US 5172056

I'll verify this against live sources before summarizing.

Let me do two more targeted checks on litigation/CAFC activity.

US Patent 5,172,056 — Verification Summary

Search scope note: I searched for the exact number 5172056 in connection with USPTO and CAFC 2026 dockets. I found no CAFC 2026 docket, appeal, or district court litigation naming US 5,172,056. I also found no 2026 PTAB proceeding. Because I could not query Docket Navigator / PACER / CourtListener directly from here, this is a negative search finding, not authoritative confirmation that no such proceeding exists. The number 5172056 does appear in unrelated contexts (a Brazilian appellate case number, a UK bankruptcy order, a Florida FEI number, a CourtListener docket-entry ID) — those are coincidental matches and not this patent.

Bibliographic Data (from the patent text and Google Patents)

Assignee caveat: The patent's own front-matter/assignment data lists Sextant Avionique, while Google Patents lists the current assignee as Thales Avionics SAS. These are consistent with a later corporate renaming/acquisition rather than a contradiction, but I have not independently verified the chain of title. Note also that several later patents citing this one render the inventor's name as "Voision" — that is a typographical error in the citing documents; the correct spelling is Voisin.

Abstract (verbatim)

"The radiator and the sensor each comprise three pairs of Helmholtz coils which are disposed along three orthogonal axes respectively. The coils are wound in pairs of grooves which have different depths and are recessed in a cubic support. The radiator and sensor are particularly useful for helmet-type viewfinders."

Independent Claims — Plain Language

Claim 1 — the radiator (transmitter)
A magnetic-field transmitter for position/orientation tracking, comprising:

• a support (e.g., a cube) with two mutually orthogonal symmetry axes;
• a first pair of Helmholtz coils on the first axis, and a second pair on the second axis;
• each pair has roughly the same number of circular turns (so each pair is a thin disc-like winding), the same average turn radius and diameter, and a winding thickness smaller than its diameter;
• each pair sits in two parallel planes spaced apart along the axis by an axial distance approximately equal to that average turn radius (the Helmholtz condition).

Claim 8 — the sensor (receiver)
Word-for-word the same structure as claim 1, but claimed as a magnetic-field sensor for receiving the field. This is the "unexpected application" the specification emphasizes: Helmholtz coil geometry used as a point-like receiver, not merely as a field source.

Claim 15 — the combined arrangement
A complete position/orientation system: a radiator (support with two orthogonal axes + a pair of Helmholtz coils on each) transmitting toward an object, plus a sensor mounted on the object (its own support with two orthogonal axes + a pair of Helmholtz coils on each). The Helmholtz geometric limitations (equal turns, equal average radius/diameter, thickness < diameter, plane spacing ≈ average radius) apply to all four coil pairs on both supports.

Dependent claims (2–7 radiator; 9–14 sensor): add a third orthogonal axis/coil pair; cube of non-magnetic material; coils seated in three pairs of grooves; grooves of different depths; symmetric arrangement about each axis; coils fully contained within their grooves.

Technical Point of the Invention

The specification frames the problem as conformance to dipole theory. Prior radiators/sensors did not behave as true point dipoles, which broke the rotation-invariance of the measurement matrix product MRTMR used for cartography-based pose recovery. The inventors show (FIGS. 1–2) that among planar coil pairs of varying diameter, only the pair satisfying the Helmholtz condition (plane separation = average radius) yields ~zero field-modulus error (εm) and ~zero angular orientation error (δ) versus an ideal dipole. A stated commercial benefit for the radiator is interchangeability — swapping radiators without re-running a cartography, since the point-like fields can be corrected by mixing transmissions across the three axes.

A practical detail worth flagging: in the sensor embodiment, the smallest coil pair is so small that both windings occupy a single groove and physically merge into one coil; the Helmholtz condition is then met "on the level of the two middle turns."

Sources Consulted

• Google Patents full text: https://patents.google.com/patent/US5172056/en
• USPTO.report grant record: https://uspto.report/patent/grant/5172056
• FR family member: https://patents.google.com/patent/FR2665530B1/en
• Citing patents confirming the 1992-12-15 date and inventor (as "Voision"): https://patents.justia.com/patent/[6266551](/patent/6266551), https://www.freepatentsonline.com/[7558616](/patent/7558616).html

Uncertainties to note: (1) no litigation/CAFC 2026 record could be located — absence of evidence, not proof of absence; (2) the Sextant Avionique → Thales Avionics assignee transition is unverified; (3) the patent expired 2011-08-02, so any current enforcement activity would be unlikely but is not ruled out by my searches.

I'll search for litigation involving US patent 5172056 across several sources.

Initial searches returned mostly coincidental matches (a bankruptcy case number, phone numbers, an FEI number, a Brazilian civil case). Let me search litigation-specific databases.

Let me try litigation-specific databases directly.

Litigation Search Report — U.S. Patent No. 5,172,056

Patent identified: US 5,172,056 A (application US 07/740,010)
Title: "Magnetic field transmitter and receive using helmholtz coils for detecting object position and orientation"
Inventor: Gerard Voisin
Assignee/current owner: Sextant Avionique (original); Thales Avionics SAS (current listed assignee)
Priority: 1990-08-03 (FR 9009955) · Filed: 1991-08-02 · Granted: 1992-12-15 · Status: Expired – Lifetime (anticipated expiration 2011-08-02)

Finding: No litigation found

I searched for litigation specifically involving U.S. Patent No. 5,172,056 and found none. No district court action, ITC Section 337 investigation, CAFC appeal, PTAB proceeding (IPR/PGR/CBM), or foreign counterpart proceeding was identified that asserts or challenges this patent.

What the searches returned (all coincidental — not this patent)

Every hit for the string "5172056" was an unrelated use of that numeric string, and I note these explicitly so the negative result is verifiable:

Corroborating signals from the patent record itself

• The Google Patents full-text record for US5172056A contains no "Litigation" section (Google Patents surfaces litigation data, sourced largely from Docket Navigator/Unified Patents, only when cases exist). The provided authoritative text shows only Citations (11), Cited By, and Legal Events — no litigation entries.
• The Legal Events log shows only routine prosecution/assignment/fee-payment events (assignment to Sextant Avionique 1991-11-04; maintenance fees at years 4, 8, and 12). No reexamination, no IPR, no interference.
• The patent expired in 2011 for failure to pay the 20-year maintenance fee, and any damages window is long closed — consistent with never having been asserted.
• It is, however, heavily cited by later electromagnetic-tracking patents (44 "Cited By" entries from Biosense, Ascension, GE Medical Systems, TDK, etc.), meaning it is prior art of significance even though it was never litigated. Not to be confused: the extensive litigation involving Biosense/GE/Ascension tracking patents is on those patents, not on '056.

Confidence and limitations

• High confidence that no U.S. patent litigation involving US 5,172,056 exists in the public record, based on the absence of any litigation entry in the patent's own record and the absence of any genuine match across the litigation-focused searches performed.
• Caveat: I was unable to directly query Unified Patents' litigation portal, PACER, or Docket Navigator by patent number within this session (the tool required a literal string match that was dominated by the unrelated hits above). If a definitive, database-verified negative is required for a legal opinion, that should be confirmed with a direct Docket Navigator / Lex Machina / PACER patent-number query.

Bottom line: No plaintiff, defendant, jurisdiction, case number, filing date, or outcome can be reported, because no litigation involving U.S. Patent No. 5,172,056 was found. The correct answer is that no litigation is known.

I'll verify the absence of PTAB proceedings with targeted searches before finalizing.

Let me run a couple more targeted checks for any challenge activity or litigation involving this patent family.

One more check on the litigation history and any Unified Patents–style challenge, since the Fed. Cir. case Sextant Avionique v. Analog Devices surfaced.

PTAB / AIA Trial Analysis — U.S. Patent No. 5,172,056

Patent: Magnetic field transmitter and receive using Helmholtz coils for detecting object position and orientation
Inventor: Gerard Voisin · Original assignee: Sextant Avionique (now Thales Avionics SAS)
App. No.: 07/740,010 · Priority: 1990-08-03 (FR 9009955) · Filed: 1991-08-02 · Granted: 1992-12-15
Legal status: Expired – Lifetime · Expiration: 2011-08-02 (20-year term)
Family: EP0469967B1, DE69108813T2, JP3380263B2, FR2665530B1

Proceedings overview

Total AIA trial proceedings on file: 0. No IPRs, no PGRs, and no CBM reviews — zero active, zero claims invalidated by the Board, zero claims sustained, zero settlements, zero institution denials. The structured PTAB proceedings block for this patent is empty, and targeted web searching surfaced no IPR/PGR/CBM petition, institution decision, Final Written Decision, or PTAB appeal naming U.S. Patent No. 5,172,056. The defendant's posture is therefore not "hardened patent" or "dead claims" so much as "no PTAB terrain exists and none can be created" — the patent expired 2011-08-02, more than a year before inter partes review became available on 2012-09-16, so an AIA trial was never legally possible against it. The far more consequential fact for anyone receiving a demand letter is the expiration date, not the Board's docket.

Per-proceeding detail

No proceedings to report

There is no PTAB proceeding to itemize. For completeness, here is what the negative finding rests on:

• Type: N/A — no AIA trial of any kind (IPR, PGR, or CBM).
• Filed / Status / Panel / Grounds / Institution / FWD / Settlement / Appeal: N/A on every field. I will not manufacture a proceeding number; none exists.
• Why structurally impossible: Under 35 U.S.C. §§ 311(c) and 321(c), an IPR or PGR petition may only be filed after the later of 9 months from grant or termination of any PGR — for the '056 patent, that window had long closed. More decisively, the patent term ran out on 2011-08-02, and AIA trials did not exist until 2012-09-16. PGR was additionally unavailable because the patent issued under pre-AIA law on 1992-12-15.
• Related-but-different Federal Circuit activity (flagged so you don't chase it): The only Sextant Avionique patent appeal that surfaced in searching is Sextant Avionique, S.A. v. Analog Devices, Inc., 172 F.3d 817 (Fed. Cir. 1999) — a district-court appeal under 28 U.S.C. § 1295(a)(1), not a PTAB appeal, and it concerned U.S. Patent Nos. 4,663,927 (Marcillat) and 4,711,128 (Boura), accelerometer patents unrelated to the '056 Helmholtz-coil subject matter. See https://www.courtlistener.com/opinion/[762837](/patent/762837)/sextant-avionique-sa-v-analog-devices-inc-defendant-cross-appellant/. It is not authority about the '056 patent and should not be cited as such.
• Other post-grant avenues: No ex parte reexamination, inter partes reexamination (pre-AIA), EP opposition outcome, or JP invalidation trial naming this patent surfaced in searching. I am not representing these as exhaustively confirmed — I am representing that nothing appeared, and that any such record would have to be confirmed on the USPTO public/assignment file and the EPO register for EP0469967B1 directly.

Defensive value: Zero PTAB estoppel exists in either direction. There are no canceled claims to point at, but there is also no surviving-claim roadmap you need to litigate around — the patent's own term is the defense.

Strategic summary

Claim-by-claim status: all 15 claims UNTESTED at the PTAB, and all 15 claims EXPIRED. Because no AIA trial was ever filed, none of claims 1–15 was canceled, disclaimed, or affirmed by the Board — there is no FWD to quote and no claim-level disposition to report. What is decided is the term: the patent's 20-year term from the 1991-08-02 filing ran to 2011-08-02, consistent with the "Anticipated expiration 2011-08-02" entry and the "Expired – Lifetime" status, and with the maintenance-fee record (year-4 fee paid 1996-05-20; year-8 paid 2000-05-09; year-12 paid 2004-05-26 — all three 3.5/7.5/11.5-year fees satisfied). Accordingly, any damages for infringement of claims 1–15 could only reach acts before 2011-08-02, and 35 U.S.C. § 286's six-year lookback closed the damages window by roughly 2017. Practically: claims 1–15 are all "untested," but that is academic — none of them can support prospective relief against conduct today, and no combination of claim numbers (1–2 or 8–9 radiator/sensor pairs, 3/10 cube support, 4–7/11–14 groove limitations, or claim 15's radiator-plus-sensor arrangement) revives them.

Estoppel landscape: essentially empty. With no petitioner, there is no § 315(e)(2) or § 325(e)(2) estoppel barring anyone from raising prior-art grounds, and no § 325(e)(1) estoppel against the patent owner in the Office. Any defendant could theoretically have run § 102/§ 103 over, e.g., the reference the specification itself cites — FR-A-2 458 838 / FR 79 14441 (the Sextant helmet-sight system the patent distinguishes) — or over the prior-art patents the examiner actually cited, namely U.S. Pat. Nos. 3,439,256 (Merckle), 3,800,213 (Develco), 4,247,120, 4,287,809 (Honeywell helmet-mounted sighting system), 4,314,251 (The Austin Company), 4,396,885 (Thomson-CSF), 4,642,786, 4,829,250 (Honeywell), 4,849,692 and 4,945,305 (Ascension Technology), and 5,047,715 (Morgenstern, "equal area of turn cross-section" coils). Note the examiner's citation of Morgenstern — an electromagnetic position-measurement patent about equal-area coil turn cross-sections — is the closest thing to a material prior-art near-miss in the file and would be the obvious starting point for an invalidity theory. But since the patent is expired and off the assertion market, that work is only worth doing if a demand letter is actually directed at pre-2011 conduct and you need an invalidity counterweight in a live suit that was already timely filed.

Pattern signals: absent. There is no repeat petitioner (there are no petitioners), no patent owner PTAB-appeal pattern (the patent owner never appeared before the Board), and no defensive aggregator such as Unified Patents in the chain — a Unified-type challenge would make no sense against a patent that expired before IPR existed. Thales Avionics SAS appears as current/listed assignee, inherited from Sextant Avionique / Thomson-CSF lineage; there is no recorded assignment or post-grant contest activity of substance after the 1991-11-04 assignment to Sextant Avionique.

Recommended next steps

1. Treat the expiration date, not the PTAB docket, as the controlling fact. The prima facie defense to any current demand is that U.S. Patent No. 5,172,056 expired 2011-08-02 and cannot be infringed by post-expiration conduct. Demand-letter practice built on claims 1–15 should be rebutted on that basis first, before any validity analysis.
2. If the letter targets pre-2011-08-02 conduct, do not look to the Board for help — there is no FWD to link and no canceled claims to quote. Build the defense on (a) § 286's six-year damages bar and any laches/notice posture, and (b) invalidity over the cited prior art, with U.S. Pat. No. 5,047,715 (Morgenstern) and FR-A-2 458 838 as the lead references to develop.
3. There is no active proceeding, so there are no trial milestones to calendar — no institution deadline, no oral hearing, no statutory one-year FWD date. Nothing is pending on the PTAB docket for this patent at USPTO PTAB E2E (https://ptab.uspto.gov/).
4. If you need to confirm the negative finding on the record, verify directly rather than relying on secondary sources: USPTO Patent Center / PTAB E2E for trial numbers naming the '056 patent, the USPTO assignment record (Reel 005914 / Frame 0594), the EPO register for EP0469967B1 (opposition history), and J-PlatPat for JP3380263B2. My searches found nothing on any of these fronts, but absence of results in a web index is not the same as a certified Office record check.
5. If a case is live and this patent is a "related matter" in a co-pending IPR against a family member, note that no such family IPR was identified — the EPO/DE/JP counterparts (EP0469967B1, DE69108813T2, JP3380263B2, FR2665530B1) also showed no challenge activity in the searches performed.

Bottom line for a defendant: there is no PTAB story on US5172056 — and that is expected, not suspicious. The patent expired 2011-08-02, before AIA trials existed. You get no canceled claims to wave at a plaintiff, but you also face no live patent right: the strongest and simplest response to any assertion of this patent is the expiration of its term.

I'll research the assignment chain, corporate history, and any NPE connections before writing the report.

Let me dig further into the assignment records for this patent family and the corporate name changes.

Let me check for recorded name-change assignments covering the Sextant Avionique portfolio.

Assignment & Ownership Analysis — U.S. Patent No. 5,172,056

Patent: US 5,172,056 A · "Magnetic field transmitter and receive using helmholtz coils for detecting object position and orientation"
Application: US 07/740,010 · Priority: FR 9009955 (1990‑08‑03) · Filed: 1991‑08‑02 · Granted: 1992‑12‑15 · Expired: 2011‑08‑02
Family: FR2665530B1 · EP0469967B1 · JP3380263B2 · DE69108813T2

Note on method: The authoritative full text supplied for this patent exposes the assignment only through its Google Patents "Legal Events" table and bibliographic fields. Where a field the task asks for (correspondent of record) is not present in that data, I say so rather than invent it.

Inventors

Observations:

• No co-inventors. No inventor named outside France.
• No unusual departure pattern detectable. There is no record of Voisin assigning to anyone other than the employer, and no data in the patent record indicating inventor departures. I found no evidence of a portfolio fire‑sale dynamic originating with the inventor.
• The assignment is a routine employee/employer confirmatory assignment: French priority filed 1990‑08‑03 → US filed 1991‑08‑02 → inventor assigns to employer executed 1991‑10‑02. This "file first, paper the assignment later" sequence is standard and not a signal.

Original assignee

Entity named as assignee on the issued patent: Sextant Avionique (per recorded assignment Reel 005914/0594, and per the FR counterpart FR2665530B1, listed to "Sextant Avionique").

• Line of business: French avionics equipment manufacturer — formed 1989 from the merger of Crouzet, EAS (an Aerospatiale subsidiary) and SFENA with the general avionics division of Thomson‑CSF. Ownership at formation: Thomson‑CSF ~66%, Aerospatiale ~34%. Products included flight‑deck electronics, flight management systems, helmet‑mounted sighting/viewfinder systems, and inertial/sensor equipment — i.e. exactly the helmet‑viewfinder application recited in the '056 spec.
• Did they ship a product embodying the claims? Yes, in substance. The patent itself is directed to the transmitter/receiver pair for a helmet‑type viewfinder, which is a core Sextant Avionique product line (helmet‑mounted sighting systems for aircraft and armour). I did not locate a specific commercial part number in the record, so the "shipped a product" call rests on the company's product line and the patent's own stated application, not on a documentary product identification.
• Current status — operating, and not dissolved or bankrupt. Sextant Avionique was renamed through a corporate chain, not sold off patent‑by‑patent:
  • Aerospatiale divested its stake (~1998–99) → Sextant became a 100% Thomson‑CSF subsidiary and was renamed Thomson‑CSF Sextant.
  • Thomson‑CSF renamed itself Thales (~2000); the avionics entity became Thales Avionics SA.
  • ~2016: Thales Avionics absorbed three other Thales subsidiaries and was renamed Thales AVS France SAS.
  • 2023: Safran Electrical & Power acquired the electrical‑systems activity of Thales Avionics (≈600 staff) — a carve‑out of a business line, not a transfer of this patent.
  • Today the entity is a subsidiary of Thales Group (public, Euronext Paris), ~6,200 staff in Thales Avionics. Thales is an operating defence/aerospace prime, not a licensing vehicle.
• Prior assertion activity (context, different patents): The original assignee did litigate — Sextant Avionique, S.A. v. Analog Devices, Inc., a Federal Circuit doctrine‑of‑equivalents/prosecution‑history‑estoppel decision widely covered around 1999. That case did not involve US 5,172,056 (the '056 patent was never asserted and shows no litigation entry in its record). I flag it only to show the owner is an operating company with real enforcement experience, not a passive holder.

Assignment timeline

Recorded assignment — found (1 record)

• 1991‑10‑02 (executed) / recorded 1991‑11‑04 — Reel 005914/0594
  • Conveyance: Assignment (ASSIGNMENT OF ASSIGNORS' INTEREST)
  • Assignor: Voisin, Gérard (sole inventor, individual)
  • Assignee: Sextant Avionique (Vélizy‑Villacoublay / Meudon‑la‑Forêt, France)
  • Correspondent: Not available in the authoritative record retrieved. The Google Patents legal‑events table exposes the reel/frame and the assignor/assignee but not the recording attorney or agent. I therefore cannot attest to any correspondent name, firm, or address for this reel/frame, and I make no repeat‑correspondent finding for it. (This field should be pulled directly from USPTO Assignment Center if a correspondent‑based NPE screen is required.)
  • Context: Ordinary employee‑inventor → employer confirmatory assignment, executed ~14 months after the French priority filing and ~2 months after the US filing. This is the only conveyance recorded against the patent.

Later transfers — NOT evidenced as recorded USPTO assignments

The Google Patents bibliographic box shows "Current Assignee: Thales Avionics SAS" and likewise lists Thales Avionics SAS as "Original Assignee." This is Google's name‑harmonization, not a second recorded assignment. The patent's own legal‑events log contains no re‑assignment, no Change‑of‑Name recordation, and no Security Agreement after the 1991 filing. The Sextant Avionique → Thomson‑CSF Sextant → Thales Avionics → Thales AVS France progression is a corporate name change inside the Thales group, supported by corporate‑history sources, and appears in the patent record only as a change in how the owner's name is displayed.

I did not find a recorded USPTO assignment (with reel/frame) effecting any of these name changes for the '056 patent. If one exists, it is not in the data set supplied and I will not fabricate a reel/frame for it.

Section status

The Assignment Center does have a record for this patent — the single 1991 inventor→employer assignment above. There is no post‑issuance assignment chain. Per the task framing, the absence of further records is itself the finding: the original operating‑company assignee (and its corporate successors) retained ownership throughout the patent's life.

Timeline diagram

timeline
    title Ownership of US 5172056
    1990 : FR priority application filed
    1991 : US application filed
         : Voisin assigns to Sextant Avionique
    1992 : US patent granted
    1998 : Aerospatiale exits Sextant stake
    1999 : Entity renamed Thomson CSF Sextant
    2000 : Thomson CSF group renamed Thales
    2001 : Division renamed Thales Avionics
    2011 : Patent expires for want of fee

(1998/1999/2000/2001 rows are corporate name‑change dates from company‑history sources, not recorded USPTO assignments; ±1 year precision. See caveat above.)

NPE / troll‑pattern signals

No signal is present. One signal is unassessable (correspondent field not in the record).

Verdict

Insufficient data (no records, or only the original assignment).

Applying the rubric literally: the chain contains only the original assignment — Voisin → Sextant Avionique, executed 1991‑10‑02 and recorded 1991‑11‑04 at Reel 005914/0594 — followed by nothing but intra‑group name changes that were not recorded as assignments. That is exactly the rubric's "Insufficient data" trigger, and it should be read here as "no NPE chain exists to assess," not as genuine ambiguity about ownership: the patent and its family (FR2665530B1, EP0469967B1, JP3380263B2, DE69108813T2) stayed with Sextant Avionique and its successor Thales Avionics, an operating avionics prime, and expired for failure to pay the 20‑year fee on 2011‑08‑02. Zero of the eight NPE signals are present; the sole unassessable item is the correspondent field, which the record does not expose. On the available evidence this is a clean operating‑company ownership story with no troll signature.

Verify at:

• USPTO Assignment Center (search "5,172,056"): https://assignmentcenter.uspto.gov/
• Legacy USPTO Patent Assignment Search: https://assignment.uspto.gov/patent/index.html
• Google Patents legal events (the source of Reel 005914/0594 above): https://patents.google.com/patent/US5172056/en

Outstanding items a definitive opinion would require: (a) pull the recording attorney of record for Reel 005914/0594 from Assignment Center to close out Signal 3; (b) confirm directly in Assignment Center whether any Change‑of‑Name recordation for the Sextant Avionique → Thales Avionics progression touches this patent — I could not confirm one and did not assume one.

Consistency check vs. prior section: this report agrees with the earlier litigation finding that no suit asserts the '056 patent. One possible cross‑reference to watch: the earlier section notes heavy citing by Biosense/GE/Ascension tracking patents; that citation activity is prior‑art significance only and involves no ownership overlap with this chain, so it does not alter the verdict.

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

USPTO Record Check and Prior-Art Analysis — US 5,172,056

1. Record verified

The literal-number search on 5172056 returned one and only one U.S. patent record (the previously generated summaries are confirmed and not contradicted — no conflicting data appeared):

Sources: https://patents.google.com/patent/US5172056/en · https://uspto.report/patent/grant/[5172056](/patent/5172056) · full-text PDF http://patentimages.storage.googleapis.com/f8/0e/0d/979e87c8c2ae79/US5172056.pdf

No contradiction with the earlier sections. One clarification to flag for the file: the earlier litigation section's negative finding is consistent with this citation set — the reference list is a prosecution-era citation list (11 references), which is what one would expect for an uninterfered, unlitigated patent.

2. Legal framework applied

Because US 07/740,010 was filed 2 August 1991, the pre-AIA version of 35 U.S.C. §102 governs. The date each reference must beat depends on the subsection:

• §102(a): reference must predate the applicant's invention date (on this record, at latest the 1990-08-03 FR priority date).
• §102(b): reference must be patented or described in a printed publication more than one year before the U.S. filing date → critical date 1990-08-02. Note that under MPEP 2133.01 a §119 foreign priority claim cannot remove a §102(b) statutory bar, so the critical date is measured from 1991-08-02, not from 1990-08-03. This is a 2-day margin that matters below.
• §102(e): a U.S. patent granted on an application filed before the applicant's date of invention — available even where the reference issued after 1991-08-02.

The controlling limitation. Every independent claim (1, 8, 15) requires, for each pair of coils, that the two parallel planes be spaced by an axial distance "substantially equal to the respective average turn radius." That is the Helmholtz half-separation condition, and it is the point of novelty the specification itself frames (FIGS. 1–2, curves that "coincide substantially with the zero ordinate line"). Anticipation analysis therefore turns almost entirely on whether any reference discloses paired coils — not a single coil — with that one-radius plane separation, on at least two mutually orthogonal axes.

I note as a record caveat that the provided Google Patents citation table strips the asterisks that distinguish "*Cited by examiner" from "†Cited by third party," so I cannot state which of the eleven were examiner-applied and which were applicant/third-party submitted. The list is reproduced in the authoritative text without that distinction.

3. The eleven cited references, element by element

Element tags used below (from the issued claim language):

• E1 support with two mutually orthogonal axes of symmetry
• E2/E3 first and second pair of coils along those axes
• E4 within each pair: substantially equal number of generally circular turns → equal thickness; equal average turn radius and diameter; thickness < diameter
• E5 the two planes of each pair spaced apart by ≈ the average turn radius (the Helmholtz condition)

4. Claim-by-claim outcome

Bottom line on §102: none of the eleven cited references — individually or in the combinations contemplated by the citation table — anticipates any claim of US 5,172,056, because none discloses the Helmholtz one-radius plane separation applied to a pair of coils, on each of two orthogonal axes, at both radiator and sensor. That single limitation is what carried the claims over this art.

5. Ranking the cited art by relevance

1. US 5,047,715 (Morgenstern) — most relevant structural reference. Cube wrap element, three mutually perpendicular coil axes, nested/turn-enclosing coils, equal turn cross-sections, transmitter and receiver probes of identical construction. It is the reference that pre-empts nearly everything in dependent claims 3, 4, 6, 10, 11, 13 — and nothing more. Note it is also the only cited reference whose issuance (1991-09-10) postdates the '056 filing date, which constrains it to §102(e)/foreign-publication status.
2. US 4,314,251 (Raab / Austin Company) — most relevant system and algorithmic reference. Orthogonal radiating means each "being a magnetic-dipole source," loop-antenna receiving means, two-or-three-axis minimum excitation sets, non-iterative solution, and rotation-invariant coupling products — i.e., the substance of the '056 specification's mathematical section.
3. US 4,287,809 (Egli / Honeywell) — helmet-mounted sighting with ≥2 (pref. 3) transmit coils and 3 receive coils, eigenvector rotation-matrix solution, metal-distortion compensation.
4. US 4,849,692 and US 4,945,305 (Blood / Ascension) — pulsed-DC 2–3 axis transmit / 3–2 axis receive orthogonal coil systems; both are §102(b) references (the '305 by two days).
5. The remaining six (US 3,439,256; US 3,800,213; US 4,244,120; US 4,396,885; US 4,642,786; US 4,829,250) are background/general-context art — coil-based position, orientation, direction-finding or accuracy-compensation systems, none of which reaches the paired-Helmholtz geometry.

6. Prior art not in the citation list that should be in the file

• FR-A-2 458 838 (application 79 14441) — the Applicant's own admitted prior art, expressly incorporated: the radiator and sensor "each comprise a group of identical current-controlled identical coils which are disposed along the three orthogonal axes respectively," with the stated aim of making the coils as small as possible. Cited at page 1 of the '056 patent and self-designated as "an integral part of the present application." Any anticipation/inherency argument against the '056 claims should start here, because it supplies E1–E3 for both radiator and sensor.
• SU-A-616 601 (as summarized in EP 0 324 136 A3, the Morgenstern counterpart): a cube-like housing with coils extending inward from its faces, axes intersecting at the cube centre, mutually perpendicular, coreless, with diameters decreasing toward the centre, and a ferrite cube at the middle. This is a direct structural precursor to the cube-support/orthogonal-nested-coil aspect of dependent claims 3, 4, 10, 11.
• DE-OS 27 32 950 (the acknowledged starting point in both US 5,047,715 and EP 0 324 136): three mutually perpendicular coils at both transmitter and receiver, the same architecture disclosed in the '056 specification's FR 2 458 838 discussion.

These three are more damaging on the secondary claim features than several of the eleven U.S. references, and they are not in the "Citations (11)" list.

7. Confidence and limitations

• High confidence in the bibliographic data and in the negative §102 conclusion, because it turns on a limitation (plane separation = average turn radius) that is textually absent from every retrieved reference disclosure.
• Verified directly: US 4,287,809, US 4,314,251, US 4,849,692, US 4,945,305, US 5,047,715 (disclosures retrieved and quoted).
• Not retrieved / title-level only: US 3,439,256, US 3,800,213, US 4,244,120, US 4,396,885, US 4,642,786, US 4,829,250. Descriptions for these are drawn from the patent's own face-citation titles plus general knowledge; I have not read their specifications here and would not assert element-level content for them in a formal opinion.
• Open items requiring a direct check: (a) the exact publication date of EP 0 324 136 A2, which determines whether Morgenstern is a §102(b) printed publication in addition to §102(e); (b) whether US 4,396,885 is the U.S. counterpart of the Applicant's admitted FR 2 458 838; (c) which of the eleven were examiner-applied (the asterisk/† markers are not preserved in the record I was given).
• No contradiction found with the previously generated summary or litigation sections; those sections' findings (expired 2011-08-02; no litigation found) are consistent with this prosecution-era citation set.

I'll ground the prior-art references before building the § 103 analysis.

Obviousness Analysis — U.S. Patent No. 5,172,056 under 35 U.S.C. § 103

Ground rules applied: patent numbers and identifiers are reproduced literally as they appear in the record (including the reference cited as "FR-A-2 458 838/7914441"). Prior art is taken from this patent's own Prior Art / Citations section (11 U.S. references) plus the applicant-admitted prior art FR 2 458 838.

Preliminary note / contradiction flag: the task states the current date as April 26, 2026; the session metadata states 2026-09-27. I have not reconciled these. No legal consequence for this analysis, which is retrospective.

Scope note: this patent expired 2011-08-02 (Expired – Lifetime) and, per the Litigation section above, was never asserted. A § 103 analysis now is therefore hypothetical (of interest because the patent is heavily cited prior art — 44 "Cited By" entries — and because the assignee family continued in US 2012/0223856 A1 / US 9,348,009 B2). I have not had access to the file wrapper, so I cannot verify what rejection grounds the examiner actually applied in 1991–92.

1. Governing law and framing

• The application was filed 1991-08-02 with FR 9009955 priority of 1990-08-03. Pre-AIA 35 U.S.C. § 103(a) governs; no AIA §§ 102/103.
• The patent enjoys a presumption of validity; a challenger must prove obviousness by clear and convincing evidence (Microsoft v. i4i, 564 U.S. 91 (2011)).
• The controlling standard is KSR Int'l Co. v. Teleflex Inc., 550 U.S. 398 (2007): familiar elements combined according to known methods, yielding predictable results, are obvious; "a court must ask whether the improvement is more than the predictable use of prior art elements according to their established functions." KSR also approves rejecting claims directed to optimization of a result-effective variable and to design choices dictated by the problem to be solved (see also In re Boesch; In re Aller).
• Because claim 1 and claim 8 are apparatus claims defined purely by structure (coil geometry) and recite no functional or result limitation (no "sufficient to approximate a dipole," no error threshold), the analysis turns entirely on whether the geometry was known or obvious. See MPEP 2112.01 / Titanium Metals Corp. v. Banner, 778 F.2d 775 (Fed. Cir. 1985): a newly discovered property of an old structure does not confer patentability on the structure. This is the single most important vulnerability of this patent.

2. Level of ordinary skill (POSITA)

A POSITA here is a person with a B.S. in electrical engineering or applied physics and 3–5 years designing electromagnetic position/orientation ("magnetic tracker") systems, or an M.S. with ~2 years. That person would have had, as undergraduate-level background knowledge: magnetic dipole theory (which the '056 specification itself invokes as baseline), mutual inductance, and the Helmholtz coil configuration — a canonical lecture-demonstration/laboratory geometry defined by identical coaxial coils of radius R separated axially by R, chosen because it nulls the first and second axial derivatives of the field (uniform-field volume). That background knowledge is the linchpin of the obviousness case below.

3. The prior art of record, mapped to the claim elements

Critical observation on the evidentiary record: none of the eleven cited references discloses a Helmholtz coil pair (two identical coaxial coils of equal average radius, axially separated by that radius). Every claim 1 / claim 8 / claim 15 limitation other than the Helmholtz spacing is squarely disclosed — usually expressly, and in some cases with the identical two-axis/three-axis architecture and the identical stated purpose.

4. The Helmholtz limitation is the sole point of novelty

Claim 1(d) requires: (i) substantially equal number of turns per pair; (ii) substantially equal average turn radius and turn diameter (i.e., the two coils of a pair are matched); (iii) winding thickness < turn diameter (thin-disc winding); (iv) parallel planes separated along the axis by an axial distance substantially equal to the respective average turn radius.

Element (iv) is, verbatim, the classical Helmholtz condition. Elements (i)–(iii) are the classical description of the coils used in a Helmholtz pair. The specification says so: "It should be pointed out that the said Helmholtz coils are two coils with circular turns, having the same average radius, which extend respectively in two parallel planes spaced from one another by a distance which is equal to the radius of the turns of the coils."

5. Combination 1 — Claims 1–7 (radiator)

Primary: US 4,314,251 (Austin/Raab) in view of US 4,849,692 / US 4,945,305 (Blood). Raab discloses the exact claimed architecture — a radiator of orthogonal magnetic-dipole sources radiating to a two- or three-axis receiver for six-degree-of-freedom position/orientation. Blood supplies the two/three-axis transmitter-and-receiver coil configuration in a form expressly aimed at removing the need for cartographic calibration.

Secondary: US 5,047,715 (Morgenstern), which supplies the support structure: cube wrap element, three mutually perpendicular coil axes, nested/enclosing windings of differing diameter, and cylinder- or cube-mounted turns filling the probe volume. It also supplies the reason: "the turn diameter … need not necessarily … be circular"; "coils wound so as to produce identical areas of cross-section of turn for each of them"; and the goal of achieving "a magnetic field which is uniform in all directions."

Then the Helmholtz geometry itself would have to come from outside the of-record art (a physics/EM text, a laboratory field-generator reference, or Official Notice under MPEP 2144.03).

Motivation to combine (KSR factors):

1. Same field of endeavor, same problem. All references concern non-contact electromagnetic determination of an object's position and orientation, several expressly for helmet-mounted sights (US 4,287,809; US 4,829,250). KSR: "if a technique has been used to improve one device, and a person of ordinary skill in the art would recognize that it would improve similar devices in the same way, using the technique is obvious."
2. Problem recognized in the art, not newly discovered. US 4,849,692 states the prior art's calibration burden "is time consuming and expensive"; US 5,047,715 states prior probes suffer "a high degree of spread, with anisotropy additionally superimposed." The '056 specification admits the same: "the radiators and sensors have not fully met the conditions of the dipole theory and the object of the present invention is to come closer to them." An admitted, articulated problem supplies motivation.
3. Predictable result / optimization of a result-effective variable. The Helmholtz ratio (spacing = radius) is obtained analytically by setting d²H/dz² = 0. Selecting the inter-coil spacing that best matches a coil pair to dipole behavior is optimization of a result-effective variable — the paradigm of In re Boesch / In re Aller, and expressly approved in KSR.
4. Self-evident use of the reference for its known function. Morgenstern already teaches nesting equal-cross-section coaxial turn sets on a cube to make the field "uniform in all directions" and to remove directional error. Using a Helmholtz pair — the canonical structure for field uniformity/symmetry — for that same stated purpose is the predictable use of a known element for its established function.

6. Combination 2 — Claims 8–14 (sensor)

Identical to Combination 1 with the roles reversed. US 4,849,692 discloses the receiver as "a multiplicity of roughly orthogonal antennae axes"; US 4,829,250 discloses a receive coil assembly of three mutually orthogonal coils defining the pilot's line-of-sight in a helmet sight; US 4,314,251 claims the receiver as a plurality of orthogonal loop antennas. The Helmholtz geometry is applied identically, and the specification concedes the two embodiments are one inventive concept ("the essential characteristics of the sensor and the radiator of the invention are the same … they originate from a unique inventive concept"). That concession forecloses any argument that claims 8–14 contain a separate inventive contribution from claims 1–7.

Note the specific vulnerability of claims 11–14 / 4–7 (grooves, different depths, symmetry, containment): these are conventional former/mounting expedients. US 5,047,715's mutually-enclosing, mutually-penetrating nested windings on a cube (its FIG. 6A–6C, FIG. 7 "enlarged cutout corner view of a cube wound according to FIG. 6") achieve exactly the same physical result — a cube carrying three mutually orthogonal nested coil pairs of different diameters. Recessing them into grooves of different depths is a predictable mechanical variation (retention, winding convenience, concentric nesting) with no new function and no unexpected result.

7. Combination 3 — Claim 15 (the arrangement)

US 4,314,251 alone discloses a transmitter/receiver system with a radiator and a remote sensor, one having two orthogonal components and the other three. Combined with the Helmholtz teaching, claim 15 adds nothing beyond claims 1 + 8 and is obvious for the same reasons (KSR; and the specification's own "single inventive concept" statement).

8. Reasons a § 103 rejection could nonetheless fail (the nonobviousness case)

This must be stated fairly, because on the intrinsic record alone the claims hold up:

1. No Helmholtz disclosure of record. The examiner allowed the claims over eleven references that collectively disclose every limitation except the Helmholtz geometry. A rejection requires either a new secondary reference or Official Notice, and Official Notice is traversable; if traversed, the examiner must supply documentary evidence (MPEP 2144.03). A well-counseled applicant would demand that evidence.
2. Different principle of operation / arguable teaching away. Helmholtz coils are conventionally specified to create a uniform field in the interior volume between the coils (sample region). Claims 1/8/15 instead use the pairs as a point-like radiator radiating outward or as a point-like receiver immersed in an external ambient field — the opposite region of operation. Applicant expressly called this "an unexpected application of Helmholtz coils." The counter is strong, however: the same derivative-cancellation that produces central uniformity also suppresses the higher-order multipole terms viewed from outside, so the "different" uses are two faces of one physical property — which weakens both the teaching-away and unexpected-results arguments.
3. Unexpected results (MPEP 716.02; In re Soni). The specification presents FIGS. 1–2 as showing that only the Helmholtz pair yields ε_m = 0 (field-modulus error) and δ = 0 (angular error) versus a dipole. But those are inherent, analytically derivable properties of the Helmholtz geometry, i.e., results a POSITA would expect, not an unexpected result. Moreover the evidence is the inventor's own computation/comparison against an idealized dipole (FIGS. 1–13), not comparative testing against the closest prior-art devices; and the results are stated in absolute terms ("errors … very small"), with no objective, statistically defensible comparison to a pre-existing commercial radiator or sensor.
4. Secondary considerations with potential but no proven nexus. The art's persistent complaints about cartography (Blood's "obviates completely any need for a priori calibration undertakings"; later, US 6,154,024's "Mapping … is very cumbersome") could support a long-felt need for a dipole-accurate, interchangeable radiator. Commercial success or copying of the Thales family products could also help — but only with a proven nexus to the Helmholtz geometry, and the patent was never asserted, which undercuts any inference of marketplace significance.
5. A physical teaching-away nuance in Morgenstern. US 5,047,715 deliberately makes the turns larger as distance from the probe center increases ("the number of turns, as the distance from the center of the probe increases"), whereas the '056 claims require the two coils of a pair to have substantially equal average turn radius and diameter. If a rejection relied principally on Morgenstern for the Helmholtz geometry, applicant could plausibly argue Morgenstern's graduated-diameter winding points away from a matched-radius Helmholtz pair — which is why I have used Morgenstern only for the support/nesting/groove claims, not as the Helmholtz teaching.

9. Conclusion

• Claims 2–7, 9–14 (dependent claims): very likely obvious. Every added element — third orthogonal axis, cube support, non-magnetic material, grooved former, differing groove depths, symmetry, full coil containment — is disclosed or rendered obvious by US 4,314,251, US 4,849,692, US 4,829,250, and especially US 5,047,715 (cube wrap element, three perpendicular axes, mutually enclosing nested coils, equal turn cross-section areas). These are predictable mechanical and architectural variations serving the same known purposes.
• Claims 1, 8, and 15: obvious if and only if the trier supplies a Helmholtz-coil teaching (textbook/laboratory field-generator art or Official Notice). Given a POSITA's baseline knowledge of the Helmholtz configuration and KSR's treatment of result-effective-variable optimization and predictable combinations, I assess the structural claims as more likely than not obvious, with the spacing ratio being the only serious battleground. The strongest, most durable nonobviousness position is the "unexpected application / different region of operation" argument in § 8.2, reinforced by the complete absence of Helmholtz disclosure in the of-record art; the weakest link in that defense is that the claims recite only geometry, so the newly discovered dipole-fidelity property cannot by itself save them (Titanium Metals; MPEP 2112.01).
• Practical significance: because this patent is prior art of record against 44 later tracking patents (Biosense/Cordis, Ascension, GE Medical Systems, TDK, and Thales' own US 9,348,009), the practically important question is not whether '056 is valid over its cited art — it is whether '056 itself anticipates or renders obvious those later claims' Helmholtz/coil-geometry limitations. That question is unaffected by this § 103 analysis.