Specific Absorption Rate Reduction Research Articles

Design and analysis of dual band implantable DGS antenna for medical applications

An implantable antenna is designed for body area network, industrial scientific and medical applications with low specific absorption rate (SAR). The proposed antenna with defected ground structure (DGS) is designed on the FR4 substrate as well as on polyimide substrate. The designed antenna providing dual band characteristics at (Industrial scientific and medical) ISM band of 2.5 GHz and location application for emergency services (LAES) band at 4.2 GHz. The electromagnetic radiation is evaluated using the specific absorption rate in three layered phantom models and the SAR values of the antenna are evaluated by placing the antenna at different levels. The antenna distance is varied inside the skin layer to 5 mm away from the three-layered model and observed the reduction in SAR, when moving away from skin tissue. The observed value of SAR satisfies the IEEE-C95-1-2005 standards at ISM operating band. The proposed antenna is tested on three-layered phantom model in simulation through HFSS and in the real time on artificial layers with the help of combinational analyzer (CNA) connection.

Investigation of Nanomaterial Dipoles for SAR Reduction in Human Head

Abstract The Nanomaterial is a pioneer in the field of modern research for its unique properties. Human exposure analysis is inevitable due to the rapid growth in technology. The concern for human welfare indicates a need for reduction of human exposure towards the radiation caused by the devices. The dielectric properties of the nanomaterials can be ideal for exploration in the field of biomedical engineering. Specific absorption rate (SAR) is a vital parameter for exposure analysis. This paper investigates the impact of Nanomaterials on the human exposure analysis. For this purpose, a dipole radiating structure operating at GSM frequency of 900 MHz and 1800 MHz are designed with conventional Copper material and compared with Carbon nanomaterials such as Graphene, Single-walled carbon nanotube (SWCNT) and Multi-walled carbon nanotube (MWCNT) for performance evaluation. Further, the specific absorption rate estimates absorption of radiation in IEEE Sam phantom human head with equivalent tissue properties. The comparison of calculated SAR with the radiating structures that are designed with the equivalent properties of that of Nanomaterials. The evaluation of Nanomaterial Antennas at the center frequency is estimated, and performance is evaluated. The designed Nanomaterials interact with IEEE SAM Phantom and SAR is calculated. The analysis of SAR impact with nanomaterials is investigated in this work.

Reducing RF-induced Heating near Implanted Leads through High-Dielectric Capacitive Bleeding of Current (CBLOC).

Patients with implanted medical devices such as deep brain stimulation or spinal cord stimulation are often unable to receive magnetic resonance imaging (MRI). This is because once the device is within the radiofrequency (RF) field of the MRI scanner, electrically conductive leads act as antenna, amplifying the RF energy deposition in the tissue and causing possible excessive tissue heating. Here we propose a novel concept in lead design in which 40cm lead wires are coated with a ~1.2mm layer of high dielectric constant material (155 < ε r < 250) embedded in a weakly conductive insulation (σ = 20S/m). The technique called High-Dielectric Capacitive Bleeding of Current, or CBLOC, works by forming a distributed capacitance along the lengths of the lead, efficiently dissipating RF energy before it reaches the exposed tip. Measurements during RF exposure at 64 MHz and 123 MHz demonstrated that CBLOC leads generated 20-fold less heating at 1.5 T, and 40-fold less heating at 3 T compared to control leads. Numerical simulations of RF exposure at 297 MHz (7T) predicted a 15-fold reduction in specific absorption rate (SAR) of RF energy around the tip of CBLOC leads compared to control leads.

Microwave Emissions From Cell Phones Exceed Safety Limits in Europe and the US When Touching the Body

In our publications, we have shown both from measurements and computer modeling that the specific absorption rate (SAR) reduces by 10%-15% for every millimeter separation of the cell phone on account of rapidly diminishing EM fields in the near-field region of the cell phone antenna. This rapid reduction of SAR depending on the antenna and its location on the handset has been shown, both computationally and experimentally, regardless of the phantom model such as a flat phantom suggested for SAR compliance testing of devices in contact with the body, for a sphere phantom, and for head-shaped models used for SAR compliance testing of cell phones. Unfortunately, our observations in the past were based on SARs of only three cell phones. Expecting that the SARs for cell phones may exceed the safety limits for body contact, cell phone manufacturers have started to recommend that the devices can be used at 5-25 mm from the body even though it is difficult to see how to maintain this distance correctly under mobile conditions. The National Agency ANFR of France recently released the cell phone SAR test data for 450 cell phones that measure 10-g SARs reducing by 10%-30% for each millimeter distal placement from the planar body phantom. Their data corroborate our findings that most cell phones will exceed the safety guidelines when held against the body by factors of 1.6-3.7 times for the European/ICNIRP standard or by factors as high as 11 if 1-g SAR values were to be measured as required by the U.S. FCC.

High permittivity ceramics improve the transmit field and receive efficiency of a commercial extremity coil at 1.5 Tesla.

The purpose of this work is to investigate the use of ceramic materials (based on BaTiO3 with ZrO2 and CeO2-additives) with very high relative permittivity (εr ∼ 4500) to increase the local transmit field and signal-to-noise ratio (SNR) for commercial extremity coils on a clinical 1.5 T MRI system. Electromagnetic simulations of transmit efficiency and specific absorption rate (SAR) were performed using four ferroelectric ceramic blocks placed around a cylindrical phantom, as well as placing these ceramics around the wrist of a human body model. Results were compared with experimental scans using the transmit body coil of the 1.5 T MRI system and an eight-element extremity receive array designed for the wrist. SNR measurements were also performed for both phantom and in vivo scans. Electromagnetic simulations and phantom/in vivo experiments showed an increased in the local transmit efficiency from the body coil of ∼20-30%, resulting in an ∼50% lower transmit power level and a significant reduction in local and global SAR throughout the body. For in vivo wrist experiments, the SNR of a commercial eight-channel receive array, integrated over the entire volume, was improved by ∼45% with the ceramic. The local transmit efficiency as well as the SNR can be increased for 1.5 T extremity MRI with commercial array coils by using materials with very high permittivity.

Towards reduction of SAR in scaling up in vivo pulsed EPR imaging to larger objects.

An excessive RF power requirement is one of the main obstacles in the clinical translation of EPR imaging. The radio frequency (RF) pulses used in EPR imaging to excite electron spins must be very short to match their fast relaxation. With traditional pulse schemes and ninety degree flip angles, this can lead to either unsafe specific absorption rate (SAR) levels or unfeasibly long repetition times. In spectroscopy experiments, it has been shown that stochastic excitation and correlation detection can reduce the power while maintaining sensitivity but have yet to be applied to imaging experiments. Stochastic excitation is implemented using a pseudo-random phase modulation of the input stimulus. Using a crossed coil resonator assembly comprised of an outer saddle coil and an inner surface coil, it was possible to obtain a minimum isolation of ~50 dB across a 12 MHz bandwidth. An incident peak RF power of 5 mW was used to excite the system. The low background signal obtained from this resonator allowed us to generate images with 32 dB (>1000:1) signal-to-noise ratio (SNR) while exciting with a traditional pulse sequence in a phantom containing the solid paramagnetic probe NMP-TCNQ (N-methyl pyridinium tetracyanoquinodimethane). Using two different stochastic excitation schemes, we were able to achieve a greater than 4-fold increase in SNR at the same peak power and number of averages, compared to single pulse excitation. This procedure allowed imaging at significantly lower RF power levels than used in conventional EPR imaging system configurations. Similar techniques may enable clinical applications for EPR imaging by facilitating the use of larger RF coils while maintaining a safe SAR level.

J-slot EBG structure for SAR Reduction of Dual Band J-slot Textile Antenna

&lt;p&gt;&lt;span&gt;In this article, the dual band is achieved with J-slot on rectangular Textile antenna on Jeans fabric as substrate. It resonates at the 2.4 GHz and 5.4 GHz of Wireless Body Area Network (WBAN) bands. The novel J-slot Electromagnetic Band Gap (EBG) array consists of 2x2 elements. It is used as superstrate of J-slot textile antenna for Specific Absorption Rate (SAR) reduction and gain enhancement. The Reflection coefficient and VSWR of dual band textile antenna are simulated and measured with and without human body&lt;strong&gt;.&lt;/strong&gt;&lt;/span&gt;&lt;/p&gt;

Synthesis and characterization of biocompatible ferrofluid based on magnetite nanoparticles and its effect on immunoglobulin G as an immune protein

The investigation of interaction between protein fundamental to the immune system, immunoglobulin G (IgG), and superparamegnetic iron oxide nanoparticles (SPIONs) helps in designing the cell separation, drug delivery and hyperthermia systems. For this reason, the superparamagnetic iron oxide nanoparticles (SPIONs) were prepared and coated with chitosan (CS) due to decrease of cytotoxicity. The chitosan coated superparamegnetic iron oxide nanoparticles (CS-SPIONs) were characterized by X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM) and the magnetic hyperthermia efficiency. The coating of SPIONs minimized the agglomeration with reduction in magnetic behavior and specific absorption rate (SAR). The internalization of CS-SPIONs into the cells was performed by Prussian blue staining. Zeta potential and dynamic light scattering (DLS) of ferrofluids in cell culture medium were evaluated. The cytotoxicity studies were evaluated on human foreskin fibroblast normal cell line, HFFF2 by MTT assay and annexin V/PI staining. The binding studies were carried out by multispectroscopic approaches. Absorption spectroscopy (UV–Vis) indicated that CS-SPIONs can bind to IgG. The fluorescence emission spectroscopy of IgG was quenched by CS-SPIONs. The quenching mechanism was a combination of static and dynamic as well as binding constant (1.84 × 104 M−1, 1.34 × 104 M−1 and 1.10 × 104 M−1 at 293 K, 298 K and 313 K, respectively) and number of binding sites (n = 1) were determined. The thermodynamic signature clearly indicated that hydrogen bonds and van der Waals forces play a main role in the binding process. The binding distance (2.1 nm) and energy transfer efficiency (0.69) were determined using Förster mechanism. Synchronous fluorescence studies indicated that the binding changes the microenvironment around tryptophan residues rather than tyrosine residues. In addition, three-dimensional fluorescence (3D), Far-UV CD spectrum, near-UV CD spectrum and ellipsometry results showed additional insight into conformational changes of IgG on binding with CS-SPIONs. These results provided CS-SPIONs as a biocompatible candidate for pharmacology and nanomedicine.

Application of a Compact Electromagnetic Bandgap Array in a Phone Case for Suppression of Mobile Phone Radiation Exposure

In this paper, a mobile phone case incorporating electromagnetic bandgap (EBG) material is studied to intercept electromagnetic (EM) waves from the phone and reduce the specific absorption rate (SAR). A loop antenna for the personal communications service 1900-MHz band is considered. In addition, three different mobile phone cases associating EBG structures with optimized positions are used to improve SAR reduction. Furthermore, antenna performance with an EBG structure is investigated with a full-body EM simulation program, SEMCAD X, and an individual performance analysis of each EBG structure was carried out by using Ansoft HFSS. A human head phantom to replicate the specific anthropomorphic mannequin model was used for measurements. From simulation and measurement, it is found that placing an EBG structure in a phone case can improve antenna gain and reduce SAR. Moreover, a maximum gain increment of 19% and an SAR reduction of 24% were found. This paper reveals the future applications of EBG structures for SAR reduction in mobile phones.

Increasing robustness of radial GRASE acquisition for SAR-reduced brain imaging

PurposeTo improve a radial multi-slice 2D gradient- and spin-echo (GRASE) sequence and provide an appropriate image reconstruction technique for SAR-reduced high-resolution neuroimaging. MethodsAdditional readout gradients per radio-frequency (RF) refocusing allow for a reduced number of RF pulses. In this way, a specific absorption rate (SAR) reduction is achieved and the application at high-field systems becomes more feasible. A phase insensitive image reconstruction is proposed to reduce signal dropout artifacts originating from opposite readout polarities. In addition, the image reconstruction allows for the calculation of images with varying contrast from one measurement. ResultsResults obtained at 3T and 7T demonstrate a SAR-reduction of at least 66% for a single-slice experiment with radial GRASE. The reduced SAR is used for an increased spatial coverage without increasing the measurement time. Experiments at 3T and 7T showed that the visual image quality is comparable to standard TSE and GRASE sequences with the same measurement parameters. Using higher EPI factors and the presented image reconstruction, artifact-free images with a significant SAR-reduction can be achieved. ConclusionRadial GRASE enables SAR-reduced acquisitions of high-resolution brain images with different contrasts from one measurement and is a promising sequence for high-field neuroimaging.

A novel low SAR water-based mobile handset antenna

The effect of mobile phones on human health is becoming a serious concern in the last decade. This paper suggests a novel water-based cellular phone antenna for reducing the electromagnetic wave radiation toward human head. Two antennas are considered: a single band PIFA operating at 1.8 GHz, and a dual band PIFA operating at 900 MHz and 1.8 GHz. The specific absorption rate (SAR) is decreased up to 0.6 W/kg by limiting the propagation of near electromagnetic fields toward the human head and therefore reducing the current density distribution. The reduction of SAR is carried out by introducing an U-edge wall made of an absorbing water material at each corner of the ground plane.

Investigation into Low SAR PIFA Antenna and Design a Very Low SAR U-slot Antenna using Frequency Selective Surface for cell-phones and Wearable Applications

There are very important questions. “Do Electromagnetic waves have irreparable effects on human or not?” “Are there any relation between cancer and waves?” and finally “what should we do to be safe?”. In the present article, these questions will be answered simply and professionally. First of all, Specific Absorption rate (SAR) is define then L-Slot and U-slot antenna is designed and simulated using cell-phones and wearable applications, operating at and consist of GSM900 and GSM1800. Standard frequency band width for the first and second band is and for uplink and downlink and in the present research these numbers are obtained. The SAR of each antenna is measured and is compared with each other. Thanks to design of antenna, The SAR of U-Slot antenna is very low and it is almost stimulated and this sentence means this antenna is anti-cancer. Finally, Some SRR unit-cells are designed and when they are used in structure, SAR will be more decrease. Last SAR value is and for each bands .In the last table, There are some comparison between different creditable references and present article SAR reduction is acceptable and it is near to percentage.

Communication on SWIPT and EH Using Electromagnetic Behaviour for Power Allocation in Wireless Networks

This review paper focuses on the basic relations between wireless power transfer, wireless information transfer and combined phenomenon of simultaneous wireless information and power transfer. The authors reviewed and discussed electromagnetic fields behaviour (EMB) for enhancing the power allocation strategies (PAS) in energy harvesting (EH) wireless communication systems. Further, this paper presents relations between Friis transmission equation and Maxwell’s equations to be used in propagation models for reduction in specific absorption rate (SAR). This paper provides a review of various methods and concepts reported in earlier works. This paper also reviews Poynting vector and power densities along with boundary conditions for antennas and human body. Finally, this paper explores the usage of electromagnetic behaviour for the possible enhancement in power saving methods for electromagnetic behaviour centered-wireless energy harvesting (EMBC-WEH). At the same time, possibilities of PAS for reduction in SAR are discussed.

A specific absorption rate reduction method for simultaneous multislice magnetic resonance imaging.

This study proposes a modified Shinnar-Le Roux method to synthesize the excitation radio frequency (RF) pulse for a 2D gradient echo (GRE) based simultaneous multi-slice (SMS) magnetic resonance imaging (MRI) with features of low specific absorption rate (SAR) and small out-of-slice ripple. This synthesis method for SMS RF pulses employs thinner slice bandwidth and lower multislice offset frequencies to reduce SAR values and adopts a weighted Parks-McClellan algorithm to reduce sidelobes. Formulas for estimating relative SAR values of the SMS pulses are also introduced. Relative SAR values and out-of-slice ripples of the proposed and typical RF pulses with different parameters are presented. In simultaneous 5-slice phantom and 3-slice human brain imaging, SMS pulses synthesized with the proposed method achieve 32% and 28% SAR values of standard pulses while providing similar image qualities. Typical RF pulses such as sinc x cos can also take advantage of the proposed method and offer lower SAR values for SMS imaging. The RF pulse synthesized using the proposed method features low SAR, small sidelobes, and consistent image quality for 2D GRE-based SMS MRI. This method is applicable to the synthesis of typical SMS RF pulses for significant SAR reduction.

Parallel radiofrequency transmission at 3 tesla to improve safety in bilateral implanted wires in a heterogeneous model.

Elongated implanted conductors can interact with the radiofrequency (RF) transmission field during MRI, posing safety concerns of excessive heating in patients with deep brain stimulators. A technique using parallel RF transmission (pTx) is evaluated on an anthropomorphic heterogeneous model with bilateral and unilateral curved wires. Amplitude and phase were optimized by simulation to minimize heating surrounding the implanted wires and to minimize B1+ inhomogeneity for four-channel and eight-channel pTx in a heterogeneous model. MRI experiments were conducted in an equivalent test phantom created from a common digital mesh file. In four-channel pTx, maximum local specific absorption rate (SAR) was reduced in both unilateral and bilateral wires by 47% and 59%, respectively, but with compromised B1+ homogeneity. Optimized eight-channel pTx substantially reduced local SAR compared with birdcage coil RF excitation in both unilateral and bilateral wires (reduction of maximum local SAR of 79% and 87%, respectively). B1+ inhomogeneity was limited to 17% and 26%, respectively. Experimental validation with four-channel pTx showed 80% and 92% temperature reduction at the tips of wire 1 and wire 2, respectively. This pTx approach yields promising reductions in local SAR at the tips of unilateral and bilateral implanted wires while maintaining image quality in simulation and experiment. Magn Reson Med 78:2408-2415, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Design of PIFA With Metamaterials for Body-SAR Reduction in Wearable Applications

This letter proposes a planar inverted-F antenna (PIFA) with an artificial magnetic conductor (AMC) structure for body specific absorption rate (SAR) reduction in a wideband-code-division-multiple-access band. As wireless devices such as wearable phones and smart watches become more common, health risks originating from electromagnetic waves generated by devices worn on the body have become an important issue. AMC structures are a type of metamaterial that can act as a perfect magnetic conductor and control the radiation pattern of an antenna. Thus, an antenna with an AMC structure is capable of preventing hazardous electromagnetic fields being emitted in the direction of the body. The S-parameters, radiation patterns, total radiated power values, and SAR values of such a designed structure are presented. The results demonstrate a 43.3% reduction in the SAR value at the center frequency. Thus, the human body can be protected from electromagnetic waves using metamaterials.

SAR Reduction Using Integration of PIFA and AMC Structure for Pentaband Mobile Terminals

In this paper, a capacitive grating artificial magnetic conductor (AMC) is presented to reduce the specific absorption rate (SAR) in pentaband mobile terminals. The AMC structure is implemented using a dielectric film with the printed arrays of the metal strips placed at the top and the bottom of the dielectric. It is difficult to design the AMC structure to operate at low (824~960 MHz) and high bands (1710~2170 MHz) simultaneously, because of the limited space available for the antenna. Hence, we have designed the capacitive grating AMC to operate at a high band. Then, we attached a PIFA to the AMC structure to cover low and high bands. As the AMC structure is operated as a perfect electric conductor (PEC) in low band, the radiating branches of the PIFA for the low and high bands should be located on the non-AMC and the AMC structures, respectively. Even though the AMC structure is operated at a high band, the effect against the head could be reduced in the pentaband due to the spreading effect of the electromagnetic (EM) field at lower bands. From measured results, the 1 g SAR in the case of the AMC antenna is significantly lower than that in the case where only the PIFA is present in the pentaband.

Enhancing antenna performance and SAR reduction by a conductive composite loaded with carbon-silica hybrid filler

In this paper, we describe a technique for reducing the specific absorption rate (SAR) and human effects on antenna performance, based on combined use of rubber conductive composite loaded with carbon-silica hybrid filler used like a single director and a resonant half wave dipole. The finite-difference time-domain method was used to evaluate SAR and antenna performance for different antenna-composite configurations and distances. Bandwidth, gain, and radiation efficiency for different antenna-composite configurations were compared. It was found that the presence of a conductive composite loaded with carbon-silica hybrid filler can effectively reduce maximum SAR value (up to 70%) in a human head model, increasing the radiation efficiency (up to 67%) and the bandwidth (up to 110%) of the antenna.

Local SAR near deep brain stimulation (DBS) electrodes at 64 and 127 MHz: A simulation study of the effect of extracranial loops.

MRI may cause brain tissue around deep brain stimulation (DBS) electrodes to become excessively hot, causing lesions. The presence of extracranial loops in the DBS lead trajectory has been shown to affect the specific absorption rate (SAR) of the radiofrequency energy at the electrode tip, but experimental studies have reported controversial results. The goal of this study was to perform a systematic numerical study to provide a better understanding of the effects of extracranial loops in DBS leads on the local SAR during MRI at 64 and 127 MHz. A total of 160 numerical simulations were performed on patient-derived data, in which relevant factors including lead length and trajectory, loop location and topology, and frequency of MRI radiofrequency (RF) transmitter were assessed. Overall, the presence of extracranial loops reduced the local SAR in the tissue around the DBS tip compared with straight trajectories with the same length. SAR reduction was significantly larger at 127 MHz compared with 64 MHz. SAR reduction was significantly more sensitive to variable loop parameters (eg, topology and location) at 127 MHz compared with 64 MHz. Lead management strategies could exist that significantly reduce the risks of 3 Tesla (T) MRI for DBS patients. Magn Reson Med 78:1558-1565, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

SAR reduction using a single SRR superstrate for a dual-band antenna

ABSTRACTA dual-band microstrip antenna operating at GSM 900 and GSM 1800 MHz is designed initially. Then a single split ring resonator (SRR) structure is used as a superstrate for this dual-band antenna. A circular current is induced in the SRR due to the perpendicular plane wave excitation, which in turn leads to an electric excitation coupled to the magnetic resonance. It also exhibits higher order excitations at 0.9 and 1.8 GHz which ultimately resulted in specific absorption rate (SAR) reduction of human head at both the designed frequencies of the antenna. The antenna and the SRR superstrate are printed on a 1.6 mm thick FR-4 substrate of dimension 59.6 × 49.6 mm2. Analysis of the SRR using the classic waveguide theory approach is discussed. Radiation pattern of the antenna in the presence of SRR superstrate and human head is also discussed. Prototype of the antenna along with the SRR superstrate is fabricated and measured for return loss and radiation pattern. Measurement results fairly agree with the simulated results. A human head phantom is utilized in the calculation of SAR.