Abstract:This paper makes a concise overview of the working principle of piezoelectric drive, the nonlinearity characteristics of the piezoelectric materials, and the direct driving method of piezoelectric positioning platforms. It summarizes the structural design and decoupling optimization methods of multi?degree?of?freedom piezoelectric positioning platforms based on three driving schemes: series, parallel, and series?parallel. It focuses on the analysis of the cross?coupling and the nonlinear characteristics of the piezoelectric driver that need to be addressed in the control system of multi?degree?of?freedom nano piezoelectric positioning platforms. It is proposed that appropriate control strategies should be selected according to the different structures and motion modes of multi?degree?of?freedom piezoelectric positioning platforms. Finally, it summarizes the control algorithms suitable for multi?degree?of?freedom piezoelectric positioning platforms. It is helpful for researchers to understand the latest developments in the field of piezoelectric nano positioning platforms and serves as a valuable reference for research on control technology for piezoelectric nano positioning platforms.

Abstract:This paper introduces the types of floating elements and the measurement method of wall shear stress of floating elements. The basic principles and research status of capacitive, piezoresistive and optical wall shear stress sensors based on floating elements are described. The advantages and disadvantages of the three types of floating element wall shear stress sensors are analyzed. It is pointed out that the performance of the floating element wall shear stress sensor can be improved by optimizing the moving gap between the floating element and the sensor package, as well as the flatness between the floating element and the measured surface. The development direction of wall shear stress sensor with floating element in turbulent flow measurement, boundary layer transition judgment, aircraft safety maintenance and optimization of aircraft structure is also discussed. In the future, it is suggested that the MEMS technology can be developed, the back?end processing circuit and temperature compensation of the sensor can be optimized, and the moving gap and uniformity between the floating element sensor structures can be optimized by the integrated design and processing method to further improve the miniaturization of the floating element wall shear stress sensor, the sensitivity and accuracy of detecting the extremely low value of wall shear stress, and the reliability and accuracy of measurement.

Abstract:In active temperature?controlled dew point measurement based on a quartz crystal microbalance (QCM), the viscoelastic property of liquid water leads to a frequency dissipation which has an effect on the detection accuracy of dew point. Here, the QCM electrode was modified by hydrophobic treatment to improve the condensation form, minimize the dissipation attributed to the water viscosity, and achieve the measurement of resonance frequency offset caused by changes in liquid water quality. A hydrophobic layer with a static water contact angle of 133° ± 2° was prepared on the QCM electrode and characterized. The hydrophobic electrode and untreated electrode were applied in the dew point recognition experiments, and compared with the standard dew point obtained by a precision dew point meter. The experiments proved that the hydrophobic treatment of the electrode surface can effectively improve the dew point recognition accuracy of the QCM sensor. The optimal approach can provide basis for the design of dew point sensor structure with active temperature control.

Abstract:Temperature compensation and pressure correction methods are presented to improve the measurement accuracy of pressure and temperature in the rotor cavity. Aimed at the problem of large temperature measurement error caused by no electromotive force produced in the ordinary wires of the slip ring during rotor experiment，the temperature compensation method is used to add the electromotive force calculated from the temperature difference into the output electromotive force. Then, the true temperature of the measurement point can be calculated according to the relationship of the thermocouple between electromotive force and temperature. Aimed at the problem of the measurement error of the sensor installed in the low radius location caused by the piping effect of the air column in the tube in the rotating state of rotor cavity，the pressure correction method is presented. The air column in the tube is divided into several sections and the temperature of each section is regarded as constant. Then the correction formula is deduced. Experiments have been conducted to verify the application effects of the proposed temperature compensation and pressure correction methods. The results show that the measurement error after the compensation of temperature measured by the thermocouple is less than 1% and the measurement error of pressure after correction is less than 0.8%, and the correction effect of pressure is more obvious under high rotation speed. The corrected temperature and pressure accuracy meet the actual measurement requirements of aero?engine rotor cavity, providing important technical support for the life assessment of the rotor of aero?engines.

Abstract:To achieve electromagnetic signal recognition in complex environments, a specific emitter identification (SEI) method based on multi?feature parameter cluster analysis is proposed. By analyzing ten feature parameters related to emitter，establishing a specific emitter feature array, constructing a clustering equation, and using the separation between classes and intra?class clustering of electromagnetic signal parameters, the identification of specific emitter can be enabled. Theoretical analysis and experiments show that the multi?parameter calculation results of the expert scoring method are more discrete, which is a benefit to the identification of specific emitter. The research results provide strong support for promoting the development of electromagnetic signal detection and resolution technologies, and have technical reference value.

Abstract:In order to solve the problem that mechanical weighing table is difficult to calibrate due to static instability, we have analyzed the measuring principle and mechanical characteristics of the mechanical weighing table and proposed the calibration method of the mechanical weighing table in this paper. By reducing the maximum deflection angle of the weight frame of the mechanical weighing table under non?equilibrium state, the measurement uncertainty can be controlled during calibration and the accuracy of calibration results can be guaranteed. The method is used to calibrate the mechanical weighing table and analyze the measurement uncertainty. The results show that the extended uncertainty U = 84 g (k = 2), which verifies the effectiveness of the method. The research results have a positive impact on promoting the development of the mechanical metrology of underwater vehicle products, and provide a strong support for the experimental research of underwater vehicle products.

Abstract:In order to solve the problem of high loss of fiber Bragg gratings (FBGs) fabricated by femtosecond laser point by point, experimental research on the fabrication of femtosecond fiber Bragg gratings was completed using the plane?by?plane method. Using the basic theory of Gaussian beam propagation, the focused femtosecond laser energy distribution was contoured with equal height and width using slit shaping technology, breaking through the difficulty of inducing circular refractive index modulation within the fiber cross?section, and ultimately fabricating low loss femtosecond fiber gratings. Comparative experiments were conducted on the spectral characteristics of FBG fabricated with different slit widths. The results showed that when using a femtosecond laser beam with a spot diameter of 5.0 mm to write FBG, the insertion loss of the FBG prepared with a slit width of 1.7 mm was reduced to 0.15 dB, and the short?wavelength loss was reduced to 0.5 dB. This verified the effectiveness of the low loss femtosecond fiber grating fabrication method based on slit shaping. A method is proposed to control the filling amount of refractive index matching solution and adjust the femtosecond laser energy for the problem of dispersion of FBG reflectivity fabricated by the slit method, and the beam focusing process is optimized to successfully reduce the dispersion of FBG reflectivity. This study is of great significance in promoting the practical application of femtosecond fiber gratings in environments with high capacity and high chain loss.

Abstract:In order to match the optical performance of low?temperature optical lenses of infrared space payloads, reduce background noise, and achieve high?precision on?board calibration of payloads, a deep?low temperature on?board calibration blackbody source device based on active refrigeration (operating at a low temperature of 100 K) was proposed. The spaceborne blackbody source device is composed of a face?blackbody radiator, an active refrigeration system of a low temperature chiller, a heat pipe of cooling capacity transmission, and a precise temperature measurement and control system. It was verified through vacuum radiation calibration experiment that the requirements of infrared remote sensors for the on?board calibration blackbody source: wide spectrum (2 ~ 16 μm), high emissivity (0.987) and deep low temperature (100 K) were achieved. The blackbody source for calibration on a cryogenic satellite can be used for on?board radiation calibration of infrared payloads for the detection of extremely distant, extremely cold and weak targets. The high precision, low power consumption and universal engineering design method of the calibration source provides technical support for subsequent related research and promotion.

Abstract:Currently, the testing and calibration of atmospheric environmental sensors heavily rely on manual operations, resulting in low efficiency and poor accuracy. To address this issue, the working principles of atmospheric environmental sensors was analyzed. Based on this, a hardware testing platform for atmospheric environmental sensors was established. It consists of vacuum pump motor, pressure controller, high and low?temperature chambers, metallic sealed chamber, standard digital thermometer, industrial computer, and the atmospheric environmental sensors to be calibrated. Additionally, an automated software testing system for atmospheric environmental conditions was designed. Controlled by an industrial computer, this system periodically samples standard environmental parameters, automatically determines stability, and records calibration parameters to fit calibration curves. Automated calibration tests were performed on temperature and pressure sensors, yielding fitting correlation coefficients of 0.994 5 and 0.996, with repeatability errors of 0.087% and 0.046%, respectively. The results validate the feasibility of the testing system. This research provides robust support for the rapid deployment of atmospheric environmental sensors and holds significant implications for advancing the application of automation technology in the measurement of atmospheric environmental parameters.

Abstract:In order to solve the problem that the reference radiation field should be provided for field calibration of fixed radiation dose rate monitoring instruments used for on?site online monitoring, this work developed a portable radiation source irradiation device based on γ source using Monte Carlo simulation method. The radiation source shielding switch gears are not less than 3, the surface leakage ray is lower than 0.5% compared with the useful ray beam, and the radiation field non?uniformity is less than 5%, which meet the fixed X or γ radiation dose meter field calibration needs. The study has improved the quantity transfer ability for the field calibration of the fixed dose rate meters.

Abstract:In order to calibrate the time constant of the turbine flowmeter, a liquid step flow test device was established. The device uses a screw pump to transport fluid to form a platform flow, and an internal meshing gear pump to transport fluid to form a step flow component. The step flow component is superimposed on the platform flow by controlling the opening and closing of the high?speed solenoid valve, and the step flow is generated ultimately. The generation time of the step flow was evaluated by using a pitot tube, and the result showed that the rise time of the step flow was less than 9 ms. The time constant calibration tests of turbine flowmeter were carried out under different step conditions, and the results showed that the time constant of the turbine flowmeter was not invariable, and was greatly affected by the steady flow before the step flow, with a trend of decreasing with the increase of the steady flow before the step change, and the time constant was less affected by the step flow amplitude. In the small flow range, the dynamic flow coefficient obtained from actual measurement deviated significantly from the theoretical model derivation, while in the large flow range, the two were more consistent. Finally, the uncertainty of the calibration result of the time constant was evaluated, and the maximum expanded uncertainty was about 10 ms (k = 2). The research results are helpful for evaluating the dynamic characteristics of flowmeters and are expected to improve the accuracy of unsteady flow measurement.

Abstract:In order to solve the problem of incomplete information in the reliability evaluation of ground test measurement systems for liquid rocket engines, the factors that affect the evaluation of ground test measurement systems for liquid rocket engines are analyzed in this paper. Firstly, the performance reliability index and functional reliability index are used as the measurement standards for the reliability of the measurement system, and the definition of the reliability of the ground test measurement system for liquid rocket engines is given. The uncertainty of the measurement system is incorporated as a performance reliability indicator into the measurement system reliability evaluation system, and the relationship between measurement uncertainty and classical reliability is established. Then, the number of failures of subsystem units is used as an evaluation indicator of functional reliability. A system reliability assessment strategy that integrates multi?source reliability information is developed. Afterwards, the principles and implementation methods of reliability data collection, reliability information conversion, reliability information synthesis, pyramid system reliability evaluation, and reliability evaluation based on expert linear weighting were elaborated. Finally, taking the ground test measurement system of a certain type of liquid rocket engine as an example, the reliability of the measurement system is evaluated. The results show that the pyramid comprehensive evaluation method that integrates multi?source reliability information can accurately analyze the reliability of the ground test measurement system of liquid rocket engines, and the expert linear weighted information fusion evaluation method can locate the key focus objects in the system and identify weak links. Not only does the research result provide new ideas and methods for technical personnel in the industry to study and evaluate the reliability of measurement systems, but it also has great significance for improving the quality of model products, measurement data quality, and system reliability.

Abstract:In order to solve the calibration problem of radiation heat flux sensors in vacuum environments, a 50 mm large?diameter vacuum high?temperature blackbody radiation source device was developed by using pyrolytic graphite as the heating element, and measuring and controlling the temperature using a standard photoelectric pyrometer, and the performance indexes of the device were tested and evaluated. The temperature stability of the device within 10 min was not more than 0.5℃, and the radial temperature uniformity was not more than 0.1%t (t is the set temperature), which met the requirements of relevant regulations. Finally, the uncertainty components introduced by the performance indexes of the vacuum high?temperature blackbody radiation source in the process of heat flow calibration were calculated and analyzed. The research results provide strong support for promoting the application of the device in the calibrations of heat flow, radiation temperature and other fields.

Abstract:In order to improve the measurement accuracy of dew point temperature and find the optimal change corresponding to different dew point temperatures, the characteristic parameter test of photoelectric signal was designed and conducted. The test uses a self?developed precision dew point meter to adjust different voltage changes to measure the dew point temperature, and MBW373 cold mirror precision dew point meter as the reference. Then, the collected data was analyzed and the error was calculated. Finally, the relationship table between the photoelectric signal characteristic parameters and the dew point temperature in the temperature range of -30 ~ -10 ℃ was obtained, and the photoelectric signal characteristic parameters in this temperature range were analyzed, which confirmed the feasibility of the test scheme. It provides data reference and theoretical support for further research on the dew point measurement process in the future.