Integrating Li-Fi Wireless Communication and Energy Harvesting Wireless Sensor for Next Generation Building Management

Wireless sensors have been increasingly utilized in the design of next generation high performance buildings. When deploying wireless sensors, energy supply and data communication are the major concerns. Although energy harvest wireless sensors could automatically feed themselves by harvesting ambient energy, the presence of reliable energy sources to support dependable wireless transmission is a great challenge. The emerging Li-Fi technology is promising to fundamentally solve this problem. Li-Fi stands for Light-Fidelity, which is a new kind of wireless communication systems using light as a medium instead of traditional radio-frequency electromagnetic radiation. Li-Fi technology provides harvested energy to power wireless sensors with a unique advantage of power generation from the lighting system being controlled. The combination of Li-Fi and energy harvesting wireless sensor technologies could enable attractive features and bring in great benefits in the design of next generation high performance buildings because: (i) energy harvest sensors do not face the short-of-energy problem; (ii) Li-Fi enables much higher transmission speed compared to the existing RF electromagnetic technologies, thus, energy harvest sensors could easily deliver environmental parameters quickly for control purposes; (iii) energy harvest sensors could assist the building management team to understand the coverage area of the lighting system; (iv) the communication of sensor aggregated information can be naturally encrypted due to the combination of both technologies

Effects of Deposition Process on Poly-Si Microscale Energy Harvesting Systems: A Simulation Study

In this paper, the feasibility of a low-temperature polysilicon (LTPS) microscale energy harvester for a wireless sensor node is investigated. For that purpose, two device-level models for the LTPS solar cell and thin-film transistors are proposed and employed in system-level evaluation of an energy harvesting system. The results of our analysis indicate that: 1) the maximum power operating point for the solar cell is different when connected to a lossy power converter; 2) increasing the average grain size of the LTPS film can reduce the circuit area by 20 times, while increasing the output power by 6%; and 3) the proposed bottom–up approach enables the designers to identify system bottlenecks and improve the performance accordingly

Reconfigurable Charge Pump Circuit with Variable Pumping Frequency Scheme for Harvesting Solar Energy under Various Sunlight Intensities

We propose variable pumping frequency (VPF) scheme which is merged with the previous reconfigurable charge pump (RCP) circuit that can change its architecture according to a given sunlight condition. Here, merging the VPF scheme with the architecture reconfiguration can improve percentage output currents better by 21.4% and 22.4% than RCP circuit with the fixed pumping frequencies of 7 MHz and 15 MHz, respectively. Comparing the VPF scheme with real maximum power points (MPP), the VPF can deliver 91.9% of the maximum amount of output current to the load on average. In terms of the power and area overheads, the VPF scheme proposed in this paper consumes the power by 0.4% of the total power consumption and occupies the layout area by 1.61% of the total layout area

Efficient Archietecture for Effective Utilization of Harvested Power in Microscale Energy Harvesting

Recent developments in combining sensors, microprocessors, and radio frequency (RF) communications holds the potential to revolutionize the way we monitor and maintain critical systems. In the future, literally billions of wireless sensors may become deeply embedded within machines, structures, and the environment. Sensed information will be automatically collected, compressed, and forwarded for condition based maintenance. Energy Harvesting comprises a promising solution to one of the key problems faced by battery-powered Wireless Sensor Networks, namely the limited nature of the energy supply (finite battery capacity). By harvesting energy from the surrounding environment, the sensors can have a continuous lifetime without any needs for battery recharge or replacement

Sub 1V Charge Pump based Micro Scale Energy Harvesting for Low Power Application

Harvesting energy from our environment is a promising solution to provide power to wireless sensor network, wearable devices and biomedical implantation. Now a days, usage of battery power system has disappeared because of replacement issues, installation costs every periodic year and the possibility of health hazard in the case of biomedical implants. Considering these issues, energy harvesting proves to be the most feasible and convenient option in the case of wearable devices and biomedical implantation. Hence, we have focused on indoor single solar cell energy harvesting to power ultra-low power load. The tree topology DC-DC converter is used for power management circuit with optimized efficiency. High efficiency is achieved by using ZVT MOSCAP. The power management circuit includes DC-DC converter and feed forward maximum power point tracking algorithm to transfer maximum power from the single solar cell. The system has ultra-low power battery protection and input condition sensor circuit to extend the life of the battery by protecting from overcharging and over discharging. Also, cold start up circuit is used to run the system when battery voltage drains out to zero. The objective of this system to make complete energy harvester unit is to drive wide range of ultra-low power applications. We have driven the ZigBee receiver to validate our system and the system works effectively

From Process to Circuits: New Perspectives to Solar Cell Design

As the demand for cheap and clean energy sources increased over the last two decades, solar cells have proven to be strong candidates against the fossil fuels. From an economic perspective, in order to replace fossil fuels, it is required to reduce the cost of solar cells. This can be achieved by depositing thinner absorber layers under low process temperatures, yet these efforts lead to poorer efficiency values. Addressing such trade-offs and providing solutions to this problem have been the main objectives of this study

Voltage and capacitance sensing using time comparison

PhD ThesisWith the rapid advancement of electronic and mechanical system miniaturisation, new application types such as portable systems, internet of things (IoT) and wireless sensor networks (WSNs) have become promising areas of growth for industry. In these areas, the limits on battery life have opened opportunities for energy harvesting to become a commonplace choice as the system power source, which brings its own problems. One of these problems is that energy harvesting is in general a much more variable energy source than batteries and mains power supply, because of the unpredictable and intermittent nature of the external energy environment [1]. This implies that both energy harvesters and the loads they support require significantly more control, tuning and management than if the energy was supplied by traditional means. On the other hand, sensing is also an important aspect for such systems as many of these systems are sensors used to monitor physical parameters in the environment. Another reason is that the control, tuning and management of energy harvesting requires the support of energy/power sensing. It is therefore inevitable that sensing methods need to be developed targeting an environment where energy supply is volatile. However, sensing under a variable energy supply faces numerous problems. One such problem is the energy consumption of the sensing itself. In this regard, the capacitive sensor is widely used for sensing a physical parameter, such as pressure, position, and humidity, as it is suitable for low-power applications with limited energy budgets [2–4]. Another problem faced by sensing under energy supply variability is the difficulty of maintaining stable voltage and/or current references. This thesis is motivated by these issues. In this thesis, a new sensing method is developed based on time domain techniques, which will be shown to be 1) suitable for capacitive sensing of environmental physical parameters, 2) suitable for sensing voltage, from which power and energy information can be derived, supporting energy harvesting management uses, and 3) robust to voltage and power volatility, making sensors derived from this method useful for miniaturised and energy autonomous systems. At the centre of this work is a novel reference-free voltage level-crossing sensor, realised through time comparison techniques. By working in the time domain, it avoids the need for voltage or current references. Two more sophisticated sensors are then developed around this level-crossing sensing engine. The first is a voltage monitor which is capable of sensing the crossing of multiple predefined voltage boundaries within a range, targeting energy harvesting system management uses. The second is a capacitance-to-digital converter which senses and converts the value of a target capacitance to digital value. This could be used to support the monitoring of physical vi parameters in the environment including pressure, temperature, moisture, etc. as these might be made to directly affect the values of capacitances. This thesis describes detailed design theory and reasoning, implementation, and validation of the presented sensors. Circuits are implemented in very-large-scale integration and investigated in the Cadence Analog Design Environment. In addition to analogue simulations, experiments were also conducted on a fabricated chip. Data collected from these simulation and physical experiments show that the time-domain method developed in this work has quantitative and qualitative advantages over existing designs

GESTÃO DE ENERGIA EM REDES DE SENSORES SEM FIOS

A energia é um recurso limitado em redes de sensores sem fios, pelo que uma gestão eficiente da energia disponível é crucial para aumentar o seu tempo de vida operacional. Assim, a gestão de energia em redes de sensores sem fios tem estado focada no desenvolvimento de mecanismos de activação sincronizada de nós “adormecidos” e de tecnologias de captação de energia do meio envolvente. O objectivo deste trabalho consistiu em explorar estas duas abordagens para criar condições de disponibilidade contínua de energia nos nós de redes sem fios: em primeiro lugar, explorando tecnologias de captação de energia de importantes fontes no meio envolvente: luz solar, diferenciais térmicos e campos electromagnéticos, e, também, cultivando métodos e tecnologias de despertar por radiofrequência (wake-up radio) como forma mais adequada de gerir as oportunidades de operação dos nós de uma rede, poupando energia no tempo restante. São apresentados estudos e soluções realizadas no âmbito industrial, bem como os métodos e resultados da análise realizada para a sua validação. Assim, conseguiu-se: Uma solução baseada na captação de energia solar, com uma eficiência superior a 70% (desde a saída do painel fotovoltaico), capaz de suportar sensores e repetidores numa rede, acumulando energia correspondente a autonomias de 16 e 40 horas, respectivamente, numa aplicação de diagnóstico de seccionadores de alta-tensão em subestações de distribuição de electricidade; Uma solução de captação de energia de diferenciais térmicos, para suportar sensores de diagnóstico do estado de funcionamento de purgadores, em linhas industriais de distribuição de vapor, permitindo uma disponibilidade permanente de energia, mesmo para diferenças de temperatura de uns meros 20 °C; Uma solução de captação de energia de campos magnéticos gerados por correntes eléctricas intensas, para aplicação em sensores sem fios a utilizar em redes de distribuição de electricidade, que, nas circunstâncias dos trabalhos propostos, amplamente demonstrou a viabilidade do conceito e foi industrialmente incorporado numa unidade sem fios para a monitorização de correntes eléctricas e o diagnóstico do estado de fusíveis em postos de transformação; Duas soluções de despertar por radiofrequência, sem prejuízo da latência de comunicação: (i) despertar colectivo, sincronizado para todos os nós da rede no volume de alcance-rádio do emissor, que se revelou eficaz até aos 37 metros, no interior, consumindo 7 μA e (ii) despertar selectivo, individualizando o nó a activar, com um alcance de 33 metros, igualmente no interior, consumindo 5 μA — em campo aberto, o alcance foi de 10 metros. Em suma: as soluções industriais realizadas no âmbito deste trabalho demonstram a viabilidade de suportar a alimentação em potência de nós de redes sem fios operando em diferentes regimes e dependendo de diversas fontes de energia, em natureza e potência disponível, que, no nosso entender constitui condição necessária ao sucesso industrial das redes de objectos sem fios