Study Of Specific Absorption Rate Research Articles

Terahertz Microstrip Patch Antenna for Breast Tumour Detection

Breast cancer is one of the most common cancers among Malaysian women. It is critical to discover strategies to detect the tumour early on. Terahertz (THz) frequency provides excellent qualities for detecting tumours such as low photon energy and non-ionising radiation as compared to prior methods such as mammography, ultrasound, and magnetic resonance imaging (MRI) that use optical to X-ray frequencies. The purpose of this work is to analyse and locate a breast tumour as well as to compute the maximum specific absorption rate (SAR) value. It was designed a THz rectangular microstrip patch antenna with an inset feed. To improve the antenna's performance, graphene was used for the patch and polyimide for the substrate. This antenna covered a bandwidth of 31.6 GHz and worked in the frequency range of 0.283-0.599 THz. To identify the location of a tumour, compute the SAR value, and localise the tumour, SAR simulation was used. The maximum SAR shifted to the tumor's position due to greater absorption rate around its tissue due to higher dielectric constant features. It was calculated that 1e-05g of average mass is required to be less than total tissue mass, which is 2.0063e-05g. SAR study revealed a maximum SAR value of 2.49391e+06 W/kg, which was not more than the overall absorption rate for human body safety. The SAR calculation result revealed that the tumour is within the range of the tumor's initial location.

Effect of field strength on RF power deposition near conductive leads: A simulation study of SAR in DBS lead models during MRI at 1.5 T-10.5 T.

Since the advent of magnetic resonance imaging (MRI) nearly four decades ago, there has been a quest for ever-higher magnetic field strengths. Strong incentives exist to do so, as increasing the magnetic field strength increases the signal-to-noise ratio of images. However, ensuring patient safety becomes more challenging at high and ultrahigh field MRI (i.e., ≥3 T) compared to lower fields. The problem is exacerbated for patients with conductive implants, such as those with deep brain stimulation (DBS) devices, as excessive local heating can occur around implanted lead tips. Despite extensive effort to assess radio frequency (RF) heating of implants during MRI at 1.5 T, a comparative study that systematically examines the effects of field strength and various exposure limits on RF heating is missing. This study aims to perform numerical simulations that systematically compare RF power deposition near DBS lead models during MRI at common clinical and ultra-high field strengths, namely 1.5, 3, 7, and 10.5 T. Furthermore, we assess the effects of different exposure constraints on RF power deposition by imposing limits on either the B1+ or global head specific absorption rate (SAR) as these two exposure limits commonly appear in MRI guidelines. We created 33 unique DBS lead models based on postoperative computed tomography (CT) images of patients with implanted DBS devices and performed electromagnetic simulations to evaluate the SAR of RF energy in the tissue surrounding lead tips during RF exposure at frequencies ranging from 64 MHz (1.5 T) to 447 MHz (10.5 T). The RF exposure was implemented via realistic MRI RF coil models created based on physical prototypes built in our institutions. We systematically examined the distribution of local SAR at different frequencies with the input coil power adjusted to either limit the B1+ or the global head SAR. The MRI RF coils at higher resonant frequencies generated lower SARs around the lead tips when the global head SAR was constrained. The trend was reversed when the constraint was imposed on B1+. At higher static fields, MRI is not necessarily more dangerous than at lower fields for patients with conductive leads. Specifically, when a conservative safety criterion, such as constraints on the global SAR, is imposed, coils at a higher resonant frequency tend to generate a lower local SAR around implanted leads due to the decreased B1+ and, by proxy, E field levels.

Development of a Numerical Tablet Model in WLAN Band for SAR Study

This research proposes a numerical model for a tablet in the wireless local area network band for specific absorption rate (SAR) study. The design criteria, such as the tablet size, operating frequencies, antenna position, and target 1-g peak spatial-average SAR (psSAR) values in the flat phantom, are determined based on the SAR test reports of tablets distributed in South Korea from 2013 to 2017. An internal antenna is designed in a tablet platform to operate in dual bands of 2,450 MHz and 5,500 MHz. The numerical results illustrate that the 1-g psSAR values of the proposed numerical tablet model are within ±10% of the target values. Moreover, the return loss of the designed tablet model is larger than 10 dB, regardless of flat phantom, while its radiation efficiency is higher than 90% in free space.

Recent Insights into the Potential of Magnetic Metal Nanostructures as Magnetic Hyperthermia Agents

The advancements in magnetic nanoparticle mediated hyperthermia give so many optimistic and fruitful results that make it a promising and complementary approach for the existing treatment modalities of cancer. This thermotherapy is gaining wide acceptance among the medical community compared to the conventional treatment methods. The former provides a local heat generation in the malignant tumor cells and remains non-invasive to the adjacent healthy cells. The increased heating efficiency of magnetic nanoparticles and the control of local therapeutic temperature are the main challenges of hyperthermia. Superparamagnetic Iron Oxide nanoparticles have been intensively studied and dominating in magnetic hyperthermia. Recently many researchers successfully demonstrated high heating efficiency and biocompatibility of a wide variety of magnetic metal nanoparticles and proposed as the most promising alternative for traditional iron oxides, which opens up a new avenue for magnetic metal nanoparticles in magnetic hyperthermia. The review presents the recent advancements that occurred in the field of metal nanoparticle mediated magnetic hyperthermia. The theory underlying heat generation, synthesis methods, biofunctionalization, Specific Absorption Rate studies, challenges and future perspectives of magnetic metal nanoparticles are presented. This will inspire more in-depth research and advance practical applications of metal nanoparticles in magnetic hyperthermia.

Metasurface‐based radiative near‐field wireless power transfer system for implantable medical devices

This article presents a novel approach to improve the efficiency of a radiative near-field wireless power transfer (WPT) system by using metasurface. The WPT system is designed particularly for implantable applications, which operate at the industrial, scientific, and medical (ISM) 2.40-2.48 GHz band. To construct the WPT link, a patch antenna is used as the transmitting element whereas a small planar loop antenna is considered as the receiving element. The receiving antenna is implanted under the skin tissue model operating at 2.45 GHz. The metasurface with a high refractive index is placed above the surface of the skin layer to improve the power transfer efficiency. Regarding the motion of the human body, different misalignment tolerances between the transmitter and the implant receiver are discussed. Also, the effect in the change of the skin property and placement depth of the Rx antenna inside the skin tissue model is studied. Furthermore, the study of specific absorption rate for the proposed configuration is performed. Finally, the proposed WPT system is designed and experimentally verified with and without metasurface. The experimental result confirms a significant amount of improvement in power transfer efficiency due to the integration of metasurface.

A Study of specific absorption rate in human head due to electromagnetic exposure to 4G signals

<span>This paper presents a numerical analysis of the specific absorption rate in SAM phantom exposed to electromagnetic field. A two set dipole antenna operating with 1800MHz and 2600MHz were placed parallel to the z-axis and rotated in clockwise from 0<sup>o</sup> (vertical) to 180<sup>o</sup> in steps of 30<sup>o</sup> to investigate the effect of frequency and polarization. The maximum average of 1gram and 10gram of tissue have been presented to show the effect of SAR in SAM phantom model. A comparison of the mass average SAR in head shows the 1g of SAR at 2600MHz is double to 1800MHz frequency. While for 10g of SAR, slightly different for both 1800MHz and 2600MHz.</span>

Bi-layered/tri-layered bio-media in direct contact with metal diagonal horn for hyperthermia

AbstractIn this paper, theoretical/simulation study of specific absorption rate (SAR) and/or temperature distributions in a bi-layered bio-media (fat and muscle)/realistic tri-layered bio-media (skin, fat, and muscle layers) in direct contact with water-loaded metal diagonal horn (MDH) designed at 915 MHz are investigated. The effects of fat thickness on the input reflection coefficient, reflection coefficient at the interface between the MDH and the bi-layered bio-media, and the SAR distribution in the bi-layered bio-media are also studied through simulation and theoretically at 915 MHz. Further, the SAR parameters such as penetration depth and effective field size inside the bi-layered bio-media due to the MDH are evaluated theoretically and the theoretical results are compared with the corresponding simulation results. Finally, SAR and temperature distributions in tri-layered bio-media without and with embedded irregular/oval-shaped tumor are provided for demonstrating the hyperthermia performance of the MDH applicator.

Evaluation of Children’s Exposure to Electromagnetic Fields of Mobile Phones Using Age-Specific Head Models With Age-Dependent Dielectric Properties

Given the rapid introduction of mobile phones and other portable wireless devices into society, and the increased possibility of young children using or being exposed to electromagnetic (EM) fields, a study of specific absorption rate (SAR) in the head of young children is becoming increasingly relevant. To accurately evaluate the exposure of children to electromagnetic fields, realistic head models, which consider the age-specific anatomical structure and age-dependent tissues dielectric properties, are developed. During postnatal development of human tissues, the number and size of cells increase while the proportion of water content decreases. Such changes result generally in significant changes in the dielectric properties of tissues. The SAR levels for different ages are investigated using the developed children’s head models when young children or their parents use a standard mobile phone. The results show that the maximum SAR levels in brain tissues of young children (3 months) are higher by up to 61% and 78% than adults at the lowest (700 MHz) and highest (2600 MHz) investigated frequencies, respectively. The percentage absorption power in the heads of young children (3 months) is higher by up to 40.6% and 24% than the values for adults at 700 MHz and 2600 MHz, respectively. Our investigation shows that previous studies, which used scaled head models without considering the age-dependent variations in the head anatomy and/or age-dependent tissues’ dielectric properties, underestimated SAR levels in the children’s heads. The obtained results using the developed realistic head models indicate that for young children, a lower limit on radiated power might be required to meet the acceptable dosimetry levels.

Direct-Contact Water-Loaded Metal-Dielectric Wall Diagonal Horn Applicators for Hyperthermia

ABSTRACTThis paper describes simulation and/or experimental studies of specific absorption rate (SAR) and temperature distributions in a biological phantom (muscle)/realistic tri-layered bio-media without and with oval-/irregular-shaped tumour in direct contact with hybrid mode (water-loaded) metal-dielectric wall diagonal horn designed at 2450 and 915 MHz and their comparison among themselves with those due to respective conventional metal diagonal horns. The diagonal horns reported in this paper provide simple and effective means to enhance the penetration depth in the bio-medium/media. Moreover, effects on penetration depth and effective field size due to presence of oval- and irregular-shaped tumours in the tri-layered bio-media are also investigated at 915 MHz. It is demonstrated that desired temperature range 41 °C–45 °C can be achieved and maintained for 60 minutes with input power of 9 W at the frequency of 915 MHz for treating tumours at relatively greater depth.

Investigation on improved water-loaded diagonal horn applicators for hyperthermia

This paper describes simulation, theoretical, and/or experimental studies of specific absorption rate (SAR) distribution in biological phantom (muscle)/tri-layered bio-media without and with irregular-shaped tumors in direct contact with improved water-loaded metal diagonal horns designed at 2450 and 915 MHz. Further, thermal simulation results based on Pennes’ bio-heat equation are also provided for each of the proposed applicators, which is in direct contact with realistic tri-layered bio-media without and with irregular-shaped tumor embedded within the muscle layer. The proposed horns are improved versions of the respective conventional metal diagonal horns in which the aperture fields, which are modified by introducing four conducting pins at appropriate locations near each antenna aperture, correspond to fundamental and higher order modes. The theoretical aperture field distributions of the proposed horns designed at 2450 and 915 MHz are compared with the corresponding simulated ones. Further, the theoretical SAR parameters (penetration depth (PD) and effective field size (EFS)) in the phantom muscle medium due to the proposed horns designed at 2450 and 915 MHz are compared with the corresponding simulated and/or experimental results as well as with those obtained due to the corresponding conventional horns of identical dimensions. Moreover, effects on PD, EFS/EFS25, and temperature distribution profiles due to presence of irregular-shaped tumor in the tri-layered bio-media at 2450 and 915 MHz are also investigated. It is demonstrated that desired temperature range 41–45 °C can be achieved and maintained for 60 min with input power of 4/10 W at the frequencies of 2450/915 MHz for treating superficial tumors.

SAR Study of Mobile Phones as a function of Antenna Q

High-Q tunable antennas are good alternatives to low-Q passive antennas because the antenna size can be smaller while covering the required long-term evolution (LTE) frequency bands. However, among other things, specific absorption rate (SAR) can become a challenge due to the relative high current density associated with high-Q antennas. The higher energy stored in the electric and magnetic near-field components can result in higher SAR. Hence, SAR study of high-Q antennas is necessary which, if not addressed, might not comply with the SAR safety guidelines. In this paper, SAR as a function of antenna Q is investigated numerically as well as experimentally at two distinct frequencies (720 and 1700 MHz). It is found that SAR increases as a function of antenna Q when no losses are considered. But when losses are included, there is no more a clear trend between SAR and antenna Q. Thus, the final SAR values depend on total losses of the mock-up (MU).

Water‐loaded metal diagonal horn applicator for hyperthermia

This study presents the design of water-loaded metal diagonal horn antenna at 2450 MHz along with simulation and experimental studies of specific absorption rate (SAR) and temperature distributions in a bio-medium (muscle) in direct contact with the water-loaded antenna for hyperthermia application. The metal diagonal horn is a multimode horn antenna, with identical aperture field distribution in the E- and H-planes. The SAR distribution in a phantom muscle in direct contact with water-loaded horn antenna measured at 2450 MHz is nearly in agreement with the corresponding simulated distribution. The simulation results for SAR distribution owing to diagonal horn are also compared with those owing to square aperture horn/box horn, of same aperture cross-section/broader dimension as the diagonal horn at 2450 MHz. The results indicate that the diagonal horn provides higher penetration depth/better transverse resolution over square aperture horn/box horn. In addition, the proposed diagonal horn provides circularly symmetric effective field size. Finally, thermal simulation results are also provided for the proposed applicator, which is in direct contact with a realistic model of muscle medium without and with small spherical as well as oval-shaped tumours of different dielectric properties embedded within the muscle medium.

Study of specific absorption rate of strontium doped lanthanum manganite nanoparticles for self-controlled hyperthermia applications

Magnetic and magnetothermal properties of strontium doped lanthanum manganite La1−xSrxMnO3 nanoparticles have been studied with the strontium concentration x varying between 0.15 and 0.45. La1−xSrxMnO3 nanoparticles were prepared by the citrate gel route. XRD results show that all samples exhibit the characteristic perovskite structure with average particle sizes between 33 and 44nm. Adiabatic magnetothermia measurements were carried out in an RF magnetic field of 800A/m and 214kHz. Both magnetic and thermomagnetic behaviors are governed by the strontium content of the samples. The saturation magnetization, Curie temperature and specific absorption rate (SAR) vary non-monotonically with x. The SAR of the nanoparticles has been calculated using the linear response theory and good agreement with the experimental data has been observed. The intrinsic loss power (ILP) has been obtained from the SAR values. ILP values of our samples are comparable to those of magnetite.

SAR Study of Different MIMO Antenna Designs for LTE Application in Smart Mobile Handsets

This paper mainly focuses on the specific absorption rate (SAR) of the dual-element LTE MIMO antenna in mobile phones. Four designs of dual-element MIMO antenna (namely, dual semi-ground-free planar inverted-F antenna (PIFA), co-located antenna, dual OG PIFA in parallel position, and dual OG PIFA in orthogonal position) are studied under four typical LTE frequency points (0.75, 0.85, 1.9, and 2.1/2.6 GHz) when the ground plane length varies from 90 to 150 mm. The SAR, when dual elements operate simultaneously, is also studied through the SAR to PEAK location spacing ratio (SPLSR) according to the FCC standard. The simulations are carried out on both an SAM head phantom and a flat phantom by CST 2011, and measurements on the flat phantom are made with iSAR and DASY4 to verify the accuracy of our simulations.

The study of specific absorption rate (SAR) reduction in mobile phones using materials and metamaterials

In this paper, reducing of specific absorption rate (SAR) with materials and metamaterials attachment is investigated. The finite-difference time-domain method with lossy-Drude model is adopted in this study. The methodology of SAR reduction is addressed and the belongings of attaching position, distance, and size of ferrite sheet material properties, perfect electric conductor (PEC), and metamaterials on the SAR reduction are investigated. Materials have achieved a 47.02% reduction of the initial SAR value while metamaterials achieved a reduction of 49.21% respectively for the case of 1 g SAR. These results propose a guideline to decide assorted types of materials and metamaterials with the utmost SAR reducing effect for a phone model. Key words: Antenna, human head model, lossy-Drude model, materials, metamaterials, specific absorption rate (SAR), symmetry.

Body SAR study of the planar WWAN monopole slot antenna for tablet device application

A study on the body SAR of the planar WWAN (wireless wide area network) monopole slot antenna for tablet device application is presented. The monopole slot antenna covers penta-band WWAN operation in the 824∼960/1710∼2170 MHz bands with low near-field emission such that its body SAR (specific absorption rate) values for 1-g tissue in the bottom face, landscape and portrait orientations to the flat phantom meet the limit of 1.6 W/kg for practical applications. Effects of the monopole slot antenna disposed at various possible locations in the tablet device on the body SAR results are also analyzed. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26094

Study of Specific Absorption Rate (SAR) in the human head by metamaterial attachment

The reduction of Specific Absorption Rate (SAR) with metamaterial is performed by the finite-difference time-domain method (FDTD) with Lossy-Drude model by CST Microwave Studio in this paper. The metamaterials can be achieved by arranging split ring resonators (SRRS) periodically. The SAR value has been observed by varying the distances between head model to phone model, different width, different thickness, and different height of metamaterial design. Metamaterial has achieved 42.12% reduction of the initial SAR value. These results can endow with supportive information in designing the wireless communications equipments for safety compliance.

Small‐size coupled‐fed shorted T‐monopole for internal WWAN antenna in the thin‐profile mobile phone

AbstractA coupled‐fed shorted T‐monopole with a small size of 15× 26 mm2 (390 mm2) printed on the system circuit board of the mobile phone for WWAN operation is presented. By using a simple inverted‐L feeding strip to capacitively excite the shorted T‐monopole, two wide operating bands at about 900 and 1900 MHz, respectively, to cover GSM850/900 and GSM1800/1900/UMTS operations are obtained. The antenna is an all‐printing structure, with no external matching circuit on the system circuit board or lumped circuit elements embedded in the antenna required for size reduction or bandwidth enhancement. The antenna is hence easy to fabricate at low cost and is especially suited for thin‐profile mobile phone applications. The occupied area (less than 400 mm2) of the antenna printed on the system circuit board of the mobile phone in this study is among the smallest for the internal uniplanar printed antenna capable of penta‐band WWAN operation that have been reported. Details of the proposed antenna are described, and the obtained results, including its SAR (specific absorption rate) study, are presented and discussed. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 257–262, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24907

Evaluations of Specific Absorption Rate and Temperature Increase Within Pregnant Female Models in Magnetic Resonance Imaging Birdcage Coils

This paper presents a detailed numerical study of specific absorption rate (SAR) and temperature increase calculations within pregnant female models exposed to magnetic resonance imaging (MRI). Nine pregnant female models, representing different pregnant stages, were used for this study. SAR and temperature increase within and around fetuses at different pregnancy stages were calculated for two MRI operating modes (normal mode and first-level controlled mode) at 64 and 128 MHz. Local fetus energy deposition exceeds the International Electrotechnical Commission limit of 10 W/kg in the first-level controlled mode at 64 MHz. Fetus temperature exceeds or approaches 38 degC for both frequencies in the first-level controlled mode at later stages of pregnancy. The core temperature limits for both modes and both frequencies are not exceeded. The results show higher maximum SAR and higher temperature at 64 MHz and during later pregnancy stages with a significant increase starting with the fifth month of pregnancy. Based on the results of this study, radiologists can minimize local fetus heating, especially late in pregnancy, by using normal mode sequences, which minimize the whole body SAR in the mother

Study of specific absorption rate (SAR) induced in two child head models and in adult heads using mobile phones

This paper gives a first comparison of specific absorption rate (SAR) induced in a child-sized (CS) head and an adult head using a dual-band mobile phone. In the second study, the visible human head is considered and comparison of SAR induced in a CS or child-like (CL) head and an adult head using a dual-band mobile phone is given. All the peaks of average SAR over a mass of 10 and 1 g in the head and the power budget are determined in the two comparisons using the finite-difference time-domain method. The differences between the results for adult and CS or CL heads are given at 900 and 1800 MHz. No important differences are noted for the peak SAR averaged over 10 g (SAR10 g), between the two adult head models, as well as between the two child head models. The peak SAR10 g in the brain of the CS or CL head is slightly more significant than that for the adult one.