Research On Fundamental Principles Of Directed Wireless Power Transmission For Capsule Robots

When capsule robots perform activities such as examinations in the human body,the on-board battery is not only limited in capacity but also cannot be replaced at any time.Therefore,the energy supply problem has become a major bottleneck in the field of research on capsule robots.To this end,this paper proposes a directed wireless power transmission method for capsule robots.It features an alternating magnetic field with an arbitrary controllable direction in space as the power transmitting end,which is superimposed by tri-axial orthogonal rectangular Helmholtz coils.Then,the capsule robot at the power receiving end can induce the required voltage by embedding a single-axis induction coil,thereby performing the wireless power transmission.In order to realize this wireless power transmission method,this paper first uses the relevant principles of differential geometry and coordinate rotation transformation to perform a complete and detailed theoretical analysis and simulation for the polarization phenomenon of the spatial rotating magnetic field,and proves that the end trajectory of three orthogonal sinusoidal magnetic vectors with the same frequency has only three types of polarization: linear polarization,elliptical polarization,and circular polarization.The correspondence between the three types of polarization and amplitudes and phases of the three magnetic vectors are derived.And a discrimination and calculation process for the trajectory of a spatial rotating magnetic vector through its amplitudes and phases is established.Secondly,the magnetic field in tri-axial orthogonal rectangular Helmholtz coils is modeled so that the field strength can be calculated at any point around tri-axial orthogonal rectangular Helmholtz coils.Through the calculation of the magnetic field at the center point of tri-axial orthogonal rectangular Helmholtz coils,the relationship between the magnetic field strength generated by the single-axis coils in the uniform region and the current is derived.Based on this,combined with the linear polarization phenomenon of the spatial rotating magnetic field,the overall design of the directed wireless power transmission system and the generation method of the spatial linearly polarized alternating magnetic field are given.Furthermore,the transmission efficiency formula is derived according to the inductive coupling circuit model of the directed wireless power transmission process,thus improving the theoretical system of the directed wireless power transmission.Next,on the basis of human safety in an alternating magnetic field and human body size data,the power transmitting coil structure,i.e.tri-axial orthogonal rectangular Helmholtz coils,is designed for the directed wireless power transmission system which is capable of accommodating a torso.Two factors affecting the AC resistance of the receiving coil at high frequencies are introduced: skin effect and proximity effect.It is stated that coils carrying high-frequency alternating currents should be wound using Litz wires and calculation formula of the AC resistance for the Litz wire wound coils is introduced.Based on this,the receiving coil is further optimized to minimize the AC resistance at the transmission frequency,reduce coil heating and improve transmission efficiency.Finally,the proposed theory and detection method for the polarization phenomenon of the spatial rotating magnetic field are verified by experiments.The experimental results prove the correctness and effectiveness of the proposed theory and method.At the same time,the directed wireless power transmission efficiency is simulated and the feasibility of this method is proved,which lays a foundation for the research on directed wireless power transmission.