technique to reduce the specific absorption rate

However, in this research work, the authors introduced a multi-layered metamaterial structure with similar altering substrate layers to overcome cost constraints for the EM absorption reduction application. Purpose: To improve image quality and reduce specific absorption rate in functional cardiac imaging at 3 T. Methods: Two high permittivity dielectric pads on the anterior and posterior sides of the thorax were numerically designed and implemented using an aqueous suspension of barium titanate. The lower band resonance frequencies are difficult to obtain in unit cell design as illustrated in Fig. The first or the largest square ring was constructed with a width of 0.30mm. & Cheng, Z. Terahertz perfect absorber based on InSb metasurface for both temperature and refractive index sensing. 7a. SAR values of 1g and 10g of tissue volumes without and with the MSM design at L-band. Il Kwak S, Sim D-U, Kwon J. In this paper, the specific absorption rate (SAR) reduction in human head with metamaterial attachment is calculated. Eventually, at the feeding spot, the reflection is lost, thus the calculation of the absorption reduction values is not influenced by the default power. 2c. Numerical simulation geometry: (a) MSM structure, (b) Voxel human head and hand model, (c) Fabricated MSM structure, (d) Agilent N5227A VNA instrument. 33(5), 646652 (2011). Google Scholar. Figure7a illustrates the transmission coefficient result of the unit cell proposed MSM design. Meanwhile, Lee et al.15 proposed a SAR analysis of four different ages of anatomical head models and compared them with numerically simulated values obtained through the SAM phantom model adapted from SEMCAD X software. Numerous investigations have been performed to investigate the optimal electromagnetic absorption reduction values. The 5G network is divided into two categories, particularly, frequency range 1 (FR1) and frequency range 2 (FR2). However, the superior electromagnetic property of all time, known as the left-handed characteristic, was successfully claimed in this research work. The ICNIRP 2020 guidelines have mostly retained the similar restrictions that are set in 1998. Lastly, the position as shown in Fig. Therefore, fulfilling the conflicting goals of lightweight design, lower bands with multi-frequency band operation, and high EM absorption values is a challenging task, requiring a unique and compact metamaterial design structure. Meanwhile, the maximum point reached 3.631, 5.865, 6.087, 2.943, and 6.323 at 2.178, 2.664, 2.904, 3.120, and 3.666GHz for the S-band frequency range. During the occurrence of the magnetic response, the magnetic field induced current in the rings when the wave propagates through the split ring resonator structure. Furthermore, the lowest SAR value reported was higher than 50% at 5.872GHz for both average over 1g and 10g of tissue volumes. Our findings in Fig. 4 and and5,5, respectively. It's not about additional or Zuo, P., Li, T., Wang, M., Zheng, H. & Li, E.-P. Miniaturized polarization insensitive metamaterial absorber applied on EMI suppression. produce two distinct metamaterial structures on the same substrate material and size for C- and Ku band applications. Express 13, 084001. https://doi.org/10.35848/1882-0786/ab9877 (2020). However, the bigger metamaterial will face some difficulties for the design integration inside any miniaturized and compact wireless device. Furthermore, Fig. However, in this research work, the authors introduced a multi-layered metamaterial structure with similar altering substrate layers to overcome cost constraints for the EM absorption reduction application. Overall, the structure also has a practicable natural frequency that can be tuned by modifying the configuration of the rings. The effective medium parameter is an analysis calculation to determine the impact on the metamaterial during the external time-variant electromagnetic fields exposure. The unit cell design of the proposed metamaterial structure was simulated in CST software to compare with the S21 of the MSM design. A Review: Methods to Lower Specific Absorption Rate for Mobile Phones In conclusion, the proposed MSM met the objectives of this research study and can be employed in EM absorption reduction applications. Hence, the unique MSM design can reduce 98% of the SAR value emitted from the mobile phone. Lastly, a similar unit cell metamaterial design was placed twice at the back substrate material to form a multi-layered structure. Meanwhile, this numerical simulation data reveals acceptable magnitude values such as 25.208, 26.243, 22.194, 30.951, 23.203, 14.263, 24.422, 24.636, and 23.916dB. Waves Appl. Radiat. Two different leaf structured antennas with design, i.e., without and with metasurface were analysed in the study at the 2.40GHz WLAN ISM band. Subsequently, the values also decreased gradually when the distance was increased to 10mm. A challenging problem that arises in this domain is how to decrease the SAR values at the desired resonance frequencies that comply with these guidelines. Yan, L., He, Z., Jiang, W. & Zheng, X. Propag. This analysis was mainly focused on obtaining the most robust SAR reduction results by placing the proposed metamaterial design inside the mobile phone in different positions as demonstrated in Fig. All the resonance frequencies except 1.200 and 5.872GHz have EFD that was concentrated all over the structure as shown in Fig. The simplified SAM phantom that is homogeneous to the real human head model based on the IEEE standard is composed of two components, namely an outer shell and fill with a tissue-stimulating liquid substance. An analysis of diverse positions of antenna integrated into the wireless device and various material shields was conducted in their study. Furthermore, the permittivity and permeability values were retrieved from the S11 and S21 data. High-Frequency Structure Simulator (HFSS). Caloz C. Perspectives on EM metamaterials. The .gov means its official. Approximately all the previous works used copper material to construct the metamaterial structure because this economical material possesses superior conductivity besides gold and silver. Han NR, Chen ZC, Lim CS, Ng B, Hong MH. The performance of double-layer metamaterial structure was first investigated to identify whether the stacking affects the resonance frequencies. 3a demonstrates the outcome of numerical simulation on z-axis wave propagation with multi-resonance frequencies in L-, S- and C-bands precisely at 1.200, 1.458, 1.560, 1.896, 2.268, 2.683, 2.940, 3.580 and 5.872GHz with tolerable magnitude values of 23.862, 23.991, 20.068, 31.109, 23.026, 16.526, 20.204, 30.363, and 21.788dB, respectively. The SAR percentage values for all resonance frequencies were tabulated in Table Table11.11. Note: incurs a time or slice number penalty; not available on all scanners. https://www.ansys.com/products/electronics/ansys-hfss. The comparison of both simulation and measurement methods indicates a slight difference in the fourth resonance, while on the fifth peak point, the results majorly differ. & Tariqul, M. A dual band left-handed metamaterial-enabled design for satellite applications. A broadband metamaterial absorber based on multi-layer graphene in the terahertz region. You are using a browser version with limited support for CSS. CAS All the resonance frequencies except 1.200 and 5.872GHz have EFD that was concentrated all over the structure as shown in Fig. The simulation of the proposed metamaterial was carried out by adopting commercially available software known as Computer Simulation Technology (CST) Microwave Studio 201926. 1Space Science Center (ANGKASA), Universiti Kebangsaan Malaysia, UKM, 43600 Bangi, Selangor Malaysia, 2Dept. Meanwhile, the MSM isometric projection view is demonstrated in Fig. Two different leaf structured antennas with design, i.e., without and with metasurface were analysed in the study at the 2.40GHz WLAN ISM band. A multi-band closed-cell metamaterial absorber (CCMA) based on a low-permittivity all-dielectric structure. Meanwhile, this numerical simulation data reveals acceptable magnitude values such as 25.208, 26.243, 22.194, 30.951, 23.203, 14.263, 24.422, 24.636, and 23.916dB. The impedance value achieved a peak value in the L-band, for instance, 1.863, 0.720, 3.361 at 1.272,1.524, and 1.692GHz, respectively. The entire references stated here are successfully designed metamaterial structures exclusively for either SAR reduction or absorption applications. Castani A, Mercier J, Flix S, Maurel A. Generalized method for retrieving effective parameters of anisotropic metamaterials. Although 5G is on its way, many countries are still using the 4G network. Besides that, the MSM design is small, unintentional flaws might have happened when removing excess copper from the substrate material. A novel and effective technique to reduce electromagnetic radiation The equivalent circuit model as illustrated in Fig. Simultaneously, the proposed MSM structure was simulated in High-Frequency Structure Simulator (HFSS) to authenticate the numerical simulation data. The second stage was the numerical analysis of electromagnetic absorption reduction to identify the effect of the metamaterial attachment inside the mobile phone. Moreover, a metamaterial design that complies with this condition will obtain negative permittivity and/or permeability values. Fundamentally, in the deficiency of the ohmic loss condition, the antenna radiated power is corresponds to the reference power. Generally, the metamaterial structure has also been integrated with the mobile antenna to enhance the gain or bandwidth. A multi-band closed-cell metamaterial absorber (CCMA) based on a low-permittivity all-dielectric structure. However, the numerically simulated S11 and S21 results also demonstrate contrasting outcomes. 3c. Even though several works indicate enhanced SAR reduction values, they show several setbacks. 29(9), 112 (2019). Novel Specific Absorption Rate measurement techniques 53, 325331 (2011). For the frequency range from 2.028 to 2.178GHz and 2.376 to 2.670GHz, the proposed MSM design exhibits a negative characteristic with amplitude values from 5.434 to 1.828dB and 3.081 to 0.766dB, respectively. The SAR simulation in this parametric study utilised a similar standardized human head model filled with a specific liquid substance that is homogenous to an actual human head. This dielectric substrate material with thickness, C=0.25mm as illustrated in Fig. As the imaginary refractive index and real impedance values exhibited more than zero, the MSM structure is possibly categorised as a passive medium design. Besides that, when the dielectric constant values increase, it persuaded the capacitance value at the radiating element interval and the ground. Chen, X., Grzegorczyk, T. M., Wu, B., Pacheco, J. 32(1), 501506 (2020). For the rest of the resonance frequencies, the signs of MFD were indicated on the first few square ring and moderately reduced completely before reaching the design centre. Each technique with the prospect of reducing SAR has some shortcomings because of which it is not a sustainable option, so it is not preferred for extensive use. A wireless device with a metamaterial structure will be examined while operating at its maximum power level in all resonance frequencies to find the optimised results. active shimming. This paper seeks a terse review of various methods implemented to acquire low SAR for mobile antennas. Fast (Turbo) Spin Echo is the archetype, followed by the Inversion Recovery family. Besides that, the first seven resonance frequencies of the proposed metamaterial have successfully reduced the SAR values by more than 90%. The effectiveness and compactness of the proposed MSM design can be computed by adopting the effective medium ratio (EMR) formula as expressed in Eq. Evaluation and Optimization of the Specific Absorption Rate for Chaudhary, P. & Vijay, R. Calculation of SAR on human brain model and analysis of the effect of various dielectric shielding materials to reduce SAR. Specific absorption rate reduction for sub-6 frequency range using polarization dependent metamaterial with high effective medium ratio, $$z=\pm \surd \frac{{(1+{S}_{11})}^{2}-{S}_{21}^{2}}{{(1-{S}_{11})}^{2}-{S}_{21}^{2}}$$, $$\begin{gathered} n = \frac{1}{{k_{0} d}}\left\{ {\left[ {In\left( {e^{{ink_{0} d}} } \right)} \right]^{{\prime \prime }} + 2m\pi - i\left[ {In\left( {e^{{ink_{0} d}} } \right)} \right]^{{\prime \prime }} } \right\} \hfill \\ e^{{ink_{0} d}} = \frac{{S_{{21}} }}{{1 - S_{{11}} \frac{{z - 1}}{{z + 1}}}} \hfill \\ \end{gathered}$$, $$EMR = Wavelength (\lambda )/Unit \, cell \, length \left(L\right)$$, https://doi.org/10.1038/s41598-022-05851-2. 3b clearly show eight negative permittivity characteristics at all resonance bands. Figure3ae illustrate the plots of results that were obtained from the computer simulation such as S11, S21, permittivity (), permeability (), and refractive index (n). Results Phys. Specific absorption rate reduction for sub-6 frequency range using polarization dependent metamaterial with high effective medium ratio. Reducing SAR - Questions and Answers in MRI A similar simulation method as in the CST software was adopted for this simulation process. A wireless device with a metamaterial structure will be examined while operating at its maximum power level in all resonance frequencies to find the optimised results. In the meantime, metamaterial design is also applied for absorption applications like in the reference35. In this section, using an imported cell phone model from CST, the simulation was done while operating at the highest power level for all the resonance frequencies. The two-layered homogenous metamaterial structure exhibit nine resonance frequencies which are similar to the proposed MSM design, but has lower magnitude values at certain peak points. The https:// ensures that you are connecting to the Although the author of this reference, has successfully produced a high absorber metamaterial design, it also suffers from size miniaturization limitations. larmor. From these tables, a clear observation can be made that most of the maximum SAR values occurred only on the cheek area of the right-hand side human head. Meanwhile, the MSM metamaterial possesses far fewer magnetic field distribution (MFD) compared to EFD. Due to the three-layered metamaterial design possessing multi-bands (L-, S-, and C-bands) with nine resonance frequencies and acceptable magnitude values, it was finally selected for the SAR reduction analysis. Ramachandran, T., Faruque, M. R. I., Ahamed, E. & Abdullah, S. Specific absorption rate reduction of multi split square ring metamaterial for L- and S-band application. What MRI Sequences Produce the Highest Specific Absorption Rate - AJR Agarwal, S. & Prajapati, Y. K. Metamaterial based sucrose detection sensor using transmission spectroscopy. Tamim AM, Faruque MR, Khandaker M, Islam M, Bradley D. Electromagnetic radiation reduction using novel metamaterial for cellular applications. Table 1 describes the dimension lists of the MSM unit cell metamaterial design. Few thicknesses of substrate material were adapted in this analysis, for example, 1.6mm, 1.575mm, and 1.524mm, respectively for stated substrate material. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate. In general, these materials exhibit superior permittivity, permeability values and as well finest resonance frequencies. Meanwhile, the last two resonance frequencies manifest SAR reduction values of more than 50%. For the frequency range from 2.028 to 2.178GHz and 2.376 to 2.670GHz, the proposed MSM design exhibits a negative characteristic with amplitude values from 5.434 to 1.828dB and 3.081 to 0.766dB, respectively. One of the most commonly used methods is the metamaterial structure where it will generally block or absorb the radiofrequency energy from entering the human body. Simultaneously, the proposed MSM structure was simulated in High-Frequency Structure Simulator (HFSS) to authenticate the numerical simulation data. Internet Explorer). An analysis of diverse positions of antenna integrated into the wireless device and various material shields was conducted in their study. Design of the broadband metamaterial absorber based on dispersed carbon fibers in oblique incidence. . The MSM design is placed near to mobile antenna for the proposed position, and it indicates optimised results compare to the other three positions. Han, N. R., Chen, Z. C., Lim, C. S., Ng, B. Due to this limitation, we handle the metamaterial size miniaturization by providing reasonable interest when designing a unit cell metamaterial structure. The SAR describes the potential for heating of the patient's tissue due to the application of the RF energy to produce the MR signal. The proposed metamaterial structure needs to characterize as an effective medium homogeneous to retrieve the effective permittivity and permeability values. 1g SAR results with percentage values for various mobile distances from human head. The possibility to neglect the discrepancy between both simulated results was very high because the difference is less than 5GHz. Article Minimum SAR VERSE pulses are typically somewhat flat in their central region and amplified toward their periphery. Electromagn. 5. 216, No. Results Phys. & Hong, M. H. Broadband multi-layer terahertz metamaterials fabrication and characterization on flexible substrates. The multi-layered metamaterial also becoming a hot topic among scientists (e.g.24,25). For instance, the recently introduced 5th generation wireless communication technology requires an improvement in mobile phones to minimize the radiation effects. Federal government websites often end in .gov or .mil. The SAR reduction calculation was successfully performed in this study by adopting a finite-different time-domain method. Although the unit cell metamaterial as well manifests optimised SAR reduction values, the authors focus to produce resonance frequencies of more than five in the selected frequency range. Commonly, this type of metamaterial is composed of multi altering layers of substrate materials that are used in a wide range of applications such as sensors, absorption, perfect imaging, coatings for tailored emittance, etc. This is because the metal structure and substrate material have delocalisation of electron oscillation which causes both phenomena to happen on the Rogers RO3006 material. For example, Pandey and Singhal16 analysed the impacts of metamaterial structure with diverse sizes, distances, and locations on SAR values at 0.90GHz resonance frequency in 2017. An official website of the United States government. The comparisons between the SAR values with and without metamaterial reveal a few important details. Conolly S, Nishimura D, Macovski A, Glover G. What MRI sequences produce the highest specific absorption rate (SAR), and is there something we should be doing to reduce the SAR during standard examinations? Provided by the Springer Nature SharedIt content-sharing initiative. Moreover, fast-growing wireless communication technologies that support cellular data networks have also motivated this study. This MA-RF shield is used to improve the transmit efficiency of RF surface coils and reduce the specific absorption rate (SAR) in the region of interest (ROI). gave significant involvement to design, analysis, characterization, fabrication, and application. Broadband multi-layer terahertz metamaterials fabrication and characterization on flexible substrates. What MRI Sequences Produce the Highest Specific Absorption Rate (SAR), and Is There Something We Should Be Doing to Reduce the SAR During Standard Examinations? The penalty here is that the the relatively longer RF-pulses affect the minimum allowable TE and potentially number of slices.
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