Differential Measurement Method Research Articles

A Novel Electromagnetic Wavelength Measurement Method Based on Photoacoustic Effect and Photoacoustic Response Characteristics of Nanomaterials

This study proposes a differential wavelength measurement method based on the electromagnetic-induced photoacoustic effect. The differential method involves irradiating the sample with multiple wavelengths and utilizing differences in absorption characteristics across different materials to calculate and measure the excitation light wavelengths. Compared to traditional detection methods, this approach combines the unique properties of electromagnetic-induced photoacoustic effect, offering high sensitivity and a wider detection range from microwave to light. Furthermore, the system is structurally simple and stable, suitable for non-destructive testing of various materials, including wavelength-sensitive biological tissues. The experimental results demonstrate that combined with Polymers Benzodithiophene Triazole–Quinoxaline (PBTQ) and Single-Walled Carbon Nanotubes (SWCNTs) as absorbing media, this technique provides a rapid and cost-effective means of wavelength measurement, achieving an uncertainty of approximately 2.33 nm within the range of 680–800 nm, and it can be used for wavelength/frequency measurement of various electromagnetic waves.

Differential confocal effective measurement region extraction method based on dual measurement

Abstract Aiming at the problem that the existing differential confocal measurement (DCM) method lacks the ability to decouple the differential signals from over-range the depth data, which in turn leads to measurement errors, this study proposes a differential confocal effective measurement region extraction method based on dual measurement (D-DCM). The first measurement is a double blur depth measurement, which is a coarse measurement, and the initial acquisition of the depth map is realized by applying a known Gaussian kernel blurring to the focal plane image and calculating the edge gradient ratios between the original image and the blurred image. This depth map is used to determine whether the depth of the measured sample in the field of view is within the differential confocal range and to segment it. The second measurement is a DCM, which is a fine measurement. The effective measurement area of the segmented image is second measured with high precision depth measurement. It is shown by single and multiple step heights experiments that the proposed D-DCM method can effectively solve the problem of decoupling the differential signal from the axial depth in differential confocal.

Laser differential confocal axicon surface profile measurement method

Aiming to address the challenging problem of high-precision axicon profile measurement, a laser differential confocal axicon profile normal tracking (LDCNT) measurement method with high spatial resolution and anti-tilt capability is proposed in this paper. This method utilizes the principle of normal direction adaptive tracking for axicon profile measurements. It employs the Phase-Sensitive Detector (PSD) image plane spot position to calculate the normal angle and a high-precision rotary axis to drive the sensor normal to the measured surface to achieve the normal direction adaptive tracking measurement of the axicon profile and reduce the difficulty of pose adjustment of the measured axicon. Using the laser differential confocal focusing principle, the differential confocal signal is normalized to improve the axial resolution and avoid the Abbe error generated by the local inclination of the surface, thus realizing high-resolution and anti-tilt measurement of the axicon profile. Through the reference frame error decoupling axicon profile measurement and evaluation technique, spatial error compensation, three-dimensional profile reconstruction, and evaluation of the measurement data are performed to reduce the systematic measurement error and realize high-precision measurement and reconstruction of the axicon profile. Finally, the feasibility of the method is verified by measuring the profile of a standard cylinder and axicon at different axicon angles. The experimental analyses show that this method provides a new method for high-precision measurement of the axicon profile with Peak-to-Valley (PV) repeatability better than 40 nm (3σ) and Root-Mean-Square (RMS) repeatability better than 15 nm (3σ).

A MENTAL ILLNESS EARLY WARNING ANALYSIS MODEL USING AN IMPROVED SVM ALGORITHM AND EEG SIGNALS

The fast-paced lifestyle, intense competition, and constantly changing environment of modern society are important factors contributing to the emergence of psychological disorders. Factors such as work pressure, family conflicts, and interpersonal relationship difficulties pose challenges to individual mental health. Prolonged use of electronic devices and the widespread use of social media further exacerbate mental health issues, as the constant influx of information makes it difficult for people to relax and focus. The harm of psychological disorders to individuals and society cannot be ignored. It not only diminishes the quality of life for patients but also affects work efficiency and social participation. In extreme cases, psychological disorders can lead to serious consequences like suicide, causing immense pain to families and society. Therefore, prioritizing mental health, raising awareness of mental well-being, and timely intervention and treatment of psychological disorders are crucial for individual happiness and social stability. Based on this, this study employs an improved Support Vector Machine (SVM) and Electroencephalogram (EEG) signals for the diagnosis of psychological disorders, aiming for more effective treatment of mental health conditions. Specifically, the EEG signals of the experimental subjects are first collected as training data for the model. The dataset undergoes preprocessing operations such as cleaning and normalization. Due to the limited availability of published information about individuals with psychological disorders, an ensemble SVM algorithm is used as a warning model to improve the accuracy of psychological disorder diagnosis. This algorithm utilizes a differential measurement method to adjust the selection of SVM parameters. The training sample size remains constant, with several iterations of training performed. By combining the differential measurement method, a specific parameter combination is obtained, maximizing the differentiation between base classifiers. This ultimately addresses issues such as small sample size and insufficient sample information in the dataset. Experimental results demonstrate that the model used in this study exhibits good performance in diagnosing psychological disorders.

Laser differential confocal interference surface automatic measurement method

Considering the low accuracy, slow speed and small adjustment range of measuring an object with a spherical surface using traditional interferometry owing to adjusting the posture of the object, an automatic laser differential confocal interferometric measurement method is proposed to measure the surface shapes, which achieves the high-precision confocal axial positioning of the measured object through a precise differential confocal fixed-focus technology. The posture of the measured object is adjusted through a five-dimensional adjustment workbench. Subsequently, the Zernike fitting is used to reduce the defocus and tilt errors, and a zero-order fringe adjustment of the interferometric surface shape is achieved, automatically determining the surface shape. A laser differential confocal interferometric measurement system for surface shapes was constructed. Experiments demonstrate that the difference between the automatic interference measurement results and the Zygo interferometer measurement results is 0.0004 λ, the repeated measurement accuracy of this method can reach 0.0019 λ, the average measurement time of a single interferometric surface shape is 20.1 s, and the measurement efficiency is improved by 1.5 times compared to the manual adjustment to the zero-order fringe. Compared with the traditional adjustment based on Zernike fitting, this method has increased the lateral adjustment range by 11.5 times and the axial adjustment range by 1.5 times. This method provides an effective measurement method for the rapid and high-precision measurement of interferometric surface shapes.

A normal tracking differential confocal measurement method for multiple geometric parameters of hemispherical shell resonator with a common reference

This paper proposes a normal tracking differential confocal measurement method for the inside and outside surface profiles, shell thickness uniformity, and central asymmetry of inside and outside surfaces of the hemispherical shell resonator (HSR). A differential confocal technique with high-transmittance focusing ability is used to measure a single point on the inside and outside surfaces of the HSR. The normal alignment measurement technique is used to accurately measure the inside and outside surfaces and shell thickness of the HSR with a common reference in one measurement process. The HSR is step-rotated to synchronously collect information on the inside and outside surfaces, and using the differential confocal sensor to measure the different normal-section profiles. The experimental results indicate successful measurement of HSR central asymmetry. The repeated measurement accuracy for the inside and outside surface profiles and thickness uniformity is better than 30 nm.

Ultrathin Transparent Nickel Electrodes for Thermoelectric Applications

AbstractIn this work, ultrathin nickel films are developed for application as transparent electrodes in thermoelectric devices. The quality of the films is determined systematically by electrical, optical, and morphological characterization in a series of samples with different thickness. The thermal properties of the films show a dramatic dependence of the Seebeck coefficient on the film thickness. This dependence, with values ranging from −16 to +5 𝜇V K−1 for thicknesses from 10 to 2 nm, includes a change in the behavior of the thermoelectric response from n‐ to p‐type. It has also been demonstrated that the accurate estimation of the thermal conductivity in thin films is challenging due to substrate effects. In this situation, a differential measurement method based on scanning thermal microscopy is proposed, as in these conditions the measurements are less sensitive to the substrate effects. In further works, the dependence of the thermal properties of ultrathin nickel films can be exploited as a tuning parameter for the design of thermoelectric devices.

Miniaturized and highly-sensitive fiber-optic photoacoustic gas sensor based on an integrated tuning fork by mechanical processing with dual-prong differential measurement

A proof-of-concept gas sensor based on a miniaturized and integrated fiber-optic photoacoustic detection module was introduced and demonstrated for the purpose of developing a custom tuning-fork (TF)-enhanced photoacoustic gas sensor. Instead of piezoelectric quartz tuning fork (QTF) in conventional quartz-enhanced photoacoustic spectroscopy (QEPAS), a low-cost custom aluminum alloy TF fabricated by mechanical processing was employed as a photoacoustic transducer and the vibration of TF was measured by fiber-optic Fabry-Pérot (FP) interferometer (FPI). The mechanical processing-based TF design scheme greatly increases the flexibility of the TF design with respect to the complex and expensive manufacture process of custom QTFs, and thus it can be better exploited to detect gases with slow vibrational-translational (V-T) relaxation rates and combine with light sources with poor beam quality. The resonance frequency and the quality factor of the designed custom TF at atmospheric pressure were experimentally determined to be 7.3 kHz and 4733, respectively. Dual-prong differential measurement method was proposed to double the photoacoustic signal and suppress the external same-direction noise. After detailed optimizing and investigating for the operating parameters by measuring H2O, the feasibility of the developed sensor for gas detection was demonstrated with a H2O minimum detection limit (MDL) of 1.2 ppm, corresponding to a normalized noise equivalent absorption (NNEA) coefficient of 3.8 × 10−8 cm−1 W/Hz1/2, which are better than the QTF-based photoacoustic sensors. The proposed gas sensing approach combined the advantages of QEPAS and fiber-optic sensing, which can greatly expand the application domains of PAS-based gas sensors.

Differential multi-probe thermal transport measurements of multi-walled carbon nanotubes grown by chemical vapor deposition

Carbon nanotubes (CNTs) are quasi-one dimensional nanostructures that display both high thermal conductivity for potential thermal management applications and intriguing low-dimensional phonon transport phenomena. In comparison to the advances made in the theoretical calculation of the lattice thermal conductivity of CNTs, thermal transport measurements of CNTs have been limited by either the poor temperature sensitivity of Raman thermometry technique or the presence of contact thermal resistance errors in sensitive two-probe resistance thermometry measurements. Here we report advances in a multi-probe measurement of the intrinsic thermal conductivity of individual multi-walled CNT samples that are transferred from the growth substrate onto the measurement device. The sample-thermometer thermal interface resistance is directly measured by this multi-probe method and used to model the temperature distribution along the contacted sample segment. The detailed temperature profile helps to eliminate the contact thermal resistance error in the obtained thermal conductivity of the suspended sample segment. A differential electro-thermal bridge measurement method is established to enhance the signal-to-noise ratio and reduce the measurement uncertainty by over 40%. The obtained thermal resistances of multiple suspended segments of the same MWCNT samples increase nearly linearly with increasing length, revealing diffusive phonon transport as a result of phonon-defect scattering in these MWCNT samples. The measured thermal conductivity increases with temperature and reaches up to 390 ± 20 W m−1 K−1 at room temperature for a 9-walled MWCNT. Theoretical analysis of the measurement results suggests submicron phonon mean free paths due to extrinsic phonon scattering by extended defects such as grain boundaries. The obtained thermal conductivity is decreased by a factor of 3 upon electron beam damage and surface contamination of the CNT sample.

Characterization of developed low thermal scanner for DC voltage measurement

A low thermal scanner has been completely developed for improving DC voltage calibration from semi-automatic to fully automatic measurement system. The application of the switching system inside the built-up scanner introduced offset voltage to the measurement due to thermal electromotive force (EMF). A differential measurement method was proposed to characterize the thermal EMF of the scanner, and this method has been compared to previous characterization using the direct measurement method. The results show that the differential measurement method could minimize the thermal EMF effect, and the thermal EMF had a negligible contribution to the measurement for uncertainty levels around 10 to 11 ppm. Therefore, the differential measurement method is recommended for DC voltage calibration with uncertainty levels below 10 ppm since the thermal EMF can significantly affect the measurement. Furthermore, the direct measurement method is suggested for DC voltage calibration with uncertainty levels above 11 ppm since it can speed up the measurement process.

Study on double differential pressure measurement method of gas-liquid two-phase flow in high gas content wells

The production of natural-gas wells contains natural gas and a small amount of liquid, which is a wet gas composed of oil, gas and water. For dynamically monitor the liquid and gas production from a single well, there is an urgent need for a low-cost, small-volume online metering device for wet gas flows through a single well. Aiming at the problem, this paper designs a wet gas flow measurement device for a long-throated Venturi tube based on the double differential pressure method. By combining experiments and numerical simulations, a matching flow calculation model was developed. Based on the experimental data of NEL's 6-inch standard Venturi tube wet gas over-reading, the numerical simulation method is used to carry out the research of high-pressure wet gas measurement under the pressure condition of 2, 4 and 6 MPa. The simulation results of two multiphase flow models, DPM and Euler, are compared with the experimental values of NEL. The results show that the maximum relative error is less than 10%, and the Euler model is more suitable for the numerical simulation of high-pressure wet gas. According to the actual production from the gas well, a long-throated Venturi tube with a throttling ratio of 0.5 and a diameter of DN50 was designed, and a numerical simulation study of wet gas under a pressure of 2, 3 and 4 MPa was carried out. Numerical simulation results show that the change laws of over-reading and liquid-gas mass ratios of high-pressure wet gas are consistent with those of low-pressure wet gas. The numerical simulation results are used to correct the flow calculation model of low-pressure wet gas, and a flow calculation model suitable for high-pressure wet gas in gas wells is obtained. The gas flow prediction accuracy of the flow calculation model was lower than ±3%, and the liquid flow prediction value was lower than ±10%. Compared with other measurement methods without separation of wet gas, the long-throated Venturi tube based on the double differential pressure method has a simple structure and low measurement cost. By further optimizing and expanding the measurement model, after improving the accuracy, it can be installed in the wellhead pipeline to monitor the oil and gas production from a single well in real time. This can provide support for gas reservoir exploitation decisions.

Differential confocal measurement of microstructure surface topography based on centering error optimization and wavelet threshold denoising

This paper proposes a precise differential confocal measurement method based on centering error optimization and wavelet threshold denoising (DCM-COWD), which can realize non-contact measurement of microstructure surface topography with high precision and efficiency. Firstly, the influence of pinhole diaphragm size and offset on axial response curve is analyzed through multiple experiments to obtain the optimal pinhole diaphragm diameter and offset of the differential confocal measurement system. Secondly, a probe centering method based on grating rotation successive approximation is designed, in order to reduce the centering error of 3D topography measurement during the spiral scanning process. Thirdly, a translation invariant (TI) wavelet threshold denoising algorithm based on median filtering and whale optimization (WOA) is proposed, which can improve the signal-to-noise ratio (SNR) and reduce the root mean square error (RMSE), and effectively suppress the Pseudo-Gibbs phenomenon of discontinuous points. Finally, the surface topography of a standard sample is measured based on DCM-COWD system. The measurement results show that the center error is within 0.75 μm and the maximum deviation is within 1.45 %. The measurement results show high accordance with the commercial white light interferometer, and the processing speed is improved by 4.17 times. The proposed method has great application potential for the precise and efficient measurement of 3D surface topography.

Steep freeform measurement method based on a normal transverse differential confocal.

A normal transverse laser differential confocal freeform measurement (NTDCFM) method was proposed to address the high-precision measurement difficulty of steep freeform surfaces with large variations in inclination, scattering, and reflectance. Using D-shaped diaphragm technology, the freeform surface under test (FSUT) axial variation transformed into a spot transverse movement on the detection focal plane. Meanwhile, a 2D position sensitive detector (PSD) was used to obtain the normal vector of the sampling points so that the measuring sensor's optical axis could track the FSUT normal direction. The focus tracking method extended the sensor measurement range. Theoretical analysis and experimental results showed that the axial resolution of the NTDCFM was better than 0.5 nm, the direction resolution of the normal vector was 0.1°, the maximum surface inclination could be measured up to 90°, the sensor range was 5 mm, and the measurement repeatability of the FSUT was better than 9 nm. It provides an effective new anti-inclination, anti-scattering, and anti-reflectivity method for accurately measuring steep freeform surfaces.

Speed feedback observation algorithm based on parameter introduction and its application in asynchronous motor

In this article, three-phase asynchronous motor and photoelectric encoder are taken as the research objects. In order to solve the problem of delay in the velocity feedback measurement result of asynchronous motor by photoelectric encoder, this article proposes a velocity feedback observation algorithm which introduces parameters according to different velocity instructions. The proposed method ensures that the speed feedback of asynchronous motor can keep good tracking effect under different speed instructions, reduces feedback delay, and the oscillation of speed tracking waveform is small. Stability analysis is also carried out in this article to ensure the reliability of the system. In the whole control system, the position signal output by the photoelectric encoder is the input of the algorithm, and the output of the algorithm is the speed feedback of the system. The proposed method establishes the speed control system model of three-phase asynchronous motor through MATLAB/Simulink for simulation, and the experiment is carried out based on the simulation. The simulation and experiment are compared with the traditional differential velocity measurement method of encoder. The results show that the velocity observation algorithm proposed is verified under different velocity instructions and varying loads, and the system has smaller steady-state error, better dynamic response, and good robustness.

Drift Rejection Differential Frontend for Single Plate Capacitive Sensors

Capacitive sensing at long ranges (10x the plate diameter) for long-term environmental monitoring can be limited by slow but significant measurement drifts from charge induction, which can exceed the small capacitance variations of interest, below 0.01%. This paper proposes a slope modulation differential capacitance measurement method for single-plate capacitive sensors operating in loading mode that effectively rejects noise from quasi-constant drift currents. It is based on periodical plate capacitance charge-discharge, like the period modulation frontends (astable multivibrators) that were used in past work, but it uses a constant oscillation period and compares the slopes of adjacent plate voltage ramps. Plate capacitance is calculated by averaging the slope magnitudes, which rejects the noise from quasi-constant drift currents. The sensitivity and noise rejection are compared with the period modulation techniques analytically, and the results are validated using simulations and experiments. They show that human body sensing range doubles and the noise floor is substantially lower compared to the state-of-the-art (period modulation).

Design and Fabrication of a Differential MOEMS Accelerometer Based on Fabry–Pérot Micro-Cavities

In this paper, a differential MOEMS accelerometer based on the Fabry-Perot (FP) micro-cavities is presented. The optical system of the device consists of two FP cavities and the mechanical system is composed of a proof mass that is suspended by four springs. The applied acceleration tends to move the PM from its resting position. This mechanical displacement can be measured by the FP interferometer formed between the proof mass cross-section and the optical fiber end face. The proposed sensor is fabricated on a silicon on insulator (SOI) wafer using the bulk micromachining method. The results of the sensor characterization show that the accelerometer has a linear response in the range of 1g. Also, the optical sensitivity and resolution of the sensor in the static characterization are 6.52 nm/g and 153ug. The sensor sensitivity in the power measurement is 49.6 mV/g and its resonant is at 1372 Hz. Using the differential measurement method increases the sensitivity of the accelerometer. Based on experimental data, the sensor sensitivity is two times as high as that of a similar MOEMS accelerometer with one FP cavity.

Differential phase measurement based on synchronous phase shift determination.

Based on synchronous phase shift determination, we propose a differential phase measurement method for differential interference contrast (DIC) microscopy. An on-line phase shift measurement device is used to generate carrier interferograms and determine the phase shift of DIC images. Then the differential phase can be extracted with the least-squares phase-shifting algorithm. In addition to realizing on-line, dynamic, real-time, synchronous and high precision phase shift measurement, the proposed method also can reconstruct the phase of the specimen by using the phase-integral algorithm. The differential phase measurement method reveals obvious advantages in error compensation, anti-interference, and noise suppression. Both simulation analysis and experimental result demonstrate that using the proposed method, the accuracy of phase shift measurement is higher than 0.007 rad. Very accurate phase reconstructions were obtained with both polystyrene microspheres and human vascular endothelial.

Differential confocal measurement method of linear scanning based on dual linear array camera

针对目前微观三维表面形貌测量技术中存在检测效率和测量范围较小的问题，提出一种基于双线阵相机的线扫描差动共聚焦三维形貌测量方法。采用线扫描光源，利用线扫描拼接算法，分别合成焦前和焦后图像；再利用差动算法获得样本位于测量区域的差动图像，结合预先刻度的轴向响应曲线，完成样本的三维形貌还原，实现大范围高效测量。实验结果证明：基于双线阵相机的线扫描差动共聚焦三维形貌测量方法在相同时间内测量范围和测量效率分别是白光干涉仪的16.48倍和6.59倍，并且该方法在测量过程中不需要停顿，只需实现一次对焦，就可以对样品进行连续不间断的扫描检测。研究成果为满足智能制造中在线在位、实时高效、大范围测量的检测需求提供依据。

Study on Double Differential Pressure Measurement Method of Gas-Liquid Two-Phase Flow in High Gas Content Wells

Study on Double Differential Pressure Measurement Method of Gas-Liquid Two-Phase Flow in High Gas Content Wells

Study on Double Differential Pressure Measurement Method of Gas-Liquid Two-Phase Flow in High Gas Content Wells

Study on Double Differential Pressure Measurement Method of Gas-Liquid Two-Phase Flow in High Gas Content Wells