Changhai Wang

Bio: Changhai Wang is an academic researcher from Heriot-Watt University. The author has contributed to research in topics: Anodic bonding & Microelectromechanical systems. The author has an hindex of 16, co-authored 88 publications receiving 848 citations. Previous affiliations of Changhai Wang include University of Edinburgh.

Graphene and the related conductive inks for flexible electronics

Abstract: Fabrication of electronic components or circuits by depositing conductive inks on organic or inorganic substrates is a preferred method for manufacturing flexible electronics due to its low cost and versatility. In recent years considerable research has been carried out to synthesize graphene and graphene related hybrid inks for various applications in components and circuits for flexible electronics. In this paper the development of graphene and graphene hybrid inks is reviewed, with particular focus on their formulation, properties and applications. The challenges are also discussed and further development should be focused on ink formulation and preparation methods for low cost and eco-friendly manufacture, easy patterning and processing with good film conductivity. The rational combination of ink formulation and pattern deposition methods would be a direction to follow in the future development of graphene and related inks for commercial application in flexible electronics.

Review of Electrothermal Actuators and Applications

Abstract: This paper presents a review of electrothermal micro-actuators and applications. Electrothermal micro-actuators have been a significant research interest over the last two decades, and many different designs and applications have been investigated. The electrothermal actuation method offers several advantages when compared with the other types of actuation approaches based on electrostatic and piezoelectric principles. The electrothermal method offers flexibility in the choice of materials, low-cost fabrication, and large displacement capabilities. The three main configurations of electrothermal actuators are discussed: hot-and-cold-arm, chevron, and bimorph types as well as a few other unconventional actuation approaches. Within each type, trends are outlined from the basic concept and design modifications to applications which have been investigated in order to enhance the performance or to overcome the limitations of the previous designs. It provides a grasp of the actuation methodology, design, and fabrication, and the related performance and applications in cell manipulation, micro assembly, and mechanical testing of nanomaterials, Radio Frequency (RF) switches, and optical Micro-Electro-Mechanical Systems (MEMS).

Metal particle-free inks for printed flexible electronics

Abstract: Metal particle-free inks, composed of metal salts or metal complexes and volatile solvents, have received significant attention due to their flexibility in preparation, excellent stability and a relatively low sintering temperature in comparison with metal nanoparticle-based inks (nano inks). Formulating such inks has the potential to solve the problems occurring in the synthesis and patterning processes of metal nano inks by careful design of the ink formulation. In this paper, the development of silver and copper particle-free inks is reviewed, with particular attention on the ink formulation, patterning and post-treatment methods. The challenges are also discussed. The properties of the silver particle-free ink vary primarily with the type of silver precursor and the ligand used to solubilize and stabilize it. Highly conductive silver films with controlled microstructure features can be obtained at low sintering temperatures by the selection of appropriate precursor materials and ligands. Printability is also an issue to be solved to obtain patterns with high resolution for practical applications of these inks, which can be realized by adjusting the fluidic properties of the ink and the printing parameters. In terms of copper particle-free inks, the precursors available for selection are very limited and most of them are based on copper(II) formate. New precursors should be exploited. Besides, new sintering methods can also be explored for energy-efficient manufacturing of flexible electronics. In this respect, self-sintering, where sintering occurs spontaneously in the patterning process, is preferred. A Cu–Ag hybrid particle-free ink is also a possible choice for low-temperature fabrication of conductive patterns due to the catalytic property of silver. Finally, it will be advantageous to exploit the possible applications of such inks in the area of electronic and energy devices.

Comparison of IR LED gas sensors with thermal source products

Abstract: Physical principles for infrared gas sensing using LEDs as sources are examined. A number of LEDs from different sources are compared for power output, polar diagram and temperature dependence of output. Some of these have been incorporated in a practical gas sensor based on the Edinburgh Sensors' Gascard. Thus a direct comparison of signal levels between thermal sources and LEDs has been made using thermal detectors. Gas sensing is demonstrated for CO/sub 2/. The paper describes the ranges, accuracies and stability with time and temperature presently exhibited by thermal source sensors and suggests criteria for the widespread use of LED sensors. Some advanced concepts are mentioned with respect to future sensing requirements.

Dispersion of bound electron nonlinear refraction in solids

Abstract: A two-hand model is used to calculate the scaling and spectrum of the nondegenerate nonlinear absorption. From this, the bound electronic nonlinear refractive index n/sub 2/ is obtained using a Kramers-Kronig transformation. The authors include the effects of two-photon and Raman transitions and the AC Stark shift (virtual band blocking). The theoretical calculation for n/sub 2/ shows excellent agreement with measured values for a five-order-of-magnitude variation in the modulus of n/sub 2/ in semiconductors and wide-gap optical solids. Beam distortion methods were used to measure n/sub 2/ in semiconductors. The observations result in a comprehensive theory that allows a prediction of n/sub 2/ at wavelengths beneath the band edge, given only the bandgap energy and the linear index of refraction. Some consequences for all-optical switching are discussed, and a wavelength criterion for the observation of switching is derived. >

Nonlinear Optical Properties of Porphyrins

Abstract: Porphyrins and phthalocyanines have outstanding chemical and thermal stability. The macrocyclic structure and chemical reactivity of tetrapyrroles offers architectural flexibility and facilitates the tailoring of chemical, physical and optoelectronic parameters. The specific optical properties of the tetrapyrrole macrocycle combined with the synthetic methodologies now available and the already available theoretical and spectroscopic knowledge on their optical behavior make porphyrins a target of choice for this area. They are versatile organic nanomaterials with a rich photochemistry and their excited state properties are easily modulated through conformational design, molecular symmetry, metal complexation, orientation and strength of the molecular dipole moment, size and degree of conjugation of the π-systems, and appropriate donor-acceptor substituents. Here we review the structural chemistry and optical properties of recently synthesized porphyrin derivatives that offer potential for nonlinear optical (NLO) applications and complement existing studies on phthalocyanines. Classes of interest include the classic A4 symmetric tetrapyrroles, while optimized systems include push-pull porphyrins, oligomeric and supramolecular self-assembled systems, films and nanoparticle systems, and highly conjugated porphyrin arrays.

Gain enhancement methods for printed circuit antennas

Abstract: Resonance conditions for a substrate-superstrate printed antenna geometry which allow for large antenna gain are presented. Asymptotic formulas for gain, beamwidth, and bandwidth are given, and the bandwidth limitation of the method is discussed. The method is extended to produce narrow patterns about the horizon, and directive patterns at two different angles.