Multimodal Resonance Research Articles

The differential association between local neurotransmitter levels and whole-brain resting-state functional connectivity in two distinct cingulate cortex subregions.

We examined the association between rsFC and local neurotransmitter levels in the pregenual anterior cingulate cortex (pgACC) and the anterior mid-cingulate cortex (aMCC) by varying rsFC-strengths at the whole-brain level. Our results showed region-dependent directionality of associations in the investigated ACC subdivisions.

Low-noise Brillouin random fiber laser with Auto-tracking dynamic fiber grating based on a saturable absorption ring

A low-noise Brillouin random fiber laser (BRFL) with stabilized lasing output and narrow linewidth is proposed and demonstrated experimentally. Stimulated Brillouin scattering and Rayleigh scattering are exploited to work as the gain and random distributed feedback mechanisms, respectively. A simple unpumped Erbium-doped fiber (EDF) loop structure which consists of a section of EDF and an optical coupler is introduced into the BRFL cavity, forming a saturable absorption ring (SAR). When light with proper intensity is incident into the SAR, a dynamic fiber grating (DFG) can be built up to work as a narrow-bandwidth filter with the ability of auto-tracking the center frequency. The SAR can effectively filter out dense random longitudinal modes and suppress multi-mode resonances and frequency jitters by restricting the mode-competition-induced mode hopping within a limited frequency range of ∼ 1 MHz and auto-tracking the center frequency of light in the cavity, simultaneously. Thus, the output of BRFL with SAR is much more stabilized than existing free-running BRFLs. In the experiment, a stable lasing output with an ultra-narrow linewidth (less than2kHz) is obtained from the proposed BRFL. The measured relative intensity noise and frequency noise demonstrate that the noise level of the proposed laser is significantly lower than that of the free-running BRFLs. This proposed technique not only provides a solution to the dilemma of previously reported BRFLs with severe lasing instabilities, but also makes a step towards the development of practical and reliable BRFLs. This high-quality laser source with advantages of high stability, low cost, low threshold power, high coherence, narrow linewidth, and low noise can find useful applications in coherent optical detection, high-resolution spectrometers, microwave photonics, and optical sensing fields.

Conversion Efficiency in Kerr-Microresonator Optical Parametric Oscillators: From Three Modes to Many Modes.

Optical parametric oscillation in a Kerr nonlinear microresonator can generate coherent laser light with frequencies that are widely separated from the pump frequency, allowing, for example, visible light to be generated using a near-infrared pump. To be practically useful, the pump-to-signal conversion efficiency must be far higher than what has been demonstrated in microresonator-based oscillators with widely-separated output frequencies. To address this challenge, here we theoretically and numerically study parametric oscillations in Kerr nonlinear microresonators, revealing an intricate solution space that arises from an interplay of nonlinear processes. As a start, we use a three-mode approximation to derive an efficiency-maximizing relation between pump power and frequency mismatch. However, realistic devices, such as integrated microring resonators, support far more than three modes. Hence, a more accurate model that includes the entire modal landscape is necessary to determine potential inefficiencies arising from unwanted competing nonlinear processes. To this end, we numerically simulate the Lugiato-Lefever Equation that accounts for the full spectrum of nonlinearly-coupled resonator modes. We observe and characterize two nonlinear phenomena linked to parametric oscillations in multi-mode resonators: Mode competition and cross phase modulation-induced modulation instability. Both processes may impact conversion efficiency. Finally, we show how to increase the conversion efficiency to ≈ 25 % by tuning the microresonator loss rates. Our analysis will guide microresonator designs that aim for high conversion efficiency and output power.

Design of a polarization‐insensitive three dimensional microwave absorber for ultra‐wideband RCS reduction

AbstractA polarization‐insensitive three‐dimensional (3‐D) microwave absorber is proposed in this letter for ultra‐wideband radar section cross (RCS) reduction. The lossy layer of the designed absorber is evolved from the bent metallic strip with a center‐embedded resistor, which performs the property of absorption‐reflection‐absorption due to its multimode resonances. A short stub with a center‐embedded resistor is connected to the long‐bent strip to abolish the reflection performance, for the sake of achieving wide absorption performance. The fundamental working principle of the designed structure is explained adequately using an intuitive equivalent circuit model. Additionally, the absorber is designed, fabricated, and measured for validation, whose fractional bandwidths is 151.5% with at least 10‐dB RCS reduction.

Compact and High-Order On-Chip Wideband Bandpass Filters on Multimode Resonator in Integrated Passive Device Technology

Compact and High-Order On-Chip Wideband Bandpass Filters on Multimode Resonator in Integrated Passive Device Technology

Multistage Kondo effect in a multiterminal geometry: A modular quantum interferometer

Quantum systems characterized by an interplay between several resonance scattering channels demonstrate very rich physics. To illustrate it we consider a multistage Kondo effect in nanodevices as a paradigmatic model for a multimode resonance scattering. We show that the channel crosstalk results in a destructive interference between the modes. This interplay can be controlled by manipulating the tunneling junctions in the multilevel and multiterminal geometry. We present a full-fledged theory of the multistage Kondo effect at the strong-coupling Fermi-liquid fixed point and discuss the influence of quantum interference effects to the quantum transport observables.

Impulse control differentiates Internet gaming disorder from non-disordered but heavy Internet gaming use: Evidence from multiple behavioral and multimodal neuroimaging data

Billions of people play Internet games and some of them may develop Internet gaming disorder (IGD), yet the differences between IGD and non-disordered but heavy Internet gaming use behavior remain unclear. We used multiple behaviors and multimodal functional magnetic resonance imaging (fMRI) to examine the specificity of impulse control to differentiate IGD from non-disordered but heavy Internet gaming use. One hundred sixty subjects, including patients with IGD (PIGD), non-disordered but heavy Internet gaming participants (NIGP), and healthy controls rated Barratt Impulsiveness Scale, and 141 out of them completed delay-discounting task and resting-state during fMRI. The PIGD but not the NIGP showed altered impulsiveness and delay discounting behavior as compared to healthy controls. Moreover, the PIGD but not the NIGP showed altered activity pattern in the frontoparietal network as compared to healthy controls. The PIGD but not the NIGP showed altered functional connectivity in the frontoparietal network during delay discounting and resting-state as compared to healthy controls. Furthermore, impulse control-related behavioral and fMRI measures significantly classified PIGD from NIGP. This study provides consistent evidence supporting the specificity of impulse control for distinguishing IGD from non-disordered but heavy Internet gaming use.

Gold nanocups with multimodal plasmon resonance for quantum-dot random lasing

Reduction of symmetry in plasmonic nanostructures may lead to great opportunities in controlling their photophysics of extinction, local field, light response, and plasmonic interactions. With their strong light scattering and unique modulation of field distribution, plasmonic nanocups hold great potential for applications in random laser, three-dimensional optical nanoantenna, and optical coherence tomography imaging. Here we demonstrate a novel and robust solution-phase synthesis approach to gold nanocups, which combines templating and seeded growth techniques to precisely control the size, morphology, and composition of the nanocups. Ripening is the key strategy in this wet-chemistry process to ensure primary anisotropic growth of gold within the cup-shaped space provided by each template, consisting of a silica nanosphere and a flexible resorcinol-formaldehyde resin shell. The resulting plasmonic nanocups possess three types of plasmon resonance modes, including axial, transverse S, and transverse P modes, determined by the polarization of the incident light. This robust and scalable synthesis allows the production of gold nanocups with high quality and efficiency, opening the door to unique photophysical properties and many potential applications, as demonstrated by their excellent performance in plasmonic quantum dot random lasing.

A low resource 3D U-Net based deep learning model for medical image analysis.

The success of deep learning, a subfield of Artificial Intelligence technologies in the field of image analysis and computer can be leveraged for building better decision support systems for clinical radiological settings. Detecting and segmenting tumorous tissues in brain region using deep learning and artificial intelligence is one such scenario, where radiologists can benefit from the computer based second opinion or decision support, for detecting the severity of disease, and survival of the subject with an accurate and timely clinical diagnosis. Gliomas are the aggressive form of brain tumors having irregular shape and ambiguous boundaries, making them one of the hardest tumors to detect, and often require a combined analysis of different types of radiological scans to make an accurate detection. In this paper, we present a fully automatic deep learning method for brain tumor segmentation in multimodal multi-contrast magnetic resonance image scans. The proposed approach is based on light weight UNET architecture, consisting of a multimodal CNN encoder-decoder based computational model. Using the publicly available Brain Tumor Segmentation (BraTS) Challenge 2018 dataset, available from the Medical Image Computing and Computer Assisted Intervention (MICCAI) society, our novel approach based on proposed light-weight UNet model, with no data augmentation requirements and without use of heavy computational resources, has resulted in an improved performance, as compared to the previous models in the challenge task that used heavy computational architectures and resources and with different data augmentation approaches. This makes the model proposed in this work more suitable for remote, extreme and low resource health care settings.

Engineering multimode resonances for tunable multifrequency superscattering.

We demonstrate a rigorous multimode engineering method to achieve multifrequency superscattering with flexible controllability in a subwavelength graphene/hexagonal boron nitride (hBN) cylindrical system. Through delicately tuning the chemical potential of graphene, different resonance channels of the proposed stucture can be spectrally overlapped to construct the multiple superscattering points. Consequently, the scattering cross section is enhanced effectively and the so-called superscattering beyond the single-channel scattering limit can be attained. Numerical calculations on scattering spectra, near-field, and far-field distributions are performed to confirm the scattering enhancement. The general principles presented here may suggest an accurate and efficient approach to actively tune the light-matter interaction at the subwavelength scale.

Multi-mode surface plasmon resonance absorber based on dart-type single-layer graphene.

In this paper, a multi-mode surface plasmon resonance absorber based on dart-type single-layer graphene is proposed, which has the advantages of polarization independence, tunability, high sensitivity, high figure of merit, etc. The device consists of a top layer dart-like patterned single-layer graphene array, a thicker silicon dioxide spacer layer and a metal reflector layer, and has simple structural characteristics. The numerical results show that the device achieves the perfect polarization-independent absorption at the resonance wavelengths of λI = 3369.55 nm, λII = 3508.35 nm, λIII = 3689.09 nm and λIV = 4257.72 nm, with the absorption efficiencies of 99.78%, 99.40%, 99.04% and 99.91%, respectively. The absorption effect of the absorber can be effectively regulated and controlled by adjusting the numerical values such as the geometric parameters and the structural period p of the single-layer graphene array. In addition, by controlling the chemical potential and the relaxation time of the graphene layer, the resonant wavelength and the absorption efficiency of the mode can be dynamically tuned. And can keep high absorption in a wide incident angle range of 0° to 50°. At last, we exposed the structure to different environmental refractive indices, and obtained the corresponding maximum sensitivities in four resonance modes, which are SI = 635.75 nm RIU−1, SII = 695.13 nm RIU−1, SIII = 775.38 nm RIU−1 and SIV = 839.39 nm RIU−1. Maximum figure of merit are 54.03 RIU−1, 51.49 RIU−1, 43.56 RIU−1, and 52.14 RIU−1, respectively. Therefore, this study has provided a new inspiration for the design of the graphene-based tunable multi-band perfect metamaterial absorber, which can be applied to the fields such as photodetectors and chemical sensors.

Double-opening metal ring based terahertz metamaterial absorber sensor

Terahertz metamaterial biosensor is a label-free affinity sensor that enhances the strength of the local electromagnetic field. It is extremely sensitive to changes in the dielectric constant of the surrounding environment, thereby providing a new method of detecting micro or trace biological samples. In this work, a highly sensitive terahertz refractive index metamaterial absorber sensor for detecting the biological sample is proposed. The sensor consists of two concentric open metal rings and is a multimode resonator. With two independent adjustable operating bands in a frequency range of 0.7–2.5 THz, i.e. 1.079 THz and 2.271 THz, the sensor can observe different electromagnetic effects of the sample in the terahertz band. We evaluate the performance of terahertz sensors with indicators such as absorption characteristics and sensitivity. The sensor possesses the absorption higher than 99.9% in free space. In addition, the large Q value indicates that the sensor provides high frequency selectivity characteristics. Especially, the sensitivity of the sensor achieves 693.7 GHz/RIU, with a minimum refractive index change of 0.004 for the detection of biological samples, which provides good sensing performance. In the proposed sensor, a flexible material with low dielectric constant is used, which has the advantages of biocompatibility and portability and shows high stability at the 0°–60° oblique incidence angle and within 4% fabrication error. Moreover, the detection effectiveness of the sensor is verified by simulation experiments with ethanol-water mixtures. The sensor units designed in this paper have small interactions among them, work stably and are easily fabricated The sensor can significantly enhance the interaction between light and matter and has broad application prospects in terahertz high-sensitivity biosensing detection.

Ultra-Wideband and Lightweight Electromagnetic Polarization Converter Based on Multiresonant Metasurface

Polarization-control devices have attracted considerable interest, however, most of the polarization converters operating at lower frequencies have a heavy design and narrow bandwidth which limits their practical applications. Here we report a simple design of an ultra-wideband and lightweight polarization converter for applications in the S- and C-bands. The proposed converter is designed based on a metasurface structure with the dielectric layer modified to hollow structure to obtain a lightweight design even working at such low frequency. Theoretical analysis and simulation results indicate that the converter can convert the orthogonal polarization transformation of reflected wave. Furthermore, the measurement results show good agreement with the simulation results. The proposed polarization converter can achieve a polarization conversion ratio above 90% in an ultra-wide frequency range from 2 to 8.45 GHz due to multi-resonance modes. These performances are going beyond state of the art in terms of bandwidth and lightweight design, thus it can be applied in various applications in the operating bands.

UHF RFID Tag Design Using Theory of Characteristics Modes for Platform-Tolerant and Harsh Metallic Environments

This paper presents a wideband, long-range RFID tag antenna design with platform tolerant features using characteristic mode analysis (CMA). The proposed design consists of a two-layer structure, that are separated by an air gap. The upper layer consists of T-match and dual loop-based meandered antenna optimized for achieving long read range characteristics in free space/low permittivity dielectrics. The second layer consists of multi-resonant strips printed on a grounded substrate carefully designed using CMA for producing multi-resonant modes in the required UHF RFID band. The multi-resonant strips help in achieving wide bandwidth and isolation between different environment surfaces. This tag antenna provides a wide bandwidth ranging from 900 – 940 MHz that covers both the US UHF RFID band (902 – 928 MHz) and the upper European UHF RFID band (915 – 921 MHz). Moreover, this design achieved a read range of 14.7 m in free space, 14 m on a metal plate, and 13 m on wood, and glass. Furthermore, the proposed antenna was also tested in harsh metal environments such as car number plates and cargo metallic containers. Therefore, the proposed tag can be used for tagging metallic containers, wood containers, and other harsh platforms for cargo management, Asset tracking, supply chain visibility, and Internet of Things (IoT) Applications.

Compact Wideband Loop Antenna for Earbuds

This paper presents the compact wideband loop antenna with a small size of 7.05mm’s radius covering ultra-wideband above 6 GHz, Wi-Fi, and Bluetooth bands for earbuds. The wide bandwidth of the proposed compact loop antenna is obtained with the antenna structure consisting of the loop antenna and the capacitive loading pin inserted in the middle of the loop antenna. The loop antenna with the capacitive loading pin supports multi-resonant modes. A wider bandwidth can be obtained by adjusting the position of the capacitive loading pin. The half-wavelength resonant frequency of the basic loop can easily be tuned through the physical capacitance between the capacitive loading pin and loop antenna. Additionally, the impedance loop is considered for the impedance matching of the compact wideband loop antenna. The simulated and measured results are included to evaluate the performance of the proposed compact wideband loop antenna. Consequently, we obtained that the simulation and measurements results are consistent.

Multimode resonance triple-band metamaterial absorber from mid-infrared to very long wavelengths (invited)

Multimode resonance triple-band metamaterial absorber from mid-infrared to very long wavelengths (invited)

A Broadband Multimode Antenna With Enhanced Gain and High Efficiency by Employing Metasurface for WLAN and Car-to-Car Application

A multimode resonance patch antenna with the attractive radiation gain and efficiency is investigated in this paper. A driven patch with both sides shorted similar to the cavity model is presented to generate TM₀₃ and TM₁₁ modes. TM₂₁ mode is also excited by inserting five shorting parasitic patches on both sides of the radiation aperture to extended the impedance bandwidth and no additional feeding structure is required. Meanwhile, a novel single-layer metasurface with the positive gradient of the reflection phase is placed directly above the proposed multimode antenna. Then the characteristics of high gain and better front-to-back ratio (FBR) are acquired. The measured results show that the characteristics of 20.7% impedance bandwidth from 5.08 GHz to 6.25 GHz, stable gain of up to 12.34 dBi, high radiation efficiency of up to 89% and cross-polarization level below -20 dB are obtained. These characteristics all imply that the proposed antenna can be applied to WLAN and Car-to-Car (C2C) communications.

Miniaturized Multiband Bandpass Filters Based on a Single Multimode Resonator Loading Branches

In this paper, the operating mechanism of proposed bandpass filters with a single multimode resonator loaded with branches is introduced. Based on the design procedure, the center frequencies of the proposed bandpass filters can be controlled due to the design freedom. Meanwhile, the proposed bandpass filters (BPFs) feature compact sizes and small insertion loss. To validate the design and analysis, a prototype was fabricated and measured with six passbands centered at 1.23/1.76/2.38/4.24/5.23/6.75 GHz. The measured result of the fabricated filter agrees well with the simulation, which indicates that the proposed structure can serve as a potential candidate for multiband BPF designs.

Broadband Low-Frequency Acoustic Metamuffler

In this research, we propose and design an acoustic metamuffler (AMM) by coupling a microperforated plate and a composite waveguide formed by a main waveguide and a Helmholtz resonator. The proposed mechanism and deliberately designed structure are conducive to generating multimode resonances that help to improve the coupling absorption effect and lead to broadband (4 octaves) sound insulation. We develop an effective circuit model to analytically predict the insulation bandwidth and put forward numerical and experimental measurements that demonstrate the effectiveness of the proposed concept. The designed AMM produces sound insulation with an average of 20 dB of sound-transmission loss at a low-frequency range, extending from 100 to 1600 Hz, while having an ultrathin thickness of 6.2 cm (1/55\ensuremath{\lambda} for the lowest working frequency). Our findings could have pragmatic applications for acoustic insulators or absorbers.

Multi-mode plasmonic resonance broadband LWIR metamaterial absorber based on lossy metal ring.

Broadband perfect infrared wave absorption of unpolarized light over a wide range of angles in an ultrathin film is critical for applications such as thermal emitters and imaging. Although many efforts have been made in infrared broadband absorption, it is still challenging to cover the perfect absorption of broadband in the long-wave infrared band. We propose a long-wave infrared broadband, polarization, and incident angle insensitivity metamaterial absorber based on the supercell with four rings of two sizes. Broadband absorption covering the long-wave infrared band is realized by combining four PSPRs and LSPRs absorption peaks excited by the supercell structure. The absorptivity of our absorber exceeds 90% in the wavelength range of 7.76∼14µm, and the average absorptivity reaches 93.8%. The absorber maintains more than 80% absorptivity as the incident angle of unpolarized light reaches 60°, which may have promising applications for thermal emitters, infrared imaging, thermal detection.