Tag: City University of Hong Kong

By mimicking human skin, new kinds of tactile sensor technologies created at the City University of Hong Kong (CityU) offer hope to improving the quality of life for people suffering serious injuries and disabilities.

These breakthrough technologies, developed through two research projects co-led by CityU, are so sophisticated that they enable a robotic appendage to behave like a human hand and complete such tasks as threading a needle or grasping a fragile piece of tofu without spillage.

In the first project, Dr Shen Yajing, Associate Professor in CityU’s Department of Biomedical Engineering, has co-led joint research with the University of Hong Kong on developing a new kind of soft sensor with skin-comparable characteristics.

The research, published in Science Robotics under the title “Soft magnetic skin for super-resolution tactile sensing with force self-decoupling”, promises to advance areas such as the development of smart prosthetics and human–robot interaction.

The sensor is located in a multi-layered structure modelled on human skin. A very special feature is that the sensor can “decouple”, or decompose, the external force automatically into two components, providing an accurate measurement of these two forces respectively in order to analyse or control the stationary or moving state of an object.

Moreover, tactile “super-resolution” allows the sensor to accurately locate the stimuli’s position. “Our efficient tactile super-resolution algorithm uses deep learning and has achieved a 60-fold improvement in the localisation accuracy of the contact position, which is the best among super-resolution methods reported so far,” said Dr Shen.

“To the best of our knowledge, this is the first tactile sensor that has achieved self-decoupling and super-resolution abilities simultaneously,” he added.

By mounting the sensor at the fingertips of a robotic gripper, the team has demonstrated that robots can accomplish challenging tasks. For example, the robotic gripper can grasp fragile objects like an egg with a high degree of stability while an external force is trying to drag it away, and it can thread a needle via teleoperation.

“This proposed sensor can help develop adaptive grasping, dexterous manipulation, texture recognition, smart prosthetics and human–robot interaction. The advance of soft artificial tactile sensors with skin-comparable characteristics can make domestic robots a future reality in our daily life,” Dr Shen added.

Inspired by the delicate structure of human skin, the second research project, this time co-led by Dr Yang Zhengbao, Assistant Professor in the Department of Mechanical Engineering, has created a highly sensitive tactile sensor array that has the potential to restore touch and sensation, as well as monitor health.

Consisting of protective layers, an insulative layer and two piezo sensory layers, the dual-layer comb piezoelectric tactile sensor array that the team fabricated can measure more spatiotemporal information than similar technologies. Furthermore, the team invented the “row+column” electrode structure that can reduce fabrication costs significantly.

“The system can achieve real-time detection and differentiation of diverse external stimuli such as bending, tension and compression within one sensor element. Our sensor can respond extremely fast, with a response time down to 10 milliseconds, which is even faster than human skin,” Dr Yang explained.

The tactile sensor is so delicate that it can even grasp a fragile piece of tofu without breakage, showing great potential for the human–machine interface and promoting the development of smarter prosthetics, robotic hands, and equipment for handling multiple soft and fragile products in industry.

The system is a promising candidate for reconstructing the human tactile system, i.e. re-establishing tactile sensation for people with skin damage and assisting amputees. The sensor can also help monitor overall human health, for example by accurately detecting weak artery pulses.

The team’s findings have been published in Advanced Science under the title “Skin-inspired piezoelectric tactile sensor array with crosstalk-free row+column electrodes for spatiotemporally distinguishing diverse stimuli”.

The use of a simple organic molecule during the fabrication of a two-dimensional (2D) perovskite results in one of the highest recorded efficiencies for perovskite-based devices. Light-emitting diodes (LEDs) employing this 2D perovskite material achieved an external quantum efficiency as high as 20.5%, which rivals the best organic LEDs, according to research co-led by the City University of Hong Kong (CityU).

Led by Professor Andrey Rogach, Chair Professor at the Department of Materials Science and Engineering, CityU, and his collaborator Professor Yang Xuyong from Shanghai University, the research team has worked on 2D perovskite materials and succeeded to realise such efficient and bright green LEDs.

Their technology yielded the best-reported performance on both current efficiency and external quantum efficiency. This work has now put the perovskite LEDs close on the heels of current commercial display technologies, such as organic LEDs.

The findings were published in the scientific journal Nature Communications, titled “Smoothing the energy transfer pathway in quasi-2D perovskite films using methane sulfonate leads to highly efficient light-emitting devices”.

The key to the powerful change lies in the addition of around 10% of a simple organic molecule, called methanesulfonate (MeS). This molecule reconstructs the structure of the 2D perovskite nanosheets, while simultaneously enhancing exciton energy transfer between sheets of different thicknesses. It is also useful in reducing defects in the 2D perovskite structure, contributing to higher efficiency.

The consequences for producing better LEDs are encouraging. Brightness of 13,400 candela/m2 at a low applied voltage of 5.5 V, and an external quantum efficiency 20.5% is recorded. This is close to the maximum that can be achieved by many existing LED technologies and has almost doubled the external quantum efficiency level of 10.5% reported in the previous collaborative study of the same groups two years ago.

“The CityU team has built up its expertise on perovskite materials to a very high level in a relatively short period of time, thanks to funding support from Senior Research Fellowship by the Croucher Foundation,” said Professor Rogach.

“The high brightness, excellent colour purity, and commercial-grade operating efficiency achieved marks 2D perovskites as an extremely attractive material for future commercial LEDs, and potentially also display technology. It’s a tangible outcome from both fundamental and applied research into novel nano-scale materials” he adds.

New methods for reducing air pollution and generating solar fuels developed by scientists at the City University of Hong Kong (CityU) offer practical solutions to the energy shortage, environmental issues, and related public health risks.

The research has been generated by two projects led by Dr Ng Yun-hau, Associate Professor, and Dr Shang Jin, Assistant Professor, respectively, in the School of Energy and Environment (SEE). The research has been published in the top chemistry journal Angewandte Chemie.

Dr Ng and his team have designed a new solar-powered catalyst that can convert carbon dioxide (CO2) into methane fuel through artificial photosynthesis. Their work is published in a paper titled “Metal-Organic Frameworks Decorated Cuprous Oxide Nanowires for Long-lived Charges Applied in Selective Photocatalytic CO2 Reduction to CH4”.

“Methane is a major component of domestic fuel gases. Turning CO2 into methane fuel using sunlight has the potential to produce a clean and sustainable energy alternative, thereby reducing our carbon emissions and reliance on fossil fuels,” Dr Ng said.

However, the key problems with CO2 conversion are short excited charges in the lifetime of the catalyst and non-selective reduction. Cuprous oxide (Cu2O), commonly used for CO2 conversion, undergoes self-corrosion after brief illumination, and it creates an array of product mixture from the reduction process, hindering large scale application.

Dr Ng’s team has solved these problems by uniformly enwrapping Cu2O with a copper-based metal-organic framework (MOF) at the microscopic level. This MOF, which is a good CO2 adsorbent, strengthens the interaction between the CO2 and the catalyst, enabling a higher concentration of CO2 on the surface of catalyst. The team unveiled for the first time the presence of charge transfer between MOF and cuprous oxide, which can prolong the charges lifetime by ten times for higher activity. With the conformal coating of MOF, the Cu2O becomes stable and its corrosion is delayed.

“We hope we can recycle the unwanted CO2 from industry and transportation sectors at an affordable cost in the future and use it as the precursor to produce green and alternative fuels. We will continue to explore ways to further increase the methane production rate and scale up the catalyst synthesis and the reactor systems,” said Dr Ng.

The other study, carried out by the team led by Dr Shang, aims to control pollution resulting from nitrogen dioxide (NO2), a major roadside pollutant causing photochemical smog and damage to the human respiratory tract. The team revealed a new class of robust adsorbent materials for capturing ambient NO2 in a paper titled “Transition‐Metal‐Containing Porphyrin Metal–Organic Frameworks as π‐Backbonding Adsorbents for NO2 Removal”.

The team has developed a series of sponge-like nanoporous materials featuring tailored transition metals as active sites at the porphyrin rings, which can selectively bind and remove NO2 from gas mixtures.