10 A compact, lightweight sensor system with infrared imaging can be fitted easily to a UAV for remote crop monitoring, writes Nick Flaherty. The metasurface, flat-optics technology has the potential to replace traditional, optical lens applications for environmental sensing. The key is that the sensor system can switch rapidly between edge detection and extracting detailed infrared information without the need for creating large volumes of data and using external processors. The prototype sensor system was developed by engineers at the City University of New York (CUNY), University of Melbourne, RMIT University and the ARC Centre of Excellence for Transformative Meta-Optical Systems (TMOS). The sensor uses a filter that has a thin layer of vanadium dioxide, a phase-change material that can switch between edge detection and detailed infrared imaging. This passive edge-detection metasurface operates in the nearinfrared regime, and the response can be modified by temperature variations smaller than 10C around a phase-change transition temperature of 65C, which is compatible with a mainstream CMOS manufacturing process. This reconfigurability is achieved through the insulator-to-metal phase transition of a thin layer of vanadium dioxide, which strongly alters the metasurface response to filter the light. It also uses a simple geometry that is compatible with large-scale manufacturing. “Materials such as vanadium dioxide add a fantastic tuning capability to render devices smart,” said chief investigator using metasurfaces, most of the devices demonstrated so far are static. Their functionality is fixed in time and cannot be dynamically altered or controlled,” said Dr Michele Cotrufo, a researcher at CUNY. “The ability to dynamically reconfigure processing operations is key for metasurfaces to be able to compete with digital image-processing systems. This is what we have developed.” The sensor also operates at temperatures compatible with standard manufacturing techniques, making it well placed to integrate with commercially available systems and thus move from research to real-world use. Crop monitoring Sensor switches from edge detection to infrared fast Prof Madhu Bhaskaran at RMIT in Melbourne. “When the temperature of the filter is changed, the vanadium dioxide transforms from an insulating state to a metallic one, which is how the processed image shifts from a filtered outline to an unfiltered, infrared image. “These materials could go a long way in flat-optics devices that can replace technologies with traditional lenses for environmental sensing applications, making them ideal for use in UAVs and satellites, which require low size, weight and power capacity,” he added. “While a few recent demonstrations have achieved analogue edge detection August/September 2024 | Uncrewed Systems Technology A lightweight metasurface IR sensor (Image courtesy of CUNY)
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