Robust Radio Frequency Research Articles

Robust reconfigurable radiofrequency photonic filters based on a single silicon in-phase/quadrature modulator

Abstract Combining integrated photonics and radiofrequency (RF) signals in the optical domain can help overcome the limitations of traditional RF systems. However, it is challenging to achieve environmentally insensitive filtering in wireless communications using integration schemes. In this report, the performance of robust RF filters based on a single silicon in-phase/quadrature modulator with significantly improved temperature and optical carrier wavelength sensitivities, which were suppressed by more than three orders of magnitude compared with those of silicon resonators, was experimentally evaluated. Upconversion and the processing of signals were simultaneously realized on the modulator by setting the relative phases of the arms and the bias voltages. Moreover, the filters can be reconfigured as low-pass, high-pass, band-pass, or band-stop filters. From 25 to 75 °C, the center frequency variation was within 0.2 GHz. From 1500 to 1600 nm, the center frequency variation was within 2 GHz. The proposed scheme allows for filtering and reconfiguration without the use of optical processing modules such as resonators or delay lines, thus providing a novel approach to signal processing and a new robust filter for scenarios with dynamic environments.

Design of a Channel Robust Radio Frequency Fingerprint Identification Scheme

Radio frequency fingerprint (RFF) identification is an emerging device authentication technique that exploits the hardware imperfections resulting from the manufacturing process. Due to the varying impact of the wireless channel during RFF training and test stages, it is challenging to design channel-independent RFF techniques. This article designs a channel robust RFF identification scheme by leveraging the different spectrum of adjacent signal symbols, named the Difference of the Logarithm of the Spectrum (DoLoS), which does not rely on a single RFF feature or requires additional manipulation of the devices under test. Specifically, DoLoS exploits the fact that two different symbols in a packet exhibit different RFF features but have a similar channel response during the channel coherence time. We implemented the DoLoS with the IEEE 802.11 orthogonal frequency division multiplexing (OFDM) system as a case study. We carried out extensive experiments using seven Wi-Fi devices of the same model in different wireless channel environments, including 12 data collection positions in two completely different environments. Compared with conventional RFF identification schemes that do not eliminate channel effects, our scheme is robust to channel variations and the highest identification accuracy is 99.02% in the single-environment evaluation and 97.05% in the cross-environment evaluation.

Updates on Compositional MRI Mapping of the Cartilage: Emerging Techniques and Applications.

Osteoarthritis (OA) is a widely occurring degenerative joint disease that is severely debilitating and causes significant socioeconomic burdens to society. Magnetic resonance imaging (MRI) is the preferred imaging modality for the morphological evaluation of cartilage due to its excellent soft tissue contrast and high spatial resolution. However, its utilization typically involves subjective qualitative assessment of cartilage. Compositional MRI, which refers to the quantitative characterization of cartilage using a variety of MRI methods, can provide important information regarding underlying compositional and ultrastructural changes that occur during early OA. Cartilage compositional MRI could serve as early imaging biomarkers for the objective evaluation of cartilage and help drive diagnostics, disease characterization, and response to novel therapies. This review will summarize current and ongoing state-of-the-art cartilage compositional MRI techniques and highlight emerging methods for cartilage compositional MRI including MR fingerprinting, compressed sensing, multiexponential relaxometry, improved and robust radio-frequency pulse sequences, and deep learning-based acquisition, reconstruction, and segmentation. The review will also briefly discuss the current challenges and future directions for adopting these emerging cartilage compositional MRI techniques for use in clinical practice and translational OA research studies. EVIDENCE LEVEL: 2 TECHNICAL EFFICACY: Stage 2.

Improved bounds on Lorentz violation from composite pulse Ramsey spectroscopy in a trapped ion

In attempts to unify the four known fundamental forces in a single quantum-consistent theory, it is suggested that Lorentz symmetry may be broken at the Planck scale. Here we search for Lorentz violation at the low-energy limit by comparing orthogonally oriented atomic orbitals in a Michelson-Morley-type experiment. We apply a robust radiofrequency composite pulse sequence in the 2F7/2 manifold of an Yb+ ion, extending the coherence time from 200 μs to more than 1 s. In this manner, we fully exploit the high intrinsic susceptibility of the 2F7/2 state and take advantage of its exceptionally long lifetime. We match the stability of the previous best Lorentz symmetry test nearly an order of magnitude faster and improve the constraints on the symmetry breaking coefficients to the 10−21 level. These results represent the most stringent test of this type of Lorentz violation. The demonstrated method can be further extended to ion Coulomb crystals.

Radio Frequency Fingerprinting Improved by Statistical Noise Reduction

Radio frequency (RF) fingerprinting as an important non-password authentication technology has received extensive attention in recent years. It can be used as an underlying intrusion detection component for various wireless networks to enhance their wireless security further. In order to achieve more robust RF fingerprinting with deep learning, this paper develops a practical signal data augmentation solution consisting of two steps: 1) construction of sampling points 2) smooth filtering, which enables to enhance discriminability for individual radio examples. The underlying idea is that using a relatively long signal can implicitly perform noise reduction in a statistical sense since noise is often uncorrelated or partially correlated. As more sampling points accumulated, RF fingerprints could be more discernible. Experimental results have demonstrated that our proposed data augmentation can significantly improve recognition accuracy, especially in low signal-to-noise ratio (SNR) and small example conditions.

Design of a Robust Radio-Frequency Fingerprint Identification Scheme for Multimode LFM Radar

Radar is an indispensable part of the Internet of Things (IoT). Specific emitter identification is essential to identify the legitimate radars and, more importantly, to reject the malicious radars. Conventional methods rely on pulse parameters that are not capable to identify the specific emitter as two radars may have the same configuration or a malicious radar can perform spoofing attacks. Radio-frequency fingerprint (RFF) is the unique and intrinsic hardware characteristic of devices resulted from hardware imperfection, which can be used as the device identity. This article proposes a robust and reliable radar identification scheme based on the RFF, taking linear frequency modulation (LFM) radar as a case study. This scheme first classifies the operation mode of the pulses, then eliminates the noise effect, and finally identifies the radar emitters based on the transient and modulation-based RFF features. The experimental results verify the effectiveness of our radar identification scheme among three real LFM radars (same model) operating at four modes, each mode with 2000 pulses from each radar. The identification rates of the four modes are all higher than 90% when the signal-to-noise ratio (SNR) is about 5 dB. In addition, mode 3 achieves almost 100% identification accuracy even when the SNR is as low as −10 dB.

Generation of atomic spin orientation with a linearly polarized beam in room-temperature alkali-metal vapor

Traditionally, atomic spin orientation is achieved by the transfer of angular momentum from polarised light to an atomic system. We demonstrate the mechanism of orientation generation in room-temperature caesium vapours that combines three elements: optical pumping, non-linear spin dynamics and spin-exchange collisions. Through the variation of the spin-exchange relaxation rate, the transition between an aligned and an oriented atomic sample is presented. The observation is performed by monitoring the atomic radio-frequency spectra. The measurement configuration discussed, paves the way to simple and robust radio-frequency atomic magnetometers that are based on a single low power laser diode that approach the performance of multi-laser pump-probe systems.

Distributionally Robust Radio Frequency Localization

We consider the problem of estimating the location of an RF-device using observations such as received signal strengths, generated according to an uncertain distribution from a set of transmitters with known locations. We present a distributionally robust formulation of the localization problem that explicitly takes into account the uncertainty in the distribution that generates the observations. We identify the structure of the robust solution and demonstrate how to construct the optimization problem so that it is easily computed, and always yields the optimal solution. We show that the robust estimate outperforms traditional methods in the presence of modeling errors, while remaining close to the traditional estimate when the modeling is exact. This suggests that the formulation presented here is an attractive option in applications where we use a model that may not be an exact fit to our environment or if changes in our environment have induced errors in an empirically derived model.

Contact force with magnetic-guided catheter ablation.

Achieving adequate catheter tip-tissue contact is essential for delivering robust radiofrequency (RF) ablation lesions. We measured the contact force generated by a remote magnetic-guided catheter navigation system. A plexiglass model with an integrated scale was fashioned to mimic transvenous and retrograde access to sites in the right atrium and right and left ventricles. An 8 Fr RF ablation catheter was steered by remote magnetic guidance at fields of 0.08 and 0.10 T, with and without a long sheath positioned at the entrance of the chamber. Ten contact force readings were taken at each setting, with the scale recalibrated prior to each measurement. Generalized estimating equations were used to compare contact force measurements while adjusting for the non-independent data structure. A total of 240 contact force measurements were taken. Without a long sheath, contact forces with magnetic fields of 0.10 T (n = 60) and 0.08 T (n = 60) were similar (6.1 ± 1.4 g vs. 6.0 ± 1.3 g, P = 0.089). Contact forces were not significantly different with simulated transvenous (n = 80) and retrograde aortic (n = 40) approaches (6.2 ± 1.4 g vs. 5.7 ± 1.2 g, P = 0.132). The contact force increased substantially with a long sheath (P < 0.001) and was significantly higher with 0.10 T (n = 60) vs. 0.08 T (n = 60) fields (20.4 ± 0.6 g vs. 18.0 ± 0.5 g, P < 0.001). Magnetic fields of 0.08 and 0.10 T provide stable catheter contact forces, as reflected by the small variability between measurements. The average contact force is approximately 6 g without a sheath and increases to 20 g with a long sheath positioned at the entrance of the chamber of interest.

Robust modeling and planning of radio-frequency identification network in logistics under uncertainties

To realize higher coverage rate, lower reading interference, and cost efficiency of radio-frequency identification network in logistics under uncertainties, a novel robust radio-frequency identification network planning model is built and a robust particle swarm optimization is proposed. In radio-frequency identification network planning model, coverage is established by referring the probabilistic sensing model of sensor with uncertain sensing range; reading interference is calculated by concentric map–based Monte Carlo method; cost efficiency is described with the quantity of readers. In robust particle swarm optimization, a sampling method, the sampling size of which varies with iterations, is put forward to improve the robustness of robust particle swarm optimization within limited sampling size. In particular, the exploitation speed in the prophase of robust particle swarm optimization is quickened by smaller expected sampling size; the exploitation precision in the anaphase of robust particle swarm optimization is ensured by larger expected sampling size. Simulation results show that, compared with the other three methods, the planning solution obtained by this work is more conducive to enhance the coverage rate and reduce interference and cost.

Rapid, sensitive, and reusable detection of glucose by a robust radiofrequency integrated passive device biosensor chip.

Tremendous demands for sensitive and reliable label-free biosensors have stimulated intensive research into developing miniaturized radiofrequency resonators for a wide range of biomedical applications. Here, we report the development of a robust, reusable radiofrequency resonator based integrated passive device biosensor chip fabricated on a gallium arsenide substrate for the detection of glucose in water-glucose solutions and sera. As a result of the highly concentrated electromagnetic energy between the two divisions of an intertwined spiral inductor coupled with an interdigital capacitor, the proposed glucose biosensor chip exhibits linear detection ranges with high sensitivity at center frequency. This biosensor, which has a sensitivity of up to 199 MHz/mgmL−1 and a short response time of less than 2 sec, exhibited an ultralow detection limit of 0.033 μM and a reproducibility of 0.61% relative standard deviation. In addition, the quantities derived from the measured S-parameters, such as the propagation constant (γ), impedance (Z), resistance (R), inductance (L), conductance (G) and capacitance (C), enabled the effective multi-dimensional detection of glucose.

Wireless infrastructure protection using low-cost radio frequency fingerprinting receivers

Low-data-rate wireless networks incorporated in critical infrastructure applications can be protected through 128-bit encryption keys and address-based access control lists. However, these bit-level credentials are vulnerable to interception, extraction and spoofing using software tools available free of charge on the Internet. Recent research has demonstrated that wireless physical layer device fingerprinting can be used to defend against replay and spoofing attacks. However, radio frequency (RF) fingerprinting typically uses expensive signal collection systems; this is because fingerprinting wireless devices with low-cost receivers has been reported to have inconsistent accuracy. This paper demonstrates a robust radio frequency fingerprinting process that is consistently accurate with both high-end and low-cost receivers. Indeed, the results demonstrate that low-cost software-defined radios can be used to perform accurate radio frequency fingerprinting and to identify spoofing attacks in critical IEEE 802.15.4-based infrastructure networks such as ZigBee.

Design of parallel transmission radiofrequency pulses robust against respiration in cardiac MRI at 7 Tesla.

Two-spoke parallel transmission (pTX) radiofrequency (RF) pulses have been demonstrated in cardiac MRI at 7T. However, current pulse designs rely on a single set of B1(+)/B0 maps that may not be valid for subsequent scans acquired at another phase of the respiration cycle because of organ displacement. Such mismatches may yield severe excitation profile degradation. B1(+)/B0 maps were obtained, using 16 transmit channels at 7T, at three breath-hold positions: exhale, half-inhale, and inhale. Standard and robust RF pulses were designed using maps obtained at exhale only, and at multiple respiratory positions, respectively. Excitation patterns were analyzed for all positions using Bloch simulations. Flip-angle homogeneity was compared in vivo in cardiac CINE acquisitions. Standard one- and two-spoke pTX RF pulses are sensitive to breath-hold position, primarily due to B1(+) alterations, with high dependency on excitation trajectory for two spokes. In vivo excitation inhomogeneity varied from nRMSE = 8.2% (exhale) up to 32.5% (inhale) with the standard design; much more stable results were obtained with the robust design with nRMSE = 9.1% (exhale) and 10.6% (inhale). A new pTX RF pulse design robust against respiration induced variations of B1(+)/B0 maps is demonstrated and is expected to have a positive impact on cardiac MRI in breath-hold, free-breathing, and real-time acquisitions.

A reusable robust radio frequency biosensor using microwave resonator by integrated passive device technology for quantitative detection of glucose level.

A reusable robust radio frequency (RF) biosensor with a rectangular meandered line (RML) resonator on a gallium arsenide substrate by integrated passive device (IPD) technology was designed, fabricated and tested to enable the real-time identification of the glucose level in human serum. The air-bridge structure fabricated by an IPD technology was applied to the RML resonator to improve its sensitivity by increasing the magnitude of the return loss (S21). The resonance behaviour, based on S21 characteristics of the biosensor, was analysed at 9.20 GHz with human serum containing different glucose concentration ranging from 148-268 mg dl(-1), 105-225 mg dl(-1) and at a deionised (D) water glucose concentration in the range of 25- 500 mg dl(-1) for seven different samples. A calibration analysis was performed for the human serum from two different subjects and for D-glucose at a response time of 60 s; the reproducibility, the minimum shift in resonance frequency and the long-term stability of the signal were investigated. The feature characteristics based on the resonance concept after the use of serum as an analyte are modelled as an inductor, capacitor and resistor. The findings support the development of resonance-based sensing with an excellent sensitivity of 1.08 MHz per 1 mg dl(-1), a detection limit of 8.01 mg dl(-1), and a limit of quantisation of 24.30 mg dl(-1).

Link Adaptation for Throughput Optimization of Parallel Channels with Application to Hybrid FSO/RF Systems

Hybrid free space optical (FSO)/radio frequency (RF) communication systems provide an attractive solution for high-throughput wireless connectivity. Such systems promise high data rates (Gbps) due to the FSO channel, weather permitting. The reliability of these systems is enhanced by the more robust RF channel. A critical question is how to efficiently transmit data using hybrid systems with highly variable channel conditions. In this paper, a hybrid FSO/RF communication system is modeled as two independent parallel channels. Under the assumptions of quasi-static channels and perfect channel knowledge at the transceivers, we propose an adaptive design resulting in a capacity-approaching and seamless joint system. In our design, information bits are jointly encoded and decoded. The encoder rate, modem transmission rate, and modulation scheme of each channel are dynamically adjusted according to the channel state. Analytical and simulation results give insight into the relationship between the adaptive parameters and the performance of the hybrid system.

Design and application of robust rf pulses for toroid cavity NMR spectroscopy

We present robust radio frequency (rf) pulses that tolerate a factor of six inhomogeneity in the B 1 field, significantly enhancing the potential of toroid cavity resonators for NMR spectroscopic applications. Both point-to-point (PP) and unitary rotation (UR) pulses were optimized for excitation, inversion, and refocusing using the gradient ascent pulse engineering (GRAPE) algorithm based on optimal control theory. In addition, the optimized parameterization (OP) algorithm applied to the adiabatic BIR-4 UR pulse scheme enabled ultra-short (50 μs) pulses with acceptable performance compared to standard implementations. OP also discovered a new class of non-adiabatic pulse shapes with improved performance within the BIR-4 framework. However, none of the OP-BIR4 pulses are competitive with the more generally optimized UR pulses. The advantages of the new pulses are demonstrated in simulations and experiments. In particular, the DQF COSY result presented here represents the first implementation of 2D NMR spectroscopy using a toroid probe.

The “Analog Journal” celebrates its 20th Anniversary!

With this issue, we celebrate our 20th Anniversary! We started our first issue back in 1991. The journal appeared quarterly for a couple of years then bi-monthly for a while and since 1997 it appears monthly and on-line since 1999. Our journal is the only publication devoted exclusively to analog Integrated circuits (ICs) and signal processing research. It is becoming the premiere publication in the fields of analog, radio frequency (RF) and mixed signal IC design and applications. Many of us call it ‘‘the Analog Journal’’ or ‘‘the red and yellow’’! Indeed, the material we publish reflects a very significant portion of analog research conducted in industry, academia and research Labs worldwide. On behalf of the Editorial Board, I would like to thank our authors and reviewers who made the journal what it is today. Special thanks go to the Springer staff for their very dedicated work over the years with the journal or ‘‘ALOG’’ as they call it. Happy 20th Anniversary to ‘‘ALOG’’! and Happy New Year 2011 to you, our readers! We look forward to hearing from you with any suggestions or feedback you may have so we can serve you even better. Mohammed Ismail is a Professor and Founding Director of the Analog VLSI Lab at the Ohio State University, USA and of the RaMSiS Group at KTH, Sweden. He is also affiliated with the ElectroScience Lab at Ohio State. Currently, he conducts research on robust low power RF and mmwave ICs for wireless, bio and multimedia applications with a focus on manufacturable low cost high volume CMOS solutions for mobile and wearable embedded devices. He served as a Corporate Consultant to over 30 companies and is a Co-Founder of Firstpass Technologies, Inc. a developer of RF and mixed signal IPs. He Cofounded ANACAD-Egypt (now part of Mentor Graphics). He advised the work of 49 Ph.D. students and of over 90 M.S. students. He authored or co-authored a dozen books and over 250 journal publications. He is the Founding Editor-in-Chief of the Journal Analog Integrated Circuits and Signal Processing, Springer and the Founder of the IEEE ICECS, the flagship Region 8 conference of the IEEE Circuits and Systems Society. He received the US Presidential Young Investigator Award, the Ohio State Lumley Research Award four times, in 1992, 1997, 2002 and 2007 and the US Semiconductor Research Corporation’s Inventor Recognition Award twice. He is a Fellow of IEEE.

TU‐B‐I‐617‐01: High Field MRI — Technology, Applications, Safety, and Limitations

Signal‐to‐noise ratio in conventional magnetic resonance imaging (MRI) is inextricably tied to the static magnetic field strength (B0). Until recently, most clinical MRI scanners operated at field strengths at or below 1.5 Tesla. However, due to technological advancements in magnet design and shielding, which ease siting requirements, 3 Tesla clinical scanners are now enjoying wide commercial availability and there is a push for even higher field whole body scanners (7–9Tesla) throughout the industry. The drive towards high‐field MRI is fueled by the benefits of potentially higher signal‐to‐noise ratios, contrast‐to‐noise ratios, and spectral resolution. In many cases, these benefits translate directly into higher spatial and/or temporal resolution than previously possible with MRI at lower fields as well as the ability to explore new territory, such as molecular imaging. There are, however, very real technological, physical and safety limitations that must be navigated and may limit the full realization of these benefits at high‐field. Technology issues include homogeneity of the static and radiofrequency magnetic fields, higher gradient coil performance and linearity, and the design of robust radiofrequency array coils for signal reception. At high‐field, physics concerns include changes in relaxation kinetics, increased susceptibility effects and other changes in contrast mechanisms. Safety limitations include higher power radiofrequency pulses and the potential for tissue heating or coil burns, stimulation effects from stronger, faster switching gradients and physiological effects of motion within the high‐field environment and, most prominently, the potential dangers associated with the main magnetic field, such as ferromagnetic projectiles in the scan room and effects on implanted medical devices, many of which have yet to be evaluated at fields above 1.5 Tesla. Ultimately, design of protocols and acquisition methods that account for these limitations need to be pursued in order to reap the benefits of high‐field MRI without compromising patient safety. Many MR imaging techniques have already seen demonstrable improvement at higher fields and have driven the development and distribution of high‐field systems. Techniques in functional magnetic resonance imaging relying on blood‐oxygen level dependent contrast mechanisms, techniques in angiography and techniques in dynamic susceptibility contrast perfusion imaging all benefit from higher fields. Changes in relaxation kinetics can provide enhanced contrast for angiography and arterial spin labeling techniques. Additionally, proton MR spectroscopy methods for brain and body imaging benefit from the higher spectral resolution of high field as do multi‐nuclear techniques. This course will review the technology and physics behind the emerging high‐field systems (3–9 Tesla) with emphasis on the commercially available and widespread 3 Tesla systems. Major applications of high‐field MRI will be addressed with an eye on the future. Aspects of safety in high‐field MRI will also be covered, paying particular attention to how safety considerations may influence the development and implementation of patient protocols at higher fields.Educational Objectives:1. Introduction to relevant high‐field technology, physics and techniques.2. Understand benefits and limitations of high‐field MRI.3. Understand safety concerns associated with high‐field MRI systems.4. Awareness of some of the most relevant applications of high‐field MR imaging.

Sensor Networks for Emergency Response: Challenges and Opportunities

Sensor networks, a new class of devices has the potential to revolutionize the capture, processing, and communication of critical data for use by first responders. CodeBlue integrates sensor nodes and other wireless devices into a disaster response setting and provides facilities for ad hoc network formation, resource naming and discovery, security, and in-network aggregation of sensor-produced data. We designed CodeBlue for rapidly changing, critical care environments. To test it, we developed two wireless vital sign monitors and a PDA-based triage application for first responders. Additionally, we developed MoteTrack, a robust radio frequency (RF)-based localization system, which lets rescuers determine their location within a building and track patients. Although much of our work on CodeBlue is preliminary, our initial experience with medical care sensor networks raised many exciting opportunities and challenges.