High Modulation Research Articles

Cornerstone for MRI-compatible robots: A continuous pneumatic actuator with easy-to-connect prismatic/revolute and bidirectional encoder modules

The exceptional imaging capability of magnetic resonance imaging (MRI) enables the applications of robot-assisted surgery under MRI guidance. Essential to these robotic systems are the MRI-compatible robotic joint actuators. Among various actuation methods using MRI-compatible materials, pneumatic actuators are considered the most suitable for this application scenario due to their sterility, safety, and reliability. Yet, the current pneumatic actuators are either bulky, inefficient, or cannot achieve accurate bidirectional continuous motion. As a step forward, a novel high-performance continuous MRI-compatible pneumatic motor is proposed, along with quick-connect revolute/prismatic motion output modules and high accurate bidirectional encoder modules. The high performance of the pneumatic rotary and linear actuators are evaluated through experimental testing, where the rotary actuator can provide up to 2 Nm of output torque and over 28 W of output power, while the linear variant can deliver over 50 N of thrust, which surpass the SOTA competitors. Corresponding dynamic models are established and verified via experiments, with a maximum error of only 2.01%. Closed-loop control experiments demonstrate the high control precision and fast response frequency of the proposed pneumatic actuators, promoting the performance of joint actuators of various MRI-compatible surgical robots.

Moving target defense approach for secure relay selection in vehicular networks

Ensuring the security and reliability of cooperative vehicle-to-vehicle (V2V) communications is an extremely challenging task due to the dynamic nature of vehicular networks as well as the delay-sensitive wireless medium. In this context, the moving target defense (MTD) paradigm has been proposed to overcome the challenges of conventional solutions based on static network services and configurations. Specifically, the MTD approach involves the dynamic altering of network configurations to improve resilience to cyberattacks. Nevertheless, the current MTD solution for cooperative networks poses several limitations, such as that they require high synchronization modules that are resource-intensive and difficult to implement; and they rely heavily on attack-defense models, which may not always be accurate or comprehensive to use. To overcome these challenges, the proposed approach introduces an adaptive defense strategy within the MTD framework. This strategy proposes an intelligent spatiotemporal diversification-based MTD scheme to defend against eavesdropping attacks in cooperative V2V networks. It involves altering the system configuration spatially through relay selection and adjusting the percentage of injected fake data over time. This approach aims to balance reducing intercept probability while ensuring high throughput. Our methodology involves modeling the configuration of vehicular relays and data injection patterns as a Markov decision process, followed by applying deep reinforcement learning to determine the optimal configuration. We then iteratively evaluate the intercept probability and the percentage of transmitted real data for each configuration until convergence is achieved. To optimize the security-real data percentage (S-RDP), we developed a two-agent framework, namely MTD-DQN-RSS & MTD-DQN-RSS-RDP. The first agent, MTD-DQN-RSS, tries to minimize the intercept probability by injecting additional fake data, which in turn reduces the overall RDP, while the second agent, MTD-DQN-RSS-RDP, attempts to inject a sufficient amount of fake data to achieve a target S-RDP. Finally, extensive simulation results are conducted to demonstrate the effectiveness of our proposed solution, which improved system security compared to the conventional relay selection approach.

High performance dual-mode module for power generation and cooling based on optimized BiSbTe

Bismuth telluride is currently the most outstanding thermoelectric (TE) material near room temperature, and the high demand for solid-state refrigeration and low-grade waste heat recovery means there is an urgent need to improve its TE performance. This study investigates the enhanced TE performance of Bi0.4Sb1.6Te3 through the addition of Ag2Se. The introduction of Ag promotes an acceptor doping effect, leading to increased carrier concentration, while inhibiting lattice thermal conductivity together with Se doping. As a result, a notable enhancement in the figure of merit (ZT) to 1.35 at 373 K is achieved, with an average ZT of 1.17 spanning temperatures from 300 K to 523 K. More significantly, a 7-pair TE module was integrated using p-type Bi0.4Sb1.6Te3-0.00125Ag2Se and n-type extruded BiTeSe for cooling and power generation. A competitive conversion efficiency of 5.54 % at a temperature difference of 230 K and a maximum cooling temperature difference of 63.1 K at Th = 300 K are achieved, demonstrating the enormous practical application potential of this dual-mode module.

Terahertz binary computing in a coupled toroidal metasurface

The applications of terahertz metamaterials are being actively explored in recent times for applications in high-speed communication devices, miniature photonic circuits, and bio-chemical devices because of their wide advantages. The toroidal resonance, a new type of metasurface resonance, has been examined with great interest to utilize its properties in terahertz metasurface applications. This study reports a proof of concept design of a toroidal metasurface that experimentally demonstrates binary computing operations in the terahertz frequency regime. The analog computing of binary operations is achieved by the passive tuning of distance between the split ring resonators comprising the meta-molecule. The amplitude modulation is utilized as a method of determining the Boolean logic outputs of the system. The proposed metasurface could be further optimized for high amplitude modulations and active logic gate operations using tunable materials including graphene and ITO. The proposed metasurface consists of three split-ring resonators, and the near-field coupling between the adjacent resonators dictates the Boolean operations. A multipole analysis of the scattered powers of terahertz radiation determines the toroidal excitation in the metasurface. The proposed metasurfaces experimentally define AND Boolean logic operation at 0.89 terahertz, and OR Boolean logic operation at 0.97 terahertz. Numerical simulations support the experimentally obtained results. Additionally, we numerically report the excitation of NAND operation at 0.87 THz. Such toroidal analog computing metasurfaces could find applications in digitized terahertz circuits and integrated photonic devices.

Nanolasers

Abstract As the demand for smaller and more compact lasers increases, the physical dimensions of laser diodes are already at the diffraction limit, which impairs this miniaturization trend and limits direct laser integration into photonic and especially nanophotonic circuits. However, plasmonics has allowed the development of a novel class of lasers that can be manufactured without being limited by diffraction, exhibiting ultralow energy consumption, small volumes, and high modulation speeds that could someday compete with their modern macroscale counterparts. Nevertheless, a wide variety of issues create roadblocks for further development and commercial adoption. Here we conduct a monolithic review in which we formulate the definition of a nanolaser, categorize nanolasers, and examine their properties and applications to determine if nanolasers do present a potential technological revolution as they seem to exhibit or are too restricted by the issues that plague them to ever succeed.

Frequency selective low-loss transmission in negative curvature hollow-core fibers

A new low-loss negative curvature fiber design, named as the pole-anchored nested tubular negative curvature fiber, which exhibits frequency selective capabilities in the near-infrared region is proposed. This unique approach involves the addition of nested tubular elements anchored by vertical poles, which serve as an in-fiber resonator. The resulting frequency selective resonant loss dips exhibit high finesse and relative loss modulation depth. The concept of frequency selectivity in negative curvature fibers introduces unique possibilities for future applications of hollow-core structures.

Efficient and high-speed coupling modulation of silicon racetrack ring resonators at 2 µm waveband.

Significantly increased interests have been witnessed for the 2 µm waveband which is considered to be a promising alternative window for fiber and free-space optical communications. However, the less mature device technology at this wavelength range is one of the primary obstacles toward practical applications. In this work, we demonstrate an efficient and high-speed silicon modulator based on carrier depletion in a coupling tunable resonator. A benchmark high modulation efficiency of 0.75 V·cm is achieved. The 3-dB electro-optic bandwidth is measured to be 26 GHz allowing for up to 34 Gbit/s on-off keying modulation with a low energy consumption of ∼0.24 pJ/bit. It provides a solution for the silicon modulator with high-speed and low power consumption in the 2-µm waveband.

Holographic Polymer Nanocomposites with High Refractive Index Modulation by Doping Liquid Crystal E6M

Holographic Polymer Nanocomposites with High Refractive Index Modulation by Doping Liquid Crystal E6M

Biological material spider silk by direct incorporation onto fiber ferrule for wavelength tunable Q-switched application

This study presents a novel structure saturable absorber (SSA) based on spider silk for wavelength tunable Q-switched erbium-doped fiber laser (EDFL) operation from S to L bands. The nonlinear optical absorption of spider silk was measured, showing a high modulation depth of 64.92%, a low saturation intensity of 0.03 MW cm−2, and a non-saturable loss of 24%. By adjusting the polarization controller, a wavelength tunable Q-switched EDFL was achieved, with a tuning range of 64 nm from 1522 nm to 1586 nm. The Q-switched pulses had a repetition rate varying from 20.62 kHz to 6.57 kHz and a pulse width ranging from 14.02 μs to 26.30 μs, corresponding to an output power from −11.31 dBm to −9.02 dBm at the maximum pump power of 151.40 mW. The proposed SSA using spider silk offers a low-cost, eco-friendly, and high-performance solution for wide wavelength tunable Q-switched EDFL applications in optical testing, fiber communication, optical fiber sensing, and ultrafast lasers.

Out‐Of‐Phase Articulation Strategy of CsPbBr3/CsPb2Br5 Perovskite for High Sensitivity X‐Ray Detection

AbstractPolycrystalline CsPbBr3 perovskite materials exhibit exemplary stability, and desirable optoelectronic characteristics are promising for direct X‐ray detection. In this study, polycrystalline 2D phase of CsPb2Br5 hinged on CsPbBr3 is investigated for X‐ray array detector. The incorporation of CsPb2Br5 will modify the carrier transport environment, acting as an amplification factor that significantly enhances carrier mobility and response sensitivity. Finally, the devices demonstrates excellent performance growth. Carrier mobility of CsPbBr3 is improved by a significant 2 orders of magnitude, leading to the sensitivity increased from 2.64 × 104 to 2.58 × 105 µC Gyair−1 cm−2 at a bias voltage of 25 V mm−1. Even at a low bias voltage of 2 V mm−1, still got the value of 3.075 × 103 µC Gyair−1 cm−2, accompanied by a notable increase in the minimum detection limit of 127.9 nGyair s−1 at 0.5 V. Furthermore, a high modulation transfer function (MTF) of 1.57 lp mm−1 is obtained, and achieved a clear and high contrast X‐ray imaging with 64 × 64 TFT board. The perovskite exhibits outstanding light stability (RH ≈ 70 ± 5%) in the atmosphere following the introduction of 2D phase. This excellent carrier transport effect and good long‐term stability present significant commercial potential.

Facile and dynamic infrared modulation of durable VO2/CuI films for smart window applications

Vanadium dioxide (VO2) has been widely investigated as a smart window material due to its excellent thermochromic properties. However, with the increasing abundance of studies on VO2-based structures, its low solar modulation capability, environmental durability and high phase transition temperature have limited its commercial applications. Finding a simple way to solve the above problems simultaneously remains challenging. Here, we propose a bilayer structure combining VO2 and a transparent conductive material, copper iodide (CuI), for functional integration of thermochromic smart windows. The CuI layer is used as an anti-reflective layer and a protective layer to ensure high solar modulation capability (ΔTsol=15.41 %) and good expected service life (ESL=27 years), while realizing the dynamic modulation of infrared spectra at room temperature by Joule heating. This facile structure with overall performance offers a new possibility for the commercialization of VO2-based smart windows and room temperature dynamic modulation of infrared devices.

Thermal and structural analysis of the DONES target system under steady state and transient loading conditions

One of the crucial steps in the European Roadmap to the realisation of fusion energy is the design and construction of the Demo-orientated NEutron Source (DONES) facility. DONES is a fusion-like neutron source, based on the International Fusion Materials Irradiation Facility (IFMIF) concept, aimed at qualifying and testing the materials to be used in fusion reactors. The Target System (TSY) is a crucial system as it is the component where the interactions between deuterons and a liquid lithium target, flowing on a solid surface (i.e. the Back Plate), take place to produce neutrons for irradiating the testing materials. In this regard, an investigation campaign has been performed to evaluate the thermo-mechanical behaviour of the DONES TSY under selected steady state and transient loading conditions, in light of the most recent design updates (new bellows and connection systems). The first part of the assessment concerned the analysis of the TSY under the normal operation steady state loading scenario. A detailed 3D FEM model has been set up, considering the newest updates of the TSY geometry and of the operational parameters, and a thermo-mechanical analysis has been launched. Results have been mainly checked in terms of TSY global deformation, focusing on the Back Plate and on the connecting bellows displacements, in order to exclude overlapping with the High Flux Test Module and misalignments with the beam footprint. Afterwards, since the lithium inlet temperature has been increased from 250 °C to 300 °C, a transient thermo-mechanical analysis of the TSY under the start-up loading conditions has been performed to check if it is able to withstand the hotter lithium flow according to the RCC-MRx criteria. Therefore, the reference pre-heating strategy has been adopted, assessing the thermal and mechanical behaviour of the TSY, focusing on the Back Plate. The obtained results are presented and critically discussed, suggesting important recommendations for the follow-up of the design.

High efficiency independent modulation at dual-wavelength based on Pancharatnam–Berry and propagation phases

Metasurfaces capable of controlling multiple wavelengths independently have attracted broad interests these years due to their significance in multi-channel information processing applications. Previous solving strategies include spatial multiplexing or extensive searching for appropriate structures, both of which have their own disadvantageous, such as low efficiency, large computer resource requirement, or time consumption. In this paper, by combining the Pancharatnam–Berry (PB) phase and propagation phase, we propose a strategy to simplify the design complexity in a dual-wavelength metasurface system, in which two simple rectangular-shaped dielectric pillars (T1 and T2) with different aspect ratios are chosen as basic structures and crossed at the geometric center to achieve manipulation. The larger pillar T2 controls the longer wavelength through the PB phase while the smaller T1 acts as a perturbation to T2. The crossed T1&T2 is studied as a whole to tune the short wavelength. The investigations by the multipole expansion method reveal that the polarization conversion ratio of the meta-atoms is dependent on the interference of the formed multipoles. To validate the proposed strategy, a dual-wavelength achromatic metalens and a wavelength-multiplexed holographic metasurface operating at the infrared thermal imaging band are designed. Our design strategy can find widespread applications in metasurfaces where multiple objectives are required to be realized.

Evaluation of the Minimum Segment Width and Fluence Smoothing Tools for Intensity-modulated Techniques in Monaco Treatment Planning System.

This study aims to minimize monitor units (MUs) of intensity-modulated treatments in the Monaco treatment planning system while preserving plan quality by optimizing the "Minimum Segment Width" (MSW) and "Fluence Smoothing" parameters. We retrospectively analyzed 30 prostate, 30 gynecological, 15 breast cancer, 10 head and neck tumor, 11 radiosurgery, and 10 hypo-fractionated plans. Original prostate plans employed "Fluence Smoothing" = Off and were reoptimized with Low, Medium, and High settings. The remaining pathologies initially used MSW = 0.5 cm and were reoptimized with MSW = 1.0 cm. Plan quality, including total MU, delivery time, and dosimetric constraints, was statistically analyzed with a paired t-test. Prostate plans exhibited the highest MU variation when changing "Fluence Smoothing" from Off to High (average ΔMU = -5.1%; P < 0.001). However, a High setting may increase overall MU when MSW = 0.5 cm. Gynecological plans changed substantially when MSW increased from 0.5 cm to 1.0 cm (average ΔMU = -29%; P < 0.001). Organs at risk sparing and planning target volumes remained within 1.2% differences. Replanning other pathologies with MSW = 1.0 cm affected breast and head and neck tumor plans (average ΔMU = -168.38, average Δt = -11.74 s, and average ΔMU = -256.56, average Δt = -15.05 s, respectively; all with P < 0.004). Radiosurgery and hypofractioned highly modulated plans did not yield statistically significant results. In breast, pelvis, head and neck, and prostate plans, starting with MSW = 1.0 cm optimally reduces MU and treatment time without compromising plan quality. MSW has a greater impact on MU than the "Fluence Smoothing" parameter. Plans with high modulation might present divergent behavior, requiring a case-specific analysis with MSW values higher than 0.5 cm.

Non-binary codes approach on the performance of short-packet full-duplex transmissions

This paper illustrates the enhancement of the performance of short-packet full-duplex (FD) transmission by taking the approach of non-binary low density parity check (NB-LDPC) codes over higher Galois field. For the purpose of reducing the impacts of self-interference (SI), high order of modulation, complexity, and latency decoder, a blind feedback process composed of channels estimation and decoding algorithm is implemented. In particular, this method uses an iterative process to simultaneously suppress SI component of FD transmission, estimate intended channel, and decode messages. The results indicate that the proposed technique provides a better solution than both the NB-LDPC without feedback and the binary LDPC feedback algorithms. Indeed, it can significantly improve the performance of overall system in two important factors, which are bit-error-rate (BER) and &lt;a name="_Hlk155778233"&gt;&lt;/a&gt;mean square error (MSE), especially in high order of modulation. The suggested algorithm also shows a robustness in reliability and power consumption for both short-packet FD transmissions and high order modulation communications.

Optimization of the Symmetrical SVPWM for Three-Level T-Type Inverters With Unbalanced and Oscillated Neutral-Point Voltages

The symmetrical space-vector pulse-width-modulation (SVPWM) has been widely adopted in three-level (3L) T-type inverters due to its low current harmonics and high linear modulation index. However, when faced with unbalanced and oscillated neutral-point (NP) voltages, extra current harmonics will be generated. In this paper, a new solution is provided. Other than adopting the existing strategies for balancing the NP voltage, the symmetrical 3L SVPWM is optimized to work with unbalanced and oscillated NP voltages. Firstly, the vectors are idealized, based on which ideal dwell times are obtained by an analytical simplified symmetrical 3L SVPWM. Then, a dc-zero-sequence component is calculated and injected to maximize the linear modulation index, and the real dwell times are further derived after the adjustment according to the ‘volt-second balance’ principle. In addition, a control strategy is investigated to actively adjust the NP voltage. Finally, the optimized symmetrical 3L SVPWM is verified by comparative experiments, showing its low current harmonics with unbalanced and oscillated NP voltages.

Demonstration of IM/DD 3-Tbit/s PS-PAM8 transmission with wavelength and mode multiplexing based on neural network equalizer

We experimentally demonstrate 8-channel wavelength division multiplexing (WDM) signal transmission in 4 modes over 20-m multimode fiber (MMF) in an intensity modulation and direct-detection (IM/DD) system. By combining the probabilistic shaping (PS) technique with high order pulse amplitude modulation (PAM) format, 40-GBaud PS-PAM8 signal transmission in the WDM + MDM IM/DD system achieves a total net bit rate of 3-Tbit/s. With the aid of a multiple input single output (MISO) neural network (NN) equalizer, we obtain a 1.6-dB receiver sensitivity gain compared with traditional digital signal processing (DSP), including multiple input multiple outputs (MIMO) time domain equalizer (TDE).

A Hybrid PWM Strategy for Switching Loss Reduction in Three-Level Inverters

The advanced bus-clamping PWM (ABCPWM) sequences are well known to reduce line current THD in a three-level neutral point-clamped inverter. This paper deals with ABCPWM sequences employed optimally to achieve minimum switching loss throughout the linear operating region in a three-level inverter. The work extensively analyzes the performance of these sequences in terms of inverter switching loss and compares them with centered space vector modulation PWM (CSVPWM). Based on the analysis, a hybrid PWM scheme termed as <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">switching loss reduction</i> is proposed by optimally employing ABCPWM sequences in conjunction with variation in power factors. At a given average switching frequency, the proposed hybrid scheme reduces inverter switching loss compared to CSVPWM and the recently proposed discontinuous PWM-based optimization strategy at all power factors and modulation indices. With this scheme, switching loss reduces to 22% to 36% compared to CSVPWM and a maximum of 12% reduction than the existing optimization strategy. Furthermore, the scheme gives lower harmonic distortion compared to these two existing PWM schemes near high modulation indices and near unity power factor load. The theoretical, simulated, and real-time simulation results are presented with experimental results using TMS320F28335 DSP controller for validating the proposed work.

Free‐Standing Bacterial Cellulose‐Templated Radiative Cooling Liquid Crystal Films with Self‐Adaptive Solar Transmittance Modulation

AbstractPassive radiative cooling materials can efficiently reflect solar radiation and spontaneously dissipate heat through the long‐wave infrared (LWIR) transmission window to the coldouter space. They are highly attractive for application in walls and roofs of sustainable energy‐efficient buildings, but it is a challenging task to develop switchable radiative coolers for transparent windows. Herein, free‐standing bacterial cellulose‐templated radiative cooling liquid crystal films with high LWIR emissivity and self‐adaptive solar transmittance are reported. Biosynthetic silanized bacterial cellulose with 3D interconnected porous nanostructure is harnessed as a robust template for confining novel liquid crystals with smectic A to chiral nematic phase transition, thereby endowing the film with high solar transmittance modulation ability. The resulting film is found to not only exhibit a remarkable LWIR emissivity, but also adaptively change its solar transmittance between a transparent state and an opaque state according to environmental temperature variation. Outdoor radiative cooling experiments are performed, and the energy‐saving performance is evaluated through a simulation of a 12‐story reference office building with the films applied as radiative cooling windows. This research can shine light on the development of advanced radiative cooling materials with switchable transmittance and their widespread applications in buildings, vehicles, and transparent photovoltaics.

Efficient catalytic ozonation for hexazinone degradation by Fe/Ce-doped MOF derivatives

High catalytic efficiency and strong anti-interference catalyst for refractory pollutants removal remains a challenge for the catalytic ozonation. Metal-organic framework (MOF) have shown excellent performance in catalysis filed, but there is a risk of metal ion leaching. Designing MOF derivatives by high temperature modulation is considered to be an effective way to enhance the performance and reduce leaching risk of MOFs. In this paper, Fe/Ce bimetallic metal–organic framework (FeCe-MOF) was synthesized and three MOF derivatives were prepared by calcination at different temperatures. The performance of MOF derivatives in the degradation of hexazinone via catalytic ozonation and the effects were investigated. The mechanism of catalytic ozonation by FeCe@C-600 was also elucidated by the analysis of structural characterization of the fresh and used FeCe@C-600, electron paramagnetic resonance (EPR) and quenching experiment. FeCe@C-600/O3 system achieved 78.78 % removal of hexazinone and 42.37 % degradation of TOC within 20 min. During the catalytic ozonation, FeCe@C-600 has high structural stability and avoiding the release of metal ions. FeCe@C-600 showed excellent performance to degrade and mineralize of hexazinone, and it is more stable and has wider pH applicability. The electron transfer and redox cycling of Mn+/Mn+1 were promoted along with the conversion of lattice oxygen to oxygen vacancies. The degradation of hexazinone was mainly attributed to the generation of reactive oxygen species (•OH, •O2–, 1O2) during catalytic ozonation. MOF derivatives exhibited good adsorption capacity during the degradation of hexazinone. FeCe@C-600 effectively reduces metal leaching while retaining high catalytic activity, providing new ideas for the development of new efficient and environmentally friendly ozone catalysts.