Radio Frequency Research Articles

3D-printed fiber-bundle fluorescence microscope for quantifying single-cell responses to high-power radiofrequency sources

Modern telecommunications systems rely on the ubiquitous use of radiofrequency (RF) fields. To ensure the safety of living systems under RF exposure, standards have been developed which rely on observed thresholds that produce an adverse response. Unfortunately, real-time imaging of single-cell responses to high-peak power RF exposures is experimentally difficult, as high-power RF may damage sensitive electronics such as cameras or photodetectors, and any metal in the exposure zone (such as a microscope objective or translation stage) interacts with the RF by reflecting the RF field, acting as an antenna, or altering the dose delivered to the sample. In this work, we present a custom fluorescence microcopy system compatible with high-power RF environments. Our device uses a custom, 3D-printed objective consisting entirely of plastic and glass components as well as a coherent fiber bundle to relay light between the exposure zone and the fluorescence detection scheme. Our device was validated against a high-end commercial confocal microscope by comparing cellular responses to a well-characterized nanosecond pulsed electric field (nsPEF) stimulus delivered via an electrode pair. Our system performed well under extreme RF exposure, demonstrating continuous fluorescence imaging and maintenance of the focal plane despite >40°C temperature variation at the sample caused by high peak power free-field RF exposure at a frequency of 2.8 GHz. This system is intended to aid researchers in investigating real-time biological responses to radiofrequency and microwave sources.

RF Detection of Split-Gate Modes in Si-MOS Quantum Dots

Abstract Radio frequency (RF) reflectometry is an effective and sensitive technique for detecting charge signal in semiconductor quantum dots, and its measurement bandwidth can reach the MHz level. However, in accumulation mode devices, the presence of parasitic capacitance makes RF reflectometry more difficult. The universal approach is relocating the ion implantation region approximately 10 μm from the center of the Single-Electron Transistor (SET) and optimizing the design of the accumulation gates. But, this method puts forward more stringent requirements for micro-nano fabrication processing. Here, we propose a split-gate structure that enables RF reflectometry when the ion-implanted region and the ohmic contact are farther from the SET center. In Si-MOS devices, we employ a split-gate structure to achieve RF detection, with the ion-implanted region located 150 μm away from the center of the SET. Within an integration time of 140 nanoseconds, we achieved a readout fidelity exceeding 99.8% and a detection bandwidth of over 2 MHz. This is an alternative solution for micro-nano fabrication processing that cannot achieve ion implantation areas closer to the center of the chip, and is applicable to various silicon-based semiconductor systems.

Observation of radio-frequency Mie resonances in high-permittivity dielectric spheres

Abstract We investigate Mie resonances in a high-permittivity dielectric (ceramic) sphere within the radio-frequency (RF) range, exploring its potential application in magnetic resonance imaging (MRI). Using a transmitting and a receiving RF coil, we observe Mie resonance signatures in both the transmission frequency spectrum and the magnetic field distribution surrounding a 40 mm-diameter sphere. Through full-wave numerical simulations and a standard fitting technique, we identify and characterize the lowest-frequency transverse-electric resonance modes of the sphere at 141.6, 201.4, 259.6, and 282.6 MHz, each exhibiting high-quality factors ( ∼ 300 ). Remarkably, we experimentally map the magnetic field distributions corresponding to each Mie resonance. Our results provide valuable insights for developing innovative approaches to manipulate RF waves, particularly by shaping and controlling the near-field outside the dielectric resonator through Mie resonances, an area largely unexplored in MRI technology.

Investigating the optoelectronic device performance of p-Si/WO3/Ag sandwich structure

The electrical and photoelectrical properties of a p-Si/WO3/Ag sandwich structure fabricated utilizing radio frequency (RF) sputtering of WO3 thin films were investigated. A comprehensive analysis of the surface morphology, structural, and optical characteristics of the WO3 thin films was performed. The findings demonstrated that the RF-sputtered WO3 thin films with smooth and uniform surface morphology are well-applicable in large-area applications. The WO3 thin films exhibited well-crystallized structures with a 2.92 eV optical band gap, indicating their suitability for optoelectronic applications. Current-voltage and current-time measurements in the dark and under various illumination conditions were used to evaluate the optoelectronic performance of the p-Si/WO3/Ag sandwich structure. The electrical and optoelectronic parameters, including ideality factor, barrier height, series resistance, and photosensitive were calculated. The results showed that the p-Si/WO3/Ag sandwich-type device obtained using RF sputtered WO3 thin film demonstrates remarkable rectification properties, highlighting its potential for use in photodiodes and optoelectronic devices.

8 W at 10 GHz in AlGaN/GaN High Electron Mobility Transistors on Silicon Without Any Carbon or Iron Doping

X‐band power performance in AlGaN/GaN high electron mobility transistors (HEMTs) on silicon without intentional carbon (C) or iron (Fe) doping anywhere in the stack is reported. A reverse polarization‐graded AlGaN buffer depletes background charge and provides a superior breakdown, while an optimized AlN nucleation layer reduces substrate radio frequency (RF) losses. HEMTs with 0.22 μm gate length and 4 μm source‐drain spacing demonstrate >80 V 3‐terminal breakdown voltage for 12 × 125 μm gate width. Pulsed load‐pull at 10 GHz shows 8 W saturated power at 2 dB compression under deep class‐AB bias at 35 V with 46% drain efficiency. Further improvements are expected with substrate thinning and improved thermal management.

Advanced Digital Solutions for Food Traceability: Enhancing Origin, Quality, and Safety Through NIRS, RFID, Blockchain, and IoT

The rapid growth of the human population, the increase in consumer needs regarding food authenticity, and the sub-par synchronization between agricultural and food industry production necessitate the development of reliable track and tracing solutions for food commodities. The present research proposes a simple and affordable digital system that could be implemented in most production processes to improve transparency and productivity. The system combines non-destructive, rapid quality assessment methods, such as near infrared spectroscopy (NIRS) and computer/machine vision (CV/MV), with track and tracing functionalities revolving around the Internet of Things (IoT) and radio frequency identification (RFID). Meanwhile, authenticity is provided by a self-developed blockchain-based solution that validates all data and documentation “from farm to fork”. The system is introduced by taking certified Hungarian sweet potato production as a model scenario. Each element of the proposed system is discussed in detail individually and as a part of an integrated system, capable of automatizing most production flows while maintaining complete transparency and compliance with authority requirements. The results include the data and trust model of the system with sequence diagrams simulating the interactions between participants. The study lays the groundwork for future research and industrial applications combining digital tools to improve the productivity and authenticity of the agri-food industry, potentially increasing the level of trust between participants, most importantly for the consumers.

Trends in Smart Restaurant Research: Bibliometric Review and Research Agenda

Background The automation of processes and services has transformed various industries, including the restaurant sector. Technologies such as the Internet of Things (IoT), machine learning, Radio Frequency Identification (RFID), and big data have been increasingly adopted to enhance service delivery, improve user experiences, and enable data traceability. By collecting user feedback and analyzing sentiments, these technologies facilitate decision-making and offer predictive insights into future food preferences. This study aims to explore current research trends in intelligent restaurants, focusing on technological applications that improve service and decision-making. Methods A bibliometric analysis was conducted in accordance with the PRISMA-2020 guidelines. A total of 94 academic documents were reviewed from the Scopus and Web of Science databases, focusing on publications related to intelligent restaurant systems, particularly involving IoT and automation technologies. Results The analysis revealed that the United States, India, and China have contributed the most to the field, with a particular emphasis on China’s implementation of IoT architecture and robotics in restaurant settings. Chinese restaurant innovations, particularly in robotics, are among the most frequently cited in the literature. The study identifies these countries as leading the research in the intelligent restaurant domain. Conclusions Technologies such as IoT, machine learning, RFID, and big data are driving advancements in restaurant automation, enhancing service efficiency and user experience. The United States, India, and China are leading research in this area, with China standing out for its application of robotics and IoT in restaurants. This research provides a foundation for future studies aimed at improving predictive models for food selection and service optimization.

Application of Anti-Collision Algorithm in Dual-Coupling Tag System

Radio Frequency Identification (RFID) is a key component in automatic systems that address challenges in environment monitoring. However, tag collision continues to be an essential challenge in such applications due to high-density RFID deployments. This paper addresses the issue of RFID tag collision in large-scale intensive tags, particularly in industrial membrane contamination monitoring systems, and improves the system performance by minimizing collision rates through an innovative collision-avoiding algorithm. This research improved the Predictive Framed Slotted ALOHA–Collision Tracking Tree (PRFSCT) algorithm by cooperating probabilistic and deterministic methods through dynamic frame length adjustment and multi-branch tree processes. After simulation and validation in MATLAB R2023a, we performed a hardware test with the RFM3200 and UHFReader18 passive tags. The method’s efficiency is evaluated through collision slot reduction, delay minimization, and enhanced throughput. PRFSCT significantly reduces collision slots when the number of tags to identify is the same for PRFSCT, Framed Slotted ALOHA (FSA), and Collision Tracking Tree (CTT); the PRFSCT method needs the fewest time slots. When identifying more than 200 tags, PRFSCT has 225 collision slots for 500 tags compared to FSA and CTT, which have approximately 715 and 883 for 500 tags, respectively. It demonstrates exceptional stability and adaptability under increased density needs while improving tag reading at distances.

Adapting a Trapped Ion Mobility Spectrometry-Q-TOF for High m/z Native Mass Spectrometry and Surface-Induced Dissociation.

Native mass spectrometry (nMS) is an increasingly popular technique for studying intact protein quaternary structure. When coupled with ion mobility, which separates ions based on their size, charge, and shape, it provides additional structural information on the protein complex of interest. We present here data from a novel prototype TIMS (trapped ion mobility spectrometry)-quadrupole-SID (surface-induced dissociation)-time of flight, TIMS-Q-SID-TOF, instrument for nMS. The modifications include changing the TIMS cartridge from concave to convex electrode geometry with a dual TIMS tunnel design and operating TIMS at 425 kHz radio frequency (RF) to improve the trapping efficiency for high mass-to-charge (m/z) ion mobility analysis, such as 3 and 4 MDa hepatitis B virus capsids. The quadrupole RF driver was lowered to 385 kHz, which extends the isolation range from 3,000 to 17,000 m/z and allows isolation of a single charge state of GroEL at 16,200 m/z with an isolation window of 25 m/z. Finally, a 6 mm thick, 2-lens SID device replaced the collision cell entrance lens. SID dissociated 801 kDa GroEL into all combinations of subcomplexes, and the peaks were well-resolved, allowing for confident assignment of product ions. This is the first time a novel prototype timsTOF Pro for nMS has been introduced with high resolving power ion mobility separation coupled to high m/z quadrupole selection and SID for protein complex fragmentation with product ion collection and detection across a broad m/z range of 1,500 to 40,000.

Single-Particle Radiation Sensitivity of Ultrawide-Bandgap Semiconductors to Terrestrial Atmospheric Neutrons

Semiconductors characterized by ultrawide bandgaps (UWBGs), exceeding the SiC bandgap of 3.2 eV and the GaN bandgap of 3.4 eV, are currently under focus for applications in high-power and radio-frequency (RF) electronics, as well as in deep-ultraviolet optoelectronics and extreme environmental conditions. These semiconductors offer numerous advantages, such as a high breakdown field, exceptional thermal stability, and minimized power losses. This study used numerical simulation to investigate, at the material level, the single-particle radiation response of various UWBG semiconductors, such as aluminum gallium nitride alloys (AlxGa1−xN), diamond, and β-phase gallium oxide (β-Ga2O3), when exposed to ground-level neutrons. Through comprehensive Geant4 simulations covering the entire spectrum of atmospheric neutrons at sea level, this study provides an accurate comparison of the neutron radiation responses of these UWBG semiconductors focusing on the interaction processes, the number and nature of secondary ionizing products, their energy distributions, and the production of electron–hole pairs at the origin of single-event effects (SEEs) in microelectronics devices.

Smartphone administered pulsed radio frequency energy therapy for expedited cutaneous wound healing

Pulsed radio frequency energy (PRFE) therapy is a non-invasive, electromagnetic field-based treatment modality successfully used in clinical applications. However, conventional PRFE devices are often bulky, expensive, and require extended treatment durations, limiting patient adherence and efficacy. Here, we present a lightweight, cost-effective wearable PRFE system consisting of a flexible electronic bandage and a smartphone. The bandage, mainly composed of an NFC Frequency Doubler (NFD) and a Radiofrequency Energy Radiator (RER), is powered and administered by the smartphone to generate 27.12 MHz radio wave pulses, for simplified, smartphone-enabled PRFE therapy. Its ultra-flexible, battery-free design supports personalized wound care at a low-cost (<US$1). Both electromagnetic field simulation and measurement demonstrated that the proposed PRFE bandage achieves the field strength of clinical-grade PRFE equipment. In rat full-thickness wound models, PRFE therapy improved wound closure rates by ~20%, with enhanced re-epithelialization and angiogenesis compared to controls.

Increasing Pulsar SNR by Using Spectral Kurtosis as a Radio Frequency Mitigation Technique

Increasing Pulsar SNR by Using Spectral Kurtosis as a Radio Frequency Mitigation Technique

In-hospital safety of cryoballoon and radiofrequency ablation in patients with atrial fibrillation - German-wide analysis of more than 300 000 procedures.

Pulmonary vein isolation (PVI) can be performed using radiofrequency (RF) or cryoballoon (CB) ablation. Guidelines do not favor one technique and knowledge about complication rates is limited. To report the procedural safety of RF and CB ablation using data from a German nation-wide real-world registry. Using health records, all left atrial catheter ablation procedures using RF or CB ablation in Germany from 2013-2021 were analyzed. After adjustment for confounders, safety performance endpoints were compared. From 2013 to 2021, RF ablation was performed in 184,613 patients and CB ablation in 118,980 patients with increasing trends in patient numbers and performing centers for both procedures. Patients with RF ablation had slightly more comorbidities. In-hospital mortality (RF 0.08%; CB: 0.06%) and other investigated complications were rare. After adjustment for patient baseline characteristics, the risk of in-hospital mortality, serious bleeding, stroke, intracerebral bleeding and acute kidney injury did not differ. The risk of pericardiocentesis (RR 0.50; 95% CI: 0.46-0.55; p<0.001), vascular complication (0.36; 0-33-0.39; p<0.001) and ventilation > 48h (0.81; 0.66-0.99; p=0.042) was significantly lower for CB ablation. Pericardiocentesis risk negatively correlated with annual procedure numbers per center with a faster learning curve for CB ablation (both p<0.01). RF and CB ablation had low overall procedural complication rates, with CB ablation showing a 50% reduced risk of pericardiocentesis. Centers with higher volume provided a better in-hospital safety with a faster learning curve for CB ablation.

A novel fiber-based radio frequency phase synchronization scheme without time benchmark

A novel fiber-based radio frequency phase synchronization scheme without time benchmark

Novel Continuous-Time Markov Chain-Based Model for Performance Analysis of Hybrid Free Space Optics and Radio Frequency Communications

Novel Continuous-Time Markov Chain-Based Model for Performance Analysis of Hybrid Free Space Optics and Radio Frequency Communications

Radio dimming associated with filament eruptions in the meter and decimeter wavebands

Filament eruptions are considered to be a common phenomenon on the Sun and other stars, yet they are rarely directly imaged in the meter and decimeter wavebands. Using imaging data from the DAocheng solar Radio Telescope (DART) in the 150--450 MHz frequency range, we present two eruptive filaments that manifest as radio dimmings (i.e., emission depressions). Simultaneously, portions of these eruptive filaments are discernible as dark features in the chromospheric images. The sun-as-a-star flux curves of brightness temperature, derived from the DART images, exhibit obvious radio dimmings. The dimming depths range from 1.5% to 8% of the background level and show a negative correlation with radio frequencies and a positive correlation with filament areas. Our investigation suggests that radio dimming is caused by free-free absorption during filament eruptions obscuring the solar corona. This may provide a new method for detecting stellar filament eruptions.

Feasibility Study on Heat Pipes for Radio Frequency Antennas

The applicability of a heat pipe is investigated for the cooling of radio frequency antennas in fusion reactors operating at high temperatures. A heat pipe is a passive cooling device that transfers a large amount of heat through the liquid-vapor phase change and pumps the working fluid by the surface tension of the wick structure without moving parts. As the heat pipe is expected to operate near 1000 K, refractory metals or ceramics should be used for wall materials, and liquid metals are primarily considered as the working fluid. However, liquid metals are electrically conductive, and the strong magnetic field perpendicular to the flow direction imposes significant magnetohydrodynamic (MHD) flow resistance in addition to viscous friction, which impairs heat transfer performance. Since a strong magnetic field is inevitable in magnetic confinement fusion reactors, materials with low electrical conductivity should be applied to wall coatings to reduce the MHD effect. Heat flux limitations at a magnetic field of 10 T and a condenser coolant temperature of 773 K are estimated using COMSOL multiphysics, which can capture the fully developed MHD wick flow, laminar/turbulent vapor flow, and heat transfer simultaneously. For simplicity, the generic heat pipe geometry of a straight horizontal cylinder with a length of 2 ft (0.6096 m) is employed. Optimal geometrical parameters are evaluated to meet radial evaporator/condenser heat fluxes greater than 0.1 MW/m2, even under a strong MHD effect.

The low-frequency flattening of the radio spectrum of giant HII regions in M 101

In galaxies, the flattening of the spectrum at low radio frequencies below 300 MHz has been the subject of some debate. A turnover at low frequencies could be caused by multiple physical processes, which can yield new insights into the properties of the ionised gas in the interstellar medium. We investigate the existence and nature of the low-frequency turnover in the regions of M,101. We study the nearby galaxy M,101 using the LOw Frequency ARray (LOFAR) at frequencies of 54 and 144,MHz, Apertif at 1370,MHz, and published combined map from the Very Large Array (VLA) and Effelesberg telescope at 4850,MHz. The spectral index between 54 and 144,MHz is inverted at the centres of regions. We find a significant low-frequency flattening at the centres of five out of six regions that we selected for this study. The low frequency flattening in regions of M,101 can be explained with two different free-free absorption models. The flattening is localised in a region smaller than 1.5,kpc and can only be detected with high resolution (better than 45 The detection of low frequency flattening has important consequences for using radio continuum observations below 100,MHz to measure extinction-free star-formation rates.

Frequency-aware denoising using a diffusion model for enhanced band-limited and white noise removal in x-ray acoustic computed tomography.

Radiation therapy delivers precise doses to tumors, but accurately measuring internal tissue doses remains a challenge. Current methods, such as ionization chambers and radiographic films, rely on external measurements, which cannot provide direct, in vivo dose feedback. X-ray acoustic computed tomography (XACT) was developed to generate thermoacoustic signals when x-rays deposit energy into water or tissue, enabling the reconstruction of dose distribution patterns through acoustic signals. However, the longer pulse width of x-rays from linear accelerators reduces the efficiency of thermoacoustic signal conversion, lowering the signal-to-noise ratio (SNR) of radiofrequency (RF) signals. This noise significantly affects the quality of reconstructed XACT images. Overcoming the impact of noise is essential for advancing XACT toward accurate dose detection. This study aims to develop a frequency-aware denoising (FAD) method for overcoming the impact of band-limited and white noise in RF signals for XACT. Real RF signals were acquired from an XACT system using radiotherapy megavoltage (MV) x-rays, a water tank, and an ultrasound transducer. To capture the frequency characteristics of these RF signals, we first estimated the probability density function (PDF) of their frequency spectrum. To generate synthetic RF data that closely approximates realistic noisy signals for model training, noise was sampled from this PDF, incorporating both magnitude and random phase components, and combined with simulated signals and white noise. A conditional diffusion model was trained on these synthetic signals to obtain the FAD model. A total of 3150 frequency-aware RF data samples were used to train the FAD model. For testing, acoustic RF signal data excited by five different x-ray shapes were measured, denoised by the FAD model, and finally reconstructed into XACT. The performance of the method was evaluated based on XACT image quality using SNR analysis and γ passing rate, and compared with results from Raw-RF and background noise-removed (BNR-RF) methods. The FAD-RF method produced XACT images with clearer structural details and fewer artifacts. It achieved the highest SNR among the tested methods, with a mean SNR of 27.6±5.0, outperforming both Raw-RF (22.9±2.2, p<0.05) and BNR-RF (22.0±3.0, p<0.05). In terms of spatial accuracy, the FAD-RF method also outperformed in γ analysis, achieving a mean γ passing rate of 79.0%±2.4%, significantly higher than Raw-RF (50.2%±20.0%, p<0.05) and BNR-RF (73.5%±3.6%, p=0.078). The FAD-RF method relies solely on the RF signals for denoising, making it practical and efficient for real-world applications. It demonstrates effective noise suppression and enhanced spatial accuracy in XACT image reconstruction.

Design of a Board-Level Integrated Multi-Channel Radio Frequency Source for the Transportable 40Ca+ Ion Optical Clock

As one of the most precise timekeeping instruments ever developed, the optical clock will be used as the measuring equipment for the next generation of second definition. The demand for the miniaturization of optical clocks is progressively urgent. In this paper, a multi-channel radio frequency (RF) module with a 20% volume of the commercial module is designed and implemented for the transportable 40Ca+ ion optical clock. Based on the double-crystal oscillator interlocking technique, a 1 GHz low-phase noise reference source is developed for direct digital synthesis. Through the simulation and optimization of the signal link design, the frequency range of the low phase-noise RF signal can reach 0–400 MHz with a 4 μHz resolution. Through two-stage power amplifying with different kinds of filters, it can achieve an output power of up to +33 dBm (2 W) at 100 MHz with a 25 dB phase noise lower than the commercial module at 1 Hz, and its third harmonic suppression ratio has been reduced by more than 20 dB at the frequency point of 300 MHz. This multi-channel RF module is used for the power stability and timing control test of a 729 nm clock laser to meet the requirements of the transportable 40Ca+ optical clock. Additionally, this module can also be applied to other quantum systems such as the quantum absolute gravimeter, quantum gyroscopes, and quantum computers.