Smart lighting protection skin using QTC pills for aircraft realtime load monitoring

For real-time load monitoring, we present a new smart lighting protection skin using resistive touchpad techniques that covers measuring objects with a flexible sheet composed of multiple tiny sensors. We measured loading from off-plate direction, including quasi-static indentation and dynamic impact. We believe our method is suitable for load monitoring of composite aircraft structures. A metal film or mesh coving the fiber composite components of our system acts as both the load sensor and wiring, and a lightning protection shield (LPS). The sheet consists of an upper LPS layer and a lower layer, with multiple pressure-sensitive elastomer pills arranged between layers. The lower layer is a grid consisting of high-electrical-resistance nichrome wires and low-resistance copper wires. The pressure-sensitive pill becomes conductive when compressed. When the sensor sheet is indented, a compressed pill creates a new electrical path between the two layers and the electrical potential equalizes at that point. This event triggers the application of a potential across the nichrome wires that form the x axis, enabling measurement of the x coordinate. The orthogonal potential gradient is then applied to the lower layer so that the y coordinate can be measured. The x and y coordinates are recorded quickly and describe the quasi-static load point with an error of 29 mm or less. Additionally, we can estimate the peak value of the impact load by measuring the electrical resistance of the pressure-sensitive pill with an error of 17 %.