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MEMS sensor technology. Professor Hejun Du
1 Introduction
Pressure imaging is a method of graphically displaying the pressure distribution between two interface surfaces in real time using a pressure sensing matrix with specialized electronics connected to a computer. XSENSOR has developed a leading pressure imaging technology by implementing a matrix of capacitive pressure sensors formed into a continuous film. This film is placed between two interface surfaces, and connected to an electronics module that translates the physical compression of each cell of the matrix into a capacitance value that is correlated to pressure. This data is then displayed on a computer screen to show a map of the interface pressures between the two surfaces. Even slight variations in the pressure distribution between the two surfaces can be detected. This information is valuable to engineers who need to validate the pressure fit between two parts or surfaces. Applications include assessing wheelchair bound patients for the risk of developing pressure ulcers, verifying the effectiveness of door seals, analyzing the grip profile and contact area of a tire tread under different loading and tire inflation levels, statistically validating consistency of automotive seats on a production line, and a sales tools in the mattress retail industry.
2 System operation
2.1 Sensor
The XSENSOR pressure sensor is comprised of two grids of parallel conductive strips that are set perpendicular in orientation. The grids are separated by a thin compressible elastomer (Figure 1 [Figure omitted. See Article Image.]). The intersection of any two perpendicular strips forms a capacitive node. The capacitance at each node is determined by the surface area of the intersection of the two conductive strips, and the distance of separation between the two strips as determined by the compressible elastomer. As pressure is applied to the node, the elastomer compresses, the strips are forced closer together, and the capacitance increases. The change in capacitance is correlated to pressure through a process of calibration. By using multiplexing circuitry the system sequences through each line on the input and output sides of the sensor matrix, thereby measuring the capacitance and therefore the pressure distribution over the entire sensor matrix.
XSENSOR's proprietary manufacturing process can produce pressure imaging pads at various resolutions and for different pressure ranges. Spatial resolutions as high...