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Terfenol-D, known as a giant magnetostrictive material, is used in many sensors such as force sensor. In these sensors, external force is measured due to variation of magnetic flux density passing through Terfenol-D. To improve the performance, Terfenol-D is exposed to bias magnetic field and mechanical pre-stress. In this paper, Effects of bias magnetic field and mechanical pre-stress on sensitivity and linear measurement range of a force sensor are studied and optimum values of them are recognized. Initially based on magnetomechanical coupling equations, theoretical model of sensor that includes effective parameters on sensitivity and linear measurement range is developed. Then using experimental set-up, magnetomechanical properties of Terfenol-D are investigated and values of essential parameters for theoretical model are extracted. Finally, employing theoretical model and experimental results, the response of sensor under dynamic external forces is simulated and effects of bias magnetic field and mechanical pre-stress on sensitivity and linear measurement range of the sensor are studied. Based on the obtained results, to increase sensitivity and linear measurement range of sensor, values of bias magnetic field and mechanical pre-stress should be relatively determined considering the amplitude of external force.

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In this article, the influences of different effective parameters on sensitivity of a magnetostrictive force sensor are investigated and then, a high sensitive magnetostrictive force sensor is designed and fabricated. Initially, the operational principles related to magnetostrictive force sensors are presented. Then, conceptual design of the sensor is illustrated and sensors geometry and applied materials are determined. In the next step, measurement of magnetic hysteresis and optimization of the magnetic properties through heat treatment are presented. To this end, magnetic hysteresis curves of not-annealed low carbon iron and annealed low carbon iron under different currents and magnetic hysteresis curve of bulk TERFENOL-D under different preloads and currents are obtained. Then, through numerical simulations using finite element method software, parameters affecting sensor sensitivity were identified and designed. Finally magnetostrictive force sensor is fabricated and its sensitivity and functional specifications are tested under different conditions. The magnetostrictive force sensor sensitivity and linearity error are found as 0.51mV/N and 2.8% FSO respectively, which is a higher value compared to similar magnetostrictive force sensors.

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This paper proposes a new inexpensive soft force sensor suitable for soft robotics applications that require high flexibility and wide range of sensing area. All Hall Effect sensors developed so far use a Hall Effect sensor to detect the magnetic field of a piece of solid magnet. The proposed force sensor in this paper uses a Hall Effect sensor to detect the magnetic flux density change induced by aligned magnetic powder blended with silicone rubber when a normal force is applied. The sensor is designed and tested with different magnetic powder density and sensor dimensions to achieve an optimum design in sensitivity as well as linearity. The experimental results show that different force measurement range with specific desired sensitivity can be achieved by adjusting certain physical properties of the sensor. This is a useful feature for lots of soft sensing elements in today's applications requiring more compliance and reliable sensors, especially in soft robotics applications.