FBG-Embedded Oblong Diaphragms with Extended Dynamic Range

This article presents a pressure sensor based on fiber bragg grating (FBG) positioned between two oblong diaphragms. This particular shape is suitable for applications requiring a sensitive (i.e., large area diaphragms) and yet compact assembly of the optical sensor. However, the oblong diaphragm deformation mechanism suffers from an early saturation effect, which limits its dynamic range. In order to overcome this drawback, we here propose to apply a differential pretension pattern to oblong diaphragms. A finite element analysis is employed to investigate our technique for a sensor assembly designed to the range of 0–55 kPa. Experimental results confirm that without the differential pretension, the sensor shows a poor correlation coefficient with a linear fit (around 0.8). In contrast, when the proposed differential pretension is applied, the sensor linearity correlation coefficient improves to 0.99, which is a twofold increase on the dynamic range. Our results also include a linearized analytical approach for investigating a tradeoff between dynamic range and sensitivity in our technique. The expanded range is capable of providing a 50% increase of the sensitivity when compared with the corresponding circular diaphragm.