Which of the following is NOT a characteristic of impingement filters?

Impingement filters operate primarily by causing airborne particles to collide with a filtration medium. Their effectiveness is indeed influenced by particle size, as larger particles tend to be captured more effectively than smaller ones. The dependence on airflow velocity is also a crucial characteristic; higher velocities can enhance the impaction of particles onto the filter medium, thereby increasing the filter's efficiency. Additionally, the functionality of impingement filters can be significantly affected by dust density since a higher concentration of dust can lead to an increased likelihood of clogging and reduced airflow.

The characteristic identified as relying on static electricity for filtration is not typical of impingement filters. While some filters, such as electrostatic filters, utilize static electricity to capture particles, impingement filters primarily function through mechanical means of particle collision rather than electrostatic attraction. Thus, this characteristic is accurately noted as not belonging to impingement filters.