Radio-frequency Resonator Research Articles

Design of a RF-resonant set improving locally the B1+ efficiency. Applications for clinical MRI in andrology and urology

Modern diagnostic imaging methods for andrology and urology fall behind other well-developed applications such as cardiology or neurology. Particularly, MRI despite its superior soft tissue contrast is hardly used for MR-imaging of the penis, primarily due to the lack of the corresponding receive or transmit coils. In order to fix this, a new radio frequency resonator, based on the birdcage operating principles has been designed, simulated, fabricated, tested and compared experimentally to existing RF coils. In order to provide high transmit efficiency and high sensitivity, while maintaining the coil safety, the resonator spatially separates alternating magnetic and electric fields. The transmitted magnetic field (B1+) is concentrated in the centre of the imaging volume, while the electric field remains on its edge and does not lead to tissue heating. The resonator design was optimised for human MRI in 1.5 T scanners. Both simulations and experiment showed the resonator to provide around 100-fold specific absorption rate reduction, around 10-fold improvement of the transmit efficiency and more than 10-fold enhancement of the signal to noise ratio (SNR) in a phantom compared to the body coil, around 2-fold SNR enhancement in a phantom compared to the commercial flexible 4-element coil, and up to 1.5-fold enhancement compared to the same coil in-vivo.

Flux-mediated optomechanics with a transmon qubit in the single-photon ultrastrong-coupling regime

We propose a scheme for controlling a radio-frequency mechanical resonator at the quantum level using a superconducting qubit. The mechanical part of the circuit consists of a suspended micrometer-long beam that is embedded in the loop of a superconducting quantum interference device (SQUID) and is connected in parallel to a transmon qubit. Using realistic parameters from recent experiments with similar devices, we show that this configuration can enable a tuneable optomechanical interaction in the single-photon ultrastrong-coupling regime, where the radiation-pressure coupling strength is larger than both the transmon decay rate and the mechanical frequency. We investigate the dynamics of the driven system for a range of coupling strengths and find an optimum regime for ground-state cooling, consistent with previous theoretical investigations considering linear cavities. Furthermore, we numerically demonstrate a protocol for generating hybrid discrete- and continuous-variable entanglement as well as mechanical Schr\"{o}dinger cat states, which can be realised within the current state of the art. Our results demonstrate the possibility of controlling the mechanical motion of massive objects using superconducting qubits at the single-photon level and could enable applications in hybrid quantum technologies as well as fundamental tests of quantum mechanics.

Detector clothes for MRI: A wearable array receiver based on liquid metal in elastic tubes

In modern magnetic resonance imaging, signal detection is performed by dense arrays of radiofrequency resonators. Tight-fitting arrays boost the sensitivity and speed of imaging. However, current devices are rigid and cage-like at the expense of patient comfort. They also constrain posture, limiting the examination of joints. For better ergonomics and versatility, detectors should be flexible, adapt to individual anatomy, and follow posture. Towards this goal, the present work proposes a novel design based on resonators formed by liquid metal in polymer tubes. Textile integration creates lightweight, elastic devices that are worn like pieces of clothing. A liquid-metal array tailored to the human knee is shown to deliver competitive image quality while self-adapting to individual anatomy and adding the ability to image flexion of the joint. Relative to other options for stretchable conductors, liquid metal in elastic tubes stands out by reconciling excellent electrical and mechanical properties with ease of manufacturing.

Parahydrogen-Induced Radio Amplification by Stimulated Emission of Radiation.

Radio amplification by stimulated emission of radiation (RASER) was recently discovered in a low-field NMR spectrometer incorporating a highly specialized radio-frequency resonator, where a high degree of proton-spin polarization was achieved by reversible parahydrogen exchange. RASER activity, which results from the coherent coupling between the nuclear spins and the inductive detector, can overcome the limits of frequency resolution in NMR. Here we show that this phenomenon is not limited to low magnetic fields or the use of resonators with high-quality factors. We use a commercial bench-top 1.4 T NMR spectrometer in conjunction with pairwise parahydrogen addition producing proton-hyperpolarized molecules in the Earth's magnetic field (ALTADENA condition) or in a high magnetic field (PASADENA condition) to induce RASER without any radio-frequency excitation pulses. The results demonstrate that RASER activity can be observed on virtually any NMR spectrometer and measures most of the important NMR parameters with high precision.

Recovery of eigenvectors from eigenvalues in systems of coupled harmonic oscillators

The eigenvector-eigenvalue identity relates the eigenvectors of a Hermitian matrix to its eigenvalues and the eigenvalues of its principal submatrices in which the jth row and column have been removed. We show that one-dimensional arrays of coupled resonators, described by square matrices with real eigenvalues, provide simple physical systems where this formula can be applied in practice. The subsystems consist of arrays with the jth resonator removed, and thus can be realized physically. From their spectra alone, the oscillation modes of the full system can be obtained. This principle of successive single resonator deletions is demonstrated in two experiments of coupled radiofrequency resonator arrays with greater-than-nearest neighbor couplings, in which the spectra are measured with a network analyzer. Both the Hermitian as well as a non-Hermitian case are covered in the experiments. In both cases the experimental eigenvector estimates agree well with numerical simulations if certain consistency conditions imposed by system symmetries are taken into account. In the Hermitian case, these estimates are obtained from resonance spectra alone without knowledge of the system parameters. It remains an interesting problem of physical relevance to find conditions under which the full non-Hermitian eigenvector set can be obtained from the spectra alone.

RF-resonator for clinical MR imaging in urology and andrology

New diagnostic visualisation and quantification methods of nerve tracks are needed in andrology and urology applications. In order for magnetic resonance imaging (MRI) to properly image the nerves of interest a dramatic signal-to-noise ratio (SNR) increase is required. For this purpose, radiofrequency (RF) resonator based on the birdcage operating principles has been designed, fabricated, measured and compared to simulation model obtained by time domain method in CST microwave studio. The resonator concentrate RF magnetic field in the centre of the resonator, while electric field remains on the edge thus preventing tissue heating. Design and parameters of resonator was optimised for human MRI on 1.5T scanners. Using the resonator allowed to improve RF-safety for 2 times, transmit efficiency for 10 times and SNR for 14 times compared to body coil only system. Measured and computed resonance frequencies and transmit efficiency are in good agreement.

Multi-Functional Hydrogel-Interlayer RF/NFC Resonators as a Versatile Platform for Passive and Wireless Biosensing.

Wearable sensors promise to transform human understanding of body state. However, despite many wearable sensor modalities that exist, few demonstrate the raw capabilities required for many emerging healthcare applications-passivity (and microelectronics-free), wireless readout, long-term operation, and specificity. Hydrogel-interlayer radio-frequency resonators are demonstrated as a versatile platform for passive and wireless biosensing. Fabricated using a simple vinyl cutter, the base resonator is composed of unanchored, broad-side coupled coils interceded by multifunctional hydrogels-such resonators are tuned to be sensitive to specific analytical or physical signals by modifying hydrogel composition. These resonators are transformed into near-field communication (NFC) sensor circuits through the simple attachment of an LED. These enable direct quantification of sensor state by cellphone and eye with no specialized electronics required. Resonator arrays are finally fused with silicone to form soft, wireless sensor skins that enable co-readout of analytical to physical signals while molded to human subjects. Such low-cost, accessible platforms can integrate with environments in transformative ways, enabling new applications in wireless sensing.

Study of the Distribution of Epicardial Vagal Ganglion and the Relationship Between Delayed Enhancement Magnetic Resonance Imaging and Radiofrequency Ablation in Patients with Atrial Fibrillation

This article presents a retrospective study of patients undergoing radiofrequency ablation of atrial fibrillation (AF); analyzes the characteristics of heart rate variability (HRV) in patients; and explores the role of delayed enhancement magnetic resonance imaging and autonomic nervous system function, changes in autonomic nervous system function, and recurrence of AF after radiofrequency ablation to understand the effect of denervation of the autonomic nervous system on the efficacy of radiofrequency ablation of AF. The study found that there were no significant differences in clinical baseline characteristics, mean heart rate, and HRV indicators between patients without relapse and patients with relapse (P > 0.05). The overall HRV index was significantly reduced after surgery as well as before surgery. In the relapse-free group, the high-frequency power that responded to vagal tone was more significant, the low-frequency/high-frequency power ratio increased, and other HRV indicators were significantly reduced; in the relapse group, mean heart rate increased, sympathetic response to the low-frequency power of nerve tension was significantly reduced, and the low-frequency/high-frequency power ratio was decreased. The difference was statistically significant (P < 0.05). Therefore, sympathetic and parasympathetic nerve function were significantly reduced after radiofrequency ablation of the pulmonary veins in patients with AF. Reducing vagus nerve tension may inhibit early recurrence of paroxysmal AF in patients after left atrial ring pulmonary vein ablation.

Design of a Resonant Radiofrequency Driver for Ion Transmission in a Desktop Mass Spectrometer and Its Application in Volatile Organic Compound Determination

The ion transformation efficiency from a high-pressure ion source region to a low-pressure mass analysis region is one of the important indices for the mass spectrometer performance. To decrease the ion loss and improve the sensitivity of ions, a radiofrequency driver was designed in a home-made time-of-flight mass spectrometer (TOF-MS), which adopted a resistance-inductance-capacitance (RLC) resonant amplification pattern to drive the radiofrequency quadrupole (RFQ). The peak-to-peak voltage Vp-p of the radiofrequency driver was continuously adjusted from 50 to 1000 V with a relative standard deviation of 2.5‰. The performance of the radiofrequency quadrupole in the mass spectrometer was assessed by the characterization of a mixture of benzene, toluene, and p-xylene. The limits of detection for benzene, toluene, and p-xylene were 0.07, 0.05, and 0.04 ppbv, respectively. Moreover, the performance and stability of radiofrequency quadrupole were assessed by the determination of volatile organic compounds (VOCs) in newly decorated rooms and exhaled breath. The results indicated that the developed radiofrequency driver has potential for use in mass spectrometers.

Passive and wireless, implantable glucose sensing with phenylboronic acid hydrogel-interlayer RF resonators

A phenylboronic acid-based, hydrogel-interlayer Radio-Frequency (RF) resonator is demonstrated as a highly-responsive, passive and wireless sensor for glucose monitoring. Constructs are composed of unanchored, capacitively-coupled split rings interceded by glucose-responsive hydrogels. Phenylboronic acid-hydrogels exhibit volumetric and dielectric variations in response to environmental glucose concentrations—these are efficiently converted to large shifts in the resonant response of interlayer-RF sensors. These tiny, stretchable and scalable sensors (5 mm × 5 mm x 250 μm) require no microelectronics or power at the sensing node and can be read-out remotely via near-field coupling. Sensors exhibit high sensitivities (~10% shift in resonant frequency—corresponding to 50 MHz—per 150 mg/dL of glucose), possess a limit of detection of 10 mg/dL, and a step response time of approximately 1 h to abrupt shifts in carbohydrate concentration. Notably, these sensors exhibited no signal drift or hysteresis over the time periods characterized herein (45 days at room temperature). We transform sensors into bioelectronic RF reporter-tags via the attachment of a single LED—these remotely report on glucose concentration via emitted light. We anticipate the non-degradative, long-term nature of both RF read-out and phenylboronic acid-based hydrogels will enable biosensors capable of long-term, remote read-out of glucose.

Complementary Split-Ring Resonator (CSRR)-Loaded Sensor Array to Detect Multiple Cracks: Shapes, Sizes, and Positions on Metallic Surface

Single-resonance-based radio frequency (RF) resonators cannot detect multiple cracks simultaneously nor localize the position of a crack. To address these drawbacks, we propose a complementary split-ring resonator (CSRR)-loaded array. In this array, there are four channels and each channel consists of three CSRRs, forming a 4 × 3 sensing array that is developed in the ground plane of a microstrip line using a low-cost FR4 substrate. A voltage-controlled oscillator (VCO) generates three discrete frequencies: 1.88 GHz, 2.60 GHz, and 3.61 GHz to each channel, which is sequentially selected using a single-pole four-throw (SP4T) switch. The transmitted RF signals are converted into the DC voltage levels and are interpreted by a microcontroller. Aluminum sheets with cracks embedded in the surface are used to demonstrate the detection of cracks of various shapes, sizes and locations/orientations (horizontal, diagonal, and vertical) with simulations and measurements. The detection of the minimum detectable crack (W c × L c × D c = 1 mm × 10 mm × 0.1 mm) is experimentally verified. Full-length longer cracks (L c = 100 mm) are also detected using our proposed detection system with the SP4T switch in addition to our proposed algorithm that scans the CSRRs of each selected channel.

Methodology of improving sensitivity of silicon vacancy spin-based sensors based on double spiral coil RF resonance structure

&lt;sec&gt; Due to the power instability and field non-uniformity of radio frequency (RF), microwave (MW) and laser signals, inhomogeneous broadening of spin magnetic resonance line causes the absorption to decrease in a nuclear resonance system, which can reduce the sensitivity of spin-based sensing and testing technology. In this paper, we propose and design a double solenoid coil RF resonance antenna structure. The nearly uniform RF field density is produced by the two solenoid coil antenna structures that are parallel to the symmetry axis. The size of the uniformity in the center region of double solenoid coil RF resonance antenna structure is about π×375 mm&lt;sup&gt;2&lt;/sup&gt; × 10 mm. And the non-uniformity is less than 0.9%. Comparing with a single straight wire antenna and the single solenoid coil RF resonance antenna structure, the uniformity is improved by about 56.889 times and 42.889 times, respectively. At the same time, based on the near-field mutual inductance coupled resonance effect, the intensities of RF field in the center region of the two-solenoid coil antenna structure is enhanced. Comparing with the single solenoid coil antenna structures, it is enhanced by about 1.587 times. And the equivalent sensitivity of the silicon vacancy color center spin based sensor is enhanced by about 4.833 times.&lt;/sec&gt;&lt;sec&gt; In the experiment, an optical detection magnetic resonance measurement system based on the spin magnetic resonance effect of silicon vacancy color center in single crystal SiC is built. Comparing with the single straight wire antenna and the single solenoid coil RF resonance antenna structure, the contrast of the silicon vacancy color center spin magnetic resonance signals of the double solenoid coil RF resonance antenna structure increases about 6 times and 2.4 times, respectively. The sensitivity of the spin-based sensor is increased by 4.833 times and 2.071 times through using the modulation and demodulation method, and the noise decreases by 8 times and twice. Hence, based on this double solenoid coil RF resonance antenna structure, the sensitivity of the silicon vacancy spin sensor can be improved. Combined with chip manufacturing technology of SiC wafer, it proves to be a potential approach to developing the high precision, chip scale spin sensor devices and measurement technology.&lt;/sec&gt;

Полностью оптический магнитометрический датчик для задач магнитоэнцефалографии и томографии сверхслабого поля

A version of the scheme of an atomic cesium vapour magnetometric sensor using magnetic resonance excitation by modulated radiation transverse to the magnetic field of hyperfine optical pumping is proposed and experimentally studied. It is shown that when using a cell with a volume of 0.125 cm3, the variational sensitivity of the sensor, estimated from the ratio of the steepness of the signal at the center of the magnetic resonance to the shot noise of the detecting radiation, reaches a level of less than 10 fT/Hz1/2 in the frequency band determined by the magnetic resonance line width (of the order of 800 Hz). The sensor, which does not use and does not emit resonant radio-frequency fields, is designed to operate in magnetoencephalographic complexes. Possible ways to increase the frequency response of the circuit for detecting relatively fast (~ 4.2 kHz in a field of 0.1 mT) proton magnetic moment precession signals in promising ultralow field tomography schemes are considered.

Cardiorenal sodium MRI in small rodents using a quadrature birdcage volume resonator at 9.4T.

Design, implementation, evaluation and application of a quadrature birdcage radiofrequency (RF) resonator tailored for renal and cardiac sodium (23Na) magnetic resonance imaging (MRI) in rats at 9.4T. A low pass birdcage resonator (16 rungs, din = 62mm) was developed. The transmission field (B1+) was examined with EMF simulations. The scattering parameter (S-parameter) and the quality factor (Q-factor) were measured. For experimental validation B1+-field maps were acquired with the double-angle method. In vivo sodium imaging of the heart (spatial resolution: (1 × 1 × 5) mm3) and kidney (spatial resolution: (1 × 1 × 10) mm3) was performed with a FLASH technique. The RF resonator exhibits RF characteristics, transmission field homogeneity and penetration that afford 23Na MR in vivo imaging of the kidney and heart at 9.4T. For the renal cortex and medulla a SNRs of 8 and 13 were obtained and a SNRs of 14 and 15 were observed for the left and right ventricle. These initial results obtained in vivo in rats using the quadrature birdcage volume RF resonator for 23Na MRI permit dedicated studies on experimental models of cardiac and renal diseases, which would contribute to translational research of the cardiorenal syndrome.

Topological modes in radiofrequency resonator arrays

Topological properties of solid states have sparked considerable recent interest due to their importance in the physics of lattices with a non-trivial basis and their potential in the design of novel materials. Here we describe an experimental and accompanying numerical toolbox to create and analyze topological states in radiofrequency resonator arrays including non-local coupling. These arrays are very easily constructed, offer a variety of geometric configurations, and their eigenfunctions and eigenvalues are amenable to detailed analysis. They offer well defined analogs to coupled oscillator systems in general in that they are characterized by resonances whose frequency spectra depend on the individual resonators, their interactions, and boundary conditions. A comparison of a small one-dimensional experimental system with theory by means of easy to measure S-parameters shows excellent agreement. The numerical toolbox allows for simulations of arbitrarily large systems, revealing an astonishing richness of band structures under systematic parameter variation.

Synthesizing multi-phonon quantum superposition states using flux-mediated three-body interactions with superconducting qubits

Massive mechanical resonators operating at the quantum scale can enable a large variety of applications in quantum technologies as well as fundamental tests of quantum theory. Of crucial importance in that direction is both their integrability into state-of-the-art quantum platforms as well as the ability to prepare them in generic quantum states using well-controlled high-fidelity operations. Here, we propose a scheme for controlling a radio-frequency mechanical resonator at the quantum scale using two superconducting transmon qubits that can be integrated on the same chip. Specifically, we consider two qubits coupled via a capacitor in parallel to a superconducting quantum interference device (SQUID), which has a suspended mechanical beam embedded in one of its arms. Following a theoretical analysis of the quantum system, we find that this configuration, in combination with an in-plane magnetic field, can give rise to a tuneable three-body interaction in the single-photon strong-coupling regime, while enabling suppression of the stray qubit-qubit coupling. Using state-of-the-art parameters and qubit operations at single-excitation levels, we numerically demonstrate the possibility of ground-state cooling as well as high-fidelity preparation of mechanical quantum states and qubit-phonon entanglement, i.e. states having negative Wigner functions and obeying non-classical correlations. Our work significantly extends the quantum control toolbox of radio-frequency mechanical resonators and may serve as a promising architecture for integrating such mechanical elements with transmon-based quantum processors.

High frequency guided mode resonances in mass-loaded, thin film gallium nitride surface acoustic wave devices

We demonstrate high-frequency (&amp;gt;3 GHz), high quality factor radio frequency (RF) resonators in unreleased thin film gallium nitride (GaN) on sapphire and silicon carbide substrates by exploiting acoustic guided mode (Lamb wave) resonances. The associated energy trapping, due to mass loading from gold electrodes, allows us to efficiently excite these resonances from a 50 Ω input. The higher phase velocity, combined with lower electrode damping, enables high quality factors with moderate electrode pitch and provides a viable route towards high-frequency piezoelectric devices. The GaN platform, with its ability to guide and localize high-frequency sound on the surface of a chip with access to high-performance active devices, will serve as a key building block for monolithically integrated RF front-ends.

An ECCD—Electronic Charge Compensation Device—As a Quantum Dissipative System

An electronic charge compensation device (ECCD) is a passive device that carries electrical currents away, on time, to the electrical Earth field. It prevents lightning’s impacts, derivative electric current pulses, and reduces the radiofrequency disturbances in the protected area. The objective of this paper is to give a physical explanation of the operation of an ECCD’s performance and advantages. The operation of an ECCD is the result of two actions: the static electric field and the evanescent and resonant electrical radiofrequency field in the nearby external adjoining to dielectric-metal zone of ECCD. The energy absorption only is logically justified considering a super-absorption process as an end of chain of resonant quantum event. In this study, a multi-resonant process was inferred from an exhaustive radiofrequency simulation analysis made on an ECCD. The primary experiment was a long-time-frame statistical analysis of seven different, real stations. Those empirical results were derived from real METEORAGE environmental services data. Finally, a prospective for new applications is given.

Alkali-metal spin maser for non-destructive tests

Radio-frequency atomic magnetometers offer attractive alternatives to standard detection methods in nondestructive testing, which are based on inductive measurements. We demonstrate a magnetometer in the so-called spin maser configuration, which addresses two important challenges of the technique: shifts in the radio frequency resonance position caused by magnetically permeable samples and the sensor bandwidth. Key properties of the self-oscillating sensor are presented in both a magnetically shielded and an open environment. Demonstration of defect detection via magnetic induction tomography in a ferromagnetic carbon steel sample is presented. The configuration discussed paves the way for a simple, rapid, and robust nondestructive material defect detection system based on an atomic magnetometer.

Wirelessly Heating Stents via Radiofrequency Resonance toward Enabling Endovascular Hyperthermia.

Thermal therapy known as hyperthermia has served as an effective method for cancer treatment. This therapeutic approach has also been attracting attention for treatment of in-stent restenosis, the most common complication of stenting. Mild heating of stents has been shown to be a possible path to addressing this problem. Despite various studies on stent-based thermotherapy, this area still lacks a clinically viable method and technology. Here, a radiofrequency-powered "hot" stent prototype is reported in vitro and in vivo. An implantable stent device based on medical-grade stainless steel acts as an electrical resonator, or an efficient wireless heater operating only when resonated using tuned external electromagnetic fields. The system architecture uses a custom-developed power transmitter for wireless resonant powering/heating of the stent. An eight-shaped antenna is shown to be highly effective for near-field power transfer to the device and potentially to other smart implants, revealing stent heating efficiencies of up to 120 °C W-1 , 206% of the level provided by a conventional loop antenna. Testing with swine models, the prototyped system achieves stent heating in blood flow by powering through air and skin tissue in vivo in a fully controlled manner. The results advance stent hyperthermia technology toward possible future clinical application.