Research Of Wireless Near-field Electromagnetic Power Transfer

At present,a variety of electronic devices have been implanted in the human body,they are used in medical monitoring,drug delivery and local stimulus treatment and help people’s lives greatly.But the diversification of function,the long working period and the miniaturization of the implanted electronic devices has been troubled by energy shortage.To this end,wireless energy transmission technology for the implanted devices in the body has become a hot topic in recent years.This work is different from the energy transfer method of electromagnetic induction or magnetic coupling resonance,and chooses the 2.45-GHz microwave frequency to transmit energy by the radiation field of electromagnetic wave.In this paper,an adaptive focusing feed method based on reciprocity principle is used to automatically focus the electromagnetic wave energy at the position of the implanted antenna,which improves the energy transmission efficiency effectively,thesis contents include:Firstly,the basic principle of microwave wireless transmission is described,the microwave frequency band is selected and the reason for it is explained.Then,the principle of adaptive focusing energy transfer method is explained.A 7-cell circular microstrip antenna array is designed as an external energy transmitting antenna.A cylindrical folded dipole antenna which can be implanted into the body is designed as the receiving antenna.Simulation results show that the adaptive focusing method can effectively improve the transmission efficiency,and 1.25% efficiency is reachable at 55 mm distance.Then the aperture of the transmitting antenna,stability of transmission efficiency to displacement and rotation is studied.Result shows that 7-cells transmitting antenna has a higher transmission efficiency,which is stable with translation and rotation through self-focusing method.In addition,the phase redundancy of phase shifter is analyzed,and the result shows that the redundancy is large.In order to improve the efficiency further,non-equal amplitude feeding method and increasing matching layer method is studied,the result proves that the two methods can improve the transfer efficiency effectively and make the efficiency up to 1.55%.The SAR value and average power density distribution of chest at 500 mW input power is calculated,which proves that this method can provide enough energy to the implanted device under a safe condition.Finally,the experimental scheme is designed and the experimental equipment is prepared.The experiment is carried out using the same phase feed,single element feed and adaptive focusing feed,which the receiving antenna has a displacement.Experimental result shows that the adaptive focus method has a higher transmission efficiency than that of the in-phase feed and single-cell feed,and the transmission efficiency has a stability against the displacement of the receiving antenna.