In this 342-record dataset, filing is heavily concentrated: the top-ranked assignee alone holds 107 records, and the top five combined account for 250 records, or 73.1% of everything in scope. The ranking covers 76 companies in total, but counts fall off sharply after the leaders — fifth place holds 19 records and tenth place only 8. That pattern means a small group of committed filers, largely in nonwoven filtration, coatings and fiber-spinning, drives most of the documented activity rather than a broad field of occasional entrants.

Filing activity peaked in 2018 at 25 published records and has since settled to a much lower, flat level, with published counts unchanged at 2 in both 2021 and 2024 — a 0% change over that span. It would be premature to call this a decline, however, because publication typically lags filing by around 18 months, so the 2025 and 2026 figures are still incomplete and will rise as more applications publish. The honest read is a plateau since the 2018 peak rather than either growth or collapse.

Nonwovens and felts (IPC class D04H) is the largest single category, appearing in 33.3% of the 342 records in scope. Glass and enamel compositions (C03C), polymer processing (C08J) and printed circuits and assemblies (H05K) each hold shares in the high teens, and no single class exceeds 40% of records. Because records can carry multiple IPC codes, these shares add up to more than 100%, which itself signals that the technology is spread across several overlapping claim types rather than concentrated in one.

The smallest IPC shares in this dataset — D21H pulp and paper compositions at 9.6% and D01D man-made filament spinning at 9.1% — mark branches with comparatively lower claim density relative to the dominant nonwoven and coating classes. That does not guarantee those areas are commercially unexplored, but it does mean fewer granted claims currently sit there, which is worth investigating before assuming the space is blocked. Fiber-diameter-graded multilayer structures and process-monitoring approaches tied to signal representation also show up thinly across the dataset.

US20220193586A1, assigned to JNC Corporation and dated 2022-06-23, describes a depth filter built from a substrate layer, a filtration layer and a skin layer, where the outer layers use nonwoven cloth with an average fiber diameter of 150 micrometres or more, and the filtration layer uses a smaller average fiber diameter than the outer layers. Its claim scope is tied specifically to that layer order and the relative fiber-diameter relationship, not to depth filtration or nonwoven filters generally. A design that varies the layer sequence, uses a different diameter relationship, or departs from the wound-and-thermally-fused construction would sit outside its likely claim scope, though a formal freedom-to-operate review is the only way to confirm that.