Fundamentals of Nanoscale Intra-body Electromagnetic Communications at Terahertz and Optical Frequencies
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Nanotechnology is enabling the development of biocompatible miniature implants that can detect events at the nanoscale with unprecedented accuracy. In-vivo Wireless Nanosensor Networks (iWNSNs), i.e., networks of implantable nan-biosensors/actuators, will enable a plethora of unprecedented applications such as the early diagnosis of a myriad of diseases at (sub) cellular level, ranging from cardiovascular disorders to different types of cancer; sensing and controlling biological processes (e.g., stem cell regulation) at single cell resolution through optogenetics; and the evolution of human-computer interfaces that translate human thoughts to direct action.To date, it is still not clear how the in-vivo nanomachines will communicate thorough biological tissues. Nanonetworks of nano-biosensors/actuators are not just a miniaturization of classical wireless networks. In particular, the very small size of the nanodevices would impose very peculiar communication constraints. First of all, the miniaturization of classical antennas would enforce the use of very high radiation frequencies which results in a major increase of the propagation loss. Also, considering the effect of phenomena such as scattering and absorption of individual cells and entities -with sizes comparable to the wavelength at such high frequencies-, is inevitable. Moreover, the expectedly very limited power and energy storing units of nanodevices would tremendously impact the communication distance and life-time of the nano-implants. Besides the communication challenges, the photo-thermal effects of electromagnetic (EM) radiation on biological tissues is another major and critical concern to be addressed. With all these challenges in the realization of this novel networking paradigm, the development of innovative solutions and the revision of well-established concepts in communication and network theory are necessary.The objective of this thesis is to establish the foundations of high frequency electromagnetic (THz) and optical wireless communications at the nanoscale with specific application in intra-body communications. First, a novel intra-body channel model is developed by considering the effect of single biological cells on the EM wave radiation. In light of developed channel model, the effect of the geometry and size of the cells on the communication channel is investigated extensively by analyzing the impulse response in the time and frequency domains. The third contribution in this thesis is the study of the photo-thermal effect of the EM radiation in living tissues. Fourth, a biocompatible modulation scheme and physical layer design is proposed and analyzed. Finally, the challenges in the link layer design of intra-body nanonetworks is studied by taking into account the device and communication interdependencies.