Energy-neutral event monitoring for internet of nano things

Advancements in nanotechnology promise new capabilities for the Internet of Things (IoT) to monitor extremely fine-grained events with sensors as small as up to a hundred nanometers. Researchers predict that such tiny sensors can be connected to the Internet using graphene-based nano-antenna radiating in the terahertz band, giving rise to the so called Internet of Nano-Things (IoNT). Powering such wireless communications with nanoscale energy supply, however, is a major challenge to overcome. Since in many application domains, different types of events discharge different amounts of energy to the environment, we propose an energy-neutral event monitoring framework, called eNEUTRAL IoNT, that allows the sensors to transmit event information using only the amount of energy harvested from the events. We design and analyze two implementation methods for this framework. The first method uses a single pulse containing the entire energy harvested from the event but manipulates its pulse width (time duration) to create unique pulse amplitude for a given combination of event type and its location. In the second option, the harvested event energy is divided into two pulses so that the energy of the first pulse uniquely defines a location and the second pulse uses the remaining energy to identify event types. To minimize classification error at the receiver, we optimize pulse durations in the single-pulse option and pulse energies in the dual-pulse option. Feasibility of eNEUTRAL IoNT is demonstrated using extensive numerical experiments involving terahertz channels. We find that the dual-pulse approach significantly outperforms the single-pulse approach achieving 99\% accuracy for detecting both location and event type in 10-node network monitoring two different event types for a radius of 28 mm. As nanoscale energy harvesters and transmitters are still not available to realize operational event monitoring nodes, we, therefore, evaluate and design a key component of the IoNT system, namely pulse generator, using COMSOL Multiphysics. We first surveyed the literature of different approaches for pulse generation that generate Surface Plasmon Polaritons (SPPs) which lead to femtosecond long pulses in graphene. Based on our analysis, we found that most of the existing configurations require complex structures including a prism, periodic slits and special circuits which may be difficult to implement in severely resource constraint nodes. Using COMSOL Multiphysics, we show that pulses in the terahertz band can be generated using the near-field method by which the matching condition for excitation of SPPs can be easily satisfied. The performance of the proposed near-field excitation method in the terahertz band is studied via numerical simulations. This includes the choice of the source, its phase angle, the chemical potential, and frequency. The proposed model can be a good candidate for a low-complexity realization of a THz pulse generator in tiny IoNT nodes