Study And Design Of An Implantable3-Coil Adaptive Wireless Power Transmission System

With the development of technology, the growing popularity of applications ofimplantable biomedical electronic devices plays a more and more important role in biologicalresearch and medical diagnostics. For practical implantable electronic devices, long-term andstability and safety of the power supply is a critical issue. Nowadays wireless powertransmission is a hot research point, which is more and more often used by implantablebiomedical devices for it can transfer power to devices inside the body through the skin. Thebasis of the wireless power transmission is the near-field mutual coupling theory, but theefficiency of the traditional mutual coupling decline rapidly when the distance increases, thereceived power fluctuates significantly with the change of distance, which leads to thedamage of biological issue. In addition, a large number of discrete components increases thedifficulty of the implant.Taking the coil coupling structure and the integrated circuit design and power feedbackcontrol as the entry points, this paper designed a three-coil implantable wireless powertransmission system with the wireless power supply and adaptive mechanism. The systemconsists of the transmitter, three-coil coupling structure, in-vivo power harvesting circuit. Theexternal transmitter includes a driver circuit, power amplifier, LSK demodulation module,MCU and digital-controlled power supply. The power harvesting circuit includes low-dropoutlinear regulator, PWM modulation and LSK circuit.Based on the mutual coupling theory, the paper analyzed the critical factor affecting thetransmission efficiency. Combining the thinking of magnetic coupling using resonator withhigh Q value to improve the efficiency, this paper proposed a three-coil coupling structure.Theoretical analysis, simulation and experimental verification is given. The results showedthat the three-coil structure improves the efficiency in the long-distance transmission; itovercomes the limit of achieving optimal efficiency with specific load and achieves a efficienttransmission in a large load range.Taking the principle of low power consumption and complexity and small size, the designand verification of the layout of the in-vivo power harvesting circuit is given with the GlobalFoundry0.18um CMOS process. Flow-chipi test results show that the power-management module achieves an output voltage of1.850V in the load current of102.4mA with loadregulation rate of2%and linear adjustment rate of0.9%. The quiescent current is68.43uAand the power supply rejection ratio is less than-80dB at DC and less than-35dB at1MHz.Finally, combing PWM and LSK modulation, the paper proposed a feedback controltechnology. Experimental results show that the feedback can effectively control thetransmission of power, which improves the safety of the system, and increase the efficiency ofnear-field transmission especially increasing the efficiency by5.7times with the distanceunder20mm.