The underwater electromagnetic coupler (UEC) with the rotating banner-type secondary core has been widely applied to wireless charging systems for underwater robots due to its advantages of easy alignment during docking

light weight

and great environmental adaptability. To explore the power distribution and transfer mechanism of the UEC

this paper first analyzes the magnetic flux density

electric field and power distribution of UEC with cylindrical and different numbers of banner-type secondary cores

and focuses on the active power and reactive power distribution characteristics in Polylactic Acid (PLA) area by using Poynting vector. The simulation and experimental results show that with the increase of the number of secondary strip cores

the fluctuation of the electric and magnetic field strengths of the UEC around the secondary coil decreases gradually

and the power transfer process is more stable. In addition

when the number of secondary strip cores is increased to 24

the slope of the fitting curve of the received power growth rate is close to zero

and the value of the received power reaches more than 96% of that of the cylinder type. Although the secondary strip cores may cause a small amount of power loss compared with the cylinder type structure

it can significantly reduce the weight and cost of the UEC

which shows its guiding potential in the design and optimization of the UEC of the autonomous underwater vehicle.