Metamaterials are artificially engineered composite materials. They have drawn much attention recently since they have new and physically realizable response functions that do not occur or may not be readily available in nature. Our research in this area covers topics such as metasurfaces; metamaterials-based on-chip interconnects; active metamaterials; metamaterials with negative / near-zero refraction index.
Metasurfaces
On-chip Metamaterials Structures
Nano-photonics explore the behavior of light and light-matter interactions at the nano-scale. Our research in this area has covered topics such as: Tunable plasmonic devices; Optical nano-antennas; Plasmonic-waveguides and related nano-circuits; Plasmonic-based sensing devices.
Array of Asymmetrical Optical Nano-Antennas Covering a Wide Spectrum
A Flattend Luneburg Lens-Based Plasmonic Waveguide (J. of Appl. Phys., 144301, 2013)
Our research in this field covers the following topics: Design of compact, broadband, and multi-band passive components; Microwave power amplifiers such as Doherty power amplifiers; High power and high performance microwave filters/multiplexers for satellite and base-station applications; Compact, tunable, reconfigurable, and multi-band microwave filters design; Synthesis of advanced filter networks.
3.1 High-power, Compact, Tunable and Reconfigurable Microwave Filters / Multiplexers: Microwave bandpass filters / multiplexers are the key components for the modern RF/microwave systems. They provide the isolations between the receiver and the transmitter circuits, which enables the integrations of these two systems in one chip. Throughout Hualiang’s research, he had design microwave filters and multiplexers (e.g. duplexers, triplexers) with high-power handling, high selectivity, compact size, tunability and reconfigurability.
3.2 Multi-Functional RF / Microwave Circuits: Rapid developments in modern communication systems have imposed requirements such as wide bandwidth, small size and multi-band operation for RF / microwave components. Among them, the multi-band operation is of special interest. Normally, to support multi-band operations, multiple sets of single band circuits were needed, which were large in size and expensive in cost. Alternatively, by replacing the original bulky circuits with the multi-band circuits, both the size and the cost of the whole system could be reduced, which is attractive.
To achieve the multi-band operation of the RF / microwave system, various microwave components need to be re-designed. Different topologies and design theories need to be developed for this purpose. So far, our effort in this area has led to several new designs of microwave baluns, couplers and Wilkinson power dividers, all of which are essential components in the microwave systems. In the future, we are going to design microwave power amplifiers for dual-band operation.
3.3 Broadband Doherty Power Amplifiers and Other Microwave Systems
Antenna as an imperative component for wireless communication system is very important. It exists in every wireless modules. According to different systems, antennas with different characteristics are required. Our research in this field has focused on the following topics: Phased-array antennas and their applications; Beam-forming networks; Reconfigurable UWB antennas; Conformal antennas; Electrically small antenna.
UWB and On-Chip Antennas
Dual-Band Beam-Forming Networks and Antenna Arrays
Transformation optics (TO) is an emerging research and engineering field that addresses the inverse engineering problem of electromagnetism with respect to how an engineered structure will perform a requested functionality. It can prescribe the path of electromagnetic waves at will, by controlling the index of refraction as a function of position, potentially to any desired profile . Transformation optics is driven by coordinate transformation and providing a profile of permittivity and permeability together with anisotropy in the transformed media. It allows for the mathematical mapping of desired distortions of space onto an actual distribution of optical material properties in normal Cartesian space. Our research in this field has relied on transformation optics techniques such as coordinate transformation, quasi-conformal mapping, and inverse quasi-conformal mapping.
Cloaking Devices
Transformation Optics-Based Reconfigurable SPP Wave Adapter (Optics Express, 13789, 2012)
There is an increasing demand for low-cost RF and microwave circuits. While the active transistors have experienced steady enhancement in device performance as a result of the advancing CMOS technology, it is still challenging to realize low-loss high-frequency interconnects and circuits on standard CMOS-grade silicon substrates with low resistivity. Through my work, I used the micro-machining fabrication technique to remove part of the lossy silicon substrate underneath the designed circuits. As a result, edge-suspended transmission lines and transmission line based circuits were fabricated and measured with reduced loss.
