We report on a novel compact wideband 90° twist with performance tolerant to small geometry variation and hence improved manufacturability through direct milling. The experimental verification shows ...44% fractional bandwidth with return loss better than 20 dB over the 140-220 GHz band. The performance, compactness, and tolerance to manufacturing inaccuracy make it very suitable for use in various waveguide systems from microwave to millimeter-wave range.
Context. We describe the new Swedish-ESO PI Instrument for APEX (SEPIA) receiver, which was designed and built by the Group for Advanced Receiver Development (GARD), at Onsala Space Observatory (OSO) ...in collaboration with ESO. It was installed and commissioned at the APEX telescope during 2015 with an ALMA Band 5 receiver channel and updated with a new frequency channel (ALMA Band 9) in February 2016. Aim. This manuscript aims to provide, for observers who use the SEPIA receiver, a reference in terms of the hardware description, optics and performance as well as the commissioning results. Methods. Out of three available receiver cartridge positions in SEPIA, the two current frequency channels, corresponding to ALMA Band 5, the RF band 158–211 GHz, and Band 9, the RF band 600–722 GHz, provide state-of-the-art dual polarization receivers. The Band 5 frequency channel uses 2SB SIS mixers with an average SSB noise temperature around 45 K with IF (intermediate frequency) band 4–8 GHz for each sideband providing total 4 × 4 GHz IF band. The Band 9 frequency channel uses DSB SIS mixers with a noise temperature of 75–125 K with IF band 4–12 GHz for each polarization. Results. Both current SEPIA receiver channels are available to all APEX observers.
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Aims. In March 2008, the APEX facility instrument was installed on the telescope at the site of Lliano Chajnantor in northern Chile. The main objective of the paper is to introduce the new instrument ...to the radio astronomical community. It describes the hardware configuration and presents some initial results from the on-sky commissioning. Methods. The heterodyne instrument covers frequencies between 211 GHz and 1390 GHz divided into four bands. The first three bands are sideband-separating mixers operating in a single sideband mode and based on superconductor-insulator-superconductor (SIS) tunnel junctions. The fourth band is a hot-electron bolometer, waveguide balanced mixer. All bands are integrated in a closed-cycle temperature-stabilized cryostat and are cooled to 4 K. Results. We present results from noise temperature, sideband separation ratios, beam, and stability measurements performed on the telescope as a part of the receiver technical commissioning. Examples of broad extragalactic lines are also included.
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We demonstrate the suitability of employing suspended GaN beams on a Π-shaped Si frame for waveguide-based cryogenic THz components and systems. This concept addresses major challenges and provides ...eased device handling, cryogenic operation, micron-alignment possibilities, high integratability and allows the electrical contacting by using bonding wires. In particular, a balanced hot electron bolometer (HEB) mixer was implemented for frequencies at 1.3 THz with state-of-the-art IF performance, which combines micro-machined all-metal waveguide components in conjunction with a suspended GaN beam. In addition, in order to accomplish a proper design of active or passive components, the accurate knowledge of the effective dielectric constant at THz frequencies is crucial when such membranes are employed. Thus, a direct measurement method based on a resonance structure and an S-parameter measurement between 1 THz and 1.5 THz is also presented.
The suitability of AlxGa1−xN epilayers to deposit onto ultra-thin NbN films has been demonstrated for the first time. High quality single-crystal films with 5 nm thickness confirmed by high ...resolution transmission electron microscopy (HRTEM) have been deposited in a reproducible manner by means of reactive DC magnetron sputtering at elevated temperatures and exhibit critical temperatures (Tc) as high as 13.2 K and residual resistivity ratio (RRR) 1 on hexagonal GaN epilayers. On increasing the Al content x in the AlxGa1−xN epilayer above 20%, a gradual deterioration of Tc to 10 K was observed. Deposition of NbN on bare silicon substrates served as a reference and comparison. Excellent spatial homogeneity of the fabricated films was confirmed by R(T) measurements of patterned micro-bridges across the entire film area. The superconducting properties of these films were further characterized by critical magnetic field and critical current measurements. It is expected that the employment of GaN material as a buffer-layer for the deposition of ultra-thin NbN films will prospectively benefit terahertz electronics, particularly hot electron bolometer (HEB) mixers.
•Field-effect transistor with nanowire channel was fabricated on the apex of silicon-on-insulator chip.•Field scanning probe sensor was proposed and demonstrated.•Proposed sensor may be useful tool ...for extremely sensitive electric field probing of solid and biological interfaces.
We report on the new active tip for scanning probe microscopy allowing the simultaneous measurements of surface topography and its potential profile. We designed and fabricated a field-effect transistor with nanowire channel located on the apex of silicon-on-insulator small chip. The field-effect transistor with nanowire channel was selected due to its extremely high electric field sensitivity even at room temperature. We developed the scanning probe operated in the tuning fork regime and demonstrated its reasonable spatial and field resolution. The proposed device can be a unique tool for high-sensitive, high-resolution, non-destructive potential profile mapping of nanoscale objects in physics, biology and material science. We discuss the ways to optimize the sensor charge sensitivity to the theoretical limit which is 10−3e/Hz−1/2 at room temperature.
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•Ridge gap resonator has been fabricated using bundles of vertically aligned carbon nanotubes as a base material.•283μm high bundles of vertically aligned carbon nanotubes grow in 3min whereas it ...takes 92–139min when the structures of same height are fabricated by etching silicon.•Resources used to fabricate ridge gap resonator using carbon nanotubes structures are cheaper and the process time is shorter resulting in a much lower process cost.
Microfabrication with Si has its benefits but it is time consuming when etching high ratio structures. Previously a ridge gap resonator has been fabricated in Si, with a pin height of 278μm. In this paper carbon nanotubes, which can grow hundreds of micrometers within minutes are being used as a base material for a high frequency device. It has been implemented on a ridge gap resonator for 220–325GHz. Carbon nanotubes based structures offer a rapid and low-cost turnover for prototyping. Measurements comparing two carbon nanotubes-based structures to a previously made Si structure and simulations are presented. From these measurements the unloaded Q-value and the loss/mm have been calculated and shows a loss of 0.079dB/mm and 0.051dB/mm for the lower frequency range respectively the higher frequency range, indicating that carbon nanotubes can be used for fast and low-cost prototyping of high-frequency devices.
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Today many applications require new effective approaches for energy delivery on demand. Supercapacitors are viewed as essential energy storage devices that can continuously provide quick energy. The ...performance of supercapacitors is mostly determined by electrode materials that can store energy via electrostatic charge accumulation. This study presents new sustainable cellulose-derived composite electrodes which consist of carbon nanofibrous (CNF) mats covered with vapor-grown carbon nanotubes (CNTs). The CNF/CNT electrodes have high electrical conductivity and surface area: the two most important features that are responsible for good electrochemical performance of supercapacitor electrodes. The results show that the composite electrodes have fairly high values of specific capacitance (101 F g−1 at 5 mV s−1), energy and power density (10.28 W h kg−1 and 1.99 kW kg−1, respectively, at 1 A g−1) and can retain excellent performance over at least 2000 cycles (96.6% retention). These results indicate that sustainable cellulose-derived composites can be extensively used in the future as supercapacitor electrodes.
We report on the signal-to-noise and gain bandwidth of a niobium nitride (NbN) hot-electron bolometer (HEB) mixer at 2 THz fabricated on a sapphire substrate with a GaN buffer layer. Two mixers with ...different DC properties and geometrical dimensions were studied and they demonstrated very close bandwidth performance. The signal-to-noise bandwidth is increased to 8 GHz in comparison to the previous results, obtained without a buffer-layer. The data were taken in a quasi-optical system with the use of the signal-to-noise method, which is close to the signal levels used in actual astrophysical observations. We find an increase of the gain bandwidth to 5 GHz. The results indicate that prior results obtained on a substrate of crystalline GaN can also be obtained on a conventional sapphire substrate with a few micron MOCVD-deposited GaN buffer-layer.
ALMA Band 5 receiver cartridge Belitsky, V.; Bylund, M.; Desmaris, V. ...
Astronomy & astrophysics,
03/2018, Volume:
611
Journal Article
Peer reviewed
Open access
We describe the design, performance, and commissioning results for the new ALMA Band 5 receiver channel, 163–211 GHz, which is in the final stage of full deployment and expected to be available for ...observations in 2018. This manuscript provides the description of the new ALMA Band 5 receiver cartridge and serves as a reference for observers using the ALMA Band 5 receiver for observations. At the time of writing this paper, the ALMA Band 5 Production Consortium consisting of NOVA Instrumentation group, based in Groningen, NL, and GARD in Sweden have produced and delivered to ALMA Observatory over 60 receiver cartridges. All 60 cartridges fulfil the new more stringent specifications for Band 5 and demonstrate excellent noise temperatures, typically below 45 K single sideband (SSB) at 4 K detector physical temperature and below 35 K SSB at 3.5 K (typical for operation at the ALMA Frontend), providing the average sideband rejection better than 15 dB, and the integrated cross-polarization level better than –25 dB. The 70 warm cartridge assemblies, hosting Band 5 local oscillator and DC bias electronics, have been produced and delivered to ALMA by NRAO. The commissioning results confirm the excellent performance of the receivers.
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