The article presents a brief review of cooling systems that ensure various temperature levels (from 0.1 K to 230 K) for radio astronomical receivers of photonic and electronic (or optical and radio) devices. The features of various cooling levels and the requirements for the design of the cooling systems are considered in detail, as well as the approaches to designing interfaces for cooled receivers: vacuum, cryogenic, electrical, mechanical, optical, and other interfaces required for effective operation. The presented approaches to design are illustrated by a series of joint developments of the authors carried out over the past 45 years, including those produced over the past year.

Several new approaches to the measurement of intrinsic noise and dynamic characteristics of superconducting bolometers based on the RFTES technology are demonstrated. The developed methods were tested with an experimental 550–750 GHz sample at reading frequency of 1.5 GHz at a temperature of 400 mK. The absorption of thin-film resistive coatings on sapphire and quartz substrates was studied, and the emissivity of the experimental heat source was estimated as 14 √(Hz) ± 30

Several new approaches to the measurement of intrinsic noise and dynamic characteristics of superconducting bolometers based on the RFTES technology are demonstrated. The developed methods were tested with an experimental 550–750 GHz sample at reading frequency of ~1.5 GHz at a temperature of 400 mK. The absorption of thin-film resistive coatings on sapphire and quartz substrates was studied, and the emissivity of the experimental heat source was estimated as ~14%. A shot noise source based on Al/AlOx/Al tunnel junction was developed, and the noise temperature of the 1.35–1.6 GHz buffer amplifier referred to the detector output was determined as ~20 K. The response time of RFTES with a hafnium film sized 6 µm × 2 µm × 0.08 µm was evaluated as ~3 µs via microwave heat modulation at the second resonance at ~4.2 GHz; the dynamic range at a modulation frequency of 10 kHz was more than 23 dB. The data obtained made it possible to determine the RFTES sensitivity as 1∙10-17 W/√Hz ± 30%, that coincided with the theoretical value up to the measurement error.

The device operates at temperatures <300 mK and comprises a hafnium microbridge and a superconducting aluminum tunnel junction both integrated into a common coplanar waveguide. The microbridge matches with a planar antenna and operates as an optical blackbody at frequencies 600-700 GHz. The coplanar terminal is the blackbody output in the 1-2 GHz frequency range. The microbridge temperature can be set in the range of 0.4-9 K and calibrated using the shot noise of the tunnel junction. Temperature modulation of each of the sources can be performed independently using a direct current which transit them from the superconducting to the normal state with characteristic times <0.1 ms and heating power ~ 1 μW. Keywords: Superconducting microbridge, superconducting tunnel junction, thermodynamic noise, shot noise, noise thermometry.

The detection of a terahertz optical signal using a bolometric detector with a planar niobium resonator loaded with a hafnium micromotor using the nonlinearity of the impedance of an electron gas at a frequency of 1.5 GHz near the critical temperature of the micromotor is demonstrated for the first time. The temperature of the electron gas was shifted by the resonator current, and the superconducting transition of the micromotor occurred under the action of a terahertz signal. The test thermodynamic signal from a thin-film Fe-Cr-Ni absorber heated in the range of 1-10 K was focused from a distance of 10 mm with an immersion lens made of sapphire onto a planar antenna matched with a micro-bridge in the range of 600-700 GHz. The measured power transmission coefficient of the bolometer was +5.5 dB with a saturation power of ~1 pW and a threshold sensitivity of the receiving system (3±1)·10-17 W/sqrt(Hz)sqrt sqrt, which is close to the theoretical values for the investigated bridge with a size of 2.5x2.5x0.08 μm. The tested detector can be used to create imaging terahertz matrices with frequency multiplexing in sorption-type cryostats. Keywords: RFTES bolometer, superconducting micro bridge, high-frequency impedance of superconductor, hafnium film, electron gas, planar resonator, frequency multiplexing, planar antenna, black body, thermodynamic noise. Keywords: RFTES bolometer, superconducting microbridge, high-frequency impedance, hafnium film, electron gas, coplanar resonator, frequency-division multiplexing, planar antenna, blackbody, noise.

The device operates at temperatures <300 mK and comprises a hafnium microbridge and a superconducting aluminum tunnel junction both integrated into a common coplanar waveguide. The microbridge is a thermodynamic source and operates as an optical blackbody at frequencies 600–700 GHz. The coplanar terminal is the blackbody output in the 1–2 GHz frequency range. The microbridge temperature can be set in the range of 0.4–9 K and calibrated using the shot noise of the tunnel junction. Activation and temperature modulation of each of the sources can be performed independently using a direct current which transit them from the superconducting to the normal state with characteristic times <0.1 ms and heating power <1 μW.

Express analysis of the dependence of the critical temperature of different superconducting films on its thickness was proposed, developed, and tested. The technique is based on a mathematical analysis of an integral equation that describes a one-time measurement of the electrical resistance temperature dependence of a sufficiently long superconductor film with variable thickness. The dependence of the film thickness and width along its longitudinal coordinate (film geometry) is set or measured using known methods. The express analysis has significant advantages over the more labor-consuming method of time-shared measurement of the critical temperature of film segments with different thicknesses.

Fiducial markers are used in vision systems to determine the position of objects in space, reconstruct movement and create augmented reality. Despite the abundance of work on analysis of the accuracy of the estimation of the fiducial markers spatial position, this question remains open. In this paper, we propose the computer modeling of images with ArUco markers for this purpose. The paper presents a modeling algorithm, which was implemented in the form of software based on the OpenCV library. Algorithm is based on projection of three-dimensional points of the marker corners into two-dimensional points using the camera parameters and rendering the marker image in the new two-dimensional coordinates on the modeled image with the use of the perspective transformation obtained from these points. A number of dependencies were obtained by which it is possible to evaluate the error in determining the position depending on markers size. Including the probability of detecting a marker depending on its area on an image.

We demonstrated and analyzed the smooth microwave-driven transition of a superconducting bridge made from Hf into its normal state at bath temperatures below the critical temperature of Hf (Tc ≈ 380 mK). The bridge is integrated on a silicon chip with both the 600-700 GHz double-slot antenna and the 1.5-GHz CPW quarter-wave resonator (Q-factor ∼104) made from 100-nm Nb film. The experimental bridge was sized 2.5 um by 2.5 um by 50 nm and tested at temperatures down to 50 mK. Similar to the technique of MKID, we measured the dependence of transmission S21 on microwave power at the bottom of the resonance curve. It was found that the microwave power absorbed in the bridge fits to the model of hot electron gas, P∼Te6-Tph6. The internal NEP down to ≈10−18 W/⎷Hz is estimated due to thermal noise at the optimum electron gas temperature, Te ≈ 320 mK. The NEP can be scaled down below ≈10−19 W/√Hz via reasonable reduction of the bridge volume. The new detector circuit is suitable for integration within a large imaging array exploiting the FDM-readout.

A high-quality superconducting resonator with a microbridge of hafnium film for use in a circuit for readout a terahertz-band imaging array with frequency division multiplexing is demonstrated experimentally. The variability of the impedance of the bridge at a frequency of 1.5 GHz, which is a key factor in the control of the quality of the resonator, is studied. The bridge, having a thickness of about 50 nm, a critical temperature TC ≈ 380 mK, and a plan size of 2.5 × 2.5 μm, was connected as a load of a resonator made of niobium film with a thickness of about 100 nm (TC ~ 9 K). It is shown that the bridge smoothly changes its impedance proportionally to the bias power in the entire temperature range. The effective thermal insulation of the bridge was measured in a dilution cryostat at temperatures of 50–300 mK. Thermal conductivity G of the bridge was calculated and found to be ~4 × 10–13 W/K, which gives an estimate of the sensitivity of the structure in the bolometric mode NEP ≈ 8 × 10–19 W/Hz1/2 at a temperature of 150 mK.

AbstractA high-quality superconducting resonator with a microbridge of hafnium film for use in a circuit for readout a terahertz-band imaging array with frequency division multiplexing is demonstrated experimentally. The variability of the impedance of the bridge at a frequency of 1.5 GHz, which is a key factor in the control of the quality of the resonator, is studied. The bridge, having a thickness of about 50 nm, a critical temperature T _ C ≈ 380 mK, and a plan size of 2.5 × 2.5 μm, was connected as a load of a resonator made of niobium film with a thickness of about 100 nm ( T _ C ~ 9 K). It is shown that the bridge smoothly changes its impedance proportionally to the bias power in the entire temperature range. The effective thermal insulation of the bridge was measured in a dilution cryostat at temperatures of 50–300 mK. Thermal conductivity G of the bridge was calculated and found to be ~4 × 10^–13 W/K, which gives an estimate of the sensitivity of the structure in the bolometric mode NEP ≈ 8 × 10^–19 W/Hz^1/2 at a temperature of 150 mK.

We present proof-of-operation for a new method of electron thermometry using microwave impedance of a hafnium micro-absorber. The new method leads to an ultimate THz-range detector suitable for microwave readout and frequency division multiplexing. The sensing part of the device is a hot-electron-gas absorber responding to the incident radiation by variation of its impedance measured at probing frequency about 1.5 GHz. The absorber is a microbridge made from hafnium (Tc = 375 mK, RN = 30 Ohm) sized 2.5 um by 2.5 um by 50 nm and integrated with a planar 600-700 GHz antenna placed near the open end of a quarter-wave CPW resonator (Q-factor about 10^4). All elements of the circuit, except the microbridge, are made from 100-nm thick Nb, including the resonator, which is weakly coupled to a throughput line. The device was tested at 50-350 mK smoothly responding with its transmission coefficient S21 to applied microwave power at the resonance frequency. We have found that the power absorbed by the bridge fits to the model of hot electron gas, P=k(Te^n-Tph^n) (n = 5...6). The idle NEP down to about 10^-18 W/Hz^(-1/2) and the corresponding cross-over temperature for photon background about 5 K are estimated from the measured data. The saturation power of about 1 pW and possibility of moderate gain are anticipated for a practicable device operating at temperature 200 mK. Since the optimum readout frequency is found exactly at the resonance, the detector is insensitive to most phase instabilities at the probing frequency.

We analyze the microwave-driven transition of a superconducting bridge into its normal state. The micro-bridge made from Hf is studied well below its critical temperature, Tc=375 mK, for a number of bath temperatures down to 30 mK. The bridge sized 2.5 {mu}m by 2.5 {mu}m by 50 nm was integrated near the open end of 1.5-GHz CPW quarter-wave resonator made from Nb yielding the Q-factor about $10^4$. The integrated circuit is designed for FDM readout of the bridge impedance and operates similar to MKID. We observe a smooth dependence of the Q-factor and S21, the transmission parameter of the chip, on applied microwave power. A novel method of steady state Q-factor is used for evaluating thermal conductance of the bridge. The microwave power absorbed by the bridge is found fitting the model of hot electron gas, $P=a({Te}^6-{Tph}^6)$, that allows to calculate thermal conductance of the bridge and evaluate NEP down to $10^{-18}$ W/Hz$^{1/2}$. This number estimated for the first experiment can be scaled down to and below $10^{-19}$ W/Hz$^{1/2}$ via reduction of both the bridge size and Tc of the hafnium film. Since it was found that the major part of the microwave impedance is active, the proposed detection technology is beneficial for reducing phase jitter in a high-Q resonator. According to our experimental data, a bridge made from Hf may operate as a THz signal sensor using readout frequencies above few GHz.

We describe the first phase of experimental study of the superconducting bridge RFTES detector at temperatures 20-300 mK including the measurement of its thermal conductance, which fits the model of electron gas heating. We discuss the idea of the RFTES scheme, which is based on the probing of microwave loss near superconducting transition of the bridge. The heat applied to the bridge is generated by the probing signal at the frequency of the high-Q resonator. Since the real part is dominating in the nonlinear impedance of the bridge, the applied heat provides merely amplitude modulation of Q suggesting the suppression of phase jitter of the resonator. The bridge was made from a 50-nm-thick hafnium film (T-c approximate to 380 mK) sized to 2.5 mu m x 2.5 mu m. The resonator and the rest of the circuit were made from 200-nm-thick film of niobium (T-c approximate to 9 K) demonstrating the loaded Q-factor up to and above 10 000 at 1.5 GHz. A cryogenic semiconductor amplifier was used in the readout circuit. The thermal conductance was measured using the steady Q regime of the resonator and found to follow 76 down to and below G approximate to 1 x 10(-1)(3) W/K. The NEP below 10(-18) W/root Hz is estimated for the electron temperature of the bridge about 300 mK.

We present a superconducting noise bolometer for terahertz radiation, which is suitable for large-format arrays. It is based on an antenna-coupled superconducting micro-bridge embedded in a high-quality factor superconducting resonator for a microwave bias and readout with frequency-division multiplexing in the GHz range. The micro-bridge is kept below its critical temperature and biased with a microwave current of slightly lower amplitude than the critical current of the micro-bridge. The response of the detector is the rate of superconducting fluctuations, which depends exponentially on the concentration of quasiparticles in the micro-bridge. Excess quasiparticles are generated by an incident THz signal. Since the quasiparticle lifetime increases exponentially at lower operation temperature, the noise equivalent power rapidly decreases. This approach allows for large arrays of noise bolometers operating above 1 K with sensitivity, limited by 300-K background noise. Moreover, the response of the bolometer always dominates the noise of the readout due to relatively large amplitude of the bias current. We performed a feasibility study on a proof-of-concept device with a 1.0 × 0.5 μm2 micro-bridge from a 9-nm thin Nb film on a sapphire substrate. Having a critical temperature of 5.8 K, it operates at 4.2 K and is biased at the frequency 5.6 GHz. For the quasioptical input at 0.65 THz, we measured the noise equivalent power ≈3 × 10−12 W/Hz1/2, which is close to expectations for this particular device in the noise-response regime.

The joint action of the matching to a common RC-load and thermal noise on the spectral properties of parallel Josephson junction array is studied. It is demonstrated that proper matching suppresses the chaotic dynamics of the system. The efficiency of radiation is found to be highest within a limited frequency band, which corresponds to transformation of the shuttle soliton oscillating regime into the linear wave resonance synchronization mode. In this frequency band the spectral linewidth agrees well with a double of the linewidth for a shuttle fluxon oscillator, divided by a number of the oscillators in the array. When the oscillations demonstrate strong amplitude modulation, the linewidth increases roughly by a factor of five compared with theoretical linewidth formula.

Our new detector and readout concept brings together TES (Transition Edge Sensor) and MKID (Microwave Kinetic Inductance Detector) technologies and exploits the idea of a microwave-induced superconducting transition in a small thin-film microbridge. The superconducting transition of the bridge manifests itself as variation in the Q -factor of niobium resonators at 5-8 GHz, somewhat similar to MKID operation. We present data showing the potential for developing this concept into multipixel detector arrays. Single-pixel sensitivity was measured at 4.5 K for an input band of 600-700 GHz using a prototype 10-nm-thick Nb bridge of size 1 μm × 500 nm. Radiation from human skin was detected with a resolution better than 1 K/rtHz, which is encouraging for terahertz imaging applications. To further improve device sensitivity, we are also developing Hf-based devices that operate near 0.35 K. Details about the physics and stability of these devices are discussed.

Aeroelastic instability of skin panels, known as panel flutter, can occur in the form of coupled-mode or single-mode flutter. While the first type of flutter usually occurs in one eigenmode (composed of the first and the second natural modes in vacuum) and yields well-studied nonlinear limit cycle oscillations, the single mode flutter can occur in several simultaneously growing eigenmodes, leading to complex nonlinear panel dynamics, including different co-existing limit cycles, periodic and non-periodic higher-mode oscillations. Structural nonlinearity and linear aeroelastic growth mechanism play the major role in this dynamic. While the linear panel flutter boundaries in the two-dimensional formulation have been studied in detail, there are only few investigations of the boundaries in the three-dimensional case. Since the linear growth mechanism plays an essential role in nonlinear oscillations, its comprehensive study is an important step toward understanding of complex dynamics of skin panels in the three-dimensional case. In this paper, we investigate the flutter boundaries of rectangular panels simply supported at all edges, and use potential flow theory to calculate the unsteady pressure. The problem is considered in two formulations: a series of rectangular plates, attached to each other, and a single rectangular plate. Flutter boundaries of the first four modes are calculated, and their transformations with the change of the spanwise plate width are studied in detail.

To control phase velocity in superconducting transmission lines using short electrical pulses, a few approaches are being developed. A new design is developed for left-to-right (L2R) and right-to-left (R2L) tunable transmission lines based on a CPW with embedded paired resonators containing dc-SQUIDs. Experimental layouts are designed according to rules of 2-μm Nb-Al/AlO x -Nb technology for J c ≈ 0.1 kA/cm 2 and compared numerically with a scheme-model containing 40 cells at frequencies up to 20 GHz. Characteristic impedance of new dispersive transmission lines is increased above 30 Ohm; a thin-film attenuator is integrated for suppression of standing waves. A stop-band is found for R2L line demonstrating slower phase velocity; this transmission gap is due to effect of shorter wavelength (up to 100 times) reaching electrical length of the paired resonators cell (70 μm). In case of L2R line with faster phase velocity, the transmission band can be almost flat, if simultaneous tuning of frequency for all paired resonators is provided. No negative phase velocity is found in the simulations; however, the increment of differential phase velocity is positive for R2L near edge of the stop-band and negative near the resonance for L2R case.