Sökning: "high frequencies"

Visar resultat 21 - 25 av 776 avhandlingar innehållade orden high frequencies.

  1. 21. High-temperature superconducting magnetometers for on-scalp MEG

    Författare :Silvia Ruffieux; Chalmers tekniska högskola; []
    Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; NATURVETENSKAP; NATURAL SCIENCES; TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; MEDICIN OCH HÄLSOVETENSKAP; MEDICAL AND HEALTH SCIENCES; TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; NATURVETENSKAP; NATURAL SCIENCES; on-scalp MEG; multi-channel system; SQUID optimization; kinetic inductance magnetometer; magnetoencephalography; magnetometer; crosstalk; SQUID magnetometer calibration; high-Tc SQUID; kinetic inductance;

    Sammanfattning : In the growing field of on-scalp magnetoencephalography (MEG), brain activity is studied by non-invasively mapping the magnetic fields generated by neuronal currents with sensors that are flexibly placed in close proximity to the subject's head. This thesis focuses on high-temperature superconducting magnetometers made from YBa2Cu3Ox-7 (YBCO), which enables a reduction in the sensor-to-room temperature standoff distance from roughly 2 cm (for conventional MEG systems) down to 1 mm. LÄS MER

  3. 22. 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

  4. 23. Ultra High Speed InP Heterojunction Bipolar Transistors

    Författare :Mattias Dahlström; KTH; []
    Nyckelord :InP HBT carbon high-speed;

    Sammanfattning : This thesis deals with the development of high speed InPmesa HBT’s with power gain cut—off frequencies up toand above 300 GHz, with high current density and low collectordischarging times.Key developments are Pd—based base ohmics yielding basecontact resistances as low as 10 Ωµm2, base—collector grades to enable to use ofInP in the collector, and an increase in the maximum currentdensity through collector design and thermal optimization. LÄS MER

  5. 24. On the Dielectric Losses of Polyethylene at Medium and High Frequencies

    Författare :Martin Strååt; Chalmers tekniska högskola; []
    Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; Dielectric properties; foaming; crystallinity; polyethylene; frequency; porosity;

    Sammanfattning : AbstractAs mobile communication moves from 3G to 4G, the bandwidth used will be extended from 2 GHz to 5 GHz. The propagation loss is related to the 2.6:th power of frequency, thus a large increase in power consumption may be expected. LÄS MER

  7. 25. Safety and health effects in high and ultra-high field MR

    Författare :Boel Hansson; Lund Diagnostisk radiologi; []
    Nyckelord :MEDICIN OCH HÄLSOVETENSKAP; MEDICAL AND HEALTH SCIENCES; Magnetic Resonance Imaging; UHF; MR safety; Patient compliance;

    Sammanfattning : Background: More than 70 million magnetic resonance (MR) examinations are produced every year. Patients and personnel are exposed to electromagnetic fields at levels that exceed those normally found in our surroundings or in industry. LÄS MER