Soft-switching Inverter-fed Single-phase Collector Motor Drive

AbstractThis paper deals with the performance analysis of a hand power tool (HPT). The HPT is being driven by a single-phase collector motor drive fed by a PWM voltage source soft-switching inverter. A mathematical model of an electro-mechanic system of a HPT has been worked out. The dynamic model of an electric motor consists of a system of non-linear differential equations that include the resistance and dynamic inductance of an armature and field winding and spinning E.M.F. The proposed drive system is modeled and its performance is simulated in Matlab/Simulink. The simulation results show that a smaller switching loss and higher conversion efficiency are obtained by the proposed soft-switching inverter. The performance of the drive is improved by using voltage regulator when compared with direct connection to the voltage source

Thin Films and Component Technologies for Low-Noise Terahertz Electronics

This thesis deals with several distinct subjects such as thin film deposition, design, fabrication and characterization of components for low-noise THz electronics. High energy-gap superconducting materials are of specific importance for low-noise THz mixer applications. Extending the upper operation frequency of superconductor-insulator-superconductor (SIS) mixers above 1.5 THz is of particular interest. Here, a novel approach of producing Nb3Al thin film based on DC magnetron co-sputtering using heteroepitaxial, as well as epitaxial growth techniques, has been employed. As a result, a superconducting transition temperature, as high as 15.7 K has been observed. Structural and electrical characterization techniques have been utilized to evaluate the set of material and superconducting parameters of the deposited Nb3Al thin films. The superconducting properties of the obtained Nb3Al films have revealed strong potential for using them in practical applications. It has been also demonstrated that Nb3Al can be epitaxially grown on yttria-stabilized-zirconia substrates, thus opening a possibility for hot-electron bolometer (HEB) applications. Another substantial part of this work deals with the in-house development of phonon-cooled HEB mixers. A reliable deposition process for high-quality ultra-thin NbN films has been established. Epitaxial ultra-thin NbN films grown on 3C-SiC/Si substrate with state-of-the-art performance have shown a strong potential to be used in THz HEB mixers with a purpose for improving the intermediate frequency (IF) bandwidth. A novel membrane-like layout for 1.6-2.0 THz HEB mixer has been suggested, developed and implemented for use with micromachined all-metal waveguides. Being the most used in mm- and submillimeter mixer technology for radio astronomy, Nb/Al-AlOx/Nb tunnel junction stability properties are of great importance. In this thesis, the behaviour of a large number high-quality Nb/Al-AlOx/Nb tunnel junctions, subjected to long-term room temperature aging and thermal annealing is systematically studied and explanations of the observed phenomena are suggested. Finally, the work on development of a planar superconducting IF/biasing circuit for use with a SIS mixer is presented. The circuit was integrated into a 385-500 GHz DSB SIS mixer currently under operation at the APEX telescope. Circuit design methodology, measurement results and overall mixer performance with the integrated circuit are shown

A Technology Demonstrator for 1.6–2.0 THz Waveguide HEB Receiver with a Novel Mixer Layout

In this paper, we present our studies on a technology demonstrator for a balanced waveguide hot-electron bolometer (HEB) mixer operating in the 1.6–2.0 THz band. The design employs a novel layout for the HEB mixer combining several key technologies: all-metal THz waveguide micromachining, ultra-thin NbN film deposition and a micromachining of a silicon-on-insulator (SOI) substrate to manufacture the HEB mixer. In this paper, we present a novel mixer layout that greatly facilitates handling and mounting of the mixer chip via self-aligning as well as provides easy electrical interfacing. In our opinion, this opens up a real prospective for building multi-pixel waveguide THz receivers. Such receivers could be of interest for SOFIA, possible follow up of the Herschel HIFI, and even for ground based telescopes yet over limited periods of time with extremely dry weather (PWV less than 0.1 mm)

Terahertz components packaging using integrated waveguide technology

We present an integrated waveguide based packaging solution compatible with different THz component technologies, both for room temperature and cryogenic operations, employing space-qualified wire-bonding for electrical contacts. The proposed waveguide packaging relies on the combination of all-metal micro-machined THz waveguide and active component chip layouts suitable for the realization of systems from 200 up to 5000 GHz. It provides possibility of making 3-dimensional structures via facilitating of multi-level (layered) designs. The surface roughness of the fabricated THz waveguide structure was demonstrated to be 20 nm, while a 2 μm alignment accuracy of the active component chip was verified. \ua9 2011 IEEE

Aging-and annealing-induced variations in Nb/ Al-AlO x / Nb tunnel junction properties

In this paper, we present studies of room temperature aging and annealing of Nb/ Al-AlO x / Nb tunnel junctions with the size of 2 -3 m 2 . We observed a noticeable drop of junction normal resistance R n unusually combined with increase in subgap resistance R j as a result of aging. Variation in both R n and R j are subject to the junction size effect. An effect of aging history on the junction degradation after consequent annealing was discovered. Discussion and interpretation of the observed phenomena are presented in terms of structural ordering and reconstruction in the AlO x layer, driven by diffusion flows enhanced due to stress relaxation processes in the Al layer interfacing the AlO x layer

A Swedish heterodyne facility instrument for the APEX telescope

In March 2008, the APEX facility instrument was installed on the telescope at the site of Lliano Chajnantor in northern Chile. The main objective of the paper is to introduce the new instrument to the radio astronomical community. It describes the hardware configuration and presents some initial results from the on-sky commissioning. The heterodyne instrument covers frequencies between 211 GHz and 1390 GHz divided into four bands. The first three bands are sideband-separating mixers operating in a single sideband mode and based on superconductor-insulator-superconductor (SIS) tunnel junctions. The fourth band is a hot-electron bolometer, waveguide balanced mixer. All bands are integrated in a closedcycle temperature-stabilized cryostat and are cooled to 4 K. We present results from noise temperature, sideband separation ratios, beam, and stability measurements performed on the telescope as a part of the receiver technical commissioning. Examples of broad extragalactic lines are also included

Growth and Characterization of Nb3Al Thin Films for Low-Noise Terahertz Electronics

Demand on ultimately sensitive heterodyne receivers for, e.g., radio astronomy and environmental science instrumentation, has driven large research activities on novel materials and devices for extending the frequency range into the THz domain. The useful RF band of traditionally used niobium-based superconductor-insulator-superconductor (SIS) mixers is limited by the niobium superconducting gap frequency to 700 GHz. Therefore, for mixing applications at higher frequencies, high-energy gapsuperconductors are needed. As an alternative mixing component, the hot electron bolometer (HEB) device can also offer a compromise solution at THz frequencies and new materials could be an useful extension of this technology as well.This thesis presents the work on deposition and characterization of Nb3Al superconducting high-energy gap material thin films. The focus of the study aims at Nb3Al as a promising material for SIS tunnel junctions and HEB devices. A heteroepitaxial growth on a thin niobium underlayer has been applied to the preparation of the Nb3Al thin films by means of dc magnetron co-sputtering. Subsequent ex-situ rapid heat treatment of the deposited Nb3Al films has been proved to enhance the crystal orderingand thus, the superconducting properties of the film. The grown films have been studied by XRD, AFM, TEM, etc. techniques. The highest critical temperature observed in this work was 15.7 K and the values of all major superconducting parameters, such as penetration depth, coherence length etc. were consistent with previously reported results on A15 materials, hence, confirming the prospective to use such films in SIS tunnel junctions. In addition, an epitaxial growth of Nb3Al films on yttriastabilized zirconia substrate showed substantial possibility to grow monocrystalline Nb3Al ultra thin films.It was also found that the studied Nb3Al thin films possess the ability to carry substantially high current densities in the range of above 10E7 A/cm2 and can possibly find appropriate application where high magnetic fields are to be used

Thin Films and Component Technologies for Low-Noise Terahertz Electronics

This thesis deals with several distinct subjects such as thin film deposition, design, fabrication and characterization of components for low-noise THz electronics.High energy-gap superconducting materials are of specific importance for low-noise THz mixer applications. Extending the upper operation frequency of superconductor-insulator-superconductor (SIS) mixers above 1.5 THz is of particular interest. Here, a novel approach of producing Nb3Al thin film based on DC magnetron co-sputtering using heteroepitaxial, as well as epitaxial growth techniques, has been employed. As a result, a superconducting transition temperature, as high as 15.7 K has been observed. Structural and electrical characterization techniques have been utilized to evaluate the set of material and superconducting parameters of the deposited Nb3Al thin films. The superconducting properties of the obtained Nb3Al films have revealed strong potential for using them in practical applications. It has been also demonstrated that Nb3Al can be epitaxially grown on yttria-stabilized-zirconia substrates, thus opening a possibility for hot-electron bolometer (HEB) applications.Another substantial part of this work deals with the in-house development of phonon-cooled HEB mixers. A reliable deposition process for high-quality ultra-thin NbN films has been established. Epitaxial ultra-thin NbN films grown on 3C-SiC/Si substrate with state-of-the-art performance have shown a strong potential to be used in THz HEB mixers with a purpose for improving the intermediate frequency (IF) bandwidth. A novel membrane-like layout for 1.6-2.0 THz HEB mixer has been suggested, developed and implemented for use with micromachined all-metal waveguides.Being the most used in mm- and submillimeter mixer technology for radio astronomy, Nb/Al-AlOx/Nb tunnel junction stability properties are of great importance. In this thesis, the behaviour of a large number high-quality Nb/Al-AlOx/Nb tunnel junctions, subjected to long-term room temperature aging and thermal annealing is systematically studied and explanations of the observed phenomena are suggested.Finally, the work on development of a planar superconducting IF/biasing circuit for use with a SIS mixer is presented. The circuit was integrated into a 385-500 GHz DSB SIS mixer currently under operation at the APEX telescope. Circuit design methodology, measurement results and overall mixer performance with the integrated circuit are shown

Growth and Characterization of Nb3Al Thin Films for Low-Noise Terahertz Electronics

Demand on ultimately sensitive heterodyne receivers for, e.g., radio astronomy and environmental science instrumentation, has driven large research activities on novel materials and devices for extending the frequency range into the THz domain. The useful RF band of traditionally used niobium-based superconductor-insulator-superconductor (SIS) mixers is limited by the niobium superconducting gap frequency to 700 GHz. Therefore, for mixing applications at higher frequencies, high-energy gapsuperconductors are needed. As an alternative mixing component, the hot electron bolometer (HEB) device can also offer a compromise solution at THz frequencies and new materials could be an useful extension of this technology as well.This thesis presents the work on deposition and characterization of Nb3Al superconducting high-energy gap material thin films. The focus of the study aims at Nb3Al as a promising material for SIS tunnel junctions and HEB devices. A heteroepitaxial growth on a thin niobium underlayer has been applied to the preparation of the Nb3Al thin films by means of dc magnetron co-sputtering. Subsequent ex-situ rapid heat treatment of the deposited Nb3Al films has been proved to enhance the crystal orderingand thus, the superconducting properties of the film. The grown films have been studied by XRD, AFM, TEM, etc. techniques. The highest critical temperature observed in this work was 15.7 K and the values of all major superconducting parameters, such as penetration depth, coherence length etc. were consistent with previously reported results on A15 materials, hence, confirming the prospective to use such films in SIS tunnel junctions. In addition, an epitaxial growth of Nb3Al films on yttriastabilized zirconia substrate showed substantial possibility to grow monocrystalline Nb3Al ultra thin films.It was also found that the studied Nb3Al thin films possess the ability to carry substantially high current densities in the range of above 10E7 A/cm2 and can possibly find appropriate application where high magnetic fields are to be used