Advances in Aeroengine Cooling Hole Measurement: A Comprehensive Review.

Film cooling technology is of great significance to enhance the performance of aero-engines and extend service life. With the increasing requirements for film cooling efficiency, researchers and engineers have carried out a lot of work on the precision and digital measurement of cooling holes. Based on the above, this paper outlines the importance and principles of film cooling technology and reviews the evolution of cooling holes. Also, this paper details the traditional measurement methods of the cooling hole used in current engineering scenarios with their limitations and categorizes digital measurement methods into five main types, including probing measurement technology, optical measurement technology, infrared imaging technology, computer tomography (CT) scanning technology, and composite measurement technology. The five types of methods and integrated automated measurement platforms are also analyzed. Finally, through a generalize and analysis of cooling hole measurement methods, this paper points out technical challenges and future trends, providing a reference and guidance for forward researches.

Optimization of under-sampling phase detection accuracy in phase laser ranging.

Under-sampling is an advantageous way for lowering sampling circuit complexity in phase laser ranging while maintaining high modulated frequency operation. Improving the accuracy of the ranging system is the aim of the proposed selection criteria with involved under-sampling parameters. These parameters include signal frequency, sampling frequency, and calculation points. Setting the number of one periodic sampling points to be an integer power of 2 (p o w e r=2-6) optimizes the accuracy in integral periodic sampling. Levering up calculated periods with limited calculated points and averaging the calculated phase by employing the corresponding average parameter can both enhance accuracy in non-integral periodic sampling. These criteria are verified through derivation and simulation and are applied to the ranging system. The experimental results demonstrate that, by applying these selection criteria, the phase detection accuracy in the under-sampling ranging system can be potently improved without any pre-processing or algorithmic refinement.

Focal plane coincidence method for a multi-view telecentric 3D imaging system.

Multi-view microscopic fringe projection systems, which use high-resolution telecentric lenses and the Scheimpflug condition, face challenges in coinciding focal planes accurately, resulting in inconsistent measurements between views. In this Letter, we developed a sharpness evaluation function based on the total power of the line-spread function, which was subsequently used to generate a full-field sharpness distribution map. Then we employed the correlation between the sharpness map and orientation of the focal plane to precisely coincide the focal planes. Experimental results validate the proposed method and demonstrate its improved consistency in 3D reconstruction.

Anti-crosstalk absolute phase retrieval method for microscopic fringe projection profilometry using temporal frequency-division multiplexing.

In microscopic fringe projection profilometry (MFPP), the traditional absolute phase retrieval method using composite frequency fringe has the shortcomings of low accuracy and poor robustness due to mutual crosstalk of harmonic from the different channels of frequency-division multiplexing. In this study, an absolute phase retrieval method that avoids the inter-channel crosstalk is proposed. By introducing guard bands to accommodate the frequency channels corresponding to the second harmonic that dominate the high order harmonics, the aliasing between the second harmonic and the fundamental is eliminated. Consequently, phase maps without crosstalk can be demodulated using appropriate phase-shifting algorithms. The proposed method is well-suited for high-precision three-dimensional shape measurement scenarios in many fields such as integrated circuit manufacturing process control and micro-electro-mechanical system quality inspection. The experiment results demonstrate that the anti-crosstalk method is effective and can realize three-dimensional reconstruction for discontinuous planar surface and spherical surface.

On-site accuracy evaluation of laser tracking attitude measurement system.

In this study, an on-site attitude accuracy evaluation method based on parallel mechanism model and indirect traceability from length to angle is proposed. Firstly, the mathematical model is established. Through orthogonal experimental design, quantitative analysis shows that the ranging accuracy and control layout have a significant impact on the accuracy of the evaluation system. On this basis, the layout of control field is optimized by genetic algorithm. Finally, the practicability of the evaluation method is verified by experiments. The results show that the yaw and pitch accuracy of the method are 0.008°and 0.007°respectively in the range of -25°to 25°within the working distance of 8 m. This method can accurately and effectively evaluate the attitude angle information of the measurement system and is adapted to various on-site environments. The research provides an innovative idea which can be used to ensure the strict requirements of attitude angle measurement in fields such as intelligent manufacturing and in situ processing.

Near-zero beam drift laser tracking and measurement system with two-stage compression structures.

This paper introduces a scheme of near-zero beam drift tracking technology with two-stage compression structures for the coordinate accuracy measurement of a laser tracker. The Galileo telescope system, with a magnification of 21.43, is designed to compress the beam drift in a dual-frequency interferometer. The azimuth and pitch of the beam drift are compressed to 2.41 in. and 2.92 in., and the compression rates are 95.0% and 91.9%, respectively. The improved four degrees of freedom position-sensitive detector system is used to further compress the beam drift. The peak-to-peak value of the beam drift is 0.9 in. in the azimuth direction and 2.1 in. in the pitch direction. The standard deviation of azimuth is within 0.15 in, and the pitch is within 0.43 in. The coordinate accuracy of the laser tracker can be improved 6.85 parts per million by simulation. The developed two-stage compression near-zero beam drift system can be used in the laser tracker to realize large-scale precision instrument geometric measurement.

High-velocity measurement method in dual-frequency laser interference tracker based on beam expander and acousto-optic modulator.

The laser tracker, as a new large-scale measuring instrument of combining conventional measurement technology and modern control technology, has the advantages of intelligence, portability, large measurement space, high measurement accuracy and short detection period. However, the laser tracker has strict requirements on the moving speed of the spherically mounted retroreflector. This deficiency not only limits the application of the measuring instrument in the field of high-velocity measurement, but also greatly reduces the measurement efficiency. In this work, we analyze the factors that affect the tracking velocity of the laser tracker, and propose for the first time to use the beam expander device to improve the transverse tracking measurement velocity of the instrument. The experimental results show that the laser tracker miss distance can reach 2.25 mm. The transverse tracking velocity and acceleration can reach 4.34 m/s and 2.4 g, respectively. Additionally, the acousto-optic modulator is used to increase the frequency difference between the reference beam and the measuring beam, so that the value is greater than 19 MHz. The radial tracking measurement velocity can reach 6.2 m/s. The high-velocity laser interference tracker developed by this new method can be used in the field of large-scale space precision measurement such as nuclear power, medical treatment and rail transit.

A Novel Optical Instrument for Measuring Mass Concentration and Particle Size in Real Time.

Particle mass and particulate size are two important parameters used to characterize the aerosol. Currently, there are a few methods for measuring particle mass concentration and particle size. However, the existing methods have their own shortcomings. In this article, we describe a novel laser scattering instrument that measures mass concentration and particle size in real time over a wide concentration range. This instrument combines laser scattering and time-of-flight aerodynamics in one optical device. There are two innovations in this paper: (1) Two APD detectors are used to receive scattered light. One receives forward-scattered light and the other receives side-scattered light. The advantage is that the sensitivity of the detector is increased greatly, and the ratio of forward and side scattering is used to further obtain the size and shape information of the particles. (2) In order to measure the high concentrations of aerosol, a high-speed ADC and FPGA is combined to achieve an anti-overlap algorithm objective. It has been verified by experiments that the anti-overlapping algorithm can effectively improve the applicability of the aerodynamic particle size spectrometer under high concentration conditions.

Height measurement of microbumps using a white-light triangulation method.

As the electronic interconnection between chips, microbumps are crucial components in advanced packaging for the demand of better performance and higher packaging density. The height and coplanarity of microbumps are critical to ensure the reliability of connections. The poor uniformity in bump height will lead to disconnect or insufficient contact, which will directly result in the failure of the chip's function and a lower yield rate. In this paper, we proposed a height measurement method of microbumps using white-light triangulation combined with geometrical characteristics of bumps. A linear light projection module composed of a lens group and LED light source was set up as well as a high-quality imaging module consisting of a CCD camera and microscope objective group. The projection and imaging model of microbumps illuminated by the light plane at different positions during the scanning process was analyzed. The microbump height is computed from a simple formula based on the geometry of the specimen and the system configuration. The measurement results are compared with that obtained from a commercial optical profiler, and the measurement uncertainty is analyzed in detail.

Strong anisotropic enhancement of photoluminescence in WS2 integrated with plasmonic nanowire array.

Layered transition metal dichalcogenides (TMDCs) have shown great potential for a wide range of applications in photonics and optoelectronics. Nevertheless, valley decoherence severely randomizes its polarization which is important to a light emitter. Plasmonic metasurface with a unique way to manipulate the light-matter interaction may provide an effective and practical solution. Here by integrating TMDCs with plasmonic nanowire arrays, we demonstrate strong anisotropic enhancement of the excitonic emission at different spectral positions. For the indirect bandgap transition in bilayer WS2, multifold enhancement can be achieved with the photoluminescence (PL) polarization either perpendicular or parallel to the long axis of nanowires, which arises from the coupling of WS2 with localized or guided plasmon modes, respectively. Moreover, PL of high linearity is obtained in the direct bandgap transition benefiting from, in addition to the plasmonic enhancement, the directional diffraction scattering of nanowire arrays. Our method with enhanced PL intensity contrasts to the conventional form-birefringence based on the aspect ratio of nanowire arrays where the intensity loss is remarkable. Our results provide a prototypical plasmon-exciton hybrid system for anisotropic enhancement of the PL at the nanoscale, enabling simultaneous control of the intensity, polarization and wavelength toward practical ultrathin photonic devices based on TMDCs.

Temporally modulated laser with an alkali vapor amplifier.

A diode-pumped alkali laser has gained rapid development in recent years. In this study, we take the advantages of high-gain cross section and low upper energy lifetime of an alkali laser to propose, to the best of our knowledge, a novel type of time-domain-modulated alkali vapor amplifier. By using the amplifier, we experimentally demonstrate the power scaling of a modulated seed laser. The study should offer a new methodology to construct a practice high-power and high-modulated laser source for long-distance light detection and ranging systems in the future.

[Separation performance of vancomycin-bonded stationary phase].

Vancomycin is one of the macrocyclic antibiotics with complex molecular structure. Based on the various functional groups of vancomycin, a vancomycin-bonded stationary phase using glutaraldehyde as the spacer was prepared. Its chromatographic properties in reversed-phase, ion exchange and hydrophilic phase modes were investigated separately. The prepared stationary phase showed the typical characteristic of the reversed-phase stationary, when the organic solvent content was low in the mobile phase. On the contrary, its chromatographic characteristic transformed into hydrophilic phase mode with the organic solvent content increased in the mobile phase. Owing to the amino groups of vancomycin, ion exchange mode can also be applied to the separation method development. The vancomycin-bonded stationary phase was applied to the separation of eight achiral drugs and stevioside in reversed-phase, ion exchange and hydrophilic phase modes. The separations were achieved in three different kinds of separation modes by using appropriate chromatographic conditions. The results provide guidance for the design of new types of stationary phase, and method development of chromatographic stationary phases modified by special compounds with complex construction in corresponding separation modes.