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Software-Defined Radios are radio communications devices that have been growing and developing on a larger scale in recent years. Communications are intrinsically embedded in our day by day, thus presenting a higher motivation to use software-defined radios due to its attractive cost. However they present technical limitations. This paper addresses this problem, which is the non-linearity behaviour of gain and frequency in the LimeSDR-USB. That is, this equipment is used to produce a FM signal with an associated frequency and gain before being parameterised according to the internal parameters of each software-defined radio. Each software-defined radio presents a value of frequency and gain of its own, which correlates to the generated signals at the output level. To avoid this, machine learning networks were used, in which networks were trained to adapt to the non-linearity of these devices and correct it without the user noticing. This way, the user sets a desired frequency and gain in a signal, at the output of the software-defined radios, and a neural network calculates which values the software-defined radios should be parameterised, thus mitigating the non-linearity behaviour. This paper presents the evaluation of a laboratory prototype based on low-cost commercial software-defined radios equipment, to replace an expensive metrologically calibrated equipment used for radio frequency tests on a new concept of industrial test station, with description of the integration of Digital Twins, with their physical and virtual parts. [ABSTRACT FROM AUTHOR]

With 5G and millimeter-wave technologies evolving rapidly, the high communication frequency leads to high integration and miniaturization of the Luneburg lens (LL). In this paper, a miniaturized K-band flat LL with 0.95MgTiO 3 –0.05CaTiO 3 (95MCT) ceramic was designed and successfully printed by vat-photopolymerization 3D printing. Optimal 3D printing parameters and thermal treatment processes of 95MCT ceramic were investigated. The as-prepared 95MCT ceramic showed excellent properties: a density of 3.40 g/cm3, a high flexural strength of 81.78 MPa, a dielectric constant of 17.7, and a remarkably low dielectric loss value of 4.56 × 10-4. Based on the 95MCT ceramic, a flat LL with a diameter of 40 mm and thickness of 6 mm was printed with sophisticated metastructure. While miniaturization was accomplished with a high degree of dimensional compression, the printed flat LL showed a maximum gain enhancement over 5 dBi. Thus, this study provides a novel viewpoint on the fabrication of microwave dielectric ceramic and miniaturized ceramic radio frequency (RF) devices with complex structures. [ABSTRACT FROM AUTHOR]

This paper proposes a novel direct detection lidar compatible with software-defined radio, which can effectively absorb the advantages of radio frequency technology. The radio frequency signal is firstly loaded onto the output light of the lidar through a fiber phase modulator and then demodulated from its backward reflected light through a combination of fiber Fabry-Perot interferometer and photodetector. The generation of the transmitting radio frequency signal and the sampling and processing of the receiving radio frequency signal are completed by a software-defined radio. Theoretically, it has been proven that the range and velocity of the target cause phase delay and Doppler frequency shift of the radio frequency signal loaded on the lidar, just like using the radio frequency signal to directly detect the target in radar. In the experiment, by programming the software-defined radio, the ranging and velocimetry algorithms of radar have been applied to this lidar. The theoretical and experimental results indicate that the lidar proposed in this paper has software definable characteristics. Through programming, different functions can be achieved, and in the future, more advanced algorithms of radar can be easily transplanted to further improve its performance. • We stall radar with Software-Defined Radio as component on a direct detection lidar. • The advantages of radar improve direct detection lidar detection capability. • The software of advanced radar algorithm upgrades the functionality of direct detection lidar. [ABSTRACT FROM AUTHOR]

Visible light communication (VLC) is a disruptive technology that uses light-emitting diodes (LEDs)/LASERs to transmit data wirelessly using visible light spectrum. VLC has many potential applications in various domains such as indoor wireless networking, vehicular communication, underwater communication, and smart lighting. VLC offers advantages such as free spectrum, high data rate, low power consumption and security. However, VLC also faces some challenges such as limited coverage range, interference from ambient light sources and mobility issues. In this paper, we present a comprehensive state-of-the-art survey of VLC, covering its physical aspects and communication architecture. We also discuss its main applications and research challenges in different scenarios. Furthermore, we review the main research platforms available today for VLC experimentation and evaluation. Finally, we highlight the future directions and open issues in this emergent field. • Visible light communication provides a revolutionary method of wireless communication that has numerous advantages over standard radio frequency based systems. • We investigated the current state-of-the-art in VLC research in this review article, covering recent breakthroughs in VLC technology, its applicability in various industries, and the problems that still need to be solved. • While there is still much work to be done, tremendous progress has been achieved in the field, and it is obvious that VLC will play a big part in the development of next- generation wireless networks. • As researchers continue to investigate new VLC systems and applications, we may anticipate even more exciting breakthroughs in this subject soon. • We hope that this paper will serve as a useful reference for researchers and practitioners who are interested in VLC and its potential impact on future 6G networks. [ABSTRACT FROM AUTHOR]

• Enhanced security risks are emerging from handling of numerous UAVs (drones), especially in particularly crowded areas or areas of strategic importance for national security. • Implementing drone detection systems can involve various sensor types, including imaging, radar, acoustic, and radio frequency (RF) sensors. Localizing the target drone through direction finding (DF) methods is a crucial aspect of these systems. • An RF-based direction-finding testbed (employing a DJI Mavic Air UAV as target, software defined radio (SDR) platforms from the USRP family as hardware and MUSIC as signal processing algorithm) is designed and experimentally assessed. • The measurement scenarios include a static one (46 selected points) and a dynamic one (38 selected points) measured in approx. 15 mins (total flight time), determining Latitude, Longitude, Altitude (relative to sea level), and Height (above ground). • The testbed's performance is assessed by comparing the direction derived from the drone's flight record with that estimated using the proposed testbed. This comparison yields an average estimation error of 1.15 degrees from the drone's actual position for the static scenario and of 1.86 degrees for the dynamic one, highlighting the successful implementation of this approach. Nowadays, drones, also known as unmanned aerial vehicles (UAVs), are used for a wide range of purposes in the civil, industrial, and military domains. The greater the number of UAVs, the more serious the potential security risks correlated to them. To address these risks, it became necessary to develop systems that can detect, locate, and possibly neutralize such an object. The detection can be performed using different sensors such as imaging, radar, acoustic, and radio frequency (RF) sensors. The localization of the target drone, which can be done using direction finding (DF) methods, is an essential part of such a system. Thus, an RF-based DF testbed is designed and experimentally assessed in this paper. The testbed is implemented using software defined radio (SDR) platforms from the Universal Software Radio Peripheral (USRP) family as hardware equipment, and the MUSIC algorithm for processing the signals received on four different phase-coherent RF channels. A DJI Mavic Air UAV is used as target. For assessing the DF estimation performance, the direction obtained from the drone flight record is compared with the one estimated using the proposed DF testbed. Two different scenarios, a static one and a dynamic one, are considered to highlight the effectiveness of the proposed DF testbed across various conditions. The obtained results indicate an average estimation error of 1.15 degrees from the drone's actual position, in the case of the static scenario, and of 1.86 degrees in the case of the dynamic scenario, results which are on parity with or surpassed those of other drone DF systems described in the literature. The paper also outlines the benefits and challenges of the current approach. [ABSTRACT FROM AUTHOR]

This paper presents a 39-GHz broadband image-rejection down-conversion mixer for 5G millimeter-wave (mmWave) communication. To achieve a broadband image rejection, this paper proposes an on-chip compact transformer-based image-rejection filter, which exhibits the ability to track the pole and zero frequencies simultaneously. Moreover, the working mechanism and design guideline of the transformer-based image-rejection filter are illustrated with theoretical analysis, simulations and measurements. To enhance the mixer linearity performance, the transconductance stage of the conventional Gilbert mixer is utilized as a current source, and the radio frequency (RF) signal is directly fed into the switching stage. Fabricated in a 65-nm CMOS process, using a single-stage image-rejection filter with a compact area of only 0.013 mm2, the measurement results show that the proposed down-conversion mixer achieves a gain of 0 dB, a 3-dB RF bandwidth from 34 to 42 GHz, an input 1-dB compression point (IP 1dB) of 5.6 dBm, and an image rejection ratio (IRR) of about 25 dBc. [ABSTRACT FROM AUTHOR]

This paper presents and compares the implementation of a digital predistortion (DPD) linearizer for radiofrequency power amplifiers (PAs) considering two different hardware acceleration platforms. Both graphics processing unit (GPU)-based and field programmable gate arrays (FPGA)-based implementations of the DPD are capable to meet the high throughput requirements for linearizing the PA with current 5G new radio (NR) wideband signals. A comparison in terms of hardware resources usage, precision, throughput and linearization performance is provided for both GPU and FPGA implementations of a DPD based on the generalized memory polynomial (GMP) behavioral model. [Display omitted] • This paper focuses on the implementation of the GMP DPD model in both FPGA and GPU. • A trade-off among precision, resources usage and throughput performance is given. • The DPD performance is validated with a SLMBA with a hardware-in-loop test setup. [ABSTRACT FROM AUTHOR]

[Display omitted] Applications emitting radiofrequency electromagnetic fields (RF-EMF; 100 kHz to 300 GHz) are widely used for communication (e.g. mobile phones), in medicine (diathermy) and in industry (RF heaters). The objective is to systematically review the effects of longer-term or repeated local and whole human body radiofrequency electromagnetic field (RF-EMF) exposure on the occurrence of symptoms. Primary hypotheses were tinnitus, migraine and headaches in relation to RF-EMF exposure of the brain, sleep disturbances and composite symptom scores in relation to whole-body RF-EMF exposure. Eligibility criteria: We included case-control and prospective cohort studies in the general population or workers estimating local or whole-body RF-EMF exposure for at least one week. Information sources: We conducted a systematic literature search in various databases including Web of Science and Medline. Risk of bias: We used the Risk of Bias (RoB) tool developed by OHAT adapted to the topic of this review. Synthesis of results: We synthesized studies using random effects meta -analysis. Included studies: We included 13 papers from eight distinct cohort and one case-control studies with a total of 486,558 participants conducted exclusively in Europe. Tinnitus is addressed in three papers, migraine in one, headaches in six, sleep disturbances in five, and composite symptom scores in five papers. Only one study addressed occupational exposure. Synthesis of results: For all five priority hypotheses, available research suggests that RF-EMF exposure below guideline values does not cause symptoms, but the evidence is very uncertain. The very low certainty evidence is due the low number of studies, possible risk of bias in some studies, inconsistencies, indirectness, and imprecision. In terms of non-priority hypotheses numerous exposure-outcome combinations were addressed in the 13 eligible papers without indication for an association related to a specific symptom or exposure source. Limitations of evidence: This review topic includes various challenges related to confounding control and exposure assessment. Many of these aspects are inherently present and not easy to be solved in future research. Since near-field exposure from wireless communication devices is related to lifestyle, a particular challenge is to differentiate between potential biophysical effects and other potential effects from extensive use of wireless communication devices that may compete with healthy behaviour such as sleeping or physical activity. Future research needs novel and innovative methods to differentiate between these two hypothetical mechanisms. Interpretation: This is currently the best available evidence to underpin safety of RF-EMF. There is no indication that RF-EMF below guideline values causes symptoms. However, inherent limitations of the research results in substantial uncertainty. Funding: This review was partially funded by the WHO radioprotection programme. Registration: The protocol for this review has been registered in Prospero (reg no CRD42021239432) and published in Environment International (Röösli et al., 2021) [ABSTRACT FROM AUTHOR]

In this paper, we show the mathematical equivalence of two popular modulation schemes: OSDM and OTFS. The former is mainly used in underwater acoustic communications, while the latter scheme is a promising modulation technique in radio-frequency communications. Although literature suggests a link between the two modulation schemes by connecting them to related modulation schemes like V-OFDM and A-OFDM, to the best of the authors' knowledge, a direct mathematical comparison between the schemes has not been presented yet. The main purpose of this paper is therefore to show the mathematical equivalence of the two schemes. In addition, by combining the knowledge of acoustic and radio-frequency communications, we give insight in the performance of OSDM/OTFS in terms of intersymbol interference (ISI) and intercarrier interference (ICI) by analyzing its signal structure. • The OSDM scheme is mathematically equivalent to the OTFS scheme used in literature. • OSDM/OTFS spreads symbols over time–frequency, yielding diversity gains over OFDM. • OSDM/OTFS sequences are not orthogonal in channels with Doppler shifts and delays. [ABSTRACT FROM AUTHOR]

In this paper, the p-GaN/n-In 0.27 Al 0.73 N heterojunction light-emitting diode (LED) was fabricated by radio frequency magnetron sputtering (RF-MS) and the electroluminescence (EL) characteristics of the p-GaN/n-In 0.27 Al 0.73 N heterojunction diode was investigated. Based on the preparation of the In X Al 1-X N thin films at different substrate temperatures (Ts), the crystal structure, optical and electrical properties were investigated by XRD, SEM and other material characterization techniques. With increasing Ts, the grain size and surface morphology of the In X Al 1-X N thin films change dramatically. The film has the best optical and electrical properties when the Ts is 300℃. On the basis of this, the compositional content of indium in the In X Al 1-X N film was calculated to be 0.27. The heterojunction LED was fabricated on a commercial p-GaN substrate and the In 0.27 Al 0.73 N alloy film. The EL was successfully achieved at various forward and reverse voltages at room temperature and the temperature-dependent EL has been investigated. Furthermore, research is being conducted on the characteristics of the interface of p-GaN/n-In 0.27 Al 0.73 N heterojunction and the elucidation of the light-emitting mechanism of diode. The present work uses a simple and low-cost RF-MS method to fabricate UV/Violet bidirectional drive p-GaN/n-In 0.27 Al 0.73 N heterojunction LED, which provides a new reference for the fabrication of LED using In X Al 1-X N alloy material. [Display omitted] • The UV-violet bidirectional drive LED was fabricated by radio frequency magnetron sputtering. • The EL behavior was studied under different voltages of different magnitude (20–100 V) and different polarities. • The temperature-dependent EL characteristics of the LED were investigated under forward and reverse voltages @100 V. • The luminescence mechanism of the LED was investigated based on the energy band and Gaussian peak fitting. [ABSTRACT FROM AUTHOR]

This paper proposes a closed-loop detection and guidance method for optimizing the detection effectiveness of Radio Frequency (RF) stealth targets by terminal-guided hypersonic glide vehicles (HGV) during the terminal-guidance phase. This method divides the guidance process into two stages based on the detectability of the target. In the search stage, the Twin Delayed Deep Deterministic Policy Gradient (TD3) coupled with Successive Convex Optimization (SCO) guidance method is employed. This approach separates the detection performance from the numerical solution process of the optimization problem, enabling online adjustment of performance indicator functions to refine trajectory configurations. In the tracking phase, the dynamic characteristics of the target's Radar Cross Section (RCS) are convexified and discretized, incorporated into the objective function of the optimization problem as performance indicators. The Higher-Order Soft-Trust-Region Sequential Convex Programming (HSSCP) method is employed to improve the convergence of the algorithm. Additionally, the online trajectory planning problem is integrated into the Model Predictive Control (MPC) framework to achieve closed-loop guidance. Simulation results indicate that this method can improve the detection performance of RF stealthy targets during the terminal guidance phase, the cumulative detection information for the target increased by approximately 20.6%, and the maximum instantaneous detection probability improved by about 14.3%. Moreover, it can achieve convergence of complex multi-constraint problems within a limited number of iterations. • Trajectory reconstruction can enhance the detection capability of RF stealth targets. • Second-order soft trust-region SCP achieves rapid convergence. • MPC-SCO closed-loop guidance demonstrates a certain level of robustness. • The TD3 algorithm with adaptive SCP optimizes detection of targets with unknown states. [ABSTRACT FROM AUTHOR]

Early ultrasound screening for breast cancer reduces mortality significantly. The main evaluation criterion for breast ultrasound screening is the Breast Imaging-Reporting and Data System (BI-RADS), which categorizes breast lesions into categories 0–6 based on ultrasound grayscale images. Due to the limitations of ultrasound grayscale imaging, lesions with categories 4 and 5 necessitate additional biopsy for the confirmation of benign or malignant status. In this paper, the SAE-Net was proposed to combine the tissue microstructure information with the morphological information, thus improving the identification of high-grade breast lesions. The SAE-Net consists of a grayscale image branch and a spectral pattern branch. The grayscale image branch used the classical deep learning backbone model to learn the image morphological features from grayscale images, while the spectral pattern branch is designed to learn the microstructure features from ultrasound radio frequency (RF) signals. Our experimental results show that the best SAE-Net model has an area under the receiver operating characteristic curve (AUROC) of 12% higher and a Youden index of 19% higher than the single backbone model. These results demonstrate the effectiveness of our method, which potentially optimizes biopsy exemption and diagnostic efficiency. • A breast lesions classification method based on ultrasound radio frequency signal. • The proposed SAE-Net combines the microstructure with morphological information. • Improving the identification of breast lesions with BI-RADS category 4 or higher. • Potentially optimizes biopsy exemption and diagnostic efficiency. [ABSTRACT FROM AUTHOR]

Coated superconducting radio-frequency (SRF) cavities are planned to be implemented in the Future Circular Collider (FCC) at the European Organization for Nuclear Research (CERN). The interest in industrialized and high-performance processes for fabrication of the corresponding copper substrates has thus risen. Tubular hydroforming is a well-known industrial process, but has not been thoroughly applied for ultra-pure oxygen-free electronic copper (Cu-OFE) thick products. To provide a feasibility analysis for the optimized fabrication process of copper substrate seamless cavities, a Forming Limit Diagram (FLD) of the material of interest was studied. In this paper, the methodology, test results and initial benchmark of the material model is presented, for 4 mm and 2 mm thick sheets. • Comprehensive material characterization of annealed Cu-OFE sheets reveals key properties for SRF applications. • Developed simplified Forming Limit Curve (FLC) and Fracture Forming Limit (FFL) for Cu-OFE thick sheets. • Established necking thresholds for Cu-OFE sheets using three different criteria, from less to more conservative. • Introduced a simplified method to determine the SFFL and FFL limits for Cu-OFE sheets thanks to the effective area of fracture. • Proposed the concept of 'SRFLD', integrating surface roughness, material defects, and hardness into the Forming Limit Diagram. [ABSTRACT FROM AUTHOR]

Radio Frequency (RF) energy harvesting has been used to power wireless and low-powered devices. However, RF energy harvesting has limitations in terms of the amount of power that can be collected based on signal availability. Hence, energy prediction is essential to improve energy harvesting circuits' performance. Previous research has mainly focused on improving power harvesting policies or theoretically estimating the harvested energy. Very few works have considered the prediction of the RF signal as time series data using real RF measurements. Moreover, challenges such as the power consumed by the circuit's harvesting decisions and the impact of outliers on the model performance haven't been addressed yet. This paper presents a complete pipeline for developing the best predictive model for RF energy in cellular frequency bands. Real-time measurements are taken in different frequency bands using software-defined radio technology. We use four artificial intelligence techniques to model the RF energy signal. Additionally, we propose an optimized model with an enhanced loss function, which makes the model more resilient to anomalies, saving computational power and time consumed in cleaning the data. The four algorithms are investigated, and their prediction accuracies are compared. The average power of a period of 5 min is accurately forecasted. Numerical results in the 1960 MHz band show that long short-term memory has the best performance, followed by the DeepAR algorithm with prediction accuracies of 95.76% and 95.02%, respectively. Moreover, the proposed optimized model showed a 32.2% lower prediction error than the traditional models. [ABSTRACT FROM AUTHOR]

A photonics-based radar jamming signal generator is proposed in this paper. By adjusting a polarization controller, interrupted-sampling repeater jamming (ISRJ), comb spectrum modulation jamming (CSMJ), ISRJ and CSMJ composite jamming can be respectively generated after photoelectric conversion. We have experimentally verified the generation of ISRJ signals with duty cycles of 50% and 25%, the generation of CSMJ signals with comb spectrum frequency intervals of 5 MHz and 10 MHz, and the generation of their composite jamming signals in the Ku band. Additionally, the ISRJ and CSMJ composite jamming effect of radar signals in the Ka band has been tested. After matched filtering processing, multiple false targets are produced and the total number of jamming targets can be up to 25, demonstrating significant jamming effects. The proposed structure can generate multi-format jamming signals without using digital radio frequency memory, which is suitable for producing high-frequency and large-bandwidth jamming signals. It can be applied in electronic countermeasure systems. • The scheme can generate multi-format jamming signals for LFM signal, namely interrupted-sampling repeater jamming (ISRJ), comb spectrum modulation jamming (CSMJ), ISRJ and CSMJ composite jamming. • The scheme does not use digital radio frequency memory, which is easy to generate high frequency and large bandwidth jamming signals. The experimental results show that the LFM signal with 1-GHz bandwidth in Ku band and the LFM signal with 1.2-GHz bandwidth in Ka band have good jamming effects. • After matched filtering processing, multiple false targets are generated and the total number of jamming targets can be up to 25, demonstrating significant jamming effects. The scheme has good application value in electronic countermeasure system. [ABSTRACT FROM AUTHOR]

The existing radar-communication coexistence (RCC) waveform design based on chirp signal causes the increase of the complexity in the communication receiver, and multi-dimensional reuse also introduces more interference, leading to the deterioration of dual function performance. In this paper, a frequency division RCC system with on-off keying (OOK) based on frequency modulated continuous wave is designed for near sensors wake-up or low rate broadcast. The RCC signal has the fixed whole band and the variable sub-bands for radar signal and communication signal. We propose a two-stage envelope detection (TSED) scheme by extracting data from the frequency difference component of the two signals at the receiver without generating local radio frequency signal or using a mixer. By flexibly regulating the frequency band of two signals, the anti-interference ability of TSED can be further improved. In radar system, we perform small frequency hopping (FH) on radar signal to realize the full use of the whole band, and propose a scheme of abnormal peak detection and elimination (APDE) to eliminate the chirp interference. The simulation results show that the signal-to-interference ratio of TSED scheme for the RCC waveform can be respectively enhanced by 6 dB and 2 dB if compared with that of conventional envelope detection and coherent demodulation with a bit error rate of 10−5. Besides, The APDE scheme based on small FH reduces the range sidelobe by 20 dB and completely eliminates the added in-band interference. [ABSTRACT FROM AUTHOR]

The China initiative Accelerator Driven System (CiADS) requires a stable phase reference distribution system (PRDS) to provide low-drift reference signals for over 300 radio-frequency (RF) clients on its superconducting linac and beam transport lines. PRDS is realized using a coaxial cable that transmits 162.5 MHz reference signals, and the phase averaging technique will be employed to counteract phase drift caused by changes in the cable length due to temperature variations. This paper analyzes the limitations of the current technical approach and proposes an improvement based on a bi-line structure with unidirectional transmission of the reference signal and front-end phase locking. The design of the PRDS for the CiADS and signal processing in the low level radio-frequency (LLRF) system are detailed. The feasibility of the new scheme is verified by testing a prototype PRDS. [ABSTRACT FROM AUTHOR]

• A water-cooled discharge tube of RF plasma driver for NBI application was proposed to avoid using the Faraday shield inside the driver. • Two types of the water-cooled tube have been carefully designed: the alumina ceramic welded structure and the silicon nitride ceramic bonding structure. • Some key manufacturing technologies have been tested and inspected, for example, tensile test of ceramic sealing, scanning electron microscope for ceramic. • The prototypes of both types of the water-cooled tube have been successfully manufactured. And the prototype with the alumina ceramic welded structure was conducted a plasma discharge test. A radio frequency (RF) driven ion source is favorable for high-power and long-pulse neutral beam injection (NBI) system. To reduce the damage caused by the isotropic heat and particle fluxes from the plasma, the traditional RF plasma driver of the NBI ion source introduces a Faraday shield (FS) for protection. However, the simulations and experiments show that the FS seriously affects the RF coupling and around 50 % of the input power deposits on the FS. The water-cooled discharge tubes with a double-layer ceramic structure have been developed to avoid using the FS structure. It's expected to improve the RF power transfer efficiency and to promote the development of high-power and long-pulse RF ion source. To verify the feasibility of the double-layer ceramic structure, the paper has carried out the fluid-thermal-structural coupling analysis and the fracture mechanical analysis on two proposed types: the alumina ceramic brazing structure and the silicon nitride ceramic bonding structure. The sample tests and the prototype manufacturing have been completed. Preliminary tests of the plasma discharge on the prototype of the alumina ceramic brazing structure have been launched. A plasma discharge of 30 kW and 20 s have been achieved. [ABSTRACT FROM AUTHOR]

[Display omitted] • InP Double-Heterojunction Bipolar Transistors (DHBTs) on a 3-inch InP substrate is demonstrated through stepper-based photolithography. • The fabricated DBHTs with W E = 0.6 μm and L E = 15 μm exhibits current gain = 50 at V CE = 1.0 V and an open-base common-emitter breakdown voltage of 5.7 V at J C = 0.01 mA/µm2. • The uniformity of the fabricated DHBT with W E = 0.6 μm and L E = 15 μm shows β = 49.3 ± 1.9, f T = 241.4 ± 3.8 GHz, and f max = 221.5 ± 4.0 GHz, respectively. In this paper, InP Double-Heterojunction Bipolar Transistors (DHBTs) on a 3-inch InP substrate is demonstrated through stepper-based photolithography. The performance of the fabricated InP DHBTs such as DC characteristics, high-frequency characteristics, and uniformity of the 3-inch wafer is investigated to verify the stepper-based fabrication process. To improve the high-frequency characteristics, the self-aligned base-emitter contact is realized by using the high height-to-width ratio and vertical sidewall emitter profile of the Au electroplating process. The fabricated DHBTs with W E = 0.6 μm and L E = 15 μm exhibits current gain (β) = 50 at V CE = 1.0 V and an open-base common-emitter breakdown voltage (BV CEO) of 5.7 V at J C = 0.01 mA/µm2 and 7.5 V at J C = 0.1 mA/µm2, respectively. Moreover, the fabricated DHBTs with W E = 0.6 μm and L E = 15 μm show excellent f T of 244 GHz and f max of 221 GHz at J C = 4.4 mA/μm2 and V CE = 1.6 V. In order to evaluate the uniformity of the fabricated DHBTs, we measure current gain (β) and high-frequency characteristics with W E = 0.6 μm and L E = 15 μm and the average values and standard deviation of the β, f T , and f max are β = 49.3 ± 1.9, f T = 241.4 ± 3.8 GHz, and f max = 221.5 ± 4.0 GHz, respectively. Thanks to the optimized stepper-based fabrication process, the fabricated InP DHBTs exhibit well-balanced high-frequency characteristics and excellent uniformity. [ABSTRACT FROM AUTHOR]

• Introduction of EWOD pump as a microfluidic alternative to mechanical ones. • Exploring integrating microfluidic pumps with RF for versatility. • Presenting analytical model for EWOD semi-continuous pump, filling fluid mechanics and actuation dynamics gap. • Significance of the model in optimizing EWOD-based pumps for control and understanding processes. • Impact of electrode configuration on motion smoothness and friction variation in EWOD. • Tool for understanding electrowetting, friction, and inertia in EWOD. An electrowetting on dielectric (EWOD) pump is a microfluidic pump that uses electrowetting to manipulate liquid droplets in a channel, offering an alternative approach to traditional mechanical pumps. EWOD-based pumps have significant potential for various microfluidic applications. For instance, by integrating microfluidic pumps with a radio frequency (RF) device, it is possible to create a microfluidic reconfigurable RF device. However, the current microfluidic-based devices have been primarily designed based on mechanical micropumps which require expensive clean-room fabrication methods. Here, we present an analytical model for an EWOD semi-continuous pump that can offer a promising alternative actuation for microfluidic actuation. However, a literature survey of recent advances in EWOD pumping has highlighted a gap in the modeling of the relationship between the fluid mechanics and the actuation dynamics. This paper presents an analytical model of an EWOD pump that determines the flow rate and pressure generated by taking into account the competing electrowetting force, friction force, and fluid inertia force in a one-degree-of-freedom channel. The analytical model is valuable for designing and optimizing EWOD-based pumps, as it provides insights into the dominant physical processes and could enable better control. The model is validated with an EWOD experiment and the data demonstrates less than a 6 % error between the measured and predicted maximum droplet velocity and a maximum 7.4 % error in the EWOD pump static pressure. [ABSTRACT FROM AUTHOR]

Determining the carbonation depth is of paramount importance in assessing the durability of cementitious materials as the carbonation process alters their near-surface physicochemical properties. This paper introduces a novel quantitative ultrasound (QUS) technique capable of nondestructively identifying the carbonation depth, regardless of the tortuosity of the carbonation front. A 2.5 MHz phased array transducer was employed to construct beamformed radio frequency images and measure two microstructure-dependent parameters – spectral slope (SS) and spectral intercept (SI) – based on backscatter and attenuation coefficients. The change in obtained SS and SI were then visualized as QUS images, which displayed the geometry of the carbonation front, correlating with images constructed using a phenolphthalein solution (1.6 mm difference in depth). Mineral compositions and porosities were analyzed to account for microstructural changes in each layer. This study opens an opportunity for nondestructive detection of carbonation depth, overcoming the limitations in conventional methods or regression-based approaches. • Quantitative ultrasound (QUS) technique is developed for detecting carbonation depth. • QUS images achieved based on scattering and attenuation phenomena confirm densification in carbonated layer. • Upon the QUS images, the measured carbonation depth shows great agreement with results from phenolphthalein solution. • Mineral compositions and porosities were evidenced by TG, MIP, XRD, and QXRD analyses. • The proposed method offers potential for visualizing ambiguous geometry of inclusions in cementitious materials. [ABSTRACT FROM AUTHOR]

Pre-made carrots are fresh and ready to eat or to be cooked. However, processing steps such as washing, peeling, and slicing often result in juice loss and microbial contamination. In this study, an optimal combination between nisin and radio frequency (NRF) for synergistic processing of pre-made carrots was proposed by orthogonal tests. Pre-made carrots were separately treated by NRF, single nisin or radio frequency (RF), nisin and ultrasonic waves (NUW), or blanching, and then the total bacterial count, physiological quality, and physical microstructure during storage were compared between groups. The results showed that NRF treatment effectively inactivated bacteria (Staphylococcus aureus, Bacillus subtilis, and Escherichia coli) and extended the shelf life of pre-made carrots to 42 days. Carotenoids and ascorbic acid were considerably retained. The whiteness index and unacceptable odor of pre-made carrots were also significantly suppressed. Scanning electron microscopy (SEM) showed that the cellular microstructure of NRF-treated pre-made carrots had slight curling and folding, which was superior to NUW or blanching treatments. Pearson correlation analysis found that there were different correlations between the quality of pre-made carrots with different treatments. Therefore, the experimental results of this paper can provide help for food processing industry to produce high-quality pre-made carrots, and even other pre-made foods as well. • Pre-made carrots are nutritious and convenient food. • NRF showed a synergistic effect on bacteriostasis. • NRF increased bacteria inactivation and maintained physiological quality. • NRF prolonged the shelf-life of pre-made carrots. [ABSTRACT FROM AUTHOR]

Radio frequency (RF) is a novel food processing technology, which has the advantages of strong penetration and uniform heating. The temperature of RF processing is typically not high (70–90 °C), which has little damage to the sensory quality of food and is very suitable for ready-to-eat foods for pasteurization and quality maintenance. Because of its relatively low temperature and suboptimal pasteurization effect, RF is often used in conjunction with other novel processing approaches to enhance its efficacy. This paper reviews the applications of RF in combination with additives, active packaging, conventional heat treatment, vacuum and other electromagnetic wave (EW) technologies in foods processing in the last five years. The mechanisms behind tissue integrity-induced changes in ready-to-eat, ready-to-heat, ready-to-cook, ready-to-use food texture (e.g., hardness, firmness) and corresponding changes in chemical composition were elucidated during novel assisted RF technologies compared to conventional heating methods. Future research regarding continuous industrial-scale production and innovative applications is required. [Display omitted] [ABSTRACT FROM AUTHOR]

Hot air (HA) drying caused quality damage of grains with long treatment time. Radio frequency (RF) heating as an emerging technology was applied to improve drying quality of cereals effectively. The effects of HA-RF drying (50 °C, 70 °C, 90 °C) of corn kernels on the morphology, structure, and physicochemical properties of starch were investigated and compared with HA drying. The surface of treated starch became rough, along with fragments and pores. Drying treatments increased the amylose content from 10.59 % to 23.88 % and the residual protein content of starch from 0.58 % to 1.23 %, and reduced the crystallinity from 31.95 % to 17.15 % and short–range order structures of starch from 0.918 to 0.868. The change of structures in turn resulted in the increase of pasting viscosity, gelatinization temperature, storage modulus and loss modulus. Furthermore, the HA-RF dried starch displayed stronger thermal stability, higher gelatinization degree and better gelation properties than the HA-treated starch at the same temperature. The data proved that the synergistic effects of HA and RF were more effective in modulating the starch structure and improving the functional characteristics of corn starch. This paper would like to provide potential reference for better application of HA-RF technologies to corn. [Display omitted] • HA and HA-RF increased particle size and decreased crystallinity of starch. • Both HA and RF reduced the short–range order structures of corn starch. • Heated corn starch displayed stronger thermal stability and gelation properties. • HA-RF drying markedly elevated the pasting viscosity and temperature of starch. • HA-RF treatment was more effective in altering starch property than single HA method. [ABSTRACT FROM AUTHOR]

Dual-function radar and communications (DFRC) systems based on multiple-input multiple-output (MIMO) arrays have received considerable attention in recent years due to their excellent ability to alleviate spectrum congestion. The MIMO DFRC systems enable high-resolution detection of multiple targets while communicating with multiple users simultaneously. However, MIMO arrays require numerous radio frequency (RF) units and suffer a strong mutual coupling among antennas, resulting in significant system overhead and performance degradation, respectively. In light of this, this paper investigates the joint optimization of transmit precoding and antenna selection for MIMO DFRC systems, aiming to improve the angular ambiguity function with a guaranteed communication quality of service (QoS) using a small number of antennas. To address the resultant non-convex optimization problem, both the indirect and direct precoding methods are proposed. In the former, the waveform covariance and antenna selection vector are first jointly optimized via a promoted sparsity along the covariance diagonal, followed by the precoding matrix indirectly derived from the optimal covariance. In the latter, the precoding matrix is directly optimized via an imposed group sparsity under the communication QoS and power constraints. Simulation results demonstrate that the proposed sparse MIMO DFRC system with fewer active antennas can achieve comparable dual-functional performance to that of the full array system. • The joint design of precoding and antenna selection for MIMO DFRC is proposed. • The indirect precoding method is proposed to address the joint optimization problem. • The direct precoding method is proposed to directly optimize the precoding matrix. • The proposed sparse system achieves comparable performance to that of a full system. [ABSTRACT FROM AUTHOR]

This paper explicates the design and implementation of a switch capacitor DC–DC converter system for Radio Frequency (RF) energy harvesting applications for an input voltage in the sub-150 mV range, using 180-nm CMOS triple-well BCD technology. The proposed system incorporates a charge pump architecture that employs an improvised Dynamic Gate Biasing (DGB), Forward and Reverse Body Bias technique (FRBB), along with a time axis symmetrical clocking scheme implemented using an advanced bootstrapped CMOS driver to enhance the overall drive capability of the system at low input voltages. Post-layout extracted simulations demonstrate that the proposed system achieves higher overall efficiency, delivering a peak Power Conversion Efficiency (PCE) of 85.8% at 125 mV input voltage, outperforming other state-of-the-art architectures in similar voltage ranges. Moreover, the proposed system exhibits reliable operation even at input voltages as low as 85 mV, while maintaining good overall efficiency. • Architecture with Dynamic Gate Biasing (DGB), Forward and Reverse Body Bias (FRBB) • Post-layout simulations show proposed system achieves 85.8% PCE at 125 mV input • Proposed system reliable operation with good overall efficiency at 85 mV input voltage [ABSTRACT FROM AUTHOR]

Modern superconducting radio-frequency linear accelerators require the cavity bandwidth and detuning to be within a specified range to maximize the efficiency of the machine. To correctly estimate these states during operation, the measured RF signals should be calibrated. Due to the finite isolation of the waveguide directional couplers, cross-coupling effects in the forward and reflected channels complicate the calibration of the RF signals in Low-Level RF control systems. Past work proposed a compensation method employing least-squares optimization. This method requires the directivity of the directional couplers to be much higher than one. Additionally, the algorithm requires a tuning parameter to optimize the calculated calibration. However, for some accelerating systems, finding an acceptable value for such a parameter is challenging and time-consuming. In this paper, we present a way to overcome these limitations by performing a nonlinear least square optimization constrained by energy conservation laws. The method is tested with L-band superconducting resonators at loaded quality factors of 4. 6 ⋅ 1 0 6 and 2. 8 ⋅ 1 0 7 . [ABSTRACT FROM AUTHOR]

In this paper, the effect of the post-annealing temperature on the structural and electrical properties at macro and nanoscale of Sodium Bismuth Titanate - Bi 0.5 Na 0.5 TiO 3 (BNT) films is reported. Stoichiometric BNT thin films were deposited by ex-situ radio frequency (rf) sputtering at substrate temperature of 200 °C. The as-deposited films were amorphous and post-annealing treatment was necessary to crystallize the film in the perovskite phase. 400-nm-thick stoichiometric BNT films were annealed at various temperatures from 400 °C up to 700 °C. The BNT film annealed at 400 °C remains amorphous. Film starts to crystallize at 450 °C and then the crystallization increases with the post-annealing temperature to reach an optimal at 650 °C without any secondary phase. Dielectric, ferroelectric and piezoelectric properties were also improved with the increasing of the post-annealing temperature. The piezoelectric coefficient d 33eff , measured at macroscale, reaches a maximum value of 57 pm/V for 400 nm-thick film post-annealed at 650 °C. On nanoscale, measurements performed by piezoresponse force microscopy are in perfect concordance with the performances obtained at macroscale. The efficient polarization reversal for domains and their retention when locally manipulated are observed, combined to a strong piezo-activity. • Effects of post-annealing on macro and nanoscale properties of low temperature deposited BNT thin films is reported. • A perfect control of the film composition (Na/Bi=1) using rf sputtering is achieved. • The crystallization starts at 450 °C and optimal properties were obtained with an annealing temperature of 650 °C. • Excellent electrical properties at macroscale were obtained, with a d 33eff value of 57pm/V on a 400 nm-thick BNT film. • The functional properties measured on nanoscale by PFM and c-AFM are in concordance with the performances at macroscale. [ABSTRACT FROM AUTHOR]

The paper proposes a 2.4 GHz ultra-low power wake-up receiver (WuRX) with offset-based peak detection and mixer-first based radio frequency (RF) front-end for IoT applications. The mixer-first based front-end eliminates RF modules to reduce power consumption. Based on the transparency of the passive mixing switches, a 2-path passive mixer (2-PPM) constructs the high-Q band-pass filter (BPF) at the RF port to improve out-of-band blocker rejection. The offset-based peak detection circuit adaptively extracts the reference voltage for the subsequent comparator according to the real-time signal amplitude of envelope detection, which eliminates the misjudgment of the comparator and improves the accuracy of demodulation. For low power consumption, a ring oscillator is used to generate the local oscillator (LO) signal and the frequency calibration scheme combined with coarse tuning and fine tuning is employed to improve the frequency stability, which completes 10-bit frequency tuning with 2 MHz resolution. Designed in TSMC 28 nm CMOS technology, the mixer-first based front-end achieves a conversion gain of 42 dB and a noise figure of 11.9 dB at 2.4 GHz, an S11 less than −15dB during 2.4–2.5 GHz. The frequency calibration scheme for the ring oscillator completes the 512 MHz dynamic range with a 2 MHz frequency tuning step. The WuRX can achieve −90dBm sensitivity with 55 μ W power consumption at 0.6 V supply voltage and the chip area of 0.19 mm × 0.24 mm. • A 2.4 GHz ultra-low power wake-up receiver is for IoT wireless communication. • The mixer-first based front-end eliminates RF modules to reduce power consumption. • Passive mixer forms RF band-pass filter to improve out-of-band blocker rejection. • The offset-based peak detection circuit is for OOK signal demodulation. • Ring oscillator with frequency calibration for power and frequency stability concern. [ABSTRACT FROM AUTHOR]

The High Energy Photon Source (HEPS) is a 6 GeV diffraction-limited synchrotron light source under construction in Beijing. It will use five 166.6 MHz superconducting radio frequency (rf) cavities to accelerate the 200 mA electron beam in the storage ring. In the current lattice design, each straight section is 6 meters long to accommodate two 166.6 MHz cavities. The cavity adopts β =1 quarter-wave geometry, and the damping of the higher order modes is realized by using an enlarged cavity beam pipe to 505 mm and a ferrite absorber installed on the beam pipe. The low rf frequency, as well as the large beam aperture, added great challenges to the design of the 166.6 MHz cavity module to fit into a strictly limited longitudinal space. In addition, heat load optimization for the transition from room temperature to the cryogenic temperature, smooth tapering from the 505 mm beam aperture to the small diameter of the gate valves for impedance control, proper collimation of the synchrotron light to prevent thermal damage of delicate components, are also demanding requirements for a compact design. Accessibilities are also preserved for tuners and vacuum components to enable online maintenance. Finally, rf field leakage in the vacuum seal groove of the cavity is carefully examined to prevent overheating on the superconducting flange, which, in the worst scenario, may cause a thermal runaway, thus limiting the achievable accelerating gradient of the cavity. This paper presents the first compact design of the 166.6 MHz srf section for HEPS. [ABSTRACT FROM AUTHOR]

[Display omitted] • The dissociation of nitrogen molecules can be catalyzed on the Nb(1 1 0) surface. • The nitrogen atoms on the industrially heated niobium cavity are mostly accumulated on the surface and the subsurface. • Nitrogen can act as a "protective film" for niobium products, preventing them from being oxidized and protecting their superconducting properties from loss. High-temperature nitriding has been shown to improve the quality factor (Q) of the superconducting radio frequency (SRF) cavity recently, while its inherent promoting mechanism is still unclear. Therefore, based on first-principles calculations, the adsorption and dissociation processes of nitrogen molecules on the Nb(1 1 0) surface, and the adsorption, diffusion processes of nitrogen atoms on the Nb(1 1 0) surface, were studied in this paper to explain the principle of its performance improvement. To establish the reaction mechanism, adsorption preference sites were determined. All possible reaction paths were investigated for each step including the energy barrier based on the climbing image nudged elastic band (CI-NEB) method. We establish multiple reaction paths and the only optimal one was found. It is found that the Nb(1 1 0) surface can facilitate the dissociation of nitrogen molecules (with only a 1.14 eV energy barrier), and nitrogen atomic energy can readily reach the subsurface (only a 1.73 eV energy barrier). Still, the high energy barrier (up to 6.64 eV) prevents it from diffusing inward. This revelation provides the nitriding mechanism of pure niobium and the rationale for enhancing niobium cavity performance after nitrogen mixing. [ABSTRACT FROM AUTHOR]

• In-situ doping of phosphorus is used to compensate for parasitic conductive channel in the Si substrate for the first time. • This paper confirms that the crystallization of Al can be enhanced by TBP preflow. • The TBP preflow can further improve the crystal quality of GaN. • Model of morphology change of the substrates for different samples after TMAl and TBP preflow is given. In this work, the parasitic conductive channel in a silicon substrate is compensated using in-situ doping for the first time. The experimental results show that in-situ doping of tert -butylphosphorus (TBP) has little adverse effect on the mobility and the density of two-dimensional electron gas but the compensation of the parasitic channel in the substrate is effective, and the aluminum nitride (AlN) / Si template based on the optimized conditions reduces the radio frequency loss by more than 60%. In addition, it was found that a suitable preflow of TBP can enhance the migration of Al atoms on the substrate surface and improve the crystal quality of gallium nitride (GaN), which reduces the dislocation density of GaN by 25% compared to the sample without TBP preflow. The hypothesis is that TBP preflow can affect the strain of the substrate, which makes the dislocations more likely to annihilate during the subsequent growth of AlN nucleation layer, resulting in the eventual improvement of GaN crystal quality. [ABSTRACT FROM AUTHOR]

Nano-texturing technology has received significant attention as the demand for the miniaturization of optical devices grows. In this paper, we report the fabrication process and formation mechanisms for textured nanoholes on a silicon substrate developed using a Cl 2 -based high-density plasma system to improve the performance of microscopic optical devices. The mechanisms underlying the formation of the nanoholes were determined based on the results derived from variations in the etching time and conditions for the injected gas, while the effect of the plasma on the nanohole structure was evaluated in relation to changes to the upper and lower radio frequency (RF) power. The aspect ratio of the nanoholes ranged from 0.100 to 0.796 depending on the upper/lower RF power, while it was confirmed that the surface reflectance of the silicon substrate decreased and the performance of the metal–semiconductor–metal photodetector improved as the density of the nanoholes increased. These results are expected to contribute to improving the performance of optical devices. • The fabrication process for textured Si nanoholes using AuNPs and Cl 2 plasma. • The Si etching under AuNPs is accelerated by eddy current and hole injection. • The nanohole structure depends on gas ratio, etching time, and upper/lower RF power. • As The nanohole density increases, the performance of the photodetector improves. [ABSTRACT FROM AUTHOR]