Design of a Magnetic Field Modulated Screw Containing Composite Rotors for Wave Energy Conversion

A segmented modulated magnetic lead screw (SMMLS) is designed and analyzed in this article. SMMLS consists of three coaxial tubular components, including an internal stator composed of circular ring permanent magnets (PMs), an intermediate spiral modulation ring composed of ferromagnetic materials, and an external rotor composed of segmented spiral PMs embedded in a nonmagnetic frame. This device adopts magnetic transmission technology, which can convert low-speed linear motion into high-speed rotary motion. Compared with the existing magnetic lead screw (MLS) and magnetic field modulated screw (MFMS), the segmented helical PMs on the outer rotor of SMMLS can form a composite rotor nested with the motor. Furthermore, the inner stator PMs of SMMLS have a circular structure, which reduces the difficulty of manufacturing. The middle part of SMMLS can perform linear motion without PMs, which converts low-speed high-thrust linear motion into high-speed rotational motion, making it ideal for low-speed high-thrust long-stroke applications, such as wave power generation. Then, a prototype of the MLS was built to verify its magnetic transfer capability. Simulations and experiments verify the effectiveness of SMMLS for wave energy conversion.