How does an electrostatic filter work?

Electrostatic air filters are intended to filter particles, which are considered infectious for a patient. These particles can be of different types, like pollen (10-30 μm), which can cause asthma or allergenic responses, street dust (about 10 μm), which can bear bacteria or virus or be allergenic, water droplets, which are containing bacterias or viruses (1-20 μm). Also single bacteria (1-10 μm) and viruses (0,3-3 μm) are possible.

All medical air filters are made of a matt of fibers, usually synthetic or glass fibres. Electrostatic charged filters are made of synthetic fibers. Mechanical filters can be made of both types.

All these particles pass into the filter matt in the various openings between the fibers. The particle will collide with several fibers on its way through the filter matt until it loses its speed (inertia) and is resting on a fiber inside it. The possibility for a filter to catch a particle will depend on the initial speed and size (mass) of the particle, the number of fibers available for catching it, as well as how much speed (inertia) it loses at each collision with a fiber.
If a fiber causes the particle to lose more speed on collision with the fiber, fewer fibers are needed to catch the particle.

During inhalation, aerosolized sub micron bacterias or viruses are captured by the electrically charged fibers in the filtering material.



Electrostatic filters, as used in Provox Micron HME, are made of fibers, which contain permanent electrostatic charges. These charges enhance the filtration efficiency and both uncharged and charged particles (like microorganisms, pollen and water droplets) are more efficienlty captured. The electrostatically charged fibers attract and capture these particles when they pass through the filter. As the fibers are hydrophobic, microorganisms are caught but humidity passes through. The result is a highly efficient bacterial and viral filter with low airflow resistance, which is little affected by the filtered particles.

An electrostaically charged filter needs fewer fibers than a noncharged filter to catch a certain particle. The positive effect of fewer fibers in the filter will be a more open structure of the filter with less breathing resistance for the same filtering efficiency and filter volume.