Globally, microwave frequencies are being extensively employed in numerous biomedical implementations due to its high resolution, reasonable penetration through the human tissue, and cost-effectiveness. However, the quantization of human osseous tissue through microwave sensing is still not proficient. Therefore, this article provides an insight on the prediction of onset and progression of osteoporosis developed through the use of a microwave setup for the contactless evaluation of osteoporosis. This microwave setup comprises a human wrist model as a device under test which is illuminated through a pair of planar stubbed monopole antennas to characterize the different degrees of osteoporosis through frequency domain simulation analysis. By diversifying the wrist dimensions, we are collecting the dataset of the transfer characteristics. Furthermore, different machine learning algorithms are employed on this dataset to train, classify and eventually evaluate the different degrees of osteoporosis. Finally, an optimum machine learning algorithm was obtained to work at an optimum bandwidth and optimum frequency.

The paper presents a new technique for designing a reconfigurable frequency selective surface (RFSS) by mechanical means. The combination of triangular loop element and three-legged element has been used to design the proposed single substrate two sided frequency selective surface (FSS) structure which offers variable transmission coefficient characteristics over the X-band frequencies under TE polarization for different angles of incidence. Thus, the band stop characteristics can be reconfigured by changing incident angle which describes the structure as `reconfigurable reflector'. The proposed FSS geometry is polarization insensitive under both TE and TM polarizations. The simulated results are further cross verified by conducting measurement of the fabricated structure. The equivalent circuit model (ECM) of the proposed FSS geometry has been provided, and the equivalent circuit parameters of the proposed FSS geometry have also been extracted using the curve fitting techniques. The proposed FSS structure can be used as a frequency reconfigurable reflector surface/reconfigurable intelligent surface (RIS) for advanced wireless communication.

A 3D printing and printed circuit board (PCB) hybrid fabricated modularized dual-stopband artificial magnetic conductor (AMC)-loaded filtering antenna is proposed for an X-band high-power radar system.By loading low-cost microstrip AMCs of different frequency responses into a waveguide slot array, we achieve a modularized filtering antenna whose frequency response can be simply controlled by replacing different AMCs. The waveguide slot array only works as a fixture to host different AMCs to achieve various filtering antenna frequency responses. The interchangeable modularized design helps to reduce the difficulty and cost of component fabrication by eliminating the need for complex resonant cavities inside the waveguide filtering antenna, which is time-efficient at the stage of product prototyping when numerous iterations are needed on a trial-and-error base. A dual-stopband filtering antenna is designed and fabricated in the X-band to verify the design concept. The passband covers 9.25-10.6 GHz with the passband gain greater than 10 dBi. The antenna radiates frequency-dependent scanning beams in the passband. The stopbands are 8.1-9 GHz and 10.75-11.5 GHz, and the out-of-band rejection is larger than 35 dB. The proposed design concept provides a different thought to achieve a low-cost filtering antenna by using interchangeable modularized components. The fabricated antenna prototype is a capable candidate for high-power airborne radar applications.

A dual frequency dual circularly polarized cross-slot waveguide array working at 4.9 GHz and 5.8 GHz is proposed for wireless communication/airborne weather radar applications. Different from the traditional cross-slotted waveguide antenna, to improve space utilization, two sets of cross-slots are slit on both sides of the longitudinal axis of the waveguide's E-plane to realize dual-frequency operation. When the antenna operates in the TE₁₀ mode, the cross-slots on each side radiate left-handed and right-handed circularly polarized electromagnetic waves at two different frequencies, respectively. To suppress grating lobes, phase perturbation structures are periodically loaded in the waveguide to tune the propagation phase constant, thereby changing the effective electric spacing between radiating elements while keeping the antenna a compact physical aperture. The proposed grating lobe suppression method avoids the dielectric loss caused by dielectric loading, eliminates the need for complex array arrangement, and achieves the grating lobe suppression at dual frequencies simultaneously. The metallic 3D printing technology, selective laser melting (SLM), is used to fabricate the antenna in one piece in one run using aluminum alloy. The proposed antenna has gains of 10 dBic and 14.5 dBic with 47% and 69% aperture efficiencies at 4.9 GHz and 5.8 GHz, respectively. It is a capable candidate for air-to-ground (ATG) communication applications.

This paper presents a new scheme to implement the iterative physical optics (IPO) approximation with edge diffraction for the scattering from large perfectly-conducting objects, for which, multiple reflections occur. The use of the electric field integral equation (EFIE) discretized by the Galerkin method of moments (MoM) with Rao-Wilton-Glisson basis functions leads to solving a linear system. The characteristic basis function method (CBFM) needs to invert the self-impedance sub-matrices to calculate the primary basis functions (PBFs). To accelerate this stage, these sub-linear systems are directly solved from the physical optics (PO) approximation. In addition, to improve the precision of PO, the EFIE-PO self-impedance matrix is derived analytically. This avoids to apply the magnetic field integral equation (MFIE), for which its principal value is related to PO. Numerical results showed that the resulting algorithm, CBFM-PO, predicts inherently the edge diffraction. A domain decomposition method is able to split up the geometry into blocks, for which either the PO or a LU decomposition is applied according to the sub-geometry. To accelerate the coupling steps, the adaptive cross approximation (ACA) is also implemented, and the resulting method is tested on different targets having a curvature and producing multiple reflections. The numerical results show that EFIE-CBFM-PO is more accurate than the conventional EFIE-CBFM-POJ (based on Jakobus et al. work), specially for objects with curvature.

A simple and flexible differential negative group delay (NGD) circuit topology based on defected ground structure (DGS) is proposed. The circuit consists of microstrip lines and reverse nested double U-shaped (RNDU) DGSs, in which differential transmission and common-mode suppression (CMS) are realized by microstrip lines, and the adjustment of NGD time and the center frequency is achieved by changing the RNDU DGSs. Besides, the bandwidth and NGD time can be increased by cascading double couples of RNDU DGSs. For demonstration, two circuit prototypes with single- and double-couple DGSs are fabricated and measured. The measured results show that the NGD time of the single-couple DGS circuit at the center frequency of 2.279 GHz is -0.57 ns; the insertion loss is 2.08 dB; and the NGD bandwidth is 28 MHz. The NGD time of the double-couple DGS circuit at 2.30 GHz is -2.13 ns; the NGD bandwidth is 41 MHz; and the insertion loss is 4.39 dB. The functions of increasing bandwidth and enhancing NGD are realized. The common-mode insertion loss can reach 43.2 dB, and excellent CMS characteristics are achieved.

A quasi-equal inductor filter and its corresponding multilayer realization are proposed in this paper. The circuit transformation is performed using the Norton transformation. In the proposed filter, ratio between the largest and smallest component values is reduced, which makes the design of components much easier. Meanwhile, by carefully selecting the transformation ratio, all grounding inductors are equal in value. As a result, the multilayer filter design is simplified because only one instance of grounding inductors needs to be designed instead of three. An experimental prototype is fabricated and measured. The measurement result agrees well with the desired one, which shows the effectiveness of proposed filter.

A multi-resonating coplanar waveguide (CPW) fed flexible antenna using metamaterial unit cell is designed for various UWB wireless communication systems. The designed unit cell has the total dimension of 14.8 mm × 14.8 mm × 0.25 mm. The top layer of the cell has a circular ring slot combined with four modified T shaped radiators giving metamaterial characteristics. The unit cell uses perfect boundary conditions along with y axis wave propagation, and it gives wide NRI region covering 2 to 16 GHz of frequency range. The overall gain of proposed CPW fed antenna is increased by using a 3 ×3 metamaterial array as reflector at the back of antenna. The metamaterial antenna has 2 to 16 GHz of total bandwidth and peak gain of 13.1 dB. Further the measured outcomes are in accordance with the simulated ones.

Prediction in the transition region between lit and shadowed regions is important for maintaining stable mobile communication for the beyond 5th generation. In this paper, as the difference between the reflection and diffraction from a dielectric circular cylinder and an absorber screen, respectively, a novel additional term is derived by a uniform theory of diffraction (UTD) in the lit side of the transition region. The proposed model is validated by the UTD and exact solutions of a dielectric circular cylinder. Through the proposal, we can separate the contribution of the shadowed Fresnel zone (FZ) number and boundary conditions (i.e., the surface impedance and the polarization) to the total field. The frequency characteristics of the shadowed FZ and boundary conditions are theoretically analyzed. The analyzed results show that the contributions of the boundary conditions are weaker than the shadowed FZ in the lit region at a high frequency.

A study is made of the guiding properties of a nerve fiber consisting of myelinated axons as applied to electromagnetic waves in the optical and infrared ranges. Based on rigorous expressions for the electromagnetic field in the presence of a nerve fiber, the dispersion properties and field structures of eigenmodes guided by the fiber are analyzed for different values of the dielectric permittivity of myelin. It is shown that such a complex waveguide of natural origin can support the propagation of weakly attenuated eigenmodes in the considered ranges. It is shown that the dispersion properties and field structures of the modes of the nerve fiber can differ significantly from those of a single axon.

Directed energy weapons (DEWs) have been identified as valuable assets in future land and joint combat. High-power radio frequency (HPRF) is a form of DEW which can neutralise robotic systems by discharging electromagnetic (EM) radiation over a region to couple system electronics. Its widespread effect enables the simultaneous disruption of groups of electronic systems, such as swarms of unmanned aerial systems (UASs). Since EM radiation is a distance-based effect, the arrangement of defensive HPRF systems with respect to their target is critical to understanding their utility and viability. Consequently, a mathematical model to assess the effectiveness of HPRF DEW positioned at a given location is formulated. Towards this, a combat scenario specialised to land operations is defined. The assumptions required to formulate the scenario geometrically and mathematically are also outlined. Provided with the position of an effector, it is then possible to quantify the vulnerability of a UAS swarm in terms of a disruption probability. This accounts for uncertainty stemming from UAS and swarm behaviour and assumes that UASs are independent and identically distributed. The model also draws upon work previously conducted at Defence Science Technology Group (DSTG) which derived an HPRF disruption probability function. An optimisation of the disruption probability is undertaken in terms of the position of a single narrowband HPRF effector. Under a hypothesised set of HPRF and threat parameters, maximal swarm defeat probabilities are examined in different swarm deployment regions and HPRF beam widths. This led to the discovery of various tradeoffs between aforementioned features. In particular, under a fixed beam width, proximity to the swam provided an increased defeat probability but reduced the beam's coverage of the swarm. Hence, numerous UASs might not be affected by EM radiation throughout the engagement, reflected in a reduction to the swarm defeat probability.

Planar and conformal log periodic dipole array (LPDA) antennas are proposed in this paper with circular patch and hexagonal patch top loadings for multiband applications. Due to these top loadings, the size of the antennas is reduced, and the total dimensions of the two antennas are 44 mm x 40 mm. These antennas are fabricated on polyimide material with a dielectric constant of 3.3 and thickness of 0.1 mm. These two antennas resonate at 3.5 GHz, 5.7 GHz, 7.5 GHz and 9.3 GHz frequencies in both planar and conformal modes. The antenna characteristics of the proposed antenna models such as reflection coefficient, VSWR, radiation pattern, and gain are analyzed, and the measured results are in good agreement with simulation ones.

This work describes the design and analysis of a four-element wideband circularly polarized (CP) Multiple-Input-Multiple-Output (MIMO) antenna for mid-band 5G utilizations. The proposed MIMO antenna miniaturization is obtained by the implementation of composite right/left-handed (CRLH) transmission line (TL) and loading of octagonal shaped slotted rings inside the antenna ground plane. Further, the circular polarization radiation is obtained due to the sequence arrangement of two CRLH-TL based unit cells of opposite branches, inside a conventional square patch. The intended MIMO antenna encompasses two layers, the layer-1 consists of a four-element CRLH-TL based circularly polarized MIMO antenna placed in side-by-side configuration. The layer-2 consists of 3×3 square-shaped metasurface on one side and an octagonal slotted ring on another side. The combination of two layer results in wider bandwidths of 68.84% (2.21-4.53) and 3 dB axial ratio (AR) bandwidth of 30.4% (3.1-4.21 GHz). Furthermore, the antenna has better than 10 dB isolation, a maximum gain of 7.2 dBi at 4.04 GHz, radiation efficiency of more than 65%, and lower envelope correlation coefficient (ECC) values across the whole operating band. Diversity Gain (DG) values are high and near to 10 dB. Total Active Reflection Coefficient (TARC) and Channel Capacity Loss (CCL) values are also very much acceptable. As a result, the suggested four-element MIMO antenna is appropriate for midband 5G utilizations.

This paper presents a new simplified procedure to design a fourth-order coupled resonator filter. This procedure does not require the calculation of complicated Eigenvalues to develop the required coupling matrix. It starts with studying the effects of different coupling mechanisms on the performance of the overall filter structure. Then, these coupling mechanisms are combined to obtain the design of the required filter. This procedure may be more suitable for machine learning procedure to design coupled-resonator filters. The proposed method is used to design a substrate integrated waveguide (SIW) bandpass filter for sub-six GHz 5G applications. The designed SIW bandpass filter operates in the frequency range from 3.7 GHz to 3.98 GHz which covers the New C-band 5G network with a fractional bandwidth (FBW) of 28% and is centered at 3.84 GHz. This filter is fabricated and measured for verification.

This paper presents the design of dual-band spatial filter for shielding S band and X band wireless signals. The proposed Frequency Selective Surface (FSS) geometry consisting of a square loop convoluted with four strips positioned along the conducting loop. The FSS is aimed to reject WLAN/S-band (2.64 GHz) and X-band (8.3 GHz) wireless signals. The proposed FSS is tested for its angular stability by considering the wave incidence at various angles between 0˚ and 60˚. It is also tested for its polarization insensitive feature via TE mode and TM mode. The prototype FSS is printed on an FR-4 substrate with 1.6 mm thickness and the unit cell footprint of 14.8 mm and tested in an anechoic chamber. The working principle is explained through surface current distribution and the equivalent circuit model of the FSS. Measured results have better similarity with the simulated results.

A multiband electromagnetic band gap (EBG) structure is designed and implemented with a multiband MIMO antenna for mutual coupling reduction. An area of 16 × 16 mm² on a low cost FR4 substrate is used for the proposed EBG design. The designed E-coupled slotted U-shape MIMO antenna resonates at 5.7 GHz, 7.5 GHz and 10 GHz frequencies. Edge to edge separation between the two antennas is kept as 6 mm. EBG structure is placed in the ground plane between two antennas that enable us to keep separation of antennas less than the size of the EBG. Mutual coupling gets reduced by 6.6 dB for 5.7 GHz, 4 dB for 7.5 GHz and 6.95 dB for 10 GHz. Simulated radiation properties of MIMO antenna are verified by measured results, and surface current distribution of MIMO antenna surface also verifies the mutual coupling reduction. Envelope correlation coefficient < 0.01 and channel capacity loss < 0.2 are achieved at resonating frequencies.

The advantage of the canonical filter theory approach to design inductive power transfer (IPT) systems is that values for the coupled resonator elements are readily calculated from scaled canonical filter prototypes with specific frequency response characteristics. For example, Butterworth bandpass filter prototypes can be used to synthesize resonant-coupled IPT systems with critically-coupled frequency response characteristics. In this work, we analyze two canonical filter prototype structures: one prototype has series matching elements at the ports, and the other prototype has shunt matching elements at the ports. Equations are provided to transform the networks into coupled resonator structures that implement IPT links with a transmitter, receiver, and multiple repeater coils. The filter methodology for IPT link synthesis also provides an easy framework to evaluate design trade-offs. An example of comparing resonator inductor sizes for both the series and shunt matching topologies is shown for IPT links operating in ISM frequency bands of 6.78 MHz, 13.56 MHz, 27.12 MHz, and 40.68 MHz. Experimental results are shown for four different IPT examples that were designed using filter synthesis methods.

In this study, a compact, reconfigurable, and high-efficiency Long Range (LoRa) patch antenna, which is novel, is presented for Internet of Things (IoT) applications. The antenna is designed to operate at the three major frequencies used for LoRa communication, namely 915 MHz, 868 MHz, and 433 MHz, which are widely employed for global LoRa connectivity. The compact size and impedance matching of the antenna are achieved through the use of meandered radiating patches, a partial ground plane, and a ground plane stub. The antenna is prototyped on a commercially available and cost-effective FR-4 material and measures 80 mm x 50 mm x 1.6 mm (0.12λ x 0.07λ at the lowest resonant frequency), which is smaller than the size of a standard credit card. The antenna utilizes three RF PIN diodes (SW1, SW2, and SW3) for frequency reconfiguration, which are characterized by low insertion loss and fast switching time. The RLC equivalent circuit of the antenna was validated through simulations and measurements, yielding the peak gain and radiation efficiency of 2.1 dBi and >90%, respectively. These results prove that the antenna is a promising solution for LoRa IoT applications in terms of size, cost, and performance, filling a gap in the existing literature of LoRa MPAs that are typically large, non-reconfigurable, low-gain, and single-band.

Light is widely used in life science in both controlling and observing biological processes, yet a long-standing challenge of using light inside the tissue lies in the limited penetration depth of visible light. In the past decade, many in vivo light delivery methods using photonics and materials science tools have been developed, with recent demonstrations of non-invasive, deep-tissue light sources based on systemically delivered luminescent nanomaterials. In this perspective, we provide an overview for the principles of intravital nanoscopic light sources and discuss their advantages over existing methods for in vivo light delivery. We then highlight their recent applications in optogenetics neuromodulation and fluorescent imaging in live animals. We also present an outlook section about the feasibility of combining these non-invasive light sources with other modalities to expand the utilities of light in biology.

In this paper, a 24-element microstrip antenna array with three-dimensional near-field pattern shaping capability for microwave hyperthermia is presented. The antenna array operating at 2.45 GHz is designed based on the weighted constrained method of the maximum power transmission efficiency (WCMMPTE). By setting proper constraints for the electric field distribution of several selected points within the target area, the three-dimensional (3D) shape of the electric field can be characterized, meanwhile ensuring that the power is maximally concentrated in this area. Moreover, the shape, size, and spatial location of the three-dimensional area are all adjustable according to the selection of those specific points, making the array quickly adaptable for different actual requirements. The electric field distribution of the preset 3D shape can be focused at center or off-center with optimized excitations fed into the array. The measured electric field distribution shows that the transmitting array antenna is able to achieve a preset 3D shape of the electric field distribution as well as a preset offset position in the desired direction, agreeing very well with the simulations.