83 research outputs found
CMB Observations: improvements of the performance of correlation radiometers by signal modulation and synchronous detection
Observation of the fine structures (anisotropies, polarization, spectral
distortions) of the Cosmic Microwave Background (CMB) is hampered by
instabilities, 1/f noise and asymmetries of the radiometers used to carry on
the measurements. Addition of modulation and synchronous detection allows to
increase the overall stability and the noise rejection of the radiometers used
for CMB studies. In this paper we discuss the advantages this technique has
when we try to detect CMB polarization. The behaviour of a two channel
correlation receiver to which phase modulation and synchronous detection have
been added is examined. Practical formulae for evaluating the improvements are
presented.Comment: 18 pages, 3 figures, New Astronomy accepte
Permittivity and permeability of epoxy-magnetite powder composites at microwave frequencies
Radio, millimetre and sub-millimetre astronomy experiments as well as remote
sensing applications often require castable absorbers with well known
electromagnetic properties to design and realize calibration targets. In this
context, we fabricated and characterized two samples using different ratios of
two easily commercially available materials: epoxy (Stycast 2850FT) and
magnetite () powder. We performed transmission and
reflection measurements from 7 GHz up to 170 GHz with a VNA equipped with a
series of standard horn antennas. Using an empirical model we analysed the data
to extract complex permittivity and permeability from transmission data; then
we used reflection data to validate the results. In this paper we present the
sample fabrication procedure, analysis method, parameter extraction pipeline,
and results for two samples with different epoxy-powder mass ratios.Comment: 7 pages, 18 figures, submitted to the Journal of Applied Physics
(AIP
A demonstrator for bolometric interferometry
Bolometric Interferometry (BI) is one of the most promising techniques for
precise measurements of the Cosmic Microwave Background polarization. In this
paper, we present the results of DIBO (Demonstrateur d'Interferometrie
Bolometrique), a single-baseline demonstrator operating at 90 GHz, built to
proof the validity of the BI concept applied to a millimeter-wave
interferometer. This instrument has been characterized in the laboratory with a
detector at room temperature and with a 4 K bolometer. This allowed us to
measure interference patterns in a clean way, both (1) rotating the source and
(2) varying with time the phase shift among the two interferometer's arms.
Detailed modelisation has also been performed and validated with measurements.Comment: 15 pages, 14 figure
Current status and perspectives of the official sensory control methods in protected designation of origin food products and wines
Resultado de un trabajo colaborativo dentro del Working Group PDO de la European Sensory Science SocietyProtected Designation of Origin (PDO) is part of the regulated quality schemes in the European Union
(EU). Producers of PDO food products and wines have to present EU authorities a technical specification
of their product, which includes its sensory description. European regulation 1151/12 establishes that
sensory characteristics included in PDO certification must be guaranteed. Nevertheless, there is no
standardized approach for the development of sensory control methods for PDO food products, so each
entity in charge of controlling the characteristics of the PDO products decides the best way to follow this
legal requirement. This paper presents the current situation in Spain, Italy and France in relation to the
official sensory control of PDO food products and wines and the accreditation of the laboratories for this
control (these three countries represent 68.9% of the total PDO products registered in the EU). This
manuscript also shows the main methodologies applied in the official sensory control of PDO food
products and wines. The wide diversity of methods used for the sensory control and associated panel
management among PDOs manifests the need to harmonize technical criteria and references at European
level. This is also urgent, because broad differences in the approaches and requirements for sensory
control could bring about unfair competition among PDOs. In this sense, European Sensory Science
Society (E3S) has become an EA recognized stakeholder collaborating in a framework in order to prepare
a document for the harmonization of methodological approaches and technical criteria for the sensory
control of PDO food products and wines
PROTOCALC: an artificial calibrator source for CMB telescopes
Cosmic Microwave Background experiments need to measure polarization
properties of the incoming radiation very accurately to achieve their
scientific goals. As a result of that, it is necessary to properly characterize
these instruments. However, there are not natural sources that can be used for
this purpose. For this reason, we developed the PROTOtype CALibrator for
Cosmology, PROTOCALC, which is a calibrator source designed for the 90GHz band
of these telescopes. This source is purely polarized and the direction of the
polarization vector is known with an accuracy better than 0.1deg. This source
flew for the first time in May 2022 showing promising resultComment: Presented at SPIE Astronomical Telescopes + Instrumentation 202
Efficient Differential Fourier-Transform Spectrometer for precision Sunyaev-Zel'dovich effect measurements
Precision measurements of the Sunyaev-Zel'dovich effect in clusters of
galaxies require excellent rejection of common-mode signals and wide frequency
coverage. We describe an imaging, efficient, differential Fourier transform
spectrometer (FTS), optimized for measurements of faint brightness gradients at
millimeter wavelengths. Our instrument is based on a Martin-Puplett
interferometer (MPI) configuration. We combined two MPIs working synchronously
to use the whole input power. In our implementation the observed sky field is
divided into two halves along the meridian, and each half-field corresponds to
one of the two input ports of the MPI. In this way, each detector in the FTS
focal planes measures the difference in brightness between two sky pixels,
symmetrically located with respect to the meridian. Exploiting the high
common-mode rejection of the MPI, we can measure low sky brightness gradients
over a high isotropic background. The instrument works in the range
120 cm (30600 GHz), has a maximum spectral resolution (1.9 GHz), and an unvignetted throughput of 2.3 cmsr. It
occupies a volume of 0.70.70.33 m and has a weight of 70
kg. This design can be implemented as a cryogenic unit to be used in space, as
well as a room-temperature unit working at the focus of suborbital and
ground-based mm-wave telescopes. The first in-flight test of the instrument is
with the OLIMPO experiment on a stratospheric balloon; a larger implementation
is being prepared for the Sardinia radio telescope.Comment: this version matches the published pape
Design and Verification of a Q-Band Test Source for UAV-Based Radiation Pattern Measurements
In the last years, the unmanned aerial vehicles (UAVs) generated significant innovations in in situ antenna measurements. UAV-mounted test sources have been exploited to characterize the radiation pattern of receiving antennas and arrays for HF radars, radio telescopes in very high-frequency (VHF) band, and up to the X-band for radar characterization. A UAV test source operating in the Q-band has been recently developed within the large-scale polarization explorer (LSPE) project. It will be used for the in situ validation of a ground-based cluster of coherent polarimeters for cosmology observation. This article presents the payload solution that is actually applicable to general UAV-based radiation pattern measurements in the Q-band. It is based on a phase-locked loop synthesizer and an active multiplier coupled with a power detector to compensate for signal power drifts in postprocessing. Relevant system tests have been performed in both laboratory environment and operative conditions. The measured outdoor radiation patterns are in good agreement with both the anechoic chamber measurements and simulated data
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