Wireless Power Transfer Antenna Alignment Using Intermodulation for Two-Tone Powered Implantable Medical Devices

Wireless power transfer (WPT) to the implantable medical devices (IMDs) often suffers from antenna radiation direction and polarization misalignments, which degrades the wireless power link efficiency. Although increasing the incident power density is able to solve the power hunger of IMDs, it poses safety issues to the human tissue. In this paper, an antenna alignment method using intermodulation is proposed to address WPT antenna misalignment in a safe way. Two-tone (2T) waveform excitation is employed to enhance the rectification as well as to generate intermodulation. The intermodulation power is fed back via a magnetic resonant coupling link. Due to the monotonic relation between the intermodulation power and the degree of antenna misalignments, the receiving antenna (in body) can be aligned with the transmitting one (out body). Such a scheme has the advantages of less harm to human tissue and less interference between the 2T waveform excitation and the magnetic resonant coupling link. The whole system is theoretically analyzed and experimentally validated.