17,977 research outputs found
Energy Conversion Unit with Optimized Waveform Generation
poster abstractThe ever-increasing demand for electrical energy has put pressure on identifying and implementing ways to increase the efficiency of the devices dealing with energy conversion. The power supplies devices able to generate ac voltage from dc one is crucial in automotive and computing industries. Different technologies have been developed to implement power supplies with higher efficiency, such as multilevel and interleaved converters.
This paper proposes an energy conversion unit constituted by a single-phase DC-AC converter with five levels at the output converter side. The proposed converter has an optimized relationship between the numbers of levels per number of switches (nL/nS). The proposed five-level four-switch converter has nL/nS=5/4, which is by far the best relationship among the converters proposed in the technical literature. The most important characteristics of the proposed configuration are: (i) reduced number of semiconductor devices, while keeping the high number of levels at the output converter side, (ii) only one DC source without any need to balance capacitor voltages, and (iii) high efficiency. Details regarding the operation of the configuration and modulation strategy are presented, as well as the comparison between the proposed converter and the conventional ones. Simulated results are presented to validate the theoretical expectations
Time-varying Huygens' meta-devices for parametric waves
Huygens' metasurfaces have demonstrated almost arbitrary control over the
shape of a scattered beam, however, its spatial profile is typically fixed at
fabrication time. Dynamic reconfiguration of this beam profile with tunable
elements remains challenging, due to the need to maintain the Huygens'
condition across the tuning range. In this work, we experimentally demonstrate
that a time-varying metadevice which performs frequency conversion can steer
transmitted or reflected beams in an almost arbitrary manner, with fully
dynamic control. Our time-varying Huygens' metadevice is made of both electric
and magnetic meta-atoms with independently controlled modulation, and the phase
of this modulation is imprinted on the scattered parametric waves, controlling
their shapes and directions. We develop a theory which shows how the scattering
directionality, phase and conversion efficiency of sidebands can be manipulated
almost arbitrarily. We demonstrate novel effects including all-angle beam
steering and frequency-multiplexed functionalities at microwave frequencies
around 4 GHz, using varactor diodes as tunable elements. We believe that the
concept can be extended to other frequency bands, enabling metasurfaces with
arbitrary phase pattern that can be dynamically tuned over the complete 2\pi
range
Approaching the ultimate capacity limit in deep-space optical communication
The information capacity of an optical channel under power constraints is
ultimately limited by the quantum nature of transmitted signals. We discuss
currently available and emerging photonic technologies whose combination can be
shown theoretically to enable nearly quantum-limited operation of a noisy
optical communication link in the photon-starved regime, with the information
rate scaling linearly in the detected signal power. The key ingredients are
quantum pulse gating to facilitate mode selectivity, photon-number-resolved
direct detection, and a photon-efficient high-order modulation format such as
pulse position modulation, frequency shift keying, or binary phase shift keyed
Hadamard words decoded optically using structured receivers.Comment: 9 pages, 4 figures. Presented at Free-Space Laser Communications
XXXI, 4-6 February 2019, San Francisco, C
Optimized power converters for electrically augmented on-orbit propulsion systems
Advances in satellite thruster technology have produced the requirement for high power electrical supplies to operate electrically augmented on-orbit propulsion systems. The power on board satellites is greatly limited by the solar panels that collect energy and the batteries that store the energy. In addition, satellites are constantly using power to operated their mission equipment and handle the communication requirements; This thesis investigates the power systems of modern satellites and the addition of an on-orbit electrically augmented propulsion system. The research process involves determining the system specifications, the power available and the thruster requirements. After determining the requirements, the implementation of the electrically augmented on-orbit propulsion system is characterized in terms of efficiency and potential electromagnetic compatibility. Several circuits are evaluated with the aid of PSPICE circuit simulation software and the results of the evaluation criteria for each circuit are presented
The first version Buffered Large Analog Bandwidth (BLAB1) ASIC for high luminosity collider and extensive radio neutrino detectors
Future detectors for high luminosity particle identification and ultra high
energy neutrino observation would benefit from a digitizer capable of recording
sensor elements with high analog bandwidth and large record depth, in a
cost-effective, compact and low-power way. A first version of the Buffered
Large Analog Bandwidth (BLAB1) ASIC has been designed based upon the lessons
learned from the development of the Large Analog Bandwidth Recorder and
Digitizer with Ordered Readout (LABRADOR) ASIC. While this LABRADOR ASIC has
been very successful and forms the basis of a generation of new, large-scale
radio neutrino detectors, its limited sampling depth is a major drawback. A
prototype has been designed and fabricated with 65k deep sampling at
multi-GSa/s operation. We present test results and directions for future
evolution of this sampling technique.Comment: 15 pages, 26 figures; revised, accepted for publication in NIM
Wavelet-based voice morphing
This paper presents a new multi-scale voice morphing algorithm. This algorithm enables a user to transform one person's speech pattern into another person's pattern with distinct characteristics, giving it a new identity, while preserving the original content. The voice morphing algorithm performs the morphing at different subbands by using the theory of wavelets and models the spectral conversion using the theory of Radial Basis Function Neural Networks. The results obtained on the TIMIT speech database demonstrate effective transformation of the speaker identity
Traveling wave tube development for a serrodyne re-entrant amplifier
Traveling wave tube development for serrodyne re-entrant amplifie
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