Specific Absorption Rate Reduction Research Articles

Analysis and implementation of shorting pins in microstrip patch antenna for SAR reduction

Specific absorption rate (SAR), is the safety measure to quantify human exposure to electromagnetic radiation from mobile phones and other wireless devices, which must be kept within the permissible levels to avoid various health concerns. This paper provides an experimental study on the effectiveness of SAR reduction, using shorting pins, and its corresponding effects on antenna performance. A compact, single-element, microstrip patch antenna design, using shorting pins, with reduced SAR value, is also presented. The surface current distribution on the patch can be modified by the strategic positioning of shorting pins to produce a mushroom shaped radiation pattern having nearly omnidirectional nature in the +Z direction with a near-field null in the vicinity of the user’s direction. This completely minimizes the back lobes in the E-plane, with minor back lobes in the H-Plane creating a deep null, which reduces the SAR value without compromising the signal coverage. The antenna is fabricated and cross-verified by experimental evaluation in an anechoic chamber for return loss, gain, and radiation pattern.

Development of experimental device for inductive heating of magnetic nanoparticles

Inductive heating using magnetic nanoparticles is a critical process extensively investigated for cancer treatment. However, the high cost of commercially available equipment hinders its accessibility for many research groups. In response, this paper introduces a simple electronic circuit with low-cost components, making it easy to construct even for non-electronic experts. Operating within the 50–200 kHz range, the circuit employs a parallel inductor-capacitor configuration, providing a maximum induction magnetic field of 23.6 mT. Ltspice software simulations align well with oscilloscope measurements. Using commercial iron oxide nanoparticles (∼16 nm) in water suspensions (1–10 mg ml−1), the device exhibited a concentration-dependent reduction in specific absorption rate values, consistent with literature findings. Hyperthermia temperatures were achieved in a few minutes at 52.5 kHz and 23.6 mT in the highest concentration. At 81.9 kHz and 21.5 mT, a temperature of 93 °C was achieved after 22 min at 10 mg ml−1. Additionally, the device demonstrated stable and safe operation over a 100 min period, as validated by an ice-melting experiment. These results highlight the device’s efficacy for hyperthermia experiments in both biological and non-biological systems, particularly advantageous for larger nanoparticles in a blocked state. The proposed device holds significant potential for contributing to hyperthermia studies across diverse research groups. Future development will focus on frequency adjustment without reducing the alternating magnetic field amplitude and a thorough investigation of field homogeneity inside the coils.

Investigation of SAR reduction and gain enhancement using an all-textile antenna with metamaterial structure for wireless body area network applications

This work presents a wideband, low-profile, and flexible antenna that incorporates metamaterial (MTM) structures and textile materials. The antenna design is simulated using CST Microwave Studio, incorporating flexible textile elements such as a felt substrate and conductive fabric. The developed antenna's performance was examined numerically in free space and on a human body. The antenna with MTM technology operates in the ultra-wideband (UWB) with a bandwidth ranging from 3.86 to 13 GHz. It possesses a low profile with a thickness of 5.34 mm, making it suitable for applications in wireless body area networks (WBAN). Through the integration of metamaterial structures, the antenna's gain is enhanced, reaching 8.85 dBi compared to the initial gain of 5.34 dBi. Notably, the gain consistently exceeds 6 dBi across the entire UWB range, indicating focused power in a specific direction. For applications on the human body, specific absorption rate (SAR) values were calculated and found to be well within safety limits defined by European standards. This ensures minimal back radiation when the antenna is worn on the body, enhancing signal transmission range in WBAN applications.

Warranty, free service and rework policy for an imperfect manufacturing system with SAR sensitive demand under emission taxation

The aim of this study is to illustrate the impact of warranty/free service period, specific absorption rate (SAR) of the products, rework policy and emission taxation on the optimal business policy of an imperfect production inventory system in the current highly uncertain/intensified market situation. In this study, the customers’ demand is considered to be influenced by the warranty/free service period along with a permissible SAR of the items. As a result, the manufacturer invests in order to provide warranty period/free service period and fixing an appropriate SAR for the products which are shown in production cost, service cost and SAR reduction investment. Three distinct scenarios are analysed separately regarding the marketing assimilation of defective items. Each suggested scenario relying on the system is quantitatively validated using an example. Furthermore, manufacturers are bound to pay carbon emission tax due to the carbon emission during the production process. Due to high non-linearity of the objective function, a numerical example is solved using the artificial hummingbird algorithm (AHA). From the numerical experiment, it is observed that the optimal policy of the system is strongly influenced by the price and duration of the warranty, emission taxation rate and moderately affected by the SAR of the product. Finally, a sensitivity analysis is carried out, and its effect are shown graphically in order to provide guidance to the competent manager of the firm.

Improved 1 H body imaging at 10.5 T: Validation and VOP-enabled imaging in vivo with a 16-channel transceiver dipole array.

To increase the RF coil performance and RF management for body imaging at 10.5 T by validating and evaluating a high-density 16-channel transceiver array, implementing virtual observation points (VOPs), and demonstrating specific absorption rate (SAR) constrained imaging in vivo. The inaccuracy of the electromagnetic model of the array was quantified based on B1 + and SAR data. Inter-subject variability was estimated using a new approach based on the relative SAR deviation of different RF shims between human body models. The pTx performance of the 16-channel array was assessed in simulation by comparison to a previously demonstrated 10-channel array. In vivo imaging of the prostate was performed demonstrating SAR-constrained static RF shimming and acquisition modes optimized for refocused echoes (AMORE). The model inaccuracy of 29% and the inter-subject variability of 85% resulted in a total safety factor of 1.91 for pelvis studies. For renal and cardiac imaging, inter-subject variabilities of 121% and 141% lead to total safety factors of 2.25 and 2.45, respectively. The shorter wavelength at 10.5 T supported the increased element density of the 16-channel array which in turn outperformed the 10-channel version for all investigated metrics. Peak 10 g local SAR reduction of more than 25% without a loss of image quality was achieved in vivo, allowing a theoretical improvement in measurement efficiency of up to 66%. By validating and characterizing a 16-channel dipole transceiver array, this work demonstrates, for the first time, a VOP-enabled RF coil for human torso imaging enabling increased pTx performance at 10.5 T.

SAR reduction techniques for WBAN and mobile applications

Abstract In recent years there has been a substantial growth in the usage of wireless gadgets in various fields like mobile communication, health monitoring, warfare communications, etc. However, the performance of the antenna is evaluated by the parameters like gain, directivity and bandwidth, VSWR and is enhanced as a continuous process. But on the other side, Specific Absorption Rate (SAR) is a parameter that is likely to be watched out for the safety concern which should be as low as possible for any antenna to ensure the minimum risk to human health. Many researchers have contributed an enormous amount of work to the SAR reduction. From this perspective, this work proposes a brief survey on low SAR antennas. An optimal low SAR antenna needs a perfect lossless impedance matching over a lossy medium (human body) for the eradication of spurious surface waves. The deployment of SAR reduction strategies, outcomes of the design, and open-end research challenges with the relative results are addressed as a part of the survey. The core impulse of this work is to induct the antenna designers to get indulged in designing low SAR antenna with enhanced performance for several WBAN applications like health monitoring and many more.

A tri-band flexible antenna based on tri-band AMC reflector for gain enhancement and SAR reduction

A tri-band wearable antenna fed by coplanar waveguide (CWP) with an artificial magnetic conductor (AMC) reflector is presented in this paper. The radiation patch consists of three open inverted triangles for multiband, and the ground is defected for better impedance matching The AMC unit is composed of three concentric nested regular octagonal rings. And to improve the performance of gain, the unit achieves three reflection zero phases at 1.8, 2.45 and 3.5 GHz corresponding to the three bands of the antenna. The proposed antenna based on AMC has been fabricated and measured. The working frequency bands are 1.34–1.67 GHz, 2.33–2.47 GHz and 3.55–3.7 GHz. The measured gain has increased by 3.4, 1.8, 4 dBi at 1.8, 2.45 and 3.5 GHz, respectively. The scenario that the antenna is placed on the human arm is also considered and experimented for wearable applications. The results are in good agreement with the simulation data and verify that the antenna has good robustness. When the antenna is conformal with the human tissue, the specific absorption rate (SAR) is calculated and reduced by about 99.8% after adding AMC reflector. Hence the proposed antenna has excellent wearable safety and is compatible with LTE 1800, WLAN, WiMAX communication systems.

A compact triband antenna using artificial magnetic conductor for wireless body area network communicationsFront

The proliferation of the Internet of Things devices and advancements in wireless communication have fostered the growth of Wireless Body Area Networks (WBAN). This research provides a triband antenna supported by a 4 × 4 Artificial Magnetic Conductor (AMC) array surface that has a low Specific Absorption Rate (SAR), a high Front to Back Ratio (FBR), and increased gain for use in wearable devices. For WBAN communications, the proposed antenna operates in the Industrial, Scientific, and Medical (2.4 GHz) band, the C (3.7–4.2 GHz), and the Wi-Fi 6E (5.925–7.125 GHz) bands. The dual-band AMC unit cell exhibits Double-Negative and angular stability behaviour at 2.45 GHz and 6.5 GHz. AMC-backed antenna achieved multiband functionality by incorporating slots into the unit cell and a defective ground structure into the antenna. The antenna was positioned 0.139λ0 above the AMC surface, which measured 0.556λ0 × 0.556λ0 × 0.013λ0 (at 2.45 GHz). The antenna exhibited good gain and return loss variations when mounted on curved surfaces. The proposed integrated design yielded substantial enhancements, as evidenced by the increase of 8.2 dBi in maximum gain, 25.2 dB in FBR, and over 93% in total efficiency. The AMC-backed antenna’s − 10 dB impedance bandwidth is 18.4%, 21.2%, and 22.3%, with corresponding frequency ranges of 2.25–2.66 GHz, 3.66–4.53 GHz, and 5.9–7.35 GHz. Additionally, the AMC surface showed an average reduction in SAR of 93.22%. Vector Network Analyzer and Anechoic chamber measurements proved simulation accuracy. As a result, it is strongly recommended that the integrated antenna design be acknowledged in WBAN communications.

Design of Low-SAR Terminal Antenna Using Characteristic Mode Manipulation

A novel specific absorption rate (SAR) reduction method based on the characteristic mode theory (CMT) is proposed for mobile terminal. The CMT is introduced to establish the relationship between the characteristic electric field and the induced electric field in human tissues. The design process and mechanism of a low-SAR antenna are demonstrated. To verify the effectiveness of the proposed SAR reduction method, a low-SAR loop antenna is designed. The measurement results show that the 10 g average SAR peak value of the proposed antenna is reduced by 26.1%. The measured −10 dB bandwidth of the low-SAR antenna is 320 MHz, which is increased by 60% compared with the reference antenna (200 MHz). The measured efficiency of the reference antenna and low-SAR antenna are better than 64% and 73% in the entire operating frequency band. With the advantages of bandwidth enhancement, significant SAR reduction and high antenna efficiency, the proposed SAR reduction method is a good choice for the low-SAR terminal antenna design.

Low specific absorption rate quad-port multiple-input-multiple-output limber antenna integrated with flexible frequency selective surface for WBAN applications

This paper presents the design and analysis of a multiple-input-multiple-output (MIMO) textile antenna for wireless body area network (WBAN) applications. The MIMO antenna is comprised of four identical modified rhombus-shaped monopole antenna elements of size of 0.57, where is the wavelength calculated at the lowest operating frequency. The antenna is backed by a 6 frequency selective surface (FSS) of dimensions of 0.84 to improve gain and to reduce specific absorption rate (SAR). The antenna has an impedance bandwidth (S 11 ⩽ −10 dB) of 8.8 GHz (2.8–11.6 GHz) and isolation of >19 dB between the resonating elements. In order to assess the MIMO antenna’s flexibility, the bending analysis is performed for various bending radii. The obtained diversity metrics are: envelope correlation coefficient <0.5 dB, diversity gain <10 dB, channel capacity loss <0.4 bits s−1 Hz−1, and total active reflection coefficient <−10 dB. The performance of the antenna with and without FSS is investigated for gain enhancement and SAR reduction. With the help of FSS, the antenna gain is increased to 8.44 dBi, and the SAR reduced from 6.99 Watt kg−1 to 0.0273 Watt kg−1. The FSS achieves the highest efficiency of 96%. The designed antenna is suitable for smart textile applications due to its low SAR, high gain, and wider impedance bandwidth.

A compact fully fabric I‐shaped antenna supported with textile‐based AMC for low SAR 2.45 GHz wearable applications

AbstractIntroduced in this letter is a thin, flexible, compact, and fully fabric I‐shaped quarter‐wavelength antenna, where a 3 × 3 array reflector, is in the antenna rear end. In free space, the I‐shaped antenna radiates at 2.45 GHz of the Industrial, Scientific, and Medical band with simulated realized gain of 1.65 dB and 90% worth of simulated radiation efficiency. The array reflector is utilized to diminish the specific absorption rate (SAR) in human evaluation scenarios. At the operating frequency, in free space, the antenna realized gain is improved by 75% after incorporating the artificial magnetic conductor (AMC) array. Moreover, over 1 g of tissue, a SAR reduction of 99.5% is attained at 2.45 GHz. Simulation and measured S11 and radiation pattern comparisons are highlighted in this letter. Based on the accomplished outcomes, the integrated antenna, comprised of the fully fabric I‐shaped quarter‐wavelength antenna and the AMC array, might be considered for wearable applications.

SAR reduction using dual band EBG method based on MIMO wearable antenna for WBAN applications

A wearable ultra-wideband MIMO antenna using conductor and polyester fiber fabrics is proposed in this paper. The antenna’s total dimension is 115 × 70 mm2. As a result, the antenna can be installed on curved or bent surfaces due to its flexibility. This proposed antenna has a frequency range of 2 GHz – 30 GHz, a gain of 3.75 dBi on average, and a correlation coefficient of 0.5. That can be utilized for interior installation of the 5G frequency spectrum (2.6 GHz and 26 GHz), as well as WBAN application (2.4 GHz, 5.2 GHz, and 3.1 GHz – 10.6 GHz). Additionally, the researchers designed an electromagnetic band gap (EBG) and constructed a square loop plate with a square plate that reflects resonance characteristics in the 2.4 GHz and 5.2 GHz bands by placing unit cells in 3 × 5 cells to decrease the antenna’s specific absorption rate (SAR). The proposed antenna with EBG could minimize the SAR values to 0.088 W/kg and 0.070 W/kg, which obtains a gain of 6.59 dBi and 11.6 dBi, at 2.4 GHz and 5.2 GHz, respectively. Also, the results are lower than the conventional SAR value of 2.0 W/kg at 10 g.

Radially Extended 3D Birdcage Antenna for MRI With Loop-Type Legs and Connection to the Shield

A novel radially extended 3D birdcage (BC) coil antenna was designed, simulated, and optimized for a cylindrical dielectric phantom at 4.7 T. The 3D birdcage consists of a classical birdcage with additional protrusions toward the inside and connections to the shield. To overcome the huge computational burden of the optimization process using the particle swarm optimization (PSO) method, an in-house method of moment (MoM) code exploiting the symmetry of the structure has been developed. The code produces open-circuit embedded element patterns and makes use of a Schur complement to analyze the effects of passive loads, in the presence of a phantom. The simulation results have been verified with the use of commercial software. The proposed 3D BC coil showed a 34 % improvement in the homogeneity of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> and a 37 % reduction in the peak specific absorption rate (SAR), compared with a conventional BC coil.

Investigation of the Effect of Normal Incidence of RF Wave on Human Head Tissues Employing Cu and Ni Grid PET Films

The rising number of frequency bands and the demand for wireless communication devices has become a growing concern regarding health and safety. The human head is a vulnerable body part when exposed to mobile phones. To ensure a high level of protection of the head from undesirable Electromagnetic Field (EMF) emissions, a shield is incorporated in this paper between the head and the mobile smartphone. The shielding material used to protect the head from the RF emissions is Copper (Cu) grid transparent Polyethylene Terephthalate (PET) film and Copper (Cu) grid transparent PET film with Nickel (Ni) coating forming a laminated mesh. The RF emission metric from the smartphone is determined to evaluate the Specific Absorption Rate (SAR) numerically with a variation in frequencies ranging from 850MHz to 5.47GHz at normal wave incidence by the Transmission Line Method. The variation in frequency is observed in two head models, one of an adult and one of a child. Compared with the no shield condition, a significant SAR reduction is observed when PET-Cu or PET-Cu-Ni conductive coating transparent shielded mesh is embodied on the front part of the mobile phone between the phone and the head. In the child 7-layered head model at 5.47GHz, a significant reduction in SAR is observed from 10.5W/kg to 0.00001W/kg using the Cu grid PET film and to 0.0000032W/kg using Cu and Ni grid PET film.

SAR Reduction With Antenna Cluster Technique

An efficient and straightforward antenna design method is presented that maximizes the ratio of total efficiency and specific absorption rate (SAR). This goal is achieved with a multiport antenna cluster technique where several ports are excited collectively with appropriate feeding weights. These weights are found as an eigenvalue solution formulated in terms of the radiated and near-field power of an antenna. The method relies on both the near-field (SAR) and far-field (radiation) physics of an antenna and it can be applied to various design cases. The importance of the maximization of total-efficiency-SAR ratio and the feasibility of the proposed approach are demonstrated with a simple multiple-dipole antenna example and with a more realistic antenna design where a metal-rimmed antenna is held in the user’s hand.

Reduction of Specific Absorption Rate: A Review Article

Reduction of Specific Absorption Rate: A Review Article

A novel SAR reduction technique for implantable antenna using conformal absorber metasurface.

In this paper, a conformal absorber metasurface has been designed and used for reducing the specific absorption rate (SAR) of an implantable antenna. SAR reduction of implantable antennas is one of the significant design aspects to be considered for their use in modern-day healthcare applications. The introduction of the absorber metasurface restricts the back radiation of the antenna to control the SAR value. This technique decreases the maximum SAR value by 24% and also reduces the average SAR distribution significantly without affecting the desired antenna gain. A reduction in SAR value indicates the decrease in radiation absorption by human tissue, and thus, decreases the possibility of health hazards due to EM radiation. Later, this antenna-absorber system is designed as a capsule module for increased mobility and less-invasiveness. The redundancy of invasive surgery increases acceptance of the capsule module designs of implantable antennas and devices for various biomedical usages. In vitro testing of the fabricated prototype has been carried out inside a multi-layer porcine slab to verify the effectiveness of this unique SAR reduction technique.

A co-polarization-insensitive metamaterial absorber for 5G n78 mobile devices at 3.5 GHz to reduce the specific absorption rate

Specific absorption rate (SAR) by next-generation 5G mobile devices has become a burning question among engineers worldwide. 5G communication devices will be famous worldwide due to high-speed data transceiving, IoT-based mass applications, etc. Many antenna systems are being proposed for such mobile devices, but SAR is found at a higher rate that requires reduced for human health. This paper presents a metamaterial absorber (MMA) for SAR reduction from 5G n78 mobile devices at 3.5 GHz. The MMA is co-polarization insensitive at all possible incident angles to ensure absorption of unnecessary EM energies obeying the Poynting theorem for energy conservation and thus ensuring smooth communication by the devices. The unit cell size of the absorber is 0.114 lambda making it design efficient for array implementation into mobile devices. This absorber has achieved a minimum of 33% reduction of SAR by applying to the 5G n78 mobile phone model, equivalent to SAR by GSM/LTE/UMTS band mobile phones and making it suitable for SAR reduction from next-generation 5G mobile devices.

Dual Antenna Coupling Manipulation for Low SAR Smartphone Terminals in Talk Position

A rigorous analysis of the concept of coupling manipulation utilizing two antennas suited to modern smartphone devices in talk position for voice calls is presented. By using the optimum relative phase between the elements, they can substantially reduce the specific absorption rate (SAR) but still maintain efficiency due to the splitting of power between them and by exploiting a suitable level of interelement coupling. The same antenna elements can still be used for multiple-input–multiple-output (MIMO) when not in talk position without heavily degrading their fundamental capacity limit, but this is of secondary importance. The concept could be applied to frequency ranges used in mobile communications from 1.8 to 6 GHz where the ground plane has sufficient form factor. Extensive simulations using two planar inverted-F antennas (PIFAs) operating at 2.4 GHz are carried out to demonstrate conceptually how two antennas can be optimized to reduce SAR by over 50% compared to a single antenna element. SAR reduction is maintained regardless of the user’s head composition and how they are handling the device in a talk position. Antenna prototypes are measured and compared to verify the capacity when the handset is used away from the body with two MIMO terminal antennas.

The Development of Monolithic Silicon Carbide Intracortical Neural Interfaces for Long-Term Human Implantation

Silicon Carbide (SiC) has been demonstrated as both a bio- and neuro-compatible wide-band-gap semiconductor with a high thermal conductivity and magnetic susceptibility and may be potentially compatible with human brain tissue. Two single-crystal, solid-state forms of SiC have been used to create monolithic intracortical neural implants (INI) without using physiologically exposed metals or polymers, thus eliminating many known reliability challenges in-vivo through a single, homogenous material. Amorphous SiC (a-SiC) was used to insulate 16-channel functional INI and the electrochemical and MRI compatibility (7T) performance were measured. 4H-SiC interfaces were fabricated using homoepitaxy,alternating epitaxial films of n-type and p-type forming an isolating PN junction which prevents substrate leakage current between the 16 adjacent electrodes and traces fabricated which were formed using deep-reactive ion etching (DRIE). 3C-SiC interfaces were fabricated in a similar fashion, but the epitaial conductive layers were grown on on both bulk crystalline (100) silicon and SOI wafers. In both cases a conformal coating of a-SiC was used as the top-side insulator and windows opened using RIE to allow electrochemical interaction. Electrochemical charaterization achieved through electrochemcial impedance spectroscopy (EIS) and cyclic voltammetry (CV) indicates performance on par, or exceeding, that of Pt reference electrodes with the same form fit. While magnetic resonance imaging (MRI) is an essential, non-contact method used to investigate issues with the nervous system, the high field MRI (e.g., 3 T and higher) necessary for proper diagnosis can be a safety issue for patients with INI due to inductive coupling between the powerful electromagnetic fields and the implanted device. This results in having to use lower electromagnetic field power (less than 1.5T), and therefore lower resolution, which hinders diagnostic prognosis for these patients. In this work the MRI compliance of epitaxial, monolithic SiC INI was studied. The specific absorption rate (SAR), induced heating, and image artifacts caused by the portion of the implant within a brain tissue phantom located in a 7 T small animal MRI machine were estimated and measured via finite element method (FEM) and Fourier-based simulations. Both the simulation and experimental results revealed that free-standing 3C-SiC films had no observable image artifacts compared to silicon and platinum reference materials inside the MRI at 7 T while FEM simulations predicted an ~30% SAR reduction for 3C-SiC compared to Pt. These initial simulations and experiments indicate a SiC monolithic INI may effectively reduce MRI induced heating and image artifacts in high field MRI.