Flexible Coil Research Articles

Nonoverlapped Decoupling Technique With Flexible and Stretchable Dielectric-Loaded Coil Elements for Wearable Multichannel RF Coils

Nonoverlapped Decoupling Technique With Flexible and Stretchable Dielectric-Loaded Coil Elements for Wearable Multichannel RF Coils

Design of parallel coil arrays with identifiable eigenfrequency elements for wearable human-machine interactions

Wearable electronic devices are considered as a promising platform for efficient human-machine interactions (HMI) in the advancing era of the Internet of Things (IoT). However, the limited capacity often necessitates the arraying of individual devices, which inevitably increase the number of connecting wires, communication channels, and physical chaos. Herein, we propose a high-capacity HMI interface which is composed of parallel-arranged flexible coils, a magnetized composite and a pair of electrodes for electrical connection. When the coils were deformed, the inherent oscillation occurs spontaneously once the mechanical constraint was released. Upon this, the magnetic flux variation caused by the oscillation results in induced current within the coil as defined by the law of electromagnetic induction. Assisted by theoretical model of cantilever beams, eigenfrequency could be effectively regulated and the integration of distinct coils permits a single device to transmit multiple commands and information. Taking advantage of the design, spatial position sensing, virtual piano playing and robotic control have been demonstrated as practical applications, which are mainly based on one communication channel and a pair of electrodes. We expect that the eigenfrequency-dependent mechanism can provide an inspiring solution for the design of high-capacity, effective, and comfortable HMI interfaces in the future.

Flexible and Stretchable Liquid‐Metal Microfluidic Electronics Using Directly Printed 3D Microchannel Networks

AbstractThis paper describes a method for fabricating microfluidic electronics with 3D interconnected networks by direct ink writing (DIW)‐based 3D printing. Existing 3D printing technologies have yet to simultaneously realize 1) direct printing of interconnected multilayered microchannels without supporting materials or post‐processing and 2) integration of electronic elements with microchannels during the process of printing. This research aims to develop a method to fabricate support‐free microchannels consisting of silicone sealant without the collapse of the extruded structure while integrating electronic elements during the fabrication by DIW. The injection of liquid metal into 3D‐printed microchannels allows the formation of electrical connections between 3D conductive networks and the embedded electronic elements, enabling the fabrication of flexible and stretchable liquid metal antenna coils. To demonstrate a practical application, 1) a skin‐attachable radio‐frequency identification (RFID) tag using a commercial skin‐adhesive plaster as a substrate and 2) free‐standing flexible wireless light‐emitting devices with a small footprint (21.4 mm × 15 mm) for potential implantable applications are produced. This technology will offer a new capability to realize the automated fabrication of stretchable printed circuits with 3D configuration of electrical circuits consisting of liquid metals.

Development of a flexible coil based on conductive polymer composite for PDMS-based soft electromagnetic microactuators

Development of a flexible coil based on conductive polymer composite for PDMS-based soft electromagnetic microactuators

Computational simulations on the taste mechanism of steviol glycosides based on their interactions with receptor proteins

Steviol glycoside (SG) is a potential natural sugar substitute. The taste of various SG structures differ significantly, while their mechanism has not been thoroughly investigated. To investigate the taste mechanism, molecular docking simulations of SGs with sweet taste receptor TAS1R2 and bitter taste receptor TAS2R4 were conducted. The result suggested that four flexible coils (regions) in TAS1R2 constructed a geometry open pocket in space responsible for the binding of sweeteners. Amino acids that form hydrogen bonds with sweeteners are located in different receptor regions. In bitterness simulation, fewer hydrogen bonds were formed with the increased size of SG molecules. Particularly, there was no interaction between RM and TAS2R4 due to its size, which explains the non-bitterness of RM. Molecular dynamics simulations further indicated that the number of hydrogen bonds between SGs and TAS1R2 was maintained during a simulation time of 50 ns, while sucrose was gradually released from the binding site, leading to the break of interaction. Conclusively, the high sweetness intensity of SG can be attributed to its durative concurrent interaction with the receptor's binding site, and such behavior was determined by the structure feature of SG.

Research on electromagnetic vibration energy harvester for cloud-edge-end collaborative architecture in power grid

With the deepening of the construction of the new type power system, the grid has become increasingly complex, and its safe and stable operation is facing more challenges. In order to improve the quality and efficiency of power grid management, State Grid Corporation continues to promote the digital transformation of the grid, proposing concepts such as cloud-edge-end collaborative architecture and power Internet of Things, for which comprehensive sensing of the grid is an important foundation. Power equipment is widely distributed and has a wide variety of types, and online monitoring of them involves the deployment and application of a large number of power sensors. However, there are various problems in implementing active power supplies for these sensors, which restrict their service life. In order to collect and utilize the vibration energy widely present in the grid to provide power for sensors, this paper proposes an electromagnetic vibration energy harvester and its design methodology based on a four-straight-beam structure, and carries out a trial production of prototype. The vibration pickup unit of the harvester is composed of polyimide cantilevers, a permanent magnet and a mass-adjusting spacer. The mass-adjusting spacer can control the vibration frequency of the vibration unit to match the target frequency. In this paper, a key novel method is proposed to increase the number of turns in a limited volume by stacking flexible coils, which can boost the output voltage of the energy harvester. A test system is built to conduct a performance test for the prototype harvester. According to the test results, the resonant frequency of the device is 100 Hz, the output peak-to-peak voltage at the resonant frequency is 2.56 V at the acceleration of 1 g, and the maximum output power is around 151.7 mu W. The proposed four-straight-beam electromagnetic vibration energy harvester in this paper has obvious advantages in output voltage and power compared with state-of-the-art harvesters. It can provide sufficient power for various sensors, support the construction of cloud-edge-end architecture and the deployment of a massive number of power sensors. In the last part of this article, a self-powered transformer vibration monitor is presented, demonstrating the practicality of the proposed vibration energy harvester.

Flexible multilayer MEMS coils and their application in energy harvesters

Flexible multilayer MEMS coils and their application in energy harvesters

A fast direct solver for surface-based whole-head modeling of transcranial magnetic stimulation

When modeling transcranial magnetic stimulation (TMS) in the brain, a fast and accurate electric field solver can support interactive neuronavigation tasks as well as comprehensive biophysical modeling. We formulate, test, and disseminate a direct (i.e., non-iterative) TMS solver that can accurately determine global TMS fields for any coil type everywhere in a high-resolution MRI-based surface model with ~ 200,000 or more arbitrarily selected observation points within approximately 5 s, with the solution time itself of 3 s. The solver is based on the boundary element fast multipole method (BEM-FMM), which incorporates the latest mathematical advancement in the theory of fast multipole methods—an FMM-based LU decomposition. This decomposition is specific to the head model and needs to be computed only once per subject. Moreover, the solver offers unlimited spatial numerical resolution. Despite the fast execution times, the present direct solution is numerically accurate for the default model resolution. In contrast, the widely used brain modeling software SimNIBS employs a first-order finite element method that necessitates additional mesh refinement, resulting in increased computational cost. However, excellent agreement between the two methods is observed for various practical test cases following mesh refinement, including a biophysical modeling task. The method can be readily applied to a wide range of TMS analyses involving multiple coil positions and orientations, including image-guided neuronavigation. It can even accommodate continuous variations in coil geometry, such as flexible H-type TMS coils. The FMM-LU direct solver is freely available to academic users.

Miniature and flexible Bazooka balun for high-field MRI

Flexible coils offer improved patient comfort and better imaging quality. However, rigid and bulky baluns in RF coils limit flexibility and manufacturing. A miniaturized and flexible balun design was proposed to address this issue. It replaced rigid components with an ultra-flexible rubber tube and a flexible coaxial capacitor. Simulations validated the concept, and bench tests confirmed its performance, including a measured common-mode rejection ratio of −15.8 dB. The flexible balun was integrated into a 4-channel coil array, evaluating impedance changes caused by the “hand effect.” Compared to coils without the balun, the flexible coil with the proposed balun showed improved robustness in impedance matching and inter-element couplings. Transmit efficiency of the flexible coil with the balun was compared to coils without a balun and with a rigid, shielded cable trap. Results demonstrated that the proposed balun circuit maintained high transmit efficiency. Overall, the flexible balun design offers a promising solution for improving the flexibility and performance of RF coil arrays in MRI applications.

Flexible multi-purpose integrated RF/shim coil array for MRI and localized B0 shimming.

To develop a flexible, lightweight, and multi-purpose integrated parallel reception, excitation, and shimming (iPRES) coil array that can conform to the subject's anatomy and perform MR imaging and localized B0 shimming in different anatomical regions with a high SNR, shimming performance, ease of positioning, and subject comfort. A four-channel flexible iPRES coil array was constructed by enabling RF and direct currents to flow on the same flexible coil elements for imaging and shimming, respectively. Shimming experiments were performed with the coil array wrapped around the knee or neck of healthy subjects to demonstrate its high shimming performance and versatility. Additionally, its SNR and shimming performance in the knee were compared to those obtained with the coil array wrapped around a larger rigid tube designed to fit most knee sizes. Shimming with the coil array wrapped around the knee or neck resulted in an average reduction in B0 RMSE of 50.1% and 40.5% relative to first-order and second-order spherical harmonic shimming, respectively, and substantially reduced distortions in DWI images. In contrast, shimming the knee with the coil array wrapped around the rigid tube only provided a 29.6% reduction in B0 RMSE, whereas the SNR was reduced by 58.7%. The flexible iPRES coil array can conform to different anatomical regions and perform imaging and localized B0 shimming with a higher SNR, shimming performance, ease of positioning, and comfort compared to a rigid iPRES coil array, which should be valuable for many applications throughout the human body.

Flexible array coil for cervical and extraspinal (FACE) MRI at 3.0 Tesla.

Objective.High-resolution MRI of the cervical spine (c-spine) and extraspinal neck region requires close-fitting receiver coils to maximize the signal-to-noise ratio (SNR). Conventional, rigid C-spine receiver coils do not adequately contour to the neck to accommodate varying body shapes, resulting in suboptimal SNR. Recent innovations in flexible surface coil array designs may provide three-dimensional (3D) bendability and conformability to optimize SNR, while improving capabilities for higher acceleration factors.Approach.This work describes the design, implementation, and preliminaryin vivotesting of a novel, conformal 23-channel receive-only flexible array for cervical and extraspinal (FACE) MRI at 3-Tesla (T), with use of high-impedance elements to enhance the coil's flexibility. Coil performance was tested by assessing SNR and geometry factors (g-factors) in a phantom compared to a conventional 21-channel head-neck-unit (HNU).In vivoimaging was performed in healthy human volunteers and patients using high-resolution c-spine and neck MRI protocols at 3T, including MR neurography (MRN).Main results.Mean SNR with the FACE was 141%-161% higher at left, right, and posterior off-isocenter positions and 4% higher at the isocenter of the phantom compared to the HNU. Parallel imaging performance was comparable for an acceleration factor (R) = 2 × 2 between the two coils, but improved forR= 3 × 3 with meang-factors ranging from 1.46-2.15 with the FACE compared to 2.36-3.62 obtained with the HNU. Preliminary human volunteer and patient testing confirmed that equivalent or superior image quality could be obtained for evaluation of osseous and soft tissue structures of the cervical region with the FACE.Significance.A conformal and highly flexible cervical array with high-impedance coil elements can potentially enable higher-resolution imaging for cervical imaging.

In vivo MRI of knee using a metasurface-inspired wireless coil.

To investigate the application of a metasurface-inspired wireless coil and evaluate its performance in clinical knee MRI. A metasurface surface coil is designed for knee MRI at 1.5T. The image SNR and uniformity are assessed using a water phantom. In vivo studies are performed on 10 healthy volunteers (age range, 24-30 y; three males) and two patients (ages 31 and 76 y; two males) with knee conditions. A commercial 4-channel flexible coil and a 12-channel knee coil are used for comparison. The SNRs of different tissues on knee MRI images are evaluated and compared. The image quality is evaluated using a five-point Likert scale. The SNRs of the images acquired by the metasurface coil with spine coil as receiving coil are similar to the 12-channel knee coil, whereas the uniformity from groups where the metasurface coil was used is higher than that acquired by conventional coils in phantom studies. For in vivo knee MRI, the SNRs of the images acquired by the metasurface coil with spine coil as receiving coil are between that of the 4- and 12-channel phased-array coils. The image quality scores evaluated by radiologists are higher when metasurface is used. The metasurface-inspired wireless coil is applicable to clinical knee MRI. When used in conjunction with the spine coil, it provides a favorable SNR between that of the 4- and 12-channel phased-array coil at 1.5T MRI system. The metasurface coil improves image uniformity regardless of which coil is used as the receiving coil.

A Design of Magnetic Resonant Wireless Power Transfer System using Flexible Resonator Coils

A Design of Magnetic Resonant Wireless Power Transfer System using Flexible Resonator Coils

Unraveling the role of flexible coil near calcium binding site of levansucrase on thermostability and product profile via proline substitution and molecular dynamics simulations.

Due to its bioactivity and versatile applications, levan has appeared as a promising biomaterial. Levansucrase is responsible for the conversion of sucrose into levan. With the goal of enhancing levan production, the strategy for enhancing the stability of levansucrase is being intensively studied. To make proteins more stable under high temperatures, proline, the most rigid residue, can be introduced into previously flexible regions. Herein, G249, D250, N251, and H252 on the flexible coil close to the calcium binding site of Bacillus licheniformis levansucrase were replaced with proline. Mutations at G249P greatly enhance both the enzyme's thermodynamic and kinetic stability, while those at H252P improve solely the enzyme's kinetic stability. GPC analysis revealed that G249P synthesize more levan, but H252P generate primarily oligosaccharides. Molecular dynamics simulations (MD) and MM/GBSA analysis revealed that G249P mutation increased not only the stability of levansucrase, but also affinity toward fructan.

Locating Everyday Objects Using NFC Textiles

This paper builds a Near-Field Communication (NFC) based localization system that allows ordinary surfaces to locate surrounding objects with high accuracy in the near-field. While there is rich prior work on device-free localization using far-field wireless technologies, the near-field is less explored. Prior work in this space operates at extremely small ranges (a few centimeters), leading to designs that sense close proximity rather than location. We propose TextileSense, a near-field beamforming system that can track everyday objects made of conductive materials (for example, a human hand) even if they are a few tens of centimeters away. We use multiple flexible NFC coil antennas embedded in ordinary and irregularly shaped surfaces we interact with in smart environments---furniture, carpets, and so forth. We design and fabricate specialized textile coils woven into the fabric of the furniture and easily hidden by acrylic paint. We then develop a near-field blind beam-forming algorithm to efficiently detect surrounding objects, and use a data-driven approach to further infer their location. A detailed experimental evaluation of TextileSense shows an average accuracy of 3.5 cm in tracking the location of objects of interest within a few tens of centimeters from the furniture.

Miniaturized S-shaped flexible magnetic pulse welding coil design for engineering applications

Magnetic pulse welding (MPW) as a new solid-phase welding technology in the manufacturing field has vast application prospects. However, the application of MPW in engineering is severely limited by the large working area required for existing coils resulting in poor flexibility of the process. In this paper, a highly flexible, miniaturized S-shaped stereoscopic coil was proposed to reduce the working area required for the MPW process. The required working area was reduced to 32 × 30 mm. Numerical simulations were performed to determine the most suitable coil cross-section size. In addition, the feasibility of the coils was verified by welding AA5052 aluminum alloy and 316 L stainless steel through the new stereoscopic coils. Quasi-static tensile testing, laser microscopy, Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometer (EDS) were used to characterize the mechanical properties of the joints, weld interface morphology and element diffusion, respectively. It was revealed through simulation that the impact velocity of the new stereoscopic coil during MPW (342 m/s) was slightly higher than that of the conventional flat coil (327 m/s) at the same discharge energy. This indicated that the coil could achieve reliable welding. The AA5052-316 L joint welded by the new stereoscopic coil was demonstrated to be reliable by experiments. Furthermore, microscopic observation revealed that two effective bonding regions were formed at the interface. In addition, continuous interfacial waves and element diffusion were observed at the welding interface. Finally, the typical parts of AlFe double-cap beam structure were successfully welded by using a new stereoscopic coil. The coil is beneficial to broaden the application field of MPW.

Dual-Channel Stretchable, Self-Tuning, Liquid Metal Coils and Their Fabrication Techniques.

Flexible and stretchable radiofrequency coils for magnetic resonance imaging represent an emerging and rapidly growing field. The main advantage of such coil designs is their conformal nature, enabling a closer anatomical fit, patient comfort, and freedom of movement. Previously, we demonstrated a proof-of-concept single element stretchable coil design with a self-tuning smart geometry. In this work, we evaluate the feasibility of scaling this coil concept to a multi-element coil array and the associated engineering and manufacturing challenges. To this goal, we study a dual-channel coil array using full-wave simulations, bench testing, in vitro, and in vivo imaging in a 3 T scanner. We use three fabrication techniques to manufacture dual-channel receive coil arrays: (1) single-layer casting, (2) double-layer casting, and (3) direct-ink-writing. All fabricated arrays perform equally well on the bench and produce similar sensitivity maps. The direct-ink-writing method is found to be the most advantageous fabrication technique for fabrication speed, accuracy, repeatability, and total coil array thickness (0.6 mm). Bench tests show excellent frequency stability of 128 ± 0.6 MHz (0% to 30% stretch). Compared to a commercial knee coil array, the stretchable coil array is more conformal to anatomy and provides 50% improved signal-to-noise ratio in the region of interest.

The impact of variations in subject geometry, respiration and coil repositioning on the specific absorption rate in parallel transmit abdominal imaging at 7 T.

Parallel transmit MRI at 7 T has increasingly been adopted in research projects and provides increased signal-to-noise ratios and novel contrasts. However, the interactions of fields in the body need to be carefully considered to ensure safe scanning. Recent advances in physically flexible body coils have allowed for high-field abdominal imaging, but the effects of increased variability on energy deposition need further exploration. The aim of this study was to assess the impact of subject geometry, respiration phase and coil positioning on the specific absorption rate (SAR). Ten healthy subjects (body mass index[BMI] = 25 ± 5 kg m-2 ) were scanned (at 3 T) during exhale breath-hold and images used to generate body models. Seven of these subjects were also scanned during inhale. Simplifications of the coil and body models were first explored, and then finite-difference time-domain simulations were run with a typical eight-channel parallel transmit coil positioned over the abdomen. Simulations were used to generate 10 g averaged SAR (SAR10g ) maps across 100,000 phase settings, and the worst-case scenario 10 g averaged SAR (wocSAR10g ) was identified using trigonometric maximisation. The average maximum SAR10g across the 10 subjects with 1 W input power per channel was 1.77 W kg-1 . Hotspots were always close to the body surface near the muscle wall boundary. The wocSAR10g across the 10 subjects ranged from 2.3 to 3.2 W kg-1 and was inversely correlated to fat volume percentage (R = 8) and BMI (R = 0.6). The coefficient of variation values in SAR10g due to variations in subject geometry, respiration phase and realistic coil repositioning were 12%, 4% and 12%, respectively. This study found that the variability due to realistic coil repositioning was similar to the variability due to differing healthy subject geometries for abdominal imaging. This is important as it suggests that population-based modelling is likely to be more useful than individual modelling in setting safe thresholds for abdominal imaging.

Simulation analysis of effect of wheel out-of-roundness on dynamic stress of coil springs in metro vehicles

Many Chinese metros experienced numerous fatigue failures of the coil springs in the suspension of vehicles. The field test results presented in our previous work showed that wheel out-of-roundness (OOR) was responsible for the failure of the coil springs. It is believed that the most effective countermeasure to eliminate wheel OOR is to reprofile wheel. The fatigue life of coil springs is an important reference for determining the reprofiling parameters. A sophisticated vibration model for train and track with flexible coil springs and flexible track was established and validated with field test results. The effects of wheel OOR and P2 resonance on the coil spring can be evaluated with this model. The relationship between wheel OOR and coil spring dynamic stresses was determined using multibody simulation (MBS). The fatigue life of the coil springs was evaluated using the parameters of the amplitude of the wheel OOR and the mileage. Under the premise of finding a balance between improving the service life of the coil springs and reducing the cost of reprofiling the wheel, viable proposals were made to solve the problem of coil spring fracture.

Extended and weightbearing wrist 3-T MRI using a novel harness and flexible 24-channel glove coil to evaluate carpal kinematics: a pilot study in 10 volunteers.

Wrist pain in the extended or extended weightbearing positions may be incompletely evaluated using standard magnetic resonance imaging (MRI) with standard rigid clamshell coils in the neutral position. To evaluate a flexible 24-channel glove coil and harness when imaging the wrist in neutral, dorsally extended, and weightbearing positions. Ten wrists in 10 asymptomatic volunteers (mean age = 29 years) were scanned. Participants underwent 3-T MRI using the harness and flexible glove coil, acquiring sagittal turbo spin echo (TSE) and half-Fourier acquisition single-shot turbo spin echo (HASTE) pulse sequences. Static TSE images were obtained in neutral, extended, and weightbearing positions using proton density parameters and independently evaluated by two radiologists for: dorsal radiocarpal ligament thickness; radiocapitate, radiolunate, and capitatolunate angles; palmar translation of the lunate on the radius; angulation of the extensor tendons; and distance from the distal extensor retinaculum to Lister's tubercle. Cine HASTE images were dynamically acquired between neutral-maximum extension to measure the radiocapitate angle. Good reader agreement was observed (r > 0.73) for all measurements except palmar translation in the neutral position (r = 0.27). Significant increases in dorsal radiocarpal ligament thickness; radiocapitate, radiolunate and capitolunate angulation; and extensor tendon angulation were observed between the neutral and extended positions (P < 0.001). A further significant increase in these metrics between extended and weightbearing positions was also seen (P < 0.01). Significant increases in dorsal radiocarpal ligament thickness, articular and tendon angulations occur during wrist extension, that further increase with dorsal weightbearing.