Multi-channel Radio Frequency Research Articles

Theoretical Demonstration of Improved Performance in Multi-Channel Photonic RF Signals Based on Optical Injection Locking of Optical Comb and Array Lasers

Multi-channel radio frequency (RF) signal generation, facilitated by photonic technology, offers significant potential for generating coherent signals with a high frequency and low phase noise, providing multifunctional capabilities across diverse platforms, including RF and photonic systems. Traditional methods for multi-channel photonic RF signal generation typically entail the integration of diverse optical components, such as filters and amplifiers. However, this integration often results in compromises related to power efficiency, cost-effectiveness, and implementation simplicity. To address these challenges, we propose a novel method for generating multi-channel photonic RF signals based on optical injection locking technology. This approach eliminates the necessity for traditional optical components, leading to a substantial enhancement in the performance of photonic RF signals. We present the design of an optical injection locking-based multi-channel photonic RF signal generation schematic and theoretically evaluate its Signal-to-Noise Ratio (SNR) and eye pattern performance for data modulation using the Lumerical INTERCONNECT simulator. Our results reveal a significant 1.3-dB and 3.6-dB enhancement in SNR for 30-GHz and 60-GHz signals, respectively. Furthermore, we observed an improved communication performance, as evidenced by enhanced eye patterns in 3-Gbps data transmission compared to passive photonic RF signal generation methods.

Phase Offset Calibration in Multi-Channel Radio-Frequency Transceivers

Phase Offset Calibration in Multi-Channel Radio-Frequency Transceivers

Compact multi-channel radio frequency pulse-sequence generator with fast-switching capability for cold-atom interferometers.

Cold-atom interferometers have matured into a powerful tool for fundamental physics research, and they are currently moving from realizations in the laboratory to applications in the field. A radio frequency (RF) generator is an indispensable component of these devices for controlling lasers and manipulating atoms. In this work, we developed a compact RF generator for fast switching and sweeping the frequencies and amplitudes of atomic-interference pulse sequences. In this generator, multi-channel RF signals are generated using a field-programmable gate array (FPGA) to control eight direct digital synthesizers (DDSs). We further propose and demonstrate a method for pre-loading the parameters of all the RF pulse sequences to the DDS registers before their execution, which eliminates the need for data transfer between the FPGA and DDSs to change RF signals. This sharply decreases the frequency-switching time when the pulse sequences are running. Performance characterization showed that the generated RF signals achieve a 100ns frequency-switching time and a 40 dB harmonic-rejection ratio. The generated RF pulse sequences were applied to a cold-atom-interferometer gyroscope, and the contrast of atomic interference fringes was found to reach 38%. This compact multi-channel generator with fast frequency/amplitude switching and/or sweeping capability will be beneficial for applications in field-portable atom interferometers.

Measurement of Complex-Ratio Between Two RF Signals With Spectrum Analysis

A novel method to measure the amplitude-phase differences between two radio frequency (RF) signals is presented, based on spectrum analysis after periodic modulation. Two input signals are alternatively selected to enter the single-channel RF channel by a single-pole double-throw (SPDT) switch, which generates harmonics related to the channel unbalance. Amplitude-phase differences between two input signals can be obtained by analyzing the spectrum of received signal using discrete Fourier transform (DFT) in digital domain. Compared to conventional multichannel RF receivers, the proposed method has a concise structure and low-computational complexity. Simulation results are provided to verify its effectiveness over dynamic ranges of 60 dB and 360 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^\circ$</tex-math> </inline-formula> . A <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L$</tex-math> </inline-formula> -band RF circuit is fabricated to measure the amplitude-phase differences over 35 dB and 360 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^\circ$</tex-math> </inline-formula> dynamic ranges. The measured results show good agreement to those by the vector network analyzer (VNA), certifying the effectiveness of proposed method.

Photoionisation detection of a single Er3+ ion with sub-100-ns time resolution.

Efficient detection of single optical centres in solids is essential for quantum information processing, sensing and single-photon generation applications. In this work, we use radio-frequency (RF) reflectometry to electrically detect the photoionisation induced by a single Er3+ ion in Si. The high bandwidth and sensitivity of the RF reflectometry provide sub-100-ns time resolution for the photoionisation detection. With this technique, the optically excited state lifetime of a single Er3+ ion in a Si nano-transistor is measured for the first time to be [Formula: see text]s. Our results demonstrate an efficient approach for detecting a charge state change induced by Er excitation and relaxation. This approach could be used for fast readout of other single optical centres in solids and is attractive for large-scale integrated optical quantum systems thanks to the multi-channel RF reflectometry demonstrated with frequency multiplexing techniques.

RF Frequency Selective Switch by Multiple PMIM Conversions

Nowadays, broadband and multi-channel radio frequency (RF) processing has been widely used in communication, radar, countermeasure, and other applications. At present, multiple-input and multiple-output (MIMO)-oriented microwave photonic signal processing technology is relatively scarce, so this paper proposes an RF frequency selective switch (FSS) based on multiple phase modulation to intensity modulation (PMIM) conversions. PMIM conversion has been used in narrowband microwave photonic filtering in the past. We extend it to a wideband and arbitrarily reconfigurable RF spectrum processing unit through an optical frequency comb and periodic optical filter. Although we use the incoherent combination of a multi-wavelength light source, we can obtain any frequency response including rectangles only by using all positive tap coefficients. Using an optical wavelength selective switch (WSS), we obtain RF FSS, and the spectral resolution of RF FSS is much better than that of optical WSS, which is improved by more than two orders of magnitude. The above principles, including single-channel reconfigurable filtering and multi-channel RF FSS, are verified by experiments. Our technology provides a stable solution for future RF MIMO signal processing.

A New Combination of Radio-Frequency Coil Configurations Using High-Permittivity Materials and Inductively Coupled Structures for Ultrahigh-Field Magnetic Resonance Imaging.

In ultrahigh-field (UHF) magnetic resonance imaging (MRI) system, the RF power required to excite the nuclei of the target object increases. As the strength of the main magnetic field (B0 field) increases, the improvement of the RF transmit field (B1+ field) efficiency and receive field (B1- field) sensitivity of radio-frequency (RF) coils is essential to reduce their specific absorption rate and power deposition in UHF MRI. To address these problems, we previously proposed a method to simultaneously improve the B1+ field efficiency and B1- field sensitivity of 16-leg bandpass birdcage RF coils (BP-BC RF coils) by combining a multichannel wireless RF element (MCWE) and segmented cylindrical high-permittivity material (scHPM) comprising 16 elements in 7.0 T MRI. In this work, we further improved the performance of transmit/receive RF coils. A new combination of RF coil with wireless element and HPM was proposed by comparing the BP-BC RF coil with the MCWE and the scHPM proposed in the previous study and the multichannel RF coils with a birdcage RF coil-type wireless element (BCWE) and the scHPM proposed in this study. The proposed 16-ch RF coils with the BCWE and scHPM provided excellent B1+ field efficiency and B1- field sensitivity improvement.

A Comparative Study of Birdcage RF Coil Configurations for Ultra-High Field Magnetic Resonance Imaging.

Improvements in transmission and reception sensitivities of radiofrequency (RF) coils used in ultra-high field (UHF) magnetic resonance imaging (MRI) are needed to reduce specific absorption rates (SAR) and RF power deposition, albeit without applying high-power RF. Here, we propose a method to simultaneously improve transmission efficiency and reception sensitivity of a band-pass birdcage RF coil (BP-BC RF coil) by combining a multi-channel wireless RF element (MCWE) with a high permittivity material (HPM) in a 7.0 T MRI. Electromagnetic field (EM-field) simulations, performed using two types of phantoms, viz., a cylindrical phantom filled with oil and a human head model, were used to compare the effects of MCWE and HPM on BP-BC RF coils. EM-fields were calculated using the finite difference time-domain (FDTD) method and analyzed using Matlab software. Next, to improve RF transmission efficiency, we compared two HPM structures, namely, a hollow cylinder shape HPM (hcHPM) and segmented cylinder shape HPM (scHPM). The scHPM and MCWE model comprised 16 elements (16-rad BP-BC RF coil) and this coil configuration demonstrated superior RF transmission efficiency and reception sensitivity along with an acceptable SAR. We expect wider clinical application of this combination in 7.0 T MRIs, which were recently approved by the United States Food and Drug Administration.

Research on Key Technology of Tile T/R Module Design

Tile T/R module has the characteristics of miniaturization, lightweight, high integration and high performance, which are very difficult to develop. This paper studies the key technologies involved in the development of T/R module, and focuses on the key technologies such as high integrated multifunction chip technology, high performance Radio Frequency (RF) 3D interconnection technology, high integrated multichannel RF design technology and thermal design technology. Through research and analysis, a design scheme of tile T/R module with miniaturization, high performance and high reliability is proposed.

Dynamic 13 C MR spectroscopy as an alternative to imaging for assessing cerebral metabolism using hyperpolarized pyruvate in humans.

This study is to investigate time-resolved 13 C MR spectroscopy (MRS) as an alternative to imaging for assessing pyruvate metabolism using hyperpolarized (HP) [1-13 C]pyruvate in the human brain. Time-resolved 13 C spectra were acquired from four axial brain slices of healthy human participants (n = 4) after a bolus injection of HP [1-13 C]pyruvate. 13 C MRS with low flip-angle excitations and a multichannel 13 C/1 H dual-frequency radiofrequency (RF) coil were exploited for reliable and unperturbed assessment of HP pyruvate metabolism. Slice-wise areas under the curve (AUCs) of 13 C-metabolites were measured and kinetic analysis was performed to estimate the production rates of lactate and . Linear regression analysis between brain volumes and HP signals was performed. Region-focused pyruvate metabolism was estimated using coil-wise 13 C reconstruction. Reproducibility of HP pyruvate exams was presented by performing two consecutive injections with a 45-minutes interval. [1-13 C]Lactate relative to the total 13 C signal (tC) was 0.21-0.24 in all slices. [13 C] /tC was 0.065-0.091. Apparent conversion rate constants from pyruvate to lactate and were calculated as 0.014-0.018 s-1 and 0.0043-0.0056 s-1 , respectively. Pyruvate/tC and lactate/tC were in moderate linear relationships with fractional gray matter volume within each slice. White matter presented poor linear regression fit with HP signals, and moderate correlations of the fractional cerebrospinal fluid volume with pyruvate/tC and lactate/tC were measured. Measured HP signals were comparable between two consecutive exams with HP [1-13 C]pyruvate. Dynamic MRS in combination with multichannel RF coils is an affordable and reliable alternative to imaging methods in investigating cerebral metabolism using HP [1-13 C]pyruvate.

Multi-link channel simulation based on propagation graph theory and application in performance evaluation of TDOA positioning system

In order to solve the problems of high measurement cost and many uncontrollable interference factors in the accuracy evaluation of time difference of arrival (TDOA) localization method by measurement, a method of evaluating the accuracy of a TDOA localization system based on multi-link channel propagation graph theory is proposed. In this paper, we use the propagation graph theory to generate different channel impulse responses, and ultilize software-defined radio devices to generate channel-distorted radio frequency signals as inputs to multiple TDOA sensors and construct a novel TDOA localization evaluation method. In order to verify the accuracy of the TDOA technology effectively, we simulate the method in 4 typical scenarios. It is the first time that a complex scenario is simulated using multi-channel radio frequency signal to test the localization accuracy of the TDOA system. The simulation result shows that when the signal bandwidth is not smaller than 200 kHz, the multi-link localization system based on graph modeling shows good and stable performance. Moreover, graph modeling method with diffraction model embedded enhances the accuracy of performance simulation for the TDOA system, particularly in the non-line-of-sight scenarios.

Simultaneous Head and Spine MR Imaging in Children Using a Dedicated Multichannel Receiver System at 3T

The purpose of this work was to enable simultaneous head and spine Magnetic Resonance imaging (MRI) in children at 3T by using a dedicated multichannel radiofrequency coil array system. A 24-channel head and spine pediatric coil system was developed and constructed. The coils performance was compared with a commercially available 24-channel adult head-neck coil and a spine coil (1-4 spine of 16-channel were selected). Signal-to-noise ratio (SNR) and parallel imaging capability were quantitatively evaluated by phantom studies and in vivo imaging experiments. With Institutional Review Board and Ethics Committee approval, the designed coil was used to acquire head and spine images on 27 children in clinical settings. The pediatric coil provided substantial SNR improvements with an increase of 32 % to 40 % in the brain region and up to a two-fold increase in the surface. SNR increased by at least 18 % in the spine region. The coil enabled higher resolution and a faster imaging speed, owing to significantly improved SNR. Extensive coverage of the coil enabled high-quality fast imaging from head-neck to the whole spine. Good image quality with an average score 4.63 out of 5 was achieved using the developed pediatric coil in clinical studies. Simultaneous head and spine MRI with superior performance have been successfully acquired in children subjects at 3T using the dedicated 24-channel head and spine pediatric coil system. The 24-channel pediatric coil system potentially can enhance pediatric head and spine MRI in clinical research and diagnosis.

Multi-Channel RF Supervision Module for Thermal Magnetic Resonance Based Cancer Therapy.

Simple SummaryGlioblastoma multiforme (GBM) is the most lethal brain tumor. Combining hyperthermia with chemotherapy and/or radiotherapy improves survival of GBM patients. For radio frequency (RF)-induced hyperthermia, the RF signals’ power and phase need to be supervised to achieve a precise formation of the power deposition focal point, accurate thermal dose control, and safety management. Patient position during treatment also needs to be monitored to ensure the efficiency of the treatment and to avoid adverse effects in healthy tissue. This work demonstrates the development, implementation, evaluation, validation, and application of a multi-channel RF supervision module that meets the technical requirements of hyperthermia and provides a cost-effective solution for broad-band RF signal supervision and patient monitoring. It is a key component for a hyperthermia hardware system and facilitates future thermal magnetic resonance applications that integrate RF-induced heating, in vivo temperature mapping, and anatomic and functional imaging in a single RF applicator.Glioblastoma multiforme (GBM) is the most lethal and common brain tumor. Combining hyperthermia with chemotherapy and/or radiotherapy improves the survival of GBM patients. Thermal magnetic resonance (ThermalMR) is a hyperthermia variant that exploits radio frequency (RF)-induced heating to examine the role of temperature in biological systems and disease. The RF signals’ power and phase need to be supervised to manage the formation of the energy focal point, accurate thermal dose control, and safety. Patient position during treatment also needs to be monitored to ensure the efficacy of the treatment and avoid damages to healthy tissue. This work reports on a multi-channel RF signal supervision module that is capable of monitoring and regulating RF signals and detecting patient motion. System characterization was performed for a broad range of frequencies. Monte-Carlo simulations were performed to examine the impact of power and phase errors on hyperthermia performance. The supervision module’s utility was demonstrated in characterizing RF power amplifiers and being a key part of a feedback control loop regulating RF signals in heating experiments. Electromagnetic field simulations were conducted to calculate the impact of patient displacement during treatment. The supervision module was experimentally tested for detecting patient motion to a submillimeter level. To conclude, this work presents a cost-effective RF supervision module that is a key component for a hyperthermia hardware system and forms a technological basis for future ThermalMR applications.

Adjustable RF Transmitter Head Coil: Improving Transmit Efficiency With SAR Management for 7-T Magnetic Resonance Imaging

In ultrahigh field magnetic resonance imaging (MRI) using a static magnetic field over 7 T, the inhomogeneity in the time-varying magnetic field ( $B_{1}$ ), which is caused by its short wavelength, is mitigated by using a multichannel radio frequency (RF) coil as an antenna. However, the conventional multichannel RF coil has a fixed configuration; consequently, its transmit efficiency (TE) changes according to the head shape of the patient. In this study, a geometrically adjustable eight-channel RF transmitter head coil for 7-T MRI was proposed. All resonators and supporting structures (called bridges) in the coil have interlocking teeth at their sides, allowing each channel to adjust its geometric location according to the head shape of the patient. Scenarios for conventional and proposed coils in three different configurations were simulated and compared in terms of the transmitted component of the $B_{1}$ field ( $B_{1}^{+}$ field) and specific absorption rate (SAR) maps. The simulation results indicate that, for a given configuration and head shape, the TE of the proposed coil was higher than that of the conventional coil, while the SAR efficiency remained unchanged. Furthermore, the S-parameter matrix of the proposed coil and the measured $B_{1}$ field produced by the two channels facing each other show that the proposed coil resonates at 298 MHz with acceptable mutual coupling and effectively improves the $B_{1}$ field intensity. Moreover, the obtained signal-to-noise ratio (SNR) maps and magnetic resonance (MR) images prove that the proposed coil is an efficient candidate for an RF transmitter or transceiver head coil used in 7-T MRI.

Breast calcification detection based on multichannel radiofrequency signals via a unified deep learning framework

Breast calcifications in radiographic images suggest a high likelihood of breast lesion malignancy. However, it is difficult to detect calcifications in traditional B-mode ultrasound images due to resolution limits and speckle noise. In this paper, we propose a unified deep learning framework for automatic calcification detection based on multichannel ultrasound radio frequency (RF) signals. First, beamforming is used during preprocessing to merge and blend multichannel signals into one-channel RF signals. Each scan line is converted into a spectrogram by the short-time Fourier transform (STFT) to utilize the frequency domain characteristics. Then, an improved fully convolutional neural network called the RF signal Spectrogram-Calcification-Detection-Net (SCD-Net) is proposed to detect calcifications from spectrograms. This method employs a deep learning architecture based on YOLOv3 and combines features via convolutional long short-term memory (ConvLSTM). Next, a Kalman filter for tracking calcifications between consecutive spectrograms based on SCD-Net detection results is applied since the spatial coherence of calcifications in neighboring frames can be taken into account. Finally, the detected calcification is mapped from the time domain of spectrograms to B-mode images for clinical diagnosis. Experiments were conducted on a database of 337 experienced doctor-marked breast tumors with calcifications. Compared to the state-of-the-art methods for detecting calcifications, the proposed method achieved an average precision (AP) of 88.25%, an accuracy of 84% and an F1 score of 91%. The experimental results demonstrate that the unified framework has great performance for tumor calcification detection. The system can be effectively applied in a portable ultrasound instrument to accurately help radiologists and provide guidance for breast tumor diagnosis. This implies that the proposed approach can be implemented in real practice for analyzing breast RF signals, which have many useful medical applications in clinical breast tumor diagnosis.

Parallel high-frequency magnetic sensing with an array of flux transformers and multi-channel optically pumped magnetometer for hand MRI application

We investigate an approach for parallel high-frequency magnetic sensing based on a multi-channel radio frequency (RF) optically pumped magnetometer (OPM) coupled to multiple flux transformers (FTs) with a focus on hand magnetic resonance imaging (MRI) application at ultra-low field (ULF). Multiple RF OPM sensing channels are realized by using a single large-area alkali-metal vapor cell and two laser beams for pumping and probing, shared for all the channels. This design leads to significant cost reduction when multi-channel sensing is desirable, as in the case of ULF MRI. The FT, composed of two connected coils, serves as a transmitter of a target magnetic field to the OPM, while decoupling the OPM from untargeted magnetic fields in the sensing area that can limit the OPM performance. For hand MRI application, theoretical and numerical analysis is performed to determine an optimal geometry for the FT array that could improve signal-to-noise ratio (SNR) and sufficiently reduce crosstalk between FTs. We estimate that the optimized multi-channel FT-OPM sensor can achieve a magnetic field sensitivity of the order of 1fT/Hz1/2 above 100 kHz, which would be sufficient for 1 mm resolution MRI. In general, the multi-channel capability enables simultaneous magnetic measurements, thus reducing the sensing time and improving the SNR, and we anticipate many applications of the multi-channel FT-OPM sensor beyond the targeted here hand MRI: anatomical parallel ULF MRI of the human brain and other parts of the body, airport security screening, magnetic material imaging, and many others.

Investigating the influence of dielectric pads in 7T magnetic resonance imaging – simulated and experimental assessment

Abstract Dipole radiofrequency (RF) elements have been successfully used to compose multi-channel RF coils for ultrahigh fields (UHF) magnetic resonance imaging (MRI). As magnetic components of RF fields (B1) can be very inhomogeneous at UHF (B0≥7T), dielectric pads with high dielectric constants were proposed to improve the B1 efficiency and homogeneity [1]. Dielectric pads can be used as a passive B1 shimmimg technique thanks to inducing a strong secondary magnetic field in their vicinity. The use of such dielectric pads affect not only the B1 field but also the electric field. This in turn affects the specific absorption rate (SAR) and consequently the temperature distribution inside the patient’s body. To study these effects, a 29 cm-long transmission dipole RF coil element terminated by two meander was used for 7T MRI [2]. Using a cylindrical agarose-gel phantom, numerical and experimental results were analyzed with respect to homogeneity and amplitude of the magnetic and electric fields generated by the RF element in various configurations with and without dielectric pads. Calculated and measured B1 results were cross-checked and found to be in good agreement. When using dielectric pads B1 homogeneity and magnitude increase in regions where it was previously weak or insufficient. Calculations suggest that SAR distribution will change when using the pads.

Design, Implementation, Evaluation and Application of a 32-Channel Radio Frequency Signal Generator for Thermal Magnetic Resonance Based Anti-Cancer Treatment.

Thermal Magnetic Resonance (ThermalMR) leverages radio frequency (RF)-induced heating to examine the role of temperature in biological systems and disease. To advance RF heating with multi-channel RF antenna arrays and overcome the shortcomings of current RF signal sources, this work reports on a 32-channel modular signal generator (SGPLL). The SGPLL was designed around phase-locked loop (PLL) chips and a field-programmable gate array chip. To examine the system properties, switching/settling times, accuracy of RF power level and phase shifting were characterized. Electric field manipulation was successfully demonstrated in deionized water. RF heating was conducted in a phantom setup using self-grounded bow-tie RF antennae driven by the SGPLL. Commercial signal generators limited to a lower number of RF channels were used for comparison. RF heating was evaluated with numerical temperature simulations and experimentally validated with MR thermometry. Numerical temperature simulations and heating experiments controlled by the SGPLL revealed the same RF interference patterns. Upon RF heating similar temperature changes across the phantom were observed for the SGPLL and for the commercial devices. To conclude, this work presents the first 32-channel modular signal source for RF heating. The large number of coherent RF channels, wide frequency range and accurate phase shift provided by the SGPLL form a technological basis for ThermalMR controlled hyperthermia anti-cancer treatment.

Designing of an Efficient Electronic module for Sensory Network used in Smart City

(Please read carefully abstract of the template). Now-a-days the world population is rapidly increases for which a dreadful requirement is necessary for developing a livable city. Hence the term Smart City is introduced which focus on the Smart environment and environment development, smart waste management and sanitation, smart water management and harvesting, smart energy management etc. In order to monitoring the entire city in a smart way, all the related information is required to collected in an efficient manner. Hence, the Sensory Network operated in wireless mode is a best choice for collecting useful information in several points of the cities. Though, the sensory Network operated in wireless mode consumes a high power so the sovereignty of the module. This paper projected a designing of an efficient electronic circuit module which operate with less power for sensory network used in a smart city. The proposed module consists of a sensory module along with storage unit. The Sensory module operates in wireless mode is implemented by multi-channel Radio Frequency (RF) with a frequency range of 310 to 910 MHz and an External Memory as Electrically Erasable Programmable Read Only Memory (E2PROM) with Real Time Clock Chip (RTC-DS1307IC) is considered as storage unit. Finally, the designed module is operated by considering both the information from sensory nodes and storage unit.

Software receiver design for GNSS‐R using multiple GNSS satellites as transmitters

A novel global navigation satellite system-reflectometry (GNSS-R) software receiver and its preliminary experimental results are presented in this study. The antenna systems, the multi-channel radio-frequency front end, and the digital signal processing unit of this receiver are described in detail. With this developed software receiver, the signals in the Global Positioning System L1 band (GPS L1), BeiDou-2 B1, GLObal NAvigation Satellite System L1, and Galileo E1 bands can be tracked and used as the transmissions of GNSS-R to obtain more information about the scattering properties of ground objects. The preliminary experimental results show that various GNSS signals can be successfully acquired and tracked by this receiver. Furthermore, when it was applied to the soil moisture estimation with the ground-based GNSS-R technique, a relative measure error of 5.79 and 1.39% can be obtained with GPS L1 and BeiDou-2 B1 signals, respectively, by comparing the retrieval results with the measuring results provided by a moisture metre.