Gradient Optics of subwavelength nanofilms

Propagation and tunneling of light through subwavelength photonic barriers, formed by dielectric layers with continuous spatial variations of dielectric susceptibility across the film are considered. Effects of giant heterogeneity-induced non-local dispersion, both normal and anomalous, are examined by means of a series of exact analytical solutions of Maxwell equations for gradient media. Generalized Fresnel formulae, visualizing a profound influence of gradient and curvature of dielectric susceptibility profiles on reflectance/transmittance of periodical photonic heterostructures are presented. Depending on the cutoff frequency of the barrier, governed by technologically managed spatial profile of its refractive index, propagation or tunneling of light through these barriers are examined. Nonattenuative transfer of EM energy by evanescent waves, tunneling through dielectric gradient barriers, characterized by real values of refractive index, decreasing in the depth of medium, is shown. Scaling of the obtained results for different spectral ranges of visible, IR and THz waves is illustrated. Potential of gradient optical structures for design of miniaturized filters, polarizers and frequency-selective interfaces of subwavelength thickness is considered

Advanced filters and components for power applications

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (p. 159-163).The objective of this thesis is to improve the high frequency performance of components and filters by better compensating the parasitic effects of practical components. The main application for this improvement is in design of low pass filters for power electronics, although some other applications will be presented. In switching power supplies the input and output filters must attenuate frequencies related to the fundamental switching frequency of the converter. The filters represent a major contribution to the weight, volume and price of the power supply. Therefore, aspects of the design of the switching power converter, especially those related to the switching frequency, are limited by the high frequency performance of the filters. The usual methods of improving the high frequency performance of the filter includes using larger, better components. Filter performance can improve by using higher quality inductors and capacitors or by adding high frequency capacitors in parallel with the filter capacitor. Also, an additional filter stage can be added. All of these methods add significant cost to the design of the power supply. If the effect of high-frequency parasitic elements in the components can be reduced (at a low cost) the performance of the filter can be enhanced. This allows the development of filters with much better high frequency attenuation, or the reduction of filter size and cost at a constant performance level. In filtering and other applications, the ability to reduce the effect of parasitic elements will be a technique that will enable many high-frequency designs. Specifically, this thesis will present two techniques that can be used to reduce the effects of parasitic inductance and capacitance. One technique,(cont.) called inductance cancellation, is used to reduce the amount of parasitic inductance in a path of interest. The other technique, capacitance cancellation, will reduce the effect of a parasitic capacitance in an inductor. The techniques introduced here cannot be used to improve performance of passive components in all applications. These techniques, though, do provide major improvements in most filtering applications, an application in which parasitic components play an important role in the design.by Timothy C. Neugebauer.Ph.D

Inductance cancellation techniques with application to EMI filters and components

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (p. 85-87).Inherent parasitic effects in passive circuit components, such as the equivalent parallel capacitance of magnetic windings and the equivalent series inductance (ESL) of capacitors, become dominant factors limiting the attenuation of high frequency signals in power filter networks. These limitations have generated recent interest in methods for compensating or mitigating parasitics to increase filter performance, including the use of coupled magnetic windings to cancel the effects of capacitor parasitic inductance. The use of these inductance cancellation windings allows for a reduction in filter volume and cost and/or an increase in its attenuation performance. This thesis extends the efficacy of inductance cancellation techniques by enhancing the manufacturability and usability of self-contained integrated filter elements, and by more effectively addressing cancellation in common- and differential-mode filter topologies, such as those designed for reducing electromagnetic interference (EMI). A design methodology and fabrication process is presented for packaging a capacitor and matched inductance cancellation winding together to create a self-contained integrated filter element.(cont.) Experimental results from the creation of three independent designs clearly illustrate the high level of performance and repeatability that is achievable. Discrete magnetic windings are used to implement inductance cancellation in filter topologies designed to attenuate both common- and differential-mode signals. The number of capacitors required for even simple designs motivate the use of a single cancellation winding for two capacitors. An analytical model along with extensive experimental results successfully demonstrate. This approach is demonstrated in an adaptation of a commercially-available EMI filter.by Brandon J. Pierquet.S.M

Miniaturised and reconfigurable planar filters for ultra-wideband applications

An increasing demand for electromagnetic spectrum has resulted from the emergence of feature-rich and faster throughputs wireless applications. This necessitates the developments of dynamic reconfigurable or multifunctional systems to better exploit the existing spectrum. Future wireless devices will be expected to communicate over several bands with various other devices in order to fine tune the services they provide to the user. Each band may require a separate RF transceiver and such modern wireless multi-band multi-mode communication systems call for high performance, highly integrated compact modules. Since the Federal Communications Commission (FCC) released the unlicensed frequency band 3.1-10.6 GHz for ultra-wideband (UWB) commercial communications, the development race for commercialising UWB technology has seen a dramatic increase around the world. The aim of this research is to develop reconfigurable planar microwave filters for ultrawideband applications. The project investigates some key design issues of reconfigurable filters, which are being observed constantly in the latest development and realisation of microwave filters. Both analytical and numerical methods are performed to construct a realistic and functional design. Two different types of frequency reconfigurability are investigated in this thesis: discrete (e.g. PIN diode, Optical switch) and continuous (e.g. varactor diode). Using the equivalent circuits and considering the direct coupled filter structure in most cases, several topologies with attractive features are developed for future communication systems. The proposed works may be broadly categorised into three sections as follows. The first section explores a square ring shape close loop resonator along with an opencircuited stub in the symmetry plane. To realise a reconfigurable frequency states within the same spectrum, an innovative approach is developed for this case. An optical or photoconductive switch, comprised of a silicon die activated using near infrared light is investigated as a substitute of PIN diode and performances are evaluated to compare the feasibilities. In addition, a in-band interference rejection technique via externally coupled Tshape resonator is shown. However, it is observed that both structures achieve significant size reductions by utilising the inner part of the resonators. To improve the filter selectivity, a convenient design approach generating a pair of transmission zeros between both passband edges and a single zero in the stop band for harmonic suppression is discussed in the second section. Moreover, the development of notched rejection bands are studied and several novel methods to create a single and multiple notched bands employing the square ring shape structure are proposed. On inspection, it is found that the notch structure can be implemented without deteriorating the filter performances. The discussions are supplemented with detailed design examples which are accompanied by theoretical, simulated and experimental results in order to illustrate the filter development process and showcase practical filter performance. The third section reveals a novel highly compact planar dual-mode resonator with sharp rejections characteristics for UWB applications. A bandwidth reconfiguring technique is demonstrated by splitting its even-mode resonance. Filter structure with the dual-mode resonator is shown to have a relatively wide tuning range, significantly low insertion loss and a constant selectivity along with frequency variations in comparison to similar published works. Finally, the earlier dual-mode structure are modified to realise a dual wideband behaviour. A detail analysis with comprehensive design procedures is outlined and a solution for controlling the frequency bandwidths independently according to the application interest is provided. In line with the previous section, experimental verification is presented to support and supplement the discussions

Design of an Active Harmonic Rejection N-Path Filter for Highly Tunable RF Channel Selection

As the number of wireless devices in the world increases, so does the demand for flexible radio receiver architectures capable of operating over a wide range of frequencies and communication protocols. The resonance-based channel-select filters used in traditional radio architectures have a fixed frequency response, making them poorly suited for such a receiver. The N-path filter is based on 1960s technology that has received renewed interest in recent years for its application as a linear high Q filter at radio frequencies. N-path filters use passive mixers to apply a frequency transformation to a baseband low-pass filter in order to achieve a high-Q band-pass response at high frequencies. The clock frequency determines the center frequency of the band-pass filter, which makes the filter highly tunable over a broad frequency range. Issues with harmonic transfer and poor attenuation limit the feasibility of using N-path filters in practice. The goal of this thesis is to design an integrated active N-path filter that improves upon the passive N-path filter’s poor harmonic rejection and limited outof- band attenuation. The integrated circuit (IC) is implemented using the CMRF8SF 130nm CMOS process. The design uses a multi-phase clock generation circuit to implement a harmonic rejection mixer in order to suppress the 3rd and 5th harmonic. The completed active N-path filter has a tuning range of 200MHz to 1GHz and the out-ofband attenuation exceeds 60dB throughout this range. The frequency response exhibits a 14.7dB gain at the center frequency and a -3dB bandwidth of 6.8MHz

Magnetless circulators based on linear time-varying circuits

In a crowded electromagnetic spectrum with an ever‐increasing demand for higher data rates to enable multimedia‐rich applications and services, an efficient use of the available wireless resources becomes crucial. For this reason, full‐duplex communication, which doubles the transmission rate over a certain bandwidth compared to currently deployed half-duplex radios by operating the uplink and the downlink simultaneously on the same frequency, has been brought back into the spotlight after decades of being presumed impractical. This long‐held assumption has been particularly due to the lack of high performance low-cost and small-size circulators that could mitigate the strong self-interference at the RF frontend interface of full-duplex transceivers while, at the same time, permitting low-loss bi-directional communication using a single antenna. Traditionally, such non-reciprocal components were almost exclusively based on magnetic biasing of rare-earth ferrite materials, which results in bulky and expensive devices that are not suitable for the vast majority of commercial systems. Despite significant research efforts over the past few decades, none of the previous works managed to eliminate the magnet while satisfying all the challenging requirements dictated by the standards of real systems. In this dissertation, we introduce several newly invented magnetless circulators based on linear time-varying circuits that can overcome for the first time the limitations of all previous approaches. We analyze the presented circuits rigorously and validate them through simulations and measurements, showing unprecedented performance in all relevant metrics, thus holding the promise to enable full-duplex radios in the near futur

Discrete Fourier transform techniques for power transmission line protection

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