Zhengang Lu

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.

Contiguous metallic rings: an inductive mesh with high transmissivity, strong electromagnetic shielding, and uniformly distributed stray light

This paper presents the experimental study on an inductive mesh composed of contiguous metallic rings fabricated using UV-lithography on quartz glass. Experimental results indicate that, at the same period and linewidth as square mesh, ring mesh has better transmissivity for its higher obscuration ratio, stronger electromagnetic shielding performance for its smaller maximum aperture, and less degradation of imaging quality for its lower ratio and uniform distribution of high order diffraction energy. It is therefore concluded that this kind of ring mesh can be used as high-pass filters to provide electromagnetic shielding of optical transparent elements.

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...

Analysis of Fraunhofer diffractive characteristics of a tilted metallic mesh for its effect on optical measurement

In order to analyse the Fraunhofer diffractive characteristics of a tilted metallic mesh for its effect on optical measurement, a model is built for Fraunhofer diffraction optical intensity distribution using Huygens–Fresnel diffraction theory; a stretch factor is introduced to represent the stretching of diffraction spots along axis x, as a result of variation in the effective area of a clear aperture after mesh tilting, and an offset factor is introduced to represent the asymmetrical distribution of diffraction spots caused by mesh tilting and the distance between the centre of zero-order diffraction and the observation point. The diffraction characteristics of the tilted mesh are in good agreement with experimental results, which proves the correctness of the model established for it. The location of the centre of zero-order diffraction does not change with θ in an aerial optical measurement, and an increase by 1/cos(θ) times its primary maximum radius along axis x due to the prevailing stretch factor causes a decrease in the resolution of an optical system by the same magnitude. The model established for a tilted mesh can also be used to remove any error due to a tilted slot during slot width measurement.

Analysis of transmitting characteristics of high-transparency double-layer metallic meshes with submillimeter period using an analytical model.

The transmitting characteristics of high-transparency double-layer metallic meshes with submillimeter period were analyzed using an analytical model, which was established using angular spectrum propagation theory and verified through experiments. It was found through analysis that rotating misalignment has significant effect on the distribution of diffraction spot intensity. Large period and small linewidth can be used to obtain high transmittance and low levels of stray light. Substrate thickness has little effect on transmitting characteristics of mesh, and so it is a variable free to choose in optimizing shielding characteristics of mesh. We think, together with other ways and means of optimizing shielding characteristics of mesh, the model can also be used for the optimization of a high-pass mesh filter.

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.

Two-degree-of-freedom displacement measurement system based on double diffraction gratings

A two-degree-of-freedom (2-DOF) displacement measurement system based on double diffraction gratings is proposed in this paper, which consists of a reflective-type scale grating and a grating read head with a scanning transmission grating. Combining the traditional three-grating interference principle with the Michelson interference principle, the system can measure the displacements of a precision stage along the horizontal direction (X-axis, in the scanning grating plane and vertical to the scanning grating lines) and vertical direction (Z-axis, vertical to the scanning grating plane) simultaneously. The system has the merits of compact structure and uncoupled interference signals in the two axes. By simulating the output signals of the system and comparing them with the experimental results, the validity and feasibility of the system have been verified. The 2-DOF system will be favorable in the displacement measurement of multi-dimensional stages and multi-DOF machines.

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.