabricated prototype are in good correlation with the simulated results.Originality/valueIn the proposed work, vias and lumped elements are not used for lower band excitation, and most of the wireless applications in the tablet computers have been covered. Further, the effect of antenna with different orientation has been tested for the estimation of SAR.

Application of Different Methods to Quantify Uncertainty in Specific Absorption Rate Calculation Using a CAD-Based Mobile Phone Model

This paper focuses on parameter uncertainty quantification (UQ) in specific absorption rate (SAR) calculation using a computer-aided design mobile phone model. The uncertainty in SAR calculation is quantified by three nonintrusive UQ methods: unscented transformation, stochastic collocation, and nonintrusive polynomial chaos. Their performances for the cases of one and two random variables are analyzed. To simplify the UQ procedure for the case of multiple uncertain inputs, it is demonstrated that uncertainties can be combined to evaluate the parameter uncertainty of the output. To quantify the relative importance of each uncertain input parameter with respect to the uncertainty of the output, the polynomial chaos based Sobol’ indices method is used in SAR calculation for sensitivity analysis. The results of the investigations are presented and discussed.

Probabilistic analysis of the specific absorption rate intersubject variability safety factor in parallel transmission MRI.

Specific absorption rate (SAR) calculations in parallel transmission are commonly performed by using electromagnetic simulations on generic models. In this study, we propose a probabilistic analysis to study the safety factor employed to account for SAR intersubject variability versus risk relationship in head imaging at 7T. Thirty-three finite-element electromagnetic simulations were conducted to sample the four-dimensional parameter space consisting of the head length, head breadth, and shifts in Z and Y random variables. Based on the SAR matrices for each configuration, a multivariate second-order polynomial of the SAR versus the different parameters was reconstructed for different types of radiofrequency pulses. A Monte Carlo calculation was then performed to compute the probability of occurrence of a given SAR value. By testing a large number of radiofrequency excitation pulses, the SAR calculated for the average model amplified by a safety margin of 1.5 was found to return a probability of less than 1% to be exceeded across the adult Caucasian population given the investigated parameters. The proposed method to study SAR intersubject variability uses a reasonable number of electromagnetic simulations. Look-ahead SAR safety margins can be deduced based on risk/benefit ratio assessments. Magn Reson Med 78:1217-1223, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Specific Absorption Rate Calculation and Motion Channel Models of Body Area Networks

Specific Absorption Rate Calculation and Motion Channel Models of Body Area Networks

No Effects of Acute Exposure to Wi-Fi Electromagnetic Fields on Spontaneous EEG Activity and Psychomotor Vigilance in Healthy Human Volunteers.

Mobile equipment use of wireless fidelity (Wi-Fi) signal modulation has increased exponentially in the past few decades. However, there is inconclusive scientific evidence concerning the potential risks associated with the energy deposition in the brain from Wi-Fi and whether Wi-Fi electromagnetism interacts with cognitive function. In this study we investigated possible neurocognitive effects caused by Wi-Fi exposure. First, we constructed a Wi-Fi exposure system from commercial parts. Dosimetry was first assessed by free space radiofrequency field measurements. The experimental exposure system was then modeled based on real geometry and physical characteristics. Specific absorption rate (SAR) calculations were performed using a whole-body, realistic human voxel model with values corresponding to conventional everyday Wi-Fi exposure (peak SAR10g level was 99.22 mW/kg with 1 W output power and 100% duty cycle). Then, in two provocation experiments involving healthy human volunteers we tested for two hypotheses: 1. Whether a 60 min long 2.4 GHz Wi-Fi exposure affects the spectral power of spontaneous awake electroencephalographic (sEEG) activity (N = 25); and 2. Whether similar Wi-Fi exposure modulates the sustained attention measured by reaction time in a computerized psychomotor vigilance test (PVT) (N = 19). EEG data were recorded at midline electrode sites while volunteers watched a silent documentary. In the PVT task, button press reaction time was recorded. No measurable effects of acute Wi-Fi exposure were found on spectral power of sEEG or reaction time in the psychomotor vigilance test. These results indicate that a single, 60 min Wi-Fi exposure does not alter human oscillatory brain function or objective measures of sustained attention.

A novel method to assess human population exposure induced by a wireless cellular network.

This paper presents a new metric to evaluate electromagnetic exposure induced by wireless cellular networks. This metric takes into account the exposure induced by base station antennas as well as exposure induced by wireless devices to evaluate average global exposure of the population in a specific geographical area. The paper first explains the concept and gives the formulation of the Exposure Index (EI). Then, the EI computation is illustrated through simple phone call scenarios (indoor office, in train) and a complete macro urban data long-term evolution scenario showing how, based on simulations, radio-planning predictions, realistic population statistics, user traffic data, and specific absorption rate calculations can be combined to assess the index. Bioelectromagnetics. 36:451-463, 2015. © 2015 Wiley Periodicals, Inc.

How to prepare head tissue-equivalent liquids for SAR calculations, dosimetry and hyperthermia researches at 900 and 1800 MHz GSM frequencies.

The potential harmful effect of electromagnetic fields on human health is an important issue that has been widely discussed in the scientific community. The investigation of temperature rise in human body following exposure to electromagnetic fields has been found impractical in many aspects. Therefore, fabrication of the tissue-equivalent liquids (TELs) is required. TELs have been widely employed in specific absorption rate calculations, dosimetry and hyperthermia researches. In this study, two separate head tissue-equivalent liquids (HELs) were prepared for 900 and 1800 MHz frequencies. The conductivity and relative permittivity of the HEL prepared for 900 MHz frequency were found to deviate from The Institute of Electrical and Electronics Engineers (IEEE) standards at the rates of 6.20 and 2.70 %, whereas the HEL prepared for 1800 MHz applications exhibited 1.83 and 3.22 % deviations from IEEE standards, respectively. This study provides a method for researchers to prepare their own HELs in a practical way.

Uncertainty evaluation in numerical modeling of complex devices

Numerical simulation is an efficient tool for exploring and understanding the physics of complex devices, e.g. mobile phones. For meaningful results, it is important to evaluate the uncertainty of the numerical simulation. Uncertainty quantification in specific absorption rate (SAR) calculation using a full computer-aided design (CAD) mobile phone model is a challenging task. Since a typical SAR numerical simulation is computationally expensive, the traditional Monte Carlo (MC) simulation method proves inadequate. The unscented transformation (UT) is an alternative and numerically efficient method herein investigated to evaluate the uncertainty in the SAR calculation using the realistic models of two commercially available mobile phones. The electromagnetic simulation process is modeled as a nonlinear mapping with the uncertainty in the inputs e.g. the relative permittivity values of the mobile phone material properties, inducing an uncertainty in the output, e.g. the peak spatial-average SAR value.The numerical simulation results demonstrate that UT may be a potential candidate for the uncertainty quantification in SAR calculations since only a few simulations are necessary to obtain results similar to those obtained after hundreds or thousands of MC simulations.

Power balance and loss mechanism analysis in RF transmit coil arrays.

To establish a framework for transmit array power balance calculations based on power correlation matrices to accurately quantify the loss contributions from different mechanisms such as coupling, lumped components, and radiation. Starting from Poynting's theorem, power correlation matrices are derived for all terms in the power balance, which is formulated as a matrix equation. Finite-difference time-domain simulations of two 7 T eight-channel head array coils at 297.2 MHz are used to verify the theoretical considerations and demonstrate their application. Care is taken to accurately incorporate all loss mechanisms. The power balance for static B1 phase shims as well as two-dimensional spatially selective transmit SENSE pulses is shown. The simulated power balance shows an excellent agreement with theory, with a maximum power imbalance of less than 0.11%. Power loss contributions from the different loss mechanisms vary significantly between the investigated setups, and depending on the excitation mode imposed on the coil. The presented approach enables a straightforward loss evaluation for an arbitrary excitation of transmit coil arrays. Worst-case power imbalance and losses are calculated in a straightforward manner. This allows for deeper insight into transmit array loss mechanisms, incorporation of radiated power components in specific absorption rate calculations and verification of electromagnetic simulations.

A Benchmark CAD Mobile Phone Model for Specific Absorption Rate Calculations

Specific absorption rate (SAR) calculation using a computer-aided design (CAD)-based mobile phone model is still a challenging task. Seven international laboratories participated in an interlaboratory comparison of SAR calculations using a CAD-based model of a commercially available dual-band mobile phone. Return loss and peak 10 g average SAR results obtained using six different electromagnetic solvers were compared. Considering the differences in the techniques implemented in the solvers-either time or frequency domain-used for the interlaboratory comparison, overall a good agreement is observed. Proposed as a benchmark, results of the measured return loss and peak 10 g average SAR using the actual mobile phone are also provided.