11,239 research outputs found
Techniques for achieving magnetic cleanliness on deep-space missions
Techniques for obtaining magnetic cleanliness on deep space missions to allow interplanetary magnetic field mappin
Thermionic converter and generator tests
Performance and life test on thermionic converters and generator
Elliptic supersonic jet morphology manipulation using sharp-tipped lobes
Elliptic nozzle geometry is attractive for mixing enhancement of supersonic
jets. However, jet dynamics, such as flapping, gives rise to high-intensity
tonal sound. We experimentally manipulate the supersonic elliptic jet
morphology by using two sharp-tipped lobes. The lobes are placed on either end
of the minor axis in an elliptic nozzle. The design Mach number and the aspect
ratio of the elliptic nozzle and the lobed nozzle are 2.0 and 1.65. The
supersonic jet is exhausted into ambient at almost perfectly expanded
conditions. Time-resolved schlieren imaging, longitudinal and cross-sectional
planar laser Mie-scattering imaging, planar Particle Image Velocimetry, and
near-field microphone measurements are performed to assess the fluidic behavior
of the two nozzles. Dynamic Mode and Proper Orthogonal Decomposition (DMD and
POD) analysis are carried out on the schlieren and the Mie-scattering images.
Mixing characteristics are extracted from the Mie-scattering images through the
image processing routines. The flapping elliptic jet consists of two dominant
DMD modes, while the lobed nozzle has only one dominant mode, and the flapping
is suppressed. Microphone measurements show the associated noise reduction. The
jet column bifurcates in the lobed nozzle enabling a larger surface contact
area with the ambient fluid and higher mixing rates in the near-field of the
nozzle exit. The jet width growth rate of the two-lobed nozzle is about twice
as that of the elliptic jet in the near-field, and there is a 40\% reduction in
the potential core length. Particle Image Velocimetry (PIV) contours
substantiate the results.Comment: 19 pages, 16 figures. Revised version submitted to Physics of Fluids
for peer review. URL of the Video files (Fig. 6 & Fig. 14) are given in the
text files (see in '/anc/*.txt'
Energy harvesting from body motion using rotational micro-generation
Autonomous system applications are typically limited by the power supply operational lifetime when battery replacement is difficult or costly. A trade-off between battery size and battery life is usually calculated to determine the device capability and lifespan. As a result, energy harvesting research has gained importance as society searches for alternative energy sources for power generation. For instance, energy harvesting has been a proven alternative for powering solar-based calculators and self-winding wristwatches. Thus, the use of energy harvesting technology can make it possible to assist or replace batteries for portable, wearable, or surgically-implantable autonomous systems. Applications such as cardiac pacemakers or electrical stimulation applications can benefit from this approach since the number of surgeries for battery replacement can be reduced or eliminated.
Research on energy scavenging from body motion has been investigated to evaluate the feasibility of powering wearable or implantable systems. Energy from walking has been previously extracted using generators placed on shoes, backpacks, and knee braces while producing power levels ranging from milliwatts to watts. The research presented in this paper examines the available power from walking and running at several body locations. The ankle, knee, hip, chest, wrist, elbow, upper arm, side of the head, and back of the head were the chosen target localizations. Joints were preferred since they experience the most drastic acceleration changes. For this, a motor-driven treadmill test was performed on 11 healthy individuals at several walking (1-4 mph) and running (2-5 mph) speeds. The treadmill test provided the acceleration magnitudes from the listed body locations. Power can be estimated from the treadmill evaluation since it is proportional to the acceleration and frequency of occurrence. Available power output from walking was determined to be greater than 1mW/cm³ for most body locations while being over 10mW/cm³ at the foot and ankle locations. Available power from running was found to be almost 10 times higher than that from walking.
Most energy harvester topologies use linear generator approaches that are well suited to fixed-frequency vibrations with sub-millimeter amplitude oscillations. In contrast, body motion is characterized with a wide frequency spectrum and larger amplitudes. A generator prototype based on self-winding wristwatches is deemed to be appropriate for harvesting body motion since it is not limited to operate at fixed-frequencies or restricted displacements. Electromagnetic generation is typically favored because of its slightly higher power output per unit volume. Then, a nonharmonic oscillating rotational energy scavenger prototype is proposed to harness body motion. The electromagnetic generator follows the approach from small wind turbine designs that overcome the lack of a gearbox by using a larger number of coil and magnets arrangements.
The device presented here is composed of a rotor with multiple-pole permanent magnets having an eccentric weight and a stator composed of stacked planar coils. The rotor oscillations induce a voltage on the planar coil due to the eccentric mass unbalance produced by body motion. A meso-scale prototype device was then built and evaluated for energy generation. The meso-scale casing and rotor were constructed on PMMA with the help of a CNC mill machine. Commercially available discrete magnets were encased in a 25mm rotor. Commercial copper-coated polyimide film was employed to manufacture the planar coils using MEMS fabrication processes. Jewel bearings were used to finalize the arrangement. The prototypes were also tested at the listed body locations. A meso-scale generator with a 2-layer coil was capable to extract up to 234 µW of power at the ankle while walking at 3mph with a 2cm³ prototype for a power density of 117 µW/cm³.
This dissertation presents the analysis of available power from walking and running at different speeds and the development of an unobtrusive miniature energy harvesting generator for body motion. Power generation indicates the possibility of powering devices by extracting energy from body motion
Generation of tunable, high repetition rate optical frequency combs using on-chip silicon modulators
We experimentally demonstrate tunable, highly-stable frequency combs with
high repetition-rates using a single, charge injection based silicon PN
modulator. In this work, we demonstrate combs in the C-band with over 8 lines
in a 20-dB bandwidth. We demonstrate continuous tuning of the center frequency
in the C-band and tuning of the repetition-rate from 7.5GHz to 12.5GHz. We also
demonstrate through simulations the potential for bandwidth scaling using an
optimized silicon PIN modulator. We find that, the time varying free carrier
absorption due to carrier injection, an undesirable effect in data modulators,
assists here in enhancing flatness in the generated combs.Comment: 10 pages, 7 figure
High energy efficient solid state laser sources
Recent progress in the development of highly efficient coherent optical sources is reviewed. This work focusses on nonlinear frequency conversion of the highly coherent output of the Non-Planar Ring Laser Oscillators developed earlier in the program, and includes high efficiency second harmonic generation and the operation of optical parametric oscillators for wavelength diversity and tunability
The reconfigurable Josephson circulator/directional amplifier
Circulators and directional amplifiers are crucial non-reciprocal signal
routing and processing components involved in microwave readout chains for a
variety of applications. They are particularly important in the field of
superconducting quantum information, where the devices also need to have
minimal photon losses to preserve the quantum coherence of signals.
Conventional commercial implementations of each device suffer from losses and
are built from very different physical principles, which has led to separate
strategies for the construction of their quantum-limited versions. However, as
recently proposed theoretically, by establishing simultaneous pairwise
conversion and/or gain processes between three modes of a Josephson-junction
based superconducting microwave circuit, it is possible to endow the circuit
with the functions of either a phase-preserving directional amplifier or a
circulator. Here, we experimentally demonstrate these two modes of operation of
the same circuit. Furthermore, in the directional amplifier mode, we show that
the noise performance is comparable to standard non-directional superconducting
amplifiers, while in the circulator mode, we show that the sense of circulation
is fully reversible. Our device is far simpler in both modes of operation than
previous proposals and implementations, requiring only three microwave pumps.
It offers the advantage of flexibility, as it can dynamically switch between
modes of operation as its pump conditions are changed. Moreover, by
demonstrating that a single three-wave process yields non-reciprocal devices
with reconfigurable functions, our work breaks the ground for the development
of future, more-complex directional circuits, and has excellent prospects for
on-chip integration
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