## 1 Introduction  
Electromagnetic energy harvesters generate induced voltage according to Faraday's Law [1; 2; 3; 4; 5]. The arrangement of the magnet and the relative movement speed between the magnet and the coil are the direct influencing factors in electromagnetic energy harvesters. The Halbach array is widely used in the field of electromagnetic energy conversion, which has been a hot research topic in recent years. The Halbach array has the characteristic that the magnetic flux density increases on one side and decreases on the other side because it uses a certain regular arrangement of magnets. On the side where the magnetic induction intensity increases, the maximum magnetic induction intensity is improved, and the distribution range is expanded. On the other side, the magnetic induction intensity is reduced and the distribution range is reduced. Researchers have proposed a variety of Halbach arrays to be used in electromagnetic energy conversion. [PERSON] [6; 7; 8; 9; 10] proposed a hybrid energy harvester that includes a stacked in-plane Halbach array. In addition, some in-plane Halbach arrays [11; 12; 13] and cylindrical Halbach arrays [14; 15; 16; 17; 18] have been presented and utilized. [PERSON] [19] and [PERSON] [20; 21] designed an electromagnetic energy harvester employing a Halbach array and a coil. The coil, which is attached to the end of the cantilever beam, vibrates and results in the generation of induced voltage. [PERSON] [22; 23] proposed an electromagnetic energy harvesting structure that includes a meander spring and an in-plane Halbach array. Some researchers have studied the application of Halbach magnet arrays arranged in a circle in a rotating environment. [PERSON] [24] reported a non-resonant finger-triggered energy harvester with a disc-shaped Halbach array. [PERSON] [25] proposed a circular Halbach array magnetic disk, which was used in a natural-frequency self-tuning energy harvester. [PERSON] [26; 27] proposed a circular Halbach array for monitoring the health condition of bearings. Because of the low fabrication cost, 16 cubic magnets instead of arc-shaped magnets were embedded in a ring area to form a Halbach array. The maximum magnetic induction intensity is increased and the minimum magnetic induction intensity is decreased on one side of the Halbach array ring. The induced voltage of each of two coils in the three coils exhibits a phase difference of 120 degrees. The induced voltage of the three coils forms a three-phase alternating current, which can be a delta connection or a star connection according to the application requirements. [PERSON] [28] proposed a circular Halbach array to concentrate the magnetic flux density in the radial direction. The coils are arranged inside of the circular Halbach array in order to better integrate the system. The studies above show that the use of a circular Halbach array in a rotational electromagnetic energy harvester (REMEH) can improve the electromagnetic energy harvesting performance to a certain extent. However, there are also some areas with almost no magnetic induction in the above-mentioned Halbach arrays even though the magnetic induction of the magnetic poles was concentrated. In fact, the magnetic flux density of a circular Halbach array is affected by many factors. The size, shape, material, residual magnetic flux density, and gap between the cube magnets are factors that affect the magnetic flux density of the Halbach array. The magnetic induction intensity at the magnetic poles is close to the residual magnetism of the NdFeB magnet. In addition, reducing the gap between the magnet and the coil is a common way to improve the electromagnetic induction. The above-mentioned studies utilized the excellent effects of the circular Halbach array. However, there is little research comparing the effects of the magnet arrangement on energy conversion. The above-mentioned research did not reveal the advantages of a Halbach array composed of cubic magnet blocks.