Sharif Digital Repository

The need to supply energy of low voltage electronic circuits such as sensors and wireless systems has attracted many researchers in recent years. As a solution to this problem, the energy needed for electronic devices can be obtained from the surrounding environment. An important part of energy harvesters are the systems that use vibrating energy of mechanical devices known as vibration power generators. Most linear vibration generators are systems that operate in resonance mode. As the frequency of the environment moves away from the natural frequency of the generator, the amount of converted energy decreases significantly. For this reason, some solutions are needed to solve this problem. ... 

In recent years, with the continuous growth and development of wireless communication systems, the demand for the use of radio spectrum has increased significantly, which has led to problems such as a shortage of spectrum. An effective solution to the spectrum shortage problem is to use cognitive radio. One of the main functions of cognitive radio networks is spectrum sensing and our focus in this study is to examine machine learning and deep learning methods to improve cooperative spectrum sensing. Since channel and noise parameters are not accurate in telecommunication systems, we need to use a method to estimate these parameters. In this regard, the structure of Bayesian with neural... 

Harvesting energy by magnetic shape memory alloy has many advantages against other various methods which harvested from environmental vibrations and has been considered due to high long longevity, large strain amplitude and good performance in low frequencies. These materials can display up to % recoverable strain in response to the application of a magnetic field or compressive mechanical stress. Microstructure of these materials changes under applying mechanical loading and/or magnetic field which cause magnetic vector rotating in magnetic domain. Change in magnetization of these materials, lead to harvesting energy by considering Faraday's law of induction. The model of this... 

Power harvesters are used to generate energy for electronic devices. These electrical energy generators consist of three main parts: energy source, power electronic converter and energy storage. In order to minimize some of the weaknesses of these devices, including low power density and low reliability, the hybrid power harvesting method can be utilized. In this thesis, we design and build a hybrid energy harvester considering the advantages of simultaneous usage of solar and thermal energies for a wearable sensor, focusing on "efficiency enhancement" and "availability improvement". In the designed device, both solar and thermal energy harvesting units operate independently. In the solar... 

Energy consumption is considered as one of the key constraints in the design of Embedded Systems. Exploiting abundant ambient energy offers a practical solution for designing embedded systems. In this regard, emerging trends are surging towards replacing battery-powered embedded systems in various different applications such as wearable systems, Internet of Things, and pervasive computing. Also, with the development and ommercialization of emerging Non-volatile memory technologies,the potential to reduce the static energy consumption and the ability to retain data in the absence of input energy, has become practically feasible for Embedded Systems. Consequently, recent researches have... 

Harvesting energy from renewable sources in nature, such as wind energy, solar energy, water energy and vibrations has always attracted researchers. There exist different ways to harvest energy from environmental vibrations. In this thesis, energy harvesting via Magnetic Shape Memory Alloys (MSMAs) has been taken into account due to important advantages of these alloys, such as their long fatigue life and good performance at high amplitudes and low frequencies.In this system, applying strain on alloy changes the magnetization and this change generates voltage in the pick-up coil around the MSMA. On the other hand, since the strain-magnetization relation is nonlinear and hysteresis,... 

Fabrication of various microelectromechanical sensors and actuators with low levels of energy consumption on one hand and the recent advances of microelectronic circuits technology leading to vast reduction in size and power consumption of CMOS circuitry on the other hand, have proposed the idea of developing MEMS-based environmental energy harvesting devices to provide their required power. These energy harvesters are an appropriate alternative for former heavy batteries of limited lifetime and can be utilized as a sustainable energy source for small intelligent systems. In the present research, the behavior of MEMS piezoelectric vibrational energy harvesters in nonlinear regime considering... 

In the last decade, harvesting energy from renewable phenomena in nature has attracted the attention of many researchers and turned it into a hot research focus. Wind flow around the world is an endless, repeatable and available source of energy. Therefore, harvesting wind energy disrupts the damaging cycle of fossil fuels to nature and fades over time. Therefore, in order to convert the mechanical green energy in the wind into electricity, mechanisms based on aeroelastic instabilities have attracted the attention of researchers. In this research, it is intended to design and build a test platform that is a suitable platform for research and testing on the aeroelastic instability of... 

Energy harvesting systems have been recently considered as an alternative to battery- operated systems, especially when the usage of battery-based systems is limited or the process of charging the batteries becomes infeasible. As one of the most important marketing factors for IoT devices, these systems are expected to reach around 100 billion objects in the near future.On the other hand, the emergence of nonvolatile memories due to useful features such as high density and low leakage energy has received much attention that allows the system designer to store the CPU state while the system’s input power is lost. Moreover, system parameters such as capacitance size, frequency, and power... 

During the last decades, the exponential population growth as well as the adverse impacts of climate change have brought about serious challenges in supplying freshwater demands. In this regard, buildings account for a considerable portion of freshwater withdrawal. Accordingly, urgent measures should be taken to tackle this crisis. Rainwater harvesting (RWH), Greywater recycling (GWR), and Hybrid rainwater greywater (HRG) systems are considered efficient substitute resources that are able to reduce the consumption of water supplied by centralized networks in buildings. Nonetheless, there is a vital need for the financial and technical assessment of these systems. Additionally, multiple... 

Energy Harvesting is one of the techniques which can be utilized in Green Communications and increase the wireless networks lifetime. In an EH system, each resource is supplied with the energy harvested from the environment. When we confront with a situation that the users of one channel want to increase their rates and this action negatively affects the other user’s rates, the user’s cooperation problem for obtaining a fair rate will be created. In this study, at first we consider a Multiple Access Channel and we assume that the energy resources of transmitters are harvested according to a known probability. In addition, we assume that the transmitters do not know the instantaneous amount... 

Magnetic shape memory alloys (MSMAs) are a new class of smart materials which exhibit properties such as large reversible strains and high performance frequencies. These unique properties, offer magnetic shape memory alloys as an option in applications such as actuators, sensors and energy harvesters. In this thesis, the equations of magnetic shape memory alloys by considering nonlinear terms of Von karaman in strain-displacement relations, is expanded by using the theory of thin plates in two dimensions which can be used for plate equations with any boundary conditions by applying elastic boundary. In order to verify the obtained model, the equations of motions of magnetic shape memory... 

Considering energy efficiency ways a key role in designing future wireless networks( 5G mobile networks). Moreover Spectrum efficiency is another critical issues in designing wireless networks. Cognitive radios can improve the spectrum efficiency. On the other hand, radio frequency (RF) energy harvesting has emerged as a promising technique to supply energy for wireless networks and thereby increase their energy efficiency. In this thesis, we propose a new technique for the RF-powered CRNs.To this end,We consider a cognitive radio network comprised of a primary user and a secondary user. The primary user, uses a typical frequency band for transmit data in a time slot basis and both the... 

Wireless Sensor Networks (WSN) are wildly utilized in surveillance and controling applications, and because of their remote and standalone operation, lifetime and reliability of a typical WSN are two main concerns in these networks. One of the reliability threatening issues in a WSN is residual accessible energy for each node. Nowadays, energy harvesting systems are used in WSN nodes to catch environmental energy, and reduce the energy limitation. However, because of inherent uncertainty of energy harvesting systems, the networks that operate using environmental energy have new reliability issues. Different rate of energy harvesting, according to environmental conditions, is one of the most... 

Providing energy for small but out-of-access devices has led industries to harvest energy from the environment, especially environmental vibrations. The problem of vibrational energy harvesters with linear behavior, is their small bandwidth and consequently, their high sensitivity to frequency content and excitation spectra. Particularly in random excitations with vibrational energy spreading over a frequency range, linear harvesters do not seem appropriate. Under these conditions, harvesters with nonlinear stiffness are possible substitutes for linear systems. However, prediction and estimation of the behavior of systems with nonlinear stiffness under random excitation has been complicated,... 

Energy harvesting from wasted environmental energy to power low-power electronic devices has emerged as an enabling technology for wireless applications in the past decade. The purpose of this technology is to provide remote power sources and/or recharge storage devices such as batteries and capacitors. This concept has environmental implications in reducing chemical waste produced by replacing batteries and potential monetary benefits that also reduce maintenance costs.Energy harvesting (EH) from untapped natural energy sources is common nowadays due to the increasing demand for electricity. Sources have the potential to generate micro to milliwatt power, depending on environmental... 

One of the unusual features of some ceramic materials is the piezoelectric effect. The piezoelectric effect results from the linear electromechanical interaction between the mechanical and electrical states in crystalline materials with no inversion symmetry. The piezoelectric effect is a reversible process: materials exhibiting the piezoelectric effect (the internal generation of electrical charge resulting from an applied mechanical force) also exhibit the reverse piezoelectric effect, the internal generation of a mechanical strain resulting from an applied electrical field. In the last decades, many research has been done on the use of these materials for the self-charging low-power... 

Energy crisis has always been a crucial issue faced by the development of wireless communication techniques. As a more energy-efficient network architecture, green communications and networks (GCNs) have recently attracted significant attention from academia and industry. In order to enable the technical and economical GCNs, several emerging techniques have been proposed including energy-efficient and energy harvesting techniques. Although these emerging techniques have drawn considerable attention and have been studied recently, there are still many open theoretical and practical problems to be addressed. Energy harvesting (EH) is a key technology to achieve the objectives of GCNs. This... 

In this dissertation, we focus on two types of EH cooperative networks. In the first type, the source and relay nodes access a shared channel according to a random access protocol. Also, they harvest energy from non-RF environmental resources. The relay node has data and energy buffers to store the packets of the source and the harvested energy, respectively. Our main goal is to find the optimal relaying protocol at the relay node. In this regard, the first type of the EH cooperative networks are investigated in two different scenarios. In the first one, the MAC channels of the nodes are independent of the applied policy at the relay node, and thus the throughput of the network is fixed.... 

Heat sources with temperatures less than 100 °C are available in various processes in the form of waste heat and from renewable sources such as solar energy. One of the methods of gaining benefit from these ubiquitous and abundant heat sources is using thermal harvesters that convert low-temperature heat into electrical energy without the need for the power grid. Portable harvesters can be a reliable and low-cost option for providing stable energy for low-power electronic devices such as wireless sensors. Many studies have been conducted at the global level to design and develop efficient low-temperature heat harvesting mechanisms. However, each of them is associated with fundamental...