Progressing towards a new era via Electronics and Photonics

Education | 20 May 2022

Following the success of the last Distinguished Lecture Series last semester, the Hong Kong Institute for Advanced Study (HKIAS) at City University of Hong Kong (CityU) are continuing its online seminars of connecting scholars worldwide to address real-world issues and exchange interdisciplinary ideas.

Supported in part by Kwang Hua Educational Foundation, five new online lectures on the Electronics and Photonics Series were held in March and April. The series attracted over 2000 scholars and guests to attend. To inspire audiences and stimulate new thinking, the lectures have united current remarkable ideas in nanotechnology, antenna design, wireless communications and beyond to unlock new and fascinating ideas about our everyday life. 

The power of Plasmonic Biosensors

Nanotechnology and its biosensor applications are becoming ever more prevalent in the field of biomedical microsystems. Kicking off the HKIAS Distinguished Lecture Series on Electronics and Photonics was Professor Stella W. Pang, Head of the Department of Electrical Engineering and Director of the Centre for Biosystems, Neuroscience, and Nanotechnology at CityU, who presented a lecture titled ‘Nanotechnology for High-Performance Devices and Sensors’ on March 1, 2022. 

Well known for her work in nanofabrication technology, Professor Pang addressed the advantages of plasmonic sensors produced by nanoimprint technology. “The ability to generate a large area of nanostructures within a few seconds highlights nanoimprint’s high reproducibility and uniformity with high throughput,” explained Professor Pang.

She went on to explain that the novel 3D multiple layer plasmonic biosensors exhibit enhanced electric fields to provide a much higher sensitivity. “To share a few notable examples related to our sensor applications, we were able to detect larger size lung cancer A549 live cells and nanoscale DNAs at different concentrations. Using the resonance peak shift of these highly sensitive, nanoplasmonic sensors, cancer cells and DNAs can be detected at very low concentrations, which is beneficial for early disease diagnosis.”

“When photonic crystal defects are placed in desired locations by stacking 3D asymmetrical nanopillars on top of nanoholes, this can enhance the electromagnetic field intensity of the 3D localized surface plasmon resonance biosensors. Hybrid coupling of the plasmonic and photonic crystal modes leads to a record high sensitivity of 1376 nm/refractive index unit,” said Professor Pang. “Moreover, by combining plasmonic sensors with 3D platforms in a microfluidic microsystem, we can separate cancer cells from normal cells for cell control and identification. This will further improve the biosensor sensitivity such that cancer patients could be diagnosed at a much earlier stage, potentially saving millions of lives.”

The Magic of Antennas

Professor Kwai Man Luk, Chair Professor of the Department of Electrical Engineering and the Founding Director of the State Key Laboratory of Terahertz and Millimeter Waves of CityU. On March 17, 2022, this awardee of the 2017 IEEE APS John Kraus Antenna Award gave a lecture titled ‘Antenna Scientists - Magicians in the era of Wireless Connectivity’

Professor Luk proceeded to investigate the structure and popularity of the microstrip antenna over the past four decades. “Made of a very simple structure of just a printed circuit board with a grounded plane and a patch on top of it, this antenna has a very narrow bandwidth of 2% and has broadside or conical radiation patterns, but there are limitations to this invention.” 

Over the years, Professor Luk and his team developed many techniques to improve the bandwidth by either adding parasitic elements on top of the original patch antenna, using a U-shaped slot or combining both methods. “In 1998, my team and I proposed the L-probe patch antenna. The non-contact and flexible feed is a parasitic structure which couples the energy electromagnetically to the patch; this way the antenna can radiate a wider bandwidth of over 30%.”

The magneto-electric (ME) dipole structure was proposed in 2006, this variation of the L-shaped probe can serve as a complementary antenna and has an array of applications. “ME dipole has been observed to be quite useful in medical imaging applications”, said Professor Luk. “Used to detect brain haemorrhages, the antenna’s directional pattern functions over a wide frequency range. A high percentage of the energy passes inside the human head with very little radiation outside.”

Professor Luk has 301 papers from IEEE Xplore with a total of 460,000 full text views. He shared his highest ranked paper with 10,919 views titled “Circularly Polarized Patch Antenna for Future 5G Mobile Phones”, which discussed the principles of folding down edge patches with open slots for size reduction and surrounding the patch with dielectric substrate for wider beamwidth.

Professor Luk concluded his talk by acknowledging the contributions made by all antenna magicians who developed antenna technologies to push forward modern wireless connectivity.

Seeing with Metalenses

Professor Din-ping Tsai, Chair Professor of the Department of Electrical Engineering at CityU, gave a lecture titled ‘Meta-Devices: From Sensing and Imaging to Quantum Optical Chip’ on March 30, 2022. He reported on the current progress of his research on the development of high-dimensional optic meta-devices and their applications. 

Professor Tsai focused on the design, fabrication and application of metalenses arrays. He shared a case of continuous broadband achromatic metalens in reflection mode. “We integrated the differential phase equation and the edge alignment method with the Berry phase effect. To implement the broadband achromatic metalens focusing, we used multiple resonance antennas to form the integrated-resonant unit instead of a single, narrow antenna.” 

The GaN Achromatic Metalens was made for transmission and shares a similar design principle to the previous examples Professor Tsai mentioned. “Using different dimensions for the different nano antennas helps cover the 2-pi phase change and offers a broadband coverage, from a range of 440 to 660 nm.” 

Having overcome the issue of single wavelength metalens, Professor Tsai can now use achromatic metalenses to show full colour images which have great performance on focal length and efficiency when experimenting on full colour imaging movies.

Microlenses are considered as one of the top 10 emerging technologies for 2019 and have great prospects in robotic vision, nano robots, drones, AR/VR/MR, and autonomous driving. “Small lenses have larger depths of field and higher sensitivity in optic imaging. For this reason we designed and fabricated a 60x60 GaN Metalens array for light field imaging, it can be used for depth and edge detection.”

Future Power Grids for Sustainable Development 

Professor Michael Chi Kong Tse, Chair Professor of the Department of Electrical Engineering and Associate Vice President (Strategic Research) of CityU, shared his recent research on power systems through his lecture titled ‘Challenges of Modern Power Grid in the Midst of Deepening Power Electronics Penetration and Increasing Renewable Energy Use’ on April 12, 2022. 

The power grid is considered the most indispensable infrastructure that supports all sorts of activities we have in modern society, said Professor Tse. In his talk, he highlighted the impact of power electronics penetrations and cautioned the development of rapidly increasing charging stations. 

“Conventional power systems are synchronised machine based where significant inertia in the system provides the key mechanisms for control. However, power electronics do not have inertia, and when a power converter plugs on to the grid, it assumes the grid is a voltage source and does not contribute to any inertia. It also has no switching mode but instead a toggle of two or more circuit topologies, yielding a highly nonlinear operation”, explained Professor Tse. Engineers are struggling to tackle the design challenges that come with power electronics due to the inherent nonlinearity, multi-time scale and oscillations; an unwanted form of instability. 

In 2015, Professor Tse and his team developed a physical law based model and incorporated it with the complex network model in order to make it more realistic. The timing between failures could be a stochastic process but through applied stochastic modelling, they were able to solve the timing issue and were able to mimic the progression profile of a cascading failure, which was highly consistent with previous historical data.

“In the future when talking about power electronics penetration, the failure mechanisms of PE nodes have to be re-examined and incorporated in this model in order to assess the risk and robustness. We also have to face the issue of developing control strategies to balance the grid-following and forming functions.”

Pushing for a 6G Future 

Professor Chi Hou Chan, Chair Professor of the Department of Electrical Engineering, and Director of State Key Laboratory of Terahertz and Millimeter Waves at CityU, gave a lecture titled ‘Are We Ready for 6G’ on April 22, 2022.

Professor Chan started off his lecture by addressing the standardisation for the high data-rate 6G is expected by 2025. Its important applications include holographic telepresence, tactile internet, chip to chip and machine to machine connections that could be used in future big data centres.

The conventional approach of millimetre waves has been extended to develop a THz Guided-Wave-Driven Metasurface Antenna. The beam in the antenna is normally directed in a certain direction, but with a change in frequency, the beam can be steered to a different direction. This approach uses silicon based metasurface antenna for higher efficiency and is fully compatible with CMOS technologies and integrated photonic technologies. It can be used in wireless transmission in data centres, said Professor Chan. 

Professor Chan also shared his recent collaboration with Professor Cui Tie Jun and his group, “We developed the Space-Time-Coding Metasurface Antenna (STCMA) that can control output beam directions and spatial periodicity by using a 1-bit ON-OFF switch and can be extended to on-chip integration, this is exciting progress for 6G development.”

Innovative antennas are needed to develop effective THz sources, either through the IC approach or the photoconductive approach. We found out that we can also make use of the silicone substrate with Chip-Integrated Dielectric Resonator to increase bandwidth. The developed On-Chip Beam Steering THz device can steer the beam from -30° to 30° by controlling the phase. 

Professor Chan and his team will continue their work on IC implementation of beam steering devices based on STCMA and plans to incorporate baseband signalling into their THz ICs for 6G with their sister institutions. 

For more upcoming events of HKIAS, please visit: www.ias.cityu.edu.hk/en/event/upcoming



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