Large-Scale, Cost-Effective Pressure Mattress Using Flexible Touch Sensor

There is a growing demand for personalized medical diagnostics to improve the quality of life and health. In particular, measuring large-area pressure distributions can broaden the scope of personal medical diagnoses, including applications such as workout monitoring, sleep monitoring, and bedsore prevention. As a result, the demand for pressure mattresses has increased. Among various pressure sensors (e.g., resistive, piezoelectric, triboelectric), capacitive sensor arrays offer advantages such as lower power consumption, higher sensitivity, and temperature insensitivity. However, conventional capacitive pressure sensor arrays face challenges. Misalignment of electrodes during the fabrication process can lead to poor uniformity between individual cells, and the need for stretchable electrode layers adds to the complexity and cost, particularly when fabricating large-area sensors. Moreover, optimizing the capacitance measurement system for arrays with a large number of sensors is critical for accurate performance.
To address these limitations, we propose a large-scale pressure sensor array system using a projected capacitance (P-cap) touch sensor. This system is designed to be flexible, cost-effective, and suitable for human pressure distribution and healthcare monitoring. The sensor consists of a fixed P-cap touch sensor, a deformable dielectric layer, and a ground (GND) layer. By using a fixed electrode layer, the system offers higher reliability and cost-efficiency compared to conventional systems that require stretchable electrode layers. Additionally, we leveraged a commercially available P-cap measurement board, commonly used in cell phones and tablets, to detect touch signals. This board can measure the capacitance change of up to 2,800 cells at a rate of 40 Hz, making it suitable for healthcare and exercise monitoring applications. To enhance sensor sensitivity, we conducted simulations to compare the electric field changes resulting from different electrode pattern shapes. UV laser patterning was employed to increase the stretchability of the ground layer, addressing issues related to wrinkles caused by differences in properties between the ground and dielectric layers.
This flexible, large-scale, cost-effective capacitive pressure mattress demonstrated high spatial density (2,800 sensing units per mattress), a fast sampling rate of 0.5 μs per unit sensor, sensing range of 140kPa, small hysteresis (< 3.3%), detection limit of 0.1 kPa, excellent linearity (R^2 > 0.99), and robust durability through 10,000 cycles of testing. The pressure sensor has been applied in various real-time healthcare scenarios. For example, deep learning was used to classify sleeping postures with 98% accuracy, and the sensor was integrated into a pressure-sore prevention mat for monitoring patient pressure points. Furthermore, we developed a posture monitoring system for exercise, ensuring reliable and stable data acquisition.


Acknowledgment
This work was supported by (1) the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2021R1A2C3008742).(2) Alchemist Project grant funded by Korea Evaluation Institute of Industrial Technology (KEIT) & the Korea Government (MOTIE) (Project number: 1415179744, 20019169).