CMOS-Based Gas Direction Sensors with a Surface-Integrated Pillar.

Conventional gas direction estimation methods that rely on concentration gradients or time-of-arrival differences typically require multiple spatially dispersed sensors, leading to increased system bulkiness and complexity. Furthermore, previous CMOS-based approaches that relied on gas diffusion struggled to achieve stable direction estimation in high-speed airflow environments. To address these challenges, we propose a streamlined method integrating a pillar onto a single CMOS gas-sensor array, eliminating additional MEMS fabrication. This approach exploits a fluid dynamic phenomenon where the pillar creates a distinct flow "shadow" pattern (a region of localized gas dilution) on the sensor surface. Experimental verification using ammonia gas confirmed that this "shadow" is clearly observable as a localized reduction in sensor output under high-speed turbulent flow. Crucially, the spatial position of this pattern correlates strongly with the direction of gas inflow. This study demonstrates the feasibility of gas direction estimation using a single chip, paving the way for high-precision detection in challenging, rapid-airflow environments.