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Switchable adhesives are materials of utmost importance due to their capability of having their adhesion/cohesion properties reversibly triggered upon stimuli, allowing on‐demand surface attaching/detaching. Still, several challenges mainly associated with complex uncontrolled chemical processes hinders their production. In this study, it is found that unexpectedly vinyl ethers are able to react with thiols in the presence of a catalytic concentration of base, which allows the preparation of well‐defined phase‐separated switchable adhesives. Indeed, these findings show that base‐catalyzed thiol‐acrylate and thiol‐vinyl ether are highly orthogonal, making the acrylate reaction faster. This is explored to react in the first stage thiols with acrylates in the presence of vinyl ethers to end‐cap all the oligomers with stable vinyl ethers and suppress undesirable disulfide formation. In a second stage the UV‐triggered thiol‐ene “click reaction” is carried out, forming the network. It is shown that the network prepared by this approach presents superior adhesion due to greater backbone length, a controlled crosslinking motif, and better‐defined microphase separation. Additionally, the adhesives made by this strategy are thermo‐switchable due to the temperature‐triggered base‐catalyzed thioether dynamic covalent character at 200 °C. Despite providing superior adhesive properties, the proposed technology endows scalable, thermo‐switchable, and O2‐resistant adhesives with huge industrialization potential. [ABSTRACT FROM AUTHOR]

Conventional chiral metasurfaces are constrained by predetermined functionalities and have limited versatility. To address these constraints, we propose a novel chirality-switchable terahertz (THz) metasurface with integrated heating control circuits tailored for spin-selective anomalous reflection, leveraging the phase-change material vanadium dioxide (VO2). The reversible and abrupt insulator-to-metal phase transition feature of VO2 is exploited to facilitate a chiral meta-atom with spin-selectivity capabilities. By employing the Pancharatnam–Berry phase principle, complete 2 π reflection phase coverage is achieved by adjusting the orientation of the chiral structure. At the resonant frequency of 0.137 THz, the designed metasurface achieves selective absorption of a circularly polarized wave corresponding to the state of the VO2 patches. Concurrently, it reflects the circularly polarized wave of the opposite chirality anomalously at an angle of 28.4° while maintaining its handedness. This chirality-switchable THz metasurface exhibits promising potential across various applications, including wireless communication data capacity enlargement, polarization modulation, and chirality detection. [ABSTRACT FROM AUTHOR]

Although the research of tunable THz absorbers has attracted considerable attention, improving the multifunctional switching of the absorbers to fulfill more application scenarios is still worth studying. This paper proposes an integrated design of a dynamically switchable multi-narrowband and wideband absorber based on graphene and vanadium dioxide(VO2) in the terahertz region through voltage and thermal manipulation. A compact structure with five layers, from top to bottom, namely, graphene layer, dielectric layer, vanadium dioxide-metal layer, dielectric layer, and metal reflective layer, is proposed. Simulation results show that the absorption of the broadband absorber exceeds 90% in the frequency range of 2.44–4.48 THz when the VO2 is in the metallic state and the Fermi energy level of graphene is 1 eV. Meanwhile, a wide-band reflector with a reflection rate of more than 80% in the entire THz frequency range of 0–10 THz is shown. When adjusting VO2 to a dielectric state, while the Fermi energy level of graphene is controlled at 0.7 eV, a multi-narrowband absorber with four frequency points, respectively at 3.41 THz, 6.66 THz, 8.9 THz, and 9.79 THz, and three points of high frequency have an absorption rate close to 100%. In addition, we analyze the physical mechanism of the proposed absorber by impedance matching theory and electric and magnetic field distribution, and the robustness of the angle of incident wave. Due to its switchable function, the proposed metamaterial absorber has great potential for applications in terahertz switching, sensing, and electromagnetic stealth. [ABSTRACT FROM AUTHOR]

Microwave heating has attracted interests in many industrial applications, yet heating inhomogeneity remains a critical issue. This study proposes a novel approach to enhance microwave heating uniformity employing a switchable frequency selective surface (FSS). The PIN diodes in each FSS unit cell can be toggled ON or OFF by controlling voltage biases, enabling the FSS to either reflect or transmit incident electromagnetic waves. Placing this switchable FSS in front of a heating cavity wall creates a dynamic reflecting boundary, which, through periodic alterations of the FSS and metallic wall, effectively improves the heating uniformity. To validate this method, we simulated the heating of a potato sample at 2450 MHz using COMSOL Multiphysics and conducted experimental tests. Both simulation and experimental results demonstrate that the proposed method significantly enhances microwave heating uniformity across various materials and sample sizes. This work provides a promising solution for designing microwave heating reactors.

ABSTRACTNanoionic and photoionic reconfigurable oxides and chalcogenide semiconductors are emerging material platforms for field-based, non-volatile control of electrons and photons in nanoscale optoelectronic device architectures. Their potential low-power requirements, athermal switching mechanism and mixed-mode operation, have facilitated the demonstration of a wealth of highly promising application-driven optoelectronic devices over the last decade that address growing global demands requiring low-power, high-speed, and high-density data storage and signal modulation in ultra-compact architectures. This review highlights advancements in such ion-migration-based materials, fundamental mechanisms, device architectures, and their impact on the observed reconfigurable performance with a view to applications in optical and electronic data storage, signal modulation and beyond-classical computing.

Phase‐change thermal diodes with asymmetric and adjustable heat transfer capacity exhibit great application prospects in spacecraft heat management and solar energy storage. Current heat modulation strategies mainly depend on the anisotropic assistance from gravity and the rectification ratio can hardly be adjusted due to the immobilized inner structures. Here, a novel bioinspired thermal diode vapor chamber has been carried out with magnetic microgroove cones array sealed between two copper plates, where the evaporating plate with porous copper foam can reserve water and the condensing plate with patterned wettability can coagulate vapor into droplets at designated spot. With microgroove cones rooting from the evaporating plate and their tips contacting the condensing plate, these cones can directionally and rapidly transport condensed liquid from the condensing plate to evaporating plate under the unbalanced strong capillarity while prohibiting water flowing backward. This eventually leads to unidirectional liquid‐vapor circulation and anti‐gravitational directional heat transferring with a rectification ratio as high as 7.4. Such flowing of liquid can also be regulated by magnetically controlling the bending of cones to realize switched ON–OFF of thermal diode and achieve further modulation of heat management. This bioinspired thermal diode vapor chamber provides new ideas for intelligent thermal management systems. [ABSTRACT FROM AUTHOR]

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A photonic method for the reconfigurable generation of switchable multi-format linearly frequency modulated (LFM) signal using a dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM) is proposed and experimentally verified. By properly controlling the bias voltage applied on the DP-DPMZM, different chirp waveforms, including dual-chirped, down-chirped and up-chirped LFM signals, can be obtained when a radio frequency (RF) signal and a baseband chirped signal are injected into the modulator. Besides, the central frequency of the generated LFM signal can be converted from X-band to K-band by adopting -2nd-order sideband instead of -1st-order sideband of the modulated RF signal. Moreover, the RF signal is always single sideband modulated, thus eliminating the dispersion-induced power fading, which is essential for the photonics-based distributed multi-function radar. In the proposed scheme, no optical filter is required, which also improves the stability and feasibility of the system.

This paper presents a groundbreaking advancement in terahertz (THz) technology through the introduction of a novel ultrathin absorber. Composed of vanadium dioxide (VO2) and graphene, this absorber offers a non-metallic solution for wideband absorption, covering an impressive frequency range from 1.198 THz to 8.752 THz (7.554 THz). Our absorber exhibits exceptional tunable and switchable performance, a significant achievement considering the challenge of achieving frequency tunability across broadband absorption ranges, which was the primary focus of our research endeavor. Furthermore, our proposed absorber demonstrates remarkable characteristics, achieving up to 80% absorption even at high incidence angles of up to 80°. Additionally, the absorber enhances Shielding Effectiveness in electromagnetic interference (EMI) shields and stealth systems, further highlighting its versatility and potential impact in various applications.

A single‐sheet structure‐based switchable broadband FSR/absorber is proposed. The lossy layers I, II, and the FSS are printed along the direction of electromagnetic (EM) wave propagation (z‐direction) at the top, middle, and bottom positions of the substrate, respectively. A PIN diode is used in the lossy layer II and the FSS to switch their operating states. By activating or deactivating the PIN diodes, the design can operate as either an FSR or absorber. The FSR achieves a passband with an insertion loss of 0.64 dB at 3.9 GHz, and two absorption bands with fractional bandwidth of 87.6% and 20.8%, respectively. The absorber has a wide absorption band from 1.6 to 5.4 GHz (109%). It is transparent to EM waves of orthogonal polarization. The measured and simulated results are in close agreement, which exhibits stable performance under 30° of oblique incidence in both the xz‐ and yz‐planes. [ABSTRACT FROM AUTHOR]

We present an optically reconfigurable multifunctional metamaterial with switchable wideband absorption and transmission across the THz frequency range. The reconfigurability is achieved by introducing optically active silicon into the resonator of the metamaterial unit which could be effectively modulated through external electrical pumping. When the silicon conductivity reaches 50,000 S/m, the metamaterial shows significant absorption of electromagnetic waves ranging from 3.1 to 10 THz. By reducing the applied external pump power and decreasing the silicon conductivity to 150 S/m, the proposed metamaterial exhibits transmission of the incident waves at 5.12 THz with a transmission coefficient of 61%. The proposed optically reconfigurable metamaterial has the advantages of simple structure, wideband absorption, and switchable between absorption and transmission modes, showing potential applications in stealth, communication, or radar systems. [ABSTRACT FROM AUTHOR]

Conventional chiral metasurfaces are constrained by predetermined functionalities and have limited versatility. To address these constraints, we propose a novel chirality-switchable terahertz (THz) metasurface with integrated heating control circuits tailored for spin-selective anomalous reflection, leveraging the phase-change material vanadium dioxide (VO2). The reversible and abrupt insulator-to-metal phase transition feature of VO2 is exploited to facilitate a chiral meta-atom with spin-selectivity capabilities. By employing the Pancharatnam–Berry phase principle, complete 2π reflection phase coverage is achieved by adjusting the orientation of the chiral structure. At the resonant frequency of 0.137 THz, the designed metasurface achieves selective absorption of a circularly polarized wave corresponding to the state of the VO2 patches. Concurrently, it reflects the circularly polarized wave of the opposite chirality anomalously at an angle of 28.4° while maintaining its handedness. This chirality-switchable THz metasurface exhibits promising potential across various applications, including wireless communication data capacity enlargement, polarization modulation, and chirality detection.

This article presents a novel design of a switchable dual‐band frequency‐selective rasorber/absorber, which is a double‐layered structure. At the top layer, two electric‐field‐coupled resonators with different size are utilized to achieve two transmission bands. At the bottom, to achieve low insertion loss, the frequency‐selective surface based on slots with different lengths resonates at the same frequency as the top layer. By controlling the bias voltage of PIN diodes, the structure can be switched between dual‐band rasorber/absorber mode. The operating principle is analyzed by an equivalent circuit model. When the diodes are in the OFF state, it shows two transmission bands at 2.86 GHz with 0.47 dB insertion loss and 3.61 GHz with 1.04 dB insertion loss. When the diodes are in the ON state, it exhibits a wide fractional absorption bandwidth of 90.1%. Meanwhile, the proposed dual‐band switchable structure is fabricated and measured. There is a good agreement between simulation and measurement. [ABSTRACT FROM AUTHOR]

This paper proposes a switchable polarization-insensitive frequency selective rasorber (FSR) within the X-band. The FSR comprises a lossy layer, a lossless layer, and an intermediate air layer. The lossy layer consists of metal patches, folded wires, and lumped resistors, while the lossless layer is formed with square and cross patches loaded with PIN diodes. An equivalent circuit model (ECM) has been developed to analyze and verify the working principle of the system. By altering the state of the PIN diodes, it is feasible to switch between absorbing and transmitting modes. In the rasorber mode, the switchable FSR attains a transmission window ranging from 10.13 to 12.27 G H z with a minimum insertion loss below 2 d B and a broad absorption band covering 5.79–15.37 G H z . When switched to absorber mode, the passband is negated, and the FSR exhibits a low transmission band from 10.68 to 18.00 G H z . This innovation can improve the omni-directional stealth capability and battlefield survivability of radar systems, possessing substantial research importance and practical applications. [ABSTRACT FROM AUTHOR]

In order to meet the increasing demand for adjustable devices in the modern wireless communication system, a compact bandpass filter with active switchable passband is proposed. The filter is based on the half mode substrate integrated waveguide (HMSIW), and uses its cut-off characteristics to form the lower stopband. The resonant characteristics of a quarterwavelength shorted stub generates a transmission zero (TZ) at higher frequency, which forms the upper stopband. The active control of DC power supply determines the biased states of PIN diodes to change the electrical size of the filtering parts. When the diodes are reverse biased, the filter works in C band with the passband of 3.9-5.2 GHz; when the diodes are forward biased, the passband shifts to S band of 2.7-3.6 GHz. The 28.6% relative bandwidth in both frequency bands remains constant. The simple design realizes the active switching between bands, providing a promising idea for active adjustable devices. [ABSTRACT FROM AUTHOR]

A switchable and tunable terahertz (THz) metamaterial based on photosensitive silicon and Vanadium dioxide (VO2) was proposed. By using a finite-difference time-domain (FDTD) method, the transmission and reflective properties of the metamaterial were investigated theoretically. The results imply that the metamaterial can realize a dual electromagnetically induced transparency (EIT) or two narrow-band absorptions depending on the temperature of the VO2. Additionally, the magnitude of the EIT and two narrow-band absorptions can be tuned by varying the conductivity of photosensitive silicon (PSi) via pumping light. Correspondingly, the slow-light effect accompanying the EIT can also be adjusted. [ABSTRACT FROM AUTHOR]

Tunable/switchable devices are more and more required in modern communication systems. However, the realization of the tuning requires the presence of active devices, which in turn must be biased. The current paper comes up with a solution for designing and experimentally validating such a switchable Frequency Selective Surface. Two different metallic structures are simulated and measured, having incorporated the same topology control network (CN). In this scenario, the main innovation of this paper is the presence of the feeding part, namely the control network. In this work, the main FSS structure is flanked by three parallel CN microstrip lines and several via holes that allow biasing the active elements, namely PIN diodes. The switchability of the proposed structure is achieved through PIN diodes, whose bias determines the values of the elements in the equivalent circuit. At different biases, the response of the FSS changes accordingly. From all possible values of the bias, the extreme cases when the diodes act as (almost) short- and open-circuits are considered in the submitted manuscript for the sake of brevity. These cases are modeled by the main and cut-slot structures, respectively. The proposed structures have been evaluated using electromagnetic simulation and implemented on an FR4 substrate having a thickness of 1.58 mm. With the periodicity of the square-shaped unit cell of 18 mm edge length, different filtering bands are obtained below 12 GHz. Another novelty that has received very little consideration in the existing literature is the use of a finite array of unit cells instead of an infinite one. And finally, tests in an anechoic chamber have proved that there is a good agreement between practical and simulation results and also demonstrated the proper performance of the devices for wide angular incidence for both TE and TM polarizations. [ABSTRACT FROM AUTHOR]

Spatial frequency processing is an essential technology for extracting morphological information from an optical image. Although various Fourier-based flat optical elements have been proposed as spatial-frequency filters to realize image processing, their transfer functions are statically fixed once fabricated, thus limiting the versatile, dynamic functionalities and practical applications. Here, a novel practical tuning strategy is demonstrated to realize switchable spatial-frequency processing for edge-enhanced and bright-field imaging by employing a tunable hydrogel-scalable nanoslide. By utilizing multilayered metallic and hydrogel stacks construction, the nanoslide directly manipulates the optical spatial frequency in the wavevector domain and exhibits opposite image processing at different wavelength channels due to the cavity-induced wavelength-sensitivity. More intriguingly, via controlling the ambient humidity, the angular-dependent optical response of the nanoslide can be effectively tuned for dynamic edge-enhanced imaging due to the hydrogel's inflation from moisture. In addition, the nanoslide is readily fabricated at a large scale and integrated into compact imaging systems, such as a biomicroscope. With the advantages of a high numerical aperture -0.8, polarization-insensitive, microscopy-compatible, and facile architecture, the proposed hydrogel-based nanoslide can find potential applications in machine vision, real-time image processing, biological imaging, and analog computing. [ABSTRACT FROM AUTHOR]

Urban centers across the globe are responsible for a significant fraction of energy consumption and CO2 emission. As urban centers continue to grow, the popularity of glass as cladding material in urban buildings is an alarming trend. Dynamic windows reduce heating and cooling loads in buildings by passive heating in cold seasons and mitigating solar heat gain in hot seasons. Here, reduced energy consumption in highly glazed buildings in a mesoscopic building energy model is demonstrated when thermochromic windows are employed. Savings are realized across eight disparate climate zones of the United States. The model is used to determine ideal critical transition temperatures of 20–27.5 °C for thermochromic windows based on metal halide perovskite materials. Ideal transition temperatures are realized experimentally in composite metal halide perovskite films composed of perovskite crystals and an adjacent reservoir phase. The transition temperature is controlled by cointercalating methanol, instead of water, with methylammonium iodide and tailoring the hydrogen‐bonding chemistry of the reservoir phase. Thermochromic windows based on metal halide perovskites represent a clear opportunity to mitigate the effects of energy‐hungry buildings. [ABSTRACT FROM AUTHOR]

A switchable polarization converter based on a graphene–vanadium dioxide (VO2) metamaterial is proposed, which is capable of switching between transmission mode and reflection mode. The proposed structure consists of a graphene resonator placed along the diagonal, a dielectric layer of SiO2, and a VO2 substrate with a metal grating. By changing the Fermi level of the graphene and the state of the VO2 , the simulation results show that the polarization converter can operate in the switching state, whether it is a transmission mode or a reflection mode. When the VO2 is in the insulating state, the transmitted polarization conversion ratio ( PCR t ) can be tuned to below 2% (off-state) and above 99.5% (on-state) from 3.00 to 6.00 THz by controlling the graphene. When the VO2 operates in the metallic state, the reflected PCR r can achieve nearly 0 (off-state) and larger than 90.0% (on-state) from 3.76 THz to 4.15 THz by controlling the Fermi level of the graphene. In addition, the designed structure can maintain a stable performance during the reflected polarization conversion within the incidence angle of 60°. Furthermore, we believe that this switchable polarization converter with a switching function has potential application prospects in high-density integrated and switching devices. [ABSTRACT FROM AUTHOR]

The objective of this study is to give a deep knowledge on band notched reconfigurability in ultra-wideband (UWB) and ultra-wideband multi-input multi-output (UWB-MIMO) antennas. Reconfigurability over notched bands refers to having switchable and tunable notched properties. It is well known that the UWB system undergoes several narrow band interferences. Therefore, rejection of interferences is a challenging task which in turn becomes more challenging when there is a requirement of reconfigurable notched property. Different techniques for realizing single/dual/triple notched-band functions are broadly discussed. Further, to investigate various approaches and techniques for realizing reconfigurability in UWB and UWB-MIMO antennas an exhaustive review of the existing literature is conducted. Based on their notched realizing techniques UWB reconfigurable antennas are broadly classified into three different categories like slotted, Parasitic/Stub, and Electromagnetic Bandgap (EBG) structure-based geometry. Besides, generation of notched band characteristics over UWB-MIMO antennas with notched reconfigurability has also been detailed, which will be helpful for readers to understand their switching mechanisms from one band to another band. [ABSTRACT FROM AUTHOR]

In this work, poly(N,N-diethylacrylamide) (PDEA) hydrogel films were polymerized on glassy carbon (GC) electrode surface, and isoniazid (INH) was chosen as an electroactive pharmaceutical molecule probe, aiming to investigate the switchable electrochemical behaviors of INH. Determining the contents of INH tablets under different external stimuli conditions and constructing its logic gate computing systems. The triple-sensitive electrochemical CV behaviors of INH on this film system toward pH, temperature and salt concentration were observed and explored. Thus, a 3-input/8-output combinational pharmaceutical logic gate network and a 3-to-8 decoder were designed and constructed based on the stimulus-responsive characteristics of the electrochemical response of INH on PDEA hydrogel-modified electrodes. Besides, the relationship between the oxidation peak current (Ipa) and concentration of INH (CINH) was studied by the differential pulse voltammetry (DPV) method. Apply this film system, and the INH tablets could be switchable detected. The construction of the logic-gate computing system based on isoniazid drug molecule may provide a novel approach and model to design new style drug sensors, which might be applied to intelligent medical diagnostics and drug release.

We present an optically reconfigurable multifunctional metamaterial with switchable wideband absorption and transmission across the THz frequency range. The reconfigurability is achieved by introducing optically active silicon into the resonator of the metamaterial unit which could be effectively modulated through external electrical pumping. When the silicon conductivity reaches 50,000 S/m, the metamaterial shows significant absorption of electromagnetic waves ranging from 3.1 to 10 THz. By reducing the applied external pump power and decreasing the silicon conductivity to 150 S/m, the proposed metamaterial exhibits transmission of the incident waves at 5.12 THz with a transmission coefficient of 61%. The proposed optically reconfigurable metamaterial has the advantages of simple structure, wideband absorption, and switchable between absorption and transmission modes, showing potential applications in stealth, communication, or radar systems.

In this article, a coding metasurface is specifically designed to switch transmission and reflection functionalities between two different frequency bands for linearly polarized waves within wide incidence angles. A metasurface consists of four metallic patterns, where the middle two structures are inserted to ensure effective performance of transmission and reflection, while the top and bottom patterns are designed based on simultaneously controlling the reflection phase for both polarization states. It has been experimentally demonstrated that the proposed metasurface can convert a transmission band into a complete reflection band (meanwhile, the reflection band is translated into a complete transmission band) by changing the incident polarization state. Highly efficient transmission and reflection characteristics have been achieved from 21.1 to 24.5 GHz as well as from 33.3 to 38.3 GHz, whereas more than 10 dB radar cross-section (RCS) reduction has also been obtained for both TE and TM modes in their respective reflection bands. The performance of the proposed metasurface is well sustained up to 40° oblique incidence. This work will help to open a new aspect in metasurfaces to manipulate the electromagnetic waves at preferable frequency bands to achieve desirable functionalities. [ABSTRACT FROM AUTHOR]

This paper proposes graphene-coated cylindrical nano-hole arrays as switchable and re-configurable reflector/absorber devices. Initially, a free-standing graphene-coated nano-hole array is considered, and its reflectivity engineering using the geometrical, material, and optical parameters is discussed in detail. It is observed that the electromagnetic reflection is due to the excitation of localized surface plasmon resonances in the cylindrical shells embedded in the low-index dielectric background. Later, a reflecting mirror is introduced as the substrate of the graphene-wrapped hole array, and higher-order plasmonic resonances are used to design optically re-configurable absorbers in different spectra. The high absorption rate is maintained for the oblique plane waves with a wide range of incident angles under transverse electric (TE) and transverse magnetic (TM) wave illumination. Finally, the metallic mirror is replaced by the VO2 phase change material to switch between the reflecting and absorbing modes. The switching capability arises from the robust performance of the reflecting mode with respect to the substrate height. [ABSTRACT FROM AUTHOR]

We propose and realize a novel high-performance switchable perfect composite vortex beam (PCVB). We introduce the concept of composite vortex beam and then present a design for a PCVB generator based on halogen perovskite metasurfaces, which can convert circularly polarized light into a parametrically tunable PCVB using a single halogen perovskite fully dielectric metasurface. The PCVB exhibits a constant toroidal intensity distribution and the ability to superimpose different topological charges. We demonstrate the high feasibility of this design to generate PCVBs with different operating wavelengths, topological charges, and numerical apertures. Additionally, we explore the practical application potential of our design by demonstrating reversible exchange between three halogen perovskite metasurfaces using chemical vapor deposition. This exchange leads to corresponding imaging effects at specific wavelengths. The proposed generator has significant application prospects in optical communication encryption, optical data storage, and optical tweezers. • We proposed the high-performance swithable perfect composite vortex beam generator based on halogen perovskite metasurfaces. [ABSTRACT FROM AUTHOR]

This paper puts forward a terahertz multifunctional device based on reversible phase transition property of VO 2 , which can realize active switching from multiple narrowband perfect absorption to plasma-induced transparency (PIT). By means of impedance matching theory and electric field distributions, we analyze the mechanism behind three absorption formants, and the absorption spectrum is consistent with data obtained from coupled mode theory. Three perfect absorption formants at the frequencies of 4.37 THz, 5.27 THz and 6.1 THz are extremely sensitive to the changes in external environment, which possesses a higher sensitivity up to 1.29 THz/RIU and FOM up to 9.45, indicating prominent sensing performance. By regulating the Fermi energy in a unified manner, three absorption formants can be observed within a specific frequency range. When the Fermi energy of three graphene patterns is individually manipulated, trimodal narrowband perfect absorption will transform into one bimodal and two unimodal ones. While the device is under PIT operation mode, two transmission windows are formed at 5.1 THz and 5.92 THz. It can be concluded that dual PIT arises from the mutual coupling between two bright modes and a dark mode formed by patterned graphene, when combined with the transmission spectra and the corresponding electric field distributions. Similarly, the modulation of graphene Fermi energy can realize dynamic tuning of the transmission performance, and single PIT can be achieved when graphene patterns are regulated separately. In summary, the proposed device can meet various functional requirements for multiple perfect absorption and PIT under different conditions and promote developments of terahertz technology in fields of environmental detection, electromagnetic modulation, multi-function devices and other application. [Display omitted] [ABSTRACT FROM AUTHOR]

An ultrathin and wideband reflective cross-polarization converter is presented in this paper. The design consists of a pair of modified dumbbell shaped resonators which are connected together with a conductive strip. The proposed single-layer THz metasurface achieved a high polarization conversion ratio (PCR) of $\ge$95% in the operating frequency ranging from 1.76–4.26 THz. This wide-bandwidth cross-polarization conversion is obtained by exciting multiple closely spaced resonant frequencies at 1.98 THz, 2.61 THz, 2.95 THz, and 3.93 THz. The working mechanism of the proposed structure is analyzed and the polarizer exhibits an excellent angular stability upto 40$^{0}$ of incidence. Further, the proposed cross-polarizer exhibits continuous tunability of PCR over the operating frequencies when photoconductive silicon (Si) is filled in the gap between pair of dumbbell-resonators. The wideband characteristics and the switchable property show that the proposed reflective cross polarizer is an excellent candidate for manipulation and control of polarization in THz communication systems.

A reversible amine-carbamate approach has been developed to reduce the use of antisolvents such as water in the coagulation of biopolymers from ionic liquid (IL) solution and thus improve the economy of IL recycle. Cellulose and chitin were recovered from 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) solution by introducing the miscible amines triethanolamine (TEA), ethylenediamine (EDA), or butylamine (BA) and bubbling CO2 at 40 °C and atmospheric pressure through the solutions to form carbamate salts in situ which resulted in biopolymer coagulation. BA gave the best results because of its low boiling point and low viscosity, which benefited both biopolymer recovery and IL recycle. Cellulose films and fibers could be formed by extrusion of an MCC/[C2mim]‐[OAc] solution into a coagulating bath comprised of a 1:1 M mixture of [C2mim][OAc] and butylammonium butylcarbamate (BA-carbamate). The cellulose, IL, amine, and CO2 were easily separated, although the cellulose recovered required some water washings to remove traces of IL. Up to 96.4% of the [C2mim][OAc] could be recovered, 76.2% from the coagulation bath and 20.2% from the water washings. The recycled IL was suitable for another cycle of cellulose dissolution and extrusion and 84.6% of the IL used for the second cycle was recovered. Although further work is needed, not the least of which will be reducing the amount of water needed for washing steps, some promising features of this process point the way for new directions for more economically viable IL recycling processes in biomass treatment with ILs.

As an emerging storage medium, DNA is a crucial carrier for future data storage. DNA has a better storage density and a longer storage life than conventional storage media. However, DNA's key limitations as a storage medium are the precision of information reading and storage stability. Herein, we designed and successfully developed a switchable DNA storage nanocomposite structure (MM-DNA/DNA'-SiO2). The composite structure employs magnetic microspheres (MMs) based on Fe3O4 nanoparticles as the DNA carrier for storing information (MM-DNA) and silicon dioxide nanoparticles modified with complementary strands as the protective outer layer (DNA'-SiO2), and its switchability and DNA sequence reading accuracy were both validated in this study. This method provides a novel nanostructure medium and technical proposal for efficient DNA storage with potential application value. [ABSTRACT FROM AUTHOR]

This paper presents two novel on-chip bandstop to bandpass reconfigurable filters in C and X bands. Designed on a silicon substrate, filter reconfigurability is achieved using semiconductor-distributed doped areas (ScDDAs), such as an N+PP+ junction integrated into the substrate. The active element is therefore co-designed with the passive parts, allowing flexibility in ScDDA size and position. This flexibility offers advantages in terms of integration, ease of manufacture, and performance. The synthesis was developed in the OFF-state in order to match with the well-known one in the ON-state. As proof of concept, 5 GHz and 10 GHz filters were built. The simulated and measured results showed good agreement in both bandpass and bandstop configurations. [ABSTRACT FROM AUTHOR]

Fano resonance is based on plasmonic metasurfaces and has many applications in all kinds of fields. In this paper, we propose an independently switchable double-layer raster structure based on graphene. Depending on the highly adjustable nature of graphene, the Fermi energy level can be adjusted to control the Fano resonance at different wavelengths. The equivalent resonator coupling mode method is used to simulate the Fano resonance, and the transmission spectrum fits well. Functional switch at different wavelengths can be achieved using Fano resonance technology. The simulation obtained a fantastic group refractive index of the designed structure, indicating that there is a possibility to apply it in slow light. The effect of the environmental refractive index on sensing performance was studied and we found the structure has great potential in making high-sensitivity sensors. To sum up, it is hoped that this structure can make a great contribution to the manufacture of integrated optics. [ABSTRACT FROM AUTHOR]

An ultrathin and wideband reflective cross-polarization converter is presented in this paper. The design consists of a pair of modified dumbbell shaped resonators which are connected together with a conductive strip. The proposed single-layer THz metasurface achieved a high polarization conversion ratio (PCR) of $\ge$ 95% in the operating frequency ranging from 1.76–4.26 THz. This wide-bandwidth cross-polarization conversion is obtained by exciting multiple closely spaced resonant frequencies at 1.98 THz, 2.61 THz, 2.95 THz, and 3.93 THz. The working mechanism of the proposed structure is analyzed and the polarizer exhibits an excellent angular stability upto 40 $^{0}$ of incidence. Further, the proposed cross-polarizer exhibits continuous tunability of PCR over the operating frequencies when photoconductive silicon (Si) is filled in the gap between pair of dumbbell-resonators. The wideband characteristics and the switchable property show that the proposed reflective cross polarizer is an excellent candidate for manipulation and control of polarization in THz communication systems. [ABSTRACT FROM AUTHOR]

Recently, slippery surfaces with controllable droplet sliding have aroused much attention in both fundamental research and realistic applications. However, for almost all existing surfaces, constant stimuli such as heat, light, magnetic field, etc., are indispensable. Herein, by constructing pit structures on a shape memory polymer and further infusing oil with low surface tension, we report a shape memory slippery surface that can overcome the above imperfection. Based on the shape memory performance, the surface can memorize a diverse pit size as the surface is stretched or recovered. With the variation of pit structure, the sliding performances for both water and organic liquid droplets can be reversibly adjusted between the rolling and pinning states. This work, based on the shape memory effect, reports smart droplet sliding control through regulating the surface microstructure, which not only provides a strategy for droplet sliding control, but also offers some ideas for designing novel intelligent slippery surfaces. [ABSTRACT FROM AUTHOR]

The increasing environmental protection demand has prompted the development of passive thermal regulation systems that reduce temperature fluctuations in buildings. Here, it is demonstrated that the heat generated by the sun can trigger a spin crossover (SCO) in a molecule‐base material, resulting in a concomitant color variation (from pink to white) and a phase transition. This leads to a cooling effect with respect to other thermochromic materials. In addition, when the material is cooled, a dampening of the temperature decrease is produced. Therefore, these materials can potentially be implemented for passive temperature control in buildings. Furthermore, SCO materials are remarkably stable upon cycling and highly versatile, which allows for the design of compounds with properties tailored for the desired climatic conditions and comfortable temperature. [ABSTRACT FROM AUTHOR]

Graphene has the capability of dynamically tuning its conductivity through gate voltage. Based on this fact, an electrically switchable wideband metamaterial absorber at low frequencies is presented and investigated in this paper. Our calculated results show that its absorption is over 90% from 400 to 1,000 MHz with the Fermi level of graphene being at 0 eV and the absorption band can be switched by adjusting the Fermi level of graphene without changing its physical structure. Moreover, the surface current distribution enables us to reveal the switchable wideband absorption characteristics of our designed metamaterial absorber. At last, we prove that its absorption property is polarization-insensitive due to the rotational symmetry of the structural unit. This work may provide a further step in the development of switchable sensors and absorbers at low frequencies.

Abstract The increasing environmental protection demand has prompted the development of passive thermal regulation systems that reduce temperature fluctuations in buildings. Here, it is demonstrated that the heat generated by the sun can trigger a spin crossover (SCO) in a molecule‐base material, resulting in a concomitant color variation (from pink to white) and a phase transition. This leads to a cooling effect with respect to other thermochromic materials. In addition, when the material is cooled, a dampening of the temperature decrease is produced. Therefore, these materials can potentially be implemented for passive temperature control in buildings. Furthermore, SCO materials are remarkably stable upon cycling and highly versatile, which allows for the design of compounds with properties tailored for the desired climatic conditions and comfortable temperature.

A switchable and tunable terahertz (THz) metamaterial based on photosensitive silicon and Vanadium dioxide (VO2) was proposed. By using a finite-difference time-domain (FDTD) method, the transmission and reflective properties of the metamaterial were investigated theoretically. The results imply that the metamaterial can realize a dual electromagnetically induced transparency (EIT) or two narrow-band absorptions depending on the temperature of the VO2. Additionally, the magnitude of the EIT and two narrow-band absorptions can be tuned by varying the conductivity of photosensitive silicon (PSi) via pumping light. Correspondingly, the slow-light effect accompanying the EIT can also be adjusted.

Tunable/switchable devices are more and more required in modern communication systems. However, the realization of the tuning requires the presence of active devices, which in turn must be biased. The current paper comes up with a solution for designing and experimentally validating such a switchable Frequency Selective Surface. Two different metallic structures are simulated and measured, having incorporated the same topology control network (CN). In this scenario, the main innovation of this paper is the presence of the feeding part, namely the control network. In this work, the main FSS structure is flanked by three parallel CN microstrip lines and several via holes that allow biasing the active elements, namely PIN diodes. The switchability of the proposed structure is achieved through PIN diodes, whose bias determines the values of the elements in the equivalent circuit. At different biases, the response of the FSS changes accordingly. From all possible values of the bias, the extreme cases when the diodes act as (almost) short- and open-circuits are considered in the submitted manuscript for the sake of brevity. These cases are modeled by the main and cut-slot structures, respectively. The proposed structures have been evaluated using electromagnetic simulation and implemented on an FR4 substrate having a thickness of 1.58 mm. With the periodicity of the square-shaped unit cell of 18 mm edge length, different filtering bands are obtained below 12 GHz. Another novelty that has received very little consideration in the existing literature is the use of a finite array of unit cells instead of an infinite one. And finally, tests in an anechoic chamber have proved that there is a good agreement between practical and simulation results and also demonstrated the proper performance of the devices for wide angular incidence for both TE and TM polarizations.

This article presents a switchable phase‐modulated metasurface (PMM) whose reflection phase can be modulated between two states using PIN diodes. The PMM is composed of a switchable surface loaded with four PIN diodes in each unit cell, as well as a ground plane and an air spacer. The reflection phase can be modulated when the PIN diodes are switched between two states (ON and OFF). Theoretical analysis indicates that the phase‐modulation bandwidth is determined by the thickness of the PMM. The phase‐modulation bandwidth with a phase difference of 180 ± 37° achieves 2.6–4.25 GHz and a fractional bandwidth of 48.2%. [ABSTRACT FROM AUTHOR]

In this letter, a broadband switchable active frequency selective surfaces (AFSSs) is presented, and the proposed structure is comprised of three metallic layers and two Rogers RT5880 substrates. In order to realize broadband transmission, a second-order bandpass filter is constructed, and the multilayer coupling effect is utilized. A modified equivalent circuit model of the p-i-n diode is proposed to reduce the simulation error and improve the design accuracy. By controlling the bias voltage of the p-i-n diodes, two completely different functions are realized. At the function of dual-polarized shielding, the shielding bandwidth is 2–18 GHz, and the transmission bandwidth is 8.2–10.5 GHz with a fractional bandwidth of 24.6% at the function of dual-polarized transmission. A prototype has been fabricated and measured, and the measurement results are in good agreement with the simulation results, indicating that the AFSSs has good polarization stability for X-band radar applications. [ABSTRACT FROM AUTHOR]

The additive‐free 1,3‐dipolar cycloaddition reaction of isatin‐derived azomethine ylides with α‐cyano‐α,β‐unsaturated compounds was developed, which enabled diversity‐oriented synthesis of a series of novel and structurally complex 3,3′‐pyrrolidinyl‐spirooxindoles derivatives containing four contiguous and two quaternary stereogenic centers in high yields (up to 92%) and excellent diastereoselectivities (up to >25:1 dr). The reaction displays switchable regioselectivity depending on the steric effect of the substrates. [ABSTRACT FROM AUTHOR]

In this article, a transmission and reflection states switchable Luneburg lens (LL) reflector based on active frequency selective surface (AFSS), namely LL‐AFSS reflector, is proposed. The reflector is composed of a miniaturized AFSS reflector, which can change the working state, and a LL composed of six layers and five media from inside to outside. By changing the bias voltage of the PIN diode loaded on the AFSS reflector, the transmission and reflection working states of the LL reflector can be freely switched in the frequency range of 3.5–5 GHz. When the PIN diodes are in ON state, the incident electromagnetic wave will not be reflected through the LL reflector. When the PIN diodes are in OFF state, the radar cross section (RCS) generated by the LL reflector to the incident electromagnetic wave reaches about 15 dB within the angle range of −30 ≤ φ ≤ 30°. The electromagnetic numerical simulation and experimental sample verification of LL‐AFSS reflector are carried out. The results show that the proposed design method is feasible and the RCS changes of transmission and reflection characteristics of LL reflector are obvious. [ABSTRACT FROM AUTHOR]

Microwave power transmission (MPT) has many advantages. However, previous studies have indicated that MPT interferes with wireless data communication. In this paper, an adaptive polarization switchable rectenna architecture is proposed for simultaneous wireless information and power transfer. When the rectenna is activated by a wireless energy transmitter, the antenna automatically switches to another quadrature polarization state for wireless data communication. The experimental results show that the adaptive switching characteristic provides a wireless channel isolation of more than 23 dB between wireless power transfer and data communication. In a practical indoor environment, the measurement of packet error rate of the communication link shows that the power level of MPT could be increased by 16 dB and still keep the wireless connectivity. Thus, the proposed design is suitable for devices powered by MPT and for simultaneous wireless information and power transfer applications. [ABSTRACT FROM AUTHOR]

A mechanically controlled switchable wideband frequency–selective rasorber/absorber, with the transmission window inside the absorption band, based on a frequency–selective surface and a rotatable metal plate, is presented in this paper. The absorption of the switchable rasorber/absorber is over 90%, from 3.9 GHz to 11.77 GHz, when the rotatable metal plate is parallel to the rest of the layers, and its transmission coefficient can reach up to 0.62 at 11.6 GHz, with the rotatable metal plate perpendicular to the rest of the layers. The mechanism of wideband absorption and transmission are explained by monitoring and analyzing the surface current distribution at the absorption and transmission frequencies. The control method is simple, reliable and accurate. It has application value in communication and radar stations. [ABSTRACT FROM AUTHOR]

A compact dual-mode bandpass filter with independently tunable second passband is proposed based on modified V shaped resonators. By switching the pin diodes at each end of the studied resonators, the second passband is independently tuned without affecting the first passband. A prototype of the dual-mode bandpass filter with a dual-passband of 2.54 GHz and 3.36 GHz or a single passband of 2.54 GHz is designed and verified experimentally. [ABSTRACT FROM AUTHOR]

Metasurfaces possess the ability to manipulate wavefront of light at sub-wavelength scales, enabling flexible multi-functional integrations, such as simultaneous nanoprinting and holography. However, previous near-field nanoprinting and far-field holographic technologies present limitations in terms of dynamic switching and flexible tunability. Here, we propose an optical encryption scheme based on non-volatile and switchable metasurface with low-loss phase change material Sb 2 Se 3 that allows active manipulation of both the amplitude and the phase. A modified Gerchberg-Saxton algorithm is developed to achieve near-field amplitude and far-field phase distributions, and anisotropic Sb 2 Se 3 nanobricks act as dynamic meta-atoms for amplitude and propagation phase modulation. In particular, the simulation results show that the dynamic switching for near-field nanoprinting patterns and far-field holographic images can be achieved by controlling the polarization states of the incident light, the imaging distance, as well as different crystallization level of Sb 2 Se 3. The metasurface with two-level encryption mode effectively enhances the information storage capacity and encryption security level by utilizing the active modulation characteristic of Sb 2 Se 3. Such scheme has potential applications in secure communications, dynamic image displays, and high-capacity information storage. • The Sb 2 Se 3 -based optical encryption metasurface is proposed, achieving encrypted display and dynamic switching for images. • With a two-level encryption mode, the far-field encrypted information can be reconstructed only after decrypting the hidden key from the near-field nanoprinting images. With a two-level encryption mode, the far-field information can be reconstructed only after decrypting the hidden key. • The scheme can effectively improve the information storage capacity and encryption security level. [ABSTRACT FROM AUTHOR]