US 5939986

I'll verify the patent against external sources, then summarize.

Let me run two more targeted checks — one for USPTO/assignment/status data and one for any litigation or Federal Circuit activity.

Verification / search scope

I ran targeted queries against public patent sources (Google Patents, USPTO grant records via uspto.report, Unified Patents portal, USPTO/DOE-UNT digital library, Federal Register / HHS tech-transfer listings) and general web sources for any 2026 CAFC activity citing 5,939,986.

No CAFC 2026 docket entry, appeal, or Federal Circuit opinion referencing US 5,939,986 was found. Caveats, stated explicitly:

• I do not have a direct, authoritative PACER/CAFC docket-query tool. My negative result is based on web-level searching, not on a proprietary docket feed, so I cannot certify that no 2026 appeal exists.
• A 2026 CAFC appeal is a priori unlikely: the patent expired 2016‑10‑18 (anticipated expiration, 20 years from the 1996‑10‑18 filing). Litigation value after expiry is limited to back damages.
• Numbers matching "5939986" appear in unrelated records (e.g., JP5939986B2, a Myriant Corporation E. coli patent, and a mailing-list entry for a person). Per your strict rule, I did not treat those as the same identifier — they are distinct documents/records that merely share the digit string.

Primary source used (authoritative full text): https://patents.google.com/patent/US5939986/en (fetched 2026‑09‑24); PDF: https://patentimages.storage.googleapis.com/18/cc/4a/18ea6ccce849cb/US5939986.pdf ; grant record: https://uspto.report/patent/grant/5,939,986

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Bibliographic summary — US 5,939,986

Abstract (as published): "A warning system is provided for a mobile working machine to alert an individual of a potentially dangerous condition in the event the individual strays into a hazardous working zone of the machine. The warning system includes a transmitter mounted on the machine and operable to generate a uniform magnetic field projecting beyond an outer periphery of the machine in defining a hazardous working zone around the machine during operation thereof. A receiver, carried by the individual and activated by the magnetic field, provides an alarm signal to alert the individual when he enters the hazardous working zone of the machine."

Cited prior art of record (6): US 4,100,529 (Mews, Inc.); US 5,047,752 (Murata Wiedemann); US 5,086,290 (Murray); US 5,198,800 (Shin Caterpillar Mitsubishi); US 5,477,210 (Harris Corp.); US 5,575,242 (Davis).

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Plain-language overview of the independent claim

There is exactly one independent claim: claim 1. Claims 2–14 all depend from it (directly or indirectly).

Claim 1 — the core invention (two-part "comprising" structure):

1. (a) Transmitter on the machine — mounted on the mobile working machine, it generates a magnetic field that projects beyond the machine's outer periphery, thereby defining a hazardous working zone that envelops the machine when the machine is operating. Notably, claim 1 does not require the word "uniform," does not specify a frequency, wire loops, or any particular circuit — those limitations are added only in dependent claims.
2. (b) Receiver carried by a person and responsive to that magnetic field — the receiver produces an alarm signal to alert the individual when they enter the hazardous working zone.

So the claimed inventive core is: machine-mounted magnetic-field generator defines a keep-out envelope around the machine; a wearable field-responsive receiver alerts the wearer on entry. It is a "marker-field" proximity concept, not a radar/ultrasonic/optical obstacle detector.

Dependent-claim scaffolding (what claim 1 is narrowed to downstream):

• 2 → transmitter has a tuneable transmitter that generates a current signal + a transmitter antenna that converts that current into the magnetic field.
• 3 (from 2) → at least one wire loop around the machine's outer periphery.
• 4 (from 2) → multiple wire loops, each at a location identified as potentially dangerous, producing a uniform field whose outer envelope envelops the machine.
• 5 (from 4) → per-loop current is adjustable, so the envelope shape can be tuned.
• 6 (from 2) → transmitter circuit architecture: tuneable oscillator → loop driver means (amplifier) → antenna, with a buffer amplifier between oscillator and loop drivers for isolation.
• 7 (from 6) → one dedicated loop driver per wire loop.
• 8 (from 6) → oscillator adjustable between 500 Hz and 100 kHz.
• 9 (from 2) → receiver architecture: ferrite loop antenna → bandpass filter tuned to the transmitter frequency (strips all other frequencies, "leaving only said alarm signal") → amplifier → signal detector producing a DC voltage proportional to alarm-signal strength.
• 10 (from 9) → below a selected DC threshold, the DC voltage drives a first LED to visually caution the wearer of position relative to the zone.
• 11 (from 10) → that first LED is a yellow warning light.
• 12 (from 9) → above a selected DC threshold, the DC voltage drives a second LED plus an alarm driver that excites a peizo alarm for combined visual + audible warning.
• 13 (from 12) → that second LED is a red warning light.
• 14 (from 12) → the alarm driver can generate a shutdown signal that stops all movement of the machine at the danger threshold.

Plain-language takeaway: two-zone graded alerting (caution/yellow vs. danger/red + audible) driven by received field strength, culminating optionally in automatic machine shutdown. The spec describes the working example as an underground, radio-controlled coal continuous mining machine with loops around the cutting head, main body, and articulating rear discharge chute.

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Textual quirks in the patent (reported as-written, not corrected)

• The specification states "the loop driver 48 is connected to the wire loop antenna 44," while the rest of the document and FIG. 1 use loops 32, 34, 36. I have not silently corrected this; it reads as an internal reference-numeral inconsistency.
• The receiver component list numbers the red LED as 65 and the peizo alarm device as 64, while the alarm driver is 62 and the yellow LED is left unnumbered; claim 10/11 refers to a "first light emitting diode device" and claims 12/13 to a "second."
• The patent consistently spells the sounder "peizo" (claims 12; spec) rather than "piezo." Recorded literally.
• Terminology: claim 1 recites "receiver means responsive to the magnetic field"; the Summary of the Invention/abstract phrase it as "operably associated with the transmitter means."

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Commercial / downstream footprint (context, sourced)

• US 6,810,353 ("Non-directional magnet field based proximity receiver with multiple warning and machine shutdown capability," HHS/CDC) is a related line of the same government work and lists US 5,939,986 in its family/citation context.
• US 7,420,471 (Strata/Geosteering Mining Services) expressly states that "important progress was made with the proximity concepts offered by the Schiffbauer U.S. Pat. Nos. 5,939,986 and 6,810,353, which are incorporated herein in their entireties," while criticizing multiple-loop field uniformity — useful evidence of the '986 disclosure's perceived scope and its limitations.
• Frederick Energy Products' HIT-NOT® Proximity Protection System product literature (Personal Alarm Device, Model HN-2Z guides) lists "Patent #'s US7420471, US5939986, US6810353, US8169335, US8232888, AU2005289704…" — i.e., the '986 patent has been asserted/listed on a commercial magnetic marker-field pedestrian-struck-by system.
• The technology is described in NIOSH/CDC literature as HASARD (Hazardous Area Signaling and Ranging Device), e.g., Schiffbauer & Mowrey, "An Environmentally Robust Proximity Warning System for Hazardous Areas" (2001). HHS technology-transfer listings (Federal Register Feb. 4, 2014) market it as "Warning System for Mobile Machinery Hazardous Zones," HHS Ref. No. E-239-2013/0, inventors Schiffbauer and Ganoe (CDC).

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Uncertainty flags

• Assignee: I report the listing literally. Records show DOE → HHS/CDC transfer in 2001 (effective 1998), yet the Department of Energy is still shown among current assignees; assignment statuses are assumptions per the source and are not a legal conclusion.
• CAFC 2026: as stated above, no 2026 Federal Circuit activity was found for this patent, but I lack a direct docket-query tool for PACER/CAFC, so this is a "not found," not a certified negative.
• Expiry: 2016‑10‑18 is the anticipated expiration listed; actual termination would also be affected by any terminal disclaimer or fee lapse not visible in the fetched data.

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

Let me check dedicated litigation databases directly for this patent number.

Bottom line

No litigation involving U.S. Patent No. 5,939,986 could be identified. I found no complaint, district court case, CAFC appeal, ITC investigation, PTAB proceeding, or reported settlement/verdict that names US 5,939,986 as an asserted patent.

Because the strict instruction is to interpret identifiers literally, I want to be explicit that I ran the search on US 5,939,986 (application 08/733,846) specifically — not on look‑alike numbers. That matters here, because searches for the bare string "5939986" surfaced a substantial amount of false-positive noise that is not this patent:

Patent identity confirmed before searching

• Patent: US 5,939,986 — "Mobile machine hazardous working zone warning system"
• Inventors: William H. Schiffbauer; Carl W. Ganoe
• Original assignee: U.S. Department of Energy (confirmatory license recorded 1997-02-12, effective 1996-09-16)
• Reassignment: 2001-05-24 — transfer from DOE to HHS / Centers for Disease Control and Prevention (effective 1998-09-28)
• Filed / priority: 1996-10-18; granted: 1999-08-17
• Status: Expired – Lifetime; anticipated expiration 2016-10-18 (fee payments at years 4, 8, and 12 only — no 16-year/20-year maintenance payment recorded)
• Sources: https://patents.google.com/patent/US5939986/en ; https://www.osti.gov/biblio/[872459](/patent/872459) ; https://portal.unifiedpatents.com/patents/patent/US-5939986-A

Requested case table

Why "none found" is the correct answer here, not merely an absence of evidence

Three independent factors make litigation on this patent unlikely, and none of them contradict the search result:

1. It is a U.S. Government–owned patent. The specification opens with a STATEMENT OF GOVERNMENT INTEREST, and title passed DOE → HHS/CDC. Enforcement would have had to be brought by the United States (or a licensee under 35 U.S.C. § 207 / Bayh‑Dole-style authority granted by the agency). There is no record of any such enforcement action, and no government patent-licensing docket entry surfaced.
2. It expired on 2016-10-18. Any infringement action would have had to be filed well before then, and any resulting judgment would long predate today's date.
3. Public availability appears to have been the point. The corresponding technology was published openly by the inventors (see Schiffbauer, "An Active Proximity Warning System for Surface and Underground Mining Applications," 2001, listed as non-patent literature on the Unified Patents page) — consistent with government-disseminated research rather than commercial assertion.

Important caveats on my confidence level

I want to be candid rather than overstate what I verified:

• I could not directly query the sources you named. My attempts to reach the Unified Patents litigation caselist, PACER, and CourtListener/RECAP for this specific number returned empty or were cut off before returning results. So my conclusion is based on: (a) a confirmed Unified Patents patent record for US-5939986-A; (b) the full Google Patents record; and (c) the absence of any litigation hit across broad litigation-oriented searches.
• The Google Patents page lists no "Litigation" section for this patent, and its cited-by list (81 entries) contains only later-issued patents and publications — no litigation documents.
• I did not verify whether any of the citing patents' owners ever asserted '986 as prior art in litigation. Patents in this family appear in several later cases and portfolios — e.g., Strata Proximity Systems / Strata Safety Products (US 8,288,178; 8,842,880; 8,817, that line of filings), Frederick Mining Controls (WO 2009/055606), Geosteering Mining Services / Strata Products Worldwide (US 7,420,471), and Crown Equipment. Those are separate patents citing '986 as prior art. A citation relationship is not litigation, and I have no evidence that '986 itself was ever asserted.
• A search of the '986 record would not surface a case filed elsewhere if the patent were cited only in an invalidity contention rather than asserted. That channel is essentially invisible to the tools I had.

A related patent worth flagging (do not conflate)

The same government program produced US 6,810,353 — "Non-directional magnetic field based proximity receiver with multiple warning and machine shutdown capability" (priority 2000-10-26; assignee HHS/CDC). It appears in the '986 family/citation network. I found no litigation on '353 either, but I mention it because it is the most likely source of confusion if you are tracing assertions by this group of inventors.

Recommended verification steps if you need court-grade certainty

1. PACER / RECAP — search both "5,939,986" and "5939986" in the full-text docket field; also search by patentee name ("United States of America," "Centers for Disease Control," "Department of Energy") with patent-related cause codes for 1999–2016.
2. Unified Patents Litigation Portal — https://portal.unifiedpatents.com/litigation/caselist, filtered by the patent number.
3. Docket Navigator / Lex Machina — the only tools that reliably capture patents cited in invalidity contentions but never asserted.
4. Agency records — DOE Office of General Counsel and HHS/CDC technology-transfer offices, for any administrative enforcement or license-dispute record not docketed in Article III courts.
5. CAFC — no appeal involving '986 was found, but a Federal Circuit docket search by patent number is warranted given the 1999–2016 window.

If you'd like, I can draft those search strings for PACER and Docket Navigator, or run a follow-up sweep on the '353 patent and the citing Strata/Crown/Frederick families to make sure the "no litigation" conclusion holds across the whole family.

I'll verify the structured "no proceedings" result against live sources before writing this up.

Let me run a few more targeted checks — including ex parte reexamination (not an AIA trial, but often conflated) and the PTAB E2E docket.

One more verification pass — checking for any appeal or reexamination certificate, plus the PTAB E2E record.

PTAB / AIA Trial Proceedings — US 5,939,986

Proceedings overview

Total AIA trial proceedings on file: 0 (zero). The structured canonical list from the USPTO Open Data Portal returns no AIA trial proceedings, and my independent web searches surfaced no IPR, PGR, CBM, or post-grant proceeding naming US 5,939,986 — there is therefore no breakdown into active / invalidated / sustained / settled / institution-denied because the denominator is zero, and no claim of the patent has ever been canceled or sustained at the PTAB. The defensive posture this gives a defendant is unusual and worth stating precisely: the patent is not "hardened" by PTAB survival — it is simply untested at the Board and expired, which means a defendant's strongest move is not an IPR at all but a § 286 damages-window argument (more below).

I want to be explicit about the limits of my verification, per the operating rules:

• The structured block states the ODP API returns no AIA trial proceedings for this patent as of the most recent ingest. I take that as authoritative for the count.
• My search sweep to corroborate claim-level outcomes, panels, and appeals returned only false positives, none of which relate to this patent: JP 5939986 B2 (Myriant Corp., metabolic evolution of E. coli, unrelated), a QC Lot "5939986" in an environmental lab report, a USPS mailing-list entry "5939986 Stacia Warren…" in an FWS docket, and USPTO trademark Registration No. 5,939,986 ("SURFACE HERO", TapeCase Ltd / TAPE CASE, LLC) — a trademark, not a patent.
• My final two verification queries were cut off by a tool step limit (a check for "final written decision" text and a check for a reexamination certificate). I therefore could not complete a last-mile confirmation that no ex parte reexamination certificate exists. I have no record of one — the Google Patents legal-events trail for '986 shows only the 1997 assignment, 1999 grant, 2001 DOE→HHS transfer, and fee payments at years 4/8/12 — but I flag that single gap rather than claim certainty.

There is no proceedings-by-proceedings section to write, because there are no proceedings and I will not invent proceeding numbers. Instead, here is the substantive substitute a defendant actually needs: why each AIA vehicle is unavailable or strategically useless against this patent.

Why no AIA trial exists (and why one is now near-impossible to file successfully)

Why the window closed unused. Three converging facts, all consistent with the litigation section already generated: (1) '986 is a U.S. Government–owned patent (DOE → HHS/CDC), so there was no commercial patentee positioned to assert it; (2) no litigation was ever filed on it, so no § 315(b) one-year clock was ever triggered and no accused infringer ever had the incentive to petition; (3) the inventors published the technology openly (Schiffbauer, "An Active Proximity Warning System for Surface and Underground Mining Applications," 2001), consistent with government dissemination rather than enforcement.

And if someone tried today (2026-10-01): '986's term ended 2016-10-18 (year-12 fee paid 2011-02-15; no year-16 or year-20 payment recorded; Google Patents status "Expired – Lifetime," anticipated expiration 2016-10-18). IPR of an expired patent is legally permissible, but a petition would face a very high discretionary-denial risk under the current settled-expectations practice — a patent in force for over 19 years presents the paradigm case. It would also be economically irrational: see the § 286 point below.

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What is actually in the record (as distinct from a PTAB proceeding)

I want to distinguish carefully between PTAB challenges to '986 (zero) and '986 being cited as prior art against other people's patents (extensive). These are frequently conflated in secondary sources:

Discrepancy flag (cross-reference to the previously generated litigation section). That section cites the Alliance Coal patent as "US 8,288,178." The '986 record lists Alliance Coal's proximity-detection patent as US 8,289,170 ("System and method for proximity detection," filed 2008-04-29, granted 2012-10-16). The digits appear transposed. I flag it per the cross-reference instruction but it does not change the substantive conclusion — no PTAB activity either way.

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Strategic summary

Claim status. All 14 claims — independent claims 1, 2, and 6, and dependents 3, 4, 5, 7, 8, 9, 10, 11, 12, 13, 14 — are UNTESTED at the PTAB. None is canceled; none has been adjudicated patentable by the Board. There is no narrowing, no certificate of correction from a post-grant proceeding, and no substitute claim on file. A defendant therefore cannot say "claim 1 is dead," and equally cannot be met with "the patent survived two IPRs." The entire claim set is exactly as granted on 1999-08-17.

Estoppel landscape. No § 315(e)(2) estoppel exists against anyone, because estoppel attaches only on issuance of a final written decision and none has issued. Likewise there is no § 325(d) "same or substantially the same art" history at the Office from any AIA trial — so a hypothetical petitioner would not face a § 325(d) bar from PTAB art. The Office's prosecution history does exist (the six examiner-cited references: US 4,100,529; US 4,507,752; US 5,086,290; US 5,198,800; US 5,477,210; US 5,575,242), and those remain available as § 325(d) considerations and as obviousness combinations in any forum.

Pattern signals. There is no repeat petitioner (there are no petitioners), no PTAB appeal activity by the patent owner (HHS/CDC has no AIA trial history on this patent), and no defensive aggregator in the chain — no Unified Patents, RPX, or similar challenge appears. This is the signature of a dormant government safety-research patent, not a monetized asset: patents that are actually asserted reliably attract IPRs within 12–18 months of the first complaint, and this one was never asserted. The absence of PTAB activity here is a weak signal about validity and a strong signal about non-enforcement.

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Recommended next steps

For a defendant receiving a demand or complaint citing US 5,939,986 today (2026-10-01), the recommended order of operations is:

1. Lead with the term, not with invalidity. The patent expired 2016-10-18 and the record shows no 16-year or 20-year maintenance payment. Confirm the expiration through the USPTO Patent Center fee history (https://patentcenter.uspto.gov, application 08/733,846) and the full legal-events trail at https://patents.google.com/patent/US5939986/en. If expiration is confirmed, then under 35 U.S.C. § 286 recovery is limited to six years before filing — i.e., to acts before 2016-10-18 at the earliest, and any act occurring on or after 2016-10-18 is outside the term entirely. For essentially all modern proximity-warning products, that ends the case without touching the PTAB.

2. Do not reflexively file an IPR. It is legally possible against an expired patent, but you would be filing a ~$300K+ petition against the Director's settled-expectations doctrine (patent in force >19 years) with no offsetting need, since no injunction and only a closed damages window are at stake. If a reexam angle is genuinely needed, ex parte reexamination is the cheaper lever and carries no § 315(e) estoppel — but note the In re Dahle line on improper non-estoppel certifications; that only bites if a prior IPR reached FWD, which here it has not.

3. If assertion proceeds anyway, get the family straight. Confirm your product is not accused under the later Strata / Frederick Mining Controls / Crown Equipment patents (US 8,288,170; US 8,844,880; US 9,896,930; US 11,380,205; US 7,420,471; US 8,722,877; US 9,522,817 and related), which are separate, still-live-until-their-own-expiry patents that cite '986 as prior art. That is where the assertion risk in this technology space actually lives — not in '986.

4. Verify the negative directly before relying on it. Confirm zero AIA trials via the PTAB E2E / PTAB Center docket at https://ptacts.uspto.gov/ptacts/ and the ODP API, and confirm no Federal Circuit appeal via CourtListener (https://www.courtlistener.com) and the CAFC docket, searching both "5,939,986" and "5939986" across the 2012-09-16 to 2016-10-18 window and after. My searches returned nothing, but the last two confirmation queries were truncated, so treat the "no reexamination certificate" point in particular as unverified rather than established.

Bottom line for the file: there are no AIA trial proceedings on US 5,939,986 — none ever. No claims are canceled, none are sustained, no estoppel attaches to anyone, and no appeal exists. The patent's dispositive defensive feature is not a PTAB outcome but its expiration on 2016-10-18.

I'll verify the assignment record for US 5,939,986 against the sources you named before reconstructing the chain.

Let me try to surface the recorded correspondents of record directly.

Assignment-chain reconstruction — US 5,939,986

Sources actually reached for this section: the authoritative full patent text supplied in this thread (Google Patents legal-events block for US5939986A), the OSTI/DOE Patents record (https://www.osti.gov/biblio/[872459](/patent/872459) and https://www.osti.gov/doepatents/biblio/872459), the USPTO grant record (https://uspto.report/patent/grant/[5939986](/patent/5939986)), the Unified Patents patent page (https://portal.unifiedpatents.com/patents/patent/US-5939986-A), and general web search.

Correspondent-field disclosure up front: the Assignment Center / Assignment Search UI was not reachable in this session (no direct fetch capability, and targeted queries returned no Assignment Center record page for this patent). The legal-events block I do have reproduces owner name, conveyance description, assignor, reel/frame and effective date — but not the correspondent of record. I therefore report the correspondent as not determinable from available evidence rather than guessing. See the explicit caveat under signal 3.

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Inventors

• Both residences are in southwestern Pennsylvania, matching PETC's location — consistent with the two inventors being federal laboratory employees, not contractor personnel. The application was filed by the U.S. Department of Energy itself on 1996-10-18, which corroborates in-house government employment rather than a contractor filing.
• Unusual-pattern check: the classic fire-sale precursor (all inventors departing the assignee within 12 months of filing) is not present and structurally cannot be present here — the inventors are not a departing private-sector team; they are government scientists whose invention was filed by and assigned to the agency. No inventor-side assignment to a private entity exists at any point in this chain.
• Context for the transfer that follows: the federal mining-safety research functions of this period (Bureau of Mines / PETC adjacency) migrated toward NIOSH under CDC, which is the programmatic backdrop for the 1998/2001 transfer below. I flag this as programmatic context, not as a recorded fact in the assignment documents themselves.

Original assignee

The United States of America, as represented by the Secretary of the Department of Energy (Google Patents lists "US Department of Energy" as Original Assignee; OSTI lists "United States of America as represented by United States (Washington, DC)").

• Primary line of business: sovereign / government research administration — DOE operates the national laboratory system, including the Pittsburgh Energy Technology Center (later folded into the National Energy Technology Laboratory, NETL).
• Product embodying the claims? No commercial product. The claimed system was built and tested as a research prototype. The underlying technology was published openly (NIOSH/CDC literature as HASARD — Hazardous Area Signaling and Ranging Device; Schiffbauer & Mowrey, 2001), which is the standard government dissemination path.
• Current status: operating (a United States executive department; no bankruptcy, acquisition, or dissolution possible in the commercial sense). The relevant sub-unit, PETC, no longer exists under that name — its functions were reorganized into NETL.
• Government-rights status: the specification carries a STATEMENT OF GOVERNMENT INTEREST and the patent is government-owned (not Bayh-Dole contractor-owned), so there is no private licensor upstream at all.

Assignment timeline

Only two post-filing assignment records exist in the fetched legal-events data, both of them government-side. Verbatim reel/frame and dates as recorded:

1. Executed 1996-09-16 / recorded 1997-02-12 — Reel 008463/0007

   • Conveyance: Assignment (recorded under the description "CONFIRMATORY LICENSE; ASSIGNORS: SCHIFFBAUER, WILLIAM H.; GANOE, CARL W."; code AS)
   • Assignor: William H. Schiffbauer and Carl W. Ganoe (the inventors)
   • Assignee / owner name of record: ENERGY, UNITED STATES DEPARTMENT OF, DISTRICT OF C[OLUMBIA]
   • Correspondent: not exposed in the record available to me — see signal 3.
   • Context: Confirmatory license executed contemporaneously with filing — a government-interest formalization, not a transfer to a private party. It is the paper trail required when a federal agency files and the Government's rights must be perfected of record. (Note: per DOE's published patent-filing procedures, a "confirmatory license" is the instrument used when the Government holds the application; the recording here matches that pattern.)
   • Timing note: execution (1996-09-16) precedes filing (1996-10-18) by ~1 month, and recording followed ~4 months later.

2. Executed 1998-09-28 / recorded 2001-05-24 — Reel 011837/0288

   • Conveyance: Assignment (free-format description: "TRANSFER OF INTELLECTUAL PROPERTY FROM DEPARTMENT OF ENERGY TO DEPARTMENT OF HEALTH AND HUMAN SERVICES, CENTERS FOR DISEASE CONTROL AND PREVENTION"; code AS)
   • Assignor: DEPARTMENT OF ENERGY, THE UNITED STATES OF AMERICA AS REPRESENTED BY THE UNITED STATES
   • Assignee / owner name of record: HEALTH AND HUMAN SERVICES, THE UNITED STATES OF AMERICA AS REPRESENTED BY THE SECRETARY OF THE DEPARTMENT OF, CENTERS FOR DISEASE CONTROL AND PREVENTION (name truncated in the source rendering)
   • Correspondent: not exposed in the record available to me — see signal 3.
   • Context: Intra-government reorganization / transfer between agencies (DOE → HHS/CDC, i.e. toward NIOSH), following the migration of federal mining-safety research from the Bureau of Mines/PETC orbit to NIOSH. This is a government-to-government title transfer, not a sale, securitization, or transfer to an asserter.
   • Timing note: executed 1998-09-28, recorded 2001-05-24 — a ~32-month lag between execution and recording. That lag is consistent with administrative inter-agency paperwork, and I found no evidence of any intervening assignment in that window.

No third assignment, license-to-private-party, security interest, merger, name change, or release is of record. Fee events (2002-12-20 year 4, 2007-01-10 year 8, 2011-02-15 year 12) are maintenance-fee payments by the government owner, not conveyances.

Cross-reference flag (contradiction with the earlier-generated litigation section): that section cited "fee payments at years 4, 8, and 12 only — no 16-year/20-year maintenance payment recorded" as evidence of expiry. That inference is wrong on the fee mechanics and should be corrected: for a 1996-filed patent the maintenance-fee schedule has exactly three payments due (at 3.5, 7.5, and 11.5 years). The 2011-02-15 payment was the final fee due, and it carried the patent to its full 20-year term; the 2016-10-18 expiry is normal term expiry, not a fee lapse. The other sections' conclusions (no litigation, no private assignee) are unaffected and are consistent with this chain.

Timeline diagram

timeline
    title Ownership of US 5939986
    1996 : Application filed by US Department of Energy
         : Inventors execute confirmatory license
    1997 : Confirmatory license recorded at USPTO
    1998 : Transfer to HHS CDC executed
    1999 : Patent issued
    2001 : Interagency transfer recorded at USPTO
    2016 : Patent expires at full term

NPE / troll-pattern signals

Two further value-relevant facts worth recording as ownership findings (not troll signals):

• The Government interest is not merely a license. The specification says the invention "may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon." Combined with government ownership, there was never a private royalty stream to monetize.
• Assignee-of-record ambiguity. The listing shows both DOE and HHS/CDC among current assignees even though reel 011837/0288 transferred title DOE → HHS/CDC effective 1998-09-28. This is a listing artifact / stale field, not a recorded re-transfer — there is no DOE-side assignment back. Do not read it as DOE retaining a co-ownership interest; I flag it because a reader pulling the Google Patents assignee field alone would draw the wrong conclusion.
• Assignee-directory cross-checks (RPX Insurance / Unified Patents asserter directories): the Unified Patents patent page for US-5939986-A is reachable and lists no campaign, no litigation and no NPE-linked assignee; I could not reach the RPX/Unified asserter directories or the Unified litigation caselist from this session, so I cannot certify those dockets as checked. The absence of a hit across every source I did reach is unambiguous, but this is a "not found," not a certified negative.

Verdict

Insufficient data — for the NPE question specifically; not because records are missing, but because the chain contains no private party at all.

Justification: the complete assignment record comprises exactly two links — inventors → U.S. Department of Energy, executed 1996-09-16 and recorded 1997-02-12 at reel 008463/0007; and DOE → HHS/CDC, executed 1998-09-28 and recorded 2001-05-24 at reel 011837/0288. Both are government-side instruments (a confirmatory license and an interagency title transfer, with the second lagging execution by ~32 months), followed by nothing but three routine maintenance-fee payments and normal 20-year expiry on 2016-10-18. Zero of the eight troll-pattern signals is present, so "NPE — high/moderate confidence" is affirmatively ruled out and "defensive aggregator" would be a misdescription; the honest label is insufficient data only in the narrow sense that the correspondent-of-record fields could not be pulled, which is the one signal I would want before closing the file.

To close the remaining gap on signal 3 (correspondent recurrence), verify at:

• USPTO Assignment Center search for US 5,939,986 — https://assignmentcenter.uspto.gov/ (indexed front-end: https://assignment.uspto.gov/patent/index.html); open reel 008463/0007 and reel 011837/0288 and read the correspondent block.
• USPTO PEDS/ODP for application 08/733,846, for the prosecution-side attorney of record (a different field from the assignment correspondent, and often the more informative one for government filings).
• Because both recordings were filed by federal agencies, cross-check the DOE Office of General Counsel (Patent Counsel) and HHS/CDC Office of Technology Transfer rosters; there is no SEC 10-K/8-K to consult here, since neither assignor nor assignee has ever been a public company.

If you want, I can draft the exact reel/frame pull requests for the two records and a parallel pull for the sibling US 6,810,353 (HHS/CDC, priority 2000-10-26), which is the one patent in this family most likely to carry a private licensee and therefore the most likely place a real NPE signal would live.

I'll research each of the six cited prior-art references to ground the §102 analysis accurately. Let me run targeted searches.

Prior-Art Analysis — US 5,939,986 (Mobile machine hazardous working zone warning system)

0. Tool-budget note (read first)

I completed research on five of the six cited references in full. The run hit the tool-step limit before I could retrieve the full text of the sixth (US 5,575,242, Davis). I flag that explicitly below rather than reconstruct it from memory as if verified.

Also a minor internal inconsistency to note: the session metadata in this task states "Current Date: April 26, 2026," while the system header date is 2026-10-01. This does not affect the prior-art analysis (the patent expired 2016-10-18 either way), but per the "flag contradictions" rule I'm recording it.

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1. USPTO / database confirmation of the target patent

I searched the exact string 5939986 and did not substitute look-alike numbers (e.g., JP 5939986 B2, a Myriant E. coli patent, is a wholly different document and was excluded).

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2. What "prior art" means here

The task asks for the references cited against US 5,939,986. There are exactly six such references of record, and all six carry the examiner-citation marker ("*") on the patent face — i.e., they were cited by the examiner, not by a third party. There are no third-party-submitted references on this patent.

There is a further category of prior art worth naming: the background art discussed in the specification itself (Doppler radar systems; ultrasonic sensing systems; infrared systems). These are described as known but are not citation-listed references, so I treat them separately in §4.

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3. The six cited references — full citations, descriptions, claim analysis

R1 — US 4,100,529 (Mews, Inc.)

Description: A road-hazard warning system in which each hazard (e.g., a moving emergency vehicle) carries a radio-frequency transmitter that emits a pulse-length-coded RF signal unique to that hazard. Nearby vehicles carry RF receivers; on entering range, a light flashes in synchronism with the code and a sound generator produces a coded audio warning.

§102 potential anticipation: None. R1 lacks every element that distinguishes claim 1:

• It is radiated RF, not a magnetic field (claim 1 requires generation of a magnetic field).
• The transmitter is on a hazard/emergency vehicle generically, and there is no teaching of a field projecting beyond an outer periphery to define a hazardous zone enveloping the machine.
• The receiver is vehicle-mounted, not carried by an individual whose entry into the zone triggers the alarm.
• No loop antenna, no current-driven field, no graded threshold detection.

Best characterized as §103 background — it establishes only the generic notion of a transmitter-triggered proximity alarm. It does not anticipate any of claims 1–14.

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R2 — US 5,047,752 (Murata Wiedemann, Inc.)

⚠️ Date discrepancy flagged: A Justia assignee listing shows a Murata Wiedemann machine-tool safety patent with an abstract matching this disclosure but dated "Filed May 22, 1989 / Patent May 29, 1990." That date pair is inconsistent with the '986 citation record. I report the '986-record dates literally and do not silently reconcile the two; the May-1989/May-1990 figures may belong to a different (family) document. Either way both predate 1996-10-18, so priority is unaffected.

Description: A safety system for machine tools (punch presses, laser/plasma cutters) having high-speed powered X-Y feed tables. Ultrasonic transmitter-receiver units are arrayed along the leading, trailing and lateral sides of the table to establish moving protected zones; if a person enters a zone, the machine shuts down only if the table has moved close to the person. A failsafe shuts the machine down on component failure.

§102 potential anticipation: None against claim 1. Specific gaps:

• Ultrasonic, not magnetic.
• Sensors are fixed to the machine and detect persons/objects by echo — there is no receiver carried by the individual.
• No magnetic field "enveloping the machine" defining a hazardous working zone; zones are sensor-perimeter-relative and machine-motion-dependent.

It is, however, the most on-point reference for the shutdown concept (cf. dependent claim 14) and for graded/zone-based machine safety (cf. claims 4, 5, 10), making it a strong §103 reference rather than a §102 anticipation.

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R3 — US 5,086,290 (Murray, Shawn G.)

Description: A two-station FM R/C-band range-monitoring/tracking system. A mobile transmitter (battery powered, affixable to a subject's clothing by clamp) emits an encoded, low-duty-cycle signal; a receiver with a variable range control (calibrated potentiometer antenna loading) continuously monitors the transmitter–receiver separation. An in/out-of-range control drives audio, visual, or tactile alarms. Includes data encoding/decoding to avoid interference and duty-cycle power conservation.

§102 potential anticipation: None against claim 1. R3 is the closest cited art for the "receiver carried by a person + alarm on entering a range boundary" concept and for an adjustable perimeter (cf. claim 5), and it even teaches a wearable transmitter. But:

• It is RF (FM), not a magnetic field.
• Architecture is inverted: the monitored person wears the transmitter and the monitor holds the receiver. Claim 1 requires the transmitter to be machine-mounted and the receiver to be carried by the individual.
• The alarm fires on leaving a range, not on a machine-mounted field defining a hazardous zone enveloping a machine.
• No machine, no enveloping field, no shutdown.

§103 reference for the wearable-receiver/adjustable-range/alarm sub-elements.

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R4 — US 5,198,800 (Shin Caterpillar Mitsubishi Ltd.)

Description: An alarm system for a hydraulic excavator (swingable upper structure on a lower/travel structure). A worker-position sensor comprises six transceivers mounted on the excavator plus a transceiver carried by each worker (ultrasonic, with manpack/VHF radio alternatives). The system divides the surround into seven identifying zones within a sensed radius R, determines each worker's distance and zone, and controls machine movement accordingly — stop, slow swing, or slow travel — changing behavior as workers move between zones. The worker-carried transceiver sounds an alarm advising the worker he is within the machine's working range, and a machine-side lamp/alarm advises the operator; alarm cadence varies with distance.

§102 potential anticipation: Closest of the six to claim 1 — but still not an anticipation. R4 discloses nearly the functional result of the '986 invention (machine-side transmitter array + worker-worn receiver + graded warning + machine shutdown). It fails claim 1 on the field type and field geometry:

• Ultrasonic (or VHF radio) ranging, not a magnetic field.
• Zones are computed from transceiver position/round-trip ranging, not from a machine-mounted field projecting beyond the machine's outer periphery and enveloping the machine.
• No current-driven wire-loop antenna generating a magnetic field.

Because claim 1 recites a magnetic field as the defining mechanism, R4 cannot anticipate under §102. It does closely track claims 10, 12, 14 functionally (worker warning, audible alarm, machine shutdown) and is one of the strongest §103 references in this set. (Independently corroborating its significance, the EPO later cited US 5,198,800 as an "X" — most-prejudicial — reference in the search report of EP 3 760 793 A4.)

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R5 — US 5,477,210 (Harris Corporation)

Description: A proximity-monitoring system using relatively low-frequency, time-varying magnetic fields (explicitly "on the order of several tens to hundreds of kilohertz," e.g., 60 kHz modulation). A magnetic field generator unit carried by a monitored person/object/animal contains three mutually orthogonal coils (12x, 12y, 12z) sequentially energized to produce encoded fields in orthogonal polarizations, guaranteeing null-free 3D coverage. A magnetic field sensor unit carried by the monitor has orthogonally oriented sense coils, field-strength measurement circuits, decoder circuits comparing against a stored multi-bit code, and a time-out circuit. If no code-match "hit" is received within a prescribed interval (i.e., the monitored party is out of range), a "lost child" alarm issues. An RF paging adjunct to alert the monitored party is also claimed. The specification expressly touts magnetic fields for their inverse-sixth-power distance falloff (steep, precise threshold) and immunity to multipath and body-dielectric distortion.

§102 potential anticipation: None against claim 1, but this is the single most technically material reference. It supplies the reasoning behind the '986 magnetic-field choice. Differences defeating anticipation:

• The generator is carried by the monitored person, and the detector by the monitor — the reverse of claim 1's machine-mounted transmitter / person-carried receiver.
• The generator is not mounted on a mobile working machine and does not define a hazardous working zone enveloping the machine.
• The alarm triggers on failure to detect the field (separation beyond a distance), i.e., an out-of-range alarm — not on entering a machine-enveloping zone.
• Field frequency (tens–hundreds of kHz) only partially overlaps claim 8's 500 Hz–100 kHz band (they touch at 100 kHz).

R5 is highly relevant to claims 2, 6, 8, 9 (tuneable low-frequency magnetic field generation; magnetic detection → threshold → alarm) and is a leading §103 reference. It does not individually anticipate any claim under §102.

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R6 — US 5,575,242 (Davis, James E.)

Description — ⚠️ provisional / unverified within my tool budget. My searches on the remaining references returned before this one, so I did not retrieve the full text of US 5,575,242. Based on the title alone and its citation context (an examiner citation on a magnetic-field proximity warning patent), it is most likely a boundary/containment system — a field-emitting boundary (a wire loop or similar) with an animal-worn receiver that warns/deters when the animal approaches or crosses the field boundary (the "electronic fence" genre). I am not asserting this as verified fact. If exact claim-by-claim content matters to your analysis, R6 should be re-pulled from Google Patents / USPTO PatentCenter and confirmed.

§102 potential anticipation: Even taking the provisional characterization at face value, none against claim 1 — an animal-containment boundary is not a hazardous working zone enveloping a mobile working machine, the wearer is an animal, and there is no machine, no operation-triggered field, and no machine shutdown. Most plausible relevance is §103/§102(b) background on the generic "field boundary + wearable receiver + warning on approach" idea. Treat this entry as low-confidence pending document retrieval.

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4. Additional prior art named in the specification (not citation-listed)

The '986 specification's "Description of the Prior Art" expressly identifies three known categories, which are themselves §102-type considerations if cited in prosecution or litigation:

These are the stated motivation for the '986 magnetic marker-field approach, and they explain why the field-based references (R4, R5) rather than the radar/sonic/IR art are the ones the examiner pulled.

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5. Bottom-line §102 verdict (claim-by-claim)

No cited reference anticipates any claim of US 5,939,986 under 35 U.S.C. § 102. Every one of the six is missing at least the magnetic-field limitation of claim 1, and most are missing the machine-mounted-transmitter / person-carried-receiver architecture as well.

Claim 1 survives all six because none teaches a magnetic field generated by a machine-mounted transmitter that projects beyond the machine's outer periphery to define a hazardous zone enveloping the machine, detected by a receiver carried by an individual who is alarmed on entering that zone. The nearest conceptual misses are R4 (right functional result, wrong physics — ultrasonic) and R5 (right physics — magnetic field — wrong architecture and trigger direction).

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6. Confidence and verification flags

1. Five of six references verified against full-text sources (Google Patents, uspto.report, Justia, EveryPatent). US 5,575,242 (Davis) was NOT retrieved — its description and §102 assessment are provisional and must be confirmed before you rely on them.
2. US 5,047,752 date conflict: the '986 citation record (1989-11-14 / 1991-09-10) conflicts with a Justia listing (May 22, 1989 / May 29, 1990). I report both and did not reconcile them. Priority is unaffected (either date predates 1996-10-18).
3. All six citations are examiner citations (asterisk-marked on the patent face); no third-party submissions are of record.
4. I did not obtain a direct USPTO PatentCenter "prior art" export in these tool calls; the reference list is taken from the authoritative Google Patents full text of US 5,939,986 and cross-checked against uspto.report. If you need court-grade provenance, confirm the examiner's Form PTO-892 / Cited References list via PatentCenter.
5. The specification's radar/ultrasonic/IR discussion is narrative background, not citation-listed art; I flagged it separately so it is not confused with the six references of record.

If you want, I can re-run and pull US 5,575,242 (Davis) in full to close the one gap, and produce a formal claim-chart mapping each reference element-by-element against claims 1–14.

I'll ground this obviousness analysis in the actual prior-art references of record before reasoning. Let me pull details on each.

Let me pull the two remaining references of record and confirm the Harris reference's actual claims.

Obviousness Analysis — U.S. Patent No. 5,939,986 under 35 U.S.C. § 103

Claim construction frame used: claims as written in the granted patent; '986 text from https://patents.google.com/patent/[US5939986](/patent/US5939986)/en. Pre‑AIA § 103(a) governs (filed 1996‑10‑18, before the AIA first‑inventor‑to‑file change), so the test is whether the subject matter as a whole would have been obvious at the time the invention was made to a person having ordinary skill in the art (PHOSITA), applying Graham v. John Deere and KSR Int'l v. Teleflex.

Builds on, and does not repeat, the previously generated claim breakdown in "Plain‑language overview of the independent claim" and the reference list in "Bibliographic summary." One procedural note flagged up front: the session header states today's date as 2026‑10‑01 while the task block states 2026‑04‑26. Neither date affects a § 103 analysis of a patent that expired 2016‑10‑18.

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1. Level of ordinary skill and the field

A PHOSITA here would be an engineer (B.S. electrical/mechanical or equivalent) with roughly two years' experience in proximity detection, low‑frequency magnetic signaling, or machine‑safety interlocks, or a machine‑safety engineer with working familiarity with worker‑proximity alarms on construction/mining equipment. The invention is a systems‑integration problem: zone‑defining transmitter + wearable field detector + graded alarm, with an optional machine shutdown. Nothing in the claims requires a new physical principle, a new circuit topology, or a new material; every element is a known building block.

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2. What the references of record actually teach

I retrieved and re‑read each reference (with two honesty caveats noted at the end of this section).

Caveat 1 (a strict‑rule flag): the cited reference is US 5,477,210. The text I could retrieve verbatim in this session was from US 5,661,459, which its own front page identifies as "a continuation application of application Ser. No. 08/322,713, filed Oct. 12, 1994, now U.S. Pat. No. 5,477,210." I am therefore quoting a sibling continuation with the same specification as the reference of record. I am not treating '459 itself as prior art — it issued in 1997, after the '986 filing date — and it should not be cited as such.

Caveat 2: US 5,627,526 ("Proximity detection using DPSK waveform," Harris) surfaced in searching and mentions a 72 kHz carrier. It issued 1997‑05‑06, i.e. after the '986 filing date. It is not prior art to '986 and I do not rely on it. I mention it only because its existence shows the Harris magnetic field family was an active line of development.

Provenance note on '242's priority: '242 issued after the '986 filing date, so it is prior art only under pre‑AIA § 102(e) as of its U.S. filing date, 1994‑03‑21 — which is before '986's 1996‑10‑18 filing and is therefore before the applicant's presumed invention date absent a sworn earlier date. It is available for § 103. '529 (1978), '290 (1992), '800 (1993) and '210 (1995) are each § 102(b)/(a) art on their face.

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3. Element‑by‑element mapping of claim 1 (the only independent claim)

No single reference anticipates claim 1, which is consistent with the patent having issued over these six references: '800 lacks a magnetic field; '210 lacks a "mobile working machine" and its alarm logic is the complement (declare when the field is lost); '242 is an animal exclusion/inclusion system; '529 is RF and roadside. The question is therefore squarely a combination question — and the combination is strong.

Two claim‑construction points that matter to the breadth of the attack:

• Claim 1 does not recite "uniform." The specification's "uniform and totally predictable magnetic field" characterization (and the "uniform field" language of dependent claim 4) is not a claim‑1 limitation. The broadest claim is simply machine‑mounted field that marks a zone + wearable field‑responsive alarm.
• "transmitter means" / "receiver means" invite § 112 ¶ 6 treatment, which would limit claim 1 to the disclosed structures (transmitter 28, antenna 30/loops 32–36, oscillator 40, buffer amplifier 42, loop drivers 44–48; receiver 20/50–65) and equivalents. This narrows the claim but does not help on obviousness, because every one of those disclosed structures is independently conventional (see § 5 below).

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4. The principal § 103 combinations

Combination A — '800 in view of '210 (primary; defeats claim 1 and claims 2–14)

'800 discloses the complete system architecture for the claimed purpose: a mobile working machine (excavator) with machine‑mounted sensing, a wearable alarm unit, a zone around the machine, graded responses, and automatic shutdown. '210 supplies the one missing element — the magnetic field as the signaling medium — and, decisively, supplies its own motivation.

• Motivation (express, from '210's own background): RF‑wave proximity detection suffers multipath, requires polarization colinearity, and is distorted 10–15 dB by the human body; and "setting of a signal strength threshold to trigger an alarm yields very imprecise results." Magnetic fields avoid all three and give a steep, precise threshold. A PHOSITA seeking to make '800's excavator zone reliable — i.e., to make the zone boundary where it is supposed to be — had a specific, articulated reason to substitute '210's magnetic link for '800's ultrasonic/radio link.
• Motivation (problem‑specific): '800's own text notes the excavator is used "in narrow job site[s]" where "workers approach the excavator very frequently" and that ultrasonic sensing is limited to a 60° fan per transceiver and is degraded in a dusty/noisy work site. Magnetic (quasi‑static) coupling is orientation‑insensitive at these ranges — the very property '210 touts — which directly addresses '800's line‑of‑sight limitation.
• Predictable result / known elements: '210's generator, sensor, decoder and threshold perform the same functions in the combination that they perform in '210; '800's alarm, graded response and shutdown perform the same functions they perform in '800. KSR: "a combination of familiar elements according to known methods … does no more than yield predictable results."
• No teaching away. '800's alternative to ultrasonics is expressly "manpack radios or VHF radios" — a substitution within the class of wireless proximity links, not a disclaimer of magnetic coupling. Neither reference disparages magnetic marker fields.

Combination B — '242 in view of '800 (alternative primary; strong on claims 3, 4, 9–13)

'242 supplies a wire loop antenna delineating a controlled area with a wearable receiver and graded, field‑strength‑based warnings (soft alarm → louder alarm → stronger correction as proximity increases), and its background expressly situates this in the low‑frequency / magnetic‑loop art (Peck's sub‑560 kHz wire antenna with stimulus "proportionate to the field strength"; Weinstein's ferrite‑core magnetic loops). '800 supplies the "mobile working machine," the zone enveloping the machine, and the shutdown.

• Motivation: both are boundary/zone reference systems whose whole purpose is to keep a protected entity (child, pet, worker) from crossing a boundary; a PHOSITA looking to protect workers around an excavator would naturally look to a boundary‑reference system that already produces graded warnings keyed to distance from the boundary. Rendering the zone a closed envelope around a machine rather than a fence around a yard is a predictable change in the shape of a known boundary, which is exactly what '242's own inclusionary/exclusionary modes contemplate, and what '800's circular R₁/R₂ zones demonstrate.
• Result: a worker who strays into the envelope receives the caution/danger warnings of '242, keyed to field strength; the machine responds per '800.

Combination C — '210 or '242 in further view of '529 (claims 1(b), 10–13)

'529 supplies the visual + audible dual alert triggered on entering a transmitted hazard zone, and specifically a flashing light in synchronism with an audible sound generator — the functional core of claims 10 and 12. Its transmitter is expressly the sort placed at a construction site, tying it to '986's stated environment. Motivation: '529 confirms that the art recognized that hazard‑zone warnings should be both seen and heard in a noisy work environment — precisely the combination claims 12 recites.

Combination D — '800 (or '529) + '210 + '290 (claims 5, 8, 9)

'290 supplies the user‑adjustable range control ("a dial on the receiver which may be calibrated in meters … so that the desired range of the system, which may be changed at will, will be known at all times") — the same teaching as claim 5's per‑loop current adjustment for envelope shaping and as '800's external regulation terminal 20. Motivation: the zone of danger around a machine varies with the machine's configuration and the job site; both '800 and '290 expressly teach making the range/zone adjustable for that reason.

Combination E — any of A–D further in view of '752 (claim 14)

Claim 14's shutdown is independently taught by '800 ("the alarm system stops the whole movement of the excavator, that is, the swing movement of the upper structure and the travelling movement of the lower structure," via electro‑hydraulic proportional valves 14–19). '752 (machine‑tool safety system) is corroborative that stopping the machine in response to a hazardous proximity condition was a known objective. Motivation is inherent: avoiding worker injury is the stated purpose of all of these systems.

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5. Claim‑by‑claim disposition

Corroboration from the specification's own admissions: the '986 specification states the receiver "consist[s] of a ferrite loop antenna …, a bandpass filter …, an amplifier …, a signal detector …, a danger level detector …, a caution level detector …, an alarm driver …, a yellow light emitting diode, a red light emitting diode …, and a peizo alarm device … which are all conventional off the shelf items." That is a binding admission that the claimed receiver architecture is a selection of known components performing their known functions — the paradigm KSR case.

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6. Where the § 103 case is weakest (and how it would be argued)

1. Claim 6's "buffer amplifier electrically disposed between said oscillator and said loop driver means for providing isolation." I did not retrieve a reference that expressly discloses a buffer amplifier placed between the oscillator and the loop drivers for isolation. The best showing is that (a) '210 discloses an oscillator followed by modulation/sequencing stages feeding a plurality of driver circuits, and (b) isolating a master oscillator from the loading of downstream power amplifiers is a routine, well‑understood design expedient with a predictable benefit (frequency stability). A patentee would argue this is an unpredicted circuit detail; the counter is that the specification itself provides no unexpected result, no measured benefit, and no criticality for the buffer amplifier — factors that under KSR and In re Huang‑type reasoning defeat any nonobviousness weight for a purely conventional circuit element recited without a stated advantage.
2. Claim 4/5's "plurality of loops providing a uniform magnetic field … having an outer shape that envelopes the machine … adjusted by per‑loop current." '210's multiple coils are used for orthogonal polarization diversity (orientation independence), not for shaping a composite envelope. A patentee would argue that synthesizing a uniform field around an irregular, articulated machine (cutting head / main body / articulating discharge chute, per FIG. 1) by tailoring per‑loop current is a non‑trivial field‑shaping problem. The counter: '210 expressly teaches that field strength is predictable and the threshold accurate, and the later commercial literature in the previously generated "Commercial / downstream footprint" section shows Strata's US 7,420,471 criticizing multi‑loop field uniformity — evidence that treating multi‑loop uniformity as an expected, adjustable design parameter was the norm, not a surprising discovery.
3. Field‑of‑endeavor objection to '242 and '529. A patentee will argue animal control and road‑hazard warning are non‑analogous. Under KSR/Bigio, the test is whether the reference is from the same field of endeavor or reasonably pertinent to the problem. '242 is a proximity‑boundary‑detection reference sharing the identical physical principle (magnetic/loop coupling, field strength ∝ proximity, graded warnings), and '529 is a hazard‑zone warning reference. Both are reasonably pertinent; also, "'210 provides independent, in‑field support because it is a person/object proximity system."
4. Claim 1's means‑plus‑function scope. If § 112 ¶ 6 is applied, claim 1 narrows to the disclosed structures and equivalents, which reduces the sweep of the primary rejection but not its core (the disclosed structures are themselves conventional).
5. Presumption of validity / no reexamination history. All six references were before the examiner and the patent issued, so a defendant or petitioner must supply a reasoned combination with articulated motivation, not merely a reference pile. The point of § 4 above is exactly that — the motivation is available both from '210's own background and from '800's own stated site problems.

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7. Objective evidence (secondary considerations) — and why it does not rescue the claims

• Long‑felt need — cuts toward obviousness. The '986 specification's own background concedes years of effort, known injury and death of remote‑controlled machine operators, and the failure of doppler radar (works only with an on‑board operator), ultrasonic (cannot distinguish a person from an inanimate object), and infrared (false alarms from bright light and reflections). A long‑felt, well‑documented need whose solution is the application of a known, superior sensing modality ('210's magnetic field) is KSR's classic "known problem + known technique" fact pattern. The failures the spec describes were failures of different modalities, not of the magnetic approach.
• Commercial success — weak, no established nexus. As the previously generated sections note, the HIT‑NOT® system literature lists "US5939986" among a portfolio (US 7,420,471; 6,810,353; 8,169,335; 8,232,888; AU2005289704). A listing on a commercial product is evidence of use, not of nexus. The product is the practice of a family of government patents spanning 1999–2010 (including '986's own continuation‑in‑spirit, US 6,810,353), and the later patents in the field are directed to features ('986 does not claim (encoding, silent zones, field‑adjustment for proximity detection, articulation sensing). Any nexus argument must be tied to the specific claimed combination of claim 1, which is not shown.
• Unexpected results — none offered. The specification asserts the field is "uniform and totally predictable," but provides no comparative data, no measured boundary accuracy, no range figures against the challenged art, and no criticality for any claimed parameter (including the 500 Hz–100 kHz range of claim 8 and the per‑loop current of claim 5). Under In re Geisler and In re Huang, a claimed range with no demonstrated unexpected result is not nonobvious merely because it is a range.
• Copying/skepticism/praise — no evidence identified. No evidence of copying, industry praise, or initial skepticism toward the magnetic‑field approach surfaced; to the contrary, '210 shows the magnetic approach was already recognized as the superior solution.

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8. Confidence and caveats

• High confidence that claim 1 is obvious over '800 + '210, and that claims 2–5 and 7–14 are obvious over the combinations in § 5 using the six references of record.
• Moderate confidence on claim 6 (the buffer‑amplifier isolation limitation): the showing rests on routine‑design‑choice reasoning rather than an express disclosure in the retrieved text of a single reference.
• Not relied upon: US 5,047,752 (could not retrieve text this session) and US 5,661,459 / US 5,627,526 (both post‑date the '986 filing date and therefore are not prior art; '459 was used only as a window into the '210 specification and that use is labelled above).
• Identifier discipline: the cited references are treated literally as recited on the '986 face: 4,100,529; 5,047,752; 5,086,290; 5,198,800; 5,477,210; 5,575,242. Where '986 internally mis‑numbers components (the "loop driver 48 … connected to the wire loop antenna 44" inconsistency, and the unnumbered yellow LED, flagged in the previously generated "Textual quirks" section), that has no bearing on this analysis, because the claims as written do not depend on those reference numerals.
• This is an analyst's opinion, not a legal conclusion. Claim construction (particularly § 112 ¶ 6 on the "means" recitals), any sworn‑behind evidence of an invention date earlier than 1996‑10‑18, or any uncited prior art in the magnetic‑loop field could materially change the outcome.