Instruments and Experimental Techniques最新文献

Atomic force microscopy (AFM) is a valuable method for measuring the surface properties of a sample, where the accurate estimation of the relative distance between the probe and the sample (depth) is a prerequisite for fast, accurate measurement. This paper uses geometric optical modeling to establish a function model between the blur amount in the AFM probe image and depth. This model estimates the depth by the lens via the blur information of strong edge images according to the characteristics of a small depth of field and multiple blurs in microscopic images. To estimate the probe position, the study embedded the convolutional block attention module attention mechanism model into the Resnet18 network, allowing the network to learn blur target classification under different depths. After being trained with a custom dataset, the neural network achieved 99.26% accuracy and the error of 1.25 μm in the measurement range to ±100 μm. In actual operational application, the neural network achieved an accuracy of 90.10% with an error of 1.35 μm over a measurement range of ±100 μm. Experimental results illustrate the effectiveness of the proposed method, and have guidance in implementing efficient, accurate, and fully automatic probe depth estimation.

The purpose of this review is to provide researchers involved in the development of time-to-digital converters (TDC) on FPGAs with the most complete understanding of the existing approaches and methods for implementing such converters. The paper summarizes the most significant characteristics of TDCs and describes the basic time interval measurement methods used in the implementation of TDCs on FPGAs. The main problems arising in the development of such circuits are outlined. The FPGA elements on which the TDC is implemented and the procedure of TDC calibration are briefly considered. The approaches used to increase the resolution and to reduce the nonlinearity of TDC on FPGA are analyzed. Different structures of encoders used in the TDCs are considered. Based on the results of the analysis, recommendations for the development of an FPGA-based TDC are given.

The article presents a concept of an uncooled subterahertz radiometer designed for estimating the atmospheric absorption in the 1.3-mm atmospheric transparency window, which can possibly operate under mountain expedition conditions. Estimation of the atmospheric absorption is based on radiometric measurements of the sky brightness temperature. A comparative analysis of two typical schemes of radiometer receivers (heterodyne and tuned radio frequency receiver schemes) was carried out based on the modern stage of development of the subterahertz electronic components. The noise temperature and fluctuation sensitivity of both schemes were estimated. The results of designing a horn–lens antenna with a radiation pattern of 3° at a level of –3 dB at a frequency of 230 GHz are presented. The general structure of the high-frequency part of the radiometer is described, including some design features that are necessary to provide continuous measurements in a wide range of climatic conditions.

The article relates to the field of contact power nano- and microlithography used for marking samples and surface areas examined with high-resolution microscopes. The device of a marking machine built on the basis of a commercially available Generic-CNC2418 engraving machine with program control in G-codes and using a tungsten probe as a working tool is described. A process for operating the motors of the marking machine based on the monitoring of the probe-surface contact by means of an optical microscope is described. The marking obtained with the help of such a probe is a pattern of individual probe imprints. The marker drives ensure positioning accuracy of 10 μm. The transverse size of the resulting marking prints is 10–15 μm. The marker is recommended for use on surfaces with a roughness of Ra no more than 0.1 μm and a Mohs hardness of no more than 7.5.

This paper presents an effective approach to the fabrication of glass microfluidic chips for studying physical and chemical processes on the pore scale during multiphase flows in porous media, including the description of material selection, methods of microchannel formation and substrate bonding, and the fabrication of tooling for chip fixation and connection to fluid sources. The main advantage of the proposed method is related to the availability of the materials used and relative ease of fabrication. At the same time, the chips produced in this way have good mechanical properties, high optical transparency, and chemical inertness. The influence of different material-processing parameters during chip fabrication on their characteristics and properties is studied. The described experience of the authors can be used by a wide range of researchers in developing their own microfluidic platforms based on glass chips not only for studying multiphase filtration in porous media but also for chemical reactions and various studies in the field of biomedicine.

A generator of powerful nanosecond pulses that contains a storage capacitor, a segment of a coaxial cable, and closing and opening semiconductor switches has been developed. With a storage-capacitor charging voltage of 12 kV, the generator allows switching quasi-rectangular voltage pulses with an amplitude of ~26 kV, a rise time of ~4 ns, and a fall time of ~6 ns into a 75 Ω load. The half-maximum pulse duration is ~45 ns, and the “jitter” relative to an external triggering signal is less than 2 ns. The possibility of increasing the generator output power and the duration of output-voltage pulses is shown.

The Baikal-GVD deep-sea Cherenkov detector, whose deployment in Lake Baikal has been ongoing since 2016, currently represents the largest neutrino telescope in the Northern Hemisphere. The principle of the telescope’s operation is based on the registration of Cherenkov radiation produced by the products of neutrino interaction in the aquatic environment using the spatial structure of photodetectors. Laser light sources specially designed for the Baikal project are used to calibrate and measure the characteristics of the telescope’s detecting system. The article describes the design and features of the functioning of calibration laser sources, presents the results of their operation as part of the telescope, and discusses issues of further development of the laser-calibration system.

A dilution cryostat is described, which is designed to carry out observations at dusk in the millimeter range on an optical telescope with a mirror with a diameter of 6 m, when observation in the optical range is still impossible. The cryostat, which cools the detector down to 0.1 K, is built according to the scheme of dissolving ³He in ⁴He with ³He circulation due to its condensation on a cold wall cooled by sorption pumping of pure liquid ³He from a separate volume. The working conditions are provided by the contact with the stabilizing unit, which accumulates 0.6 L of liquid ⁴He during active operation of a Gifford–McMahon refrigerator within the time between measurement cycles. During measurements, the refrigerator turns off, which completely eliminates vibrations that interfere with measurements.

Over the last two decades, the superconducting qubits have become a promising and rapidly growing area of research. However, there are specific challenges when working with such a delicate system. One of them is the qubit state readout. Since a very small signal (of the order of 1 photon) is used for the readout, its detection is challenging and it requires low-noise cryogenic amplifiers working in the 3–12 GHz frequency range. Josephson parametric amplifiers (JPAs) are one of the most studied and developed candidates. Currently, several JPA designs offer low noise performance and instantaneous bandwidth from tens of MHz to several GHz; they are also becoming an integral part of circuit quantum electrodynamics (cQED) setups. In the current work, results are presented of the measurements of a JPA made of a coplanar waveguide with an array of three SQUIDs. Nondegenerate amplification and an amplifier added noise being close to the quantum limit are demonstrated.

The theoretical and experimental characteristics of depth dose distributions of protons in the Bragg peak region are investigated. Results of the Monte Carlo calculations in the TOPAS MC software package and experimental data obtained from film detectors and ionization chambers at the high-current proton linear accelerator of the Institute for Nuclear Research are used. The interrelationship between the results and the applicability of these detectors for measuring the absorbed dose are considered. The calculated dose distributions are in good agreement with the dose distributions measured using the ionization chambers for the pristine and spread-out Bragg peaks. Possible interrelationship between the linear energy transfer and the accuracy of dose measurements with the film detectors is shown. The discrepancy between the readings of the film detectors in the Bragg peak region, on the one hand, and the results of calculations and measurements with the ionization chambers, on the other hand, may be important for irradiation of biological samples, in particular, in the FLASH therapy modes.