Heyan Wang

Transparent multi-layer graphene/polyethylene terephthalate structures with excellent microwave absorption and electromagnetic interference shielding performance

A high-performance electromagnetic interference (EMI) shielding structure based on pure graphene (without doping) consists of several graphene sheets separated by transparent polyethylene terephthalate (PET) films. We report the theoretical and experimental design, and characterization of the multi-layer graphene/PET structures. With a total graphene thickness of only 4 nm, the graphene/PET sample demonstrated an average shielding effectiveness of 19.14 dB at 18-26.5 GHz, with a maximum microwave absorbance of 95.82% at 25.7 GHz, while maintaining a normalized visible transmittance of 80.5%. For the multi-layer graphene/PET samples, the contribution of absorption to the total shielding exceeds 96%, indicating that absorption is the dominant shielding mechanism, instead of reflection. The microwave absorbance of the multi-layer graphene/PET structure increases rapidly from the mono- to the four-layer structures, and then more gradually as the number of layers continues to increase when the thickness of PET is 1 mm. In addition, the microwave absorbance can be improved two-fold by increasing the separation between graphene layers. We believe that this multi-layer graphene/PET structure, which exhibits high-performance microwave absorption and shielding, has great potential for applications in transparent EMI shielding devices, especially if EMI absorption is required.

Microwave shielding enhancement of high-transparency, double-layer, submillimeter-period metallic mesh

We demonstrate both theoretically and experimentally that the microwave-shielding effectiveness of a double-layer metallic mesh with a submillimeter period can be improved by increasing the separation between the two mesh layers (without affecting transmittance). This double-layer mesh consists of two layers of square aluminum mesh separated by a quartz-glass substrate. By increasing the substrates optical thickness from zero to λ/4  of the shielding bands upper frequency, the shielding of the double-layer mesh improves considerably, owing to the increased reflectivity of the double-layer mesh with increasing separation in the low-frequency band. A Ku-band shielding effectiveness of over 32 dB is observed for the double-layer mesh with a normalized visible transmittance greater than 91%. It is found that the electromagnetic shielding effectiveness is enhanced by over 7 dB (80.0% energy attenuation) across the Ku-band, compared with that of a single-layer mesh, while the optical transmittances are almost...

Single-polarization polarization maintaining optical fiber with large stress birefringence and high homogeneity

A type of high-birefringence polarization maintaining (PM) fiber was designed and fabricated using a modified chemical vapor deposition (MCVD) process. Different from conventional stress-applied PM fibers, the shape of the stress jacket is like a “capsule.” By study of the cross sectional component distribution and a calculation of stress birefringence using the finite element method, the structure and composition of capsule PM fiber were optimized and the hybrid MCVD process was developed. With advantages in homogeneity and temperature performance, capsule fiber has great potential in applications such as fiber gyroscopes, fiber hydrophones, and other optical fiber sensors.

Achieving an ultra-uniform diffraction pattern of stray light with metallic meshes by using ring and sub-ring arrays.

We provide theoretical and experimental evidence that introducing metallic rings and sub-rings in mesh unit cells significantly decreases the high-order diffraction energy. Moreover, rotating the sub-rings results in increased uniformity in the diffraction distribution without affecting the transmittance. Experiments show that the triangular ring mesh with rotated sub-rings exhibits a normalized visible transmittance greater than 95% as well as an ultra-uniform diffraction pattern of stray light, whose maximal normalized high-order diffraction energy is lower than 0.0167%. This kind of metallic mesh will be favorable in transparent electromagnetic interference shielding devices and touch screens.

Generation of uniform diffraction pattern and high EMI shielding performance by metallic mesh composed of ring and rotated sub-ring arrays

We present an optical transmission model and a fast shielding effectiveness (SE) evaluation method for the inductive mesh comprising metallic rings with rotated sub-ring arrays, which can be extended for designing and optimizing other ring-based mesh structures. The theoretical analysis and experimental verification show that the established model and method are valid. A Ku-band SE >17 dB (98% energy attenuation) is observed for a triangular ring mesh with rotated sub-rings, and a normalized visible transmittance >95% is obtained with an ultra-uniform diffraction pattern, thus indicating the possibilities of our approach for high-optical-transmittance, strong-SE, reduced-image-degradation shielding applications.

Optically transparent frequency selective surface based on nested ring metallic mesh

An optically transparent frequency selective surface (FSS) based on a nested ring metallic mesh is proposed, whose diffraction distribution is uniform and normalized higher-order diffraction intensity is lower than that of an existing transparent FSS based on metallic meshes. Compared with non-meshed FSSs, the proposed FSS has a remarkably higher optical transmittance, lower -3 dB bandwidth, and higher maximum transmittance in the microwave band. Experimental results indicate that the FSS sample achieved a normalized visible transmittance of 94.84%, uniform diffraction distribution, and stable filtering passband around 31.00 GHz simultaneously, which are attractive properties for transparent FSS applications.

Optical bistability of an optical waveguide coated with nonlinear Langmuir-Blodgett films

A 30 layer copper tetra-4-(2,4-di-t-amylphenoxy)phthalocyanine(tapCuPc) film was deposited onto an optical glass waveguide of K ion-exchanges by the Langmuir-Blodgett (LB) technique. A four-layer dielectric waveguide with a LB film cladding was formed. Optical bistability of the optical waveguide coated with nonlinear tapCuPc LB film was observed at room temperature for the first time.

Double-layer interlaced nested multi-ring array metallic mesh for high-performance transparent electromagnetic interference shielding

We report a nested multi-ring array metallic mesh (NMA-MM) that shows a highly uniform diffraction pattern theoretically and experimentally. Then a high-performance transparent electromagnetic interference (EMI) shielding structure is constituted by the double-layer interlaced NMA-MMs separated by transparent quartz-glass substrate. Experimental results show that double-layer interlaced NMA-MM structure exhibits a shielding effectiveness (SE) of over 27 dB in the Ku-band, with a maximal SE of 37 dB at 12 GHz, normalized optical transmittance of 90%, and minimal image quality degradation due to the interlaced arrangement. It thus shows great potential for practical applications in transparent EMI shielding devices.

Verification and improvement of equivalent refractive index models for evaluating the shielding effectiveness of high-transmittance double-layer metallic meshes

The validity of real and complex equivalent refractive index models (ERIMs) is verified for a shielding effectiveness evaluation of high-transmittance double-layer metallic meshes. Theoretical and experimental studies show that the real ERIM is invalid for thin substrates and inaccurate for thick substrates for double-layer meshes, although it has long been used successfully for single-layer meshes. However, the complex ERIM shows more reasonable results not only for double-layer but also for single-layer meshes, and the evaluation accuracy is further improved by modifying the equivalent reactance coefficient using least-squares fitting. Therefore, the modified complex ERIM is applicable in most conditions.

KINETIC MONTE CARLO SIMULATION OF HETEROEPITAXIAL GROWTH OF InSb BUFFER LAYER AND EFFECTS ON InSb/GaAs FILMS

InSb films on GaAs (001) substrates have been grown using a two-step method by molecular beam epitaxy (MBE). The Kinetic Monte Carlo (KMC) method, based on solid-on-solid (SOS) model has been introduced to simulate the Volmer–Weber growth of InSb buffer layer on GaAs substrate. The buffer surface becomes rough obviously and produces an undulating profile during the last coverage of the substrate. The undulating buffer surface would play an adverse role in the surface morphology of the following InSb epilayer. Therefore, the growth of InSb epilayer before the formation of undulating buffer surface would get a better surface, which has been convinced by the results of atomic force microscope (AFM) observations.