Specific Absorption Rate Performance Research Articles

A reconfigurable band‐notched wearable super ultra‐wideband antenna utilizing a split‐ring resonator

AbstractThis article presents a flexible ultra‐wideband (UWB) antenna that can be used in wireless body area networks (WBAN). The antenna has a switchable slotted split ring resonator (SRR) structure on the radiating patch, which creates band‐notch functionality. The antenna has three switchable states: UWB and two band‐notched states at central frequencies of 5.5 and 3.5 GHz. The antenna has compact dimensions of 30 × 38 × 0.38 mm3 and is fabricated on an RT5880 substrate. Its impedance bandwidth ranges from 2.7 to 50 GHz (a relative bandwidth of 180%). The antenna's performance has been evaluated under deformation, and its impact on the human body has been assessed using the specific absorption rate (SAR) parameter. The antenna has been manufactured, and its key features have been measured, demonstrating good agreement with simulations. Due to its low SAR, minimal thickness, and UWB performance, the antenna is a good candidate for WBAN applications.

A threefold increase in SAR performance for magnetic hyperthermia by compositional tuning in zinc-substituted iron oxide superparamagnetic nanoparticles with superior biocompatibility

In this work, we report a ultrahigh specific absorption rate (SAR) performance in Zn-substituted magnetite superparamagnetic (SPM) nanoparticles (NPs) for potential application in magnetic hyperthermia (MHT)-based cancer treatment. Although MHT shows promise in cancer therapy, challenges such as low heating performance, agglomeration of magnetic nanoparticles (MNPs) in blood veins, cytotoxicity, and hemocompatibility have hindered clinical uses. To overcome these challenges, we adopted a reverse-micelles based coprecipitation synthesis approach to prevent MNPs agglomeration and optimized the substitution of Zn ions in magnetite to enhance heating performance. Calorimetric measurements showed SAR values of 118 W/g and 181 W/g for magnetite NPs using the initial slope method (ISM) and Box Lucas method (BLM), respectively. Through our compositional optimizations, we achieved a significant increase in SAR value by consciously substituting Zn2+ ions in the magnetite lattice. Specifically, we obtained SAR values of 325 W/g and 579 W/g (>300% increase) for Zn0.3Fe2.7O4 MNPs using ISM and BLM, respectively. This enhancement can be attributed to improved saturation magnetization (174–257 kA/m) and magneto-crystalline anisotropy (12–24 kJ/m3). The increase in saturation magnetization in the magnetite MNPs can be explained by the higher magnetic moment resulting from increased Zn concentration up to ZnxFe3-xO4(x = 0.3), strengthening the JAB interaction. However, further increases in Zn concentration lead to a decrease in saturation magnetization due to non-collinearity, as described by the Yafet-Kittle model. Our optimized MNPs exhibit improved heating performance, enabling the use of lower MNPs concentrations for cancer treatment, reducing potential toxicity effects. Biocompatibility investigations demonstrated a low hemolysis rate (<5%) in a hemolysis assay with red blood cells and high cytocompatibility (>92% cell viability) in MTT assays for all compositions, confirming their potential suitability for clinical applications. This study offers a promising approach to enhance SAR performance, addressing MHT-based cancer treatment challenges, and improving clinical suitability.

Study of chitosan coated copper substituted nano-ferrites for hyperthermia applications

In this study, copper (Cu +2 ) was substituted with CoFe 2 O 4 nanoparticles (Cu x Co 1-x Fe 2 O 4 where x = 0.15, 0.31 and 0.47) to make them more efficient for hyperthermia treatment. To enhance the heating efficiency, chitosan was used to coat the nanoparticles. The emergence of well-crystalline structures in the single phase inverse spinel structure was confirmed by Rietveld refinement of X-ray diffraction. FTIR analysis confirmed that the chitosan was coated on the surface of the nanoparticles. An appropriate amount of weight loss of chitosan coating in the samples was also identified by thermogravimetric analysis (TGA). Magnetic nanoparticles with an average particle size in the range of 10–11 nm were revealed by transmission electron microscopy (TEM), with nanoparticles spherical in shape. The vibrating sample magnetometer (VSM) study indicates that the magnetic characteristics such as H c and M r decrease as the Cu +2 doping increases, whilst the M s (saturation magnetization) increases and reduces as the Cu +2 doping concentration increases in CoFe 2 O 4 nanoparticles. The self-heating characteristics of all nanoparticles show that as concentration increases, temperature increases but specific absorption rate (SAR) decreases. Interestingly, the chitosan coating at x = 0.37 nanoparticles with a dosage of 1 mg/ml indicates better SAR performance reaching a targeted temperature for magnetic hyperthermia therapy. • Nanoparticles were synthesized and functionalized with biopolymers (chitosan) using the solvo-thermal route. • The nanoparticles showed ferromagnetic behavior while having significantly lower coercitivity (H c ) and retentivity (M r ) for coated nanoparticles than uncoated nanoparticles. • The surface modified CoFe 2 O 4 nanoparticles demonstrated higher SAR than the uncoated nanoparticles, owing to the reduced anisotropy constant.

SAR Performance of Rectangular Microstrip Antenna for Breast Cancer Hyperthermia Treatment with Different Period of Treatment Procedure

Cancer treatment using hyperthermia techniques recently become the interest among researchers in investigating and improving certain deficiencies of the treatment since this treatment has the potential to denaturate cancer into necrotic tissue. Hyperthermia uses high heat from 41°C to 45°C at a certain period of time. It is difficult to control the focus position distance of heat distribution on the treated tissue. Therefore, this paper presents the rectangular microstrip as hyperthermia applicator, which deliver the heat on the targeted treated breast cancer tissue with different period of time in order to obtain sufficient heat or SAR distribution. Sim4LifeLight software simulator is used to design, simulate and generate the specific absorption rate (SAR) distribution on the treated tissue. Three frequencies of 434MHz, 915MHz and 2450MHz are used to be compared. Based on the results, 2450MHz shows better performance than the other two frequencies. However, there is a certain limitation, such as skin burn and unwanted hotspots, that need to be further improved. The cancer is sufficiently heating at different operating frequencies at different periods of procedures.

Bio-Matched Horn: A Novel 1–9 GHz On-Body Antenna for Low-Loss Biomedical Telemetry With Implants

We present the Bio-Matched Horn antenna: a novel 1.773 cm3 on-body antenna for very low-loss communication with wireless implants across the 1–9 GHz bandwidth. To achieve this unique performance, the Bio-Matched Horn is composed of water-filled holes used to mimic the frequency-dependent permittivity of the underlying tissue over its entire bandwidth. The horn shape further allows the proposed antenna to communicate efficiently through the biological tissue for both subcutaneous and deep-tissue wireless implants. Measurement results at 2.4 GHz are in good agreement with simulations and show a transmission loss of 8.01 dB to a 4 mm-deep implant and 19.21 dB to a 2 cm-deep implant. Compared to the previous designs, this is a remarkable improvement by 14.5 and 10.8 dB for subcutaneous and deep-tissue communication, respectively. In this paper, we discuss the operation principle and design of the Bio-Matched Horn, its performance for subcutaneous and deep-tissue implant telemetry, sensitivity to rotational and positional misalignments, and specific absorption rate performance.

IMPULSE: A scalable algorithm for design of minimum specific absorption rate parallel transmit RF pulses.

Managing local specific absorption rate (SAR) in parallel transmission requires ensuring that the peak SAR over a large number of voxels (> ) is below the regulatory limit. The safety risk to the patient depends on cumulative (not instantaneous) SAR thus making a joint design of all RF pulses in a sequence desirable. We propose the Iterative Minimization Procedure with Uncompressed Local SAR Estimate (IMPULSE), an efficient optimization formulation and algorithm that can handle uncompressed SAR matrices and optimize pulses for all slices jointly within a practical time frame. IMPULSE optimizes parallel transmit pulses for small-tip-angle slice selective excitation to minimize a single cost function incorporating multiple quantities (local SAR, global SAR, and per-channel power) averaged over the entire multislice scan subject to a strict constraint on excitation accuracy. Pulses for an 8-channel 7T head coil were designed with IMPULSE and compared with pulses designed using generic optimization algorithms and VOPs to assess the computation time and SAR performance benefits. IMPULSE achieves lower SAR and shorter computation time compared with a VOP approach. Compared with the generic sequential quadratic programming algorithm, computation time is reduced by a factor of 5-6 by using IMPULSE. Using as many as 6 million local SAR terms, up to 120 slices can be designed jointly with IMPULSE within 45 s. IMPULSE can handle significantly larger number of SAR matrices and slices than conventional optimization algorithms, enabling the use of uncompressed or partially compressed SAR matrices to design pulses for a multislice scan in a practical time frame.

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.

Incorporating specific absorption rate constraints into wireless signal design

Portable wireless devices used in close proximity to the human body have transmitter power constraints that are dictated in part by regulatory limits on a form of electromagnetic exposure called specific absorption rate (SAR). SAR, measured in Watts per kilogram, is a measure of electromagnetic energy absorption by the body, which can cause the heating of tissue. Some portable wireless devices sold today operate near the accepted human SAR limit. This article examines how SAR constraints can be incorporated into wireless signal design for multiple transmitters. A SAR constraint, although related to a power constraint, differs sufficiently that signals designed specifically for the constraint are needed. Although it is well known that multiple transmitters subject only to a power constraint can improve the link performance of a wireless system compared to a single transmitter, it is not clear when the device is also subject to a SAR constraint: how to model the constraint; whether performance advantages still exist; and how to realize any advantages. In this article, we introduce SAR constraints and discuss the SAR measurement, simulation, and modeling process. We then show how to incorporate the SAR constraint into system performance analysis and code design. We show how SAR codes use multiple transmit antennas to get good combined farfield error performance and near-field SAR performance, improving handset transmitter performance in the critical uplink of a communication system.

SAR and radiation performance of balanced and unbalanced mobile antennas using a hybrid computational electromagnetics formulation

A procedure to reduce the effect of the mobile antenna on the handset by using balanced antennas has been investigated. Use of this type of antenna may degrade the antenna performance, such as bandwidth and gain, although it can cause less effect on the body to which they are adjacent. If the antennas are well designed, the maximum specific absorption rate (SAR) values are likely to be reduced when placed next to the head, since the coupling of such antennas to the body of the handset is very weak. A study on balanced and unbalanced antennas for mobile handsets next to the human head is presented, using a hybrid electromagnetics method for the analysis. The method uses the hybridisation technique between the frequency-domain method of moments (MoM) and the finite-difference time-domain method (FDTD). The antenna was modelled using MoM whereas the head tissues were modelled using FDTD. Two antennas were designed and investigated with respect to the SAR and radiation performance for two different antenna positions on the top edge of a mobile handset. Radiation patterns are presented and compared, with and without the head, and the maximum SAR values and field distributions inside the head are discussed. The balanced antenna shows good improvements with respect to the unbalanced antenna in terms of the SAR values and variations of the input impedances.