Dissertations / Theses on the topic 'Mode engineering'

This dissertation describes three related studies regarding the imbalance difference theory in modeling the conversion between differential mode and common mode/antenna mode signals. The topics covered are: rigorous derivation of imbalance difference theory for modeling radiated emission problems, modeling the conversion between differential mode and common mode propagation in transmission lines, and modeling the loading impedance on differential mode signals due to radiated emissions.

The imbalance difference theory describes a method for calculating the coupling between differential mode signals and common mode signals due to changes in electrical balance on a transmission line. It provides both physical insight and a simple technique for modeling the conversions between the two modes.

The first chapter presents a rigorous derivation of imbalance difference theory for modeling radiated emission problems. Although the theory has been successfully used to model a wide variety of important EMC problems over the past, it has not been rigorously derived. The derivation carefully defines the important quantities and demonstrates that imbalance difference calculations are exact provided that the differential-mode propagation is TEM and the current division factor, h, represents the actual ratio of currents on the two transmission line conductors excited by a common-mode source. This chapter also discusses the acquisition of the current division factor from 2D calculations of the cross-section of the transmission line.

The second chapter provides a rigorous development of the imbalance difference theory for three-conductor transmission lines where both the differential mode and common mode exhibit TEM propagation. It also derives expressions for the mode conversion impedances, which account for the energy converted from one mode to the other. They are essential for modeling the conversion between the two modes when they are strongly coupled.

The third chapter introduces conversion impedance to the existing imbalance difference theory model for modeling radiated emission problems, so that when the coupling between differential mode and antenna mode are strong, the imbalance difference theory can more accurately estimate the antenna mode current.

All three papers are about confirming, enriching and expanding the imbalance difference theory. The first chapter focuses on the rigorous derivation of theory for its most common application, radiated emission problems. The second chapter expands the theory to multi-conductor transmission line structure when the two modes are strongly coupled. The last chapter introduces conversion impedance to the theory in modeling radiated emission problems and improves the accuracy of the model at resonant frequencies.

Resonators are a major component in RF electronic products. They are used in a host of ways to filter radio signals. Modern and Future RF communications have placed high demands on the industry; requiring low power usage, wide array of applications and resistance to noise.

In this thesis, a discussion of the motivation for RF MEMS filters and basic theory is given with an explanation of the concepts of Q factor, piezoelectricity, acoustics theory, the major types of resonators (SAW, BAW, CMR or LAMB), apodization theory and techniques as well as design, simulation of CMR and BAW devices, testing and process development of aluminum nitride by RF reactive sputtering at RIT.

Finite element analysis was performed on a number of factors of aluminum nitride contour mode resonators (CMR) from piezoelectric film thickness, to electrode pitch, electrode thickness and electrode configuration; to understand the effects. First order and second order vibration modes were seen including symmetric S₀, S₁ and antisymmetric A₀, A₁ resonant modes in the pizeoacoustic devices and higher. A series of time dependent video simulations of SAW, BAW and LAMB wave resonators were also performed, perhaps the first of their kind.

The RF reactive sputtering deposition for aluminum nitride was developed at RIT by a fractional factorial experiment with the factors being RF power, nitrogen to argon flow rate ratios, changing the distance of the wafer to the platen from 5 to 4 cm, use of a aluminum, molybdenum or virgin silicon seed layer and chamber pressure. In nearly all cases it was found that an RF power of 1000W is the most important factor contributing to the ⟨002⟩ orientation. The decreasing of the target distance may inhibit a reaction mechanisms in the plasma resulting in a more amorphous deposition. It may be due to the increase in temperature resulting from the higher RF power that promotes the growth of ⟨002⟩ oriented aluminum nitride. A molybdenum seed layer tends to have a stronger ⟨002⟩ peak relative to aluminum and a chamber pressure of 3mT was found to exhibit a deposition that most favors the ⟨002⟩ oriented aluminum nitride.

It was found that molybdenum is not consumed in a wet etch of KOH. Molybdenum is oxidized during photo resist ashing. The Contact Vias were necessarily over retched in order to ensure complete removal of Al-N over the Bottom Electrode.

C-V measurements were done on the aluminum nitride to determine its quality, the measured extensional piezoelectric coefficient d ₃₃ is -0.000108716 nm/V, which is -0.108716 pm/V lower than 8pm/V typically reported. The lower piezo electric coefficient measured as compared with typical values, may be due to low film density a result of the high power used in the RF reactive sputtering that was used to heat the platen to a high enough temperature to promote the?002?oriented growth of AlN.

A series of iterations were designed and S11 frequency response measured. The electrode overlap from 25 to 50 to 75μm, it does not appear to have an effect on the resonant frequency, but does increase the amplitude of the response at that die's given frequency. Increasing the anchor width from 5μm to 10μm to 20μm lowers the relative amplitude of the response therefore lowering the Q of the resonator. It may be that the increasingly wide anchor, increases the mechanical resistances within the device and thereby lowers the Q factor of the resonator. Increasing the number of electrodes increases the relative amplitude of the response. Increasing pitch from 5μm to 6μm seems to have a small effect on the resonant frequency of the devices, shifting them from 4.57 to 4.59 GHz. A quality factor was measured, with an anchor width of 5μm, pitch of 5μm, 24 electrodes and an electrode overlap of 75μm had a measured Q value of 98.8.

Space division multiplexing (SDM) has become a promising approach in the telecom industry to reduce the cost-per-bit of optical fiber transmission and to resolve the approaching bandwidth crunch. Meanwhile, intermodal nonlinear effects in few-mode fibers (FMF) potentially provide some novel applications along with sophisticated optical signal processing functionality. Recently, such spatial channels and modes have been applied in optical sensing applications with the returned echo analyzed for the collection of essential environmental information. The key advantages of implementing SDM techniques in optical measurement systems include the multi-parameter discriminative capability and accuracy improvement. In this dissertation, we conduct theoretical and experimental study on the SDM systems using FMFs for both optical transmission and sensing applications.

We first investigate a fast-convergence single-stage adaptive frequency-domain recursive-least-square algorithm for simultaneously compensating chromatic dispersion and differential mode group delay in a 224 Gbit/s six-mode polarization-division multiplexed 16 quadrature amplitude modulation FMF transmission system, which increases convergence speed by 53.7% over conventional frequency-domain least-mean square method, with 11% hardware complexity reduction over two-stage recursive-least square approach.

We then present an ultrafast all-optical simultaneous wavelength and mode conversion scheme based on intermodal four-wave mixing, with the capability of switching polarization and mode degeneracy orientation in FMFs. The relation among the conversion efficiency, pump power and phase matching conditions is investigated in theory analysis and simulation. The cross-polarization modulation and cross-mode modulation can be achieved, by in the best case up to 50% conversion efficiency.

Finally, a single-end FMF-based distributed sensing system that supports simultaneous temperature and strain monitoring is demonstrated via Brillouin optical time-domain reflectometry and heterodyne detection. Theoretical analysis and experimental assessment of multi-parameter discriminative measurement applied to the distributed sensors are presented, which endows with good sensitivity characteristics and can prevent catastrophic failure in many applications.

In recent years, the growth demand of information transmission has promoted the development of communication technology. Many modulation methods are used in many fields, such as QPSK and OFDM, which are used in long-distance communication. In this thesis, I discussed the PAM-4, which can be used in inter-data center (<80km) links due to its better performance and lower cost. Then I tested one channel 4?50Gbps PAM-4 system and eight channels 4?50Gbps PAM-4 system with varying degrees of gain of optical amplifier and length of DCF. Finally, I discussed the performance of the two designs and figured out the factors that affect the transmission system.

Digital imaging is growing rapidly making Complimentary Metal-Oxide-Semi conductor (CMOS) image sensor-based cameras indispensable in many modern life devices like cell phones, surveillance devices, personal computers, and tablets. For various purposes wireless portable image systems are widely deployed in many indoor and outdoor places such as hospitals, urban areas, streets, highways, forests, mountains, and towers. However, the increased demand on high-resolution image sensors and improved processing features is expected to increase the power consumption of the CMOS sensor-based camera systems. Increased power consumption translates into a reduced battery life-time. The increased power consumption might not be a problem if there is access to a nearby charging station. On the other hand, the problem arises if the image sensor is located in widely spread areas, unfavorable to human intervention, and difficult to reach. Given the limitation of energy sources available for wireless CMOS image sensor, an energy harvesting technique presents a viable solution to extend the sensor life-time. Energy can be harvested from the sun light or the artificial light surrounding the sensor itself.

In this thesis, we propose a current-mode CMOS hybrid image sensor capable of energy harvesting and image capture. The proposed sensor is based on a hybrid pixel that can be programmed to perform the task of an image sensor and the task of a solar cell to harvest energy. The basic idea is to design a pixel that can be configured to exploit its internal photodiode to perform two functions: image sensing and energy harvesting. As a proof of concept a 40 × 40 array of hybrid pixels has been designed and fabricated in a standard 0.5 µm CMOS process. Measurement results show that up to 39 µW of power can be harvested from the array under 130 Klux condition with an energy efficiency of 220 nJ /pixel /frame. The proposed image sensor is a current-mode image sensor which has several advantages over the voltage-mode. The most important advantages of using current-mode technique are: reduced power consumption of the chip, ease of arithmetic operations implementation, simplification of the circuit design and hence reduced layout complexity.

Dixit, Ravindra Krishna. Sliding Mode Observation and Control for Semiactive Vehicle Suspen-sions.(Under the direction of Dr. Greg Buckner).This thesis investigates the application of robust, nonlinear observation and control strategies,namely sliding mode observation and control (SMOC), to semiactive vehicle suspensions using amodel reference approach. The vehicle suspension models include realistic nonlinearities in thespring and magnetorheological (MR) damper elements, and the nonlinear reference models incorpo-rateskyhook damping. Since full state measurement is difficult to achieve in practice, a sliding modeobserver (SMO) that requires only suspension deflection as a measured input is developed. The per-formanceand robustness of sliding mode control (SMC), SMO, and SMOC is demonstrated throughcomprehensive computer simulations and compared to popular alternatives. The results of thesesimulations reveal the benefits of sliding mode observation and control for improved ride quality,and should be directly transferable to commercial semiactive vehicle suspension implementations.

Over the last several decades, there has been consistent growth in the research and development of multilevel voltage-source inverter-based adjustable speed motor drives (ASDs) as a result of low cost, high reliability power semiconductors. The three-level neutral-point-clamped (NPC) ASD is a popular multilevel inverter used in low and medium voltage applications because of its ability to produce lower levels of total harmonic distortion (THD) and withstand higher voltages while preserving the rated output power compared to two-level ASDs.

As with other voltage-source inverters, three-level NPC ASDs produce common-mode voltage (CMV) that can cause motor shaft voltages, bearing currents, and excess voltage stresses on motor windings, resulting in the deterioration of motor bearings and insulation. Furthermore, the CMV and resultant currents can generate electromagnetic interference that can hinder the operation of sensitive control electronics. In this thesis, three carrier-based, three-level pulse-width-modulation (PWM) strategies were investigated to examine the levels of CMV, common-mode current, and dv/dt produced by the three-level NPC ASD. Additionally, the effects that each PWM strategy has on the THD in the output waveforms, as well as the total switching and conduction losses were analyzed through software simulation programs using a resistive-inductive load over a range of modulation indices. The first of the three methods, in-phase disposition sub-harmonic PWM (PD-SPWM), was verified experimentally using a laboratory-scale, 7.5 kVA three-level NPC ASD prototype.

It was determined that PD-SPWM produced the highest CMV amplitude of one-third the dc bus voltage, but the lowest values of differential-mode dv/dt, THD, and drive losses. The second strategy, phase-opposition (PO)-SPWM, reduced the CMV amplitude to one-sixth the dc bus voltage, at the cost of higher THD and drive losses and a doubling of the differential-mode dv/dt. The final strategy, zero common-mode (ZCM)-SPWM, was modified (MZCM-SPWM) to accommodate IGBT dead-time by delaying the output voltage transitions based on the polarity of the output currents and the direction of the commanded voltage transitions. The MZCM-SPWM method nearly eliminated all CMV pulses while maintaining comparable levels of THD, but produced twice the switching losses compared to PD- and PO- SPWM, and twice the differential-mode dv/dt compared to PD-SPWM.