China’s “dual carbon” strategy advocates for a green, environmentally friendly, and low-carbon lifestyle, which relies on the continuous development and innovation of green energy technologies. In the current context of vigorously developing renewable energy in China, the recovery and reuse of micro-energy sources such as magnetic energy in the real environment has attracted the attention of many researchers.
The team of young teachers and associate professor Chu Zhaoqiang from the School of Underwater Acoustic Engineering at Harbin Engineering University has designed a new type of weak magnetic energy harvester structure, which allows IoT sensors to avoid cumbersome manual operations such as battery replacement and maintenance, achieving “self-powering” under weak magnetic conditions, with an output power about 120% higher than traditional magnetic energy collection structures. Recently, the academic paper titled “Significantly Enhanced Weak Magnetic Energy Recovery Performance in Two-Ended Clamped Magnetic-Force-Electric Harvesting Devices” was published online in the internationally renowned journal Advanced Energy Materials in the field of energy materials.
Recovering and Reusing Micro-Energy in the Environment
“The Internet of Everything” is an important engine for building an intelligent world and has also spawned the rapid development of IoT technology. Currently, one major challenge in developing IoT is finding self-sustaining energy technologies for sensor communication nodes to support the construction of large-scale, distributed sensor networks.
In response to this technological challenge, various fields in China are actively planning to find solutions. The 2021 National Key R&D Program “Intelligent Sensors” focused on the self-sustaining energy acquisition issues of multi-parameter biological sensors in wireless scenarios, proposing research on self-sustaining energy technologies that acquire energy from the human body; in 2022, the same program addressed the energy acquisition issues of distributed sensors for power distribution network state perception, proposing project guidelines for magnetoelectric coupled self-sustaining magnetic field sensitive components and sensors; the 2022 National Natural Science Foundation also included the research on micro piezoelectric vibration harvesting technology for aerospace applications in its guidelines.
It can be said that developing distributed energy acquisition technologies and realizing the recovery and reuse of micro-energy in the environment has significant value and is an effective measure to respond to the national energy conservation and emission reduction strategy, contributing to peak carbon emissions.
Regarding the recovery and utilization of environmental micro-energy, among numerous collectible energy sources such as vibration energy, radiation energy, and near-field electromagnetic energy, the stray magnetic energy generated by power cables, industrial machinery, and household appliances has received much attention from researchers due to its fixed frequency and wide distribution, resulting in higher acquisition efficiency compared to low-frequency energy sources like wind energy. Especially in the context of building smart grids, there is an urgent need to capture energy from overhead cables for online monitoring of transmission line state parameters and fault diagnosis to construct sustainable self-sustaining sensor networks.
Just like the beautiful new world depicted in the novel “The Three-Body Problem,” where cups can self-heat without a power source or battery, and flying cars can keep flying without batteries due to wireless power fields generated by microwaves or other forms of electromagnetic oscillation.This technology is actually similar to the technology currently used for wireless charging of mobile phones.Initially, people’s attention was drawn to traditional coil-based induction power generation devices.However, this technology has prominent issues such as large size, inconvenient installation, and difficulty in withstanding short-term high current impacts.
As a result, researchers began to study energy harvesting devices that convert magnetic energy into mechanical energy and then into electrical energy (MME), which is expected to become a new choice for low-frequency magnetic field energy harvesting.
Chu Zhaoqiang introduced that this new type of energy harvesting device utilizes the magnetic torque effect and magnetic hysteresis effect, and then uses the piezoelectric effect to achieve the conversion between mechanical energy and electrical energy. Its advantages lie in not requiring the closed magnetic circuit needed by coil-based induction devices, and it can achieve higher efficiency energy conversion and better tolerance to strong current pulses.
A New Method for Low-Field Energy Harvesting
Since 2016, Chu Zhaoqiang has been involved in the energy harvesting technology of vibrations and magnetic fields. From 2016 to 2021, he has been dedicated to research on materials and devices based on traditional cantilever beam resonator structures. This structure is an energy harvester with one end fixed and the other end free, with a mass block (magnet) added at the free end. This structure provides driving torque from the magnetic mass block at the free end, contributing over 90% of the equivalent mass. In this case, to maintain the resonator’s resonant frequency at 50 Hz, it is difficult to enhance the magnetic-force coupling performance simply by increasing the mass of the free-end magnet. This is also the reason why most current research on cantilever beam magnetic-mechanical-electrical devices is limited to energy harvesting in strong magnetic fields, specifically those greater than 5 Oe. The World Health Organization has pointed out that the safety threshold for public exposure to 50/60 Hz alternating magnetic fields is 1 Oe, and the stray magnetic fields in the environment are generally lower than this reference value. Therefore, it is also necessary to explore new principles and methods suitable for low-field energy harvesting.
Based on the thought of “how to reduce the equivalent mass of the magnetic mass block at the free end in magnetic-mechanical-electrical harvesting devices,” Chu Zhaoqiang boldly innovated and proposed a design idea of a two-ended clamped beam. This design fixes both ends of the magnetic-mechanical-electrical harvesting device, adopting a second-order vibration mode, which reduces the kinetic energy of the central magnetic mass block, thereby reducing its contribution to the equivalent mass of the resonant system, significantly improving the system’s output performance under weak field conditions at 50 Hz while increasing the volume of the magnet.
Experiments have shown that under the same excitation conditions in a weak magnetic environment, this energy harvester can output more than twice the electrical energy of traditional cantilever beam structures in the same unit time, fully capable of allowing sensors without installed batteries to operate normally and communicate with mobile terminals.
Chu Zhaoqiang stated, “In scientific research, a small and seemingly inconspicuous design method often plays a key role. However, the source of this method must be based on long-term research and contemplation.”
Future Applications for Underwater Small Bionic Platforms
“Currently, this magnetic field energy harvesting technology still has certain limitations in application; science always solves one problem and brings many new problems in the process,” Chu Zhaoqiang told the Science and Technology Daily reporter. In the future, he will mainly consider further optimizing the material and geometric parameters design of the two-ended clamped magnetic-mechanical-electrical harvesting devices, further achieving an increase in the adaptable magnetic field variation range and miniaturization integration, providing key technologies for developing self-sustaining magnetic field sensitive components, intelligent perception of power grid transmission and transformation, and identifying the topological relationships of power distribution networks.
Chu Zhaoqiang also stated that the team will combine the research characteristics and advantages of Harbin Engineering University in marine engineering to deeply study underwater small bionic platforms such as underwater robotic fish and unmanned underwater vehicles based on ultrasound and magnetic field wireless power technologies, which can not only solve the energy “acquisition” problem for small bionic platforms but also address the energy “supply” issue.
The team led by Chu Zhaoqiang at Harbin Engineering University’s School of Underwater Acoustics and the Innovation Development Base “Marine Magnetic Sensors and Detection” was established in 2017 and has been continuously growing. The team focuses on the fundamental theories, key technologies, and engineering applications of multi-sensor detection of underwater targets and has comprehensively conducted research on basic magnetic materials, magnetic sensor development, underwater information perception, and processing technologies.
