Low-Cost Electronic Nanodevices for High-Frequency Applications
Date: 20 October 2014(ex)
A novel nanodevice, known as the self-switching diode (SSD), has recently shown promising properties as a room-temperature detector at terahertz frequencies. The SSD is a unipolar two-terminal device. It has a nonlinear current-voltage characteristic which resembles the behaviour of a conventional diode. The device therefore can be exploited as a rectifier. The planar structure of the SSD provides intrinsically low parasitic capacitance that enables signal rectification at higher speed than a standard vertical diode. It also allows the fabrication of a large number of SSDs in a single lithography step without the need for interconnection layers, which may introduce parasitic elements. Indeed, this is the key feature of the SSD that makes the whole fabrication process simpler, faster and at lower cost when compared with other conventional electronic nanodevices. Moreover, the SSD works very well with low-cost materials such as zinc oxide and organic thin films. This would be the center of my research with the aim of functioning SSDs at room temperature and at high speed using low-cost materials including graphene. The research will also explore the possible designs of novel planar diodes (other than SSD) that can be utilized as a high-speed rectifier. This will be performed using device simulation software such as ATLAS from Silvaco.
Mitigating Interference in a Heterogeneous Wireless Network using Channel Selection
With the extensive development of heterogeneous wireless communication technology, combined with the advances of data acquisition, emerges a new trend of networked acquisition systems. Among this range of wireless technology, Wireless Sensor Networks (WSNs) has attracted much interest and visibility due to its huge application space. One challenge using the WSN is the short range of the sensor nodes that increases the complexity of transporting the data to a central server. The integration with Wireless Mesh Networks (WMNs) expands the communication range and allows mobility of the device. Thus, WSN can be used for forming the underlying sensing and WMN supports the network infrastructure in pervasive computing environments. However, interference is a problem as these networks share the same 2.4GHz industrial, scientific and medical (ISM) unlicensed band. The impact of the interference on the IEEE 802.11g (WMN) using OFDM modulation and on IEEE 802.15.4 (WSN) using DSSS is investigated in this research. Results from a series of experiments on the AIT wireless mesh campus network under realistic load conditions are presented. Packet retransmission and packets drop rate were measured and based on this knowledge, a channel interference classification (CIC) method is presented to identify the interfering operating channel. The method introduced is based on a technique proposed by Chowdhury et. al. for channel selection based on reference power values. This work modifies the technique to account for differences on channel spectrum characteristic found in tests on the Mesh Campus Network. A channel selection algorithm was then developed for WSN to decide on the operating transmission channel that is not under interference, hence reducing packet losses in the network. This paper will be of interest to network operators and organisations where critical information retrieval over wide area networks is required.
Nowadays, wind energy is crucial for electricity companies as it is renewable and free resource. Malaysia has a good prospective in wind energy and have decided to opt for the wind energy to replace the fossil fuel which is non-renewable energy. Malaysia faces the four seasons such as southeast monsoon, northeast monsoon and two shorter periods of inter monsoon seasons. Hence, wind over in Malaysia is generally light with the speed less than 8 m/s.
The objective of this article is to analyse the performance of 300 Watts wind turbine to supply the energy for a power system. A wind turbine is instilled in front of Electrical Energy and Industrial Electronic System (EEIES) Research Cluster, Perlis. This small horizontal wind turbine manages to generate energy to charge the 600 Ah battery systems in the research lab and is pointed by a simple wind vane. Meanwhile, the maximum output voltage is 40V dc at the 5.54 m/s of wind speed.
Wind turbine is a rotating machine which converts the kinetic energy of wind into mechanical energy. When the wind flows past the turbine’s rotor blades, the blades turn and convert the wind energy into kinetic energy. This energy spins a rotor inside a generator and coverts into electrical energy. The more electrical energy generated the greater wind speed. Meanwhile, windmill is a machine that used mechanical energy. If mechanical energy is converted to electricity, the machine is called wind generator, wind turbine, wind power unit (WPU), wind energy converter (WEC), or aero generator. Furthermore, Horizontal-axis wind turbines (HAWT) consists of motor raft and electrical generator which is must be pointed into the wind. It comprises a gearbox which turns the slow rotation of the blades into the speedy rotation that is suitable to drive an electrical generator. The turbine is constantly pointed upwind of the tower as a tower produces turbulence behind it.
It is essential to note that wind resource evaluation is a critical element in projecting turbine performance. Generally, annual average wind speeds of 5 m/s are required for grid-connected applications. Meanwhile, annual average wind speeds of 3 to 4 m/s may be adequate for non-connected electrical and mechanical applications.
The authors also added that Wind Power Density is a useful way to evaluate the resource available at the potential site. The wind power density reveals how much energy is available at the side by a wind turbine.
Nevertheless, the wind power is fluctuated as it will calm one day and howling the next. One of the most important tools in working with the wind, whether designing it or utilizing it, is a firm understanding of what factors that influent the power in the wind. The wind power could be classifies into two type which are Rotor Swept Area and Weibull Distribution.
In order to collect the data, the researcher utilized DAVIS Weather Station Vantage Pro2 (DWS) and Electrocoder. It manages to record the solar radiation, temperature, rain falls, wind speeds, wind direction, pressure and humidity. Speed and direction of the wind were measured by it which is installed at the top of the tower nearby the wind turbine. The Electrocoder is to measure the voltage where it records the data every second and manage to save the data for seven days. It will be downloaded once a week. The data on DWS and Electrocoder will be synchronizing to be recorded in every second.
From the data that have been collected, it has been proved that the wind speed is consistent at the specific time from 10.00 pm to 3.00 pm. Nevertheless, the wind fluctuates afterwards and at 3.00 pm, it drops. It starts to increase back at 4.00 pm until 10.00 pm. The maximum speed of wind blows is 6.22 m/s at the time of 6.39 pm and the maximum speed is 0 m/s at the time of 4.06 pm. This average value of the output voltage and wind speed has been recorded using the Electrocoder and DWS. The batteries merely can be charged after the wind turbine can produce voltage more than 12 Vdc systems.
In a nutshell, the performance of the wind turbine has been recorded and being analyzed by the authors. From the collected data, it has been proven that the wind turbine is reliable as it produced 40 Vdc at the speed of wind, 5.54 m/s have been recorded. Plus, it also has a good potential to meet the nominal power performance as specified by the manufacturer.
A self-organizing porous material, Nanoporous Alumia (NPA) is an economical template for the fabrication of various nanomaterials.
This is due to its minute spaces and holes through which liquid and air may pass easily, without the need of the high-priced lithographic technique.
The characteristics of NPA (easily-controlled pore diameter, interpore distance and pore depth) form a befitting template for the synthesis of nanomaterials.
A well-ordered NPA can be employed through the fabrication of nanomaterials by template synthesis method, such as i) a two-step anodizing method and ii) pre-patterning method.
It is crucial to combine nanomaterials of uniform dimensions, as the properties of nanomaterials are significantly influenced by the dimensions.
However, the mentioned methods above are not feasible for large scale manufacturing due to the exorbitant cost and low throughput.
Hence, the objective of the study is to confirm on a simple method of oxide dissolution treatment to attain well-ordered NPA in shorter anodizing duration and higher temperature to enlarge the application on NPA in template synthesis of nanomaterials.
The study uses a single step anodizing at 50 V in 0.3 M oxalic acid at 15 degrees Celsius for 60 minutes, to produce NPA on aluminum surface.
By subjecting the nanoporous alumina to oxide dissolution treatment in a mixture of chromic acid and phosphoric acid, well-ordered pore and cell structure were obtained.
As a result, it was found that the oxide dissolution treatment improves the regularity of the cell and pore structure significantly and that this method is more convenient.
The post oxide dissolution treatment also exhibits ordered and nearly perfect hexagonal cell structure, a uniform closely honeycomb structure of NPA.
In addition, the pore diameters and the interpore distance are nearly uniform over the analyzed surface. Thus, the uniformity of the pore diameter and interpore distance are enhanced immensely.
Epoxy based nanocomposites incorporating nanoclay and several types of geopolymer raw materials obtained from Saudi Arabia were explored for piping application. The flexural and compressive properties and performance were studied from several series of epoxy nanocomposites containing different ratio of epoxy/hardener, and nanoclay/geopolymer. In addition, different kinds of geopolymer raw materials such as fly ash, kaolin, pozzolonic, silica sand and white clay were employed as filler. The effect of different combination and ratio of these materials on the mechanical properties and morphology of the resulted nanocomposites were investigated. Preliminary studies showed promising properties of these nanocomposites for further development in pipe application.