Simultaneous measurement of load and position with an embedded chirped sampled fibre grating

Abstract

In this paper we present the use of a chirped sampled grating for distributed sensing of pressure over a small area (e.g. a few centimetres). The grating is embedded in fibre-reinforced composite. It is found that the shift in the central wavelength of each sub-grating in the chirped sampled grating increases monotonically with an increase in the applied force. The central wavelength of the sub-grating gives the location of the applied pressure. When a surface comes into contact with the sensor, the distribution of the pressure determines the shift in central wavelength of the various sub-gratings. The sub-grating that experiences the maximum pressure will show maximum wavelength shift whereas adjacent sub-gratings will show less shift. This method gives the location and magnitude of the load even when the load is not directly applied to any of the sub-gratings. The sensor design comprises of a sampled chirped grating embedded in unidirectional fibre-reinforced composite prepreg. The prepreg enhances the mechanical strength and the unidirectional embedding reduces birefringence. The number of layers in the prepreg stack varies the sensitivity.