Sökning: "High frequency approximations"

Visar resultat 1 - 5 av 36 avhandlingar innehållade orden High frequency approximations.

  1. 1. Computational electromagnetics : software development and high frequency modeling of surface currents on perfect conductors

    Författare :Sandy Sefi; Jesper Oppelstrup; Francisco Saez de Adana; KTH; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; High frequency approximations; Maxwell’s equations; Method of Moments; Physical Optics; Geometrical Theory of Diffraction; Extraction Extrapolation; Numerical analysis; Numerisk analys;

    Sammanfattning : In high frequency computational electromagnetics, rigorous numerical methods be come unrealistic tools due to computational demand increasing with the frequency. Instead approximations to the solutions of the Maxwell equations can be employed to evaluate th electromagnetic fields. LÄS MER

  3. 2. High-order finite difference approximations for hyperbolic problems : multiple penalties and non-reflecting boundary conditions

    Författare :Hannes Frenander; Jan Nordström; Philipp Birken; Linköpings universitet; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY;

    Sammanfattning : In this thesis, we use finite difference operators with the Summation-By-Partsproperty (SBP) and a weak boundary treatment, known as SimultaneousApproximation Terms (SAT), to construct high-order accurate numerical schemes.The SBP property and the SAT’s makes the schemes provably stable. LÄS MER

  4. 3. High Temperature Superconducting and Tunable Ferroelectric Microwave Devices

    Författare :Erik F. Carlsson; Chalmers tekniska högskola; []
    Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; varactors; tunable microwave circuits; conformal mapping; cryogenic probe station; ferroelectrics; high temperature superconductors; microwave circuits; narrow-band filters; phase-shifter;

    Sammanfattning : This thesis addresses some applications of High Temperature Superconductors (HTS) and ferroelectric materials in tunable microwave devices and circuits. The work is divided into three main areas: i) modeling of multilayered structures including ferroelectric layers, ii) realization and characterization of tunable coplanar waveguides (CPW), capacitors and resonators based on ferroelectrics, and iii) an investigation of microstrip HTS K-band filters. LÄS MER

  5. 4. Device Technology Based on High Temperature Superconductors and Microwave Breakdown in Gases

    Författare :Martin Löfgren; Chalmers tekniska högskola; []
    Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; distortion; penetration depth; surface resistance; transmit-receive switch; coupled-grain model; high-power; microwave; pulse; surface impedance; breakdown; propagation; modulator; air; superconductor; transmission line; resonator; coplanar waveguide; plasma;

    Sammanfattning : This thesis deals with two separate fields of microwave technology. The first section treats microwave characterization and applications of high temperature superconducting (HTS) thin films, while the second section treats microwave breakdown in transmit-receive (TR) switches and in air. Within the first section, four main topics are adressed. LÄS MER

  7. 5. Elastic Wave Scattering by Cracks - Interfacial Forces and High Frequency Diffraction

    Författare :Gert Persson; Chalmers tekniska högskola; []
    Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; ultrasonic testing; Wiener-Hopf calculations; Geometrical Theory of Diffraction; edge diffracted body waves; PEDGE; two-dimensional diffraction; geometrical elastodynamic waves;

    Sammanfattning : This thesis treats elastic wave scattering by cracks with interfacial forces. The results are of practical interest in ultrasonic testing and includes development of numerical methods used to predict such testing. First the canonical problem of two-dimensional (2-D) diffraction from a semi-infinite crack is solved. LÄS MER