Intrabody communication for real-time monitoring of implanted medical devices based on piezoelectric micromachined ultrasonic transducers

Abstract

Nowadays when we think about medical devices and patient monitoring, we can easily imagine ourselves laying down in a hospital bed, wires coming out of everywhere, and being looked after by nurses and physicians. Scary and not that comfortable. For this reason, medical wearable devices are becoming more popular for at-home monitoring and transmitting data back to the hospital. Sometimes wearables are not enough, this is why Implantable Medical Devices (IMD)s are still required to monitor many vital signs (blood flow, insulin level, neurons reading etc.) and act upon these readings (nerve stimulation, heart defibrillation, insulin pumping etc.). In order to be minimally invasive, reduce the risk of infection and rejection from the body, and last a long time (avoiding any further surgery) the IMDs require robust wireless communication technology to communicate with the external world. In this work I am going to show how we can implement an ultrasonic wireless communication link based on Piezoelectric Micromachined Ultrasonic Transducers (pMUT) arrays. pMUT arrays can be integrated with existing IMDs, used for wireless power charging, and can enable communication links for receiving and transmitting data. Moreover, I will show the modeling and design of the pMUT arrays, followed by the fabrication process and the device's characterization for system level validation. At this point, the communication link is implemented with arrays implanted in a tissue phantom and the channel is characterized at several distances. During the second part of this manuscript, I will show novel techniques to improve the ultrasonic communication link such as duplexing matching networks for bandwidth definition and direct modulation for implantation depth increase and direct bitstream feeding. In the future I envision that the number of IMDs are going to increase, and therefore I developed a scanning protocol that will allow medical doctors to find all implanted devices. This is the equivalent of an "ultrasonic stethoscope". Given the small form-factor of the IMDs these will have little to no space for a battery, limiting the operation lifetime. For this reason, I developed an Ultrasonic Wakeup Receiver (UWuRx) based and on the direct modulation system and on a Micro Electro-Mechanical System (MEMS) switch which allows for near zero-power consumption in the idle state. This UWuRx enabled on-demand device usability and limited the idle power consumption, which leads to battery life extension. Finally, I will show the development of a novel class of pMUTs based on thin-film X-cut Lithium Niobate (LN) piezoelectric layer to increase the transmission bandwidth and increase the communication data-rate of an arbitrary communication scheme.--Author's abstract