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Design and development of a 3-axis MRI-compatible force sensor

Magnetic resonance imaging (MRI) has been gaining popularity over standard imaging modalities like ultrasound and CT because of its ability to provide excellent soft-tissue contrast. However, due to the working principle of MRI, a number of conventional force sensors are not compatible. One popular solution is to develop a fiber-optic force sensor. However, the measurements along the principal axes of a number of these force sensors are highly cross-coupled. One of the objectives of this paper is to minimize this coupling effect. In addition, this paper describes the design of an elastic frame structure that is obtained systematically by an algorithm and not purely based on design intuition. We used a topology optimization technique, which has two major advantages: 1) aids engineers in design when given a constrained boundary, and 2) optimize the displacement amplification, which will in turn increase stiffness, bandwidth, and improve sensing resolution. To ensure that the frames are linked from the input to output, a solution for topology optimization is proposed. The sensor is then fabricated using plastic material (ABS) as it is one of the ideal material for MRI environment. However, the hysteresis effect seen in the displacement-load graph of plastic materials is known to affect the accuracy. Hence, this paper also proposes modeling and addressing this hysteretic effect using Prandtl-Ishlinskii play operators. Finally, experiments are conducted to evaluate the sensor's performance, as well as its compatibility in MRI under continuous imaging.