Some commercial devices contain up to twenty sensors. Furthermore, their high price is mainly due to the use of expensive laser sources and a large number of detectors, i.e., one sensor for each scattering angle to be monitored. On the one hand, the large size of common devices is due to the large distance needed between the sample and the detectors to provide the desired angular resolution. However, these devices are generally large in size (~700 × 300 × 450 mm), heavy (~30 kg) and expensive (in the 50–200 K€ range). In the latter case, prior knowledge of the refractive index of the particle being measured as well as the dispersant is required.Ĭommercial LD PSAs have gained popularity due to their broad dynamic range, rapid measurement, high reproducibility and the capability to perform online measurements. Thus, by measuring the angle-dependent scattered intensity, one can infer the particle size distribution using Fraunhofer or Mie scattering models 11, 12. The smaller the particle is, the larger the scattering angle of the laser beam is. The light scattered by the particles in the forward direction is focused by a lens onto a large array of concentric photodetector rings. In LD PSAs, a laser beam is used to irradiate a dilute suspension of particles. Similar scattering theory is also utilised in systems based on non-electromagnetic wave propagation, such as ultrasonic analysers 9, 10. While the above-mentioned techniques are best suited for measuring particles typically in the submicron region, particle size analysers (PSAs) based on static light scattering or laser diffraction (LD) 7, 8 have become the most popular and widely used instruments for measuring particles from hundreds of nanometres to several millimetres. NTA also measures the hydrodynamic size of particles from the diffusion coefficient but is capable of overcoming some of the limitations posed by DLS 5, 6. Other scattering techniques have emerged, such as nanoparticle tracking analysis (NTA) 5, which tracks individual particle movement through scattering using image recording. For example, DLS is a low-resolution method that is not suitable for measuring polydisperse samples, while the presence of large particles can affect the size accuracy 4. Although DLS is a useful approach to determine the size distribution of many nano- and biomaterials systems, it does suffer from several disadvantages. This method analyses the fluctuations of scattered light by particles in suspension when illuminated with a laser to determine the velocity of the Brownian motion, which can then be used to obtain the hydrodynamic size of particles using the Stokes-Einstein relationship. For submicron particle measurement, dynamic light scattering (DLS) 4 has now become an industry standard technique. Recent years have seen many advancements in light scattering technologies for particle characterisation. Particle size analysis based on light scattering has widespread application in many fields, as it allows relatively easy optical characterisation of samples enabling improved quality control of products in many industries including pharmaceutical, food, cosmetic, polymer production, etc. Given that it is compact (on the order of ten cm) and built with low-cost consumer electronics, the newly designed particle size analyser has significant potential for use outside a standard laboratory, for example, in online and in-line industrial process monitoring. When only spherical particles were analysed, the former error was significantly reduced (0.72%). We were able to correct for multiple scattering effects and predict the particle size with mean absolute percentage errors of 5.09% and 2.5% for the cases without and with concentration as an input parameter, respectively. To validate the proposed device, glass beads with diameters ranging from 13 to 125 µm were measured in suspension at several concentrations. From these images, a machine learning model predicts the volume median diameter of the particles. The filter is combined with a light-emitting diode and a complementary metal-oxide-semiconductor image sensor array to acquire angularly resolved scattering images. The key novelty is a small form factor angular spatial filter that allows for the collection of light scattered by the particles up to predefined discrete angles. In this paper, we introduce the concept of a new particle size analyser in a collimated beam configuration using a consumer electronic camera and machine learning. Compared to other non-light-based counterparts, such a laser diffraction scheme offers precision, but it does so at the expense of size, complexity and cost. The most common particle size analyser relies on measuring the angle-dependent diffracted light from a sample illuminated by a laser beam. Light scattering is a fundamental property that can be exploited to create essential devices such as particle analysers.
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