1,721,068 research outputs found
A millimeter unilateral finline SIS mixer with a wide IF bandwidth
Get PDFSuperconductor-Insulator-Superconductor (SIS) tunnel junction mixers are now commonly used in as- tronomical receivers at (sub)millimeter wavelengths because of their superb sensitivity, high dynamic range and stability of operation. Niobium SIS mixers operating at frequencies well below the super- conducting gap (∼680 GHz) have already achieved quantum limited sensitivity. Therefore to further enhance the receiver sensitivity, increasing the Intermediate Frequency (IF) bandwidth of SIS mixers has became crucial. This thesis focuses on the theoretical modeling, design and experimental verifi- cation of Nb SIS mixers operating around 230 GHz with a wide IF bandwidth of 1–15 GHz. These mixers were designed for a single baseline heterodyne interferometer (GUBBINS), which is being built to observe the Sunyaev-Zel’dovich effect in the Cosmic Microwave Background. The combination of wide IF bandwidth SIS mixers and complex analogue correlators will allow GUBBINS to feature high surface brightness sensitivity, that helps to distinguish the weak SZ effect from the background noise. The SIS mixer detector system was assembled inside the GUBBINS cryostat together with the IF electronics and RF/LO optical systems. Low noise temperatures of around 71 K were then measured in the GUBBINS system. The Nb SIS mixer we have developed uses a unilateral finline and fully integrated planar circuits deposited on a silicon substrate, to couple the electromagnetic radiation from the waveguide into the SIS junction. The finline mixer allows a broad-band RF coupling, an easy integration of the on-chip planar circuits and an easy-to-fabricate mixer block. To achieve a wide IF bandwidth, the output impedance of the SIS mixer was well matched to the input impedance of the amplifier by a multi-stage microstrip circuit. Additionally, the planar circuit of the SIS mixer was also designed to have a small lumped inductance and capacitance. The SIS mixer chip was extensively simulated by rigorous electromagnetic software (HFSS) and the S-parameter was exported to a quantum mixing package SuperMix to produce a full-wave model of the mixer. Experimental testing yielded a best noise temperature of 50 K with an average noise temperature of 75 K over an RF bandwidth of 160 GHz– 260 GHz. We have performed thorough experimental and computational investigation of the IF system in particular the constraints on the bandwidth caused by the lumped element capacitance of the mixer chip and the matching of the output impedance of the mixer to the IF amplifier. Our conclusion is that a bandwidth of 1–15 GHz could be achieved using our mixer design, subject to the performance of the amplifier. Finally, a variable temperature load system was successfully developed and tested inside the cryostat, to avoid the losses from the room-temperature optics. We have showed that the noise temperature of the SIS detector could be reduced by as much as 15 K by testing the mixer using a variable temperature load inside the cryostat
Development of superconducting bolometer device technology for millimeter-wave cosmology instruments
Get PDFThe Cold-Electron Bolometer (CEB) is a sensitive detector of millimeter-wave radiation, in which tunnel junctions are used as temperature sensors of a nanoscale normal metal strip absorber. The absorber is fed by an antenna via two Superconductor-Insulator-Normal metal (SIN) tunnel junctions, fabricated at both ends of the absorber. Incoming photons excite electrons, heating the whole electron system. The incoming RF power is determined by measuring the tunneling current through the SIN junctions. Since electrons at highest energy levels escape the absorber through the tunnel junctions, it causes cooling of the absorber. This electron cooling provides electro-thermal feedback that makes the saturation power of a CEB well above that of other types of millimeter-wave receivers. The key features of CEB detectors are high sensitivity, large dynamic range, fast response, easy integration in arrays on planar substrates, and simple readout. The high dynamic range allows the detector to operate under relatively high background levels. In this thesis, we present the development and successful operation of CEB, focusing on the fabrication technology and different implementations of the CEB for efficient detection of electromagnetic signals. We present the CEB detector integrated across a unilateral finline deposited on a planar substrate. We have measured the finline-integrated CEB performance at 280-315 mK using a calibrated black-body source mounted inside the cryostat. The results have demonstrated strong response to the incoming RF power and reasonable sensitivity. We also present CEB devices fabricated with advanced technologies and integrated in log-periodic, double-dipole and cross-slot antennas. The measured CEB performance satisfied the requirements of the balloon-borne experiment BOOMERANG and could be considered for future balloon-borne and ground-based instruments. In this thesis we also investigated a planar phase switch integrated in a back-to-back finline for modulating the polarization of weak electromagnetic signals. We examine the switching characteristics and demonstrate that the switching speed of the device is well above the speed required for phase modulation in astronomical instruments. We also investigated the combination of a detector and a superconducting phase switch for modulating the polarization of electromagnetic radiation
Development of coherent detector technologies for sub-millimetre wave astronomy observations
Get PDFSuperconductor-Insulator-Superconductor (SIS) mixers are now used regularly in sub- millimetre astronomical receivers. They have already achieved sensitivity approaching the quantum limit at frequencies below the superconducting gap of niobium (~680 GHz). Above that, the mixer performance is compromised by losses, unless materials with higher superconducting gap are employed in conjunction with the niobium tunnel junction. In this thesis, we present the development of 700 GHz niobium SIS mixers, employing a unilateral finline taper on a thin Silicon-On-Insulator (SOI) substrate. These mixers are broadband with full on-chip planar circuit integration, and require only a very simple mixer block. They were designed using rigorous 3-D electromagnetic simulator (HFSS), in conjunction with a quantum mixing software package (SuperMix), and have demonstrated good performance with the best noise temperature measured at 143 K. Our mixer devices were fed by multiple flare angle smooth-walled horns, which are easy to fabricated, yet retain the high performance of corrugated horns. The radiation patterns measured from 600–740 GHz have shown good beam circularity, low sidelobe and cross-polarization levels. In this thesis, we also present SIS mixer designs with balanced and sideband separ- ating capability. These mixers employ back-to-back finline tapers, so that the RF and local oscillator (LO) signals can be injected separately without a beam splitter. We have fabricated and tested the performance of the balanced mixers, and analysed their performance thoroughly. We have also investigated a new method of generating LO signals by beating the tones of two infrared lasers. Using the current 16-pixel 350 GHz SIS receiver, HARP-B, we have observed the 12CO J=3→2 emission lines from two nearby galaxies. An important result we found is that the 12CO J=3→2 correlates strongly with the 8 μm Polycyclic Aromatic Hydrocarbon emission
TELIS: TErahertz and subMMW LImb Sounder – Project summary after first successful flight
No full textThe TELIS instrument is a balloon-borne cryogenic three-channel heterodyne spectrometer for limb sounding of stratospheric trace gases. The instrument is flown together with the MIPAS-B Fourier-transform spectrometer of the IMK, Karlsruhe. TELIS was developed by a European consortium involving research institutions, universities, and industrial partners.
Thermal emission radiation is coupled in by a 26x13 cm dual offset Cassegrain telescope controlled to maintain constant tangent height during measurement. Radiometric calibration is achieved by a blackbody and deep space view. The radiation is divided into three channels by means of a polarizer and a dichroic. Within a special lightweight cryostat three complete heterodyne receivers are kept at liquid helium temperature: THZ channel, 1750-1890 GHz, hot electron bolometer mixer, DLR; SIR channel, 450-650 GHz, integrated receiver, SIS mixer, SRON (see poster ‘TELIS instrument performance analysis’); subMMW channel, 499-503 GHz, SIS mixer, RAL. A digital autocorrelator spectrometer with 4 GHz bandwidth and ca. 2 MHz resolution serves as backend shared among the channels.
The first successful flight was in March 2009 in Kiruna, Sweden. Calibrated spectra are so far only available as quicklook data. Sideband ratios have been characterized recently. The radiometric accuracy of the autocorrelator is under investigation (see poster ‘Characterisation of the TELIS autocorrelator spectrometer’).
The present paper will present the instrument as well as first results from the flight
A dual-polarization receiver for multi-beam interferometry
Get PDFSuperconductor/Insulator/Superconductor (SIS) mixers are today the best heterodyne receivers for detecting astronomical signals in the range from 100 GHz to 1 THz. Existing receivers have noise performance approaching the fundamental quantum limit, but large format arrays have not yet been realised. Developing large format arrays is, therefore, the most efficient method for increasing the observational speed.
In this thesis, we describe the development of a planar dual-polarisation SIS receiver. The integration of the receiver circuit on the chip with the SIS mixers for both polarisations simplifies the receiver architecture. Upon this more compact receiver design, extending to a large focal plane array with a high pixel count is simplified. The cost of this simplified receiver is the need for the development of more complicated on-chip circuits. We demonstrate this technology development in the frequency band of the wideband Submillimetre Array (wSMA) low band from 190 GHz to 290 GHz. The dual-polarisation receiver chip with a size of 4.0 mm by 4.1 mm comprises a polarisation splitting 4-probe orthomode transducer (OMT) and the mixers for each polarisation. All planar circuits are fabricated on the same quartz chip alongside some auxiliary circuits needed to connect the OMT with the mixers. We use the twin junction tuning scheme because it offers a compact and robust way of matching the highly capacitive SIS junctions.
As part of this development, we investigate the twin-junction tuning to improve the matching to the feeding RF circuit during the design phase. Furthermore, we extended existing techniques of embedding impedance recovery to apply to twin junction mixers to have a reliable tool to test our integrated receiver experimentally.
Based on these ideas, we designed an on-chip dual polarisation receiver, deployed it in a test setup and finally characterised the receiver. We describe in detail the test setup, including the 40 mm by 40 mm mixer block, which reserves margins on the size for the IF board and the magnetic bias options, and allows the extension into a 2x2-pixel 70 mm by 70 mm array. The preliminary experimental results we obtained with a single receiver chip demonstrate that sufficient local oscillator (LO) power can be coupled on the receiver chip, and it lines out a procedure for testing and characterising the receiver.
In addition, we present the design of a two-pixel balanced dual-polarisation receiver with an on-chip LO distribution. The design uses the same method we employed for the receiver chip described above but has the capability of rejecting LO noise. This design allows the construction of large format SIS receiver arrays with an improved noise temperature performance
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A 230 GHz focal plane array using a wide IF bandwidth SIS receiver
Get PDFSuperconductor-Insulator-Superconductor (SIS) mixers offer the best noise properties of any heterodyne mixing technique at millimetre wavelengths. In astronomy, they are used for sensitive spectroscopy, which is vital for understanding the properties of the cold interstellar medium, including regions of star formation activity. Modern SIS receivers have noise properties that are ∼3 times the quantum limit, and it is now becoming increasingly difficult to lower the noise properties any further. In this thesis, I investigate two techniques that extend the capability of SIS receivers. The first technique is extending the instantaneous bandwidth of the receivers, i.e., the intermediate frequency bandwidth (IFBW). For spectral line sources, wide IFBW expands the survey depth to allow multiple emission lines to be observed simultaneously. Here, I present a new SIS mixer device at 230 GHz. The planar circuit was minimised to reduce any parasitic capacitances that may limit the IFBW. Experimentally, the device provides excellent noise temperatures down to 36 K and an IFBW extending from approximately 0–11 GHz. Simulation software was developed to better understand the performance of this device, and it suggests that the IFBW can be extended to higher frequencies if the IF measurement chain is upgraded. The second technique that I investigate is increasing the number of receivers in the focal plane of the receiver, i.e., adding more pixels. There are many challenges involved in this task including how to fit multiple receivers into a small space, how to properly cool the receiver, and how to deliver the local-oscillator signal. Here, I present a new 1 × 4 focal plane array. This array is acting as a demonstrator for a new array architecture that can be expanded into many more pixels in the future. It uses cascaded waveguide power splitters to divide the local-oscillator signal, and then waveguide directional couplers to combine the LO with the astronomical signals. Finally, I present CO(J=1→0) measurements from 34 galaxies in the 5MUSES survey. These measurements trace the amount of cold molecular gas present in these galaxies. By comparing these measurements to other metrics that trace star formation activity (e.g., infrared luminosity), I was able to form empirical relationships between the observed quantities. I also combined these results with other star formation studies from nearby and high redshift galaxies to form scaling relationships spanning a large fraction of cosmic time
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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