Mechanically Adjustable 4-Channel RF Transceiver Coil Array for Rat Brain Imaging in a Whole-Body 7 T MR Scanner.

Investigations of human brain disorders are frequently conducted in rodent models using magnetic resonance imaging. Due to the small specimen size and the increase in signal-to-noise ratio with the static magnetic field strength, dedicated small-bore animal scanners can be used to acquire high-resolution data. Ultra-high-field (≥7 T) whole-body human scanners are increasingly available, and they can also be used for animal investigations. Dedicated sensors, in this case, radiofrequency coils, are required to achieve sufficient sensitivity for the high spatial resolution needed for imaging small anatomical structures. In this work, a four-channel transceiver coil array for rat brain imaging at 7 T is presented, which can be adjusted for use on a wide range of differently sized rats, from infants to large adults. Three suitable array designs (with two to four elements covering the whole rat brain) were compared using full-wave 3D electromagnetic simulation. An optimized static B1+ shim was derived to maximize B1+ in the rat brain for both small and big rats. The design, together with a 3D-printed adjustable coil housing, was tested and validated in ex vivo rat bench and MRI measurements.

Spectral Efficiency Maximization for Mixed-Structure Cognitive Radio Hybrid Wideband Millimeter-Wave Transceivers in Relay-Assisted Multi-User Multiple-Input Multiple-Output Systems.

This paper proposes a cognitive radio network (CRN)-based hybrid wideband precoding for maximizing spectral efficiency in millimeter-wave relay-assisted multi-user (MU) multiple-input multiple-output (MIMO) systems. The underlying problem is NP-hard and non-convex due to the joint optimization of hybrid processing components and the constant amplitude constraint imposed by the analog beamformer in the radio frequency (RF) domain. Furthermore, the analog beamforming solution common to all sub-carriers adds another layer of design complexity. Two hybrid beamforming architectures, i.e., mixed and fully connected ones, are taken into account to tackle this problem, considering the decode-and-forward (DF) relay node. To reduce the complexity of the original optimization problem, an attempt is made to decompose it into sub-problems. Leveraging this, each sub-problem is addressed by following a decoupled design methodology. The phase-only beamforming solution is derived to maximize the sum of spectral efficiency, while digital baseband processing components are designed to keep interference within a predefined limit. Computer simulations are conducted by changing system parameters under different accuracy levels of channel-state information (CSI), and the obtained results demonstrate the effectiveness of the proposed technique. Additionally, the mixed structure shows better energy efficiency performance compared to its counterparts and outperforms benchmarks.

Automated test apparatus for bench-testing the magnetic field homogeneity of NMR transceiver coils.

We describe an automated hands-off bench testing method for measuring the magnetic field profile of transceiver coils for nuclear magnetic resonance (NMR). The scattering parameter (S-parameter) data is measured using a portable network analyzer, and the results are automatically exported to a computer for plotting and viewing. This assay dramatically reduces the time needed to measure the magnetic field (B1) homogeneity profile of a transceiver coil while also improving accuracy relative to manual operation. Here, we demonstrate the method on a saddle coil of a solution-state NMR probe in comparison to profiles obtained using NMR spectroscopy measurements. We also measure the axial and radial homogeneity of a variable-pitch solenoid.

An Intermodulation Radar for Non-Linear Target and Transceiver Detection.

The design and the characterization of a non-linear target to test an intermodulation radar was performed using the AWR design environment Version 22 by Cadence software. Two experimental setups for intermodulation measurements were realized in order to characterize connectorized or antenna-equipped devices. Both setups were modeled using the VSS software available inside AWR Version 22. The comparison between measurements and simulations on the designed target showed a very good agreement. Intermodulation measurements were performed on connectorized devices present inside electronic systems and on various transceiver available on the market. This experimental study evidenced that the non-linearities of devices such as amplifiers and mixers are visible at their access ports even when the device is switched off. Moreover, this study highlights the ability of an intermodulation radar to remotely detect the presence of a particular transceiver, even when the latter is switched off, thanks to the specific frequency response of its intermodulation products.

Fully Integrated 24-GHz 1TX-2RX Transceiver for Compact FMCW Radar Applications.

A fully integrated 24-GHz radar transceiver with one transmitter (TX) and two receivers (RXs) for compact frequency modulated continuous wave (FMCW) radar applications is here presented. The FMCW synthesizer was realized using a fractional-N phase-locked loop (PLL) and programmable chirp generator, which are completely integrated in the proposed transceiver. The measured output phase noise of the synthesizer is -80 dBc/Hz at 100 kHz offset. The TX consists of a three-bit bridged t-type attenuator for gain control, a two-stage drive amplifier (DA) and a one-stage power amplifier (PA). The TX chain provides an output power of 13 dBm while achieving <0.5 dB output power variation within the range of 24 to 24.25 GHz. The RX with a direct conversion I-Q structure is composed of a two-stage low noise amplifier (LNA), I-Q generator, mixer, transimpedance amplifier (TIA), a two-stage biquad band pass filter (BPF), and a differential-to-single (DTS) amplifier. The TIA and the BPF employ a DC offset cancellation (DCOC) circuit to suppress the strong reflection signal and TX-RX leakage. The RX chain exhibits an overall gain of 100 dB. The proposed radar transceiver is fabricated using a 65 nm CMOS technology. The transceiver consumes 220 mW from a 1 V supply voltage and has 4.84 mm2 die size including all pads. The prototype FMCW radar is realized with the proposed transceiver and Yagi antenna to verify the radar functionality, such as the distance and angle of targets.

Evaluation of the performance of a 7-T 8 × 2 transceiver array.

The decoupled 8 × 2 transceiver array has been shown to achieve a mean B1 + of 11.7 uT with a coefficient of variation of ~11% over the intracranial brain volume for 7-T MR imaging. However, this array may be thought to give lower signal-to-noise ratio (SNR) and higher g-factors for parallel imaging compared with a radio frequency (RF) receive-only coil due to the latter's higher coil count and use of coil overlap to reduce the mutual impedance. Nonetheless, because the transceiver's highly decoupled design (pertinent for transmission) should also be constructive for reception, we measured the noise correlation, g-factors, and SNR for the decoupled transceiver in comparison with a commercial reference coil. We found that although the transceiver has half the number of receive elements in comparison with the reference coil (16 vs. 32), comparable g-factors and SNR over the head were obtained. From five subjects, the transceiver versus reference coil SNR was 65 ± 10 versus 67 ± 15. The mean noise correlation for all coil pairs was 10% ± 5% and 12% ± 9% (transceiver and reference coil, respectively). As changes in load impedance may alter the S parameters, we also examined the performance of the transceiver with tuned and matched (TM) versus untuned and unmatched (UTM) conditions on five subjects. We found that the noise correlation and SNR are robust to load variation; a noise correlation of 10% ± 5% and 10% ± 6% was determined with TM versus UTM conditions (SNRUTM/SNRTM = 0.97 ± 0.08). Finally, we demonstrate the performance of the array in human brain using T2-weighted turbo spin echo imaging, finding excellent SNR performance in both caudal and rostral brain regions.

A chip-based C-band ODNP platform.

In this paper, we present a chip-based C-band ODNP platform centered around an NMR-on-a-chip transceiver and a printed microwave (MW) Alderman-Grant (AG) coil with a broadband tunable frequency range of 528MHz. The printable ODNP probe is optimized for a high input-power-to-magnetic-field conversion-efficiency, achieving a measured ODNP enhancement factor of -151 at microwave power levels of 33.3dBm corresponding to 2.1W. NMR measurements with and without microwave irradiation verify the functionality and the state-of-the-art performance of the proposed ODNP platform. The wide tuning range of the system allows for indirect measurements of the EPR signal of the DNP agent by sweeping the microwave excitation frequency and recording the resulting NMR signal. This feature can, e.g., be used to detect line broadening of the DNP agent. Moreover, we demonstrate experimentally that the wide tuning range of the new ODNP platform can be used to perform multi-tone microwave excitation for further signal enhancement: Using a 10mM TEMPOL solution, we improved the enhancement by a factor of two.

Intensive and Efficient Design of a Two-dimensional 8 × 8 Silicon-Based Optical Phased Array Transceiver.

In recent years, the silicon-based optical phased array has been widely used in the field of light detection and ranging (LIDAR) due to its great solid-state steering ability. At the same time, the optical phased array transceiver integration scheme provides a feasible solution for low-cost information exchange of small devices in the future. Based on this, this paper designs a two-dimensional optical phased array transceiver with high efficiency and a large field of view, which can realize a dense array with antenna spacing of 5.5 µm × 5.5 µm by using low crosstalk waveguide wiring. Additionally, it can realize the conversion between the receiving mode and the transmitting mode by using the optical switch. The simulation results show that the scanning range of 16.3° × 16.3° can be achieved in the transmitting mode, and the overall loss is lower than 10dB. In the receiving mode, we can achieve a collection efficiency of more than 27%, and the antenna array receiving loss is lower than 12.1 dB.

A Synthetic Ultra-Wideband Transceiver for Millimeter-Wave Imaging Applications.

In this work, we present a transceiver front-end in SiGe BiCMOS technology that can provide an ultra-wide bandwidth of 100 GHz at millimeter-wave frequencies. The front-end utilizes an innovative arrangement to efficiently distribute broadband-generated pulses and coherently combine received pulses with minimal loss. This leads to the realization of a fully integrated ultra-high-resolution imaging chip for biomedical applications. We realized an ultra-wide imaging band-width of 100 GHz via the integration of two adjacent disjointed frequency sub-bands of 10-50 GHz and 50-110 GHz. The transceiver front-end is capable of both transmit (TX) and receive (RX) operations. This is a crucial component for a system that can be expanded by repeating a single unit cell in both the horizontal and vertical directions. The imaging elements were designed and fabricated in Global Foundry 130-nm SiGe 8XP process technology.

Avalanche Education Is Associated with Increased Avalanche Safety Practices in the New Hampshire Backcountry.

INTRODUCTION: Avalanche risk can be mitigated by adhering to certain safety practices. Previous studies of these practices have focused on western United States and European cohorts. We conducted a survey of backcountry users in the White Mountains of New Hampshire to determine local adherence to 5 previously studied avalanche safety practices. We assessed whether participants were carrying transceiver, probe, and shovel (TPS); had formal avalanche education; had awareness of the day's avalanche danger level; had a route plan; and were traveling in a group. METHODS: Backcountry users in the White Mountains were directed to an online survey from December 2020 to June 2021. The survey was completed individually and queried demographics and avalanche safety practices. RESULTS: A total of 133 users participated. Not all surveyed participants answered all questions. Avalanche training was reported by 87% of users, 86% checked the avalanche forecast prior to recreating, 93% had a travel plan, 87% traveled in a group, and 59% carried TPS. All 3 items were carried by all group members only 48% of the time. Only 28% of users met all 5 safety practices. CONCLUSIONS: White Mountains backcountry users are less likely to meet avalanche safety practices than users in previous studies. There is an association between meeting these defined safety practices and formal avalanche education.

Measurement and risk perception of non-ionizing radiation from base transceiver stations in Dhaka City of Bangladesh.

Multiple harmful health effects can have on the population from non-ionizing radiation (NIR) sources. To date, there has been no extensive data collection about NIR emitted from base transceiver stations in Dhaka City, Bangladesh. This study aims to remedy that by collecting data and comparing the processed data to the international standards, International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines, and standards of other countries. For this, measurement data were collected from 361 different publicly accessible locations in Dhaka City applying a convenience sampling approach. The measured average electric field exceeded the 1800 MHz threshold values of 36.84, 33.5, and 7.5% of the time compared with the thresholds of China, India, and Japan, respectively, followed by the measured average electromagnetic field values, which were 57, 52, and 29%, respectively. No exceedance was seen for radiofrequency power flux for the investigated countries. Approximately 35% of the calculated average specific energy absorption rate values exceeded the ICNIRP recommended public exposure limit of 0.08 W/kg. Based on this data, it is suggested that detailed NIR exposure regulations need to be created and proper oversight and enforcement over operators are required to avoid potential health effects.

A 22-pJ/spike 73-Mspikes/s 130k-compartment neural array transceiver with conductance-based synaptic and membrane dynamics.

Neuromorphic cognitive computing offers a bio-inspired means to approach the natural intelligence of biological neural systems in silicon integrated circuits. Typically, such circuits either reproduce biophysical neuronal dynamics in great detail as tools for computational neuroscience, or abstract away the biology by simplifying the functional forms of neural computation in large-scale systems for machine intelligence with high integration density and energy efficiency. Here we report a hybrid which offers biophysical realism in the emulation of multi-compartmental neuronal network dynamics at very large scale with high implementation efficiency, and yet with high flexibility in configuring the functional form and the network topology. The integrate-and-fire array transceiver (IFAT) chip emulates the continuous-time analog membrane dynamics of 65 k two-compartment neurons with conductance-based synapses. Fired action potentials are registered as address-event encoded output spikes, while the four types of synapses coupling to each neuron are activated by address-event decoded input spikes for fully reconfigurable synaptic connectivity, facilitating virtual wiring as implemented by routing address-event spikes externally through synaptic routing table. Peak conductance strength of synapse activation specified by the address-event input spans three decades of dynamic range, digitally controlled by pulse width and amplitude modulation (PWAM) of the drive voltage activating the log-domain linear synapse circuit. Two nested levels of micro-pipelining in the IFAT architecture improve both throughput and efficiency of synaptic input. This two-tier micro-pipelining results in a measured sustained peak throughput of 73 Mspikes/s and overall chip-level energy efficiency of 22 pJ/spike. Non-uniformity in digitally encoded synapse strength due to analog mismatch is mitigated through single-point digital offset calibration. Combined with the flexibly layered and recurrent synaptic connectivity provided by hierarchical address-event routing of registered spike events through external memory, the IFAT lends itself to efficient large-scale emulation of general biophysical spiking neural networks, as well as rate-based mapping of rectified linear unit (ReLU) neural activations.

A Multimode 28 GHz CMOS Fully Differential Beamforming IC for Phased Array Transceivers.

A 28 GHz fully differential eight-channel beamforming IC (BFIC) with multimode operations is implemented in 65 nm CMOS technology for use in phased array transceivers. The BFIC has an adjustable gain and phase control on each channel to achieve fine beam steering and beam pattern. The BFIC has eight differential beamforming channels each consisting of the two-stage bi-directional amplifier with a precise gain control circuit, a six-bit phase shifter, a three-bit digital step attenuator, and a tuning bit for amplitude and phase variation compensation. The Tx and Rx mode overall gains of the differential eight-channel BFIC are around 11 dB and 9 dB, respectively, at 27.0-29.5 GHz. The return losses of the Tx mode and Rx mode are >10 dB at 27.0-29.5 GHz. The maximum phase of 354° with a phase resolution of 5.6° and the maximum attenuation of 31 dB, including the gain control bits with an attenuation resolution of 1 dB, is achieved at 27.0-29.5 GHz. The root mean square (RMS) phase and amplitude errors are <3.2° and <0.6 dB at 27.0-29.5 GHz, respectively. The chip size is 3.0 × 3.5 mm2, including pads, and Tx mode current consumption is 580 mA at 2.5 V supply voltage.

X-band MMICs for a Low-Cost Radar Transmit/Receive Module in 250 nm GaN HEMT Technology.

This paper describes Monolithic Microwave Integrated Circuits (MMICs) for an X-band radar transceiver front-end implemented in 0.25 µm GaN High Electron Mobility Transistor (HEMT) technology. Two versions of single pole double throw (SPDT) T/R switches are introduced to realize a fully GaN-based transmit/receive module (TRM), each of which achieves an insertion loss of 1.21 dB and 0.66 dB at 9 GHz, IP1dB higher than 46.3 dBm and 44.7 dBm, respectively. Therefore, it can substitute a lossy circulator and limiter used for a conventional GaAs receiver. A driving amplifier (DA), a high-power amplifier (HPA), and a robust low-noise amplifier (LNA) are also designed and verified for a low-cost X-band transmit-receive module (TRM). For the transmitting path, the implemented DA achieves a saturated output power (Psat) of 38.0 dBm and output 1-dB compression (OP1dB) of 25.84 dBm. The HPA reaches a Psat of 43.0 dBm and power-added efficiency (PAE) of 35.6%. For the receiving path, the fabricated LNA measures a small-signal gain of 34.9 dB and a noise figure of 2.56 dB, and it can endure higher than 38 dBm input power in the measurement. The presented GaN MMICs can be useful in implementing a cost-effective TRM for Active Electronically Scanned Array (AESA) radar systems at X-band.

Design of Wideband FMCW Radar Transceiver System Using Photonic Elements.

This paper proposes a FMCW radar transceiver with photonic elements. The proposed radar system is efficiently designed by budget analysis, and a wideband signal is generated using photonic elements. To verify the performance of the proposed radar system, field tests including changes in bandwidth are conducted. The results confirm that the resolution of ISAR images improves as the bandwidth increases as expected through the budget analysis.

Self-Sustainable IoT-Based Remote Sensing Powered by Energy Harvesting Using Stacked Piezoelectric Transducer and Thermoelectric Generator.

We propose a self-powered remote multi-sensing system for traffic sensing which is powered by the collective energy harvested from the mechanical vibration of the road caused by the passing vehicles and from the temperature gradient between the asphalt of the road and the soil underneath. A stacked piezoelectric transducer converts mechanical vibrations into electrical energy and a thermoelectric generator harvests the thermal energy from the thermal gradient. Electrical energy signals from the stacked piezoelectric transducer and the thermoelectric generators are converted into usable DC power to recharge the battery using AC-DC and DC-DC converters working simultaneously. The multi-sensing system comprises an embedded system with a microcontroller that acquires data from the sensors and sends the sensory data to an IoT transceiver which transmits the data as RF packets to an ethernet gateway. The gateway converts the RF packets into Internet Protocol (IP) packets and sends them to a remote server. Laboratory and road-testing results showed over 98% sensory data accuracy with the system functioning solely powered by the energy harvested from the alternative energy sources. The successful maximum transmission distance obtained between the IoT, and the gateway was approximately 1 mile, which is a considerable transmission distance achieved in an urban environment. Successful operation of the self-powered multi-sensing system under both laboratory and road conditions contributes considerably to the fields of energy harvesting and self-powered remote sensing systems. The energy flow chart and efficiency for the steps in the system were found to be mechanical power from vehicles to the energy harvester of 0.25%, stacked PZT transducer efficiency was found to be 37%, and for the TEGs the efficiency is 11%. AC-to-DC and DC-to-DC converters' efficiencies were found to be 90% and 11%. The wireless communication RF transceiver efficiency was found to be 62.5%.

Double-row 16-element folded-end dipole transceiver array for 3D RF shimming of the whole human brain at 9.4 T.

Homogeneity and longitudinal coverage of transmit (Tx) human head RF coils at ultrahigh field (UHF, ≥7 T) can be improved by 3D RF shimming, which requires using multi-row Tx arrays. Examples of 3D RF shimming using double-row UHF loop transceiver (TxRx) and Tx arrays have been described previously. Dipole antennas provide unique simplicity and robustness while offering comparable Tx efficiency and signal-to-noise ratio to conventional loop designs. Single-row Tx and TxRx human head UHF dipole arrays have been previously described by multiple groups. Recently, we developed a novel type of dipole antenna, a folded-end dipole, and presented single-row eight-element array prototypes for human head imaging at 7 and 9.4 T. These studies have shown that the novel antenna design can improve the longitudinal coverage and minimize peak local specific absorption rate (SAR) as compared with common unfolded dipoles. In this work, we developed, constructed, and evaluated a 16-element double-row TxRx folded-end dipole array for human head imaging at 9.4 T. To minimize cross-talk between neighboring dipoles located in different rows, we used transformer decoupling, which decreased coupling to a level below -20 dB. The developed array design was demonstrated to be capable of 3D static RF shimming and can be potentially used for dynamic shimming using parallel transmission. For optimal phase shifts between the rows, the array provides 11% higher SAR efficiency and 18% higher homogeneity than a folded-end dipole single-row array of the same length. The design also offers a substantially simpler and more robust alternative to the common double-row loop array with about 10% higher SAR efficiency and better longitudinal coverage.

A 28 GHz Phased-Array Transceiver for 5G Applications in 22 nm FD-SOI CMOS.

This paper presents the design and implementation of a 28 GHz phased array transceiver for 5G applications using 22 nm FD-SOI CMOS technology. The transceiver consists of a four-channel phased array receiver and transmitter, which employs phase shifting based on coarse and fine controls. The transceiver employs a zero-IF architecture, which is suitable for small footprints and low power requirements. The receiver achieves a 3.5 dB NF with a 1 dB compression point of -21 dBm and a gain of 13 dB.

A Low-Power Wireless System for Predicting Early Signs of Sudden Cardiac Arrest Incorporating an Optimized CNN Model Implemented on NVIDIA Jetson.

The survival rate for sudden cardiac arrest (SCA) is low, and patients with long-term risks of SCA are not adequately alerted. Understanding SCA's characteristics will be key to developing preventive strategies. Many lives could be saved if SCA's early onset could be detected or predicted. Monitoring heart signals continuously is essential for diagnosing sporadic cardiac dysfunction. An electrocardiogram (ECG) can be used to continuously monitor heart function without having to go to the hospital. A zeolite-based dry electrode can provide safe on-skin ECG acquisition while the subject is out-of-hospital and facilitate long-term monitoring. To the ECG signal, a low-power 1 µW read-out circuit was designed and implemented in our prior work. However, having long-term ECG monitoring outside the hospital, i.e., high battery life, and low power consumption while transmission and reception of ECG signal are crucial. This paper proposes a prototype with a 10-bit resolution ADC and nRF24L01 transceivers placed 5 m apart. The system uses the 2.4 GHz worldwide ISM frequency band with GFSK modulation to wirelessly transmit digitized ECG bits at 250 kbps data rate to a physician's computer (or similar) for continuous monitoring of ECG signals; the power consumption is only 11.2 mW and 4.62 mW during transmission and reception, respectively, with a low bit error rate of ≤0.1%. Additionally, a subject-wise cross-validated, three-fold, optimized convolutional neural network (CNN) model using the Physionet-SCA dataset was implemented on NVIDIA Jetson to identify the irregular heartbeats yielding an accuracy of 89% with a run time of 5.31 s. Normal beat classification has an F1 score of 0.94 and a ROC score of 0.886. Thus, this paper integrates the ECG acquisition and processing unit with low-power wireless transmission and CNN model to detect irregular heartbeats.

Transceiver Optimization for mmWave Line-of-Sight MIMO Systems Using Hybrid Arrays.

The performance of millimeter wave (mmWave) line-of-sight multiple input multiple output (LOS MIMO) systems using hybrid arrays of planar subarrays was studied. We characterized the achievable maximum spatial multiplexing gain for such LOS MIMO systems by the measures of spectral efficiency and effective degree of freedom (EDoF). By proposing a joint plane-wave and spherical-wave-based general 3D channel model, we derived the optimal design parameters in the analog domain, i.e., the optimal subarray separation products, and analyzed their sensitivity on the system performance. We also gave analytical eigenvalue expressions of the equivalent LOS MIMO channel matrix, which are applicable to the case of a non-optimal design, as well as the upper and lower bounds of the EDoF for system performance evaluation. A piecewise uniform quantization codebook was further designed for quantizing phase shifter values in practical applications. The numerical and simulation results show that planar subarrays are superior to traditional arrays in terms of spectral efficiency and EDoF in Ricean fading channels because they are more robust to the change in the communication distance and the deviation from the optimal design. The use of hybrid arrays of planar subarrays effectively removes the limitation of mmWave LOS MIMO systems using traditional arrays, through which, the conventional Rayleigh distance criterion has to be satisfied to achieve the optimal performance.