| Summary: | This study designs a closed-loop magnetic circuit using permeable materials to increase the uniformity and intensity of the magnetic field based on an internal conductive square Magnetohydrodynamics (MHD) thruster that consists of a pair of NdFeB magnets. To reduce the magnetic leakage from the thruster, magnetic shields made of various permeable metals are used to encase the MHD thruster. The experimental results show that a stainless steel shell lighter than a black iron shield and moderately increases the magnetic field strength is more suitable for applications in seawater. For a single shield, the field intensity inside the thruster increases linearly with the thickness of the shell. The field strength increases further when a second shell is used. However, the field intensity decreases when the distance between the two shells is increased. An MHD thruster that is 100 mm long, 5mm wide, and 50mm high is hung on a sliding track with negligible friction and is fully submerged in the saline water for the verification of its performance. Increasing the thickness of the stainless steel shell from 2mm to 4mm results in the increase of the propulsive force from 0.064 N to 0.265 N, and the speed of the thruster from 0.075m/s to 0.098 m/s, respectively. The experimental results are used to propose a modified design for a magnetic circuit that increases the uniformity and strength of the magnetic field in the central region of a square MHD thruster that consists of permanent magnets.
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