Design and Characterization of a Micro-opto-mechanical Displacement Sensor
Fiber optic-based mechanical sensors, thanks to their reduced sensitivity to external electromagnetic fields, are promising in the development of biomechatronic systems able to work in demanding environments, such as MRI chambers. In this chapter we repor
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Introduction
The growth of interest around micro-fabricated and fiber optic-based sensors (FOS) can be explained in terms of both economic factors, such as the cost reduction of micro-fabrication techniques and of key optical components, and technological factors, including the increase of components quality and the improvement of metrological characteristics. In the last decades, a big research effort has been devoted in the design of FOS for monitoring parameters of physiological interests [1–3], and it is expected that such sensors will have a central role in several application fields, including medicine and the life sciences. When a micro-optical element, such as a diffraction grating, is invested by a light source, diffraction patterns are observed on a screen placed beyond it. This phenomenon determines a characteristic light intensity distribution. Several authors investigated the application of diffraction gratings for the measurement of various physical parameters, including force [4] and displacement/strain [5]. The working principle of the proposed transducer is based on the light intensity modulation caused by the relative displacement between two overlapped gratings. A fiber optic is used to transport the laser radiation investing the two microdiffraction gratings, thus solving issues related to the alignment of optical components as well as to electromagnetic interferences. E. Schena • M. Cidda • E. Guglielmelli • S. Silvestri Measurements and Instrumentation Lab, Università Campus Bio-Medico di Roma, Via Alvaro del Portillo, 21-00128 Rome, Italy D. Accoto (*) • M. Francomano Biomedical Robotics and Biomicrosystems Lab, Università Campus Bio-Medico di Roma, Via Alvaro del Portillo, 21-00128 Rome, Italy e-mail: [email protected] G. Pennazza Laboratory for Electronics for Sensor Systems, Università Campus Bio-Medico di Roma, Via Alvaro del Portillo, 21-00128 Rome, Italy C. Di Natale et al. (eds.), Sensors and Microsystems: Proceedings of the 17th National Conference, Brescia, Italy, 5-7 February 2013, Lecture Notes in Electrical Engineering 268, DOI 10.1007/978-3-319-00684-0_12, © Springer International Publishing Switzerland 2014
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Fig. 1 (a) Snapshot of the microgratings, (b) detail of the microgeometry, (c) diffraction pattern
The aim of this work is to experimentally provide a proof of concept of the novel transduction strategy, also estimating the influence of grating geometry on sensitivity and range of measurement.
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Sensor Description
The working principle is based on the light modulation induced by the relative displacement of two micro-fabricated diffraction gratings, interposed to a laser source and a fiber tip. Light modulation is monitored by a photodetector, connected to the distal extremity of the fiber in order to avoid misalignment of optical components. Therefore, light intensity can be considered an indirect measurement of the displacement. The two micro-fabricated gratings were micro-fabricated by lift-off, according to the following steps: (1)
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