Hussein A. Konber

Performance improvement of quantum well infrared photodetectors through modeling

We study the performance of quantum well infrared photodetectors (QWIPs) in the case of infrared irradiation. This type of photodetector is interesting from the point of view that QWIPs have numerous advantages over photodetectors based on HgCdTe in terms of large array size, high uniformity, high yield, radiation hardness and lower cost of the systems. Therefore, it is important to evaluate their characteristics theoretically. We develop a simple modeling for this interesting type of photodetector. This model describes a nontrivial evaluation of the most important characteristics. The potential distribution of the developed model is obtained by self-consistently solving the Poisson equation. On the other hand, it is used to calculate the dark current, responsivity and detectivity as a function of the structural parameters. These parameters are the spacing between the wells, the number of quantum wells and the operating temperature. Also, the optimization of the characteristics of QWIPs is of primary concern. The effect of uniformity of the dopant density in the QWIP is studied theoretically. We find that the uniformity of the dopant distribution in the plane of QW decreases the dark current.

Development and characterization of a neutron tomography system for a Research Reactor

Abstract Neutron tomography is a very powerful technique for the nondestructive evaluation of heavy industrial components as well as for soft hydrogenous materials enclosed in heavy metals, which are usually difficult to image using X-rays. It has found a variety of applications in medicine, agriculture and other heavy industries. In our effort to use this technique for non-destructive testing, a process has begun to upgrade the neutron radiography facility from static-based film (Nitrocellulose film and Agfa Structurix D7 photographic film) neutron radiography into a dynamic neutron radiography/tomography system by using scintillation screens (ZnS (Ag)-6LiF) and a CCD-camera.

Timing Structure Mechanism of Wireless Sensor Network MAC layer for Monitoring Applications

This paper aims at designing a Timing Structure Mechanism TSM for Wireless Sensor Network WSN MAC, with specifying its respective logical topology, especially suitable to the monitoring applications, differentiated and characterized from the existing time bounding strategies, paving for a good performance channel access mechanism. The work proposed in this paper is based on classifying the monitoring applications so as to designing efficient setup and benefiting from the nodes capabilities in dividing the network into sub-networks. By evaluating TSM against a cluster-tree IEEE802.15.4 in the two cases of one channel and multi-channel clusters, the simulation results showed that with varying the area, the TSM performs better than the two cases of IEEE802.15.4 in terms of lifetime, end-to-end delay, loss percentage by on average 103.44% and 61.84%, 96.59% and 95.37%, and 88.59% and 87.52%, respectively. Also, in case of increasing the node density, TSM is better in terms of the same parameters by on average 446.58% and 356.05%, 98.04% and 95.62%, and 77.62% and 75.2%, respectively.

Block diagram modeling of quantum dot infrared photodetectors

The main objective of this paper is to evaluate the performance of quantum dot infrared photodetectors (QDIPs). The tools that we are used are the VisSim environment, along with the block diagram programming procedures. The benefits of using this modeling language are the simplicity of carrying out the performances measurement through computer simulation instead of setting up a practical procedure which becomes expensive, as well as the difficulty of its management. The roles that the parameters of fabrication can play in the characteristics of QDIPs are discussed through developed models implemented by VisSim environment. VisSim can be a powerful supplement to model the Poisson equation. MAPLE software is used to devise this model. The theoretical result confirms that implicit solution of QDIPs governed by dynamic equations provides exact handling of the device performance. As an example, dark current, photocurrent, and detectivity are investigated. In order to confirm our models and their validity on the practical applications, we make a comparison between the results obtained by MAPLE, VisSim, and that experimentally published, and full agreement is observed. The implemented models can help designers and scientists optimize their devices to meet their requirements.

Designing a Channel Access Mechanism for Wireless Sensor Network

Although there are various Medium Access Control (MAC) protocols proposed for Wireless Sensor Network (WSN), there is no protocol accepted as a standard specific to it. This paper deals with completing the design of our previously proposed MAC for WSN by proposing a channel access mechanism (CAM). The CAM is based on developing a backoff mechanism which mainly differentiates nodes’ backoffs depending on their different identification numbers, and it employs a performance tuning parameter for reaching a required performance objective. The probability distribution of the backoff period is constructed and Markov chain modeling is used to analyze and evaluate the CAM against the IEEE802.15.4 slotted CSMA/CA based on single- and multihop communication with respect to the reliability, the average delay, the power consumption, and the throughput. The analysis reveals that the required performance of CAM against the IEEE slotted CSMA/CA can be obtained by choosing the maximum backoff stages number and the tuning parameter value and that CAM performs better than the IEEE with larger nodes number. The multihop scenario results in a good end-to-end performance of CAM with respect to the reliability and delay becomes better with lengthier paths at the expense of increasing the energy consumption.

Block Diagram Programming of Quantum Dot Sources and Infrared Photodetectors for Gamma Radiation Detection Through VisSim

Quantum dots (QDs) have attracted tremendous interest over the last few years for a large variety of applications ranging from optoelectronic through photocatalytic to biomedical, including applications as nanophosphors in light emitting diodes LEDs [1]. QDs have been suggested as scintillators for detection of alpha particles and gamma-rays [1-4]. Quantum dots offer an improvement on scintillator technology in that the size of the phosphorescent material would not be restrained by crystal growth. The dots would be suspended in a transparent matrix that could be as large as desired. Moreover, the output of the QDs is a function of their dimensions. Therefore, they could be produced to emit light at wavelengths suitable for detection by avalanche photodiodes. That offer higher quantum efficiencies than photomultiplier tubes. Therefore, the sensitivity of the scintillator detector is increased [5]. To our knowledge, still models describing QD sources as gamma detection are not devised yet. In this chapter, we report on the effects of gamma irradiation on the different properties of CdSe/ZnS QDs. These characteristics are optical gain, power, population inversion and photon density. Furthermore, a new semiconductor scintillator detector was studied in which high-energy gamma radiation produces electron-hole pairs in a direct-gap semiconductor material that subsequently undergo interband recombination, producing infrared light to be registered by a photo-detector [6]. Therefore, quantum dot infrared photodetectors (QDIPs) can be used for this purpose. This chapter presents a method to evaluate, study, and improve the performance of quantum dot sources and infrared photodetectors as gamma radiation detection. This chapter is organized as follows: Section 3.2 presents the basics of VisSim simulator. QD devices as a detector are illustrated in Section 3.3. The proposed models of both quantum dot devices are represented in Section 3.4. Discussion and results are summarized in Section 3.5.

Model Development of Quantum Dot Devices for γ Radiation Detection Using Block Diagram Programming

The main objective of this paper is to develop a model of quantum dot (QD) devices for incident γ radiation detection. A novel methodology is introduced to characterize the effect of γ radiation on QD detectors. In this methodology, we used VisSim environment along with the block diagram programming procedures. The benefit of using this modeling language is the simplicity of carrying out the performance’s measurement through computer simulation instead of setting up a practical procedure, which is expensive as well as difficult in management. The roles that the parameters of fabrication can play in the characteristics of QDs devices are discussed through developed models implemented by VisSim environment. The rate equations of the QD devices under γ radiation are studied. The effect of incident γ radiation on the optical gain, power, and output photon densities is investigated. The implemented models can help designers and scientists to optimize their devices to meet their requirements.