Intrinsic fiber optic sensors have higher signal stability because the output power can be changed according to the variation of measured parameter. The fabrication of optical fiber sensors based on macro- or micro-bending is next simple, cheap and provides high signal Inhibitors,Modulators,Libraries stability. Furthermore, they can provide a wider measurement range and higher sensitivity [15].In theoretical and practical applications, the prediction of radiation loss in bent optical waveguides is an important topic [16]. Different purposes for bent optical fiber sensors have been proposed by many researchers [16�C22], such as axial strain and curvature measurements [16�C18], crack detection and vertical deflection monitoring [19], liquid-level measurement [20], signal compensation [21], humidity monitoring [22], etc.

In order to improve the bend sensitivity of the optical fiber sensors, Inhibitors,Modulators,Libraries a segment of the POF cross-sectional profile was removed or increased the structural imperfections [14,16,17,19,20]. However, a POF sensor with structural imperfections may cause stress concentration or structural defects after a long time in service and this results in signal monitoring errors, especially Inhibitors,Modulators,Libraries for the POF with tooth shape imperfections. It is known that sensitivity improvment is not obvious for a POF with a bent radius. Thus, how to increase the sensitivity of the sensor with no imperfections in the POF is an important Inhibitors,Modulators,Libraries issue. Currently, few publications have investigated the sensitivity of sensors based on cyclic bending [9,23�C30]. For example, Yin et al. [23] presented the application of a fiber specklegram sensor (FSS) to fine angular alignment.

The results indicated that FSS is highly sensitive to fiber perturbations, due to which the sensitivity measurement increases as the NA of the sensing fiber increases. Kulkarni et al. [24] investigated the use of a novel POF sensor Entinostat for measuring force in terms of weights. It was shown that increasing the corrugation pitch of the deforming plates enhanced microbend sensitivity. Sanz et al. [25] developed a POF force sensor by placing the POF in a snake-shaped mould. The results indicated that in the absence of force the POF remained undisturbed whereas with an external pressure the fiber inside the mould was stressed. Losada et al. [26�C28] showed that the application of strain to multiple curvatures POFs caused a reduction in the bandwidth and an increased power loss.

Jim��nez et al. [29] explored a plastic optical fiber-based selleck chemical Ganetespib displacement sensor. The sensor was fabricated using a POF wrapped around a flexible cylinder. The results showed that the sensitivity can be improved by predeforming the cylinder or by decreasing its radius. Lomer et al. [30] presented a quasi-distributed level sensor based on an extra attenuation arisen from bending and polishing plastic optical fibers.