(A) random number generator with a chaotic wind-driven triboelectric energy harvester

Abstract

Wind flow induces unpredictable chaotic motion for a thin flip-flop membrane intercalated in between two parallel electrodes. This structure is utilized as a random number generator (RNG) for cryptographic applications due to its inherent turbulent nature. Wind is a clean, ubiquitous and unexhausted energy source of semi-permanent energy. The RNG is also served as a triboelectric nanogenerator (TENG) due to energy harvesting by tribo-electrification. Thus, it harnesses structural duality to generate random numbers and electrical energy. In this study, a true random number generator with the aid of the wind-driven TENG is demonstrated. Without any post-processing algorithm, the electrical signals induced from the wind-based TENG, have randomness that is unpredictable, unreproducible and statistically unbiased. Here, we use the NIST SP 800-22 B statistical test to evaluate random properties. The generated random bits are applied to a cryptographic key and nonce, abbreviated from ‘number only used once’. The proposed device has a significant merit to generate both power and true random numbers in a single device. It thus helps construct a self-powered RNG and secure communication for the internet of things. It can also be used for a smart grid protocol in power management. In the first part of the chapter 2, the operation of energy harvesting – random number generator (EH-RNG) module is proposed. The EH-RNG module generates both power and random number for two in one device. When the energy harvesting mode is activated, analog output signal of current and voltage is transformed to electrical power. When the RNG mode is enabled, analog output signal of voltage is converted to 8-bit digital signals by a quantization and sampling process. In the second part of the chapter 2, the application of EH-RNG module is described. For a smart grid system and Internet of Things (IoT) system, a TENG based RNG can be used as a power generator and random number generator simultaneously. In other words, the proposed device contributes to generating power and to supporting cryptographic communications in a single device. In addition to this, in-flight system such as unmanned aerial vehicles and aircraft is one of the promising candidates for the proposed two-in-one W-TENG system. The in-flight system is important to generate high entropy random number due to operating conditions which should perform a long-distance telecommunication. In the chapter 3, the quantitative analysis for power generation is conducted. In the first part of the chapter 3, the method to fabricate W-TENG and the principle for power generation is described. In the second part of the chapter 3, the amount of power generation is experimentally demonstrated according to electrical load. In the chapter 4, the quantitative analysis for random number generation is conducted. First, the method to generate random numbers by W-TENG is described. To figure out origin for randomness theoretically, Monte-Carlo simulation is performed. As a result, variations in terms of amplitude and cycling time attribute the random characteristics by W-TENG. The experimental pass rate for randomness is demonstrated by NIST SP800-22B statistical test. The chapter 5 contains methods to enhance entropy of random numbers. The randomness of the generated random numbers from the W-TENG is improved by a structural change from a quadruple-clamped flip-flop membrane to a double clamped flip-flop membrane. In power generation point of view, the quadruple-clamped W-TENG is preferred. In randomness point of view, the double-clamped W-TENG is attractive. Thus, an end user can customize the quantity of power generation and the quality of random numbers according to a target application. The chapter 6 experimentally demonstrates that the proposed device has robustness against environmental effects such as humidity and temperature. In addition to this, geometric effects are investigated by rectangular shaped effect, the inlet direction effect, and the tilted PTFE film effect. The chapter 7 demonstrates the analysis of unpredictability. As investigating the unpredictability according bit conditions, we demonstrate the mathematical rationale to apply the random number generator.