2015 International Conference on Smart Sensors and Systems (IC-SSS) 978-1-4673-9328-7/15/$31.00 ©2015 IEEE Fiber Bragg Grating based two-dimensional Accelerometer SharathUmesh 1 , Resmi Ravi Kumar 2 , Shweta Pant 3 , Sundarrajan Asokan 4 Dept of Inst and Applied Physics 1, 3 , Dept of Optoelectronics and Com 2 , Robert Bosch Centre for Cyber Physical Systems 4 Indian Institute of Science 1,3,4 , Sarabhai Institute of Science and Technology 2 Bangalore 560012 1,3,4 , Kerala, India Abstract—Fiber Bragg Grating (FBG) sensors have become one of the most widely used sensors in the recent times for a variety of applications in the fields of aerospace, civil, automotive, etc. It has been recently realized that FBG based accelerometer’s performance meets and/or exceeds that of traditional sensors. The present work is about the development of a novel, real-time, dynamic two dimensional Accelerometer employing FBG sensors. The proposed FBG Accelerometer works on the principle of inertial mass acceleration which in turn produces strain variations on the adjoining cantilevers, obtained using the FBG sensors bonded over it. The proposed device facilitates compact size and low fabricating cost along with the inherent advantages of FBG sensor, making it an effective device for measuring acceleration. Keywords-Fiber Bragg Gratings, fiber optic sensor, 2-D Accelerometer I. INTRODUCTION Accelerometers are principal devices employed for vibration and shock monitoring in civil engineering structures such as bridges, buildings, dams etc against damages caused by collisions, earthquakes, explosions, fatigue, heavy traffic or strong winds [1]. Accelerometers have also proved their worth in Aerospace, Automobiles, Defense and Medical sectors. Usually, accelerometers are pendulum based devices, working as a spring-mass system, where the inertial mass is attached to the accelerometer base by an elastic spring. The movement of the base, caused by an external stimulus, imposes a movement of the mass relatively to the base, which is proportional to the effect of external stimulus [2]. In the traditional accelerometers, the inertial mass movements are measured by piezoelectric, piezo resistive or capacitive elements. The response of these sensors are typically processed by a signal amplifier and converted into voltage change for detection and acquisition of the measurand. However, these devices, when applied on a large scale, need a huge number of wires and will be affected by electromagnetic interferences, constraining the methodology to be employed. Fiber Bragg Grating (FBG) based Accelerometers are a growing field of research as they possess several advantages over the conventional electrical accelerometers such as immunity to EMI radiation, high sensitivity, multiplexing and distributed sensing capability [3-7]. FBG based accelerometers[8] are technologically evolving, making them suitable for a variety of vibration measurements including structural health monitoring of civil structures and seismic wave detection [9].The purpose of the present study is to develop atwo dimensional accelerometer based on FBG sensors, with the data acquired in the form of dynamic strain variation, which is an indicator of the acceleration. The direction of movement of the mass evaluates the direction of acceleration. The use of FBG sensors brings potential advantages such as compact dimensions, low fatigue and ultra- fast response, making the proposed FBG accelerometer an effective means for recording acceleration. II. PRINCIPLE OF FBG TECHNOLOGY Fiber Bragg Gratings (FBGs) are intrinsic sensing elements which are produced by inscribing a refractive index modulation along the core of a photosensitive fiber [10- 11]. When a broad band light is launched into a fiber with FBG sensor, one particular wavelength (λ B ), which satisfies the following Bragg condition (1), is reflected and other wavelengths are transmitted through the fiber. The wavelength of light reflected from the grating structure is given by λ      (1) Here, n eff is the effective refractive index of the fiber and Λ is the periodicity of the grating fabricated. III. MATERIALS AND METHODS A cubical mass made of aluminium material of dimensions 30mm×30mm×30mm (length × height × thickness) is employed as inertial mass. The cantilever beams of aluminium material with dimensions of 40mm×10mm×2mm whose one end is fixed to the inertial mass (on adjacent sides) and the other end is fixed onto a pillar beam of dimension 10mm×31mm×10mm. Two FBG sensors (FBG1 and FBG2) are bonded individually over these cantilevers as shown in Fig. 1, in order to obtain the strain variation over it. The pillars along with the mass-cantilever system are enclosed on the top and bottom by aluminium plates with dimension 80mm×80mm×3mm which constitutes to form the FBG accelerometer device as shown in Fig. 2. The working principle involves transduction of acceleration into strain variation on the adjacent cantilever beams which is obtained by the FBG sensors. Horizontal vibrations are transferred from the bottom plate of the FBG accelerometer to the pillars, allowing it to move in the direction of vibration. The inertial mass tends to remain in the state of rest when compared to the movement of the pillars, producing strain