Review of Scientific Instruments

Gluing is a critical step in aircraft sealing assembly, with glue profile inspection serving as the final quality assurance measure to ensure consistency and accuracy of the sealant coating, allowing timely detection and correction of defects to maintain assembly integrity and safety. Currently, existing glue inspection systems are limited to basic inspection capabilities, lack result digitization, and exhibit low efficiency. This paper proposes a 3D inspection technology for sealant coating quality based on line-structured light, enabling automated and high-precision inspection of sealant thickness, sealant width, positional accuracy, and overlap joint sealant contour through geometric computation. The method reduces manual inspection time and rework rates while providing detailed quality records to facilitate traceability. Additionally, it ensures that sealant application adheres to the stringent standards of the aviation industry. Experimental results demonstrate that the measurement error is within 0.2 mm compared to manual measurements, meeting the inspection requirements of practical applications.

In this paper, we present the development of a nanosecond pulse generator utilizing semiconductor opening switches (SOS), designed to deliver high voltage and operate at a high repetitive frequency. The pulse generator comprises three main components: a primary charging unit, a magnetic pulse compression unit, and an SOS magnification unit. To ensure stable operation of the high-power charging unit at high repetitive frequencies, a rectifying resonant charging and energy recovery circuit are implemented, providing a 1 kV charging voltage at a 3 kHz repetition rate. The three-stage magnetic pulse compression is designed to reduce the pulse width from tens of microseconds to tens of nanoseconds, where self-demagnetization could be completed during repetitive frequency operation. To achieve an output voltage of 300 kV, multiple SOS switches are employed in a series. The developed pulse generator achieves a final output of 300 kV with a 3 kHz repetitive frequency under a load of 2 kΩ. Furthermore, the effects of multiple factors on the output performance are characterized by both simulation and measurement for a comprehensive analysis.

We present the design of a VMI spectrometer optimized for attosecond spectroscopy in the 0–40 eV energy range. It is based on a compact three-electrode configuration where the lens shape, size, and material have been optimized using numerical simulations to improve the spectral resolution by a factor of ∼5 relative to the initial design [Eppink and Parker, Rev. Sci. Instrum. 68, 3477–3484 (1997)] while keeping a flat spectral response in the 10–40 eV range. The experimental performance is tested using an attosecond source based on high-order harmonic generation. A good agreement is observed between the measured and simulated spectral resolution. At low kinetic energy, the electrostatic lens remains the limiting factor, while the high energy range is mostly affected by the resolution of the camera objective.

Radiation from wireless communication devices inside intelligent connected vehicles has been an expeditious growth of concern regarding possible adverse effects on human health. Due to the significant differences in the working scenarios compared to traditional mobile products, the traditional measuring systems of specific absorption rate (SAR) are not applicable to in-vehicle scenarios. This paper has developed a SAR measurement system and a SAR measurement method, which are suitable for in-vehicle scenarios. Since the measurement hardware and methods are significantly different from traditional systems, it is necessary to assess the measurement uncertainty for the new measurement system. Due to the significant influence of tissue fluid on the SAR, this paper focuses on analyzing the relationship between tissue fluid and SAR. Based on the validated electromagnetic simulation model, linear and quadratic fitting models reflecting the relationship between tissue fluid properties and SAR are established. Then, the uncertainty propagation was realized using both the Guide to the Expression of Uncertainty in Measurement and MCM (Monte Carlo Method) through these models. The results of uncertainty analysis were analyzed in combination with the fitting error. The results of the analyses show that the fitting error of the quadratic measurement model is smaller because there is no simple linear relationship between the tissue fluid properties and the SAR values, and thus, it is more reasonable to use the MCM method to evaluate the uncertainty.

In multi-dimensional nanopositioning and nanomeasuring devices, interference measurement is widely used. The three-dimensional (3D) target mirror serves as the spatial reference plane to achieve multidimensional interference measurements. However, the surface shape errors of the target mirror are superimposed on the geometric dimensions of the measured workpiece, which limits the system’s overall measurement accuracy. This paper proposes a method for on-machine separation and compensation of the target mirror’s surface shape errors based on the micro–nano-coordinate measuring machine (MNCMM) that employs interference measurement. This method provides the model for the separation and compensation of the surface shape errors. The MNCMM employs a home-made resonant probe and a reference flat crystal to achieve the separation experiment. Subsequently, an interpolation algorithm is used to compensate for the surface shape errors at any point in space according to the compensation model. By comparing the flatness measurement results of a standard flat crystal with a flatness of 50 nm before and after compensation, the flatness is reduced from 175 to 77 nm. It demonstrates the reliability of the method. This method can be widely applied to on-machine compensation for surface shape errors in multidimensional interference measurement systems.

Comprehensive Research Facility for Fusion Technology (CRAFT) is a technology development and validation platform for fusion technology in China. Neutral beam injection is one of the most important auxiliary heating and current drive methods in magnetically confined controlled fusion. Consequently, a negative ion based neutral beam injector (NNBI) testing facility with a beam energy of 400 keV is being developed in CRAFT. The core snubber, which provides an equivalent parallel resistance and inductance, will be used as the main surge suppression method for the CRAFT NNBI power supply system. In this paper, a core snubber for CRAFT NNBI based on Fe-based amorphous alloy is designed. The transmission line resistance, inductance, and capacitance of the high-voltage circuit have been considered during the design process. The snubber is made thin and long for even weight distribution while ensuring choke capacity. One of the snubber units was tested on the test bench. The test results indicate that the choke capacity of the snubber meets the requirement and can achieve significant suppression of peak ignition current and oscillation.

A novel solid electrolyte sensor with considerably improved response times is presented. The new so-called eFIPEX [etched flux (Φ) probe experiment] is based on the FIPEX [flux (Φ) probe experiment] sensor applied for the measurement of molecular and atomic oxygen concentrations. A main application is the measurement of atmospheric atomic oxygen aboard sounding rockets up to altitudes of 250 km. eFIPEX employs a new manufacturing technique for its electrodes combining two manufacturing steps—the deposition of platinum films with a polyol process and electrochemical etching to carve out the electrode geometry. Selectivity toward atomic oxygen is achieved through gold plating. All work steps can be completed in ambient air. Electrodes with thicknesses of 200 nm to 1.5 μm are manufactured and characterized with optical and electron microscopy as well as with energy dispersive x-ray spectroscopy. It is shown that the significantly faster response times are related to pores in the platinum film reaching down to the substrate. The new eFIPEX were flown in comparison with conventional FIPEX sensors on the PMWE-2 sounding rocket flight showing significantly improved performance. Due to the easier fabrication and the superior transient behavior, this new sensor system will be preferentially used in future missions.

Efficient identification of the flocculation state of waste drilling fluid remains a significant challenge. This study proposes an improved You Only Look Once version 8 nano-algorithm (YOLOv8n), specifically optimized for real-time monitoring of drilling fluid flocculation under field conditions. The algorithm employs MobileNetV3 as the backbone network to minimize memory usage, improve detection speed, and reduce computational requirements. The integration of the efficient multi-scale attention mechanism into the cross-stage partial fusion module effectively mitigates detail loss, resulting in improved detection performance for images with high similarity. The wise intersection over union loss function is employed to accelerate bounding box convergence and improve inference accuracy. Experimental results show that the enhanced YOLOv8n algorithm achieves an average recognition accuracy of 98.6% on the experimental dataset, a 4.8% improvement over the original model. In addition, the model size and parameter count are reduced to 2.9 MB and 2.8 Giga Floating-Point Operations Per Second (GFLOPS), respectively, compared to the original model, reflecting a reduction of 3.2 MB and 5.3 GFLOPS. As a result, the proposed flocculation recognition algorithm is highly deployable and effectively predicts flocculation state changes across varying working conditions.

A novel robust control strategy is proposed in this work to address the dynamic control problem of permanent magnet synchronous motors (PMSM) position tracking and lessen the effect of system parameter and load fluctuations on the dynamic performance of PMSM. The tracking performance is improved by a robust control element built with the Lyapunov method to reduce the impact of uncertain factors such as parameter uncertainty, nonlinear friction, and external interference; the nominal control element is stabilized by the dynamics model. The uniformly bounded and uniformly final bounded systems are proven, and the associated conclusions are provided using the Lyapunov minimax approach. In this work, modeling and experimental investigation are conducted using the cSPACE fast controller, based on the permanent magnet synchronous motor test platform. The results of the testing and simulation show that the developed controller can effectively regulate the permanent magnet synchronous motor and achieve more accurate position tracking even in the face of ambiguity.

In this paper, a microwave thermal imaging system (MTIS) has been presented for debonding detection of radar absorbing materials (RAMs). First, an overview of the mechanism underlying microwave heating and the fundamental principle of defect detection within RAMs is presented. Then, a multifunctional MTIS capable of performing both microwave lock-in thermography (MLIT) and long-pulse microwave thermography (LPMT) has been introduced, specifically tailored for the in situ inspection of RAMs. In addition, in this system, the detection area for a single scan is 90 * 90 mm², with the emission source operating at a frequency of 5.8 GHz and boasting a maximum output power of 20 W. Next, based on MTIS, the above-mentioned two thermography techniques are applied to detect defects in RAMs. In addition, thermal contrast (Tc) and signal-to-noise ratio are introduced for the analysis of imaging results. Finally, the results show that LPMT can be used for preliminary detection of debonding defects in RAMs, while MLIT can be further used for detailed detection of debonding defects in RAMs. In addition, the minimum detection time of this MTIS is 45 s, and the minimum detectable defect aperture is 3 mm.

We introduce a novel control mode for Scanning Tunneling Microscope (STM) that leverages di/dz feedback. By superimposing a high-frequency sinusoidal modulation on the control signal, we extract the amplitude of the resulting tunneling current to obtain a di/dz measurement as the tip is scanned over the surface. A feedback control loop is then closed to maintain a constant di/dz, enhancing the sensitivity of the tip to subtle surface variations throughout a scan. This approach offers distinct advantages over conventional constant-current imaging. We demonstrate the effectiveness of this technique through high-resolution imaging and lithographic experiments on several Si(100)-2 × 1:H surfaces. Our findings, validated across multiple STM systems and imaging conditions, pave the way for a new paradigm in STM control, imaging, and lithography.

X-ray spectroscopies are uniquely poised to describe the geometric and electronic structure of metalloenzyme active sites under a wide variety of sample conditions. UV/Vis (ultraviolet/visible) spectroscopy is a similarly well-established technique that can identify and quantify catalytic intermediates. The work described here reports the first simultaneous collection of full in situ UV/Vis and high-energy resolution fluorescence detected x-ray absorption spectra. Implementation of a fiber optic UV/Vis spectrometer and parabolic mirror setup inside the dual array valence emission spectrometer allowing for simultaneous measurement of microfluidic flow and mixing samples at the Photon-In Photon-Out X-ray Spectroscopy beamline is described, and initial results on ferricyanide and a dilute iron protein are presented. In conjunction with advanced microfluidic mixing techniques, this will allow for the measurement and quantification of highly reactive catalytic intermediates at reaction-relevant temperatures on the millisecond timescale while avoiding potential complications induced by freeze quenching samples.

Capacitive sensors are commonly used in superconducting gravimeters due to their high resolution and low drift. This study developed a cryogenic front-end circuit for superconducting gravimeters to reduce the negative effects of parasitic capacitance on capacitive sensors. The front-end circuit comprises a noiseless superconducting transformer and a low-noise cryogenic preamplifier, both of which are positioned adjacent to the capacitive sensor probe. Compared with the front-end circuit operating at 300 K, the transfer coefficient of the front-end circuit increases from 131 to 1070 V/m, and the equivalent displacement noise reduces from 1.4 × 10⁻¹⁰ to 5.0 × 10⁻¹¹ m/Hz1/2 within a frequency band from 10⁻³ to 1 Hz. The temperature coefficient of the cryogenic preamplifier is 0.3%/K, and the superconducting transformer’s matching factor has adjusted as low as (2.4 ± 0.2) × 10⁻⁴. The cryogenic front-end circuit was finally applied to a superconducting gravimeter. The observed gravity data satisfactorily fit the theoretical tidal model, implying good long-term stability for the developed front-end circuit.

The spiral generator, based on the principle of the electric field vector inversion, is capable of delivering repetitive high-voltage nanosecond pulses in the commercial portable pulsed x-ray source and gas switch trigger source. However, the spiral generator suffers from extremely low output efficiency, which significantly affects the compactness and accelerates the insulation film breakdown at electrode foil edges since the high charging voltage is required. A novel output efficiency improvement method for the spiral generator was proposed, implementing the permalloy film inside the passive layer to optimize internal voltage wave propagation processes during the pulser erection. Output characteristics and influential factors of the modified spiral generator are experimentally determined, and the wave propagation processes are analyzed. The significant output efficiency improvement (approximately from 10% to 30% combined with ferrite cores at the center) is seminal for the portable x-ray source and gas switch trigger source of compactness and long operation lifetime.

The Particle Time of Flight (PTOF) diagnostic is a chemical vapor deposition diamond-based detector and is the only diagnostic for measuring nuclear bang times of low yield (<1013) shots on the National Ignition Facility. Recently, a comprehensive study of detector impulse responses revealed certain detectors with very fast and consistent impulse responses with a rise time of <50 ps, enabling low yield burn history measurements. At the current standoff of 50 cm, this measurement is possible with fast 14 MeV neutrons from deuterium–tritium (DT) fusion plasmas. PTOF-inferred DT burn width numbers compare well with widths inferred from the gamma reaction history diagnostic on mid-yield (10¹³–10¹⁵) shots, where both systems are capable of making this measurement. These new capabilities could be extended to 2.5 MeV deuterium–deuterium neutrons from D plasmas and to even lower yield by reducing the detector standoff distance to 10 cm; a design for this is also presented.

Aiming at the effects caused by stress and deformation on Micro-Electro-Mechanical System (MEMS) sensors, the stress distribution in the radiation area of the MEMS infrared light source is investigated, and by simulating and optimizing the thickness of the composite support film of the chip structure in COMSOL, a film layer thickness matching with lower stress and deformation for the MEMS infrared light source is derived. The utilization of the particle swarm algorithm and backpropagation neural network model allowed for the optimization of simulation data, enabling regression prediction over a broader range of thicknesses and providing a more precise depiction of the stress distribution trend. In addition, the specifications of the MEMS device help us to analyze the design of the support film thickness in the processing of the residual stress within the controllable range. To ensure the long-term stability and functionality of MEMS infrared light source chips in harsh environments, a comprehensive set of packaging schemes has been devised. Through simulations, it has been demonstrated that these packaging schemes effectively enhance the thermal efficiency of the light source while mitigating thermal stress and deformation that may arise during its operation. Consequently, this packaged configuration proves to be more advantageous for the sensor’s normal operation under challenging conditions such as rain and temperature fluctuations, as compared to utilizing a bare chip. Finally, the manufacturing flow and layout design for the MEMS infrared light source chip are provided to guide the process of chip fabrication.

A method to determine electron temperature within a plasma by the spectral analysis of atomic tungsten emission has been explored. The technique was applied to a post-discharge region immediately following a high voltage nanosecond pulsed discharge in air with tungsten electrodes. Atomic tungsten lines are readily observed in the weak emission spectrum within the post-discharge region for many microseconds. Intensity ratios were measured at various times after the pulsed discharge for a select pair of neutral tungsten emission lines at 400.88 and 401.52 nm, where the upper electronic levels of each transition are at 3.46 and 5.52 eV respectively. This significant difference in upper state energy causes their line intensity ratio to vary as the electron temperature changes. In addition to the emission spectra, the absolute electron temperature could be accurately measured in our lab using laser Thomson scattering to calibrate the new tungsten emission line intensity ratio method. An analysis is presented that calculates electron temperature from these tungsten emission data assuming a Maxwellian electron energy distribution contributing to direct electron impact excitation to the upper states of each transition. The results included the derivation of a calibration factor between the two experimental methods representing a previously unreported ratio of Einstein A coefficients for the 400.88–401.52 nm transitions. This derivation provides a method for future measurement of absolute electron temperature by the 400.88–401.52 nm tungsten line intensity ratio without the need for laser Thomson scattering calibration.

Diagnostic tools for understanding the edge plasma behavior in fusion devices are essential. The main focus of the present work is to present the infra-red (IR) diagnostics installed on Tokamak Energy’s spherical tokamak (ST40) and the IR thermographic inversion tool, Functional Analysis of Heat Flux (FAHF). FAHF is designed for multi-2D thermographic inversions within the divertor tiles using the finite difference method and an explicit time stepping scheme. ST40’s re-entrant endoscope allows the acquisition of IR data with the highest available effective spatial resolution. With these data, FAHF calculates the plasma perpendicular heat flux density on the divertor—a crucial quantity for edge plasma analysis. Although FAHF demonstrates significant sensitivity to user-selected settings, precise heat flux values are recoverable by ensuring a sufficiently high resolution. Implications for the optimal resolution of both the code and the IR diagnostic system are discussed. FAHF’s simplifications are shown to give an error within 10% with respect to COMSOL Multiphysics® simulations. Finally, by means of comparison with Langmuir probe heat flux data, the accuracy of the FAHF heat fluxes is estimated to be satisfactory. As such, FAHF is proven to be a precise and accurate tool for IR thermographic inversions in ST40.

In this paper, two models for simulating the shot noise and electronic noise performances of resonant photodetectors designed for homodyne measurements are presented. One is based on a combination of a buffer and a low-noise amplifier, and the other is based on an operational amplifier. Through the comparisons between the numerical simulation results and the experimentally obtained data, excellent agreements are achieved, which show that the models provide a highly efficient guide for the development of a high signal-to-noise ratio (SNR) resonant photodetector. Furthermore, we demonstrate a high SNR resonant photodetector for homodyne measurements at the 147 MHz optical sideband, achieving a 20.8 dB SNR of the shot noise to the electronic noise with a 2 mW optical signal input, utilizing a combination of a buffer and a low-noise amplifier. Concurrently, we have obtained another resonant photodetector at the 1.14 GHz optical sideband, which exhibits a 13 dB SNR based on an operational amplifier.

This paper presents a flat-type piezoelectric motor utilizing in-plane vibration modes. Two piezoelectric ceramic plates in combination with a brass metal sheet were used to construct the stator. The superposition of two second order in-plane vibration modes can generate a traveling-wave inside the stator. The greatest advantage of the proposed motor lies in its sheet structure configuration, which significantly reduces the overall size of piezoelectric motors exploiting in-plane vibrations, particularly in terms of thickness. Meanwhile, the stator also demonstrates greater vibration displacements when compared to higher-order operating modes. Through discussing the impact of stator structure parameters on the vibration deflection angle θ, the excitation ways of operating modes were investigated. Subsequently, the finite element method was utilized to explore both the static and dynamic vibration properties of the stator. Simulation results suggest that at a steady state, stator driving points achieve vibrations at the micro-meter level, satisfying actual application requirements. Finally, a prototype motor was fabricated. Driven by two-phase alternating voltage with a frequency of 69.4 kHz, the no-load speed and stall torque of the prototype motor are 52 rpm and 3.2 mN m, respectively.

We present an active alignment and stabilization control system for laser setups based on a thin-disk regenerative amplifier. This method eliminates power and pointing instability during the warm-up period and improves long-term stability throughout the entire operation. The alignment method is based on a four-mirror control system consisting of two motorized mirrors placed within the regenerative amplifier cavity, two additional motorized mirrors external to the amplifier cavity, and four camera detectors. The implemented stabilization system achieves significant performance improvements, increasing the power stability from 1.87% to 0.79% RMS and the peak-to-peak stability from 7.43% to 3.88%. Furthermore, the system significantly enhances beam positional stability, achieving up to a sixfold improvement in certain sensor measurements. The advantage of this method is the removal of long-term pointing instability by adding a second controlled motorized mirror to the cavity, in addition to using only one cavity end mirror for optimizing the overlap with the pump spot on the cavity medium. To achieve higher precision in pointing, the nonlinear hysteresis effect of the piezoelectric actuator is mitigated. Although the power and pointing stability of the cavity are secured, pointing instability at the input of the compressor occurs. This issue is resolved by two additional controlled motorized mirrors external to the cavity.

Carbon fiber reinforced polymers (CFRPs) are widely used in fields such as aviation and aerospace. However, subtle defects can significantly impact the material’s service life, making defect detection a critical priority. In this paper, delamination defects in CFRP are detected using line laser infrared thermography, and a defect characterization algorithm that combines differential thermography with a frequency-domain filter is proposed. This approach effectively eliminates the trailing phenomenon caused by line laser scanning and produces defect feature images with a higher signal-to-noise ratio. The size of the processed defects is then measured using pixel deviation values combined with K-means edge detection. The results show that the measured dimensions of defects are larger than the actual dimensions at the initial stage of cooling after excitation and smaller than the actual dimensions at the end of the cooling phase. The maximum measurement error for defect size was 2.74 mm² throughout the measurement interval. In addition, defect depth evaluation was achieved by fitting the curve of defect depth against the peak value in the frequency domain, with the resultant R-square value were all higher than 0.9877. This confirms the validity and accuracy of the methodology used in this study.

The measurement of thermal conductivities of anisotropic materials and atomically thin films is pivotal for the thermal design of next-generation electronic devices. Frequency-domain thermoreflectance (FDTR) is a pump–probe technique that is known for its accurate and straightforward approach to determining thermal conductivity and stands out as one of the most effective methodologies. Existing research has focused on advancing a measurement system that incorporates beam-offset FDTR. In this approach, the irradiation positions of the pump and probe lasers are spatially offset to enhance sensitivity to in-plane thermal conductivity. Previous implementations primarily adjusted the laser positions by modifying the mirror angle, which inadvertently distorted the laser spot. Such distortion significantly compromises measurement accuracy, which is especially critical in beam-offset FDTR, where the spot radius has a crucial impact on measured values. This study introduces an advanced FDTR measurement system that realizes probe laser offset without inducing spot distortion, utilizing a relay optical system. The system was applied to measure the thermal conductivities of both isotropic standard materials and anisotropic samples, including highly oriented pyrolytic graphite and graphene. The findings corroborate those of prior studies, validating the measurement’s reliability in terms of sensitivity. This development of a beam-offset FDTR system without laser spot distortion establishes a robust basis for accurate thermal conductivity values of anisotropic materials via thermoreflectance methods.

Emotion recognition based on electroencephalogram (EEG) has always been a research hotspot. However, due to significant individual variations in EEG signals, cross-subject emotion recognition based on EEG remains a challenging issue to address. In this article, we propose a dynamic domain-adaptive EEG emotion recognition method based on multi-source selection. The method considers each subject as a separate domain, filters suitable source domains from multiple subjects by assessing their resemblance, then further extracts the common and domain-specific features of the source and target domains, and then employs dynamic domain adaptation to mitigate inter-domain discrepancies. Global domain differences and local subdomain differences are also considered, and a dynamic factor is added so that the model training process first focuses on global distribution differences and gradually switches to local subdomain distributions. We conducted cross-subject and cross-session experiments on the SEED and SEED-IV datasets, respectively, and the cross-subject accuracies were 89.76% and 65.28%; the cross-session experiments were 91.63% and 67.83%. The experimental outcomes affirm the efficacy of the EEG emotion recognition approach put forward in this paper.

We design and construct an ultrafast optical spectroscopy instrument that integrates both on-site in situ high-pressure technique and low-temperature tuning capability. Conventional related instruments rely on off-site tuning and calibration of the high pressure. Recently, we have developed an on-site in situ technique, which has the advantage of removing repositioning fluctuation. That instrument only works at room temperature, which greatly hampers its application to the investigation of correlated quantum materials. Here, we further integrate low temperature functioning to this instrument, by overcoming enormous technical challenges. We demonstrate on-site in situ high-pressure ultrafast spectroscopy under a tunable temperature, from liquid-helium to above-room temperatures. During the pressure and temperature tuning process, the sample neither moves nor rotates, allowing for reliable systematic pressure- and temperature-dependence data acquisition. Ultrafast dynamics under 10–60 GPa at 130 K, as well as 40–300 K at 15 GPa, is achieved. Increasing and decreasing pressure within 5–40 GPa range at 79 K has also been achieved. The precisions are 0.1 GPa and 0.1 K. Significantly, temperature-induced pressure drifting is overcome by our double-pneumatic membrane technique. Our low temperature on-site in situ system enables precise pressure and temperature control, opening the door for reliable investigation of ultrafast dynamics of excited quantum states, especially phase transitions in correlated materials, driven by both pressure and temperature.