Dielectric Sensing and Multiphysics Modelling for Electrostatic Separation in Rice Cleaning Systems

Agricultural threshing mixtures are moist, heterogeneous, and dynamically disturbed, conditions that reduce the selectivity of cleaning systems based solely on size, density, and aerodynamic response. Electrostatic separation introduces an additional property dimension, but its application to raw paddy rice remains constrained by moisture-sensitive charging, irregular particle motion, wall deposition, and variable feed conditions. This critical review synthesizes rice-specific studies on dielectric and material-state sensing with evidence concerning particle charging, electro-aerodynamic transport, multiphysics modelling, and process control. The available literature shows that dielectric measurements can characterize moisture- and density-dependent material states, but they do not directly quantify charge retention or electrostatic separability. Rice-specific evidence remains concentrated in dielectric characterization and machinery operating conditions, whereas electrostatic processing studies mainly concern processed rice-derived materials or analogous particle systems. Direct evidence from raw paddy threshing mixtures under continuous and field-relevant operating conditions remains limited. Based on the evidence, a four-zone framework is proposed comprising feed dispersion, charge acquisition, electro-aerodynamic deflection, and outlet collection. The framework identifies the measurements, model parameters, and validation steps required to relate dielectric state, charge decay, particle trajectories, and control actions, thereby providing a research basis for the development and rice-specific validation of electrostatic cleaning systems.