Evaluation of low viscosity variations in fluids using temporal and spatial analysis of the speckle pattern

Abstract

The noninvasive detection of a material's viscoelasticity is of great importance in the medical field. In fact, certain diseases cause changes in tissue structure and biological fluid viscosity; tracking those changes allows for detection of these diseases. Rheological measurements are also imperative in the industrial field, where it is necessary to characterize a material's viscoelasticity for manufacturing purposes. In this Letter, we present a noncontact, noninvasive, and low cost method for determining low viscosity values and variations in fluids. Laser speckle and viscometric measurements are performed on test samples having low scattering coefficients and low viscosities. The speckle spatial analysis proved to be as accurate as the speckle temporal correlation method reported in previous studies. Very low viscosities of the order of 1 mPa.s were retrieved for the first time using speckle images with either a frame rate of 1950 fps or a single acquired image.

Assessing White Wine Viscosity Variation Using Polarized Laser Speckle: A Promising Alternative to Wine Sensory Analysis

“…We undertake the spatial analysis by calculating the contrast of a single speckle image [ 20 , 22 ]. The contrast is defined as the ratio between the intensity standard deviation and the mean intensity of the speckle pattern image, as follows: …”

“…An example of the temporal correlation curve is plotted in Figure 2 a as a function of time, giving an idea of the analyzed sample activity evolution. Taking into account the analyzed light polarizations (linear parallel and cross circular) in a backscattered geometry [ 27 ], as well as the low scattering nature of our samples [ 20 ], we regard the collected speckle fields to be mainly generated by photons that have undergone a simple diffusion. Therefore, an exponential fit of the correlation curve , where , and , allows for an estimation of the speckle decorrelation time constant .…”

“…As the viscosity of the wine is of the order of only a few mPa.s, and low viscosity variations are measured when the terroir, grape variety, vintage, or wine temperature are considered [ 11 , 12 , 13 , 14 ], a sensitive and yet efficient method to determine this relative variation is thus needed. Since a polarized laser speckle method showed a high sensitivity for the measurement of small variations in viscosity [ 20 ], we employed it in our study to measure the viscosity of mono-variety white wines, and hence to characterize commercial wines. Speckle is produced when coherent light is scattered off an illuminated diffusing medium.…”

“…In our work, we evaluate and compare various approaches of the polarized speckle field. Speckle patterns are analyzed by evaluating the spatial contrast [ 20 , 22 ], the temporal correlation coefficient [ 23 ], and the temporal history of the speckle pattern (THSP) [ 23 , 24 , 25 ].…”

Strong cytoskeleton activity on millisecond timescales upon particle binding revealed by ROCS microscopy

“…For instance, at a given sampling rate f s = 1/Δt = 100 Hz, only processes with a speckle correlation time τ 0 ≥ τ min = 2ÁΔt = 20 ms can be reliably sampled (Nyquist's sampling theorem). Recent studies on laser speckle rheology on weakly absorbing fluids were recorded with a fast sCMOS camera at 945 Hz (Hajjarian & Nadkarni, 2014) or even at 1950 Hz (Nader et al, 2016), but without providing any spatial resolution or imaging. Studies which are comparable to our approach are fluorescence-based with the aforementioned advantages (protein-specific) and drawbacks (slow, subject to bleaching).…”