Harmonic-based wireless pressure sensor and wireless power transfer system for implantable wireless sensor networks

An implantable wireless sensor network is a key technology to enable smart healthcare in the future. As the sensor network might include multiple implanted devices for functions such as disease-monitoring and rehabilitation, miniature implementation of the devices and effective wireless power transfer to the devices will be important issues for the implantable wireless sensor network. In this dissertation, a passive harmonic-based pressure sensor implanted inside a mouse eye is presented as a representative example of smallest implantable devices for which power budget is not enough to turn on active devices. Methods to fabricate a MEMS capacitive pressure sensor on a biocompatible and flexible polymer substrate are presented. Then, a MEMS pressure sensor is integrated with a diode and a Nitinol antenna on a Parylene substrate to implement a harmonic-based implantable pressure sensor. A pressure sensing exploiting the harmonic-based IOP sensor implanted inside a mouse eye shows that the compatibility of the polymer-based ultra-miniature sensor with implantation. However, more accurate monitoring using active implanted devices is required for most of biomedical applications. Therefore, as a feasible solution for effective wireless power transfer to active implanted components, a mixed system of RF and inductive magnetic resonance coupling (MRC) using diode-generated harmonic is proposed. In the system, the design methodologies of the MRC based on bandpass filter (BPF) synthesis enables effective power transfer to the complex impedance of a rectifier, compensation for the efficiency drop by tolerance in placement of coils, and effective power distribution to multiple implanted devices. Additionally, an interface module using harmonic generated by a diode enables the integration of the RF radiation and the magnetic resonance coupling (MRC). The system is useful for a possible application such as neural interface in brain. Finally, polymer-based 3D packaging techniques can be utilized for miniature implementation of the proposed system in an implantable. If the techniques explored in this thesis are tied together, a selective power transfer system for more effective power transfer and the implementation of power transfer system in an implantable size will be feasible