Radio Frequency Signal Research Articles

Reference values of carotid intima-media thickness and arterial stiffness in Chinese adults based on ultrasound radio frequency signal: A nationwide, multicenter study.

Carotid intima-media thickness (IMT) and diameter, stiffness, and wave reflections, are independent and important clinical biomarkers and risk predictors for cardiovascular diseases. The purpose of the present study was to establish nationwide reference values of carotid properties for healthy Chinese adults and to explore potential clinical determinants. A total of 3053 healthy Han Chinese adults (1922 women) aged 18-79years were enrolled at 28 collaborating tertiary centers throughout China between April 2021 and July 2022. The real-time tracking of common carotid artery walls was achieved by the radio frequency (RF) ultrasound system. The IMT, diameter, compliance coefficient, β stiffness, local pulse wave velocity (PWV), local systolic blood pressure, augmented pressure (AP), and augmentation index (AIx) were then automatically measured and reported. Data were stratified by age groups and sex. The relationships between age and carotid property parameters were analyzed by Jonckheere-Terpstra test and simple linear regressions. The major clinical determinants of carotid properties were identified by Pearson's correlation, multiple linear regression, and analyses of covariance. All the parameters of carotid properties demonstrated significantly age-related trajectories. Women showed thinner IMT, smaller carotid diameter, larger AP, and AIx than men. The β stiffness and PWV were significantly higher in men than women before forties, but the differences reversed after that. The increase rate of carotid IMT (5.5μm/year in women and 5.8μm/year in men) and diameter (0.03mm/year in both men and women) were similar between men and women. For the stiffness and wave reflections, women showed significantly larger age-related variations than men as demonstrated by steeper regression slopes (all P for age by sex interaction <0.05). The blood pressures, body mass index (BMI), and triglyceride levels were identified as major clinical determinants of carotid properties with adjustment of age and sex. The age- and sex-specific reference values of carotid properties measured by RF ultrasound for healthy Chinese adults were established. The blood pressures, BMI, and triglyceride levels should be considered for clinical application of corresponding reference values.

Resource allocation for relaying cognitive network with energy harvesting

This paper investigates a relay-based cognitive wireless-powered communication network with multiple secondary receivers and a secondary relaying network. In the secondary network, a relay adopts an energy model to harvest energy from radio frequency signals of the primary and secondary sources and subsequently utilizes the harvested energy to cooperate with the source for information transmission to multiple Internet-of-things users over time-division multiple access. The research group formulated a novel optimization problem that jointly optimizes the power and time fraction for energy and information transmission to maximize the sum throughput of the secondary network. The authors first converted the non-convex problem to a more computationally tractable problem and then proposed an iterative algorithm in which closed-form solutions are obtained at each iteration. Thus, simulation results verify and demonstrate the effectiveness of the proposed approach.

Long-Range Wireless Power Transfer for Moving Wireless IoT Devices

Wireless technologies are revolutionizing communications, with recent deployments, such as 5G, playing a key role in the future of the Internet of Things (IoT). Such progress is leading to an increasingly higher number of wirelessly connected devices. These require increased battery use and maintenance, consequently straining current powering solutions. Since most wireless systems rely on radiofrequency (RF) waves for communications and feature low-power technologies, it is increasingly feasible to develop and implement wireless power transfer solutions supported by RF. In this paper, a simultaneous wireless information and power transfer (SWIPT) solution targeting small mobile devices is presented. This solution uses beamforming to mitigate the path loss associated with the RF power propagation. It relies on an RF backscattering tracking algorithm to power moving devices. The feasibility to power wearable devices is demonstrated by tracking a walking individual (approximately 5 km/h) at a distance of 0.5 m while transferring a minimum of 6 dBm to a wearable device using 2 GHz RF signals. Simulations were used to determine the viability of such a solution to deliver useful power levels to a 1.2 × 1.4 m2 working area without exceeding specific absorption rate (SAR) limits.

Inter-comparison of World Wide Lightning Location Network (WWLLN) and Lightning Detection Sensor Network (LDSN) data over India

Atmospheric lightning is a dominant weather related disaster which requires continuous monitoring efforts. While the world wide lightning location network (WWLLN) measures the very low frequency (VLF) signals emanating from the lightning, other regional networks, such as Lightning Detection Sensor Network (LDSN) use the broad band radio frequency signals. Present investigation compares the cloud-to-ground (CG) lightning occurrences recorded by the WWLLN and LDSN during 02 October – October 09, 2022 over India. Results show that though the WWLLN monitored the CG lightning occurrences about 20% lesser than the LDSN, spatial distribution of the occurrences and trends were in very good agreement.

Frequency down-conversion system with image rejection using thin film lithium niobate parallel modulation phase-shifting structure

The frequency down-conversion system based on microwave photonics has been widely employed in radar, electronic warfare, and satellite communication systems. In this paper, we propose an image rejection frequency down-conversion system, wherein the phase modulator and phase shifter are integrated on thin film lithium niobate platform. The working principle is elucidated through the establishment of a theoretical model. Subsequently, the system successfully down-converts a 40 GHz radio frequency (RF) signal to a 5 GHz intermediate frequency signal, achieving an image rejection ratio of approximately 30 dB. Simultaneously, varying degrees of image rejection are observed for different RF signals. The system maintains robust image rejection performance across varying RF and image signal power, as well as different levels of input optical power.

Photonic-assisted RF phase difference detector with full 0° to 360° phase detection capability

A microwave photonic structure for detecting the phase difference of two radio frequency (RF) signals is presented. It is capable of determining the RF signal phase difference unambiguously over the full 0° to 360° range, which overcomes the 0° to 180° phase detection range limitation in the reported structures. The proposed RF phase detector is designed to generate two DC voltages with amplitudes depending on the phase difference of the two input RF signals. An RF signal phase difference in the 0° to 360° range can be obtained from the ratio of the two system output DC voltages. The proposed RF phase detector has a wide operating frequency range, as it is free of microwave components. It overcomes the drawbacks of complex structures, large phase detection errors, limited phase detection range, and limited operating frequency range in the reported photonics-based RF phase detectors. Experimental results are presented that demonstrate 0° to 360° phase difference detection with errors below ±3∘ for different input RF signal frequencies.

Microwave Photonic Frequency Multiplier with Low Phase Noise Based on an Optoelectronic Oscillator

A microwave photonic frequency multiplier with low phase noise based on an optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. In this scheme, a dual-parallel Mach–Zehnder modulator (DPMZM) is employed to generate the third-harmonic frequency of the input radio frequency (RF) signal, while the oscillation frequency of the OEO is also three times the RF signal frequency. By adjusting the bias voltages of different arms in the DPMZM, a triple-frequency signal with a high side-mode suppression ratio of 64.8 dB can be obtained. The experimental results indicate that the output of the frequency-multiplier has a better single-sideband phase noise value, for instance, −126 dBc/Hz@10 kHz at 20.019 GHz. It has improvements of 34 dB and 43.5 dB compared with the input RF signal and the simulated electrical frequency tripler module, respectively.

Clinical performance of ultrasonic backscatter parametric and nonparametric statistics in detecting early hepatic steatosis

Diagnosis of early hepatic steatosis would allow timely intervention. B-mode ultrasound imaging was in question for detecting early steatosis, especially with a variety of concomitant parenchymal disease. This study aimed to use the surgical specimen as a reference standard to elucidate the clinical performance of ultrasonic echogenicity and backscatter parametric and nonparametric statistics in real-world scenarios. Ultrasound radio-frequency (RF) signals of right liver lobe and patient data were collected preoperatively. Surgical specimen was then used to histologically determine staging of steatosis. A backscatter nonparametric statistic (h), a known backscatter parametric statistic, i.e., the Nakagami parameter (m), and a quantitative echo intensity (env) were calculated. Among the 236 patients included in the study, 93 were grade 0 (<5% fat) and 143 were with steatosis. All the env, m and h statistics had shown significant discriminatory power of steatosis grades (AUC = 0.643–0.907 with p-value < 0.001). Mann-Whitney U tests, however, revealed that only the backscatter statistics m and h were significantly different between the groups of grades 0 and 1 steatosis. The two-way ANOVA showed a significant confounding effect of the elevated ALT on env (p-value = 0.028), but no effect on m or h. Additionally, the severe fibrosis was found to be a significant covariate for m and h. Ultrasonic signals acquired from different scanners were found linearly comparable.

Microwave-Based State Diagnosis of Three-Way Catalysts: Impact Factors and Application Recommendations.

This study reassesses an overview of the potential of the radio frequency (RF)-based state diagnostics of three-way catalysts (TWC) based on a previous study with an emphasis on the defect chemistry of the catalyst material during reoxidation and reduction. Some data are based on the previous works but are newly processed, and the signal parameters resonant frequency and inverse quality factor are evaluated with respect to applicability. The RF-based method uses electromagnetic resonances in a cavity resonator to provide information on the storage level of the oxygen storage component. The analysis focuses on a holistic investigation and evaluation of the major effects influencing the RF signal during operation. On the one hand, the response to the oxygen storage behavior and the resolution of the measurement method are considered. Therefore, this study merges original data from multiple former publications to provide a comprehensive insight into important measurement effects and their defect chemistry background. On the other hand, the most important cross-sensitivities are discussed and their impact during operation is evaluated. Additionally, the effect of catalyst aging is analyzed. The effects are presented separately for the two resonant parameters: resonant frequency and (unloaded) quality factor. Overall, the data suggest that the quality factor has a way higher signal quality at low temperatures (<400 °C) and the resonant frequency is primarily suitable for high operating temperatures. At most operating points, the quality factor is even more robust against interferences such as exhaust gas stoichiometry and water content. Correctly estimating the catalyst temperature is the most important factor for reliable results, which can be achieved by combining the information of both resonant signals. In the end, the data indicate that microwave-based state diagnosis is a powerful system for evaluating the oxygen storage level over the entire operating range of a TWC. As a research tool and in its application, the system can therefore contribute to the improvement of the emission control of future gasoline vehicles.

Resource-constrained narrowband optoelectronic oscillator-based reservoir computing for classification of modulated signals.

We experimentally investigate the performance of narrowband optoelectronic oscillator (OEO) reservoir computers using the standard 10th-order nonlinear autoregressive-moving-average (NARMA10) task. Because comparing results from differently parameterized photonic time-delay systems can be difficult, we introduce a new, to the best of our knowledge, metric that accounts for system size, computational accuracy, and training effort overhead in order to provide an "at-a-glance" method to holistically determine a reservoir computer's performance. We then demonstrate the first experimental effort of narrowband OEO-based reservoir computing for the RADIOML dataset, which consists of recognizing and classifying IQ-modulated radio signals including analog and digital modulations. Our results indicate that narrowband OEOs are capable of achieving reasonable accuracies with exceptionally small training sets, thereby paving the way to real-time machine learning for radio frequency signals.

Compact silicon-based Ka-band tunable-phase photonic microwave frequency downconverter.

In this paper, a compact silicon-based photonic microwave frequency downconverter with broadband operation capability and continuous phase shift tunability is proposed and experimentally demonstrated. The photonic converter mainly comprises two micro-ring modulators (MRMs) connected in parallel and a cascaded resonator-based optical bandpass filter (OBPF) whose size is merely 200 × 700 µm2. In the proposed device, a radio frequency (RF) signal and a local oscillator (LO) signal drive the two MRMs for realizing the electro-optic conversion. The OBPF is utilized for selecting the first-order sidebands of both RF and LO signals. By manipulating the phase difference between the RF and LO optical sidebands through thermal-optic effect, the phase of the obtained intermediate frequency (IF) signal from a photodiode can be tuned continuously. Experimental results demonstrate a 137° phase shift while the RF signals of 20 and 40 GHz are downconverted to an IF signal of 0.4 GHz, which indicates the photonic microwave downconverter can be used in the Ka-band phased-array receiver.

Synthesis and Experimental Characterization of the Potting Material to Reduce the Radio Frequency Signal Attenuation

Synthesis and Experimental Characterization of the Potting Material to Reduce the Radio Frequency Signal Attenuation

A Study on Design and Microwave Characteristics of a RF/IR Multispectral Absorber

In this paper, a design for a radio frequency(RF) and infrared(IR) absorber with metasurfaces is discussed in microwave frequency bands. The RF absorber includes double layers of metasurfaces to operate in S- and X-bands. Effects of sheet resistance of the metasurfaces and thicknesses of dielectric supporting layers on reflection responses are investigated. An IR stealth layer incorporates an array of conductive grids with slits to reflect IR signals but to transmit RF signals and visible rays. Periodicity of the grids and slits is studied for transmission responses in the X-band and a surface area ratio. Reflection responses of the RF/IR multispectral absorber are found to be lower than -10 dB and -16 dB in the S- and X-bands, respectively, from full-wave simulation. Finally, the RF/IR multispectral absorber is fabricated and its reflection responses are measured to verify designed performance.

Ferromagnetic resonance measurement with frequency modulation down to 2 K.

Ferromagnetic resonance (FMR) spectroscopy is a powerful technique to study the precessional dynamics of magnetization in thin film heterostructures. It provides valuable information about the mechanisms of exchange bias, spin angular momentum transfer across interfaces, and excitation of magnons. A key desirable feature of FMR spectrometers is the capability to study magnetization dynamics over a wide phase space of temperature (T), frequency (f), and magnetic field (B). The design, fabrication, and testing of such a spectrometer, which uses frequency modulation techniques for improved detection of microwave absorption, reduces heat load in the cryostat and allows simultaneous measurements of inverse spin Hall effect (ISHE) induced dc voltages, is described in this paper. The apparatus is based on a 2-port transmitted microwave signal measurement using a grounded co-planar waveguide. The input radio frequency (RF) signal, frequency modulated at a tunable f-band, excites spin precession in the sample, and the attenuated RF signal is measured phase sensitively. The sample stage, inserted in the bore of a superconducting solenoid, allows magnetic field and temperature variability of 0 to ±5T and 2-310K, respectively. We demonstrate the working of this Cryo-FMR and ISHE spectrometer on thin films of Ni80Fe20 and Fe60Co20B20 over a wide T, B, and f phase space.

The Optimization Research on RF Chip Signal Processing Based on Deep Learning Algorithms

With the rapid development of wireless communication technology, radio frequency (RF) chips, as the core components of communication systems, directly influence the overall system performance through their signal processing capabilities. Traditional signal processing methods often struggle to achieve optimal results in the face of complex and variable communication environments. In recent years, deep learning technology, due to its powerful feature learning and pattern recognition capabilities, has shown tremendous potential in various fields. This paper addresses the signal processing issues of RF chips and proposes an optimization method based on deep learning algorithms. Firstly, the status and challenges of RF chip signal processing are analyzed, followed by the design of a deep learning model suitable for RF signal processing. Through data pre-processing and feature extraction, the generalization ability of the model is enhanced. Experimental results demonstrate that the proposed method outperforms traditional methods in signal noise suppression, interference cancellation, and signal distortion compensation, significantly improving the signal processing performance of RF chips. This research provides new ideas and methods for the application of deep learning in the field of RF chip signal processing and holds significant theoretical and practical importance for the future development of wireless communication systems.

Photonics-Based Multidomain Features Extraction for Radio Frequency Signals

Photonics-Based Multidomain Features Extraction for Radio Frequency Signals

A novel direct detection lidar compatible with software-defined radio

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.

A Multipath Approach to Self-Interference Cancellation in MIMO Rayleigh Fading Channels

An optically enabled multipath self-interference (MSI) cancellation technique for in-band full duplex (IBFD) multiple input multiple output (MIMO) Radio over Fiber RoF systems under Rayleigh fading channels is proposed. A digitally assisted Rayleigh fading channel model generates the MSI signal. An optically tunable multipath delay lines (OTMDL) module is designed using optical delay lines and an optical attenuator for coarse and fine-tuning of time delays and amplitude matching between the locally generated reference (LR) signal and the MSI signal. The OTMDL module adjusts the LR signal to cancel the effect of MSI on the signal received through the fading channel. The concept is validated using a remote sensor node of a 3 × 3 IBFD MIMO RoF system with a Rayleigh fading channel. The system's performance is evaluated by determining the MSI cancellation depths using the OTMDL section for various cancellation channels and by computing the MSI cancellation for both single band and wideband signals across different cancellation channels. An average value of MSI cancellation depth of 20.38 dB is obtained for a single-tone radio frequency signal in the range 15–25 GHz. Thus, the proposed system for MSI cancellation can be utilized in wireless communication systems in multiple ways.

A 1 bit Raw Voltage-recording System for Dedicated Observations of Transients at Low Radio Frequencies

Recently we had reported commissioning of a prototype for pulsar observations at low radio frequencies (<100 MHz) using log-periodic dipole antennas in the Gauribidanur Radio Observatory (≈77°E, 14°N) near Bangalore in India (https://www.iiap.res.in/?q=centers/radio). The aforementioned system (the Gauribidanur Pulsar System) is currently being augmented to directly digitize the radio-frequency signals from the individual antennas in the array. Our initial results using a 1 bit raw voltage-recording system indicate that such a back-end receiver offers distinct advantages like (i) simultaneous observations of any set of desired directions in the sky with multiple offline beams and smaller data rate/volume, and (ii) archival of the observed data with minimal resources for reanalysis in the future, either in the same or a different set of directions in the sky.

A Vector Representation of Multicomplex Numbers and Its Application to Radio Frequency Signals

Hypercomplex numbers, which are multi-dimensional extensions of complex numbers, have been proven beneficial in the development of advanced signal processing algorithms, including multi-dimensional filter design, linear regression and classification. We focus on multicomplex numbers, sets of hypercomplex numbers with commutative products, and introduce a vector representation allowing one to isolate the hyperbolic real and imaginary parts of a multicomplex number. The orthogonal decomposition of a multicomplex number is also discussed, and its connection with Hadamard matrices is highlighted. Finally, a multicomplex polar representation is provided. These properties are used to extend the standard complex baseband signal representation to the multi-dimensional case. It is shown that a set of 2n Radio Frequency (RF) signals can be represented as the real part of a single multicomplex signal modulated by several frequencies. The signal RFs are related through a Hadamard matrix to the modulating frequencies adopted in the multicomplex baseband representation. Moreover, an orthogonal decomposition is provided for the obtained multicomplex baseband signal as a function of the complex baseband representations of the input RF signals.