Specific Absorption Ratio Research Articles

Simulation of Rectangular Microstrip Patch Antenna u sing ANSYS

This paper presents the design and simulation of a rectangular microstrip patch antenna with enhanced results. Antennas are playing the most important key role in wireless communication systems and especially microstrip patch antenna is the simplest and best form for mobile communication systems. Therefore, the design of antenna for mobile satellite communication and space to earth communication is described in this proposed work. The working of rectangular micro strip patch antenna is studied and the effect of height of the substrate on antenna performance is analyzed and the results are plotted. It has been noticed that the height of substrate should be neither small nor large. The effect of inserting a slot in the patch is also observed in this paper. Return Loss results are plotted for the designed structure and it is noticed that return loss is almost doubled by inserting a slot. Further two symmetrical slots are inserted in the patch and the respective results are plotted. Insertion of two slots gave multiple operating frequencies to the antenna with a compromise of s11. The simulation of proposed structures of antennas is done using ANSYS HFSS (high-frequency structure simulator) which is commercially used as a finite element method solver for electromagnetic structures. A sphere with human brain characteristics is created and average SAR (specific absorption ratio) is plotted on the head model. The proposed antenna has enhanced return loss of -52dB and VSWR of 1.005 at 2.24GHz. This work also introduces multiple operating frequencies using two slots of same size.

In vivo potassium MRI of the human heart.

Potassium ions (K+ ) play a critical role in cardiac electrophysiology, and changes in their concentration reflect pathophysiological processes related to cardiovascular diseases. Here, we investigated the feasibility of in vivo 39 K MRI of the human heart. To achieve this, we developed, evaluated, and applied a 39 K/1 H RF coil, which is tailored for 39 K MRI of human heart at 7.0T. The performance of the 39 K/1 H RF coil was evaluated by electromagnetic field and specific absorption ratio simulations using 2 (male/female) human voxel models. The RF coil was evaluated at the bench and applied in an in vivo proof-of-principle study involving 7 healthy volunteers. The experiments were performed using a 7.0T whole-body MR system in conjunction with a 3D density-adapted projection reconstruction imaging technique. For in vivo 39 K MRI of the human heart, a nominal spatial resolution of 14.5 × 14.5 × 14.5 mm3 within a total scan time of 30 min was achieved. The average SNR within the heart was 9.6 ± 2.4. This work validates the design of a 39 K/1 H RF coil for cardiac MR at 7.0T and demonstrates for the first time in vivo the feasibility of 39 K MRI of the human heart.

Dual‐band and enhanced‐isolation MIMO antenna with L‐shaped meta‐rim extended ground stubs for 5G mobile handsets

A novel compact planar dual-band multiple input multiple output (MIMO) antenna with four radiating elements for 5G mobile communication is proposed. Each radiating element has a planar folded monopole, which is surrounded by L-shaped meta-rim extended ground stubs. The compact folded arms act as the main radiating elements, while combined with the L-shaped meta-rim stubs, the proposed antenna forms multiple resonances so as to achieve dual-band coverage. The simulated and measured results show that the proposed antenna has two wide bands of −6 dB return loss, consisting of 1.6 to 3.6 and 4.1 to 6.1 GHz, respectively. Without any additional isolation structure between the elements, the isolation for the proposed 2 × 2 MIMO antenna in both desired bands can be achieved better than 12 dB. The measured results show that the proposed MIMO antenna with good performance, that is, stable radiation patterns, high efficiencies, low specific absorption ratio (SAR) to human tissues, is suitable for WLAN/LTE, 4G and future 5G mobile phone applications.

Computer simulated assessment of radio frequency electromagnetic waves for the detection of obstructive sleep apnea

Abstract Obstructive sleep apnea/hypopnea syndrome (OSAHS) is the most common form of sleep-disorder breathing (SDB). Recurring restriction or occlusion of the upper airway throughout the night concurrent with continued respiratory efforts lasting more than 10 s characterizes the disorder. Prevalence of OSAHS is increasing globally, with a high association with obesity, hypertension, and heart failure. Nocturnal polysomnography (NPSG), which is the gold standard for OSAHS diagnosis, is scarce, expensive, and cumbersome. Methods for home screening and diagnosis of the disorder, directly and indirectly, are highly sought after to amend or replace NPSG. Well-established norms and procedures for electromagnetic (EM) antenna design, radiation pattern and characterization, and signal reception and measurements can be employed for the direct detection of upper airway occlusion. The utilization of radio-frequency (RF) EM antennas is desirable, as it is inexpensive, and simple to design and implement. In this paper, a computerized simulation of a new EM sensing system for direct detection of the occlusion in the upper airway is presented. Electromagnetic, anatomical, and RF safety constraints are taken into consideration. The theoretical basis of EM, antenna design, and physiological interactions with EM waves are presented. The proposed methodology for creating an anatomically-correct neck and airway simulated phantoms to test the hypothesis and the results of the tests are presented. Hypothesis Radio-frequency electromagnetic waves transmitted through an open airway will have different energy levels at the distal side of the neck compared to those associated with a fully occluded airway. Methodology A system is designed comprising a simulated phantom model of the upper airway and neck with the approximate anatomical dimensions and dielectric properties of homogenous neck tissue. Additionally, an RF patch antenna is designed and matched to the phantom neck. An iterative process is developed and implemented for the patch antenna design and coupling with a tissue. Simulation of the EM wave propagation and dissipation throughout the neck in the open and closed airway cases is provided and calculated based on the specific absorption ratios (SAR). The results of several permutations of antenna orientation with respect to the neck and several gaps between the antenna and the neck are provided. Results the Computer simulations for all antenna orientation and location have shown that the EM energy levels recorded from open airway phantom models are statistically different and lower than those recorded from the occluded airway phantom models. Conclusions The results of this study support the hypothesis that it is theoretically feasible to use electromagnetic energy to distinguish between open and occluded upper airway.

Development of Voxel Models Adjusted to ICRP Reference Children and Their Whole-Body Averaged SARs for Whole-Body Exposure to Electromagnetic Fields From 10 MHz to 6 GHz

New child voxel models that are adjusted to the International Commission on Radiological Protection (ICRP)'s reference values (1-, 5- and 10-yr-old children) have been developed. The whole-body averaged specific absorption ratios (WBA-SARs) of these child voxel models were calculated for the whole-body exposure conditions with the E-polarization and H-polarization plane wave incidence from 10 MHz to 6 GHz. The WBA-SARs are 40% to 60% higher for the child voxel models than for adult voxel models adjusted to the ICRP's reference values (NORMAN and NAOMI). The WBA-SARs of the child voxel models exceed the basic restriction by at most 20% or 0.08 W/kg for the general environment when the incident power density is set to the reference level at each frequency of the ICNIRP's RF safety guidelines.

Specific Absorption Rate (SAR) value of mobile phones: An awareness study among mobile users

Mobile phone is an inevitable part of ones life. Once been luxury has now become necessity. It’s been used by all age group people for different application apart from calling and texting. The advance in mobile technology has brought many new applications using mobile. But while using cell phone for talking or being connected to someone the user gets exposed to harmful Electro Magnetic Radiations. The exposure rate to these radiations vary from handset to handset. When cell phones are used in close proximity to human body, the radiations emitted from cell phones penetrate deep inside the human skin. Penetrated radiations produce induced electric field inside the body, resulting in absorption of power, which can be analyzed using a parameter called specific absorption rate (SAR). But still one question arises in mind that are people really aware of Safety standard especially SAR value. What does SAR value mean? It’s the specific absorption ratio measure of amount of radio frequency intensity or energy absorbed by body while connected on cellular network. It is defined as the power absorbed per mass of tissue and has units of watts per kilogram (W/kg) and in a way defines safety range of mobile handset .This study aims to measure the knowledge and awareness of SAR value of handset and the factors that influence awareness of SAR value. This is the largest sample study about mobile usage and awareness of SAR amongst mobile users .

Pulseq-Graphical Programming Interface: Open source visual environment for prototyping pulse sequences and integrated magnetic resonance imaging algorithm development

PurposeTo provide a single open-source platform for comprehensive MR algorithm development inclusive of simulations, pulse sequence design and deployment, reconstruction, and image analysis. MethodsWe integrated the “Pulseq” platform for vendor-independent pulse programming with Graphical Programming Interface (GPI), a scientific development environment based on Python. Our integrated platform, Pulseq-GPI, permits sequences to be defined visually and exported to the Pulseq file format for execution on an MR scanner. For comparison, Pulseq files using either MATLAB only (“MATLAB-Pulseq”) or Python only (“Python-Pulseq”) were generated. We demonstrated three fundamental sequences on a 1.5 T scanner. Execution times of the three variants of implementation were compared on two operating systems. ResultsIn vitro phantom images indicate equivalence with the vendor supplied implementations and MATLAB-Pulseq. The examples demonstrated in this work illustrate the unifying capability of Pulseq-GPI. The execution times of all the three implementations were fast (a few seconds). The software is capable of user-interface based development and/or command line programming. ConclusionThe tool demonstrated here, Pulseq-GPI, integrates the open-source simulation, reconstruction and analysis capabilities of GPI Lab with the pulse sequence design and deployment features of Pulseq. Current and future work includes providing an ISMRMRD interface and incorporating Specific Absorption Ratio and Peripheral Nerve Stimulation computations.

Regional Groundwater and Storms Are Hydrologic Controls on the Quality and Export of Dissolved Organic Matter in Two Tropical Rainforest Streams, Costa Rica

AbstractA paired‐watershed approach was used to compare the quality and fluxes of dissolved organic matter (DOM) during stormflow and baseflow in two lowland tropical rainforest streams located in northeastern Costa Rica. The Arboleda stream received regional groundwater (RGW) flow, whereas the Taconazo stream did not. DOM quality was assessed with absorbance and fluorescence and stable carbon isotope (δ13C‐DOC) values. RGW DOM lacked detectable fluorescence and had specific ultraviolet absorption (SUVA254) and absorbance slope ratio (SR) values consistent with low aromaticity and low molecular weight material, respectively. We attributed these properties to microbial degradation and sorption of humic DOM to mineral surfaces during transport through bedrock. SUVA254 values were lower and SR values were higher in the Arboleda stream during baseflow compared to the Taconazo stream, presumably due to dilution by RGW. However, no significant difference in SUVA254 or SR occurred between the streams during stormflow. SUVA254 was negatively correlated to δ13C‐DOC (r2 = 0.61, P < 0.001), demonstrating a strong linkage between stream DOM characteristics and the relative amounts of RGW flow and local watershed runoff containing soil and throughfall C sources. Mean DOC export from the Taconazo stream during the study period was 2.62 ± 0.39 g C m−2 year−1, consistent with other tropical streams, yet mean DOC export from the Arboleda stream was 13.79 ± 2.07 g C m−2 year−1, one of the highest exports reported and demonstrating a substantial impact of old RGW from outside the watershed boundary can have on surface water carbon cycling.

Alcoholic fermentation in the presence of microwaves

Bioethanol is the world’s leader biofuel and it is produced by fermentation from glucose feedstocks. The fermentation rate is quite low and any method of increasing the reaction rate is welcome. The main goal of our research is to identify the domain for microwave Specific Absorption Ratio (SAR) which leads to an increase in fermentation rate of Saccharomyces cerevisiae without affecting its viability. For this purpose, an installation was setup which allows for glucose fermentation to be carried out in the presence of microwave, with good control on SAR and on temperature of the fermentative medium. An optimum SAR domain, between 15 and 25 W kg−1, was determined, in which a significant boost of glucose fermentation manifests, with an increase in fermentation rates of up to 20%. Based on the observations made through electron and optical microscopy on cell growth and viability, we have noticed that microwave irradiation favours ethanol production of the cells, against their growth.

Millimeter spatial resolution in vivo sodium MRI of the human eye at 7 T using a dedicated radiofrequency transceiver array.

The aim of this study was to achieve millimeter spatial resolution sodium in vivo MRI of the human eye at 7 T using a dedicated six-channel transceiver array. We present a detailed description of the radiofrequency coil design, along with electromagnetic field and specific absorption ratio simulations, data validation, and in vivo application. Electromagnetic field and specific absorption ratio simulations were performed. Transmit field uniformity was optimized by using a multi-objective genetic algorithm. Transmit field mapping was conducted using a phase-sensitive method. An in vivo feasibility study was carried out with 3-dimensional density-adapted projection reconstruction imaging technique. Measured transmit field distribution agrees well with the one obtained from simulations. The specific absorption ratio simulations confirm that the radiofrequency coil is safe for clinical use. Our radiofrequency coil is light and conforms to an average human head. High spatial resolution (nominal 1.4 and 1.0 mm isotropic) sodium in vivo images of the human eye were acquired within scan times suitable for clinical applications (∼ 10 min). Three most important eye compartments in the context of sodium physiology were clearly delineated in all of the images: the vitreous humor, the aqueous humor, and the lens. Our results provide encouragement for further clinical studies. The implications for research into eye diseases including ocular melanoma, cataract, and glaucoma are discussed. Magn Reson Med 80:672-684, 2018. © 2018 International Society for Magnetic Resonance in Medicine.

A Frequency-Reconfigurable Tuner-Loaded Coupled-Fed Frame-Antenna for All-Metal-Shell Handsets

A frequency-reconfigurable frame-antenna integrated with a coupling strip and tuner loading is proposed for all-metal-shell mobile telephones. The coupling strip introduces additional capacitance to the feeding structure of the antenna, rendering the antenna to resonate at both the lower frequency band at “a quarter-wavelength resonant mode” and the higher frequency band at “a half-wavelength resonant mode”. Moreover, the antenna loaded with a tuner achieves broadband frequency-reconfiguration by tuning the effective length of radiating frame. The antenna is designed by taking into consideration all the metallic components, like front-and-back cameras, telephone receiver, and a steel sheet. The metal-frame and metal-shell of the handset coupled with a strip are used as parts of the antenna. This paper of a prototype operating in a practical handset test environment shows that the proposed antenna is able to cover the bandwidth of 824–960 MHz (GSM) and 1710–2690 MHz (DCS/PCS/UMTS/LTE) with acceptable radiation efficiency up to 40% and desirable patterns and specific absorption ratio, which is much lower than 1.6 W/kg for mobile communications.

An inductively coupled ultra-thin, flexible, and passive RF resonator for MRI marking and guiding purposes: Clinical feasibility.

The purpose of this study is to develop a wireless, flexible, ultra-thin, and passive radiofrequency-based MRI resonant fiducial marker, and to validate its feasibility in a phantom model and several body regions. Standard microfabrication processing was used to fabricate the resonant marker. The proposed marker consists of two metal traces in the shape of a square with an edge length of 8 mm, with upper and lower traces connected to each other by a metalized via. A 3T MRI fiducial marking procedure was tested in phantom and ex vivo, and then the marker's performance was evaluated in an MRI experiment using humans. The radiofrequency safety was also tested using temperature sensors in the proximity of the resonator. A flexible resonator with a thickness of 115 μm and a dimension of 8 × 8 mm was obtained. The experimental results in the phantom show that at low background flip angles (6-18°), the resonant marker enables precise and rapid visibility, with high marker-to-background contrast and signal-to-noise ratio improvement of greater than 10 in the vicinity of the marker. Temperature analysis showed a specific absorption ratio gain of 1.3. Clinical studies further showed a successful biopsy procedure using the fiducial marking functionality of our device. The ultra-thin and flexible structure of this wireless flexible radiofrequency resonant marker offers effective and safe MR visualization with high feasibility for anatomic marking and guiding at various regions of the body. Magn Reson Med 80:361-370, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

An Ultrawideband Conformal Capsule Antenna With Stable Impedance Matching

An ultrawideband conformal capsule slot antenna, which has a simple configuration and a stable impedance matching characteristic, is described in this paper. In the past, wideband outer-wall antennas have been proposed for capsule-type applications. However, this paper shows that the outer wall is not a good choice for placing capsule antennas, since such a choice exhibits a high specific absorption ratio, low gain, and low efficiency. Instead, the antenna proposed in this paper is conformal to the inner wall of a capsule shell, and it provides a wide impedance bandwidth ranging from 1.64 to 5.95 GHz (113.6%). Furthermore, the impedance matching remains stable even with a change in the operating environment. Since in a typical application scenario a capsule will move through the digestive system, and thus experience varying environments, a wide bandwidth and stable performance are both very desirable attributes of the antenna, whose design is discussed in this paper. Moreover, the proposed antenna continues to maintain a stable impedance match even when a battery is added inside the capsule, or when there is a change in the battery size and/or its position. Given these advantages, we argue that slot antennas are well suited for incorporation into capsule antennas for the present application.

Properties of Extrusion Concrete Panel Using Waste Concrete Powder

There has been an increasing amount of waste concrete generated in recent years, which has made recycling more important. Waste concrete is generally recycled as recycled aggregates, and many studies have been conducted to seek ways to improve their quality. Such quality improvement processes has led to the generation of byproducts such as waste concrete powder, which needs to be recycled efficiently based on further research. Accordingly, this study was conducted with the aim to use waste concrete powder (WCP) to substitute silica powder in the manufacturing of the extrusion concrete panels in cases where high SiO2 content is not a requirement. The results of this study showed a negative correlation between flexural strength and silica powder-WCP substitution ratio. For example, 50% substitution resulted in a product that satisfied the required flexural strength over 14 MPa as stipulated by the Korean Industrials Standards, and it gave rise to properties such as specific gravity, absorption ratio, length change, thermal conductivity, and fire-resistance that were similar to those of plain specimens. Based on these results, it was deemed that it would be possible to use WCP as an alternative material in place of siliceous fillers in cases where high-purity is not required.

Peak-Power-Limited Frequency-Domain Microwave-Induced Thermoacoustic Imaging for Handheld Diagnostic and Screening Tools

Coherent frequency-domain microwave-induced thermoacoustic (TA) imaging is investigated as an alternative to the traditional pulsed-based TA imaging approaches that use extremely high-energy short excitation pulses, often produced by vacuum RF sources or spark-gap generators. It is shown that under peak-power limitation of the RF source, dictated by the goals of form factor and portability of this paper, the frequency-domain approach can achieve the required signal-to-noise ratio (SNR) without sacrificing resolution or other performance metrics. Theoretical and experimental comparison of the time-domain and frequency-domain TA methods is provided with the ultimate goal of implementing the imager with solid-state hardware. Using a microwave source with 120 W of peak power, frequency-domain TA demonstrates 27-dB SNR improvement over the pulse method while the average specific absorption ratio remains below 10 W/kg. Finally, we demonstrate TA images of multilayer relatively complex muscle-fat structures. To the best of our knowledge, these are the first TA images obtained with solid-state electronic sources.

Humic acid removal from micro-polluted source water using gas phase surface discharge plasma at different grounding modes

Humic acid (HA) was a predominant natural organic matter in ground water and surface waters. The removal of HA from micro-polluted source water using a gas phase surface discharge plasma at different grounding modes was studied, and three kinds of grounding modes (iron wire mesh, aluminized paper, and water) were selected. The experimental results illustrated that approximately 95.3% of HA in water was removed within 30 min’s discharge plasma treatment in the iron wire mesh electrode system, and it was 89.5% and 84.6% in the aluminized paper electrode system and water electrode system, respectively; although the strongest streamer discharge and the highest ozone equivalent concentration were both observed in the iron wire mesh electrode system. The discharge plasma treatment resulted in a relatively more homogeneous surface topography in the HA molecules as analyzed by scanning electron microscope (SEM), especially in the iron wire mesh electrode system and in the aluminized paper electrode system. The decomposition process of HA at different grounding modes was analyzed and compared via the evolution of the UV–Vis spectrum, dissolved organic carbon (DOC), specific ultraviolet absorbance (SUVA) and UV absorption ratios with treatment time. In addition, the HA removal efficacy in this study was comparable with those of some other techniques.

0 μ Magnetic Polarizer for 1.5-T MRI

Study of human pathologies and acquisition of anatomical images without any surgical intervention inside human body is possible because of magnetic resonance imaging (MRI). This work exploits the notable properties of zero permeability (0 μ) split ring resonators (SRR) metamaterial (MM) magnetic polarizer which could distort, control and reject uniform RF (radio frequency) magnetic field for 1.5-T MRI systems. Unique polarizer was proposed to etch on PCB (printed circuit board) slabs for compact thickness of 5 mm only. In addition, polarizer was loaded with novel combination of parametric elements (capacitors, inductors) which could made the structure tunable to achieve resonance at different working frequencies. We achieved the value of relative permeability, μr=0.02+j0.1 for 1.5-T MRI systems at 63.85 MHz. Furthermore polarizer, when used with MRI scanner at optimized position, uniformly redistributed and enhanced the magnetic field while lowered specific absorption ratio (SAR), induced electric field, power dissipation, and locally improved SNR (signal to noise ratio) at the scanned region of phantom {real case was human body}. The polarizer minimized the damaging effects of RF energy absorption in human tissue and prevented them from heating.

Crashworthiness analysis of multi-cell square tubes under axial loads

In this paper, a theoretical expression for the mean crushing force Favg and the analysis of specific energy absorption (SEA) ratios of five different multi-cell square tubes were derived by applying the Simplified Super Folding Element (SSFE) theory. Then, the response surface models of the tubes were established separately based on the polynomial response surface method (PRSM). The models describe the response surfaces of SEA, peak crushing force Fmax and mean crushing force Favg under the variation of the side-length l1 of the exterior tube, the side-length l2 of the interior tube, and section form of the structure. Crashworthiness rules for tubes with different geometrical configurations including l1, l2 and different cross-sections were analysed. The numerical results matched the theoretical predictions. l2 exerted a slight influence. Compared to l1 and l2, the sectional form exerted a greater influence on the crushing force and energy absorption.

Experimental investigation on the effect of user's hand proximity on a compact ultrawideband MIMO antenna array

An experimental study of the interaction between user's hand and an ultrawideband multiple-input multiple-output (MIMO) antenna array is presented for mobile terminals. The dual-element array covers the frequency ranges 698–990 MHz and 1710–5530 MHz with a good efficiency in free space. Depending on the standard, it can be used for channel sensing in cognitive radio networks or for communications in cellular networks. Hand phantoms for three usage scenarios are used for the investigation, namely, personal digital assistant (PDA) right hand, PDA left hand, and two hands. The absorption in the immediate located hand is the main factor causing degradation of the total efficiency (slightly affected by the hand induced changes in the S-parameters), reduction and imbalance in the antennas mean effective gain contributing to a deteriorated diversity gain (DG). The user caused changes in the antennas radiation patterns reduce the correlation in the lower band which enhance the DG and multiplexing efficiency. The exposure of the hand in each scenario is studied by the specific absorption ratio.

Influence of low temperature on dynamic behavior of concrete

Aimed at finding out the influence degree of temperature, strain rate, water to cement ratio (w/c ratio) and maximum aggregate size on dynamic behavior of cement concrete, an orthogonal test on dynamic compressive strength of cement concrete applying a self-designed low temperature split Hopkinson pressure bar (SHPB) apparatus has been conducted on 8 groups of cylindrical cement concrete specimens (74mm diameter and 34mm thickness). The dynamic compressive strength of concrete specimens with different w/c ratios (0.5, 0.6) and maximum aggregate sizes (12mm, 22mm) have been tested at different temperatures (28°C, 0°C, −15°C, −30°C) and strain rates (33.5s−1, 46.7s−1). The influence sequence of factors is: temperature>strain rate>w/c ratio>maximum aggregate size. According to the results of orthogonal test, a further experimental study concerning the influence of temperature (28°C, 0°C, −15°C, −30°C, −45°C, −60°C, −75°C) and strain rate (34.33s−1, 44.25s−1, 63.18s−1) on dynamic compressive strength of concrete has been conducted on 21 groups of cylindrical specimens. Also a mechanical calculation model has been built for force analysis. The results demonstrate that: When −75°C<T<28°C, increase ratio of specific energy absorption (SEA) rises as temperature decreases; the sensitivity of dynamic compressive strength to strain rate increases as temperature decreases; the relationship between dynamic compressive strength and temperature conforms to a growth curve, and finally the increase ratio of dynamic compressive strength stabilizes at a maximum level of 65% at T=−75°C.