US 5420825

I'll search for authoritative information on this specific patent number.

US 5,420,825 — "Noise control composite"

Searches surfaced only the Google Patents record and mirror listings; I could not query USPTO PatentCenter or CAFC docket systems directly (no direct API/docket access in this session). No CAFC 2026 docket or litigation involving this number appeared in any result. Treat the litigation finding as a negative search result, not a certified clearance.

Identifier caution: the string "5420825" also matches unrelated documents — e.g. JP 5420825 B2 (a 2014 Japanese patent on fluoropolymer/electrolyte chemistry) and MY-167419-A. Those are not this patent and are excluded here.

Bibliographic data (per the authoritative record)

Discrepancy worth flagging: the recorded assignment (1982-10-22, effective 1982-08-30, Reel/Frame 004055/0883) names only Fischer and Montemarano as assignors, while the front-page inventor list adds Castelli and Dickey. I have no record explaining the gap (e.g., separate assignment instruments). Flagging rather than resolving.

Notable pendency: ~12 years 9 months from filing (1982) to grant (1995). The Navy/undersea-sonar subject matter makes a secrecy order under 35 U.S.C. § 181 the usual explanation, and the record's "anticipated expiration 2012-05-30" is consistent with term extended for a secrecy period — but the documents I retrieved do not state this, so treat it as inference only.

Abstract (as published)

"A composite for use on submarines and surface craft for controlling self-erated noise when listening with sonar. The composite includes two layers of PVF 2 transducers separated by a layer of phase shifting or absorbing material. The inner transducer senses noise from the ship and subtracts this from the signal from the outer transducer representing noise plus the desired signal. In a second mode the sensed noise is regenerated through the outer transducer 180° out of phase to cancel the noise and allow more accurate detection."

(The published abstract contains typographical errors, including "self-erated"; retained literally.)

Plain-language overview of the independent claims

Claim 1 — the physical laminate (a "sandwich" of layers). A composite for a sonar device, built up as: (a) a first neoprene acoustic insulator layer sitting on a solid substrate (the hull); (b) a stack of alternating transducer layers and sound-absorbing layers; (c) a second neoprene acoustic insulator layer on top of that stack; and (d) an outermost antifouling layer made of elastomeric rubber containing an organometallic polymer. Read literally, this claim is about the stack of materials rather than the electronics — note it does not itself recite a control circuit.

Claim 2 — the laminate plus active noise-cancelling electronics. A composite for a "shipborad" sonar device comprising at least one first (inner) transducer layer, at least one second (outer) transducer layer outside the first, at least one intervening layer of anechoic material acoustically insulating the two from each other, first leads to the inner layer(s), second leads to the outer layer(s), and a control circuit that receives both signals and processes them so shipboard noise is cancelled from the output. The invention's core mechanism: two spaced sensor layers let you separate self-noise from the wanted external signal, either by subtraction or by driving one layer to cancel.

Claim 6 — the tiled array with electronic steering. A ship sonar device made of many tiles, each producing a signal, arranged in an array, where each tile is the layered composite (at least two transducer layers separated by acoustical absorbing material), plus a control circuit that (i) selectively activates some tiles to achieve directionality and (ii) cancels self-generated noise. The novelty here is the electronically reconfigurable aperture — beam direction is chosen by switching tiles on and off rather than fixed by tile placement.

Dependent claims at a glance

• 3 (dep. 2): adds first insulating layer to the ship and second insulating layer to the sea.
• 4 (dep. 2): the control circuit includes a subtraction circuit (outer minus inner) for a noise-free output.
• 5 (dep. 2): the control circuit includes a phase-shifting circuit driving the outer leads.
• 7 (dep. 6): subtraction circuit variant for the array.
• 8 (dep. 6): phase-shifting circuit variant for the array.
• 9 (dep. 2): amplifying + phase-shifting means, taking the outer signal and driving the inner leads — "cancels incoming noise."
• 10 (dep. 2): amplifying + phase-shifting means, taking the inner signal and driving the outer leads — "cancels outgoing noise."

Note claims 9 and 10 are mirror images distinguished by which layer is sensed vs. driven, but both recite the output as cancelling "noise" (9 says "incoming," 10 says "outgoing") — the claim language is internally inconsistent with the ordinary inside/outside noise direction, which is a potential § 112 issue had it ever been litigated.

Prior art cited on the face; later citing documents

Cited by the examiner: US 3,971,250; US 4,158,189; US 4,184,093; US 4,236,235; US 4,295,010. Later citing documents include US 5,552,656; US 5,600,609; US 7,205,043; WO 2013/121007 A1 (DCNS submarine sound baffle) and its family; DE 10 2017 120 379 A1; and several software/controller patents (US 8,369,967; US 8,892,495; US 10,361,802) whose citation is peripheral. US 5,420,825 is itself listed as prior art in MY-167419-A (Malaysian counterpart in the DCNS submarine-baffle family). Source: https://patents.google.com/patent/US5420825/en

Uncertainty statement

I have no authoritative evidence of any CAFC 2026 docket, district court case, or PTAB proceeding involving US 5,420,825. The patent expired for nonpayment of maintenance fees effective 1999-05-30, which makes 2026 litigation extremely unlikely. My bibliographic data comes from the Google Patents record, not from a live USPTO PatentCenter query; if you need certified USPTO data (e.g., an official assignment chain explaining the Castelli/Dickey inventor discrepancy, or confirmation of any secrecy-order term extension), that requires a direct PatentCenter/Assignment-Search lookup I could not perform here.

I'll search for litigation involving this specific patent number.

Let me check litigation-specific databases and search other sources.

Let me run a few more targeted queries against litigation-specific sources.

Bottom line

No litigation is known — and I found none — involving U.S. Patent No. 5,420,825.

I searched repeatedly for the specific number and its variants (5420825, 5,420,825) and found no complaint, docket entry, PACER/RECAP record, Federal Circuit appeal, PTAB proceeding, or NPE-database entry naming this patent as an asserted patent. Every hit I obtained was either the patent's own Google Patents page or a citation to the '825 patent as prior art — not litigation.

What I searched and what came back

Important disambiguation — these are NOT litigation and NOT the same patent:

• JP 5420825 B2 is a distinct, unrelated Japanese patent (fluoropolymer/smoking-article chemistry). Do not conflate its number with US 5,420,825.
• U.S. 7,205,043 (Navy, "Pressure resistant anechoic coating") and DE 102017120379 A1 (Atlas Elektronik) merely cite US 5,420,825 as prior art in their specifications. A citation is not an assertion of infringement.

Case-by-case listing (plaintiff / defendant / jurisdiction / case no. / filing date / status)

Why this negative result is highly plausible (my analysis, not a search finding)

1. Very short enforceable life. Per the Google Patents legal-events record, the patent issued 1995-05-30 and the maintenance fee was not paid: notice of lapse 1999-05-30, "Expired due to failure to pay maintenance fee" effective 1999-05-30/1999-07-27. Its full term would have run to the anticipated expiration of 2012-05-30, but it was in force for only about four years. That is a narrow window in which suit could have been filed.
2. Navy ownership. The patent is assigned to the United States (Secretary of the Navy) and was never transferred to a private patent-assertion entity. Government-owned patents are typically licensed or enforced administratively rather than through NPE-style campaigns.
3. Subject matter. The claims are directed to submarine/shipboard sonar composite tiles with PVF₂ transducer layers (claims 1–10). Accused products would be military sonar installations, and unauthorized use by or for the U.S. Government is addressed under 28 U.S.C. § 1498 in the Court of Federal Claims, not as a district-court infringement action — so even a dispute could be invisible in ordinary district-court litigation databases.

Caveats you should weigh (as you asked, I'm flagging rather than fabricating)

• I could not directly query the paywalled/login-gated litigation databases. Unified Patents' litigation portal (including the caselist you linked), Docket Navigator, Lex Machina, and PACER require authentication I do not have here. My conclusion rests on open-web searches that surfaced no litigation, not on a completed Docket Navigator or PACER run.
• Absence of evidence ≠ proof of absence. Because the patent's ~4-year enforceability window (1995–1999) predates the broad digitization of district-court dockets, a 1990s complaint could exist as a paper filing that never made it into RECAP or free databases.
• A "no litigation" answer should be verified by running the exact number 5,420,825 (and 5420825) through Docket Navigator, Lex Machina, the Unified Patents litigation caselist, and the Court of Federal Claims docket (given the Navy ownership / § 1498 point above). I recommend that verification before you rely on this in any filing or opinion.

Sources consulted:

• https://patents.google.com/patent/US5420825/en (patent text, claims, legal events, citation lists)
• https://patents.justia.com/patent/7205043 (US 7,205,043, citing US 5,420,825 as prior art)
• https://www.freepatentsonline.com/DE102017120379A1.html (DE 102017120379 A1, citing US 5,420,825)
• https://ipjournal.myipo.gov.my/... (MY-167419-A, citing US 5,420,825 as prior art)
• https://portal.unifiedpatents.com/litigation/caselist — searched, no records for this patent (no case list returned for the number)

I'll start by verifying the canonical "no PTAB activity" signal against public sources before drafting.

Search results are dominated by unrelated patents whose numbers also end in "542." Let me run narrower checks.

Let me check for litigation/reexam history and confirm the expiry facts, since those drive the defensive posture.

PTAB / AIA Trial Analysis — US 5,420,825

Patent: US 5,420,825 ("Noise control composite")
Patent Owner of record: United States of America as represented by the Secretary of the Navy
Inventors: Eugene C. Fischer; Jean A. Montemarano; Vincent J. Castelli; Joseph W. Dickey
App. No.: 06/413,952 · Filed: 1982-08-31 · Granted: 1995-05-30
Source of record: patents.google.com/patent/US5420825/en (fetched 2026-09-30)

Proceedings overview

Total AIA trial proceedings on file: zero (0). There are no IPRs, no PGRs, and no CBM reviews — not active, not instituted, not denied, not settled, not terminated. Nothing has been invalidated because nothing was ever challenged. The USPTO ODP structured block included in this prompt reports no AIA trial proceedings for this patent as of the most recent ingest, and my independent web checks surfaced no PTAB or Federal Circuit activity tied to this patent number (§ 102/§ 103 challenges, judge panels, FWDs, appeals — all absent).

The bottom line for a defendant is not "the patent has survived two IPRs and is hardened." It is the opposite and far stronger: the patent is dead on its own terms. Per the recorded legal events, maintenance fees went unpaid and the patent expired due to failure to pay the maintenance fee, effective 1999-05-30 (maintenance-fee reminder mailed 1998-12-22; lapse 1999-05-30; expiration 1999-07-27). Google Patents' current status is "Expired - Fee Related." The nominal 17-year term would have run to 2012-05-30, but the patent actually went abandoned in 1999. There is no live patent to defend against. A demand letter citing this patent is a demand letter citing an invention that has been in the public domain for over a quarter-century.

⚠️ Search hygiene warning. A naked search for "the '542 patent" in PTAB papers and district-court filings returns hits that are almost never this patent. During this analysis, queries for the "'542 patent" returned PTAB papers on a Sarepta/Genzyme gene-therapy patent, a floor-cleaning vacuum patent, an optical-connector patent, and IPR2020-00405 on U.S. 10,066,548 — and an IPR petition for "the '825 patent" that concerned U.S. 7,458,825, not 5,420,825. If you or outside counsel run a keyword docket sweep, verify by patent number and filing date. Do not assume a "542" hit is this patent.

Proceedings

(None to report. The following records the absence explicitly rather than substituting fabricated proceeding numbers.)

No AIA trial proceedings on file — US 5,420,825

• Type: N/A
• Filed: N/A
• Status: No proceeding. The patent itself is "Expired - Fee Related" (legal-status entry, 1999-05-30 lapse; 2018-01-22 discontinuation notice citing 37 C.F.R. § 1.362).
• Judge panel: None. No APJ panel has ever touched this patent.
• Petition grounds: None filed. For completeness, the available statutory window has closed for practical purposes: IPR (§ 311(b)) would have been limited to § 102/§ 103 grounds on patents and printed publications; PGR was unavailable because the effective filing date (1982-08-31) long predates the AIA's 2013-03-16 PGR cutoff; CBM review was unavailable both on subject matter and because the CBM transitional program ended 2018-09-16.
• Institution decision: None.
• Final Written Decision: None. No claim of US 5,420,825 has ever been canceled, narrowed, or held unpatentable by the PTAB. Claims 1–10 stand exactly as issued — and expired with the patent.
• Settlement / termination: N/A.
• Appeal: None. No CAFC docket number exists for this patent.
• Defensive value: Total. You do not need an IPR to defeat this patent; you need a calendar. There is no infringement liability exposure for conduct on or after 1999-05-30 because the patent had already lapsed, and 35 U.S.C. § 286's six-year damages look-back bars recovery for anything else. § 252 intervening rights and the absolute bar on injunctive relief for an expired patent follow automatically.

Strategic summary

Claim status — CANCELED vs. SUSTAINED vs. UNTESTED. Claims 1–10 are all UNTESTED before the PTAB, and simultaneously all EXPIRED:

• Claim 1 — asserted composite (neoprene insulator on substrate / alternating transducer + sound-absorbing layers / outer neoprene insulator / antifouling elastomeric layer with organometallic polymer).
• Claim 2 — two-transducer-layer composite with anechoic interlayer, first and second leads, and a control circuit that cancels shipboard noise.
• Claims 3–5 — dependents of claim 2 (insulating layers; subtraction circuit; phase-shifting circuit).
• Claims 6–8 — sonar device of tiled composites with a control circuit for selective activation/directionality and noise cancellation.
• Claims 9–10 — dependents of claim 2 (amplify-and-phase-shift circuitry for canceling incoming / outgoing noise).

None was invalidated in an IPR, and none needed to be: the entire right lapsed in 1999, so the claim set entered the public domain intact. There is no "surviving claim" list — the correct framing is that every claim is unenforceable prospectively and time-barred retroactively.

Estoppel landscape. § 315(e)(2) estoppel is irrelevant here; there is no petitioner, no instituted ground, and no FWD from which estoppel could attach. Conversely, the absence of any estoppel means there would be no estoppel constraint on raising prior art — but the more useful point is that prior art is not the lever. The dispositive defenses are statutory and temporal: patent expiration on 1999-05-30, § 286's six-year bar, § 271(f)/(g) irrelevance for post-expiry conduct, and the unavailability of injunctive or ongoing-royalty relief for an expired patent. If you are nonetheless forced to litigate invalidity (e.g., in an indemnity dispute or a declaratory-judgment posture), the five references cited on the face of the patent remain fair game as prior art and are not estoppel-encumbered: U.S. 3,971,250 (3M, electret sensing medium with plural sensing units); U.S. 4,158,189 (Navy, baffled blanket acoustic array with indented reaction plate — the patent's own primary prior-art admission); U.S. 4,184,093 (Navy, piezoelectric polymer rectangular flexural plate hydrophone); U.S. 4,236,235 (Boeing, integrating hydrophone sensing elements — the patent concedes "only a single layer is shown and there is no attempt to control noise"); and U.S. 4,295,010 (Lectret S.A., plural piezoelectric polymer film acoustic transducer). That last reference is especially worth a hard look, since the patent's stated point of novelty over the two-layer art was the combination with a noise-canceling control circuit, not the plural-film transducer stack itself.

Pattern signals. No petitioner has ever filed against this patent — let alone a repeat petitioner. There is no defensive aggregator (Unified Patents or similar) in the chain, no litigation-driven IPR, and no patent-owner appeal activity, which is unsurprising for a Navy-owned patent that lapsed for nonpayment of a maintenance fee. The Freedom of Information/assignment trail shows a single recorded assignment to the Navy effective 1982-08-30 (Reel/Frame 004055/0883) naming only Fischer and Montemarano as assignors, even though four inventors are named on the face of the patent — a records gap worth noting only if someone purports to assert ownership today. To be clear: I cannot rule out a later, separately recorded assignment for Castelli and Dickey that is not in the ODP data I have; treat the ownership defect as a flag to verify, not a conclusion.

The only modern footprint this patent has is as cited prior art. It is cited by 29 later publications, including DCNS's submarine sound-baffle family (WO 2013/121007 A1; FR 2 987 028 A1; MY-167419-A, granted 2018-08-27) and U.S. 7,205,043 B1 (Navy, pressure-resistant anechoic coating for undersea platforms). Google Patents also maps the disclosure into the modern active-noise-control classifications G10K 11/178 and its subgroups (G10K 2210/127, G10K 2210/3217, G10K 2210/32291). That citation traffic is a prior-art liability for other people's patents, not a source of value for this one.

Recommended next steps

1. If you received a demand letter or a complaint citing US 5,420,825, do not budget for an IPR. There is nothing to institute against. Instead, serve a short, documented response citing: (a) the recorded legal events showing expiration for failure to pay the maintenance fee effective 1999-05-30 (Google Patents legal-status record, "Expired - Fee Related"); and (b) 35 U.S.C. § 286, under which any claim for infringement accruing before 1999-05-30 — the only period any claim could have accrued — was time-barred no later than 2005. Link the record page: https://patents.google.com/patent/US5420825/en.
2. If the assertion is paired with later, unexpired patents in the same claim chart (e.g., an anechoic-coating or sonar-baffle patent claiming priority to or citing the 1982 disclosure), the 5,420,825 material is nonetheless useful affirmatively: it is a § 102(b)/§ 103 prior-art reference available as of 1982-08-31/1995-05-30 for any patent whose critical date postdates those. Pull it in as prior art rather than defending against it.
3. If ownership is at issue (declaratory-judgment posture, indemnity, or a quiet-title dispute), verify the chain: the ODP record shows only the Fischer/Montemarano assignment of 1982-08-30. Check the USPTO Assignment Search and PatentCenter for any Castelli/Dickey assignment before assuming the Navy's title is complete. In a live patent, an unassigned co-inventor share is a standing problem under § 261; in an expired patent, it is a leverage point, not a case-ender.
4. No milestones to track. With no pending proceeding, there is no statutory 1-year trial deadline, no institution-decision date, no oral-hearing date, and no FWD due date. If you want the negative confirmed at the source, the USPTO PTAB End-to-End system (https://ptacts.uspto.gov/) and the PTAB Decisions page will return nothing for this patent number, as will a CourtListener docket search (https://www.courtlistener.com/).

Confidence statement. I have high confidence in the "no PTAB proceedings" conclusion — it rests on the structured ODP block plus multiple negative web checks. I have high confidence in the 1999-05-30 expiration, which is stated verbatim in the patent's own recorded legal events. I do not have independent confirmation of the full assignment history for all four named inventors, and I found no evidence either way on whether this patent was ever asserted in a district court or ITC action in the 1980s–1990s (pre-digital dockets are poorly indexed). Treat those two items as open, and verify them directly if they matter to your matter.

Sources cited: US 5,420,825 on Google Patents; US5420825A full-text PDF; USPTO ODP structured "PTAB proceedings on file" block (provided).

I'll verify the assignment record and inventor details before reconstructing the chain.

Let me verify the recorded reel/frame and check for any post-issuance transfers.

Ownership Reconstruction — US Patent 5,420,825 ("Noise control composite")

Scope note / data limitation up front: The only ownership record I could verify is the original government assignment-in. I found no post-issuance assignment, security agreement, license, merger, or change-of-name record for this patent in Google Patents' legal-events feed, and my searches for the assignment image and for any successor assignee returned nothing. I could not independently open the Assignment Center / legacy assignment image (reel 004055, frame 0883) to read the recorded correspondent of record field, and the indexed record does not expose it. I am therefore not reporting a correspondent name rather than guessing one.

Inventors

Unusual patterns:

• Only two of four inventors appear as assignors on the sole recorded assignment (FISCHER, EUGENE C.; MONTEMARANO, JEAN A.). For the other two, either (a) their rights vested in the Government by operation of law under Executive Order 10096 / the Navy's employment terms and were recorded separately or not at all, or (b) the indexing is incomplete. I cannot distinguish (a) from (b) from the available record — flagged, not resolved.
• Thirteen-year pendency: filed 1982-08-31, granted 1995-05-30. This gap is consistent with a secrecy order under 35 U.S.C. § 181 (routine for Navy submarine sonar patents of this era), but the record I retrieved does not state one. Treat as an inference, not a documented fact.
• No inventor-departure/fire-sale pattern is present or even relevant: the U.S. Government is the assignee and there is no subsequent transfer to trace.

Original assignee

• Entity on the issued patent: United States of America as represented by the Secretary of the Navy (assignee of record; also listed as current assignee by Google Patents).
• Product embodying the claims: The composite is a sonar hull-blanket/tile material (PVF₂ transducer layers separated by anechoic material, inner-sensor subtraction or anti-phase drive). This is a military application; the U.S. Navy is the practitioner/user rather than a commercial seller. No commercial product line, brand, or revenue is attributable to the assignee in the ordinary sense.
• Primary line of business: Sovereign instrumentality — naval R&D, acquisition, and fleet operation.
• Current status: Not operating/acquired/dissolved in any commercial sense — the U.S. Government is the owner of record. The patent itself expired for failure to pay the maintenance fee (reminder 1998-12-22; lapse 1999-05-30; "Expired due to failure to pay maintenance fee" recorded 1999-07-27). Anticipated term expiry would have been 2012-05-30. Per Google Patents status: Expired – Fee Related.

Assignment timeline

There is one recorded assignment for this patent. The Assignment Center has no other records for it; the chain begins and ends at the U.S. Government.

• 1982-08-30 (executed; given as "Effective date" 19820830) / recorded 1982-10-22 — Reel 004055 / Frame 0883
  • Conveyance: Assignment of assignors' interest ("ASSIGNMENT OF ASSIGNORS INTEREST")
  • Assignor: Eugene C. Fischer; Jean A. Montemarano
  • Assignee: United States of America as represented by the Secretary of the Navy
  • Correspondent: Not recoverable from the indexed record. The reel/frame citation is verified (Google Patents legal events, 1982-10-22 entry, REEL/FRAME 004055/0883), but the correspondent-of-record field is not exposed and I could not open the image. No recurring-correspondent pattern can be assessed.
  • Context: Statutory/employment assignment-in to the Government (Executive Order 10096 framework); not a commercial acquisition.

All subsequent "events" are administrative, not ownership transfers:

• 1998-12-22 — maintenance fee reminder mailed (REMI)
• 1999-05-30 — lapse for failure to pay maintenance fees (LAPS), effective date
• 1999-07-27 — "Expired due to failure to pay maintenance fee" (FP)
• 2018-01-22 — status annotation: patent discontinuation (nonpayment, 37 CFR 1.362)

Because Assignment Center carries no records beyond the original assignment-in, I will not construct a fuller chain — per the operating rule, that absence is itself the finding: the original assignee (the U.S. Navy) still owned the patent through its expiry in 1999, and no NPE ever acquired it.

Timeline diagram

timeline
    title Ownership of US 5420825
    1982 : Filed by US Navy inventors
         : Assigned to Secretary of the Navy reel 004055 0883
    1995 : Patent issued after 13 year pendency
    1999 : Expired for nonpayment of maintenance fee
    2012 : Original term would have expired

NPE / troll-pattern signals

Verdict

Insufficient data — narrowly, and only because the enumerated categories have no bucket for "sovereign-owned, never transferred, never asserted." The record contains exactly one assignment (executed 1982-08-30, recorded 1982-10-22, reel 004055/0883) conveying Fischer's and Montemarano's interests to the Secretary of the Navy; there are no further recorded transfers, and the patent expired 1999-05-30 for failure to pay the maintenance fee. On that evidence, all eight NPE signals are not present, and the commercial characterization is best stated as non-asserting government-owned art rather than any NPE pattern. (If forced into an NPE-behavior frame, the correct read is the inverse of an NPE chain: the patent was never monetized and lapsed before its 2012 term.)

Verification links:

• USPTO Assignment Center (search by patent number 5420825): https://assignmentcenter.uspto.gov/
• Legacy assignment search UI: https://assignment.uspto.gov/patent/index.html
• Google Patents record and legal events: https://patents.google.com/patent/[US5420825](/patent/US5420825)/en

Open items I could not close (stated rather than filled in): the correspondent of record on reel 004055/0883; whether separate assignments exist for inventors Castelli and Dickey; and whether a § 181 secrecy order explains the 1982→1995 pendency.

I'll verify each cited reference against live sources before mapping them to claims.

Now the remaining three cited references.

Scope and method (read first)

Two housekeeping items before the analysis:

1. Date discrepancy. The task header says "Current Date: April 26, 2026"; my session metadata says 2026-09-30. I'm not resolving this — flagging it, consistent with the discrepancy-flagging convention used earlier.
2. Source limitation (carried forward). I could not query USPTO PatentCenter / the USPTO full-text search API directly. All verification below is from Google Patents and Google-hosted patent-image OCR of the printed front pages and full texts, plus FreePatentsOnline and Semantic Scholar. This is a negative/qualitative search result, not a certified USPTO printout. Bibliographic data for US 5,420,825 itself is carried forward unchanged from the prior section.

Also important for the § 102 framing: US 5,420,825 was filed 1982-08-31, so pre-AIA 35 U.S.C. § 102 governs. The relevant sub-sections are therefore § 102(b) (statutory bar: patented or printed-publication more than one year before the US filing date, i.e., before 1981-08-31) and § 102(a)/§ 102(e) (reference published/granted before the applicant's invention, or a US patent granted on an application filed before the applicant's invention).

Critical scoping point: "patent citations" for US 5,420,825 means the five references cited by the examiner on the face of the patent ("Patent Citations (5)"). The eleven-plus entries under "Cited By" are later documents (earliest priority 1991-12-23; most 1994–2017) and therefore cannot be § 102 prior art against a 1982 filing. They are only relevant to infringement/validity of those patents. I exclude them from the anticipation analysis and say so explicitly.

The five cited references at a glance

Sources: https://patents.google.com/patent/US3971250 ; https://patents.google.com/patent/US4158189 ; https://patents.google.com/patent/US4184093 ; https://patents.google.com/patent/US4236235 ; https://patents.google.com/patent/[US4295010A](/patent/US4295010A)/en ; https://patents.google.com/patent/US5420825/en

Reference-by-reference analysis

1. US 3,971,250 — "Electret sensing medium having plural sensing units" (3M)

Disclosure. A sensing medium 1 formed of two sensing units 2 and 3, each a layer of electret material (expressly including polyvinylidene fluoride) with conductive plates on each planar surface, the two units separated by and in surface-to-surface contact with an insulating layer 4 (polyurethane foam, described as both thermal and electrical insulation). Leads 13, 14 interconnect the plates, and a sensing circuit 17 — or, in the FIG. 4 embodiment, a differential amplifier 21 with inputs 22, 23 across the two units — reads the difference. The stated object is temperature compensation (cancelling equal pyroelectric charges from both layers), and alternatively radiation or bending-stress sensing.

Claim mapping — this is the single most dangerous reference for this patent.

Bottom line: US 3,971,250 is the examiner's best art, and its silence on the active (drive) mode is precisely where this patent's asserted novelty sits.

2. US 4,158,189 — "Baffled blanket acoustic array incorporating an indented reaction plate" (Navy / Wardle)

Disclosure. A conformal blanket sonar array 10 for a submarine exterior hull 12, built as a stack: acoustic baffle 22 (compliant tubes embedded in elastomer 29) on the interior side of a corrugated/indented reaction plate 16, with acoustic sensors 18 in the corrugations/indents on the exterior side, embedded in elastomer 27, covered by a smooth elastomer sheet 28 as the outer protective/low-drag surface. The array "can comprise either a single section or a plurality of individual staves with adjacent edges abutting one another." Stated objects are reduced thickness/weight and reduced self-noise via separation of sensors from both the reaction plate and the exterior surface.

This is the reference the patent's own Background section singles out ("The sonar array shown in U.S. Pat. No. 4,158,189 is a conformal blanket sonar array… designed to avoid self-noise by separating the sensor from the external surface by a large thickness of elastomer. However, the problem of directionality is not approached and this damping structure has disadvantages already noted.").

Claim mapping.

3. US 4,184,093 — "Piezoelectric polymer rectangular flexural plate hydrophone" (Navy)

Disclosure. A rectangular PVF₂ piezoelectric polymer film transducer: two polymer films 20 affixed to the outer raised surfaces 16 of plastic plates 14, which are on either side of a plastic frame 12, creating an internal compliant air cavity 26. Leads 24 attach to electrodes on the films. The specification notes the device "is actually two transducers in one unit with active elements placed on the top and bottom," and emphasizes shape adaptation "to narrow line arrays and hull mounted arrays."

Claim mapping.

Bottom line: US 4,184,093 is background/analogous art establishing that PVF₂ films stacked in a sandwich with interposed material and independent leads were known hydrophone practice by 1978. It supports obviousness of the two-layer structure, not of the noise-cancellation function.

4. US 4,236,235 — "Integrating hydrophone sensing elements" (Boeing / Gilbert)

Disclosure. A cylindrical integrating hydrophone: a rigid cylinder 10 with two opposed semicylindrical rigid integrating surfaces 12, 14 attached at diametrically opposite points, and a piezoelectric polymer membrane spanning the cylinder interior at points 90° displaced, with electrical contacts on opposite membrane faces and an elastomeric water-impermeable cover. The object is increased sensitivity with high-hydrostatic-pressure capability; acoustic energy collected by the integrating surfaces flexes the cylinder and stretches the polymer membrane.

Claim mapping.

Bottom line: This reference is cited for the art of using piezoelectric polymer membranes in hydrophones (as the specification itself acknowledges re: US 4,236,235 — "only a single layer is shown and there is no attempt to control noise"). It carries no § 102 anticipation of any claim of US 5,420,825. It is a § 103/background reference on PVDF hydrophone practice.

5. US 4,295,010 — "Plural piezoelectric polymer film acoustic transducer" (Lectret S.A. / Murphy)

Disclosure. An acoustic transducer with a plurality of piezoelectric polymer films (polarized PVDF, gold-coated), spaced apart, mounted at their peripheries on a hollow cylindrical support, and physically connected near their centers by an epoxy dot, electrically connected in parallel with opposed polarity so both films move in the same direction. FIG. 3 shows a four-film embodiment; FIGS. 7–8 show two two-film modules. Families include EP 0 085 997 and the later US 4,453,044 (same assignee, Murphy), whose front page lists 4,295,010 10/1981 Murphy 179/110 A.

Claim mapping — and an important timing caveat.

Timing caveat (do not miss this): because US 4,295,010 issued 1981-10-13, only ~10½ months before the 1982-08-31 filing, it is not a § 102(b) statutory bar. It can only be applied under § 102(a)/(e), with an effective prior-art date of 1980-02-22 (its filing date) for § 102(e) purposes. If a contest over this patent ever turned on that reference alone, the critical date analysis would matter. (Consistent with the earlier section's caveat, I have no evidence that any such contest occurred — the patent expired for nonpayment effective 1999-05-30.)

Consolidated claim-by-claim exposure matrix

Analytical conclusions

1. The five examiner citations fall into two clean categories. US 3,971,250, US 4,184,093, US 4,236,235 and US 4,295,010 are art on layered/spaced piezoelectric-polymer (PVDF) transducers — establishing that plural PVDF layers, interposed material, independent leads and even differential readout were known. US 4,158,189 is the hull-mounted conformal array art, and the applicant's own Background section concedes it.
2. Only two claims carry real § 102 exposure, and both trace to a single reference. Claim 2's structure and claim 4's subtraction circuit are both substantially disclosed by US 3,971,250 (three of its figures). If this patent had ever been litigated, US 3,971,250 would be the reference to brief first — with the "anechoic" and "shipboard noise" limitations as the battleground.
3. The asserted invention survives the cited art on its active/electronic features. The phase-shift-and-drive limitations (claims 5, 8, 9, 10) and the selectively-switched tile array (claim 6) are not disclosed by any of the five references. Those limitations are the patent's true contribution, and none of the cited art anticipates them.
4. Language inconsistencies to carry forward. Claims 9 and 10 are mirror images (sense inner/drive outer vs. sense outer/drive inner) yet are characterized as cancelling "incoming" and "outgoing" noise respectively — internally inconsistent with the ordinary inside/outside noise geometry, as flagged in the earlier section. That inconsistency is in the claims, not in the cited art.
5. Statutory-subsection discipline matters here. Four references are § 102(b) bars; US 4,295,010 is not (issued within the one-year grace period) and is available only under § 102(a)/(e) with a 1980-02-22 effective date. Any validity chart should reflect that.

Caveats

• No live USPTO / PatentCenter / PATENT FULL-TEXT query was performed, per the same limitation noted in the prior section. The above is built from Google Patents, Google-hosted patent images, FreePatentsOnline and Semantic Scholar.
• Per the strict rule, I did not auto-correct identifiers. All five numbers are taken literally: US 3,971,250; US 4,158,189; US 4,184,093; US 4,236,235; US 4,295,010. Note that Google's citation table for this patent lists the second as US 4,158,189; the same inventor/assignee has a closely related sibling, US 4,140,992 ("Baffled blanket acoustic array"), which is a different document and is not a citation of US 5,420,825 — do not conflate them.
• Inventor field for US 3,971,250 is low confidence (OCR of the front page shows "Allen L."; the full personal name did not resolve cleanly in the sources I retrieved).
• The § 102 anticipation characterizations are potential/analytical, not legal conclusions. I am identifying which claims a reference could arguably anticipate; the "anechoic material" and "shipboard noise" limitation disputes in claim 2 are genuinely arguable and would require claim-construction and, likely, expert testimony (e.g., on whether polyurethane foam is anechoic, and on whether an intended-use statement supplies patentable weight).

I'll ground this § 103 analysis by pulling the actual disclosures of the five examiner-cited references, since obviousness turns on what each reference teaches.

Now the remaining three references.

Two elements of the claims (the antifouling layer, and the anti-phase "active" drive) aren't covered by the five cited references. Let me check whether pre-1982 art exists for those, since only art predating the 1982-08-31 filing can count.

§ 103 Analysis — US 5,420,825 ("Noise control composite")

0. Scope correction before the analysis

The instruction says to use "the results from the Prior Art section of this page." Two lists appear there, and they are not interchangeable for § 103 purposes:

So the § 103 analysis below rests on the five examiner-cited references (per the record at https://patents.google.com/patent/US5420825/en). This matters because the examiner had these five in front of him and the claims still issued after ~12 years 9 months of pendency (previously flagged as consistent with a secrecy order, inference only) — so a prima facie case must explain what the applicant presumably traversed.

1. Standard and PHOSITA

Graham v. John Deere factors, applied through KSR Int'l Co. v. Teleflex Inc., 550 U.S. 398 (2007): the level of ordinary skill, scope and content of the prior art, differences, and secondary considerations. A PHOSITA here is a naval acoustics engineer with several years' experience in piezoelectric-polymer (PVF₂) hydrophone and conformal sonar-array design. All five references are analogous art under In re Bigio / In re Clay — each is a piezoelectric or electret acoustic transducer or a hydrophone array, i.e., the same field of endeavor or reasonably pertinent to the self-noise problem.

2. What each reference actually teaches

US 3,971,250 (3M, 1976) — the most dangerous reference for the core claim. Two sensing units 2, 3, each an electret layer of polyvinylidene fluoride (5, 6) metallized on both faces (electrode plates 7–10), separated by a thermal/electrical insulating layer 4 (polyurethane foam), with leads 13, 14 feeding a sensing circuit 17. Critically, FIG. 4's sensor 20 uses a differential amplifier 21 whose inputs 22, 23 are connected to plates on the two different units and which produces an output only when the inputs differ — i.e., expressly disclosed subtractive cancellation of a signal common to both layers, there for temperature compensation. It also teaches that interconnected plates of the two units make equal-magnitude charges "cancel one another."
URL: https://patents.google.com/patent/US3971250

US 4,158,189 (Navy, 1979) — supplies the hull-mounted multilayer architecture and the self-noise motivation. Conformal blanket sonar array 10 adhered to the submarine's exterior hull surface 12: acoustic baffle 22 (compliant tubes in elastically embedded baffle) between hull and a reaction plate; sensors 18 embedded in elastomer 27; a protective, low-drag elastomer sheet 28 on the exterior; fairing 14. It states that separation "from the exterior surface minimizes self-noise problems," and that the array "can comprise either a single section or a plurality of individual staves," with sensors wired out via data cables 24 / stub cables 26. It also notes that "the spatial correlation of self-noise and signal can also exhibit directional characteristics," and lists quietness, sensitivity and directionality as the performance criteria to be met.
URL: https://patents.google.com/patent/US4158189

US 4,184,093 (Navy, 1980) — PVF₂ film (20) electrodes with leads (24) in a "rectangular sandwich arrangement," described as "two transducers in one unit with active elements being placed on the top and bottom," suited to "narrow line arrays and hull mounted arrays."
URL: https://patents.google.com/patent/US4184093

US 4,236,235 (Boeing, 1980) — PVDF membrane hydrophone transducer with electrical contacts on opposite faces of the membrane and a "water-impermeable cover such as an elastomeric tubing"; notes hydrophones "may be deployed singly or in arrays of various configurations."
URL: https://patents.google.com/patent/US4236235

US 4,295,010 (Lectret, 1981) — plural PVDF films (14, 16; four-layer embodiment in FIG. 4), gold-electroded, poled, mounted at their peripheries, electrically connected so that one film contracts while the other expands, and operable both as a receiver (microphone, FIGS. 5–6) and as a transmitter driven by an AC source (headphone, FIG. 1). This is the reference that supplies the two-way (sense-and-drive) capability of a stacked PVDF pair.
URL: https://patents.google.com/patent/US4295010

3. Motivation to combine

The rationales that a challenger would assert (MPEP 2143 / KSR):

1. Same field, same problem, same assignee. US 4,158,189, US 4,184,093 and the patent-in-suit are all Navy-owned submarine sonar work; US 3,971,250 was cited by the examiner. A PHOSITA looking for a way to suppress self-noise in a hull-mounted PVF₂ array would naturally consult stacked-transducer and differential-sensing teachings.
2. Known technique, same operation, predictable result (KSR rationale A/C). US 3,971,250's differential amplifier performs exactly the arithmetic the patent claims — subtracting one layer's signal from another layer's signal separated by an insulator to null a signal common to both. Applying that known technique to the self-noise problem (where shipboard self-noise is the common-mode component and the external target signal is not) is "the use of a known technique to improve a similar device in the same way."
3. The physics supplies the motivation, not hindsight. Because the baffle/anechoic layer attenuates interior noise more than exterior signal, the inner and outer layers necessarily see different self-noise-to-signal ratios — a structural incentive to difference them. US 4,158,189 (baffle + "minimizes self-noise problems") and US 3,971,250 (insulating layer + differencing) point in the same direction.
4. Dual-mode PVDF is admitted in the art. US 4,295,010 shows PVDF films electrically driven (transmitter mode) with polarities selected to make the films move in a coordinated, opposing manner; US 4,184,093 shows "two transducers in one unit." Using the second layer as an actuator is an expressly contemplated, known PVDF capability, not a new device.
5. Design choice / obvious variation. Which layer is sensed and which is driven (claims 9 vs. 10) is squarely "a change in a parameter... a recognized element of the prior art where the result is a predictable design choice."

4. Claim-by-claim

5. What a patent owner would argue back

• No teaching of the active mode. The strongest non-obviousness argument is that every cited reference that uses two layers (US 3,971,250; US 4,295,010) does so for temperature compensation or output summing, not for using one layer as an anti-phase cancelling actuator. If no pre-1982 ANC art is available, claim 5/8/9/10 have real force.
• US 4,158,189 arguably teaches away from differencing two sensor layers: it solves self-noise with a baffle plus a stiff reaction plate — isolation rather than electronic subtraction. This is a weak argument (a baffle attenuates but does not eliminate self-noise, and the reference acknowledges residual self-noise and directional correlation), but it is the best available.
• Antifouling layer for claim 1.
• Secondary considerations: none in evidence. No litigation (previously established as a negative search result), and the patent expired for nonpayment effective 1999-05-30, so there is no commercial-success, licensing, or industry-praise record to weigh. The ~12-year pendency is a candor/history issue to investigate, not a nexus-bearing objective indicium.

6. Bottom line

• Strongest § 103 attack: claims 2 and 4 (and 3, 7) over US 4,158,189 + US 3,971,250 — the elements are essentially all disclosed, and the only difference is the purpose to which an expressly disclosed differencing circuit is put, which the baffle-geometry physics makes predictable.
• Next tier: claim 1 over US 4,158,189 + US 4,236,235/US 4,184,093, with the antifouling organometallic-elastomer element as the vulnerable/residual limitation.
• Weakest attacks: claims 5, 8, 9, 10 (and claim 6's tile-selective beamforming), because the anti-phase, one-layer-drives-the-other noise-cancellation loop is not taught by any of the five cited references. Establishing obviousness there requires pre-1982 active-noise-cancellation art that I was unable to retrieve and therefore cannot cite; absent it, those claims survive a § 103 challenge built only on the record's Prior Art section.

7. Caveats

• This is a paper analysis of an expired, government-owned patent; I found no litigation or PTAB record (consistent with the earlier negative search result).
• I relied on the Google Patents record and on the reference texts returned by search; I did not verify any of this against USPTO PatentCenter, a certified prosecution file (whose history would show precisely how the applicant traversed these five references and whether a secrecy order issued), or a signed assignment record.
• The antifouling art and pre-1982 ANC art questions above are open in this analysis, not resolved. Both should be closed with a targeted prior-art search before any final invalidity opinion.