High-speed Polarization Camera Research Articles

High-speed photoelastic tomography for axisymmetric stress fields in a soft material: Temporal evolution of all stress components

This study presents a novel approach for reconstructing all stress components of the dynamic axisymmetric fields of a soft material using photoelastic tomography (PT) and a high-speed polarization camera. This study focuses on static and dynamic Hertzian contact as an example of transient stress field reconstructions. For the static Hertzian contact (a solid sphere pressed against a gel block), all stress components in the urethane gel, which has an elastic modulus of 47.4 kPa, were reconstructed by PT using the measured photoelastic parameters. The results were compared with theoretical solutions and showed good agreement. For the dynamic Hertzian contact (a sphere impacting gel), a high-speed polarization camera was used to reconstruct the transient stress field within the gel. PT was used to quantitatively measure the shear and axial stress waves and showed different propagation speeds on the substrate. The technique allowed the simultaneous measurement of stress fields ranging from O(10−1) to O(101) kPa during large deformations, demonstrating its accuracy in capturing rapidly changing stress tensor components in dynamic scenarios. The scaling laws of the calculated impact force agreed with theoretical predictions, validating the accuracy of PT for measuring dynamic axisymmetric stress fields in soft materials.

Physical-model-based reconstruction of three-dimensional sound field from multi-directional measurement by parallel phase-shift interferometry

The high-spatial-resolution nature of optical non-invasive measurement and the reconstruction of three-dimensional sound fields are important for evaluating acoustic transducers. The computed tomography (CT) method has been used to reconstruct sound fields from optical measurement results because of its contactless feature. However, since the CT method does not assume any physical property of sound, it may not be suitable for the reconstruction of sound fields. In contrast, a physical-model-based method is able to reconstruct sound fields more accurately by considering the physics of sound. In this study, we propose a scan-free and physical-model-based reconstruction of a three-dimensional sound field. A sound field is multi-directionally measured using parallel phase-shifting interferometry and a high-speed polarization camera by rotating an acoustic transducer. A physical-model-based method is applied to reconstruct the sound field from the recorded optical interferograms. We also discussed the effectiveness of the proposed method to evaluate acoustic transducers.

Dynamic measurement of internal strain on composite solid propellant constituents during laser induced combustion

Binder melt flow and ammonium perchlorate (AP) cracking have been topics for research for a long time. Both impact the burning rate dependence on pressure and the binder flow. Rapid depressurization of the combustion vessel is the most common tool used to study binder melt flow by studying the ripples on the quenched surface. Laminate propellants were used to study fundamental combustion phenomena such as the melt flow over the oxidizer/binder interface AP/hydroxyl-terminated polybutadiene (HTPB). This study starts with thermally induced strain measurements in single crystals of AP with thicknesses 1- to 2.5-mm and neat HTBP slabs then finishes with laminates of AP/HTPB. A CO2 laser ignited and burned samples over a range of heat fluxes. First ever in- situ mapping of the two-dimensional thermally-induced internal strain generated at ignition to steady state combustion were imaged using a high-speed polarization camera. Heating of the surface produced strain fields in the AP, HTPB, and laminate provide information on the thermal diffusion during the ignition and fully developed combustion. This paper demonstrates how using polarized high-speed video, the binder melt flow was more accurately observed and AP cracking mechanisms can be better studied.

Non-Contact And Non-Steady Rheo-Optical Measurement Of Hydrodynamic Stress Fields Inside A Cylindrical Tube

For measuring non-contact and non-steady rheo-optical measurement of hydrodynamic stress fields, we utilize a high-speed polarization camera that captures an unsteady phase-retardation field. It is known that the retardation has a proportional relationship to secondary principal stress difference. A solution of sodium iodide including crystal polymers (CNCs, cellulose nano crystals) was used as the working fluid. We have successfully measured the retardation induced by flow birefringence of CNCs without compromising the Newtonian fluid properties of the solution. In this paper, we propose a visualization technique for the retardation field of fluid in a cylindrical glass tube that incorporates index matching and discuss its comparison with the spatial intensity distribution of theoretical hydrodynamic stress field. Experimental results show that the retardation increases with an increase in flow rate. In addition, by utilizing the orientation angle data measured with the high-speed polarization camera, the vector field of principal stress difference is visualized, which is suggested to be useful for confirming the effects of direction of stresses. To investigate whether the measured retardation filed agrees with the theoretical secondary principal stress difference, the spatial intensity distribution of the two was compared. The overall trend agrees well while the retardation at the center of the tube is different, possibly owing to the effect of structure-induced retardation due to self-assembly of CNCs. The structure-induced retardation data were obtained by a combined measurement of a rotational rheometer and the high-speed polarization camera. As a result, the theoretical secondary principal stress difference distribution with considering structure-induced retardation showed better agreement with the retardation field than the case without considering it.

Three-Dimensional Measurement Of A Stress Field In A Rectangular Channel Flow Using A Photoelastic Method

The hydrodynamic stress field of a steady laminar flow in a rectangular channel was experimentally measured by using a photoelastic method. For this purpose, following two issues for a mixed solution of photoelastic material, cellulose nanoctystal (CNC), were extensively investigated. The first is to elucidate whether there are any phenomena (trends) peculiar to a CNC mixed solution that differ from those to the solid case. The second is to elucidate the extent to which the stress-optic law holds for CNC mixed solution. As a verification method for the first question, we measured retardation distributions by using a high-speed polarization camera. We compared distributions of measured retardation of a CNC mixed solution (0.5 wt %) (Newtonian fluid) and theoretical secondary-principal stress difference derived from the analytical solution of steady lam- inar flow in a rectangular channel. The results showed that a retardation, which was not affected by stress-oriented phase retardation, appeared in the CNC mixed solution. The reason is considered to be retardation induced by aggregations of CNC particles. This phenomenon is peculiar to CNC mixed solution and does not occur in solids cases. As a method of verification of the second issue, we compared the secondary principal stress difference distribution with the retardation distribution offsetting the effect of the retardation specific to the CNC mixed solution. The result showed that the spatial intensity distributions of both agreed within a relative error of 3.84 %. This indicates that the stress-optic law holds for the retardation offsetting the retardation specific to the CNC mixed solution. To evaluate the validity of the above validation results, we measured the retardation fields of flows at different flow rates (10, 20 ml/min). The measured results agree with theory with relative errors 5.67 % and 3.24 % for flow rates of 10 and 20 ml/min, respectively.

Measurements of S0 mode Lamb waves using a high-speed polarization camera to detect damage in transparent materials during non-contact excitation based on a laser-induced plasma shock wave

The demand for transparent materials has been expanding due to their ubiquity in products such as solar panels, tablet terminals, and smartphones. To mass produce high-quality products, quickly detecting damage on the µm scale and evaluating the quality are critical. Herein an Nd:YAG pulsed laser with a nanosecond order is used to generate a shock wave by laser induced plasma, which is subsequently used as a non-contact, non-destructive excitation force for transparent materials. Then, a high-speed polarization camera measures the generated Lamb wave. In this experiment, an impulse input is generated via a laser-induced plasma shock wave and the phase velocity of the generated Lamb wave in the polycarbonate plate is measured by a high-speed polarization camera. We found that this Lamb wave was in the S0 mode. Observing its propagation can detect scratches on the order of several hundred µm on the surface of a transparent plate in a non-contact, non-destructive manner.

Dynamic mechanical interaction between injection liquid and human tissue simulant induced by needle-free injection of a highly focused microjet

This study investigated the fluid–tissue interaction of needle-free injection by evaluating the dynamics of the cavity induced in body-tissue simulant and the resulting unsteady mechanical stress field. Temporal evolution of cavity shape, stress intensity field, and stress vector field during the injection of a conventional injection needle, a proposed highly focused microjet (tip diameter much smaller than capillary nozzle), and a typical non-focused microjet in gelatin were measured using a state-of-the-art high-speed polarization camera, at a frame rate up to 25,000 f.p.s. During the needle injection performed by an experienced nurse, high stress intensity lasted for an order of seconds (from beginning of needle penetration until end of withdrawal), which is much longer than the order of milliseconds during needle-free injections, causing more damage to the body tissue. The cavity induced by focused microjet resembled a funnel which had a narrow tip that penetrated deep into tissue simulant, exerting shear stress in low intensity which diffused through shear stress wave. Whereas the cavity induced by non-focused microjet rebounded elastically (quickly expanded into a sphere and shrank into a small cavity which remained), exerting compressive stress on tissue simulant in high stress intensity. By comparing the distribution of stress intensity, tip shape of the focused microjet contributed to a better performance than non-focused microjet with its ability to penetrate deep while only inducing stress at lower intensity. Dynamic mechanical interaction revealed in this research uncovered the importance of the jet shape for the development of minimally invasive medical devices.

Morphology of Cleaved Surface and Observation of In Situ Crack Propagation During Cleaving

In laser cleaving, the thermal stress caused by laser heating and water-jet cooling propagates previously induced cracks in the workpiece material. The laser-cleaving conditions affect the quality of the fracture surface, and therefore, elucidating the relationship between the cleaved surface, cleaving conditions, and crack propagation is essential. Against this backdrop, in this study, we investigated the morphology of the cleaved surface and visualized the crack propagation and stress in situ using a high-speed polarization camera. The distance between the glass edge and cleaved surface was varied. When the laser-cleavage line was close to the glass edge, twist hackles were formed on the cleaved surface. The area in which the twist hackles formed on the cleaved surface coincided with the lagging section of the crack front. Furthermore, the twist hackle reached the specimen surface, and the edge of the surface exhibited a sawtooth shape. Observations with the high-speed polarization camera revealed that the internal stress was asymmetric with respect to the crack when the twist hackles were formed.

Physical-model-based reconstruction of axisymmetric three-dimensional sound field from optical interferometric measurement

Optical interferometric measurement methods for sound fields have garnered considerable attention owing to their contactless nature. The capabilities of non-invasive measurement and reconstruction of three-dimensional sound fields are significant for characterizing acoustic transducers. However, three-dimensional reconstructions are typically time consuming because of the two-dimensional scanning and rotation of the measurement system. This paper presents a scan and rotation-free reconstruction of an axisymmetric sound field in the human hearing range. A physical-model-based algorithm is proposed to reconstruct an axisymmetric sound field from optical interferograms recorded using parallel phase-shifting interferometry and a high-speed polarization camera. We demonstrate that audible sound fields can be reconstructed from data measured in 10 ms. The proposed method is effective for the rapid evaluation of axially symmetric acoustic transducers.

Seeing the sound of castanets: Acoustic resonances between shells captured by high-speed optical visualization with 1-mm resolution.

Sound fields radiated from the castanet, a Spanish percussive instrument comprising two shells, were optically visualized. A measurement system, which used parallel phase-shifting interferometry and a high-speed polarization camera, enabled the capture of instantaneous sound fields around the castanets, while the castanets were played, with the spatial resolution of 1.1 mm and frame rate of 100 000 fps. By carefully aligning the tilt of the castanets, the sound fields within the 1-mm gaps between both the shells were captured. From the visualization results, two acoustic resonances between the shells were identified. The first mode appeared between 1000 and 2000 Hz and exhibited a frequency chirp of several hundred hertz for several milliseconds after the impact. This can be explained by the Helmholtz resonance with a time-varying resonator shape, which is caused by the movement of the shells after impact. The second mode showed a resonance pattern with a single nodal diameter at the center of the shells, i.e., the standing wave mode caused by the interior volume. These physical phenomena involved in the sound radiation were identified owing to the unique features of the optical imaging method, such as contactless nature and millimeter-resolution imaging of instantaneous pressure fields.

Flow properties of surfactant solutions of rod-like micelles passing through a small slit

Pressure drops in flows through a small slit were experimentally measured at constant flow rates to investigate flows with an abrupt contraction and expansion. The flow properties of water, 50 wt% glycerol solution, and two types of surfactant solutions (Lipoquad and Lipothoquad) with a counterion (NaSal) were examined. The slit heights used were 480 µm, 222 µm, and 129 µm, with estimated hydraulic diameters of 938 µm, 439 µm, and 256 µm, respectively. Viscosity was measured using a capillary-type viscosity meter. Water and the 50 wt% glycerol solution exhibited Newtonian viscosity, with the viscosity of the glycerol solution being 10 times that of water. By contrast, the surfactant solutions, which contained rod-like micelles, exhibited non-Newtonian viscosity. A power law model was therefore applied for the relationship between shear viscosity and shear rate on the wall. The observed flow properties of water (and the 50 wt% glycerol solution) and the numerical predictions of the Navier–Stokes equations were found to agree to within the experimental errors. In plots of the dimensionless pressure drop against the generalized Reynolds number, however, anomalous flow properties of the surfactant solutions were observed. The pressure drops of Lipoquad/NaSal agreed with those of water (and the 50 wt% glycerol solution) at low apparent strain rate (Reynolds number) but were larger at high apparent strain rate (Reynolds number). Furthermore, the pressure drops of Lipothoquad/NaSal were greater than those of water in the investigated range of the generalized Reynolds number. To examine these experimental results further, flows in a planar channel with an abrupt contraction and expansion were observed using a polarization measurement system based on a high-speed polarization camera. In contrast to polymer solutions (in which polymer chains were oriented along the flow direction), the phase difference for Lipoquad/NaSal before and in the slit region was high in regions with a strong elongational component. In addition, it was high along the centerline after the slit region. These results also differ from those of simple shear flows. Furthermore, the phase difference of Lipothoquad/NaSal was very unstable. In addition, the relationship between the resultant pressure drop and the measured phase differences was investigated, and a dependence was found on the apparent strain rate (Weissenberg number).

Examination of internal stress by photoelasticity in laser cleaving of glass

Laser cleaving is a glass-cutting technique in which thermal stress induced by laser heating and cooling produces cracks in the glass. Stress measurement during the laser cleaving process is critical in elucidating the crack-propagation mechanism and solving the problems of the laser cleaving method. In this study, we measured the birefringence retardation using a high-speed polarization camera and evaluated the relevance and accuracy of the measured values by comparing them with the results of a numerical calculation. The birefringence retardation at the crack tip was also observed in the experimental process. For the experiment, a soda lime glass was cleaved using CO2 laser irradiation. Then, the birefringence retardation and azimuthal angle obtained using the polarization camera were compared with the numerical calculation results. The birefringence retardation around the crack tip corresponded with that of the deformation caused by mode I. The crack propagation was arrested when the crack tip approached the edge of the glass. The birefringence retardation observed using the polarization camera confirmed that the mode I deformation decreased as the crack approached the edge.

Picosecond burst pulse machining with temporal energy modulation [Invited

Suppression of stress and crack generation during picosecond laser processing in transparent brittle materials such as glass was successfully demonstrated by a picosecond laser pulse with temporal energy modulation. The origin of deterioration in processing accuracy could be interpreted in terms of the discontinuous movement of plasma in the vicinity of the focus. To reveal the effectiveness of the temporal energy modulation for smooth machining, such plasma motion was simulated by the finite-difference time-domain method. Furthermore, photoinduced birefringence was observed using a high-speed polarization camera.

In-Line Film Measurement by High-Speed Polarization Camera

In-Line Film Measurement by High-Speed Polarization Camera

Local flow around a tiny bubble under a pressure-oscillation field in a viscoelastic worm-like micellar solution

The motion of a tiny air bubble in an aqueous solution of cetyl trimethyl ammonium bromide and sodium salicylate (CTAB/NaSal), which forms wormlike micelles, was observed using a high-speed polarization camera. Complex local flow is observed around the bubble surface because the bubble shape deforms repeatedly at 100 Hz. The camera can be used to measure the retardation distribution, which is related to the stress field around the bubble. Different retardation and orientation angle distributions were observed during the contraction and expansion phases. In the contraction phase, a strong retardation distribution appears at the tail of the cusped bubble. The occurrence of uniaxial elongation deformation is considered to be due to the negative wake because they are closely correlated. In contrast, a weak retardation distribution spreads at the upper side of the bubble during the expansion phase, where biaxial extensional deformation occurs due to expansion of the bubble surface. These significant changes in strong elastic stress distributions, which correspond to the orientation angle profiles, can result in increase of bubble rising velocities.

Simultaneous imaging of flow and sound using high-speed parallel phase-shifting interferometry.

In this Letter, simultaneous imaging of flow and sound by using parallel phase-shifting interferometry and a high-speed polarization camera is proposed. The proposed method enables the visualization of flow and sound simultaneously by using the following two factors: (i) injection of the gas, whose density is different from the surrounding air, makes the flow visible to interferometry, and (ii) time-directional processing is applied for extracting the small-amplitude sound wave from the high-speed flow video. An experiment with a frame rate of 42,000 frames per second for visualizing the flow and sound emitted from a whistle was conducted. By applying time-directional processing to the obtained video, both flow emitted from the slit of the whistle and a spherical sound wave of 8.7 kHz were successively captured.

Newly Developed Imaging Application by High-speed Polarization Camera

Newly Developed Imaging Application by High-speed Polarization Camera

Optical sensing of sound fields: Non-contact, quantitative, and single-shot imaging of sound using high-speed polarization camera

Imaging of a sound field aids understanding of the actual behavior of the field. That is useful for obtaining acoustical spatial characteristics of transducers, materials and noise sources. For high spatial resolution imaging, optical measurement methods have been used thanks to its contactless nature. This paper presents sound field imaging method based on parallel phase-shifting interferometry, which enables to acquire an instantaneous two-dimensional phase distribution of light. Information of sound field is calculated from the phase of light based on the acousto-optic theory. The system consists of a polarization interferometer and high-speed polarization camera. The number of the measurement points in a single image are 512 × 512 and the interval between adjacent pixels is 0.22 mm. Therefore, the system can image a sound field with much higher spatial resolution compared with conventional imaging methods such as microphone arrays. The maximum frame rate, which is corresponding to the sampling frequen...

High-speed imaging of sound using parallel phase-shifting interferometry.

Sound-field imaging, the visualization of spatial and temporal distribution of acoustical properties such as sound pressure, is useful for understanding acoustical phenomena. This study investigated the use of parallel phase-shifting interferometry (PPSI) with a high-speed polarization camera for imaging a sound field, particularly high-speed imaging of propagating sound waves. The experimental results showed that the instantaneous sound field, which was generated by ultrasonic transducers driven by a pure tone of 40 kHz, was quantitatively imaged. Hence, PPSI can be used in acoustical applications requiring spatial information of sound pressure.

0114 流通系圧力振動場における粘弾性流体中の単一気泡近傍の2次元偏光計測

We have proposed a new defoaming method by applying pressure-oscillation in the continuous flow channel. Due to the bubble expansion and contraction, there are complex flow structures in the vicinity of an air bubble in the fluid. To clarify the flow structures, we tried measuring the retardation profile around the bubble by the high speed polarization camera. As a result, strong retardation can be observed in the opposite side of the movement direction of the contracting bubble. There exists fine bubbles in the both side of the bubble. We observed the motion of fine bubbles as tracers. It turned out that a uniaxial extension is observed in the opposite side of the movement direction of the contracting bubble. It's consistent that a uniaxial extension, strong retardation and the motion of fine bubbles are caused by negative wake in the opposite side of the movement direction of the contracting bubble.