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This research proposed a planar printed antenna with circularly polarized (CP) ability. The antenna can supply an impedance bandwidth (│S11│<−10 dB) of 60% (2.3–4.3 GHz), 32.4% (4.8–6.8 GHz), 5.5% (7–7.4 GHz), and 24.4% (8.6–11 GHz) in the operative frequency band. The designed antenna has a 3 dB polarization axial ratio (AR) bandwidth (BW) of 88% (1.4–3.6 GHz), 11.3% (5–5.6 GHz), and 1.15% (8.6–8.7 GHz). The patch antenna dimensions are 20mm × 20 mm. To enhance AR bandwidth, an inverted L-formed strip line is added to the radiator to generate two electric fields with 900 phase differences. The measurement maximum gain of this patch antenna is about 7 dBi from 2.5 to 4.4 GHz. This structure has a wide AR beam width from – 30° to +110° at 2.4 GHz, – 70° to +70° at 5.2 GHz, and – 60° to +20° at 8.65 GHz. The CP antenna exhibits a miniaturized size and low-cost structure with suitable CP radiation characteristics. [ABSTRACT FROM AUTHOR]

Purpose: Data for QSM are typically acquired using multi‐echo 3D gradient echo (GRE), but EPI can be used to accelerate QSM and provide shorter acquisition times. So far, EPI‐QSM has been limited to single‐echo acquisitions, which, for 3D GRE, are known to be less accurate than multi‐echo sequences. Therefore, we compared single‐echo and multi‐echo EPI‐QSM reconstructions across a range of parallel imaging and multiband acceleration factors. Methods: Using 2D single‐shot EPI in the brain, we compared QSM from single‐echo and multi‐echo acquisitions across combined parallel‐imaging and multiband acceleration factors ranging from 2 to 16, with volume pulse TRs from 21.7 to 3.2 s, respectively. For single‐echo versus multi‐echo reconstructions, we investigated the effect of acceleration factors on regional susceptibility values, temporal noise, and image quality. We introduce a novel masking method based on thresholding the magnitude of the local field gradients to improve brain masking in challenging regions. Results: At 1.6‐mm isotropic resolution, high‐quality QSM was achieved using multi‐echo 2D EPI with a combined acceleration factor of 16 and a TR of 3.2 s, which enables functional applications. With these high acceleration factors, single‐echo reconstructions are inaccurate and artefacted, rendering them unusable. Multi‐echo acquisitions greatly improve QSM quality, particularly at higher acceleration factors, provide more consistent regional susceptibility values across acceleration factors, and decrease temporal noise compared with single‐echo QSM reconstructions. Conclusion: Multi‐echo acquisition is more robust for EPI‐QSM across parallel imaging and multiband acceleration factors than single‐echo acquisition. Multi‐echo EPI can be used for highly accelerated acquisition while preserving QSM accuracy and quality relative to gold‐standard 3D‐GRE QSM. [ABSTRACT FROM AUTHOR]

In this paper, a compact stepped slot antenna, for Global Navigation Satellite System (GNSS) applications, is proposed. The latter one, which operates in the frequency range from 1.49 GHz to 1.66 GHz, is designed to cover five GNSS bands namely GPS-L1, Galileo-E1, GLONASS-G1, BEIDOU-B1 and EGNOS-L1. The proposed composite design is carried out in three phases. Firstly, a compact slot antenna, having a size of 58.0 × 52.0 × 1.6 mm, is designed on FR4 substrate to generate the five GNSS bands. Secondly, a compact Frequency Selective Surface (FSS) reflector, with 18.0 × 18.0 × 1.6 mm unit size, is designed to produce a stop band response matching all these bands. Finally, a single layer FSS, consisting of 9 × 9 units, is combined with the optimized antenna to achieve a high-gain directional antenna structure. The final proposed combination has been investigated using the High Frequency Structure Simulator (HFSS) and validated by Computer Simulation Technology (CST) Microwave Studio. Besides, a prototype antenna is fabricated and validated by measurements. The measurement results, which illustrate a good agreement with those corresponding to the simulations, have shown that the proposed composite antenna exhibits a directional radiation pattern with a high peak gain of 7.3 dBi and a maximum gain improvement of 5.65 dBi at 1.57 GHz. Furthermore, it offers good radiation efficiency in the operating bands, which makes it a good candidate for multisystems GNSS receivers, especially to reduce the different interferences by enhancing the antenna radiation characteristics. [ABSTRACT FROM AUTHOR]

The design and response of a triple-band linear-to-circular polarization converter (LTCPC) in the terahertz frequency regime using a graphene-based transmission-type metasurface have been studied numerically and analytically. The unit cell of the converter is constructed using lossy silicon dioxide (SiO2) with a relative permittivity of 3.9 as the substrate. And two similar layers of graphene-based sub-wavelength structures are used at the top and bottom of it. Multiband linear to circular polarization conversion is achieved from 0.74 THz to 0.98 THz, 1.70 THz to 2.33 THz, and 4.06 THz to 5.19 THz, i.e., about 28 %, 31 %, and 24 % fractional bandwidths, respectively. As the same metasurface configuration is used at the top and bottom layers of the transmission-type unit cell, it can be used as a bidirectional polarization converter with identical responses from both sides. The geometrical optimization of the unit cell is done, and an equivalent lumped parameter circuit model is also proposed for the same, considering analogous responses. Tunability over the operating frequency is achieved by varying the chemical potential and relaxation time of graphene. Moreover, due to the ultrathin width and special types of identical configuration of the metasurfaces, the response of the system remains excellent over a wide range of incident angle variations up to 80° angle of incidence. [ABSTRACT FROM AUTHOR]

In this paper, deep learning–based data‐driven surrogate modeling approach is proposed for enhancing cost‐efficiency of multiband antenna design optimization. The proposed surrogate model–assisted design approach has achieved a computational cost reduction of almost 40% compared to the conventional direct electromagnetic solver–based design methodologies in case of single design example. As for the validation of the proposed method, the obtained optimal design parameters from the surrogate model are used to manufacture an antenna design. The obtained results from the experimental measurement are compared with counterpart results from the literature. [ABSTRACT FROM AUTHOR]

A miniaturized asymmetric coplanar strip fed with meander lines is developed for hexaband wireless applications. Multiband with compact size of the antenna is developed by using meander lines. The designed antenna is enhanced by an increased number of meander lines. The invented antenna is composed of three meander lines, it yields the antenna to excite 1.13, 2.35, 2.91, 3.46, 3.96, and 4.5 GHz, respectively. The prototype antenna is fed by ACS, which is printed on a 14 × $\times $ 24 × $\times $ 1.6 mm3 FR‐4 substrate and dielectric constant of Ɛr = 4.4. MATLAB tool is utilized in the ANN computation to amend the physical values of the antenna. The calibrated and simulated radiation attributes are identical with each other. The designed antenna provides distinguishing characteristics such as good reflection coefficient, impedance matching, and size miniaturization. It imparts empirical peak gains of 0.028 dBi at 1.14 GHz, 1.305 dBi at 2.35 GHz, 1.54 dBi at 2.86 GHz, 1.79 dBi at 3.43 GHz, 2.43 dBi at 3.96 GHz, and 2.58 dBi at 4.5 GHz, which is suitable for GSM/WLAN/WiMAX and C‐band wireless applications. [ABSTRACT FROM AUTHOR]

Simultaneous multi‐slice (multiband) acceleration in fMRI has become widespread, but may be affected by novel forms of signal artifact. Here, we demonstrate a previously unreported artifact manifesting as a shared signal between simultaneously acquired slices in all resting‐state and task‐based multiband fMRI datasets we investigated, including publicly available consortium data from the Human Connectome Project (HCP) and Adolescent Brain Cognitive Development (ABCD) Study. We propose Multiband Artifact Regression in Simultaneous Slices (MARSS), a regression‐based detection and correction technique that successfully mitigates this shared signal in unprocessed data. We demonstrate that the signal isolated by MARSS correction is likely nonneural, appearing stronger in neurovasculature than gray matter. Additionally, we evaluate MARSS both against and in tandem with sICA+FIX denoising, which is implemented in HCP resting‐state data, to show that MARSS mitigates residual artifact signal that is not modeled by sICA+FIX. MARSS correction leads to study‐wide increases in signal‐to‐noise ratio, decreases in cortical coefficient of variation, and mitigation of systematic artefactual spatial patterns in participant‐level task betas. Finally, MARSS correction has substantive effects on second‐level t‐statistics in analyses of task‐evoked activation. We recommend that investigators apply MARSS to multiband fMRI datasets with moderate or higher acceleration factors, in combination with established denoising methods. [ABSTRACT FROM AUTHOR]

Electromagnetic (EM) absorbers are specially designed structures that dissipate the absorbed EM energy into heat by minimizing the reflection as well as transmission. The absorbers operating in microwave and millimetre wave regimes have been found essential in applications such as radar, communication systems, EM interference prevention, and stealth technologies. Design concepts such as Salisbury, Jaunman screens, and impedance-matching layers are discussed. As a game-changing innovation in wave attribute manipulation, metamaterial behaviour provides an unprecedented command over how waves interact with matter. This review examines the significant hurdles and restrictions metamaterial absorbers must overcome, like fabrication, the tradeoff between absorption bandwidth and thickness, and material losses. Broadband absorption, tunability, and feasibility of producing thin, lightweight absorbers all contribute to their desirability for various applications. Different losses responsible for the absorption phenomena are detailed for both narrowband and broadband cases. This critical analysis highlights the enormous promise of metamaterial absorbers while emphasizing the ongoing research efforts needed to overcome the associated obstacles. Its goal is to advance state-of-the-art designs by critically assessing the existing status of the field, thereby guiding future research, development, making it easier to implement microwave and millimetre wave absorbers in a wide range of real-time applications. [ABSTRACT FROM AUTHOR]

With the accelerating development of electronic technology, how to effectively eliminate electromagnetic radiation pollution has become a critical issue. Electromagnetic wave (EMW) absorption materials have an irreplaceable position in the field of military stealth as well as in the field of electromagnetic pollution control. In order to cope with the complicated electromagnetic environment, the design of multifunctional and multiband high-efficiency EMW absorbers remains a daunting challenge. In this work, a hierarchical porous molybdenum carbide matrix with a three-dimensional porous structure was designed by salt melt synthesis (SMS) strategy. Furthermore, the relationship between the structure and the impedance matching performance was explored by stepwise modification via ultrathin layered MoS2 nanoflakes. Analysis indicates that the extent of modification of hierarchical porous molybdenum carbide by MoS2 nanoflakes modulates the dielectric performance due to differences in morphology and the introduction of heterogeneous structures, along with a dramatic impact on the impedance matching performance. In particular, the prepared MS/MC/PNC-2 composite exhibits a reflection loss (RL) of -55.30 dB at 2.4 mm, and an ultra-broad effective absorption bandwidth (EAB) of 7.60 GHz is obtained at 2.0 mm. The coordination of structure and component enables the absorber to exhibit strong absorption, wide bandwidth, thin thickness, and multi-band absorption characteristics. Noticeably, the effective absorption performance in the broadband for X and Ku is also satisfying, as well as possessing moderate marine anti-corrosion performance. This study contributes to an in-depth understanding of the relationship between impedance matching and EMW absorber performance and provides a reference for the design of multifunctional, multiband microwave absorbing materials. [ABSTRACT FROM AUTHOR]

This work encompasses a novel highly compact Split Ring Resonator (SRR) based quad-band Dielectric Resonator Antenna (DRA) for 4G and 5G applications. The proposed antenna comprises of an extended rectangular feedline and a rectangular DR in combination with two SRRs. The DRA uses the extended rectangular microstrip feedline for providing better impedance matching and enhanced performance. Remarkably, the introduction of SRRs on either side of the feedline enables the DRA to resonate at four distinct frequency bands, i.e., 1.62 GHz, 3.03 GHz and 4.7 GHz and 6.56 GHz respectively. The two lower operating bands with narrow band response are due to SRRs while two upper bands with wide band characteristics are due to rectangular DR. The simulated performance of the rectangular DRA is validated through measurements, performed on a fabricated prototype. At the corresponding resonance frequencies, the suggested design exhibits −10 dB impedance bandwidths of 9.2%, 5%, 8.3%, and 5.6%. With a notable peak gain of 2.3 dBi and an efficiency of 93%, the suggested design has excellent radiation pattern stability. To the best of authors knowledge, this is the first design where SRRs are incorporated with rectangular DR to achieve multiband operations. The simulated and measured findings show a strong agreement, highlighting the SRR-based DRA appropriateness for multiband wireless applications (such as satellite television, radio astronomy, Bluetooth, WiFi, and 6G), while demonstrating its significant contribution to the field.

This research work presents the design of a multiband dual‐polarized eight‐element MIMO antenna having dimensions (0.51 λ × 0.66 λ × 0.009 λ). The antenna is observed to be radiating between 1.7 GHz and 2.4 GHz, 4.1 GHz and 10 GHz and 10.6 GHz and 19.8 GHz, featuring 3 dB axial ratio bandwidth between 9.7 and 10 GHz, 12.1 and 13.1 GHz, 14.4 and 14.5 GHz and 17.9 and 18.9 GHz. In the proposed MIMO antenna, the triangular‐shaped monopole antenna is tapered at its two sides. The isolation between the various elements of the proposed antenna is observed to be in range of −20 dB–−70 dB for the concerned frequency range. On the basis of comparison with similar existing structures, the proposed antenna demonstrates superior performance in terms of total active reflection coefficient (TARC < −5 dB), diversity gain (DG around 10 dB), channel capacity loss (CCL < 0.3 bits/s/Hz), mean effective gain (MEG) and envelope correlation coefficient (ECC < 0.024). The proposed antenna provides wide bandwidth (15.8 GHz) and high value of peak gain (6 dB). The proposed geometry is novel as it exhibits both linear as well as circular polarization with multiband response and it provides the least ECC and maximum isolation. The experimental results are found to be in agreement with the simulated results, so the proposed antenna can be useful for WLAN, C‐band, X band and Ku band applications. [ABSTRACT FROM AUTHOR]

Previous studies have introduced topological concepts to the field of acoustics, greatly contributing to the development of acoustic wave-controlled transmission. It has evolved from acoustic wave transmission in a single frequency band to low-frequency and multiband transmission. This paper presents research on acoustic wave transmission control and the observation of transmission process properties. The paper proposes an acoustic topological insulator based on a composite resonant cavity that can change its topological boundary state and achieve controlled transmission of acoustic waves by adjusting the scatterer's rotation angle. At the same scale, this structure has a high internal space utilization and can make full use of the rotational scattering mechanism. In an air environment, the structure can create an acoustic topological transmission channel that can transmit acoustic waves in four bands. It has the advantage of having a wide frequency band. Furthermore, this study investigates the impact of channel defects on the transmission of acoustic waves, highlighting the fault-tolerant nature of these topological channels. These properties make it possible to control sound wave transmission along a predetermined path. These findings support the advancement of controllable acoustic wave transmission, which holds promise for applications in acoustic signal processing, acoustic stealth, and other related fields. [ABSTRACT FROM AUTHOR]

This paper proposes a 10 × 10 MIMO multiband broadband planar antenna for tablets or laptops. The designed antennas cover a large number of the popular sub‐6‐GHz application bands, such as 0.617–0.96, 2.1–2.7, 3.5–4.5, and 6.1–7.2 GHz for public safety communications, radio systems, Bluetooth, Wi‐Fi, and satellite communications. The proposed antenna is designed with grounded branches, which can generate a wide bandwidth and cover most of the sub‐6‐GHz application band by coupling between branches of different lengths and antennas. MIMO antennas have been measured to have an envelope correlation coefficient of less than 0.7 and have met the standards set by international organizations for human radiation absorption simulations. The proposed antenna validates the unique 10 × 10 MIMO antenna structure and feasibility. Multiple operable frequency bands are realized, and the radiation effect of the antenna on the human body is analyzed if it complies with international market standards. The proposed antenna design is well suited for multiband and broadband requirements. [ABSTRACT FROM AUTHOR]

In this article, the authors present the design of a compact multiband monopole antenna measuring 30 × 10 × 1.6 mm3, which is aimed at optimizing performance across various communication bands, with a particular focus on Wi-Fi and sub-6G bands. These bands include the 2.4 GHz band, the 3.5 GHz band, and the 5–6 GHz band, ensuring versatility in practical applications. Another important point is that this paper demonstrates effective methods for reducing mutual coupling through two meander slits on the common ground, resembling a defected ground structure (DGS) between two antenna elements. This approach achieves mutual coupling suppression from −6.5 dB and −9 dB to −26 dB and −13 dB at 2.46 GHz and 3.47 GHz, respectively. Simulated and measured results are in good agreement, demonstrating significant improvements in isolation and overall multiple-input multiple-output (MIMO) antenna system performance. This research proposes a compact multiband monopole antenna and demonstrates a method to suppress coupling in multiband antennas, making them suitable for internet of things (IoT) sensor devices and Wi-Fi infrastructure systems. [ABSTRACT FROM AUTHOR]

In this proposed article authors present the design, analysis and development of the hybrid shaped multiband microstrip patch antenna for various wireless communication applications. Multiband characteristics of the proposed antenna is achieved by modifying the conventional circular radiating patch into “DUMBBELL” shaped hybrid patch geometry along with slotted reduced finite ground plane. A circular shaped reference patch is modified into dumbbell shaped patch by loading another circular shaped patch. Initial ground plane of same dimension as substrate is first decreased in width and four rectangular shaped slots are loaded in the appropriate locations to construct the final ground plane. Physical and electrical dimension of the proposed antenna are 24 mm × 40 mm × 16 mm and 0.18λ × 0.3λ × 0.12λ where λ represents wavelength corresponding to lowest operating frequency of 2.3 GHz. Proposed antenna is designed using FR-4 substrate (1.6 mm thick, loss tangent (tanδ) of 0.02, dielectric constant (εr) of 4.4) and simulated by CST Microwave Studio software. Antenna prototype is fabricated, measured and compared with the simulated results. The proposed hybrid shaped antenna exhibits measured multiband characteristics (2.3-2.5 GHz, 2.6-3 GHz, and 6.9-7.1 GHz) with centre frequency at 2.4, 2.7 and 7 GHz. Observed Reflection Coefficient, efficiency, peak gain and E plane and H plane radiation pattern of the antenna are very close to simulation result. Antenna can be suitably used for 2.4 GHz Wi-Fi and Bluetooth application, 5G mid band spectrum (3 GHz) and 7 GHz VSAT applications as well. [ABSTRACT FROM AUTHOR]

Antennas are of great importance in energy harvesting systems. It is possible to collect more energy with RF energy harvesting systems by using multiband antennas. In this study, a microstrip antenna was designed and fabricated for operation at 307 MHz, 1721 MHz, and 5447 MHz carrier frequencies. The designed multiband antenna with size of 82.05x104.76x1.60 mm3 was optimized for collecting more energy and then, implemented on FR4 substrate. Return loss, voltage standing wave ratio, and impedance of the manufactured multiband microstrip antenna were measured by vector network analyzer. The multiband antenna gain was calculated as 2.02 dBi. Furthermore, a good agreement was noted between the measurement and simulation results of the multiband microstrip antenna. As a result, it is determined that the produced multiband microstrip antenna is a useful and suitable antenna for RF energy harvesting circuits. [ABSTRACT FROM AUTHOR]

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Benefiting from the discovery of novel organic semiconductor materials bearing tunable absorption characteristics, narrowband organic photodetectors (OPDs) with improved performance are reported. Alongside new photoactive materials synthesis, several device engineering strategies are introduced to achieve narrowband OPDs, allowing less dependence of the device performance on the synthetic variation control, such as batch‐to‐batch differences in molecular weight. However, fabrication of multiband OPDs remains a challenge. Current solutions are usually based on vertical multi‐stacking of photosensitive layers with different absorption spectra and voltage‐modulated charge collection/injection, which renders the device fabrication too complex, while their response speed and band selectivity is limited. In this work, the concept of optical cavity is adopted to demonstrate self‐powered and fast response speed single‐junction bidirectional organic photodetectors with dual narrowband detection in the ultraviolet (UV) and visible part of the spectrum. Application of these devices in encrypted UV communication is successfully demonstrated. A third band in the near infrared (NIR) is possible to be isolated, rendering these high‐performing and simple to manufacture multiband OPD devices attractive for high‐resolution imaging and optical wireless communication. [ABSTRACT FROM AUTHOR]

In this paper, a multiband microstrip antenna of compact size (0.2 × 0.25 ) is designed by loading multiple notches in the patch of antenna. The patch of antenna consist two L-shaped and two rectangular shaped notches. The modified patch of antenna provides triple resonating bands from 1.58 to 1.71 GHz, 1.89 to 2.06 GHz and 2.81 to 2.93 GHz under the − 10 dB scale resonating at frequency 1.63 GHz, 2 GHz and 2.87 GHz respectively. The bandwidth of triple band antenna is obtained 7.9% (130 MHz), 8.61% (170 MHz) and 4.18% (120 MHz) with − 16.6 dB, − 26.99 dB and − 31.88 dB reflection coefficient at resonating frequency. The lower and middle resonances are due to L-shape notches while higher resonance is due to rectangular shape notches. The presented antenna is fed by microstrip line feed of 50 Ω and the simulation is performed by IE3D software. It shows 2.6−3.1 dB, 2.9−3.5 dB and 4.2−5 dB simulated gain and 85−93%, 87−95% and 88−96% antenna efficiency in three resonating bands. The three resonating bands of proposed antenna can be used for the application of different wireless communications in L and S-bands. The proposed work is also compared with the previous published articles to find out the improvement. [ABSTRACT FROM AUTHOR]

In the present emerging trends of 5G communication, long-distance communication cannot be accomplished with a single antenna. To enhance the gain and efficiency, a multi-band double hook shaped micro strip array antenna with defected ground structure has been designed and analyzed in this work for 5G communication applications. A quarter-wave transformer with a good impedance matching network is employed to provide the antenna's radiating components, and the designed antenna is prototyped on a 0.2 mm thick polyimide substrate with a dielectric constant of 2.9. Antenna resonating in the quad band with 10 GHz bandwidth at first resonant band and 1 GHz bandwidth at other three resonant bands. Gain of 8.8 dB at 22 GHz, 11 dB at 28 GHz, 13 dB at 32 GHz and 14.2 dB at 38 GHz is attained from radiation characteristics. The antenna is flexible and conformal with respect to the host surface, providing excellent correlation in simulation and protype real time measurement. [ABSTRACT FROM AUTHOR]

The novel T-shaped patch antenna with the superstrate approach is planned in the manuscript. The FR-4 dielectric material is used as a superstrate and substrate. The hexagonal-shaped rings are loaded in the superstrate to enable the metamaterial property in the structure. The copper-loaded metamaterial and liquid Sea water-loaded metamaterial are used in the planned antenna which increases the gain and BW of the planned antenna design. Different parametric analyses like the varying height of the superstrate and changing spacing among SRR rings are considered to achieve an optimum response. The analysis concerning S11, gain, and directivity is carried out among simple patch antenna, copper ring loaded structure and seawater loaded structure. The frequency span of 1 GHz to 12 GHz is considered for analysis. The planned designs provide a minimum S11 of −49.16 dB in CMRNGS, a Gain of 6.92 dB in SMRNGS, and a highest directivity of 8.56 dB for 8.83 GHz resonance. The planned design is compared with other papers to check the improvement of this planned antenna design. The Simulated and assessed responses were also compared and analysed. The planned design is suitable for 5G, WLAN, tracking and detection applications.

The study explores a novel hexa-band metamaterial utilizing tunable split ring resonators for wireless communication and sensing applications. The proposed metamaterial structure demonstrates remarkable versatility through its hexa-band resonant behavior and adaptability, achieved by incorporating tunable split ring resonators. The proposed MTM unit cell is characterized by electrical measurements of 0.122λ0 × 0.122 λ0, where λ0 corresponds to the wavelength calculated at a resonance frequency of 2.53 GHz, leading to a total dimension of 14.5 × 14.5 mm2. It has six transmission coefficients (S21), they cover the S, C, X, and Ku bands at the resonating points of 2.53 GHz, 4.12 GHz, 7.17 GHz, 10.31 GHz, 12.18 GHz, and 14.26 GHz, respectively. The design offers flexibility for frequency-selective applications in wireless communication due to its small size, high refractive index, and the feature that it can provide frequency selectivity by tuning. Different solid materials, earth materials, hydrocarbon, and Arlon substrates are used for sensing applications. The proposed metamaterial offers greater flexibility and adaptability due to the incorporation of tunable split ring resonators. This makes it suitable for various wireless communication and sensing applications.

Recently, the relevance of multiple input multiple output (MIMO) technology has increased due to the growing user base and the surge in demand for high data rates. It provides an essential answer to the pressing requirement for high-capacity communication systems compliant with new standards. In this study, a four-element MIMO antenna with specific properties—a thickness of 0.0224 mm and a relative permittivity of 4.3 —is presented on a polyamide substrate. It is intended to operate in terahertz (THz) applications at 0.395 and 0.629 THz. The configuration of the antenna is based on a traditional fork antenna. At the resonant frequencies, this MIMO antenna can achieve bandwidths of 9.53 GHz and 24.19 GHz, with reflection coefficients of -16.19 dB and -24.27 dB, respectively. Moreover, a gain of 5.17 dB and 3.19 dB are obtained at the second and first resonant frequencies, respectively. In the effort to maintain the operational band and enhance gain, a significant challenge arises from the insufficient isolation between the four antenna elements within the limited space. A Defected Ground Structure (DGS) is constructed and the inter-element distance is carefully investigated in order to effectively address this issue. Mutual coupling effects are effectively reduced with this antenna, and an amazing MIMO diversity response is shown. Additionally, it achieves a mean effective gain of less than -3, envelope correlation coefficients below 0.0125, diversity gain of around 10 dB, and total active reflection coefficients below -4 dB. The suggested design was simulated using the ansys High-Frequency Structure Simulator program. These enhancements show that the recommended MIMO antenna is a suitable choice for terahertz applications like 5 G networks of the future and terahertz imaging systems used in medical settings for tissue imaging and cancer diagnosis.

Excitation in MRI is traditionally done at the Larmor frequency, where the energy of each radiofrequency photon corresponds to the energy difference between two spin states. However, if multiple radiofrequencies are employed, then multiphoton excitation can also occur when the sum or difference of multiple photon frequencies equals the Larmor frequency. Although multiphoton excitation has been known since the early days of NMR, it has been relatively unexplored in MRI. In this work, equations and principles for multiphoton selective RF pulse design in imaging are presented and experimentally demonstrated. In particular, the case where there are radiofrequency fields in both the traditional xy-direction and non-traditional z-direction is considered. To produce the z-direction radiofrequency field, an additional uniform coil was added to a clinical MRI scanner. Using this coil, two-photon slice-selective pulses were designed to be equivalent to traditional pulses, producing similar excitation, slice profiles, and in vivo images. Being the result of a combination of multiple radiofrequency fields instead of just one, two-photon pulses have more flexibility in how their parameters can be changed. Although individual multiphoton excitations are less efficient than their traditional counterparts, when the z-direction radiofrequency field is spatially non-uniform, multiple multiphoton resonances can be simultaneously used at different locations to produce simultaneous multislice excitation with the same pulse duration but less tissue heating than a naive implementation. In particular, non-uniform z-direction radiofrequency fields with negligible added tissue heating provided by oscillating the MRI scanners gradient fields at kilohertz frequencies were used to excite multiple slices simultaneously with less high-frequency xy-direction radiofrequency power. For an example three-slice excitation, we achieve half the xy-direction radiofrequency power compared to the naïve approach of adding three single-slice pulses. For conventional or unconventional applications, multiphoton excitation may be of interest when designing new MRI systems.

Transformation optics (TO) provides a powerful tool to manipulate electromagnetic waves, enabling the design of invisibility cloaks, which can render objects invisible. Despite many years of research, however, invisibility cloaks experimentally realized thus far can only operate at a single frequency. The narrow bandwidth significantly restricts the practical applications of invisibility cloaks and other TO devices. Here, a general design strategy is proposed to realize a multiband anisotropic metamaterial characterized by two principal permittivity components, i.e., one infinite and the other spatially gradient. Through a proper transformation and combination of such metamaterials, an omnidirectional invisibility cloak is experimentally implemented, which is impedance‐matched to free space at multiple frequencies. Both far‐field numerical simulations and near‐field experimental mappings confirm that this cloak can successfully suppress scattering from multiple large‐scale objects simultaneously at 5 and 10 GHz. The design strategy and corresponding practical realization bring multiband transformation optical devices one step closer to reality. [ABSTRACT FROM AUTHOR]

An electrically small multiband planar antenna is presented by using rectangular split ring resonator (RSRR) metamaterial element for LTE, WiMAX and WLAN applications. The designed antenna possesses asymmetric coplanar strip (ACS)-fed Hilbert Curve Fractal Antenna (HCFA) loaded with RSRR metamaterial for multiband radiation at 1.44 GHz, 3.76 GHz and 5.27 GHz. ACS-fed HCFA is responsible for creating the first (at 1.44 GHz) and second (at 3.76 GHz) resonance frequencies owing to the coupling between ACS-fed HCFA and ground plane. Moreover, the RSRR yields upper resonance at 5.27 GHz owing to the metamaterial transmission line. The stop band and pass band nature of the RSRR and its negative permeability characteristics are described using an effective medium theory. An equivalent circuit model of the proposed antenna is investigated with the help of Agilent ADS to validate the operating frequencies. Also, the geometrical parameters have been optimized using the artificial neural network (ANN), which is performed by MATLAB. The proposed antenna has been fabricated on a 18 × 16.5 × 1.6 mm3 FR-4 dielectric having ε r = 4.4 and tan δ = 0.02. It provides multiband response at 1.4 GHz, 4.4 GHz and 5.3 GHz with a − 10 dB impedance bandwidth of 330 MHz, 570 MHz, and 340 MHz, respectively, which is usable for LTE, WiMAX and WLAN band applications. [ABSTRACT FROM AUTHOR]

The demand for multiband and high-gain THz antennas is escalating due to advancements in terahertz (THz) applications, particularly in biomedical conditions. An innovative fork microstrip antenna design has been introduced, operating at THz frequencies, providing multi-band capability, soft characteristics, and high-gain results. The recommended antenna utilizes a series-fed configuration with dual patch elements constructed on a polyethylene substrate, with a thickness of 0.0224 mm, a loss tangent of 0.001, and a permittivity of 2.25. The proposed antenna, with dimensions of 1 × 0.6 × 0.0224 mm³ in its maximum configuration and operating at 0.530 THz and 0.590 THz, exhibits a 10 dB return loss bandwidth of 13 GHz and 15 GHz, respectively. Notably, the realized antenna gain is simulated at 9.01 dBi and 9.53 dBi for their respective frequencies. To assess the antenna's flexibility, simulations are conducted with the antenna configured in bent positions, considering radii of 7 mm, 6 mm, and 5 mm. Furthermore, the study includes an examination of the specific absorption rate (SAR) to validate the suitability of this pliable antenna. The outcomes underscore the potential of the recommended antenna for flexible biomedical THz applications such as the detection of skin tumours and medical imaging.

This paper deals with the design, simulation, and practical modeling of metamaterial-based multiband conformal bandpass filter (BPF) for various wireless communication applications with improved quality factors. The novel metamaterial in the form of a split ring resonator is loaded on the ground plane face of the proposed BPF. The overall dimension of the designed BPF is only 2 8 × 2 8 mm 2 . The proposed BPF is tuned initially for quality factor enhancement based on the thickness of the substrate, physical parameters of the f transmission line, ground plane, externally loaded elements, and the gap in the metamaterial loading. The suggested filter operates at triple band covering the frequency bands from 1.4 to 2.2, 3.6 to 3.9, and 4.8 to 5.9 GHz, which are suitable for sub-6 GHz 5G and other wireless applications. The insertion loss is observed as 1 dB, which is suitable for the proposed BPF. The conformal behavior of the filter is judged through bending deformation analysis at various bending positions like (15 ∘ , 30 ∘ , 45 ∘ , 60 ∘ , and 90 ∘ ). The proposed BPF retains triple pass band characteristics at various bending deformations, which makes it suitable to be used in curved structures or flexible circuitry. The theory of equivalent circuits and quality factor (Q) of the designed BPF is discussed in this paper. The results are analyzed experimentally through ANRITSU-MS2037C combinational analyzer. The proposed BPF is suitable for sub-6 GHz 5G, WLAN, and Wi-Max applications. [ABSTRACT FROM AUTHOR]

In this work, we presented the design, analysis and optimization of the multiband slotted antennas based on SINC function for 5G applications. The proposed antennas are designed and modelled by CST Studio Suite software. A parametric study is performed to determine sinc function parameters that control the performance of the proposed antenna. The parametric study is implemented by varying the amplitude of the sinc function, the frequency, the location of the slot along Y-axis, the slot width and the slot window (number of cycles). The simulated results showed that the designed slotted antennas in this paper exhibits multiband operation and they offer the feasibility of controlling and adjusting the resonant frequency by changing the sinc function parameters. The proposed antennas have various resonant frequencies at around 1.5 GHz, 2.65 GHz, 5 GHz and 5.8 GHz covering the 5G sub-6 GHz band. Extensive simulation process were carried out to determine the optimum antenna performance and three antennas were selected based on the reflection characteristics and number of operation frequency bands. Finally, the three selected antennas were manufactured and their performance were measured in the lab for validation. Experimental results showed that an excellent agreement between the measured and simulated results was achieved. [ABSTRACT FROM AUTHOR]

Purpose: The characterization of tissue microstructure using diffusion MRI (dMRI) signals is rapidly evolving, with increasing sophistication of signal representations and microstructure models. However, this progress often requires signals to be acquired with very high b‐values (e.g., b > 30 ms/μm2), along many directions, and using multiple b‐values, leading to long scan times and extremely low SNR in dMRI images. The purpose of this work is to boost the SNR efficiency of dMRI by combining three particularly efficient spatial encoding techniques and utilizing a high‐performance gradient system (Gmax ≤ 300 mT/m) for efficient diffusion encoding. Methods: Spiral readouts, multiband imaging, and sampling on tilted hexagonal grids (T‐Hex) are combined and implemented on a 3T MRI system with ultra‐strong gradients. Image reconstruction is performed through an iterative cg‐SENSE algorithm incorporating static off‐resonance distributions and field dynamics as measured with an NMR field camera. Additionally, T‐Hex multiband is combined with a more conventional EPI‐readout and compared with state‐of‐the‐art blipped‐CAIPIRINHA sampling. The advantage of the proposed approach is furthermore investigated for clinically available gradient performance and diffusion kurtosis imaging. Results: High fidelity in vivo images with b‐values up to 40 ms/μm2 are obtained. The approach provides superior SNR efficiency over other state‐of‐the‐art multiband diffusion readout schemes. Conclusion: The demonstrated gains hold promise for the widespread dissemination of advanced microstructural scans, especially in clinical populations. [ABSTRACT FROM AUTHOR]

This paper proposes a texture-enhanced network (TENet) for intertidal sediment and habitat classification using multiband multipolarization synthetic aperture radar (SAR) images. The architecture introduces the texture enhancement module (TEM) into the UNet framework to explicitly learn global texture information from SAR images. The study sites are chosen from the northern part of the intertidal zones in the German Wadden Sea. Results show that the presented TENet model is able to detail the intertidal surface types, including land, seagrass, bivalves, bright sands/beach, water, sediments, and thin coverage of vegetation or bivalves. To further assess its performance, we quantitatively compared our results from the TENet model with different instance segmentation models for the same areas of interest. The TENet model gives finer classification accuracies and shows great potential in providing more precise locations. [ABSTRACT FROM AUTHOR]