Which characteristic defines impingement filters?

Impingement filters are characterized by their operation at relatively high velocities, which facilitates the effective capture of airborne particles as they impact the filter medium. This mechanism allows particles to physically collide with and stick to the filter fibers, enhancing the filter's efficiency in trapping contaminants. Additionally, the design of these filters often helps maintain a low pressure drop, meaning that while they operate under high velocity, they do not create excessive resistance to airflow, allowing for effective performance in various applications.

This characteristic makes impingement filters particularly useful in situations where maintaining airflow is crucial, such as in HVAC systems, without sacrificing a significant amount of energy to overcome resistance, thus optimizing both performance and energy efficiency. Other options in the question describe attributes that may apply to different types of filters but do not exclusively define impingement filters. For instance, while efficiency and dust-holding capacity are important, they may not specifically highlight the unique operational dynamics that define impingement filters.