Ji’an Duan

Giant asymmetric transmission of circular polarization in layer-by-layer chiral metamaterials

In this paper, two kinds of bi-layered chiral metamaterials were proposed to enhance the asymmetric transmission effects for circular polarized electromagnetic waves which are only found in planar chiral metamaterials according to previous studies. It was found that the magnitude of the asymmetric transmission parameters mainly depends on the distances between the two metal layers. With appropriate distance, the asymmetric transmission parameter for circular polarized electromagnetic waves can increase to 0.6. Moreover, both proposed configurations show no asymmetric transmission for linear polarized electromagnetic waves which is widely studied in other bi-layered metamaterials.

Electromagnetic manifestation of chirality in layer-by-layer chiral metamaterials.

The three-dimensional (3D) and two-dimensional (2D) chiral metamaterials (CMMs) have been proved to exhibit circular dichroism and circular conversion dichroism, respectively. The layer-by-layer chiral metamaterials, as a category of 3D CMMs, are expected to show the same properties as bulk 3D structures (e.g. helices). However, in this paper, we demonstrated that the layer-by-layer CMMs exhibit circular dichroism and circular conversion dichroism simultaneously by using both theoretical and experimental methods. This work showed that asymmetric transmissions of circular polarizations can also be observed in layer-by-layer CMMs. Moreover, we provided some necessary requirements for the existing of asymmetric transmissions in layer-by-layer CMMs.

Giant circular polarization conversion in layer-by-layer nonchiral metamaterial

We studied numerically the transmission properties of a kind of layer-by-layer nonchiral metamaterial. Simulation results show that under certain off-normal incidence, giant circular polarization conversion occurs for both the right and left circularly polarized waves with a roughly 1 GHz operation band. Meanwhile, the copolarization transmissions are almost suppressed to zero, leading to the high purity circular polarization transformation. This phenomenon of giant circular polarization conversion is assumed to suffer from the strong magnetic response, which is illustrated by the surface current distributions of the structure. Compared with chiral structures, this nonchiral structure is easier to design and fabricate and is expected to be used as a promising circular polarization transformer.

A Novel High-Speed Jet Dispenser Driven by Double Piezoelectric Stacks

A novel bi-piezoelectric jet dispenser with a zoom mechanism is proposed to distribute adhesives rapidly. The work frequency of the new jet dispenser can reach 500 Hz. The volume of the minimum dot is about 25 nL, and the volume error among dots is not more than ±10%. The dot size can be controlled by adjusting the driving voltage of the piezoelectric stack, filling pressure, and the opening time of the valve. Subsystem physical models of the jet valve are presented on the basis of the bi-piezoelectric principle and the zoom mechanism, which involves an electromechanical model, dynamic model, and fluid-solid coupling model. Based on these physical models, a coupled mechanical-electrical fluid simulation model is established, which can be simulated. The simulation results of the multiphysics-coupled model are in accordance with the experiment. The coupling model will develop a reliable simulating platform for high-speed fluid jet. The effectiveness of the bi-piezoelectric method and models is confirmed, and it will provide a new technology for microelectronics packaging.

The principle and physical models of novel jetting dispenser with giant magnetostrictive and a magnifier

In order to develop jetting technologies of glue in LED and microelectronics packaging, giant-magnetostrictive-material (GMM) is firstly applied to increase jetting response, and a new magnifying device including a lever and a flexible hinge is designed to improve jetting characteristics. Physical models of the jetting system are derived from the magnifying structure and working principle, which involves circuit model, electro-magneto-displacement model, dynamic model and fluid-solid coupling model. The system model is established by combining mathematical models with Matlab-Simulink. The effectiveness of the GMM-based dispenser is confirmed by simulation and experiments. The jetting frequency significantly increases to 250 Hz, and dynamic behaviors jetting needle are evaluated that the velocity and displacement of the jetting needle reaches to 320 mm•s-1 and 0.11 mm respectively. With the increasing of the filling pressure or the amplitude of the current, the dot size will become larger. The dot size and working frequency can be easily adjusted.

Control and Jetting Characteristics of an Innovative Jet Valve With Zoom Mechanism and Opening Electromagnetic Drive

In order to develop jetting technology in LED and microelectronics packaging, an innovative electromagnetic jet valve with zoom mechanism and opening electromagnetic coil is suggested, and an improved method of double voltage drive is applied in the electromagnetic control. It is found that the needle stroke of the new jet valve is increased to 1.3 times, and the needle velocity is raised to 1.8 times, and the temperature of opening electromagnetic coil is lowered to 6.7 °C. The jet valve can successfully jet 4 Pa·s high-viscosity adhesives at room temperature due to the improvement of dynamic characteristics. It will provide a new method for jetting high-viscosity adhesives.

Adjustable annular rings of periodic surface structures induced by spatially shaped femtosecond laser

In this study, we propose a favorable method to modulate femtosecond laser Gaussian beams into annular beams by using an axicon for the fabrication of periodic surface structures. Adjustable annular rings of uniform oriented periodic surface structures with a period of approximately 600~750 nm are fabricated in one illumination step without complicated movements of the translation stage. The orientations of the fabricated periodic surface structures are controllable by changing the electric vector of the laser beam. In addition, by adjusting the distance between the sample and microscope objective, the diameters of the fabricated annular rings can be flexibly controlled in a wide range without changing the optical elements and realignment of the optical path.

Polarization-insensitive resonances with high quality-factors in meta-molecule metamaterials.

Achieving narrow resonance is an area of interest within the field of metamaterials. However, only a few studies have investigated the polarization-insensitive resonances. A general principle for improving quality Q-factor of a sharp resonance is still unclear. In this work, we proposed a kind of planar meta-molecule metamaterials, which can exhibit polarization-insensitive resonance with high Q-factor. The proposed structures have a unit cell consisting of four arrayed ring resonant elements with two different sizes. Moreover, the investigation on surface current and two referential simulated structures confirm a principle for improving Q-factor.

Alignment algorithms for planar optical waveguides

Abstract. Planar optical waveguides are the key elements in a modern, high-speed optical network. An important problem facing the optical fiber communication system is optical-axis alignment and coupling between waveguide chips and transmission fibers. The advantages and disadvantages of the various algorithms used for the optical-axis alignment, namely, hill-climbing, pattern search, and genetic algorithm are analyzed. A new optical-axis alignment for planar optical waveguides is presented which is a composite of a genetic algorithm and a pattern search algorithm. Experiments have proved the proposed alignment’s feasibility; compared with hill climbing, the search process can reduce the number of movements by 88% and reduce the search time by 83%. Moreover, the search success rate in the experiment can reach 100%.

Superamphiphobic miniature boat fabricated by laser micromachining

We fabricated a superamphiphobic miniature boat with marked drag reduction and excellent loading capacity using femtosecond laser direct writing technology. The as-prepared superamphiphobic surface of the boat exhibited apparent contact angles larger than 150° toward both water and oil. Miniature boats with the superamphiphobic surface slid effortlessly on both water and oil-polluted water surfaces, with an increase in sliding distance by up to 52% and load increase of up to 27% compared with those of a boat with an untreated surface. A potential mechanism that explains the excellent performance of the superamphiphobic miniature boat was also discussed. This work provides a simple and economically viable strategy to obtain advanced surfaces for use in microfluidics and marine engineering.