Instruments and Experimental Techniques最新文献

The stick-slip piezoelectric actuators have the disadvantage of backward motion, which reduces the efficiency of the piezoelectric actuator and triggers problems such as abrasion of the driving foot and will seriously affect the life of the actuator. In this study, a new flexible mechanism with inertial block is proposed. The structural parameters and the trajectory of the driving foot are verified by the finite element method. A prototype of the piezoelectric actuator is fabricated and various experiments on the trajectory of the driving foot and the performance of the actuator are conducted. The experimental results show that the piezoelectric actuator can achieve smooth motion with a maximum motion speed of 5.54 μm/s at f = 1 Hz and U = 100 V with symmetry 0% sawtooth wave drive, while the maximum speed can reach 1278.81 μm/s at f = 3000 Hz and U = 100 V. The piezoelectric actuator can realize a maximum horizontal load of 50 g and a maximum vertical load of 1400 g. The results show that the new flexible mechanism and its driving method proposed in this study are practicable, which can effectively reduce the sliding friction in the rapid rise period and effectively increase the static friction in the slow fall period and can achieve smooth motion with high load capacity and driving frequency. It has certain significance for the performance improvement and market application of piezoelectric actuator.

The article offers ways to create two-phase helium flowmeters in the range of mass flow rates from approximately 5–6 to more than 1000 g/s. The principle of operation of flowmeters is based on a combination of capacitive void fraction sensors with a uniform electric field inside the sensing elements to determine the average density of the two-phase mixture and conical narrowing devices to find the average flow velocity. In this case, capacitive sensors with sensitive elements of both circular and annular cross sections, which significantly differ in their sensitivity, can be used. The features and problems inherent in two-phase flowmeters of this type are considered, which include, first of all, the influence of a variety of flow patterns on the characteristics of the narrowing device. Another problem is to consider the influence of the structure of a two-phase flow on the determination of its average density. One more problem is related to possible differences between the measured values of the pressure drops in the narrowing device and the expected values, which are estimated using a homogeneous model in one of the limiting cases of a two-phase flow. The ways of minimizing these problems are shown using a combination of individual technical solutions that have already been tested in practice. Specific technical variants of two-phase helium flowmeters, including a flow-through horizontal cryostat, are presented, which are operable in the entire range of the void fractions from 0 to 1 with a relatively small total hydraulic resistance of the flowmeter’s flow part. The differences between the new and previous technical solutions are shown. The uncertainties of determining the flow rate of two-phase helium flows are estimated.

Determining the threshold values in case of multiple bit upsets based on impinging particles flux density is an urgent problem for radiation-hardened electronics designers. To deal with such class of problems, a special three-beam pulsed electron linac called SPRUT was developed. The linac is used to generate an electron beam with electron energy of 5–7 MeV, current of approx. 1 A, pulse width of 1–12 μs, and repetition rate up to 1 Hz. Total electron beam, not less than 20 mm in diameter, with high electron flux density is generated behind the exit foil. Configuration and position of the combined beams can be adjusted to ensure the irradiation area non-uniformity not worse than 30%. The paper describes the SPRUT linac design and operating principle, as well as the methods used to measure its characteristics and the results obtained thereby, it helps studying the possibilities to generate the radiation field with certain characteristics.

A method is considered for integral counting of the number of particles in the cross section of a homogeneous radiation beam based on measuring the number of particle tracks registered in the plane of a solid-state detector using “machine vision” technology.

An automatic frequency tuning system has been developed and implemented for probes used in nuclear magnetic resonance (NMR) and quadrupole resonance (NQR) spectroscopy. It is based on available technologies that allow for assembling this system for any probe, regardless of the control method. The control electrical part is implemented on the Arduino platform and includes platform-compatible modules: stepper motors and a servo. The equipment for placing the control system was manufactured using additive technologies, which simplified the process of prototyping and assembly a ready-made system. Due to the availability and low cost of the components, the automatic tuning system can be adapted and configured for any NMR-probes. This auto tune system made it possible to avoid manual adjustment of the probe during the experiment and reduce the time spent.

A method for stabilizing the prebreakdown state of vacuum gaps, based on the use of an anode made of a material with high specific resistance, has been proposed and implemented on an experimental stand. Traces of prebreakdown phenomena on the surface of cathodes, which usually lead to a vacuum spark and self-destruction, were identified and a preliminary study was conducted. This technique will allow for further expanding the understanding of the nature of vacuum breakdown and electroplastic phenomena in critically strong electric fields with a strength of over 1 MV/cm. It is proposed to use prebreakdown electrostatic treatment of the surface of metals and semiconductors to study the possibility of obtaining effective cold electron emitters.

A method is proposed for the results correction of the output power measurements of orotrons with two-row periodic structure (TRPS) carried out with the help of the detector graduation section in a waveguide with a cross section of 1.6 × 0.8 mm² with the detector disposition in the wide wall middle of a waveguide. The results of this method at the correction of the outputpower measurements are presented for the orotron with TRPS of the 2-mm region wavelength.

An approach to determining and describing the distribution of the longitudinal and transverse components of the magnetic field in an axisymmetric laboratory electromagnet is proposed based on a polynomial expansion of the field induction taking into account the restrictions imposed by Maxwell’s equations. It is shown that the proposed approach allows obtaining high accuracy in describing the magnetic field distribution with a small number of measurements. It may also be of interest for refining the parameters of laboratory equipment and be used as a training task in laboratory practice when studying the properties of the electromagnetic field.

Numerous devices are used in synchrotrons and storage rings to provide close-orbit continuous circulation of particle beams in pipeline of the facility. These are power supplies for the magnetic and RF systems. The high accuracy and stability of the output parameters (the output current or voltage) must be exhibited by the power supplies of the magnetic system. If it is necessary to control a facility with circulating beams (e.g., in the case of beam acceleration in a synchrotron), mutual synchronization of the performance of all devices is also required. An embedded controller with an analog interface to a controlled device is described. The relative accuracy of 100 ppm with respect to the entire operating range of the device and the possibility of mutual synchronization by external clock pulses following with a frequency as high as 10 kHz is provided by the controller. Examples of the controller application to control various devices and systems are presented.

We discuss the performance of the distributed fiber optic sensor (DFOS) interrogation unit based on the phase-optical time domain reflectometry (ϕ-OTDR) principle. This experiment focuses on improving the performance of ϕ-OTDR by controlling two selective parameters: probe power and laser pulse width. These parameters were chosen due to their significant impact on the signal-to-noise ratio (SNR), which directly influences the sensitivity and accuracy of the system. Two experiments were conducted using 10 and 40 km standard ITU-T G.652D telecom grade bare fiber optic connected to the ϕ-OTDR setup. For each experiment, two sets of probe laser parameters (launched optical power and pulse width) were varied, and the SNR was calculated as an indicator of performance. An SNR of 13.99 dB was achieved from a 10 km ϕ-OTDR setup with a pulse width of 300 ns (launched optical power fixed at 100 mW). With launched optical power fixed at 100 mW, an SNR of 12.76 dB was obtained from a 40 km ϕ-OTDR setup when the pulse width was set to 500 ns. Data analysis revealed that SNR values in both ϕ-OTDR setups (10 and 40 km) approached saturation as the probe power launched and optical power increased. This study highlights that the best signal performance can be achieved by carefully optimizing these selective parameters, as their interplay determines the balance between spatial resolution and signal strength in the ϕ-OTDR system.