An Ultrasonic Phased Array System for Detection of Plastic Contaminants in Cotton

Effective detection and mitigation of plastic contaminants in cotton is a critical challenge for the cotton industry. Despite industry efforts to remove them, contaminants such as plastic bale wrap fragments often enter the ginning stages and ultimately end up in the lint. This contamination results in degraded fiber quality and disrupted processing. Currently, most mitigation efforts rely on either manual inspection or machine-vision systems. One such system, VIPR™ (Visual Imaging Plastic Removal), detects and removes plastic contaminants using color cameras. While effective in some cases, visual approaches have limitations, especially when plastics are obstructed by surrounding cotton. To address these challenges, we propose an ultrasonic phased array detection system as a promising alternative. Ultrasonic waves offer two main advantages. First, the ability to penetrate through cotton to reveal concealed plastic contaminants, and second, the ability to detect plastics of any color. In the proposed system, phased arrays of 40 kHz frequency ultrasonic transmitters and receivers, coordinated by a field-programmable gate array (FPGA) controller, sequentially direct ultrasonic pulses along radial paths. Arrays of receivers are strategically positioned to measure both reflected and transmitted waves as ultrasound signals interact with cotton and contaminants. This configuration enables the generation of acoustic images that highlight the plastic contaminants within cotton, even when they are visually obscured. Preliminary experiments using different sizes and quantities of plastics were conducted on both seeded and seedless cotton samples. Our results revealed the system’s potential for differentiating individual contaminants from non-contaminants (cotton and seeds) across its field of view.