The assignee ranking for this corpus covers 100 companies drawn from 500 records, and it is concentrated at the top: the leading assignee holds 61 records on its own, and the top five together account for 200 records, or 40.0% of the full 500-record set. Past fifth place the gap narrows quickly, with tenth place holding 10 records, which points to a long tail of moderate and single-filing entrants beneath a small group of sustained filers. Anyone assessing competitive position should look at the leader’s specific claim scope rather than assume the field is evenly contested.

No — filing peaked in 2018 at 43 records and has since pulled back, with the 2021-to-2024 span alone showing a -72% change from 32 records down to 9. That said, the 2025 and 2026 figures in this dataset are still incomplete because publication typically lags filing by around 18 months, so the most recent years should not be read as proof the decline is continuing at the same rate. A fair read is that activity has cooled from a clear peak, not that the field is dormant.

US20040112212A1, filed by Industrial Technology Research Institute, describes a feedback control method for fan filter units that uses a bell inlet as an airflow measuring nozzle and airflow itself, rather than motor speed, as the control feedback parameter. It is one of the earlier filings in this space and defines a specific control architecture rather than fan filter units generally, so it constrains designs that use airflow-based feedback through a bell-inlet-style nozzle rather than every FFU control approach. A design using motor-speed feedback or a different sensing method would sit outside its specific claim language, though a full claim-by-claim comparison is needed before relying on that distinction.