Xiamen University / Hong Kong Polytechnic University jointly break the dilemma of pressure sensors where "high sensitivity and wide linear range cannot be obtained simultaneously."
Recently, the team led by Professor Zhou Wei from the Sabenchuang Micro-Nano Science and Technology Research Institute at Xiamen University, in collaboration with Professor Yao Haimin's team from the Department of Mechanical Engineering at the Hong Kong Polytechnic University, has made a breakthrough in the field of flexible sensor research. They proposed and validated a new strategy for pressure sensor design, referred to as "force-electric nonlinear synergy," which breaks through the traditional dilemma of pressure sensors where "high sensitivity and wide linear range cannot be achieved simultaneously." The relevant research results, titled "Nonlinearity synergy: An elegant strategy for realizing high-sensitivity and wide-linear-range pressure sensing," were published online on October 20, 2023, in the top international comprehensive journal Nature Communications (DOI: 10.1038/s41467-023-42361-9).
1. Research Background
Flexible pressure sensors are one of the indispensable core functional components of intelligent robots and wearable devices. Over the past two decades, researchers have developed various flexible pressure sensors with high sensitivity or wide linear range. To achieve the dexterity of robots, such as grasping objects of unknown weight or fragile and delicate items, pressure sensors with both high sensitivity and wide linear range are required. However, for most existing flexible pressure sensors, high sensitivity and wide linear range are like "fish and bear's paw," which cannot be obtained at the same time. This greatly hinders the development of intelligent robots. Therefore, there is an urgent need to conduct research on new sensor design strategies to break through the dilemma of sensor performance where "fish and bear's paw" cannot be obtained simultaneously, and to develop flexible pressure sensors with both high sensitivity and wide linear range.
2. Research Content
This research work addresses the current issue of flexible pressure sensors being unable to have both high sensitivity (greater than 10 kPa^-1) and wide linear range (greater than 1 MPa). A new sensor design strategy and manufacturing process were proposed, and the resulting flexible pressure sensors possess both high sensitivity (24.6 kPa^-1) and an ultra-wide linear range (1.4 MPa), with a linear impact factor (sensitivity × range) far exceeding that of most other piezoresistive flexible pressure sensors reported to date.
(1) New Strategy for Nonlinear Synergy Design
A force-electric coupling model of the "stress-strain" and "current change rate-strain" relationships of the sensor was established to study the synergistic control mechanism of the nonlinear electrical performance of the pressure-sensitive layer and the nonlinear mechanical performance of the mechanical regulator on the linearity of the sensor. A new strategy for the nonlinear synergy design of flexible pressure sensors was proposed (as shown in Figure 1).
Figure 1 Schematic diagram of the new nonlinear synergy design strategy
(2) Sensor Structure and Manufacturing Process
Based on the requirements for enhancing sensitivity and broadening the linear range, a double-sided pyramidal porous conductive microstructure (Double-sided pyramidal carbon foam, DPyCF) and a mechanical regulator (Stiffness regulator, SR) were designed to serve as the pressure-sensitive layer and pressure buffer layer, respectively. The layers were stacked and packaged to form the overall sensor structure, defined as DPyCF@SR, as shown in Figure 2a. Three-dimensional dynamic focusing laser processing technology was used to achieve high-precision and efficient manufacturing of the sensor's pressure-sensitive layer and mechanical regulator. At the same time, a high-temperature pyrolysis process was employed to render the pyramidal porous structure conductive and to reduce the size of the micro-pyramid structure in one step (reducing the volume by about 90%), as shown in Figure 2b.
Figure 2 (a) Schematic diagram of the DPyCF@SR flexible pressure sensor structure; (b) Manufacturing process flow of the DPyCF@SR flexible pressure sensor
(3) Performance and Application Integration
The sensitivity (Figure 3a), sample consistency, cyclic stability (Figure 3b), minimum detectable pressure limit, and response time of the developed high-sensitivity-wide linear range flexible pressure sensors were tested, and research was conducted on the discrimination of small pressures under high preload (Figure 3c-e), intelligent grasping of robots (Figure 4), physiological signal detection, and password-pressure dual encryption (human-computer interaction, Figure 5).
Figure 3 (a) Calibration results of DPyCF@SR sensor performance; (b) 50,000 cycle loading test results of DPyCF@SR sensor; (c-e) High-sensitive pressure discrimination under vehicle preload: monitoring changes in the load weight of a 1.5-ton car
Figure 4 (a) Robot with DPyCF@SR sensor grasping a 40g tofu block; (b) Robot with Tekscan commercial sensor grasping a 40g tofu block; (c) Robot with DPyCF@SR sensor grasping a 900g iron block; (d) Robot with Tekscan commercial sensor grasping a 900g iron block
Figure 5 (a) Schematic diagram of the password-pressure dual encryption lock system; (b) Password-pressure dual encryption lock user interface based on Unity3D; (c-d) One unsuccessful attempt and one successful unlock attempt
This research work systematically studied the structural design and manufacturing of flexible pressure sensors, sensitivity mechanisms, performance testing, and applications, and achieved good practical application effects in aspects such as the discrimination of small pressures under high preload and intelligent grasping of robots. The paper proposes a new "force-electric" coupling nonlinear synergy design strategy, breaking through the dilemma where high sensitivity and wide linear range cannot be achieved simultaneously, providing new methods and ideas for the design of flexible pressure sensors, and has important guiding and reference significance for the design and manufacturing of other similar high-performance flexible pressure sensors.
3. Research Related
This research work was supported and funded by the National Natural Science Foundation of China's Outstanding Youth Science Fund Project (52325507), the National Natural Science Foundation Regional Innovation Development Joint Fund Key Support Project (U21A20136), the National Natural Science Excellent Youth Science Fund Project (51922092), the National Natural Science Youth Science Fund Project (52205606), and the Xiamen Major Science and Technology Plan (3502Z20231009).
The paper lists Xiamen University as the first unit, with the first author being Dr. Chen Rui, a doctoral student at the Sabenchuang Micro-Nano Science and Technology Research Institute of Xiamen University. Professor Zhou Wei from Xiamen University and Professor Yao Haimin from the Hong Kong Polytechnic University are the co-corresponding authors. The research work also received guidance and assistance from teachers such as Luo Tao, Xie Yu, Qin Lifeng, and Zhang Jinhui from Xiamen University, and involved graduate students Wang Jincheng, Wang Renpeng, and Zhang Chen from Xiamen University.
