Tunable Mode Research Articles

Inverse design of Bézier curve-based mechanical metamaterials with programmable negative thermal expansion and negative Poisson's ratio via a data augmented deep autoencoder.

Controlling stress and deformation induced by thermo-mechanical stimulation in high-precision mechanical systems can be achieved by mechanical metamaterials (MM) exhibiting negative thermal expansion (NTE) and negative Poisson's ratio (NPR). However, the inverse design of MM exhibiting a wide range of arbitrary target NTEs and NPRs is a challenging task due to the low design flexibility of analytical methods and parametric studies based on numerical simulation. In this study, we propose Bézier curve-based programmable chiral mechanical metamaterials (BPCMs) and a deep autoencoder-based inverse design model (DAIM) for the inverse design of BPCMs. Through iterative transfer learning with data augmentation, DAIM can generate BPCMs with a curved rib shape inaccessible with the Bézier curve, which improves the inverse design performance of the DAIM in the data sparse domain. This approach decreases the mean absolute error of NTE and NPR between the inverse design target and the numerical simulation results of inverse designed BPCMs on the data-sparse domain by 79.25% and 83.33% on average, respectively. A 3D-printed BPCM is validated experimentally and exhibits good coincidence with the target NTE and NPR. Our proposed BPCM and the corresponding inverse design framework enable the inverse design of BPCMs with NTE in the range of -1100 to 0 ppm K-1 and NPR in the range of -0.6 to -0.1. Furthermore, programmable thermal deformation modes with a fixed Poisson's ratio are realized by combining various inverse designed BPCM unit cells. BPCMs and the DAIM for their inverse design are expected to improve the mechanical robustness of high-precision mechanical systems through tunable modulation of thermo-mechanical stimulation.

Near-unity circular dichroism enabled by toroidal dipole empowered bound states in the continuum for electrical switching and sensing.

Near-unity circular dichroism (CD) with high quality (Q)-factors has wide applications in chiral lasers, modulators, detectors, etc. In this work, we firstly suggest a feasible approach to realize near-unity CD (∼0.94) with a high Q-factor (>2 × 104) supported by a toroidal dipole (TD) empowered superchiral quasi-bound states in the continuum (BICs) metasurface. Based on intensity, excellent electrical switching is achieved by adjusting the Fermi energy of the graphene on the metasurface. High refractive index sensitivity (136.2 nm/RIU) and figure of merit (1135 RIU-1) demonstrate its superior chiral sensing detection performance. Moreover, the near-unity CD displays a large robustness to the asymmetry offset. Our work paves a feasible avenue for well-designed superchiral quasi-BIC metasurfaces with high Q-factor near-unity CD for chiral applications in electrically tunable modulators, switches, sensors, etc.

Magnetic and spectroscopic properties of chloride-bridged guanidinate dilanthanide complexes

The guanidinate ligand scaffold offers a unique combination of hard anionic charges, steric tunability, and electronic modulation, rendering it an ideal candidate for the molecular design of lanthanide complexes. Here, we present two dilanthanide chloride complexes [{(Me3Si)2NC(NiPr)2}2Ln(μ–Cl)]2 (Ln = Gd (1), and Tb (2)) where each metal ion is ligated to two guanidinate anions and bridged to the other metal ion by two chloride ligands. The isostructural complexes 1 and 2 were synthesized through salt metathesis reactions and characterized through single–crystal X–ray diffraction analysis, IR and UV–Vis spectroscopy, and SQUID magnetometry. The half-filled f-electron valence shell of GdIII ion allows an accurate study of magnetic coupling through fitting of the dc magnetic susceptibility data to a spin–only Hamiltonian, affording values of J = -0.0242 cm−1 and g = 2.0192. The operative superexchange coupling mechanism was confirmed through broken–symmetry density functional theory calculations, which additionally provide insight into the spectral analysis of 1.

Photocatalytic fenton-like system with atomic Fe on carbon nitride boost selective glucose oxidation towards gluconic acid

Peroxymonosulfate (PMS) activation is a prospective technique for pollutant degradation, but less attention has been paid to the tunable modulation and effective utilization of reactive oxygen species in selective oxidation. Herein, we develop a photocatalytic Fenton-like system with Fe single-atom supported on carbon nitride that generates singlet oxygen (1O2) as dominant active species to selectively oxidize glucose to gluconic acid. The loading of atomic Fe onto carbon nitride can notably aggrandize the light absorption and boost the photon-generated carriers transfer efficiency. With PMS and simulated sunlight, the Fe single-atom catalyst afforded a glucose conversion of 36.3% with gluconic acid selectivity up to 91.6%, as is superior to the state-of-the-art catalytic systems. Control experiments and theoretical analysis reveal that the excellent catalytic performance of Fe single-atom supported on carbon nitride is resulted from the enhanced photocatalytic activity with better PMS activation ability.

Electrohydrodynamic printing for high resolution patterning of flexible electronics toward industrial applications

AbstractElectrohydrodynamic (EHD) printing technique, which deposits micro/nanostructures through high electric force, has recently attracted significant research interest owing to their fascinating characteristics in high resolution (<1 μm), wide material applicability (ink viscosity 1–10 000 cps), tunable printing modes (electrospray, electrospinning, and EHD jet printing), and compatibility with flexible/wearable applications. Since the laboratory level of the EHD printed electronics' resolution and efficiency is gradually approaching the commercial application level, an urgent need for developing EHD technique from laboratory into industrialization have been put forward. Herein, we first discuss the EHD printing technique, including the ink design, droplet formation, and key technologies for promoting printing efficiency/accuracy. Then we summarize the recent progress of EHD printing in fabrication of displays, organic field‐effect transistors (OFETs), transparent electrodes, and sensors and actuators. Finally, a brief summary and the outlook for future research effort are presented.image

Design of Vernier ring for external cavity laser with high side mode suppression ratio and wide tuning range

Chip-scale external-cavity lasers with a wide tuning range and a narrow linewidth are widely used in optical communication, optical sensing, and optical detection systems. The reflector cavities of such lasers typically consist of Vernier ring structure, but conventional design with wide tuning range is difficult to achieve a high side mode suppression ratio. Here, we use a novel radius optimization method to achieve the product of side mode suppression ratio and tuning range 2141.2 and firstly analyze how the method works. And the external cavity laser simulation obtains side mode suppression ratio about 80 dB, tuning range 106 nm and power above 10 dBm. This result is ahead of the result obtained by conventional design method. It promotes the development of external-cavity lasers by realizing reflector cavities with high side mode suppression ratio and wide tuning range.

Programmable de novo designed coiled coil-mediated phase separation in mammalian cells

Membraneless liquid compartments based on phase-separating biopolymers have been observed in diverse cell types and attributed to weak multivalent interactions predominantly based on intrinsically disordered domains. The design of liquid-liquid phase separated (LLPS) condensates based on de novo designed tunable modules that interact in a well-understood, controllable manner could improve our understanding of this phenomenon and enable the introduction of new features. Here we report the construction of CC-LLPS in mammalian cells, based on designed coiled-coil (CC) dimer-forming modules, where the stability of CC pairs, their number, linkers, and sequential arrangement govern the transition between diffuse, liquid and immobile condensates and are corroborated by coarse-grained molecular simulations. Through modular design, we achieve multiple coexisting condensates, chemical regulation of LLPS, condensate fusion, formation from either one or two polypeptide components or LLPS regulation by a third polypeptide chain. These findings provide further insights into the principles underlying LLPS formation and a design platform for controlling biological processes.

Acoustic coherent perfect absorption based on a PT symmetric coupled Mie resonator system

Parity-time (PT) symmetric coupled resonator systems have exhibited intriguing and unexpected properties in optics and electronics. Here, we extend it to acoustics and report a coupled Mie resonators (MRs) system respecting PT symmetry. The system is constructed with two parallel waveguides connected by an aperture and two MRs placed symmetrically at both sides of the aperture. Instead of using active elements or complex refractive index modulation without gain, we exploit the incident waves of the waveguide as an effective gain so that PT symmetry with balanced loss and gain is realized by only passive materials. Coherent perfect absorption (CPA), which can completely absorb the in-phase excitations with the same intensity provided from two opposite directions, is observed in the PT symmetric phase and at the exceptional point but not in the broken phase. In addition, by varying the relative phase between the two incident waves, the coherent absorption can be tuned from CPA to zero. Our design may provide a flexible platform to research PT symmetry in acoustics and may have applications in tunable noise control, acoustic modulators, and switches.

Multi-frequency modulator of dual plasma-induced transparency in graphene-based metasurface

Graphene-based metamaterials can generate plasma-induced transparency (PIT), offering a new approach for achieving modulators with optimal modulation performance. This study presents a multi-frequency modulator based on novel monolayer graphene structure. We utilize Coupled Mode Theory (CMT) for thorough theoretical investigations, yielding theoretical values that agree well with simulation results. Moreover, we discuss the implications of the Fermi level on PIT and the influence of graphene carrier mobility on switch modulation. The research findings illustrate the successful realization of a high-performance multi-frequency modulator by indirectly controlling the phase of the dual PIT transmission spectra through an adjustable bias voltage. Notably, at a frequency of 3.93 THz, the increasing of carrier mobility enhances the modulation depth of the modulator from 89.22 % to 97.88 % and reduces the insertion loss from 0.34 dB to 0.12 dB. Hence, our research has substantial implications for designing excellent tunable terahertz optical modulator devices and contributing to the advancement of optical communication systems and optoelectronic applications.

Ferroelectric Layer‐Assisted Asymmetric Heterojunction Boosts Power Output in Silicon Hydrovoltaic Device

AbstractHydrovoltaic devices (HDs) that convert ubiquitous environmental energy via water evaporation serves as a prospective technology for renewable power schemes. However, it remains a grand challenge to perform controllable and stable modulation of hydrovoltaic power generation for multi‐scenario practical applications. Here, a ferroelectric‐field assisted silicon HD is proposed, which sandwiches an ultrathin polarizable polymer between nanostructured silicon and the top electrode, constituting an asymmetric heterojunction designed to clinch well‐regulated and robust electrical signal output. Tunable modulation of the internal electric field at the silicon/top electrode interface can be realized by facilely aligning the polarization orientation of the ferroelectric domains, thus dominating the silicon energy band bending and controlling the ultimate electrical signal. Upon effective forward polarization, the interfacial dipoles can build a stronger asymmetric electric field, which allows an efficient sweep of the charges out of the heterojunction. Accordingly, the resulting device clinches to yield a considerably modulated voltage of 1.04 V, nearly three‐fold modulation over the reverse polarization one. As prospective applications, multifunctional sensing platforms including the self‐sufficient environmental temperature detector, intelligent water‐level alarm system, and automatic‐manual dual‐mode irrigation control system are demonstrated. This work exhibits the unique characteristics of ferroelectric HDs with tunable electrical performance.

Compact filtering balun diplexer with independently tuned channels and constant fractional bandwidth

A highly-integrated frequency tunable filtering balun-diplexer (FBD) is introduced in this article. Firstly, the tunable coupled-line-loaded hairpin ring resonator (C-HRR) with two independently tunable resonant modes is analyzed. Then two tunable filtering baluns (FBs) for the two frequency tunable channels of the FBD are designed based on the tunable C-HRR. The constant fractional bandwidth (FBW) performance of two tunable FBs is discovered and discussed. Finally, a tunable FBD is designed by simply uniting the two tunable FBs and sharing the common input port and one C-HRR which reduces the circuit size effectively. The low loading effect ensures the two frequency channels of the FBD being tuned independently. For validation, a prototype of the tunable FDB is fabricated and measured. The lower and higher channels can achieve a constant 4 % FBW in a tuning range of 9 % and 14 %, respectively. The CM noise rejection is higher than 36 dB with in-band channel isolation greater than 35 dB. The circuit size is 0.27λg × 0.15λg, where λg is guide wavelength at the highest operation frequency of the lower channel.

Modulated Connection Modes of Redox Units in Molecular Junction Covalent Organic Frameworks for Artificial Photosynthetic Overall Reaction.

The precise tuning of components, spatial orientations, or connection modes for redox units is vital for gaining deep insight into efficient artificial photosynthetic overall reaction, yet it is still hard achieve for heterojunction photocatalysts. Here, we have developed a series of redox molecular junction covalent organic frameworks (COFs) (M-TTCOF-Zn, M = Bi, Tri, and Tetra) for artificial photosynthetic overall reaction. The covalent connection between TAPP-Zn and multidentate TTF endows various connection modes between water photo-oxidation (multidentate TTF) and CO2 photoreduction (TAPP-Zn) centers that can serve as desired platforms to study the possible interactions between redox centers. Notably, Bi-TTCOF-Zn exhibits a high CO production rate of 11.56 μmol g-1 h-1 (selectivity, ∼100%), which is more than 2 and 6 times higher than those of Tri-TTCOF-Zn and Tetra-TTCOF-Zn, respectively. As revealed by theoretical calculations, Bi-TTCOF-Zn facilitates a more uniform distribution of energy-level orbitals, faster charge transfer, and stronger *OH adsorption/stabilization ability than those of Tri-TTCOF-Zn and Tetra-TTCOF-Zn.

High-power vortex beams generated from a Yb:YAG thin-disk laser with spot-defect mirrors

We report the generation of high-power and high-order vortex beams based on a Yb:YAG thin-disk laser oscillator with a spot-defect mirror. High-quality vortex beams were directly emitted by the oscillator with an output power of 80 W, which is the highest output power of any vortex laser oscillator. Tunable high-order Hermite-Gaussian modes from HG1,1 to HG5,1 were also generated, and subsequently converted to Laguerre-Gaussian beams by a cylindrical-lens mode converter. The vortex characteristics of the output were confirmed with a Mach-Zehnder interferometer. This work demonstrates an effective way to generate high-quality, high-power and high-order optical vortex beams.

Efficient shRNA-based knockdown of multiple target genes for cell therapy using a chimeric miRNA cluster platform

Genome engineering technologies are powerful tools in cell-basedimmunotherapy to optimize or fine-tune cell functionalities. However, their use for multiple gene edits poses relevant biological and technical challenges. Short hairpin RNA (shRNA)-based cell engineering bypasses these criticalities and represents a valid alternative to CRISPR-based gene editing. Here, we describe a microRNA (miRNA)-based multiplex shRNA platform obtained by combining highly efficient miRNA scaffolds into a chimeric cluster, to deliver up to four shRNA-like sequences. Thanks to its limited size, our cassette could be deployed in a one-step process along with all the CAR components, streamlining the generation of engineered CAR Tcells. The plug-and-play design of the shRNA platform allowed us to swap each shRNA-derived guide sequence without affecting the system performance. Appropriately choosing the target sequences, we were able to either achieve a functional KO, or fine-tune the expression levels of the target genes, all without the need for gene editing. Through our strategy we achieved easy, safe, efficient, and tunable modulation of multiple target genes simultaneously. This approach allows for the effective introduction of multiple functionally relevant tweaks in the transcriptome of the engineered cells, which may lead to increased performance in challenging environments, e.g., solid tumors.

Tunable modulation instability spectra in negative index materials

This paper investigates the formation of tunable modulation instability windows in metamaterials. We consider the influence of third-order dispersion, fourth-order dispersion, cubic nonlinearity, quintic nonlinearity, detuning parameter, self-steepening and higher-order nonlinear dispersions on the gain spectrum in addition to the basic requirement to observe modulation instability such as group velocity dispersion and self-phase modulation. As the metamaterials provide engineering freedom, all the material parameters are tunable, which leads to tunable modulation instability gain spectrum formation. This tunable gain spectrum provides additional ways to form solitons and ultrashort pulses with desired parameters.

Development of a terahertz metamaterial polarization converter with multiple tuning modes based on graphene and vanadium dioxide

A dynamically tunable terahertz metamaterial polarization converter is proposed. By manipulating the Fermi level of graphene and the conductivity of vanadium dioxide (VO2) flexibly, multiple tuning modes for polarization conversion performance are realized. First, while graphene is in the metallic or insulating state, we can achieve an ideal broadband reflective or an ideal broadband transmissive polarization converter respectively. By manipulating the conductivity of VO2, a modulation depth of 80 % for intensity of the reflected polarization conversion rate (PCRr) and that of 70 % for bandwidth of the transmissive polarization conversion rate (PCRt) can be achieved. Then, while VO2 is in the insulating state, we obtain another broadband transmissive polarization converter. Similarly, we can achieve PCRt intensity modulation by manipulating the Fermi level of graphene. While VO2 is in the metallic state, the device can switch from a broadband polarization converter to a narrow one as the Fermi level of graphene increases. Finally, by manipulating graphene and VO2 simultaneously, the central frequency modulation of PCRt can be obtained with the bandwidth keeping unchanged. Compared with the ones reported recently, our device has some advantages on tuning mode, relative bandwidth, and polarization conversion performance.

Probing miniband structure and Hofstadter butterfly in gated graphene superlattices via magnetotransport

The presence of periodic modulation in graphene leads to a reconstruction of the band structure and formation of minibands. In an external uniform magnetic field, a fractal energy spectrum called Hofstadter butterfly is formed. Particularly interesting in this regard are superlattices with tunable modulation strength, such as electrostatically induced ones in graphene. We perform quantum transport modeling in gate-induced square two-dimensional superlattice in graphene and investigate the relation to the details of the band structure. At low magnetic field the dynamics of carriers reflects the semi-classical orbits which depend on the mini band structure. We theoretically model transverse magnetic focusing, a ballistic transport technique by means of which we investigate the minibands, their extent and carrier type. We find a good agreement between the focusing spectra and the mini band structures obtained from the continuum model, proving usefulness of this technique. At high magnetic field the calculated four-probe resistance fit the Hofstadter butterfly spectrum obtained for our superlattice. Our quantum transport modeling provides an insight into the mini band structures, and can be applied to other superlattice geometries.

Localized defect modes’ tunability by Octonacci photonic bandgap structures with thin high-Tc superconductors

The reflectance spectrum, through 1D superconducting photonic bandgap structures organized following the Octonacci sequence, is studied by employing a theoretical calculation based on the transfer-matrix method and the two-fluid Gorter–Casimir theory. The proposed hetero-structures are made up of Yttrium oxide (A) and YBa2Cu3O7 (B) materials. We report the localization of modes for specific generations of the Octonacci sequence and TEM mode. We discuss the field-localization properties for different Octonacci sequences. It is noticed that localized defect modes of intensity scale up to 99% are sensitive to the wave-incident-angle and the TEM wave polarizations. The lateral position of the localized defect mode can be notably adjusted by the operating superconductor’s temperature (T), by applying a structural strain along the stacks, and by specific thicknesses of the used superconductor. The spectra exhibit forbidden wavelength zones around the localized defect modes in which the bandwidths increase with the strain coefficient h and under critical superconductor temperatures. The given structure has potential applications in tunable localized defect modes and is very useful in optical resonators.

Study on the Technique for Wavelength Modulation Spectroscopy with Narrow Band Interference Filter Based External Cavity Diode Laser

In this study, an improved tunable external cavity diode laser (ECDL) is proposed. It is on the basis of narrow band interference filter, and its theoretical research is carried out as the light source of tunable diode laser absorption spectrum-wavelength modulation spectrum (TDLAS-WMS) system. The proposed model can use piezoelectric ceramic actuator to change and modulate its output central wavelength so that the laser central wavelength could periodically scan the absorption spectral band of the desired gas. Compared with the tunable monolithic diode laser, the narrow band interference filter based tunable ECDL might be able to accurately sense the type and concentration of a large variety of gases. Therefore, it can be used in the TDLAS-WMS system for high precision gas sensing and is expected to replace the tunable monolithic diode laser.

Coexistence of large-area topological pseudospin and valley states in a tri-band heterostructure system.

The rapid development of topological photonics has significantly revolutionized our comprehension of electromagnetic wave manipulation in recent decades. Recent research exploiting large-area topological states inserts an additional gapless PC structure between topologically trivial and nontrivial PCs, effectively introducing the mode width degree of freedom. Nevertheless, these heterostructures mainly support only single-type waveguide states operating within a single frequency band. To address these limitations, we propose a novel, to the best of our knowledge, tri-band three-layer heterostructure system, supporting both large-area pseudospin- and valley-locked states. The system showcases tunable mode widths with different operational bandwidths. Moreover, the heterostructures exhibit inherent topological characteristics and reflection-free interfacing, which are verified in the well-designed Z-shaped channels. The proposed heterostructure system can be used to design multi-band multi-functional high-flexibility topological devices, providing great advantages for enlarging the on-chip integrated communication systems.