Hong Kong University of Science and Technology

With the rapid advances in wireless sensors, implantable electronics and wearable devices, the demand for high-power-density and long-lifespan power sources is becoming increasingly stronger. Energy harvesting, emerging as an alternative energy solution to batteries, holds great potential to achieve self-powered autonomous operations of such low-power electronic devices, and thus has attracted much attention from both academia and industry recently. We present a comprehensive and critical review of state-of-the-art research on piezoelectric energy harvesting. From the viewpoint of applications, we are most concerned about whether an energy harvester can generate sufficient power under a variable excitation. Therefore, here we concentrate on methodologies leading to high power output and broad operational bandwidth. A variety of designs, nonlinear methods, optimization techniques and harvesting materials are reviewed and discussed in depth. The study also evaluates different figures of merit and presents a systematic performance comparison on recently-proposed energy harvesters. Furthermore, we identify four promising applications: shoes, artificial pacemakers, tire pressure monitoring systems, and bridge & building monitoring.

With recent developments of the automotive industry, particularly in terms of continuously variable transmission (CVT) and hybrid electric vehicle (HEV), electric cars and self-driving technologies, more and more sensors are being used to achieve better driveability, greater safety, and higher fuel efficiency.

Our group has been working on wireless power transmission via electromagnetic waves, and acoustic waves. Both short-range transmission of a few centimeters and mid-range up to a few meters have been explored. For example, we have developed an RFID-based self-powered wireless sensor module for railway condition monitoring. Details can be found in Ref. We also have developed a wood-mimetic acoustic transducer and its system that can wireless transfer power through skin, muscle, and bones, which can be used for powering medical implantable devices.

Haptic technology can create an experience of touch by applying forces, vibrations, or motions to end users. The human somatosensory system is capable of extracting features with millimeter-scale spatial resolution and sub-milli-second temporal precision. Current technologies that can render tactile stimuli with such high definition are neither portable nor easily accessible. We collaborated with Tencent and developed a wearable electro-tactile rendering system that elicits tactile stimuli with both high spatial resolution (76 dots/cm2) and rapid refresh rates (4 kHz) [Science Advances] . Our new pneuma-tactile rendering system provides 200-2300 μm deformation and pressure of 150-2400 mN;depending on the tactile sensitivity of different parts of the human body. The two systems are used as braille rendering that allows the visually impaired to use the same system to read and write as a normal person. We envision that our technology will benefit a broad spectrum of applications such as information transmission, surgical training, teleoperation, and multimedia entertainment.

We develop differnt manufacturing systems, such as electrospinning,electrospraying, sputtering, evaporation, etc, to fabricate porous thin films for air and water filtrations. Below is one project conducted in 2021-2022.

Energy Harvesting is renewable energy technology.

The piezoelectric effect is widely adopted to convert mechanical energy into electrical energy, due to its high energy conversion efficiency, ease of implementation and miniaturization.

These projects are to explore new ways to improve the power output and extend the frequency bandwidth of piezoelectric energy harvesters (PEHs). Our study indicates that the compressive operation mode of piezoelectric materials is better than other modes in terms of generating high energy. Compressive-mode prototypes generated a highest power output of ~ 50 mW [Ref], which is enough to power most potential applications. Nonlinear vibration is used to extend PEH's bandwidth [Ref]. A reversible hysteresis is achieved in experiments [Ref], which effectively extend the bandwidth in both directions. We have systematically analyzed the energy flow and efficiency of energy harvesting systems [Ref], studied new single-crystal PMN-PT materials [Ref] and developed SSHI power conditioning circuits [Ref].