Filing in this field is concentrated among a handful of large industrial, energy and aerospace groups alongside specialist inspection-equipment makers, with a long tail of universities and single-filing entrants behind them. Several of the historically dominant assignees show no filings in the most recent year, which points to consolidation of claim scope earlier in the decade rather than active expansion now. Checking assignee-level filing history alongside citation counts gives a clearer picture than raw patent totals alone, since older holders' patents are often the most-cited even without recent activity.

Conventional ultrasonic testing patents typically claim a single transducer element and its coupling or scanning mechanism, while phased array patents claim an array of elements with electronically controlled timing to steer and focus the beam. In this dataset phased array approaches appear consistently among the most-cited records and span multiple IPC classes at once (material testing, positioning and vibration generation), reflecting that they are claimed as integrated systems rather than single components. That system-level claiming is also why phased array freedom-to-operate work needs to check several IPC classes together, not just G01N alone.

The thinnest coverage relative to the core sits where ultrasonic sensing overlaps digital signal processing, structural-health monitoring and diagnostic or surgical use — IPC classes G06F, G01M and A61B each carry roughly a tenth of the record count seen in the core material-testing class. This suggests the transducer and coupling hardware claim space is largely occupied, but the processing and classification layer built on top of that hardware is comparatively open. A new filing combining an established sensing configuration with a specific defect-classification or monitoring method is more likely to find clear space than one claiming sensing hardware alone.

Filings rose from 124 in 2017 to a peak of 173 in 2021 before easing back and continuing to decline through the most recent years in the dataset. Some of that apparent decline is a data artefact: publication normally lags filing by around 18 months, so the last one to two years are always undercounted at the point of measurement. Even accounting for that lag, the plateau around the 2022 midpoint of 127 suggests the field had already moved from an expansion phase into incremental refinement of existing claim positions.

US11351628B2, assigned to Louisiana State University and published in 2022, claims a wedge body for a phased array ultrasonic transducer with a built-in coolant channel and separate couplant channel, designed to keep the array below a set temperature during friction stir welding inspection. Anyone building an on-line, high-temperature inspection fixture that cools a mounted transducer array through a channel inside the wedge body needs to check this claim specifically. It does not block phased array inspection or coupling-medium delivery generally — those elements are claimed independently elsewhere in the corpus — so the exposure is narrow but directly relevant to hot-process weld inspection tooling.