Diffusive metasurfaces based on transverse magnetized ferrite for reduction of radar cross section.

Diffusive metasurfaces have attracted a great deal of interest in recent years for their promising radar cross section reduction ability. In this work, we proposed a methodology for designing non-tunable and tunable diffusive metasurfaces with transverse magnetized ferrite (TMF). The metasurfaces are two-dimensional arrays configured by metal plates and TMFs backed by metal plates, where the TMFs are functioned as perfect magnetic conductor and magnetic absorbers in lossless and lossy cases, respectively. The designed tunable metasurface allows for control of the operating frequency by adjusting the biased magnetic field, while the non-tunable version provides a wider operation band. This paper demonstrates that the ferrite-based metasurface have exotic stealth performance at microwave frequencies and offers a new approach to design stealth structures.

The standardised Malay version of purdue pegboard test: Content validity and test-retest reliability testing.

Introduction: Purdue Pegboard Test (PPT) is a valid and reliable instrument for measuring hand dexterity among individuals with or without medical conditions. In the Southeast Asia region where Malay is widely spoken, there is a need to have a Malay translation of Purdue Pegboard Test. This study aimed to translate the PPT into the Malay version (PPT-M) and to determine the content validity and test-retest reliability of this translated version. Methods: This study involved: (1) four English teachers (translators) for forward and backward translation procedures; (2) 10 experts in the field of occupational therapy (expert reviewers) for content validity testing; and (3) 60 undergraduate students (participants) for test-retest reliability testing. Results: PPT-M had excellent content validity with Item-Content Validity Index = 0.9-1.0, Scale-Content Validity Index/Average = 0.93-0.95, and a slightly lower Scale-Content Validity Index/Universal Agreement = 0.25-0.75. Test-retest reliability for 3-trial administration (n = 30; Intraclass Correlation Coefficients, ICCs = 0.76-0.85; good) was higher compared to 1-trial administration (n = 30; ICCs = 0.34-0.46; poor) for all subtests. Both trial administrations were mostly affected by systematic errors, especially practice effect as the retests gave higher scores. Random errors mostly affected Subtest 3 of 1-trial administration, evident by its Minimal Detectable Change Percent values = 30.84% that fell beyond the acceptable range. Conclusion: PPT-M has the potential to be a valuable instrument for measuring hand dexterity among Malay speaking individuals especially when the 3-trial administration is used.

Hybrid topological photonic crystals.

Topologically protected photonic edge states offer unprecedented robust propagation of photons that are promising for waveguiding, lasing, and quantum information processing. Here, we report on the discovery of a class of hybrid topological photonic crystals that host simultaneously quantum anomalous Hall and valley Hall phases in different photonic band gaps. The underlying hybrid topology manifests itself in the edge channels as the coexistence of the dual-band chiral edge states and unbalanced valley Hall edge states. We experimentally realize the hybrid topological photonic crystal, unveil its unique topological transitions, and verify its unconventional dual-band gap topological edge states using pump-probe techniques. Furthermore, we demonstrate that the dual-band photonic topological edge channels can serve as frequency-multiplexing devices that function as both beam splitters and combiners. Our study unveils hybrid topological insulators as an exotic topological state of photons as well as a promising route toward future applications in topological photonics.

Topological edge and corner states in honeycomb-kagome photonic crystals.

We systematically study the first- and second-order band topologies, which are tied to the pseudospin and valley degree of freedoms (DOFs), in honeycomb-kagome photonic crystals (HKPCs). We first demonstrate the quantum spin Hall phase as the first-order pseudospin-induced topology in HKPCs by observing the partial pseudospin-momentum locked edge states. By employing the topological crystalline index, we also discover the multiple corner states emerging in the hexagon-shaped supercell as the manifestation of the second-order pseudospin-induced topology in HKPCs. Next, by gapping the Dirac points, a lower band gap associated with the valley DOF emerges, in which the valley-momentum locked edge states are observed as the first-order valley-induced topology. Such HKPCs without inversion symmetry are proved to be Wannier-type second-order topological insulators, which manifested with valley-selective corner states. Additionally, we also discuss the symmetry breaking effect on pseudospin-momentum locked edge states. Our work realizes both pseudospin-induced and valley-induced topologies in a higher-order manner and thus provides more flexibility in manipulating electromagnetic waves, which may find potential applications in topological routings.

Broadband radar cross section reduction by an absorptive metasurface based on a magnetic absorbing material.

A highly feasible approach to achieve a broadband radar cross section (RCS) reduction using a simple magnetic metasurface is presented. A magnetic absorbing material (MAM) with high permittivity and magnetic loss is introduced into the metasurface design instead of the more common dielectric material to considerably reduce its thickness. The metasurface is composed of an optimized two-dimensional array of MAM meta-atoms and a metal plate in back. The meta-atoms share a simple square ring shape but with variable geometrical parameters, forming strong absorption in different frequency bands with large reflection phase differences. By hybridizing the absorption and phase-cancelation technique, a 10-dB RCS reduction from 3.4 to 18 GHz is achieved at a thickness of only 4 mm. Further experimental measurements are provided to evaluate the performance. Our work provides a promising way to broaden the bandwidth of RCS reduction with low density, reduced thickness, and stable performance, which can be utilized in harsh physical and chemical environments.

An autonomously ultrafast self-healing, highly colourless, tear-resistant and compliant elastomer tailored for transparent electromagnetic interference shielding films integrated in flexible and optical electronics.

Considering the operation reliability of flexible and optical electronics (FOEs) in dynamic and real-world environments, autonomous self-healing electromagnetic interference (EMI) shielding materials with high transparency, good stretchability and excellent tear-resistance are urgently required but always difficult to achieve due to the poor dynamics of their elastic substrates. Herein, we propose a facile strategy to design a highly dynamic polyurea elastomer (PDMS-MPI-HDI) featuring with ultrahigh optical transparency (>94%), ultralow elastic modulus (<1 MPa), high tear-resistant stretchability (800%), and ultrafast autonomous self-healing (100 s for scratch-healing). Taking PDMS-MPI-HDI as a substrate for embedding silver nanowires (Ag NWs), the first transparent, stretchable and self-healable EMI shielding materials (Ag NWs/PDMS-MPI-HDI) are presented. Failure behavior of Ag NWs/PDMS-MPI-HDI is highly tolerant of prefabricated cracks under deformation. Due to the robust interfacial adhesion between Ag NWs and PDMS-MPI-HDI, the fractured Ag NW network can autonomously self-reconstruct during the healing process of PDMS-MPI-HDI substrates, contributing to the complete restoration of EMI shielding effectiveness (SE) and full erasure of scratches at both the resting and stretching states. Besides, Ag NWs/PDMS-MPI-HDI exhibits fast autonomous self-healing at high (60 °C) and low (0 °C) temperatures, and in artificial sweat, which is essential for FOEs applicable in various practical environments.

Bulk-disclination correspondence in topological crystalline insulators.

Most natural and artificial materials have crystalline structures from which abundant topological phases emerge1-6. However, the bulk-edge correspondence-which has been widely used in experiments to determine the band topology from edge properties-is inadequate in discerning various topological crystalline phases7-16, leading to challenges in the experimental classification of the large family of topological crystalline materials4-6. It has been theoretically predicted that disclinations-ubiquitous crystallographic defects-can provide an effective probe of crystalline topology beyond edges17-19, but this has not yet been confirmed in experiments. Here we report an experimental demonstration of bulk-disclination correspondence, which manifests as fractional spectral charge and robust bound states at the disclinations. The fractional disclination charge originates from the symmetry-protected bulk charge patterns-a fundamental property of many topological crystalline insulators (TCIs). Furthermore, the robust bound states at disclinations emerge as a secondary, but directly observable, property of TCIs. Using reconfigurable photonic crystals as photonic TCIs with higher-order topology, we observe these hallmark features via pump-probe and near-field detection measurements. It is shown that both the fractional charge and the localized states emerge at the disclination in the TCI phase but vanish in the trivial phase. This experimental demonstration of bulk-disclination correspondence reveals a fundamental phenomenon and a paradigm for exploring topological materials.

Topological light-trapping on a dislocation.

Topological insulators have unconventional gapless edge states where disorder-induced back-scattering is suppressed. In photonics, such edge states lead to unidirectional waveguides which are useful for integrated photonic circuitry. Cavity modes, another type of fundamental component in photonic chips, however, are not protected by band topology because of their lower dimensions. Here we demonstrate that concurrent wavevector space and real-space topology, dubbed as dual-topology, can lead to light-trapping in lower dimensions. The resultant photonic-bound state emerges as a Jackiw-Rebbi soliton mode localized on a dislocation in a two-dimensional photonic crystal, as proposed theoretically and discovered experimentally. Such a strongly confined cavity mode is found to be robust against perturbations. Our study unveils a mechanism for topological light-trapping in lower dimensions, which is invaluable for fundamental physics and various applications in photonics.

Transmission and radar cross-section reduction by combining binary coding metasurface and frequency selective surface.

A modified reflective metasurface, which is constructed by replacing the metal ground of the reflective coding metasurface with a bandpass frequency-selective surface, is proposed. The metasurface has transmission and reduction of radar cross-section characteristics. This allows the metasurface to overcome the drawbacks of conventional realizations, which use lossy materials. The modified metasurface provides high-efficiency transmission in the passband of a frequency-selective surface and broadband reduction of the radar cross section in the rejection band of the frequency-selective surface. Transmission of -0.24 dB was achieved at 4.6 GHz, as well as a -15 dB reduction of radar cross section from 8.5 to 13.5 GHz. This work provides advancements in metasurface applications.

Broadband backscattering reduction realized by array of lossy scatterers.

We propose an array of randomly distributed lossy scatterers to achieve broadband backscattering reduction. The array efficiently combines absorption and diffusion functionalities by using three subarrays made of ferromagnetic or dielectric scatterers based on resistive octagonal rings. The subarrays have strong absorption in different frequency bands, whereas they have different reflection phases in a wide frequency band, resulting in -10 dB backscattering reduction in a wide frequency range (from 3.15 to 18 GHz). The results are verified by experiments. Our work provides a new way to reduce backscattering in a wider frequency range and at lower frequencies.

Manipulating electromagnetic wave propagating non-reciprocally by a chain of ferrite rods.

We demonstrated that non-reciprocal wave propagation could be manipulated by a magnetic rod chain under bias DC magnetic fields. Made of ferrite material YIG and designed working in the microwave X-band, the rod chain exhibited almost a total reflection when the incident wave obliquely impinged on the rod chain, but exhibited nearly a total transmission when the wave reversed its propagation direction. The non-reciprocal wave propagation was due to the non-reciprocal diffraction of the rod chain for the orders 0 and ± 1. Further, the non-reciprocal wave propagation was directly observed by using the field mapping technique. The unique non-reciprocal wave property of the magnetic rod chain provides a new way to control the flow of EM waves.

Manipulating one-way space wave and its refraction by time-reversal and parity symmetry breaking.

One-way transmission and negative refraction are the exotic wave properties founded in photonic crystals which attract a great attention due to their promising applications in photonic devices. How to integrate such two phenomena in one material or device is interesting and valuable. In this work, we theoretically and experimentally demonstrate that one-way electromagnetic space wave can be realized by means of two-dimensional magnetic photonic crystals. Simultaneously breaking the time-reversal and parity symmetries of the magnetic photonic crystals designed, we observe oblique incident space wave propagating one-way in the magnetic photonic crystals with positive or negative refraction occurring at interfaces, which can be manipulated upon the incident angle and operating frequency. Our work may offer a potential platform to realize some exotic photoelectronic and microwave devices such as one-way imaging and one-way cloaking.

Realization of self-guided unidirectional waveguides by a chain of gyromagnetic rods.

To achieve a unidirectional transmission waveguide with miniature dimensions and flexible geometry, we propose a self-guided unidirectional waveguide composed of a chain of gyromagnetic rods. Two configurations of the waveguides were demonstrated. One is of a zigzag chain form, the other is a straight-line chain. These two types of waveguides have very wide one-way edge mode bandwidths. The simulated and experimental results illustrate their extraordinary wideband one-way transmission characteristics. They can also be expected to function as flexible platforms for practical applications because of their thin transverse dimensions and robustness to bending.

Observation of broadband unidirectional transmission by fusing the one-way edge states of gyromagnetic photonic crystals.

We experimentally demonstrate a broadband one-way transmission by merging the operating bands of two types of one-way edge modes that are associated with Bragg scattering and magnetic surface plasmon (MSP) resonance, respectively. By tuning the configuration of gyromagnetic photonic crystals and applied bias magnetic field, the fused bandwidth of unidirectional propagation is up to 2 GHz in microwave frequency range, much larger than either of the individual one-way bandwidth associated with Bragg scattering or MSP resonance. Our scheme for broadband one-way transmission paves the way for the practical applications of one-way transmission.

Investigation of the EDFA effect on the BER performance in space uplink optical communication under the atmospheric turbulence.

In a ground-to-satellite communication system with a preset EDFA, the EDFA's performance will be affected by space environment. With 250 Gy radiation, the EDFA's gain decreases by 2 dB from 19.97 dB at 20 °C. The BER increases by 2.5 orders of magnitude from 10(-10), and increases more with more radiation. The situation aggravates when the temperature rises by 73 °C. The laser's divergence-angle and transmitter radius have optimal values to make the lowest BER and increasing receiver diameter makes lower BERs, so setting these parameters with appropriate values will compensate the degradation caused by EDFA.

Field enhancement of nonreciprocal electromagnetic wave supported by magnetic surface plasmon.

At the zigzag edge of a magnetic photonic crystal with honeycomb lattice, the nonreciprocal surface modes (NSMs) could appear below the magnetic surface plasmon (MSP) frequency. The NSMs possess very flat slopes outside the light line, which is strikingly different from the nearly linear dispersion curve just above the MSP frequency and results in strong confinement and enhancement of the electromagnetic field. Particularly, an enhancement over 100 times in magnetic field is achieved because of the strong magnetic response arising from the MSP resonance. In addition, the branch of double-valued NSM dispersion curve provides zero group velocity away from the Brillouin zone boundary.

A circuit model for the hybrid resonance modes of paired SRR metamaterials.

To better understand the resonance modes caused by the interelement couplings in the building block of metamaterials, we propose a circuit model for the hybrid resonance modes of paired split ring resonators. The model identifies the electromagnetic coupling between the paired rings by electric and magnetic coupling networks and well explains the variation of hybrid resonance modes with respect to the distance and the twist angle between the rings. The predictions of our model are further proved by experiments.

Experimental realization of self-guiding unidirectional electromagnetic edge states.

We present an experimental demonstration of self-guiding electromagnetic edge states existing along the zigzag edge of a honeycomb magnetic photonic crystal. These edge states are shown to possess unidirectional propagation characteristics that are robust against various types of defects and obstacles. In particular, they allow for the unidirectional transport of electromagnetic energy without requiring an ancillary cladding layer.

Measurement of ac conductivity of gold nanofilms at microwave frequencies.

We proposed an application of the open-terminal method to measure the alternating current (ac) conductivity of metallic nanometer thick films at microwave frequencies. An explicit expression of the conductivity as a function of reflection has been derived. Using the application, we experimentally measured the complex conductivity of gold nanometer films in microwave X band. The results are in good agreement with those obtained by other techniques. We find that the film's surface morphology affects not only the magnitude but also the frequency dependence of the ac conductivity. In some cases, the direct current conductivity can be lower than the ac conductivity deviating from the Drude model, which can be well qualitatively explained by a circuit model for the granular films.