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In this paper, designed digital holography subsystem is shown in Fig.6. The sample designed in this experiment is shown in Fig.7, and the sample material is aluminum alloy. The groove of the ultrasonic excitation surface is circular, so that the ultrasonic transducer can be embedded in the sample to facilitate ultrasonic excitation of the bottom of the sample. A flat-bottomed hole having a diameter of 50 μm and a depth of 0.1 mm was machined at the center of the sample according to the detection requirements. This hole trap represents an internal defect in the micromechanical structure. The thickness of the sample to be tested is 0.3 mm.
The sample shown in Fig.7 was tested. The detection system used is shown in Fig.6. The microscope used in this experiment is Mitutoyo, Japan. The magnification is 50X, the working distance of the microscope is 13 mm, the recording distance is 500 mm, and the ultrasonic excitation signal is 5 MHz.
As shown in Fig.8, the ultrasonic wavefields morphology of the sample at different times are recorded separately in this experiment. Two different delay times (t1, t2) are set respectively, the maximum amplitude moment of the ultrasonic wavefields is recorded at time t1, and the maximum amplitude moment of the negative direction of the ultrasonic wavefields is recorded at time t2. In order to compare the defective and non-defective conditions, under the same conditions, the surface ultrasonic wavefields of the sample without defects was recorded at the corresponding time (t1, t2).
This paper first measured aluminum sheets with no defects (0.3 mm thick). The measurement principle is shown in Fig.2, and the detection system is shown in Fig.6. In this experiment, the ultrasonic wavefields are measured at time points t1 and t2, as shown in Fig. 9.
As shown in Fig.9, the ultrasonic wavefields on the surface of the aluminum plate does not change significantly at times t1 and t2, and is close to the flat surface. Because this experiment added a high power microscope, the recorded spot size is very small, so the shape variable of the entire ultrasonic wavefields is close to the flat surface in the spot size. The ultrasonic wavefields morphology measured in Fig.9 is small enough that its phase is not wrapped by [-π, π], and the interferogram does not need to be unwrapped.
Secondly, this experiment tests the defects described in Fig.7. Figure 10 shows the surface topography of the ultrasonic wavefields at time t1.
As can be seen from the Fig.10, compared with the defect-free ultrasonic wavefields topography in Fig. 9(a), there is a relatively obvious deformation in the results of this measurement. The deformation of the middle protrusion corresponds to the center position of the internal defect, and the protrusion gradually becomes smaller as the delay time changes.
In order to analyze the accuracy of the method and experimental system, this paper extracts the one-dimensional cross-section data on the two-dimensional ultrasonic wavefields data. The cross section is shown in Fig.11, where x = 600 and y = 600.
The amplitude of the ultrasonic wavefields can be calculated. This paper compares the one-dimensional cross-section data at time t1 without defects and defects, and the results are shown in Fig.12.
As shown in Fig.12, the blue is the morphology of the ultrasonic wavefields in the defective area, and the red is the morphology of the ultrasonic wavefields without defects. Figure 12 shows the cross-section data measured at the t1 delay time, and the maximum value of the amplitude change is 0.55 μm. It can be seen that when there is no defect, the shape of the ultrasonic wavefields changes very small, and close to a straight line. In the case of defects, the middle area will bulge and the surrounding area will be concave. The amount of change in amplitude measured in this experiment is the difference between the highest point and the lowest point in the measurement range, which is different from the actual amplitude.
The same as the method of measuring the ultrasonic wavefields at time t1, the data of the transient ultrasonic wavefields at time t2 can be obtained. The surface morphology of the ultrasonic wavefields at time t2 shows in Fig.13.
Similarly, the measurement data at time t2 is quantitatively analyzed. The result is shown in the Fig.14.
In the Fig.14, blue is the morphology of the ultrasonic wavefields of the defective area, and red is the morphology without defects. Figure 14 shows the cross-section data measured at time t2, and the magnitude of the change is up to 0.46 μm. It can be seen that when there is no defect, the shape of the ultrasonic wavefields changes in a small range close to a straight line. Deformation can occur in a defective place.
Table 1 is the maximum amplitude of the two transient
Table 1. Maximum amplitude of dynamic ultrasonic wavefields
Time point of measurement t1 t2 Maximum amplitude of transient ultrasonic
wavefield with defects/μm0.55 0.46 Maximum amplitude of transient ultrasonic
wavefield without defects/μm0.11 0.11 Deformation of ultrasonic wavefield
due to defects/μm0.44 0.35 ultrasonic wavefields obtained in this experiment. If the maximum amplitude of the transient ultrasonic wavefields with defects is used to reduce the maximum amplitude of the transient ultrasonic wavefields without defects, as shown in Tab. 1, the maximum value due to internal defects can be obtained.
Design of a hybid ultrasound and digital holography imaging system for detection of internal micro-defects
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摘要: 微机电系统与微机械零件的内部微缺陷需要高精度、强穿透性的非接触检测技术。目前缺少这样内部微缺陷的检测方法。针对上述问题,设计了超声与数字全息成像的复合系统。该系统结合了超声检测的强穿透能力和数字全息成像技术的高分辨率。该系统包括近场超声子系统、数字全息子系统和同步控制子系统。在近场超声子系统中,产生的近场超声波场穿过样品的内部缺陷,在样品表面形成表面超声波场,再通过数字全息子系统测量和分析这个表面超声波场的瞬态形貌,分析声波场中包含的内部缺陷信息。实验结果表明:该系统通过对超声波场的分析,可以测量出超声波场的瞬态三维形貌,并且可以有效的检测出50 μm的内部缺陷。Abstract: Non-contact detection of internal micro-defects of the micro-electro-mechanical system and minimechanism required a high accuracy and strong penetration test. The current detection methods were difficult to achieve high precision while also having strong penetrating power. In response to the above problems, a composite system of ultrasonic detection and digital holography imaging was designed. Ultrasonic detection technology had strong penetrating power, and digital holographic imaging had higher resolution. The composite system designed included a near-field ultrasonic subsystem, an digital holographic subsystem and a synchronous control subsystem. In the near-field ultrasonic subsystem, the generated near-field ultrasonic wavefields passed through the internal defect of the sample and formed the surface ultrasonic wavefield on the surface of the sample. The digital holographic subsystem mainly measured and analyzed the transient morphology of the surface ultrasonic wavefields, and the internal defect information contained in the surface ultrasonic wavefield could be analyzed. The experimental results show that the system can measure the transient 3D topography of the ultrasonic wavefield by analyzing the ultrasonic wavefield, and can effectively detect internal defects of 50 μm.
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Table 1. Maximum amplitude of dynamic ultrasonic wavefields
Time point of measurement t1 t2 Maximum amplitude of transient ultrasonic
wavefield with defects/μm0.55 0.46 Maximum amplitude of transient ultrasonic
wavefield without defects/μm0.11 0.11 Deformation of ultrasonic wavefield
due to defects/μm0.44 0.35 -
[1] Zhou Z, Zhang K, Zhou J, et al. Application of laser ultrasonic technique for non-contact detection of structural surface-breaking cracks [J]. Optics & Laser Technology, 2015, 73: 173−178. [2] Boone M A, Nielsen P, De K T, et al. Monitoring of stainless-steel slag carbonation using X-ray computed microtomography [J]. Environmental Science & Technology, 2014, 48(1): 674−680. [3] Hapca S, Baveye P C, Wilson C, et al. Three-dimensional mapping of soil chemical characteristics at micrometric scale by combining 2D SEM-EDX data and 3D X-Ray CT images [J]. Plos One, 2015, 10(9): e0137205. doi: 10.1371/journal.pone.0137205 [4] Shekhawat G S, Avasthy S , David V P. Probing buried defects in extreme ultraviolet multilayer blanks using ultrasound holography [J]. Nanotechnology, 2010, 6(9): 671−674. [5] Dravid V. Seeing the invisible: Scanning near-field ultrasound holography (SNFUH) for high resolution sub-surface imaging [J]. Microscopy & Microanalysis, 2013, 13(2): 1220−1221. [6] Doherty M, Sykes J M. Micro-cells beneath organic lacquers: a study using scanning Kelvin probe and scanning acoustic microscopy [J]. Corrosion Science, 2004, 46(5): 1265−1289. doi: 10.1016/j.corsci.2003.09.016 [7] Zhang G M, Harvey D M, Burton D R. Micro-nondestructive evaluation of microelectronics using three-dimensional acoustic imaging [J]. Applied Physics Letters, 2011, 98(9): 102110. [8] Kumazawa T, Toshiba K K. Ultrasound probe diagnosing apparatus, ultrasound diagnostic apparatus, and ultrasound probe diagnosing method:Japan,1839579A[P], 2007-10-03. [9] Wang X, Zhang G M, Ma H, et al. Measurement of a 3D ultrasonic wavefield using pulsed laser holographic microscopy for ultrasonic nondestructive evaluation [J]. Sensors, 2018, 18(2): 573. doi: 10.3390/s18020573 [10] Pelivanov I, Shtokolov A, Wei C, et al. A 1 kHz a-scan rate pump-probe laser-ultrasound system for robust inspection of composites [J]. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 2015, 62(9): 1696−1703. doi: 10.1109/TUFFC.2015.007110 [11] Abolhassani M, Rostami Y. Speckle noise reduction by division and digital processing of a hologram [J]. Optik - International Journal for Light and Electron Optics, 2012, 123(10): 937−939. doi: 10.1016/j.ijleo.2011.06.060 [12] Vladimirov A P, Kamantsev I S, Veselova V E, et al. Use of dynamic speckle interferometry for contactless diagnostics of fatigue crack initiation and determining its growth rate [J]. Technical Physics, 2016, 61(4): 563−568. doi: 10.1134/S106378421604023X [13] Cai X O, Lai X J. Study on information content of the 3D object's coherent imaging and hologram information redundancy [J]. Optik - International Journal for Light and Electron Optics, 2012, 123(3): 240−245. doi: 10.1016/j.ijleo.2011.03.019 [14] Melninkaitis A, Tamosauskas G, Balciunas T, et al. Time-resolved off-axis digital holography for characterization of ultrafast phenomena in water [J]. Optics Letters, 2008, 33(1): 58. doi: 10.1364/OL.33.000058 [15] Hong K M, Kang Y J, Choi I Y, et al. Ultrasonic signal analysis according to laser ultrasound generation position for the detection of delamination in composites [J]. Journal of Mechanical Science and Technology, 2015, 29(12): 5217−5222. doi: 10.1007/s12206-015-1121-y [16] Yang C, Yan X, Zhu R, et al. Diffraction study of volume holographic gratings in dispersive photorefractive material for femtosecond pulse readout [J]. Optik - International Journal for Light and Electron Optics, 2010, 121(12): 1138−1143. doi: 10.1016/j.ijleo.2008.12.023 [17] Lee Y L, Lin Y C, Tu H Y, et al. Phase measurement accuracy in digital holographic microscopy using a wavelength-stabilized laser diode [J]. Journal of Optics, 2013, 15(15): 5403. [18] Cao L, Wang Z, Zhang H, et al. Volume holographic printing using unconventional angular multiplexing for three-dimensional display [J]. Applied Optics, 2016, 55(22): 6046. doi: 10.1364/AO.55.006046