Abstract
Convolutional neural networks (CNNs) and digital holographic interferometry (DHI) can be combined to improve the calculation efficiency and to simplify the procedures of many DHI applications. In DHI, for the measurements of concentration differences between liquid samples, two or more holograms are compared to find the difference phases among them, and then to estimate the concentration values. However, liquid samples with high concentration difference values are difficult to calculate using common phase unwrapping methods as they have high spatial frequencies. In this research, a new method to skip the phase unwrapping process in DHI, based on CNNs, is proposed. For this, images acquired by Guerrero-Mendez et al. (Metrology and Measurement Systems 24, 19–26, 2017) were used to train the CNN, and a multiple linear regression algorithm was fitted to estimate the concentration values for liquid samples. In addition, new images were recorded to evaluate the performance of the proposed method. The proposed method reached an accuracy of 0.0731%, and a precision of ±0.0645. The data demonstrated a high repeatability of 0.9986, with an operational range from 0.25 gL−1 to 1.5 gL−1. The proposed method was performed with liquid samples in a cylindrical glass.
Highlights
A liquid sample can be classified using physical properties, such as concentration, color, boiling temperature, and fusion point
For the Convolutional neural networks (CNNs) evaluation as the image classifier, a perfect classification was reached in the confusion matrix
The proposed method can calculate concentration ranges from 0.25 gL−1 L to 1.5 gL−1, with a precision of ±0.0645, and accuracy of 0.0731% based on data and classes that were not used to train the CNN
Summary
A liquid sample can be classified using physical properties, such as concentration, color, boiling temperature, and fusion point. There are many methods and tools for the estimation of concentrations in liquid samples; most of them are invasive and destructive [2,3,4]. A technique that is able to perform measurements of concentration differences with high accuracy, in a non-invasive and non-destructive way, is digital holographic interferometry (DHI) [5]. DHI is a high precision, non-contact, non-invasive, non-destructive, and full-field optical metrology technique [6,7]. DHI is able to measure, with a very high sensitivity, variations in the physical properties of phase objects (i.e., a liquid sample in a glass container can be considered as a phase object), based on the comparison of wavefronts recorded as holograms at different instants in times or states of an object [8,9].
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