CMUT (capacitive micromachined ultrasonic transducer) patents typically claim electrostatic membrane actuation, bias-voltage schemes and collapse-mode operation, while PMUT (piezoelectric micromachined ultrasonic transducer) patents claim piezoelectric thin-film actuation on a MEMS membrane. Both are captured in this 284-record dataset because the search targets either term appearing in the title alongside fabrication and performance language. In practice, the IPC mix shows heavy overlap in B06B and H10N classes, meaning many filings claim structural or fabrication features common to both approaches rather than being purely CMUT- or PMUT-specific.

The ranking covers 57 companies, with the leading assignee holding 33 records against 16 for the fifth-place filer — a meaningful gap that marks genuine leadership. The top five combined account for 43.7% of all 284 records, and the top ten reach 66.5%, so activity is concentrated but far from a duopoly. Beyond the leading group, filing counts drop quickly into single digits across a long tail of academic and corporate entrants.

Filings peaked at 25 in 2021 and fell to 12 by 2024, a -52% change over that span, which reads as a genuine pullback from an earlier filing wave. However, publication typically lags filing by around 18 months, so figures for 2025 and 2026 are still incomplete and should not be read as confirmation of further decline. The safest read is that the first wave of core fabrication patents matured around 2021 and later activity has shifted toward narrower, more specific claims.

The IPC composition shows B06B and A61B carrying the bulk of filing density, at 59.9% and 26.4% of the 284 records respectively, while B81B (MEMS structural devices) covers only 11.3%. That gap suggests process-level and wafer-yield claims tied specifically to MEMS fabrication are less crowded than acoustic or imaging-integration claims. Array-uniformity and electronics-on-membrane integration are two specific sub-areas worth checking for open claim space before assuming freedom to operate.

US20210063553A1, filed by Hitachi and published in March 2021, claims a measurement method that applies a bias voltage to a capacitive micromachined ultrasonic transducer during defined periods, with an intermediate voltage step between bias periods. This is a method claim around the drive-and-measurement sequence, not a device or fabrication claim, so it is most relevant to anyone designing bias-voltage control circuitry or drive electronics for a CMUT array. Teams working on alternative bias-sequencing schemes or on PMUT devices, which do not rely on the same electrostatic bias mechanism, are less likely to be affected directly.