Use of a Lightning Protection Shield for Composite Airplanes as a Load Sensor

Abstract

A rapid diagnosis method for composite aircraft is required. In this study, a new inspection method using a lightning protection shield (LPS) as a load sensor and its wiring is proposed. The load sensor consists of upper layer and lower layer composed of an electrical circuit which has many pressure-sensitive elastomer pills in it. The upper layer is a copper mesh sheet acting as a LPS. The lower layer consists of two kinds of wires. One is high–electrical-resistance nichrome, and another is low–resistance copper. The pressure-sensitive pill changes from an electrical insulator into a conductor when it is compressed. When an impact load is applied to the sensor, the pressure-sensitive pill gives a new electrical path between the two layers at the load point. During the operation of the load sensor, a unidirectional gradient of electrical potential is applied to the lower layer. When a new electrical path is formed between the two layers by the load, potential of the upper layer comes to be equal to that of the indented part of the lower layer. Consequently, measuring the potential of the upper layer provides the X coordinate of the load point. After the X coordinate is acquired, the orthogonal potential gradient is applied to the lower layer to measure the Y coordinate. These XY coordinates can be evaluated within a few milliseconds. In addition, it comes possible to estimate the peak value of the load by measuring the electrical resistance of the pressure–sensitive pill