Sharif Digital Repository

As the applications of wireless sensor networks are expanding at an increasing rate, design of these networks so that they conform to the requirements of a specific application is considered to be a major challenge. Regarding to the specific application, network designers consider various suitable parameters to improve and then to enhance the efficiency of the network. Parameters included are such as area coverage, lifetime, reliability and etc which can significantly improve with the precise placement of nodes. Node localization problem in wireless sensor networks aiming at improvement of the performance parameters has been solved by different methods. In this thesis, in order to solve this... 

Injecting several droplets with a known size distribution function in the hot gas environment makes droplets smaller because of evaporation or reaction. Droplets lifetime specification is important in vapor-liquid interactive processes such as chemical or process industries. In previous works, different approximate semi-empirical methods are developed to specify droplets lifetime without considering their size distribution. In this work, governing equations is studiedconsidering a size distribution function for droplets. There is not any analytical method for solving this set of equations, so numerical methods using CFD packages such as Fluent, are applicable in these cases. In this study,... 

The use of electric vehicles is increasing day by day due to the reduction of pollution, reduction of fuel costs, higher efficiency, etc. Increasing the distance traveled in each charging period of the electric vehicle battery pack and increasing the lifetime of the battery cells are the most important challenges facing the electric vehicle industry. In electric vehicles, Li-Ion battery cells are used to store energy, so to improve these challenges, we first need to carefully examine the behavior of these cells with the various conditions that occur during operation to design other circuits such as balancing circuits, Battery management system, etc. In this thesis, first a model is proposed... 

Wireless Sensor Networks (WSNs) consist of sensor nodes that are connected to each other and are widely used in many applications to acquire and process information. WSN nodes are battery powered, therefore energy management is a key factor for long live network. Node radio transceiver unit uses the most part of energy resource of the node and as a result limits the network lifetime. One way to prolong lifetime of network is to utilize routing protocols to manage energy consumption. To have an energy efficient protocol, we can apply cluster organization on the network, where sensor nodes are partitioned into groups called cluster. Then, the whole cluster data is sent through Cluster Head... 

LED Drivers with near 1 power factor, Because of using electrolytic capacitors (to become flicker-free) have lifetime drawbacks. This research will focus on solutions to use magnetic energy storage instead of electrolytic capacitors (used for energy storage) to solve lifetime drawbacks and decrease output light flicker. Calculations show that magnetic energy density using iron powder cores are lower than electrolytic capacitors, also a little lower than ceramic capacitors, but obviously higher than film capacitors. After calculations, conventional isolated and non-isolated LED drivers will be reviewed and new non-isolated off-line 230v with 10w output power LED driver with magnetic energy... 

Wireless Sensor Networks (WSNs) consist of few hundred to thousand sensor nodes that are usually deployedrandomly in a sensing field. The duty of sensor nodes is to sense the environment for data collection and sending these data to a sink node for future processes. Sensor nodes are equipped with a non-rechargeable battery. Hence, network lifetime is an important issue in WSNs. When a static sink node is used in a WSN, sensor nodes that are located in the neighborhood of the sink node willdrain out of energy faster than other sensor nodes which are farther away from the sink node, because traffic load is heavier on sensor nodes which are closer to the sink node. This problem is named “the... 

The operating conditions of the battery in renewable energy systems affect its electrochemical behavior and degradation process. Recent research mainly estimates battery lifetime through conventional methods such as counting the number of equivalent battery life cycles or based on simple experimental models that may lead to optimistic predictions in battery service period. In this study, a reduced-order thermoelectrochemical-aging battery model is developed for the application of renewable energy systems and the battery degradation analysis is investigated by this model. The proposed microscopic model evaluates the effect of battery operating conditions such as state of charge, current and... 

High voltage power supplies have a wide range of applications, and due to their high cost, it is essential to monitor their condition to predict potential failures and prevent significant losses. The most common cause of power supply failure is the wear and tear of its components. However, these components can be replaced before they wear out completely to prevent the failure of the power supply and, consequently, avoid damaging the load. Estimating the lifetime of power supplies is crucial because it allows for scheduled maintenance and helps prevent significant problems in power supplies. By estimating the lifespan of a power supply, one can anticipate when it may fail, allowing for the... 

Embedded systems usually have severe limitations on power consumption. One of the reasons is that many embedded systems are battery operated. On the other hand, the battery is a non-linear source of energy, where the lifetime depends on how the system drains power from the battery, or in other words, the battery lifetime is dependent on battery discharge current curve. The nonlinear behavior of batteries is due to their inherent characteristics, where the rate capacity and the recovery effects are believed as the two most well-known and important factors. Also, embedded systems are usually fanless with limited cooling equipment, therefore temperature management is a prominent issue in these... 

In this thesis, our aim was to assess the resource allocation problem in wireless sensor netowroks and to optimize network utility and lifetime. To achieve these aims, it is nesseccary to solve resource allocation problem through optimization methods. Since the central methods need a central node to manage resource allocation, they can not be implemented in sensor networks because the nodes neighbors to this central node drain energy very quickly. Also, since central methods require transmission of all information about network topology to this central node, every change in network topology result in transmission of new network topology informations and therefore, overload for frequent... 

Wireless sensor networks (WSNs) can be used in a variety of applications. The prime shortcoming of these networks is their energy constraint. The main energy consumer in a sensor node is its radio transmitter. Therefore data prediction is one of the most effective methods to reduce the data transmission rate. By data prediction, a large amount of energy is saved; which results in the longevity of the network life. Environmental variations almost have similar effects on different sensor sources in a sensor device. So, considering the correlation between different sources reduces the noise impact and increases data prediction accuracy. In this thesis, we use temporal and multisource... 

Most of the current routing protocols in the WMSNs only consider the inter-path interference and not necessarily intra-path interference factor which is considered as one of the main causes of energy consumption in these networks. Among those protocols that consider this factor, none of them has ever come up with an algorithm capable of performing the routing without the need to use either the special hardware in the nodes (referred to as the GPS or directional antennas) or with the unrealistic assumption that the interference range is equal to the transmission range. The previously mentioned factors are critical in the sense that the former assumption results in more expensive sensor nodes... 

Wireless sensor networks consist of many small sensor nodes which suffer from some limitations like energy level, band width, processing ability and memory; therefore, decreasing energy consumption, increasing network lifetime and scalability are the main challenges in the area of routing in wireless sensor networks. In the field of routing in sensor networks, many algorithms have been suggested, one group of which is clusterbased hierarchical algorithms. The main goals of such algorithms are reducing energy consumption, distributing consumed energy within whole network and increasing scalability of algorithm. There are some problems in most of cluster-based routing algorithms which cause... 

Nowadays Wireless Sensor Networks (WSNs) are found in a variety of applications such as environmental monitoring, military surveillance and medical systems. These applications interface with the real world environments and the delivery of data is subject to certain timing constraints. Most of the protocols being used in the WSNs do not satisfy real-time requirements and only deliver data in a best-effort fashion. However, real-time support in the WSNs remains an open research topic. This dissertation first studies real-time application and then real-time approaches in WSNs. Real-time applications are applications that require bounded service time. Normally in WSNs, communication delays are...