| Compared with wired communication and power transmission,wireless communication and power transmission get rid of the cable,which are user-friendly and good for environmental protection.Compared with far field communication and power transmission,near field communication(NFC)and power transmission have the unique characteristics of convenience and safety.To achieve NFC,the inductive coupling antenna needs to be used.To realize wirelss charging,the inductive coupling or capacitive coupling antenna can be applied.Since NFC and wireless charging has the aforementioned advantages and characteristics,they are widely applied to consumer electronics,medical apparatus and instruments,transportation,smart home,mines,and they have become the prerequisite functions of mobile terminals.In recent years,with the fast development and spread of mobile terminal,how to achieve NFC and wireless charging for a mobile terminal has become an urgent problem to be solved.However,the operating environment inside the mobile terminal for electromagnetic coupling antennas is complex.Large metallic will block electromagnetic coupling,induce eddy current loss,and lower the transmission efficiency.Therefore,it is significant to do researches on how to lower the loss,increase the coupling,and enhance the transmission efficiency for near field electromagnetic coupling antenna operating in such a complex environment.On the other hand,the mobile terminal has miniaturized and compact characteristics whereas the near field antennas occupy large space inside the mobile terminal,leading to significant values to investigate the miniaturization of electromagnetic coupling antennas.Focusing on the above points,aiming at the practical requirements of mobile terminals,the wireless near field inductive coupling and electric coupling antennas are studied.The main research contents include:1.In order to solve the design problem that the performance of NFC antenna is poor with metal coverage,the near field regulation antenna,eight shaped NFC antenna,and Boost NFC methodology are proposed for metal-cover mobile terminals.Based on nonuniform meandering line and partial coverage ferrite sheet,the magnetic field generated by NFC antenna is concentrated at the designated clearance zone and the induced reverse eddy current on the specific location of the metal cover is reduced,thus achieving maximum magnetic field at the slot of the metal cover.To further increase the coupling capability of the NFC antenna,a series capacitor is connected to the metal cover and the resonant conditions of the NFC antenna and the metal cover are adjusted.As a result,the direction of the strongest induced eddy current on the metal cover becomes the same as the current flowing on the NFC antenna,which eliminates the shielding effect of the metal cover and improves magnetic coupling.By applying the aforementioned design method,the maximum measured detection range of the NFC antenna is 50 mm and the corresponding fabricated NFC antennas are certificated by NFC Forum or EMVco test.2.To solve the problem that the transmission efficiency is poor with metallic block,the three-coil magnetic coupling antenna with enhanced relay coil is proposed for wireless charging.By connecting a series capacitor across the metal cover,the metal cover is transformed from a metallic block to a single turn relay coil,which adjusts the resonant condition between the transmitting coil and receiving coil.Maximum transmission efficiency is achieved and the safety of wireless charging is improved.The experiments show that after applying the aforementioned method,the transmission efficiency is increased from 39.4 % to 71 % as compared with traditional scheme.In addition,by introducing a vertical slot on the metal rim and cross-connecting the receiving coil to the metal rim,the induced current on the metal rim becomes the same as the current flowing on the receiving coil,leading to increased magnetic coupling between the transmitting coil and the secondary coil.The coupling coefficient is increased from 0.05 to 0.46 and the corresponding experimental transmission efficiency is 87.4 %.3.To achieve free-positioning wireless charging on a plane surface,a repetitive electric coupling array is proposed.By applying a double layer non-uniform structure on the receiving metal plates,the facing area between the transmitting plates and receiving plates remain unchanged with the movement of the receiver.While the receiver moves within the transmitter area,the experimental results indicate that all of the transmission efficiencies are between 52 % and 56 % at 1 MHz working frequency.4.An NFC-CPT-integrated antenna is proposed for miniaturized metal-cover mobile terminals,whose NFC antenna and electric coupling antenna benefit each other.By embedding a cross slot structure on the metal plates,the induced reverse eddy current on the metal cover is reduced for NFC antenna,which mitigates the loss and improves the performance of NFC.By applying SN compensation topology,the voltage across the metal cover is reduced and the compensated components on the receiving side are removed.To further reduce the size of the antenna,the NFC antenna is connected with metal cover,which transforms the NFC antenna to be part of the wireless charging antenna.The NFC-connected NFC-ICPT-integrated antenna using electromagnetic coupling is thus achieved and the power is transferred wirelessly through both magnetic field and electric field.By utilizing the already existed components inside the mobile terminal,NFC and wireless power transfer are realized.The experiments indicate that the sole NFC-ICPT antenna achieves 89.3 % transmission efficiency and the corresponding voltage across the metal cover is 7.08 V,which meets the safety requirement.The power transfer ratio between the magnetic field and electric field is 2.5. |
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