The Muscle Analyzer System (MAS) project wants to create a standalone microwave device that can assess the muscle quality, called the MAS device. To achieve that an algorithm that can derive the properties of skin, fat and muscle from the measurements is needed. This paper presents a machine learning algorithm that aims to do precisely that. The algorithm relies on first predicting the skin using the data from the MAS device, then predicting the fat again using the data from the MAS but also the predicted skin value and lastly the muscle is predicted using the microwave data together with the skin and fat predictions. Data have been collected in phantom experiments, materials that mimick the dielectric properties of human tissues. The algorithm is trained to predict the properties of said phantoms. The results show that the prediction for skin thickness works well, the fat thickness prediction is okay but the muscle prediction struggles. This is partly due to the error from the skin and fat layers are propagated to the muscle layer and partly because the muscle layer is farthest away from the sensor, which makes getting information from that layer harder.

Conditioning of a metal surface in a high-voltage system is the progressive development of resistance to vacuum arcing over the operational life of the system. This is relevant for accelerator cavities, where high level of performance is only achievable after a long conditioning period. Beyond the accelerator research field, this is an important topic for any technology where breakdowns can cause device failure, either by directly disrupting device operation or by causing cumulative hardware damage.

We are developing a direct method to measure the surface resistivity of a metal surface that is being conditioned with a HV DC system by inducing a high frequency (GHz) radio-frequency current in the parallel-plate electrode system. If the system can function as a resonant cavity, the surface resistivity data would be encoded in its quality factor (Q-factor). The changes in the resistivity measured in cryogenic conditions would indicate a formation of dislocations under the surface, something that has been speculated as an important process behind the conditioning.

In this paper, we present two modified designs of the electrode system, which will act as a resonant cavity, the results of 3D EM simulations and experimental results regarding the characterization of this resonant system.

This paper outlines the results of particle-in-cell simulations of a relativistic magnetron with six cavities and a transparent cathode configuration. Excitation of the π mode in the interaction region was attained, which in turn led to $\textrm{TE}_{11}$ mode emission of microwaves to the waveguide. This mode transformation was achieved with a non-symmetric diffraction output, consisting of four large and two small tapered cavities. Simulations were performed with a voltage across the anode-cathode gap varying from 164 to 356 kV, and axial magnetic field strengths between 0.24 and 0.34 T. Maximum efficiency of 37% was obtained with a peak output power of 590 MW, having a voltage of 261 kV and a magnetic field of 0.30 T. Furthermore, a frequency of 2.57 GHz and a rise time of microwaves at the waveguide of 15 ns were demonstrated. The electron leakage current was shown to decrease from ∼10$\%$ to less than $1\%$ when employing a longer interaction region, while still exhibiting good performance. Additionally, we show that there is an optimal range of voltages given a magnetic field, for which π mode excitation with high efficiency is attained.

This paper outlines an experimental demonstration of an envelope tracking (ET) technique applied to a kilowatt-level single-ended solid-state power amplifier (SSPA), aimed at enhancing the charging efficiency of superconducting radio frequency (SRF) cavities by reducing reflection power while maintaining a high degree of efficiency. The technique is particularly designed for the pulsed operation of the European Spallation Source (ESS) at a nominal frequency of 352 MHz, with a 5% duty cycle and a pulse width of 3.5 ms. The study introduces an optimal charging scheme using a solid-state-based amplifier to maintain high efficiency, allowing for power ramp-up while minimizing reflections from SRF cavities and optimizing SSPA efficiency. A fast envelope tracking power supply (ETPS) system is implemented for the approximately 300 ms charging time required by the SRF cavities at ESS. The ETPS system, demonstrated on a single module as a proof-of-concept with scalability potential to a 400 kW power station, indicates an overall average efficiency of 70% and a 24% energy saving over traditional vacuum-tube based amplifiers. This demonstrates the ET technique’s effectiveness at the kilowatt level for efficient SRF cavity charging with reduced reflection, offering significant efficiency and energy savings.

This paper presents a method for measuring whole-body specific absorption rate (WBSAR) of millimeter-wave base stations (BSs) in a reverberation chamber (RC). The absorbed power in the phantom from the equipment under test (EUT) and hence WBSAR is determined as the difference between the total radiated power with and without the phantom. A chamber transfer function is determined and used to include only the absorption in the phantom due to direct illumination from the EUT, i.e., excluding absorption due to the RC multipath reflections. The measurement method was evaluated at 28 GHz using a horn antenna and a commercial massive multi-input–multi-output BS. The experimental results are in good agreement with simulations. The proposed method allows for measurements of WBSAR within 3 minutes, which is much shorter than traditional approaches. The method is suitable for compliance assessments of BS products with the International Commission on Non-Ionizing Radiation Protection 2020 electromagnetic field exposure guidelines, which extend the applicability of WBSAR as basic restrictions up to 300 GHz.

The mining industry is heavily dependent on energy-intensive processes, such as rock breakage, which leads to significant operational costs. This paper explores microwave-assisted rock breakage as an innovative method to enhance the efficiency of comminution within the mining industry. It introduces a system that employs a Klystron microwave power source with a maximum output of 7.5 MW, using a $\mathrm{TM}_{010}$ single-mode cavity at 3 GHz, to channel energy inside a specially designed rock cavity. The paper emphasizes the importance of designing an efficient microwave cavity for this system, focusing on the cavity’s design and simulation. Through both simulated results (using HFSS software) and experimental observations, the study reveals the promising application of microwave technology in the field of mining. The simulated frequency response of the designed cavity (S11) is −22 dB, it demonstrates significant potential for reducing both energy consumption and associated costs. Additionally, the designed cavity is fabricated from aluminum and filled with polyether ether ketone material. The measured frequency response (S11) of the cavity at 3 GHz is −17 dB.

This study proposed an effective and sustainable technique for the curing of carbon fiber reinforced polymers (CFRPs) using microwaves. The method involves applying a metallic resonance coating layer to envelop the CFRP composite’s surface. Next, the composite is positioned within a multi-mode cavity, which is used as an applicator, and is powered by four 250 W solid-state power amplifiers. To ensure precise control over the heating pattern and achieve uniform heating of the composite, a sophisticated control algorithm is developed. This algorithm can independently regulate the phase, power level, and frequency of each power amplifier. The experimental results confirm the effectiveness of this proposed approach in achieving precise control over the microwave-based curing process for CFRPs.

This paper introduces an innovative conceptual design of a 400 kW solid-state power amplifier (SSPA) station and presents preliminary measurements for the key components. Recent advancements and benefits of solid-state technology have made the prospect of replacing vacuum tubes increasingly appealing. Historically, a significant challenge was the limited output power capacity of individual solid-state transistors, necessitating the integration of numerous units to generate high-power microwave signals in the range of hundreds of kilowatts. However, modern transistors capable of producing over 2 kW of output power have emerged, facilitating this transition. Another weak point was low power efficiency in high-power operating mode. The advanced rugged technology (ART) of solid-state devices enables the utilization of these transistors in nonlinear and switching operating classes, thereby enabling the creation of high-efficiency high-power amplifiers. In this conceptual design, 264 SSPA modules based on ART, each with a power output of 1.6 kW, are combined. The measurements revealed a single SSPA capable of delivering up to 2 kW output power with a power efficiency of 73% at frequency of 352 MHz. Due to the minimal losses during module combination and working SSPA in Class-C operation mode, the power efficiency of the station is expected to closely mirror that of a single module.

A single-layer polarization converting metasurface (PCMS) with wideband is presented for polarization conversion and radar cross-section (RCS) reduction. The proposed PCMS is composed of metallic biconic shape resonator imprinted on a metal-backed F4BM dielectric substrate of relative permittivity 2.2 and loss tangent 0.001. The unit cell has a compact size of 0.16$\lambda_\mathrm{o} \times 0.16\lambda_\mathrm{o}$. A comprehensive parametric analysis, angular sensitivity study, bistatic and monostatic RCS analysis are conducted by illuminating the proposed PCMS using linearly polarized (LP) plane waves. The PCMS converts LP electromagnetic waves to their orthogonal polarization state in the frequency band of 8.7–24.8 GHz resulting in polarization conversion ratio over 90% with a fractional bandwidth of 96%. Additionally, the developed structure is applied in chessboard configuration, using phase cancellation techniques for RCS reduction, that achieve 10 dB RCS reduction across a wideband of 7.9–23.4 GHz. The unit cell and its rotated version has a cross-polarization reflection phase difference of (${180}\pm {37}{^\circ}$) in the operating band, which fulfill the criteria for RCS reduction. The chessboard configuration exhibits a scattering pattern with four strong lobes that deviates from the normal incident path because of the phase cancellation in normal direction. The experimental results are in good agreement with the simulated result. Applications for the developed structure include antenna design (gain enhancement and beam steering), target hiding, imaging, and microwave communications.

This paper introduces a three-substrate layered transmitarray design that avoids the use of vias, aiming to produce broadband orbital angular momentum (OAM) vortex beams within the Ka-band. The suggested element configuration accomplishes a full 360∘ transmission phase while upholding a 1-dB transmission loss, with an overall thickness measuring 3.4 mm (equivalent to 0.34λ0 at 30.0 GHz). Its balanced unit cell arrangement amplifies its effectiveness in applications involving dual polarization. We examine the transmitarray behavior across four OAM modes (+1, +2, +3, +4 ), unveiling notable mode purity at operating frequency. Specifically, a broadband OAM vortex beam is achieved for the +1 mode during simulation. A square aperture transmitarray fed by a horn antenna is fabricated and measured to validate these simulated findings. Experimental results confirm the successful broadband vortex beam generation for $l = +1$ mode across the frequency spectrum from 27.0 to 40.0 GHz, approximately 43.3%. Additionally, the proposed transmitarray achieves a peak gain of 21.7 dBi, accompanied by an 11.8% aperture efficiency. Noteworthy is the consistent maintenance of mode purity above 86%.

In this paper, a novel polarization conversion metasurface (PCM) is proposed. Compared with the conventional receiver-transmitter metasurface units, two metallized via holes are set up to correct the current. It can achieve better polarization conversion from linear to circular and maintain a high reflectivity performance. A patch antenna with an L-probe feed is used as a feeder. The circularly polarized Fabry–Perot resonator antenna (CP-FPRA) consists of the PCM with a 5 × 5 array and a feeder. The measurements indicate a 3 dB axial ratio (AR) bandwidth of 8.6% (22.3–24.3 GHz). And it achieves a maximum gain of 14.2 dBic at 24 GHz, compared to the feed antenna has a gain enhancement of 5.5 dBi (from 8.7 dBi to 14.2 dBic). The proposed CP-FPRA has high gain, a wide AR, and a relatively low profile, providing ideas for subsequent antenna designs.

A compact microstrip eight-channel diplexer based on quad-mode stepped impedance resonator (QMSIR) is proposed in this paper. The proposed diplexer is composed by two second-order quad-band bandpass filters (BPFs) and common-port distributed coupling matching circuit. Each quad-band BPF is formed by two coupled-QMSIRs controlling the passband characteristics. By introducing multiple coupling paths between input and output ports, the isolation between the eight channels is performed. For demonstration, an eight-channel diplexer based on QMSIR is designed and fabricated with microstrip technology. The use of the QMSIR can lead to significant size reduction for the multiplexer, this is because the required resonator number is reduced. As a result, the diplexer occupies a compact size of 0.083λ2, which is smaller than most of the eight-channel diplexers that have been proposed. And the 3 dB fractional bandwidth is 97% (2.5–7.2 GHz). Measurement results correlate well with the simulated predictions, showing that a good isolation of better than 20 dB and upper stopband of better than 10 dB.

In this article, a coupled line diplexer (operating at 2.4 GHz and 3.5 GHz) which can be used as single-band filter with tunable attenuation characteristics in the pass band has been designed. Multilayer graphene (MLG) pads are used to achieve tunable features in this circuit. The graphene pads are placed at each branch of the diplexer. Single-band tunable attenuation characteristics are achieved by applying bias to graphene pads placed at optimum locations on the filter. The proposed tunable coupled line attenuating diplexer is realized on FR-4 glass epoxy substrate of thickness 1.58 mm with a total size of 45 × 75 mm2. By varying the bias voltage (0 V –6 V) of MLG pads the resistance of graphene pad placed in the circuit gets decreases thereby attenuating/controlling the transmission power to the other port in the required band. In lower pass band (2.28–2.55 GHz) the signal is attenuated from 3 to 10.8 dB and in higher pass band (3.2–3.58 GHz) signal is attenuated from 5 to 13 dB. Simulations of the structure with and without graphene pads have been carried out and are in good agreement with measured results.

A novel microstrip filtering antenna with slot coupling feed is presented in this work. An asymmetric interdigital coupling structure is used for the feed to excite the patch antenna through gap-fed coupling. Introducing a U-shaped slot on the patch surface modifies the current path to attain different resonant modes. The asymmetric coupled fingers in the low-frequency band generate a radiation null of −64 dBi, while additional resonances introduced in the high band broaden the bandwidth from 4.9 to 5.3 GHz. A horizontally shorted microstrip branch produces another null point of −28 dBi between the bands, enabling steeper roll-off and further improvement in frequency selectivity. The proposed filtering antenna provides a flexible filter response without requiring extra filtering circuits, with appreciable peak gains (6.1 dBi and 7.1 dBi) and stable radiation characteristics. This makes it suitable for WLAN (Wireless Local Area Network) and ISM (Industrial Scientific Medical) systems applications.

A compact dual layer conformal wearable quad band antenna is proposed for wireless body area network applications. The proposed button like patch antenna resonates at 2.5 GHz (industrial, scientific, and medical bands)/3.6 GHz sub six 5G band/5.75 GHz (wireless local area network/ISM band)/ and 9.8 GHz (X band) frequencies. The circular textile antenna is constructed with jean and polydimethylsiloxane substrate having a slotted ground of radius 10 mm and thickness 1.5 mm. The simulated gains obtained at the operating bands are 1.85/2.03/1.49/3.27 dBi, respectively. The designed antenna’s directed radiation pattern assures reduced backward radiation to body tissue. The specific absorption rate (SAR) analysis for the antenna at multiple resonant frequencies has also been reported, which are well below the SAR threshold of 1.6 W/kg for 1 gm of tissue, indicating that the model works adequately for wearable applications. The experimental characterization on- and off-body of the fabricated antenna validates the simulated results.

A compact 8-port eighth-mode substrate-integrated waveguide (EMSIW) multiple-input multiple-output (MIMO) antenna is presented in this paper. It consists of eight EMSIW cavities placed side by side sharing their open-ended edges which are separated by rectangular slots. High isolation (>22 dB) between the antenna elements over the entire operating band is obtained by the strategic placement of rectangular slots and vias. The open-ended region of EMSIW cavity resonator and the edges of the diagonal slots help in the excitation of TE110 mode at 5.5 GHz. The simulated bandwidth of MIMO antenna is 180 MHz, while the measured bandwidth is 220 MHz. The proposed MIMO antenna system has potential applications for sub-6 GHz communication systems.

Massive multiple input–multiple output (MIMO) antenna is required to meet the high data transmission rate in the current 5G and future 6G mobile communication. This paper presents a novel eight-port dual-band MIMO antenna operated within the 5G new radios N77 and N79 band. The designed MIMO incorporates a self-decoupling method to obtain high isolation of 22.96 and 25 dB at the two resonances 3.48 and 4.92 GHz, respectively. The basic antenna element consists of coupling between a staircase slot and a half-wavelength size loop branch. Additionally, an inverted U-shaped microstrip section is integrated with the radiating unit to serve the purpose of self-decoupling operation. The eight antennas are symmetrically located on the two narrow substrates (of size 5.8 × 150 mm2) as a pair of four arrays. The narrow substrates make the metal rim of the 5.5″ display mobile smartphone. The designed MIMO is practically realized and experimentally tested to validate the working mechanism. The envelope correlation coefficient and peak channel capacity are obtained as 0.174 and 35.5 bps/Hz in the lower frequency and 0.069 and 39.1 bps/Hz in the higher frequency.

In this research, a novel polarization reconfigurable fractal antenna with high gain is proposed for wideband applications. This antenna consists of a Koch curve based hexagonal ring patch, two Positive-Intrinsic-Negative (PIN) diodes, and partial ground. The patch is positioned on a Rogers RT/Duroid 5880 substrate (ϵr = 2.2) with overall dimensions 33 × 30 × 1.6 mm3. It has three frequency bands with three different cases i.e., case I, 3–7.91 (90%); case II, 3–7.73 (88.16%); and case III, 3.54–6.7 GHz (61.7%). As a result, the proposed antenna’s impedance bandwidth (IBW) offers constant wideband coverage ranging from 3–7.91 GHz (90%). The axial ratio bandwidth (ARBW) is below 3 dB over 3.6–6.9 (62.86%) and 3.33–7.14 GHz (72.78%) for LHCP (Case I) and RHCP modes (Case II), respectively. The value for LP mode (Case III) is 3.54–6.7 GHz (61.7%). A peak realized gains of 4.75, 5.07, and 3.8 dBi are achieved at 6.2, 6.3, and 6 GHz for Case I, Case II, and Case III, respectively. Both linear and circular polarization prototype was developed and the performance was verified through measurements. The design confirms good polarization-reconfigurable characteristics within the band of 3.91 – 7.91 GHz.

This paper presents a systematic design approach for developing a semiflexible multiple-input–multiple-output antenna system operating in the millimeter wave frequency spectrum, specifically designed for body-worn applications in biotechnologies. The designed antenna features dual flower-shaped antenna radiators placed in a spatial diversity configuration. Strategic modifications have been implemented by integrating dual crescent-shaped slots in the ground layer to attain the targeted frequency band of 25.7–30.6 GHz. Later, the upper edge of the ground plane is truncated in order to achieve circularly polarized radiation characteristics at 29.4 GHz with 3 dB ARBW of 0.6 GHz (29.1–29.7 GHz). The realization of circular polarization in the antenna geometry is validated through the analysis of characteristic mode theory. A maximum gain of 5.6 dBi is attained along with a port isolation of >30 dB. The proposed antenna undergoes analysis to assess its performance in the bending conditions and specific absorption rate, besides validation of diversity metrics encompassing envelope correlation coefficient, diversity gain, channel capacity loss, total active reflection coefficient, and mean effective gain has also been conducted. Finally, the proposed antenna structure is fabricated, and its performance is validated and subsequently compared with that of its simulated counterpart.