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Träfflista för sökning "AMNE:(TEKNIKVETENSKAP Elektroteknik, elektronik och fotonik Övrig elektroteknik, elektronik och fotonik) "

Sökning: AMNE:(TEKNIKVETENSKAP Elektroteknik, elektronik och fotonik Övrig elektroteknik, elektronik och fotonik)

  • Resultat 1-10 av 76
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  • Fredenberg, Erik, 1979- (författare)
  • Spectral Mammography with X-Ray Optics and a Photon-Counting Detector
  • 2009
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Early detection is vital to successfully treating breast cancer, and mammography screening is the most efficient and wide-spread method to reach this goal. Imaging low-contrast targets, while minimizing the radiation exposure to a large population is, however, a major challenge. Optimizing the image quality per unit radiation dose is therefore essential. In this thesis, two optimization schemes with respect to x-ray photon energy have been investigated: filtering the incident spectrum with refractive x-ray optics (spectral shaping), and utilizing the transmitted spectrum with energy-resolved photon-counting detectors (spectral imaging).Two types of x-ray lenses were experimentally characterized, and modeled using ray tracing, field propagation, and geometrical optics. Spectral shaping reduced dose approximately 20% compared to an absorption-filtered reference system with the same signal-to-noise ratio, scan time, and spatial resolution. In addition, a focusing pre-object collimator based on the same type of optics reduced divergence of the radiation and improved photon economy by about 50%.A photon-counting silicon detector was investigated in terms of energy resolution and its feasibility for spectral imaging. Contrast-enhanced tumor imaging with a system based on the detector was characterized and optimized with a model that took anatomical noise into account. Improvement in an ideal-observer detectability index by a factor of 2 to 8 over that obtained by conventional absorption imaging was found for different levels of anatomical noise and breast density. Increased conspicuity was confirmed by experiment. Further, the model was extended to include imaging of unenhanced lesions. Detectability of microcalcifications increased no more than a few percent, whereas the ability to detect large tumors might improve on the order of 50% despite the low attenuation difference between glandular and cancerous tissue. It is clear that inclusion of anatomical noise and imaging task in spectral optimization may yield completely different results than an analysis based solely on quantum noise.
  • Chirgwandi, Z. G., et al. (författare)
  • Properties of a bio-photovoltaic nano-device
  • 2008
  • Ingår i: The Journal of Physical Chemistry C. - 1932-7455. ; 112:48, s. 18717-18721
  • Tidskriftsartikel (refereegranskat)abstract
    • Properties of an on-chip photovoltaic nanodevice are demonstrated. The dyes comprise green florescent proteins (GFP). Dependence of recently reported zero external potential bias (ZEPB) photocurrent (I) on temperature, power, and wavelength (lambda) is shown. Correlation between UV-vis spectrum of the GFP and the ZEPB I(lambda) of the device is reported. The temperature dependence suggests the ZEPB photocurrent to reflect a liquid crystal type ordering where the current declines monotonically with increasing temperature. The influence of an external bias on the photocurrent is demonstrated. The resulting light-induced current is analyzed in terms of resistive and quantum mechanical contributions.
  • Löfdahl, Lennart, et al. (författare)
  • Characteristics of a hot-wire microsensor for time-dependent wall shear stress measurements
  • 2003
  • Ingår i: Experiments in Fluids. - 0723-4864. ; 35:3, s. 240-251
  • Tidskriftsartikel (refereegranskat)abstract
    • Hot-wire microsensors for the purpose of measuring the instantaneous velocity gradient close to a wall were designed and their characteristics were evaluated. The sensors were made using MEMS (microelectromechanical systems) technology, which permits the fabrication of various microgeometrical configurations with high precision and good repeatability. The design is based on estimates of the heat rates from the sensor wire to the air, through the supports, and to the wall. Several hot-wire configurations were fabricated with wires positioned in the range 50-250 mum from the wall. Requirements for the design and details of the fabrication methodology are outlined. The hot-wire microsensors were calibrated and tested in a flat-plate boundary layer with and without pressure gradients and were found to have good steady-state characteristics. In addition, the developed sensors were used for preliminary studies of transitional phenomena and turbulence, and the sensors were found to have a good time-dependent response as well.
  • Fredenberg, Erik, 1979-, et al. (författare)
  • Energy resolution of a photon-counting silicon strip detector
  • 2010
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A : Accelerators, Spectrometers, Detectors and Associated Equipment. - 0168-9002. ; s. 156-162
  • Tidskriftsartikel (refereegranskat)abstract
    • A photon-counting silicon strip detector with two energy thresholds was investigated for spectral X-ray imaging in a mammography system. Preliminary studies already indicate clinical benefit of the detector, and the purpose of the present study is optimization with respect to energy resolution. Factors relevant for the energy response were measured, simulated, or gathered from previous studies, and used as input parameters to a cascaded detector model. Threshold scans over several X-ray spectra were used to calibrate threshold levels to energy, and to validate the model. The energy resolution of the detector assembly was assessed to range over ΔE/E=0.12–0.26 in the mammography region. Electronic noise dominated the peak broadening, followed by charge sharing between adjacent detector strips, and a channel-to-channel threshold spread. The energy resolution may be improved substantially if these effects are reduced to a minimum. Anti-coincidence logic mitigated double counting from charge sharing, but erased the energy resolution of all detected events, and optimization of the logic is desirable. Pile-up was found to be of minor importance at typical mammography rates.
  • Decharat, Adit, et al. (författare)
  • Room-Temperature Sealing of Microcavities by Cold Metal Welding
  • 2009
  • Ingår i: Journal of microelectromechanical systems. - 1057-7157. ; 18:6, s. 1318-1325
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, we present a wafer-to-wafer attachment and sealing method for wafer-level manufacturing of micro-cavities using a room-temperature bonding process. The proposed attachment and sealing method is based on plastic deformation and cold welding of overlapping metal rings to create metal-to-metal bonding and sealing. We present the results from experiments using various bonding process parameters and metal sealing ring designs including their impact on the resulting bond quality. The sealing properties against liquids and vapor of different sealing ring structures have been evaluated for glass wafers that are bonded to silicon wafers. In addition, wafer-level vacuum sealing of microcavities was demonstrated when bonding a silicon wafer to another silicon wafer with the proposed room-temperature sealing and bonding technique.
  • Park, Hyundai, et al. (författare)
  • Device and Integration Technology for Silicon Photonic Transmitters
  • 2011
  • Ingår i: IEEE Journal of Selected Topics in Quantum Electronics. - 1077-260X. ; 17:3, s. 671-688
  • Tidskriftsartikel (refereegranskat)abstract
    • The device and integration technology for silicon photonic transmitters are reviewed in this paper. The hybrid silicon platform enables on-chip lasers to be fabricated with silicon photonic circuits and can be integrated in the CMOS back-end flow. Laser arrays from multiple die bonding and quantum well intermixing techniques are demonstrated to extend the spectral bandwidth from the laser array of the transmitter. Two modulator technologies, silicon modulators and hybrid silicon modulators, are also described.
  • Xu, Tianhua, 1984-, et al. (författare)
  • Frequency-domain chromatic dispersion equalization using overlap-add methods in coherent optical system
  • 2011
  • Ingår i: Journal of optical communications. - 0173-4911. ; 27:2
  • Tidskriftsartikel (refereegranskat)abstract
    • The frequency domain equalizers (FDEs) employing two types of overlap-add zero-padding (OLA-ZP) methods are applied to compensate the chromatic dispersion in a 112-Gbit/s non-return-to-zero polarization division multiplexed quadrature phase shift keying (NRZ-PDM-QPSK) coherent optical transmission system. Simulation results demonstrate that the OLA-ZP methods can achieve the same acceptable performance as the overlap-save method. The required minimum overlap (or zero-padding) in the FDE is derived, and the optimum fast Fourier transform length to minimize the computational complexity is also analyzed. 
  • Hertz, Hans, et al. (författare)
  • Laboratory Water-Window X-Ray Microscopy
  • 2009
  • Ingår i: 2009 IEEE LEOS ANNUAL MEETING CONFERENCE PROCEEDINGS : VOLS 1 AND 2. - 978-1-4244-3680-4 ; s. 48-48
  • Konferensbidrag (refereegranskat)abstract
    • We review recent progress in laboratory water-window microscopy including 250 W/0.8 ns/2 kHz laser-plasma liquid-jet sources, 13-nm zone width diffractive optics, diffractive optical elements for phase-contrast microscopy, <25-nm resolution microscopy using compound zone plates, tomography and applications in soil science.
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