542 research outputs found
Fluctuations in the electron system of a superconductor exposed to a photon flux
We report on fluctuations in the electron system, Cooper pairs and
quasiparticles, of a superconducting aluminium film. The superconductor is
exposed to pair-breaking photons (1.54 THz), which are coupled through an
antenna. The change in the complex conductivity of the superconductor upon a
change in the quasiparticle number is read out by a microwave resonator. A
large range in radiation power can be chosen by carefully filtering the
radiation from a blackbody source. We identify two regimes. At high radiation
power, fluctuations in the electron system caused by the random arrival rate of
the photons are resolved, giving a straightforward measure of the optical
efficiency (48%). At low radiation power fluctuations are dominated by excess
quasiparticles, the number of which is measured through their recombination
lifetime
EBG enhanced feeds for the improvement of the aperture efficiency of reflector antennas
We describe the use of electromagnetic bandgap (EBG) super-layers to improve the shape of reflectors illumination function. Following an investigation of the leaky wave pole singularities of the EBG Green's function, the shape of the radiation patterns of small apertures in ground planes are optimized. The maximization of the reflector aperture efficiency can be obtained by properly tuning the super layers geometrical parameters. A prototype of such feed has been designed, manufactured and tested. The results indicate that the inclusion of the EBG, increases the aperture efficiency of the feed+reflector system to values higher than 80%, over a 10% bandwidth. These low profile feeds are compatible with printed circuit board and/or integrated technology
Properties of leaky waves supported by grounded dielectric super-layers and implications on the design of reflector feeds
The design strategy that uses dielectric super-layers with neighboring wave-guides closed in matched loads constitutes a worst case scenario as far as the performance enhancement is concerned and finds applicability in radiometric imaging arrays. On the other side the design strategy that uses dielectric super-layers with neighboring wave-guides closed in properly tuned reactive loads can be seen as best case scenario representative of a multi beam system for a telecommunication satellite with independent channels
Polymorphic fingerprint as an approach to authenticate Iberian pig categories
High-commercial-value products are often susceptible to food fraud. Among them, Iberian dry-cured ham is highly appreciated due to its particular and sensory, but also nutritional, properties. There are four different Iberian ham categories (namely bellota, recebo, cebo de campo and cebo), which directly depend on the rearing system of the pig during the last stage of the fattening phase. However, there is still a lack of a normalized and robust method capable of authenticating the different product categories and, therefore, preventing mislabeling. In the present work, we characterized the polymorphic behavior of raw (before curing) lipid extracts belonging to the four categories of Iberian pig. A total of 80 different samples were analyzed by DSC, and synchrotron radiation XRD experiments were carried out for selected ones. The results obtained showed that bellota and recebo categories exhibited essentially the same crystallization and polymorphic behavior and this was significantly different (p < 0.05) from that of cebo de campo and cebo. The latter exhibited higher crystallization and melting temperatures than bellota and recebo samples, due to the occurrence of an additional β′-2L polymorphic form. By considering the differences in rearing systems of pigs belonging to the different categories, we concluded that the key factor which determined the polymorphism of Iberian pig lipid extracts was not the physical exercise practiced by the pig, but the inclusion of acorns in the feeding system. This work demonstrated that thermal and crystallographic techniques, like DSC and XRD, may be promoted to be used as fingerprinting tools for the authentication of high-value food products
Surface wave control for large arrays of microwave kinetic inductance detectors
Large ultra-sensitive detector arrays are needed for present and future
observatories for far infra-red, submillimeter wave (THz), and millimeter wave
astronomy. With increasing array size, it is increasingly important to control
stray radiation inside the detector chips themselves, the surface wave. We
demonstrate this effect with focal plane arrays of 880 lens-antenna coupled
Microwave Kinetic Inductance Detectors (MKIDs). Presented here are near field
measurements of the MKID optical response versus the position on the array of a
reimaged optical source. We demonstrate that the optical response of a detector
in these arrays saturates off-pixel at the dB level compared to the
peak pixel response. The result is that the power detected from a point source
at the pixel position is almost identical to the stray response integrated over
the chip area. With such a contribution, it would be impossible to measure
extended sources, while the point source sensitivity is degraded due to an
increase of the stray loading. However, we show that by incorporating an
on-chip stray light absorber, the surface wave contribution is reduced by a
factor 10. With the on-chip stray light absorber the point source response
is close to simulations down to the dB level, the simulation based on
an ideal Gaussian illumination of the optics. In addition, as a crosscheck we
show that the extended source response of a single pixel in the array with the
absorbing grid is in agreement with the integral of the point source
measurements.Comment: accepted for publication in IEEE Transactions on Terahertz Science
and Technolog
Eliminating stray radiation inside large area imaging arrays
With increasing array size, it is increasingly important to control stray
radiation inside the detector chips themselves. We demonstrate this effect with
focal plane arrays of absorber coupled Lumped Element microwave Kinetic
Inductance Detectors (LEKIDs) and lens-antenna coupled distributed quarter
wavelength Microwave Kinetic Inductance Detectors (MKIDs). In these arrays the
response from a point source at the pixel position is at a similar level to the
stray response integrated over the entire chip area. For the antenna coupled
arrays, we show that this effect can be suppressed by incorporating an on-chip
stray light absorber. A similar method should be possible with the LEKID array,
especially when they are lens coupled.Comment: arXiv admin note: substantial text overlap with arXiv:1707.0214
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