Variable attenuators are important circuits that can be employed in many radio frequency (RF) applications, e.g., in automatic gain control (AGC) amplifiers, broadband gain-control blocks at RF frequencies or as broadband vector modulators. For any applications, low insertion phase shift and low power consumption are of interest. A way to implement variable attenuators is using the RF PIN diode. The PIN diode is characterized by a low doped (I = intrinsic) semiconductor region between p- (P) and n-type (N) semiconductor regions. Besides the variable attenuators, the PIN-diode is used in other RF circuits, such as RF switches, limiters and phase shifters. This project presents the design of variable attenuators at 7.5 GHz and 500 MHz frequency bandwidth for ultra-wideband (UWB) applications using two different PIN diodes. The variable attenuators have a topology based on 90° hybrid couplers. The design is performed using Advance Design Systems (ADS) from Agilent Technologies Inc. After presenting the PIN diode and its equivalent circuit, the theory of the 90° passive directional branch line coupler and the operation principle of the variable attenuators are presented. As the selection of the appropriate PIN diode is a critical step in the design, special attention is dedicated to this aspect. It follows the design of the variable attenuators with extensive descriptions of the simulations in ADS. Firstly, both series and shunt attenuators are presented. However, as these circuits normally offer narrow band variable attenuation, the 900 directional branch line coupler is used in the attenuator for broader band operation. At the end, a double hybrid coupler is found to eliminate the ripple in the high attenuation state of the single hybrid coupled attenuator. So the final topology of the variable attenuator is a double hybrid coupler variable attenuator- Moreover, in this project, different PIN diodes are investigated for variable attenuator applications. Different manufacture companies are currently providing different kinds of PIN diodes in terms of parameters and packages. Every type of PIN diodes are providing different sort of advantages to the designers. That is why it has become more difficult for the RF designers to choose the right device for the specified application. Beside the design of the variable attenuator using PIN diodes, some considerations in form of a guide line to the designers while they are using the PIN diode for designing the variable attenuator. In this work, the used PIN diodes are a beam lead PIN diode and chip PIN diode. The beam lead PIN diode is used because it is manufactured for high frequency and it produces excellent electrical performance and isolation at high frequencies. On the other hand, the chip PIN diode eliminates the problem of package parasitics. However, printed circuit board (PCB) manufacturing limitations at the university laboratory incline the balance in the favor of the beam lead PIN diode, HPND- 4005 from Avagotech, instead of the also considered chip diode MA-COM MA4P202.

This paper deals with the possibilities of designing the module for control of the attenuation of the optical signal. The paper describes basics of ber optic transmission and beam e ects. Variants of attenuation cells are characterized in this paper and based on the ndings a solution of the module for control of the attenuation of the optical signal is proposed. Practical section of the thesis deals with the design and physical construction of module for control of the attenuation of the optical signal using MEMS variable optical attenuator.

Fatty acids are an essential component of the phospholipids of the inner and outer membranes of Escherichia coli. The synthesis of both fatty acids and phospholipids is regulated. Synthesis increases when growth rate increases, is inhibited when starvation occurs, and the fatty acid composition of the membrane changes with growth temperature. Several genes encoding enzymes involved in membrane synthesis are located in the rpmF-plsX-fab operon. In this operon, a gene encoding a phospholipid synthetic gene of unknown function, plsX, lies just downstream of the ribosomal protein gene rpmF and upstream of five fatty acid biosynthetic genes, fabH, fabD, fabG, acpP, and fabF. The operon is also complex; transcription is initiated from at least eight promoters. In addition, some transcripts produced by the operon are cleaved by RNases while others terminate at one of three specific points at the 5' end of plsX. This work demonstrates that a weak transcriptional terminator (an attenuator) lies at the 5' end of plsX. The attenuator was localized to a 200 bp segment. Analysis of the secondary structure of the attenuator mRNA has lead to a model which includes four stem-loop structures. In this model, the plsX start codon lies within the loop of the second stem. Two tandem stems are located directly upstream of the mapped 3' endpoints. Mutational analysis shows that all four stem-loops play a role in attenuator activity. Regulation of the attenuator and the attenuator's mechanism of controlling downstream gene expression were investigated. Ribosome binding to attenuator mRNA, the PlsX protein, ppGpp concentration, and rate of lipid synthesis all appear to have no effect on attenuator activity. Interestingly, growth temperature appears to have an effect on both attenuator activity and the activity of one or more of the promoters upstream of rpmF, P₁, P₂, and P₃. Activity of the three promoters is 4.5-fold higher at 28°C as compared with 42°C. The attenuator also appears to increase expression of downstream genes 2-fold as temperature decreases. Though the attenuator region terminates transcription, growth temperature-regulation of attenuator activity is apparently mediated by a change in stability of the mRNA. These data demonstrate that transcriptional expression of plsX is 9-fold higher at 28°C as compared with 42°C. The striking dependence on temperature of plsX expression suggests a role for PlsX in the temperature modulation of fatty acid incorporation into the membrane phospholipids. / Ph. D.

In wavelength division multiplexed (WDM) optical communication networks, signals are amplified periodically by optical amplifiers. Since the gain profiles of optical amplifiers are not flat, equalizers are usually used to maintain signal powers at different wavelengths in equal to avoid crosstalk and data loss. However, fixed attenuation can only compensate fixed input power and amplification. In active network, input power and amplifier gain change with time. Active level compensation at each wavelength is needed. An adaptive attenuator is a device with a chromatically variable transmissivity used to equalize channel powers in wavelength-division multiplexing (WDM) fiber-optic communication lines. In this thesis, a method of Fourier analysis of multi-beam interference is developed. It is shown that the total electric field and relative phase delay of each beam form a Fourier transform pair. Thus methods and properties of Fourier analysis are applicable in multi-beam interference analysis and design. Fourier transform based design is presented. Novel devices that apply such design principles are introduced. Principles and structures of novel adaptive attenuators based on various technologies such as segment deformable mirror, liquid crystal, phase modulation array are given. Simulation results for segment deformable mirror based adaptive attenuator are presented. / Master of Science

Le travail effectué dans le cadre de cette thèse porte sur l'étude d'un atténuateur de rayonnement X à gaz et du plasma produit à l'intérieur. Un atténuateur à gaz est composé d'une chambre remplie du gaz, généralement argon ou krypton à quelques centaines de millibars, qui absorbe la partie de basse énergie d'un spectre de rayonnement X de synchrotron, en réduisant la puissance reçu par les éléments optiques en aval sans affecter les propriétés de la partie de haute énergie du spectre. L'absorption des photons crée une région de gaz chaud et ionisé autour du parcours du faisceau X, en réduisant la densité du gaz localement. A détaillé bilan énergétique entre tous les processus impliqués c'est nécessaire pour être capable de prédire l'absorption et opérer et dessiner atténuateurs a gaz efficacement. Un modèle hybride que combine techniques de modélisation Monte Carlo et fluides à été développé pour déterminer le bilan énergétique et simuler l'absorption de rayonnement X. Le modèle a été valide expérimentalement pas études incluant absorption de puissance, spectroscopie optique d'émission et spectroscopie d'absorption par laser à diodes. Les résultats des simulation et expériences montre un plasma confiné autour du parcours du faisceau X, recombinant dans le volume de gaz et avec une température maximale de plusieurs centaines de Kelvin. Le modèle a été capable de prédire l'absorption de rayons X avec un erreur de entre 10 et 20%, qui permettre son utilisation comme première approximation pour le dessin et opération de atténuateurs a gaz et aussi comme point de partie pour modèles plus affinées. / The work done in the context of this thesis focuses in the study of an X-ray gas attenuator and the plasma produced within. An X-ray gas attenuator consists on a vessel filled with gas, usually argon or krypton at a few hundreds millibars, that absorbs the low energy fraction of a synchrotron X-ray spectrum, reducing the power received by downstream optical elements without affecting the properties of the high energy part of the spectrum. The absorption of the photons creates a region of hot, ionized gas around the X-ray beam path, decreasing locally the gas density. A detailed energy balance between all the involved processes is required to be able to predict the absorption and operate and design gas attenuators efficiently. A hybrid model combining Monte Carlo and fluid modelling techniques has been developed to determine the energy balance and simulate the X-ray absorption. The model has been validated by experimental studies including power absorption, optical emission spectroscopy and tunable laser absorption spectroscopy. The results of both simulation and experiments show a plasma confined around the X-ray beam path, recombining in the bulk of the gas and with a maximum temperature of several hundreds of Kelvin. The model was able to predict the X-ray absorption within a 10-20% of error, which allows its use as a first approximation for the design and operation of gas attenuators, and also provides a starting point for more refined models.

<p>In this master degree work, a digital attenuator and a low noise amplifier (LNA) have been designed and integrated with the RF front-end receiver for IEEE 802.11b Wireless LAN standard. Firstly, the 4-bit digitally controlled attenuator has been designed with theattenuation range of 50 to 80 dB and reflection coefficient less than -25 dB. Next, the single stage wide band low noise amplifier with voltage gain larger than 14 dB and noise figure below 4 dB has been designed to operate at frequency 2.4 GHz. Finally, the integration with a down-conversion mixer has been done and evaluated its performance.</p><p>The attenuator and low noise amplifier desired in this thesis have been implemented using standard CMOS 0.35µm technology and validated by the simulation tools Cadence Spectre-RF.</p>

In this master degree work, a digital attenuator and a low noise amplifier (LNA) have been designed and integrated with the RF front-end receiver for IEEE 802.11b Wireless LAN standard. Firstly, the 4-bit digitally controlled attenuator has been designed with theattenuation range of 50 to 80 dB and reflection coefficient less than -25 dB. Next, the single stage wide band low noise amplifier with voltage gain larger than 14 dB and noise figure below 4 dB has been designed to operate at frequency 2.4 GHz. Finally, the integration with a down-conversion mixer has been done and evaluated its performance. The attenuator and low noise amplifier desired in this thesis have been implemented using standard CMOS 0.35µm technology and validated by the simulation tools Cadence Spectre-RF.

With many unique advantages compared to traditional sensors, optical fiber sensors have been studied and applied to many different areas. Interferometric sensors are one of the most useful sensor types due to their high sensitivities and relatively relaxed requirement on the stability of the optical source’s power level. In-line optical interferometric sensors received further attention as a result of compactness and robustness to the reference channel instability. Long period gratings (LPG) are one of the most useful components in the in-line optical fiber sensors. However, the fabrication cost is normally high due to the expensive masks and stringent photolithographic procedures. Two new sensor components, namely abrupt tapers and connector-offset attenuators, are proposed as couplers in the optical fiber to couple light from core to cladding (or reverse) to replace LPGs. Using OPTIBPM software, the coupling coefficients between core and cladding modes are calculated. For an abrupt taper, coupling mostly happens between LP01 and LP0m modes; the first ten LP0m modes account for 98% of the incident mode energy. For a connector-offset attenuator, coupling mainly happens between LP01 and LP1m modes; the first ten LP0m and first ten LP1m modes account for 92% of the incident mode energy. The relative direction of two connector-offset attenuators is found to be very important to the interference performance. Phase dependent interference (attenuation range from 1 dB to 35 dB) is observed in the simulation for the interferometers using abrupt tapers and connector-offset attenuators. Three interferometers are realized in the experiment using the abrupt tapers (Mach-Zehnder and Michelson) or the connector-offset attenuators (Michelson). Due to the interference between core and cladding modes, transmission is strongly dependent on wavelength ranging from 3 dB to 26 dB in the best implementation. Although it is difficult to make two perfect parallel connector-offset attenuators required by the Mach-Zehnder interferometers by using the fusion splicer, some evidence of constructive interference is observed in the experiment. The interferometers are tested as refractive index (RI) sensors using the maximum attenuation wavelength shift relative to the RI change. Given that the minimum resolution of optical spectrum analyzer is 10 pm, ~10-4 difference of the RI can be detected by the interferometric sensors using the abrupt tapers or the connector-offset attenuators. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2008-08-18 15:42:59.506

The onset of an explosion in an underground mining environment is a threat that has over years attracted a lot of attention. Much of this attention has focused on either arresting the explosion after it has been initiated or preventing the initiation. The methods devised have proved successful in most cases, but on the odd occasion that they fail, the end results can be disastrous. There have been fatalities from underground mining explosions as a result of fires burning and sapping all the oxygen in the atmosphere leading to asphyxiation. A different approach to arresting these explosions would enhance safety in the face of increased productivity. A novel method using an explosion door with a porous media acting as a shock wave attenuator and arresting the flames has been introduced. This research investigates the ability of the porous media used in the explosion door to withstand explosions. The performance of the porous media is crucial, as its failure would render the explosion door useless. In order to assess the performance of the porous media, a shock tube was built capable of generating shock waves with a Mach number of 1.5. By placing samples of the porous media within the test section of the shock tube, pressure measurements were taken fore and aft of the porous media as it was impinged upon by the shock wave. Tests were also conducted using thin orifice plates to provide data for comparing the performance characteristics of the porous media. Computational fluid dynamics (CFD) simulations of the porous media and the orifice plates were performed to validate the experimental work as well providing graphic detail of the flow around the test specimen. The work presented in this thesis makes a contribution to the efforts towards the provision of a safe underground environment. This contribution is achieved by investigating the performance of the porous media to be used in an explosion door and correlating the performance of the porous media with thin orifice plates. The porous media in the work presented here is currently used in the castings industry and its application as a shock wave attenuator and fire arrester would contribute greatly to the well being of all people working underground.

This master's thesis is engage in suggestion of low noise 70 cm band amplifier with filter and diode attenuator. At first the thesis describes the basic parameters of amplifier, for example gain, noise figure and dynamic extent. Later in detail describes individual parts, which are the device consist of. At every part of system is mentioned the diagram of connection and values of components, which are ascertained from calculation, simulation and recommendation of producer. The characteristic parameters of amplifier were measured after construction.