The microbend transducer consists of sensor housing where the measurement fiber is bonded to the housing. The fiber is installed between two deformation plates which have the periodicity ?. One of these plates is fixed to the housing. The other side is connected to a seismic mass and deflects the fiber when acceleration is applied.
The deformer, in response to an appropriate environment change ?E, applies a force ?F to the bent fiber causing the amplitude of the fiber deformation X to change by the amount ?X. The transmission coefficient for light propagating through the bend fiber T is in turn changed by an amount ?T so that
Here D is a constant which depends on the environmental change ?E. In terms of the applied force ?F=m*?a the equation becomes ?T=?T/?X*mpkf-1*?a where kf is the bend fiber force constant.
In the „Microbend fiber-optic sensors“ from Nicolas Lagakos, J. H. Cole, and J. A. Bucaro a microbend acceleration sensor is introduced. The performance characteristics of this sensor are mathematically estimated. The measurement bandwidth is about 2 kHz and the minimum resolution for acceleration changes is 3*10-7 g.
To acquire the sensor´s information, a LED is used as light source and a photo diode as detector. This solution uses cheap components and enables low priced sensors.
A second way to acquire the sensor information is to use a broadband light source. The light illuminates one FBG before the microbend transducer needs expensive components like couplers, super luminescent diodes (SLDs) and further more. This also enables cheap sensors, but the acquisition units are very expensive.
A problem of the microbend sensor is the difficult integration of the fiber between the deformer plates but also to keep a certain deformation during the curing of the adhesive. Deformation of a microbend transducer involves an elastic deformation of the optical fiber and the association spring constant is not negligible.
The multiplexing ability of microbend sensors is not given. The change of intensity can not be assigned to a certain sensor. For applications with lots of measurement points, each sensor needs its own measurement fiber. this is similar to the wiring of traditional sensors, but in terms of weight, the optical fibers have a significantly lower mass.