US 9267924

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

Let me check for any litigation or CAFC proceedings involving this patent or its owner.

US Patent 9,267,924 — Verification Summary

Sourcing note: I was able to confirm this record against the full patent text you supplied (Google Patents, fetched 2026‑09‑24), Justia Patents, the patent‑family/EP register listings, and general web search. I could not query a dedicated USPTO API/Pair endpoint or a CAFC docket system directly through the available tools, so the litigation statement below rests on web search rather than a live docket pull. Details marked "not confirmed" should be treated as such.

Bibliographic data (confirmed)

Abstract (as published)

"It is presented a method for detecting a gas (G). Acoustic waves (Wt) are generated and transmitted via a wave generating and sensing means (2) towards a reflecting wall (3) and thereafter reflected acoustic waves (Wt) are detected by the wave generating and sensing means (2) wherein a presence of the gas (G) is detected by determining a change in an output signal of the wave generating and sensing means (2). A gas detector (1) is also presented."

Overview of the disclosure

The patent exploits the fact that sound speed — and therefore wavelength for a fixed frequency — differs from gas to gas. A piezoelectric resonator + electronic oscillator (constant current) forms a resonant cavity with a parallel reflecting wall spaced at distance d. Waves reflected back and forth create constructive/destructive interference that shifts the resonator's motional resistance with gas composition, changing the oscillator's output voltage. By setting d on the slope of a resonance peak (about half peak magnitude), small wavelength shifts produce a large, easily measured signal change. Temperature compensation is achieved by moving the reflecting surface (or by differential thermal expansion of selected materials, e.g., steel, aluminium, copper, brass, glass, ceramics, amorphous quartz). The specification reports a helium-in-air detection limit of ~40 ppm by volume.

Independent claims — plain language

Claim 1 (method). A method of detecting a target gas (G) with a detector having a reflecting wall and a wave‑generating‑and‑sensing means at distance d opposite it, performed as a continuous process:

1. generate acoustic waves with the means;
2. transmit them through the gas toward the reflecting wall so that the reflected waves create constructive and destructive interference (interference depending on acoustic wavelength, which depends on the gas);
3. detect the reflected waves, where the motional resistance of the means changes due to the wavelength change; and
4. indicate presence of the gas by determining a change in the magnitude of the output signal, that change being related to the motional‑resistance change.
   The claim further requires compensating for temperature changes by moving the reflecting surface along an axis transverse to that surface, thereby adjusting d.

Claim 8 (gas detector). A gas detector for detecting a gas (G) in a reference gas (Gr), comprising: a wave‑generating‑and‑sensing means having a piezoelectric resonator with a resonator surface and an electronic oscillator feeding a constant current to it; and a reflecting wall opposite, the resonator surface forming a resonant cavity with the wall. The means generates acoustic waves and detects the reflected waves; the detected waves increase the motional resistance of the means when gas G is present in the reference gas (vibration energy absorbed), thereby raising the oscillator output voltage. Gas presence is detected as a change in that output voltage. The reflecting wall and the generating/sensing means are fixedly arranged in the detector, and the wall is spaced at distance d such that the output‑signal magnitude is less than its magnitude when resonance occurs between wall and means.

Dependent claims of note: constant frequency (cl. 2–3, 9–10, stated range 0.5–500 MHz in the description; the granted claims recite only "constant frequency" and the 0.5 MHz–500 MHz range); setting d below the resonance magnitude (cl. 4); resonance referenced to a reference gas such as air (cl. 5, 11); micrometer or piezoelectric actuator for setting d (cl. 6); automatic thermal‑expansion movement (cl. 7); thermally expanding materials dimensioned for thermo‑compensation (cl. 12); quartz or other piezoelectric material (cl. 13–14); and d in the range ~λ/2 to ~50λ (cl. 15). Total: 15 claims.

Minor textual observations (not corrections)

• Step labels in the granted claims differ from the specification's flowchart: claim 1 cites "(S6)" for the compensating step while the description uses S5, and claim 2 recites "generating (S0)." A certificate of correction issued 2016‑07‑26, so the granted text may reflect corrected wording. I did not independently retrieve the certificate of correction.
• The description contains an apparent typo ("creating and destructive interference" in the SUMMARY section) that is corrected to "constructive and destructive interference" in claim 1 — I have quoted each as it appears.

Litigation / CAFC 2026 dockets — no evidence found

Searches for "9267924" combined with litigation, infringement, IPR, and Federal Circuit 2026 docket terms returned no results tying US 9,267,924 to any CAFC appeal, PTAB proceeding, or district‑court action. References to "9267924" in search results were to unrelated records (e.g., a Brazilian corporate registration and a medical abstract). I therefore state explicitly: I have no authoritative information indicating any 2026 CAFC docket involving this patent. This is a negative search result, not a confirmation of absence from any docket; I could not query the CAFC docket system directly.

I'll search for litigation involving US patent 9267924.

Let me search more targeted litigation databases.

Let me check specific litigation databases directly.

Litigation Search Report — U.S. Patent No. 9,267,924

Patent identified: U.S. Patent No. 9,267,924 B2 — "Method for detecting gas and a gas detector therefor"

• Inventor: Vasile Mecea
• Assignee/Patent Owner: QCM Lab AB (later QCM Lab Aktiebolag), Järfälla, Sweden
• App. No. 13/640,755; PCT/SE2010/000097; filed April 15, 2010; granted February 23, 2016
• Status: Active (adjusted expiration listed as September 22, 2031)

Result: No litigation found

Based on my searches of publicly available patent-litigation sources, I found no record of any litigation (district court action, ITC investigation, or Federal Circuit appeal) involving U.S. Patent No. 9,267,924.

Specifically:

I could not identify any case in which U.S. Patent No. 9,267,924 was asserted, challenged as a counterclaim, or made the subject of a declaratory-judgment action.

Caveats and methodology notes

1. No results ≠ confirmed absence. My searches were conducted via web search rather than a direct, complete query of a definitive litigation docket. The Unified Patents litigation portal (portal.unifiedpatents.com/litigation/caselist) and PACER/Docket Alarm returned no hits tied to this specific number, but I was not able to exhaustively query every district court docket. Absence of a hit in these sources is strong but not conclusive evidence that no such suit exists, particularly for a small foreign patent owner such as this one.

2. Avoiding number confusion (per the strict literal-interpretation rule). My searches surfaced several different patents with visually similar numbers that are not U.S. 9,267,924 and must not be attributed to it:

   • U.S. 8,767,824 (Velos Media) — subject of IPR2019-00635, Unified Patents v. Velos Media. Different patent; not 9,267,924.
   • U.S. 9,338,449 (Velos Media), 9,641,849 and 10,621,228 (MemoryWeb), 9,463,324 / 8,036,756 / 8,626,314 (Medtronic v. Axonics), 7,454,002 (SportBrain) — all unrelated patents appearing in the same search results.
   • A Brazilian commercial-registry entry and an Israeli municipal phone number both containing the string "9267924" — irrelevant to patent litigation.

   None of these involve the patent-in-suit here.

3. Post-grant proceedings. I likewise found no IPR, PGR, or other PTAB proceeding directed at U.S. 9,267,924. The patent's Google Patents page lists it as "Active" with maintenance fees paid (4th year 2019, 8th year 2023), which is consistent with the owner retaining rather than litigating the asset. Note that the corresponding EP 2558851 B1 has lapsed/not-in-force in multiple jurisdictions (e.g., FR déchu as of 2025; not validated in LT; deleted in CH in 2018), but those are prosecution/maintenance events, not litigation.

4. Related non-lawsuit documents found (for completeness, not litigation): citing prior art and non-patent literature referenced during prosecution includes E. Griffiths, "A gas analysis instrument based on sound velocity measurements," Proc. Phys. Soc. (1926); Granstedt et al., Sensors Actuators B 78:161–165 (2001); and Mecea, "Tunable gas sensors," Sensors Actuators B 15–16:265–269 (1993). These are prosecution references, not litigation.

Recommendation

If a definitive negative is required, I recommend a paid/live query against:

• Unified Patents Litigation Portal — search by patent number 9,267,924
• PACER (nationwide docket search) and Docket Alarm / Lex Machina / RPX Insight
• USPTO PTAB (for any IPR/PGR) and ITC EDIS (Section 337 investigations)

Should any new hit appear, I would flag it only if the docket literally identifies 9,267,924.

Proceedings overview

Total AIA trial proceedings on file for US 9,267,924: zero (0 active, 0 claims invalidated, 0 claims sustained, 0 settled, 0 institution denied).

The structured "PTAB proceedings on file" block — the canonical list drawn from the USPTO Open Data Portal — contains no entries, and supplementary web searching surfaced no IPR, PGR, or CBM naming US 9,267,924 as the challenged patent. The bottom-line defensive posture is therefore not "the patent has survived two IPRs and is hardened," and it is also not "claims 1–5 have been canceled." The accurate posture is: the '924 patent is an untested-by-the-Board, low-signal patent with no PTAB history, no identified § 315(e) estoppel attaching to anyone, and an open § 315(b) window for a newly-sued defendant. Absence of PTAB activity on a 2010-priority patent is itself informative — see the strategic summary.

No proceedings to report — verification trail and what the record does show

Because the required per-proceeding template has no subject matter here, I am flagging explicitly what I checked and what I did not find, rather than inventing docket numbers or panels.

Verification performed (2026-09-29)

Caution on a look-alike: several search hits reference "the '926 Patent" in Wilus Institute of Standards and Technology v. Samsung (E.D. Tex. 2:25-cv-00070) and a Wi-Fi 6 pool. That is a different patent (Wilus's Wi-Fi 6 patent), not US 9,267,924. Do not let a docket-monitoring vendor's short-citation match cross-contaminate your file. I could not verify any of the Wilus '926 materials as relating to this patent, and I am treating them as unrelated.

Family / counterpart status (context only — not PTAB)

The family is small and, notably, has been eroding outside the US. All values below are as reported by the cited registries; the EP position is inconsistent across sources and should be independently confirmed before you rely on it.

The US patent also had a certificate of correction issued 2016-07-26 (per the Legal Events table). If you are working from the pre-CC printed claims, re-pull the current claims from USPTO PatentCenter before charting anything.

Strategic summary

Claim status: entirely UNTESTED. No claim of US 9,267,924 has ever been construed or adjudicated by the PTAB, and I found no district court validity ruling either. The full granted claim set is presumptively in force: independent method claim 1, dependent method claims 2–7, independent apparatus claim 8, and dependent apparatus claims 9–15. There is no narrowed set of "surviving" claims to point a defendant at, and no canceled claim to call a plaintiff's bluff on. Anyone asserting the patent today asserts the original, never-challenged scope.

Estoppel landscape: blank slate. Because no IPR/PGR was instituted, § 315(e)(2) estoppel attaches to no one. No petitioner, real party in interest, or privy has been estopped from raising § 102/§ 103 grounds in a district court or ITC. Conversely, no previous petitioner's loss gives you a "hardened patent" warning either — the patent has simply never been tested. Practical carve-outs still apply to a new defendant: § 315(a)(1) bars an IPR filed by a party that previously filed a DJ action of invalidity, and § 315(b) bars an IPR filed more than one year after service of a complaint alleging infringement on that party. If your client has already been served, the one-year clock is your binding constraint; if not, the window is open. PGR is unavailable (nine-month post-grant window closed around 2016-11-23, given the 2016-02-23 grant), and CBM is unavailable on its face — this is an acoustic gas-sensing patent, not a "financial product or service" patent.

Pattern signals: none, and that is the story. There is no repeat petitioner, no defensive aggregator (no Unified Patents-style filing), no Director Review activity, and no Federal Circuit appeal. A 2010-priority patent that is still active into 2031 and has never drawn an IPR, while its EP counterpart is reported as lapsed/not-in-force across CH, FR, and LT, is most consistent with a patent that has seen little or no enforcement. Well-asserted patents attract IPRs; this one has not. Weigh that two ways: (a) the troll-risk profile is low — there is no evidence of a campaign to defend against; but (b) if a demand letter does arrive, you may be among the first targets, and there is no prior petitioner's work product, expert report, or institution decision you can reuse.

Real prior-art signal from the face of the patent (for a future petition). The specification itself concedes the core technique: it cites E. Griffiths, "A gas analysis instrument based on sound velocity measurements," Proc. Phys. Soc. (1926), describing a quartz crystal plus parallel reflecting wall forming a resonance cavity, with resonance detected via anode-current change. The EP search report (one of the Non-Patent Citations) also lists Mecea, "Tunable gas sensors," Sensors & Actuators B 15–16:265–269 (1993) — same inventor — and Granstedt et al., "Gas sensor with electroacoustically coupled resonator," Sensors & Actuators B 78:161–165 (2001). That is a strong § 102/§ 103 starting point. The counterweight is § 325(d): most of these references (Griffiths, Mecea, Granstedt, and the examiners' cited patents such as US 5,411,709 to Fuji Xerox, "Gas detector") were already before the Office. A petitioner must explain what the Office missed, not merely re-present the same art.

Claim-drafting weak spots worth a § 112 / indefiniteness look. Independent of any IPR:

• Step-label mismatch between claim and specification. Claim 1 recites "compensating (S6) for temperature changes," while the specification's flowchart labels that step S5. Claim 2 recites "wherein the generating (S0)" — but S0 in the specification is the step of setting distance d, and generating is S1. These are drafting defects that could support a claim-construction/indefiniteness argument or at least a "which step does the label mean" dispute.
• Claimed range vs. preferred range. Claims 3 and 10 claim 0.5 MHz to 500 MHz; the specification's stated preference is 0.5 MHz–50 MHz, and the only worked example is 6 MHz. Enablement/written-description and unexpected-results angles are available at the outer claimed range.
• Internal tension in claim 8/12. Claim 8 requires the reflecting wall and the wave generating and sensing means to be "fixedly arranged," while claim 12 (dep. from 11, from 8) requires "thermally expanding materials dimensioned such that thermo compensation is obtained," and the specification achieves that thermo-compensation by the reflecting surface automatically moving along axis X. Expect a fight over what "fixedly arranged" means if the patent is ever asserted against a thermally-compensated device.

Recommended next steps

1. Confirm the negative before you build a defense on it. Re-query the USPTO PTAB E2E / AIA trial docket directly for patent number 9,267,924 (PTAB decisions portal: https://www.uspto.gov/patents/ptab/decisions), and pull the current claims and the 2016-07-26 certificate of correction from USPTO PatentCenter. The structured ODP feed is authoritative but can lag a recently filed petition — a brand-new IPR filed in the last few weeks may not yet appear.
2. Diarize the § 315(b) deadline immediately. If your client has been served with a complaint alleging infringement of the '924 patent, the IPR petition is barred one year after service, full stop. If no complaint has been served, you have room to build a stronger petition rather than a rushed one.
3. Because there is no FWD to point to, your defense must be built from scratch. The two anchor theories are (i) § 103 over the admitted Griffiths 1926 resonance-cavity method in view of a secondary reference teaching operation on the resonance slope/fixed cavity for sensitivity (the patent's own stated point of novelty), and (ii) § 112 on the step-label mismatch, the 0.5–500 MHz outer range, and "fixedly arranged" vs. thermal compensation.
4. Pre-empt the § 325(d) problem in the petition itself. Assume the Board will invoke § 325(d) given that Griffiths, Mecea, and Granstedt were before the Office. Frame the petition around what the examiner never addressed — e.g., the claim-1 "continuous process" + motional-resistance-change + slope-positioned fixed cavity combination — rather than re-presenting cited art.
5. Track the EP counterpart precisely. The reported non-validated/not-in-force status of EP 2558851 B1 across CH, FR, and LT is a cross-border signal worth verifying from the EPO Register rather than the tertiary sources cited above; if confirmed, it tells you where the patent owner's remaining leverage actually sits — the US, and possibly CN.

Confidence statement: I have high confidence in the "no PTAB proceedings" conclusion as of the 2026-09-29 ingest, based on both the canonical ODP block and independent searching. I have low-to-medium confidence in the EP counterpart status details (the sources conflict — e.g., a 2017 grant date alongside a 2018 deletion and a 2025 French déchéance — and I did not verify against the EPO Register), and I explicitly did not find any district court litigation asserting US 9,267,924; treat the "no enforcement" inference as an inference, not a verified fact.

I'll research the assignment chain and litigation history before assembling the report.

Ownership & Assignment Analysis — US 9,267,924 B2

Patent: US 9,267,924 B2 — "Method for detecting gas and a gas detector therefor"
App. No.: 13/640,755 (§371 national phase of PCT/SE2010/000097, filed 2010-04-15)
Grant: 2016-02-23 | Adjusted expiry: 2031-09-22 (active; 4th-yr fee paid 2019, 8th-yr fee paid 2023)

Sourcing note / limitation: The USPTO Assignment Center fields for correspondent of record were not retrievable in this session (searches returned no indexed Assignment Center records). All reel/frame, date, assignor and assignee facts below come from the Google Patents legal-events ledger for this patent; correspondent and full conveyance text should be confirmed directly at Assignment Center (search US 9,267,924). I have not filled in a correspondent from inference.

Inventors

Notes and patterns:

• Only one named inventor. No co-inventor departures to track, so the usual "all inventors left within 12 months" fire-sale tell cannot arise.
• Mecea is a recognized quartz-crystal-microbalance (QCM) specialist — author of "Tunable gas sensors," Sensors and Actuators B 15-16:265-269 (1993), which appears in the file's non-patent citations, and co-author of the in-memoriam piece for Günter Sauerbrey (the QCM pioneer) hosted on qcmlab.com. This is a genuine technologist-founder, not a hired inventor of convenience.
• The applicant at filing, G&M Norden AB, shares the Spånga/Järfälla address cluster with QCM Lab AB, consistent with the inventor's own holding vehicle rather than an unrelated acquirer.

Original assignee

Named on the issued patent (Google Patents "Original Assignee" and "Current Assignee"): QCM LAB AB / QCM lab Aktiebolag — Gäddvägen 16, 175 47 Järfälla, Sweden. Org. nr. 556919-8376.

• Primary line of business: R&D on piezoelectric materials for sensor applications, and the manufacture/import/sale/licensing/rental of measurement instruments and components built on piezoelectric sensors. QCM Lab crystals and QCM systems are named as the instrument source in peer-reviewed methods papers (e.g. "a QCM setup from QCMLabs AB, Sweden"), so it is a real, small operating manufacturer — not a paper entity.
• Size / status: 1–4 employees, registered as an "aktiebolag," registration data 2013-01-22; active.
• Product embodying the claims: Indirect evidence only. QCM Lab sells QCM instrumentation and crystals; no public evidence was found of a commercial gas detector built on this patent's acoustic-cavity claims. So "ships a product" is established for the company, but not specifically for the claimed gas detector.
• Important procedural history: The PCT/WO applicant was G&M Norden AB, and EP2558851's Titulaire later became QCM lab Aktiebolag. The U.S. front page names QCM Lab AB because the 2013 assignment (below) preceded U.S. grant. The family has since been trimmed: EP2558851 is not-in-force (IE lapsed 2018; FR déchu, BOPI 2026-01), KR20130094181A withdrawn, CN102844657A pending — consistent with a micro-company keeping only its most valuable U.S. right.

Assignment timeline

Two assignments are of record. Both were recorded after the 2010 priority/filing date because the U.S. case is a §371 national phase.

• 2012-09-26 (executed) / recorded 2012-10-12 — Reel 029119/0446

  • Conveyance: Assignment
  • Assignor: Vasile Mecea (inventor)
  • Assignee: G&M Norden AB (Mamrevägen 28, 163 46 Spånga, Sweden)
  • Correspondent: Not retrievable; not fabricated. (Confirm at Assignment Center.)
  • Context: Inventor-to-applicant title perfection, timed to the U.S. §371 national-phase entry (App. 13/640,755; series 13/640,xxx = Oct 2012). Ordinary housekeeping, not a sale.

• 2013-09-19 (executed) / recorded 2013-11-13 — Reel 031592/0465

  • Conveyance: Assignment
  • Assignor: G&M Norden AB
  • Assignee: QCM lab Aktiebolag (Gäddvägen 16, 175 47 Järfälla, Sweden)
  • Correspondent: Not retrievable; not fabricated. (The PCT/EP agent of record for this family is Kransell & Wennborg KB, P.O. Box 27834, 115 93 Stockholm — a conventional Swedish IP firm. This is the EP/WO agent, not confirmed as the U.S. assignment correspondent.)
  • Context: Intra-family transfer from the inventor's holding vehicle (G&M Norden AB) into the newly incorporated operating company (QCM Lab AB, registration data 2013-01-22). A corporate reorganization to consolidate the IP with the commercializing entity — not an arm's-length divestiture.

No further assignment, security interest, license, merger, or release is recorded. The only other post-issuance events are a certificate of correction (2016-07-26) and maintenance-fee payments — neither is a transfer. Title has rested with QCM Lab AB since 2013-11-13.

Timeline diagram

timeline
    title Ownership of US 9267924
    2010 : PCT filed by G and M Norden AB
    2012 : Mecea assigns title to G and M Norden
    2013 : G and M Norden transfers to QCM Lab AB
    2016 : US patent issues to QCM Lab AB
    2019 : 4th year maintenance fee paid
    2023 : 8th year maintenance fee paid

NPE / troll-pattern signals

Verdict

Defensive / non-asserting (residual category — read as "non-asserting operating company"; the chain does not terminate at a defensive aggregator).

Justification: The entire recorded chain of title is Reel 029119/0446 (Mecea → G&M Norden AB, executed 2012-09-26) followed by Reel 031592/0465 (G&M Norden AB → QCM lab Aktiebolag, executed 2013-09-19) — two intra-family transfers between an inventor-principal and his own holding/operating companies, with no third-party acquirer. The terminal owner, QCM Lab AB (org. nr. 556919-8376, 1–4 employees), is a Swedish piezoelectric-sensor manufacturer whose QCM instruments are cited in third-party literature, and no litigation, NPE-list match, or defensive-aggregator transfer is of record. Neither "NPE" nor "operating-company assertion" fits: there is no evidence of assertion at all, and the single strongest unresolved signal — repeat correspondent — cannot be scored because the Assignment Center correspondent fields were not retrievable, so this call should be re-verified there.

Verify at: https://assignmentcenter.uspto.gov/ (search patent number 9267924) — also indexed at https://assignment.uspto.gov/patent/index.html

I'll research the prior-art references cited against this patent, prioritizing the authoritative citation list in the patent text you supplied.

Now let me characterize the remaining cited references in depth.

Prior-Art Analysis — U.S. Patent No. 9,267,924 B2

Patent: Method for detecting gas and a gas detector therefor — Vasile Mecea; assignee QCM Lab AB / QCM Lab Aktiebolag
App. No. 13/640,755; §371 of PCT/SE2010/000097, filed 2010‑04‑15 (priority date); granted 2016‑02‑23.
Governing law: Because this application was filed 15 Apr 2010 — before the 16 Mar 2013 AIA change — the pre‑AIA version of 35 U.S.C. § 102 applies. Prior art therefore includes references published before 15 Apr 2010, and (for § 102(e)) U.S. patents/publications effective as of their earlier U.S. filing dates.

Sourcing note (important): The authoritative prior‑art list I use below is the citations list in the full patent text you supplied, cross‑checked against the Justia record (patents.justia.com/patent/9267924) and the Google Patents family page. I was able to retrieve full descriptive detail for only a subset of the references via search (notably US 2,536,025, US 3,697,936, US 5,411,709, US 3,482,647, and the Griffiths 1926 article). For the remainder, descriptions rest on the official title, assignee/date metadata and general knowledge of the reference; those are flagged [description not independently verified]. I was not able to pull full claim charts from USPTO PatentCenter/Pair within this session, so § 102 conclusions below are analytical judgments, not Examiner findings.

A. The complete cited prior‑art set

U.S. patents (16)

WO / PCT publications (2)

Non‑patent literature (4)

B. Reference‑by‑reference § 102 assessment

The single most important threshold point: the independent claims are narrow. Claim 1 requires (i) continuous generation/transmission/interference, (ii) a motional‑resistance change producing an output‑signal magnitude change, and (iii) temperature compensation by translating the reflecting surface transversely to adjust d. Claim 8 requires a piezoelectric resonator + constant‑current oscillator, a resonant cavity, the fixed wall arrangement, and d set below the resonance magnitude. No single reference below contains that exact combination, so strict § 102 anticipation is unlikely for claim 1 or claim 8; the cited references function principally as § 103 art. I identify the claims each reference could potentially anticipate or render obvious, with candor about the gaps.

P1 — US 2,536,025 A (Blackburn / Crystal Research Lab) — THE CLOSEST ART

• Full citation: US 2,536,025 A, "Piezoelectric interferometer system," filed 14 Apr 1945, granted 2 Jan 1951, Crystal Research Lab Inc.
• Disclosure (verified): A supersonic interferometer with a gas‑tight chamber containing a plane‑parallel piezoelectric (X‑cut) crystal driven in a tuned circuit, opposing a plane parallel reflector (piston) on a micrometer screw. "The detection of the reflected wave is accomplished by this same crystal." Resonance is detected as a change in current X in the maintaining circuit (ordinates of Fig. 1). The reflector distance is varied to maintain or destroy resonance "to accommodate changes in pressure, temperature, or chemistry." It expressly recites use to "determine the chemistry of … a gaseous or liquid sample," and to "identify very minute changes in chemical composition."
• § 102 mapping: This reference comes very close to claims 1, 2, 4, 5, 6, 8, 9, 11, 13, 14.
  • Crystal + oscillator + reflector + cavity → claims 8, 13, 14.
  • Same crystal transmits and detects the reflected wave; reflected wave reacts on the crystal to change the circuit current → the "motional resistance / output‑signal change" limitation of claim 1 (Blackburn describes the reaction on the crystal as an increase in circuit current).
  • Varying the reflector distance to accommodate temperature → arguably meets the § 102 test for the "compensating … by moving a reflecting surface along an axis transverse to the reflecting surface" element of claim 1 (though Blackburn's purpose is maintaining resonance, not thermo‑compensation per se).
  • Resonance‑condition dependence on gas/chemistry → claims 5, 11 (reference‑gas resonance).
  • Micrometer‑set distance → claim 6.
• Gaps (why anticipation is arguable, not clean): Blackburn does not in terms recite a "continuous process", a "motional resistance," "constant current" oscillator feeding, or d set below the resonance peak magnitude. Those are the novelizers. Best use: § 103 primary reference against claim 1 (in view of P3/N1 for the continuous/oscillator aspects) and claims 2–6, 8–14.

P2 — US 3,482,647 A (Lynch et al. / Bunker Ramo)

• Full citation: US 3,482,647 A, "Apparatus for precise sound path in velocimeter," filed 19 Nov 1968, granted 9 Dec 1969.
• Disclosure [description not independently verified]: By title/assignee, an acoustic velocimeter with structure for establishing a precisely defined, fixed sound path between a transducer and a reflector — i.e., the fixed‑cavity‑length concept.
• § 102 mapping: Weak as an anticipatory reference. Possibly relevant to claim 8's "fixedly arranged" wall/means and claim 15's d‑range, but discloses no gas‑detection output‑signal or motional‑resistance limitation. Best use: secondary/§ 103 art on the fixed‑path geometry.

P3 — US 3,697,936 A (Zacharias / Nusonics)

• Full citation: US 3,697,936 A, "Sound velocimeter," filed 27 Feb 1970, granted 10 Oct 1972, Nusonics.
• Disclosure (verified): Phase‑lock sound velocimeter with a transducer and reflector, exploiting a single transducer for both transmission and reception; measurement of sound velocity is used to determine a fluid's "salinity, concentration, composition." Notably, the reflector/mounting is constructed with differential coefficients of thermal expansion chosen so that the sound‑path length remains constant (L·α equalized).
• § 102 mapping: Directly relevant to claim 12 (thermally expanding materials dimensioned for thermo‑compensation) and, under § 103, to the temperature‑compensation concept of claim 1. It does not disclose gas detection via a motional‑resistance/output‑voltage change, so it cannot alone anticipate claims 1 or 8. Best use: § 103 art on the thermo‑compensation feature (claims 1, 7, 12).

P4 — US 5,411,709 A (Furuki et al. / Fuji Xerox) — *examiner‑cited (**)

• Full citation: US 5,411,709 A, "Gas detector," filed 23 Mar 1992, granted 2 May 1995, Fuji Xerox Co., Ltd.
• Disclosure (verified): A gas detector combining a piezoelectric vibrating element bearing a gas‑sensitive thin film (adsorption‑type detection, with oscillation‑frequency detection) and an optical (fluorescence/phosphorescence) detection channel, in a reaction tank with a gas passageway and a light‑transmissive window.
• § 102 mapping: Relevant as general gas‑detector art and to the notion of a piezoelectric element in a gas environment (claims 8, 13, 14). It is an adsorption/frequency detector, not a resonant‑cavity interference detector, and discloses no reflective wall, no motional‑resistance/output‑voltage sensing, no d‑below‑resonance setting. Not anticipatory; background/§ 103 art only.

P5 — US 5,557,047 A (Koide / Fuji Ultrasonic Engineering)

• Full citation: US 5,557,047 A, "Method and apparatus for ultrasonic wave measurement," filed 10 Feb 1993, granted 17 Sep 1996.
• Disclosure [description not independently verified]: Ultrasonic measurement of a medium using transmit/receive and reflected waves.
• § 102 mapping: Relevant to the generate‑transmit‑reflect‑detect sequence of claim 1, but discloses no gas‑selective resonance or output‑signal‑magnitude detection. § 103 background art.

P6 — US 5,753,797 A (Forster et al. / Cerberus Ag) — *examiner‑cited (**)

• Full citation: US 5,753,797 A, "Photo‑acoustic gas sensor and its manufacture and use," filed 9 Apr 1995, granted 19 May 1998.
• Disclosure [description not independently verified]: A photoacoustic gas sensor (light → acoustic wave → detection).
• § 102 mapping: Gas‑sensing art of a different physical principle (photoacoustic, not acoustic‑interferometric). At most background art; not anticipatory.

P7 / P8 — US 5,869,749 A and US 5,886,249 A (Bonne et al. / Honeywell) — *examiner‑cited (**)

• Full citation: "Micromachined integrated opto‑flow gas/liquid sensor," filed 30 Apr 1997; US 5,869,749 A granted 9 Feb 1999; US 5,886,249 A granted 23 Mar 1999.
• Disclosure [description not independently verified]: MEMS‑fabricated integrated opto‑flow sensor for gases/liquids.
• § 102 mapping: Microfabrication/flow‑sensing background; discloses neither resonant cavity nor motional resistance. § 103/background art only. (The two are a patent/patent pair from the same application family.)

P9 — US 6,227,040 B1 (Hastings et al. / Caldon) — *examiner‑cited (**)

• Full citation: US 6,227,040 B1, "Method and apparatus for determining the viscosity of a fluid in a container," filed 3 Feb 1998, granted 8 May 2001.
• Disclosure [description not independently verified]: Ultrasonic determination of fluid viscosity.
• § 102 mapping: Ultrasonic fluid‑characterization background; no gas‑selective resonance/motional‑resistance teaching. § 103 background art.

P10 — US 6,250,137 B1 (Takahashi et al. / Toyota Jidosha)

• Full citation: US 6,250,137 B1, "Method and apparatus for determining gasoline characteristics by using ultrasonic wave," filed 8 Oct 1996, granted 26 Jun 2001.
• Disclosure [description not independently verified]: Ultrasonic characterization of fuel (composition) via sound propagation.
• § 102 mapping: Reinforces the well‑known principle that sound velocity/attenuation identifies fluid composition — the general idea of the patent — but does not disclose the claimed cavity/output‑signal arrangement. § 103 art on the general principle.

P11 — US 6,260,408 B1 (Vig et al. / U.S. Army)

• Full citation: US 6,260,408 B1, "Techniques for sensing the properties of fluids with a resonator assembly," filed 13 May 1998, granted 17 Jul 2001.
• Disclosure [description not independently verified]: Uses a resonator assembly to sense fluid properties — potentially involving piezoelectric resonators and frequency/impedance changes analogous to motional resistance.
• § 102 mapping: Potentially the most relevant of the non‑P1 U.S. references as to the resonator‑based sensing concept (claims 1, 8, 13, 14). But without independent verification of its disclosure I will not assert a § 102 mapping; treat as § 103 candidate.

P12 — US 6,094,987 A (Suzuki et al. / Fuji Ultrasonic Engineering) — *examiner‑cited (**)

• Full citation: US 6,094,987 A, "Method and apparatus for ultrasonic wave measurement," filed 10 Jun 1998, granted 1 Aug 2000. (Same family/technical line as P5.)
• Disclosure [description not independently verified]: Ultrasonic wave measurement.
• § 102 mapping: Same posture as P5 — sequence‑level relevance only; § 103 background art.

P13 — US 6,770,032 B2 (Kaplan / Microsense Cardiovascular) — *examiner‑cited (**)

• Full citation: US 6,770,032 B2, "Passive ultrasonic sensors, methods and systems for their use," filed 3 Dec 2001, granted 3 Aug 2004.
• Disclosure [description not independently verified]: Passive (externally interrogated) ultrasonic sensor technology.
• § 102 mapping: Passive‑resonator interrogation concepts only; background/§ 103 art.

P14 — US 7,965,017 B2 (Iwashita et al. / Ube Industries) — *examiner‑cited (**)

• Full citation: US 7,965,017 B2, "Thin film piezoelectric resonator and method for manufacturing the same," filed 25 Aug 2006, granted 21 Jun 2011.
• Disclosure [description not independently verified]: Thin‑film piezoelectric resonator structure and fabrication.
• § 102 mapping: Relevant only to the "piezoelectric resonator" element of claims 8, 13, 14 (and the "quartz or any other piezoelectric material" of claim 14 as a species/genus matter). § 103 art on the resonator sub‑element; not anticipatory of any full claim.

P15 — US 2005/0109080 A1 (Hok Instrument Ab)

• Full citation: US 2005/0109080 A1, "Real time analysis for gas mixtures," filed 24 Nov 2003, published 26 May 2005.
• Disclosure [description not independently verified]: Real‑time gas‑mixture analysis (Hok Instrument's acoustic‑resonator gas sensing line).
• § 102 mapping: Potentially relevant to real‑time/continuous gas‑mixture analysis (the "continuous process" element of claim 1) and to resonant acoustic gas sensing generally. Without verified disclosure I flag this as a § 103 candidate on the continuous‑process element, not a § 102 reference.

P16 — US 2008/0011060 A1 (Lynnworth) and W1/W2 (Aviva Biosciences; Inverness Medical)

• Full citations: as tabulated.
• § 102 mapping: These are acoustic‑field / ultrasonic‑measurement references in unrelated application contexts (field‑flow fractionation; oligomer detection; noninvasive conduit measurement). They are background art only and do not map to any claim element of 9,267,924 in an anticipatory way.

P17 — US 2012/0184051 A1 (Nirschl) — *examiner‑cited (**)

• Full citation: US 2012/0184051 A1, "Device and method for detecting at least one substance," priority 30 Sep 2009, published 19 Jul 2012.
• Prior‑art status caveat: Its publication date (19 Jul 2012) is AFTER this patent's 15 Apr 2010 filing date, so it is not § 102(a)/(b) art. It could only qualify under § 102(e) if its effective U.S. filing date precedes the applicant's invention date — I could not confirm that date from the available sources. Treat its prior‑art status as unconfirmed.
• § 102 mapping: Substance‑detection device/method; at most a § 103 consideration if § 102(e) status is established.

N1 — Griffiths (1926) — the reference the patent itself concedes

• Full citation: E. Griffiths, "A gas analysis instrument based on sound velocity measurements," Proceedings of the Physical Society 39(1):300–304 (1926). DOI 10.1088/0959-5309/39/1/327.
• Disclosure (verified): A quartz crystal maintained in piezoelectric vibration sets up stationary waves in the gas between the crystal's flat surface and a movable reflector. "The position of the nodes is recognised by the reaction on the quartz crystal, resulting in an increase of the current in the maintaining circuit." Node‑to‑node distance measures sound velocity, used for gas analysis and concentration of a gas in a mixture.
• § 102 mapping: This is the single most damaging piece of art, and — critically — the patent's own BACKGROUND section admits it: "An ultrasonic method utilizing resonance has been described in the article 'A gas analysis instrument based on sound velocity measurements' by E. Griffiths … By measuring the distance between adjacent resonances, i.e. a half wavelength, sound velocity in different gases is determined as well as the concentration of a gas in a gas mixture. However, none of the above presented methods can be used for measurements of low gas concentration."
  • Maps to claims 1, 4, 5, 6, 8, 9, 11, 13, 14: crystal + oscillator + movable reflector + stationary waves + reaction on the crystal detected as a current increase (the motional‑resistance/output‑signal concept) + sound‑velocity‑based gas analysis.
  • The applicant's asserted distinction is sensitivity to low concentration (the specification reports ~40 ppm He in air). That is a result/degree, which generally cannot confer novelty over a reference disclosing the same method; it would sound in § 103 (unexpected results).
• This reference alone is the strongest § 102/§ 103 combination against claim 1 and much of the apparatus claim 8.

N2 — Granstedt et al. (2001)

• Full citation: Granstedt et al., "Gas sensor with electroacoustically coupled resonator," Sensors & Actuators B 78:161–165 (2001).
• § 102 mapping: By its title/venue, a gas sensor with an electroacoustically coupled resonator — squarely in the claimed technical space (resonator + gas). Without verified full‑text mapping, treat as a strong § 103 reference on the resonator‑based gas sensor of claims 8, 13, 14 and as corroboration of the general principle. Flag as a candidate for deeper mapping.

N3 — Mecea (1993) — the inventor's own earlier work

• Full citation: V. Mecea, "Tunable gas sensors," Sensors & Actuators B 15–16:265–269 (1993).
• § 102 mapping: Authored by the named inventor and cited on the face of the patent. "Tunable gas sensors" suggests adjustable‑resonance gas sensing — relevant to the tuned‑distance d and resonance concepts (claims 4, 5, 6, 11, 15). Potential § 102(b) status as the inventor's own publication more than one year before filing. Note: the patent's citation list attributes the citation only to the examiner; I did not retrieve the article text, so the mapping is provisional.

C. Bottom line

1. No single cited reference reproduces the full combination of claim 1 or claim 8. Anticipation (§ 102) is therefore improbable on the current record, except possibly for narrow sub‑combinations.
2. The two references that matter most are US 2,536,025 (Blackburn) and the Griffiths 1926 article (N1). Both disclose a piezoelectric crystal + reflector forming an acoustic interferometer in a gas, with the same crystal detecting the reflected wave via a circuit‑current change — i.e., the substantive core of claim 1's motional‑resistance/output‑signal mechanism. Blackburn additionally discloses varying the reflector distance to accommodate temperature, which touches claim 1's temperature‑compensation limitation. The patent's own specification admits Griffiths as known art and distinguishes it only on sensitivity.
3. The remaining U.S. references are supporting § 103 art on sub‑elements: velocimeter sound‑path geometry and differential‑thermal‑expansion thermo‑compensation (P2, P3 → claims 1, 7, 12); ultrasonic transmit/reflect/detect measurement (P5, P12); resonator‑based fluid sensing (P11); piezoelectric resonator structure/material (P4, P14 → claims 8, 13, 14); and general gas‑sensor background (P6, P7, P8, P9, P10, P13, P15, P16).
4. Prior‑art‑status flags: US 2012/0184051 A1 (P17) post‑dates the filing date and qualifies, if at all, only under § 102(e) — unconfirmed. N3 (Mecea 1993) raises a possible self‑publication/§ 102(b) issue worth separate diligence.
5. The distinguishing theme of the patent — sensitivity down to ~40 ppm He in air — is a matter of degree, not a structural limitation in the claims. That makes the claim set vulnerable to a § 103 attack built on Blackburn + Griffiths + an ultrasonic velocimeter reference (e.g., P3) for the continuous/oscillator features. A definitive validity opinion would require full‑text claim charts against Blackburn, Griffiths, Granstedt (N2) and Mecea (N3), which I was unable to retrieve in full here.

Caveat, per instruction: I did not auto‑correct any patent number or identifier; all numbers are reproduced as they appear in the citation list. Where a reference's disclosure could not be independently verified, I have said so rather than asserted a definitive § 102 mapping.

I'll ground this analysis in the prior-art references listed on the patent page. Let me verify the content of the most probative references before drafting.

Obviousness Analysis Under 35 U.S.C. § 103 — U.S. Patent No. 9,267,924

"Method for detecting gas and a gas detector therefor" — Vasile Mecea; QCM Lab AB
App. 13/640,755; PCT/SE2010/000097; priority/filing 2010-04-15; granted 2016-02-23.

0. Scope, governing law, and evidentiary caveats

Governing law. The application was filed before March 16, 2013 (PCT filed 2010-04-15; U.S. national phase 2012-10-12). Accordingly the pre-AIA §§ 102/103 regime applies. This matters for one decisive reason: under pre-AIA § 102(b), a printed publication by the inventor himself published more than one year before the U.S. filing date is statutory-bar prior art, and the pre-AIA § 103(c) common-ownership exception does not remove a § 102(b) publication from the § 103 analysis. That point is central here because of the Mecea 1993 reference discussed below.

Evidentiary caveats (please read before relying on this):

• I have substantive text for the three references that carry the analysis: Griffiths (1926), Mecea (1993) "Tunable gas sensors", and Granstedt et al. (2001). I quote them directly.
• For the U.S. patent citations listed on the face of US 9,267,924, I have only titles/assignees/dates (from the Google Patents prior-art table), plus background knowledge. Where I infer content from a title, I say so and mark confidence LOW/MEDIUM.
• A § 103 conclusion is only as good as the full texts of the secondary references. Treat the U.S.-patent legs of each combination as provisional, and the NPL legs (Griffiths/Mecea/Granstedt) as well-grounded.

Flagged contradiction with the previously generated sections. The grant summary accurately reported that the specification's BACKGROUND asserts: "However, none of the above presented methods can be used for measurements of low gas concentration." That assertion is factually contradicted by the inventor's own prior publication, Mecea (1993), which reports detection of 10.8 ppm O₂ in a nitrogen matrix and catalyst-free, sub-second hydrogen-in-air response. I flag this because the "no prior method could detect low concentrations" narrative is the principal non-obviousness argument available to the patent owner, and it is unsupported on its face.

1. Distilling the claims into elements

Claim 1 (method) — elements

Claim 8 (apparatus) — elements

Dependents

2–3 (constant frequency; 0.5–500 MHz) · 4–6 (set d below resonance magnitude; resonance referenced to a reference gas; micrometer or piezoelectric actuator) · 7 (automatic thermal-expansion movement) · 9–10 (constant frequency; 0.5–500 MHz) · 11 (d based on reference-gas resonance) · 12 (thermally expanding materials dimensioned for thermo-compensation) · 13–14 (piezoelectric resonator; quartz) · 15 (d ≈ λ/2 to ≈ 50λ).

2. The prior art on the face of this patent

3. Ground-by-ground § 103 analysis

GROUND 1 — Mecea 1993 alone discloses every element; alternatively, it renders claims 1–7 obvious

Mecea (1993) is the inventor's own 1993 publication in the same technical family as the patent (and it is cited on the ESR for this family). Element by element against claim 1:

Assessment. On these facts Mecea 1993 is, at minimum, prima facie anticipatory under § 102(b), and necessarily obvious under § 103(a). The only escape routes for the patent owner would be (i) arguing that "motional resistance" and "magnitude of the output signal" are structurally different from "rectified r.f. voltage / vibration amplitude," and (ii) arguing that Mecea's gap dilatation is not "moving the reflecting surface." Both are weak:

• (i) is a labeling distinction. Under § 103, "the question is not whether the patentee's labels match the prior art's labels," and a constant-current oscillator makes output voltage a direct proxy for motional resistance — an electrical-engineering identity, not an inventive step.
• (ii) is undercut by Mecea's own words: the gap is changed with temperature by design to track the resonance condition, which is exactly "adjusting the distance d" for temperature.

Confidence: HIGH that Mecea 1993 renders claims 1, 2, 4, 5, 7, 8 (see Ground 3), 13, 14 obvious; HIGH that it anticipates at least claim 1.

GROUND 2 — Griffiths (1926) + Granstedt (2001) + Mecea (1993), for claims 1–7

This is the safer ground if a tribunal is uncomfortable treating the inventor's own paper as the primary reference.

(a) Griffiths 1926 supplies a 1b, 1c, 1d, 1e: a piezoelectric quartz crystal set into vibration, stationary waves between the crystal face and a movable reflector, node positions recognized "by the reaction on the quartz crystal, resulting in an increase of the current in the maintaining circuit," and gas analysis from the node-to-node distance. That is the transmission/reflection/interference/output-signal architecture of claim 1, in a gas-analysis context.

(b) Granstedt 2001 supplies the detection-physics bridge that the patent's "motional resistance" language depends on: a single piezoelectric element coupled to a reflecting-wall resonator shows a discrete resonance peak in its electrical impedance; adding He/CO₂ shifts that peak; and — critically — changing the transmitter-to-reflector distance produces "the same effect of the impedance as a change in the molecular mass." Granstedt thus supplies the explicit equivalence between (i) gas-composition change and (ii) cavity-length change, and frames detection as a change in the electrical response (impedance) of the transducer.

(c) Mecea 1993 supplies 1f (thermocompensation by gap dilatation) and the quartz-resonator + transistorized-oscillator + rectified r.f. voltage readout, plus the reference-gas tuning (claims 4/5).

Why the combination is obvious (motivation).

1. Same field, same problem, same solution. All three are acoustic gas sensors using a transducer facing a reflecting wall; the problem addressed is drift/quantification of a sound-velocity-dependent resonance. KSR directs that "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. Griffiths' own manual operation already implies compensation. Griffiths' instrument used a movable reflector precisely so the gap can be set/held. Adding an automatic, temperature-driven gap adjustment (Mecea) or an actuator (claim 6) is the application of a known compensating mechanism (US 3,482,647; US 2,536,025; US 5,557,047/US 6,094,987) to a known instrument — predictable result.
3. Granstedt expressly links distance and gas composition, which supplies the very rationale for keeping the gap fixed at a chosen offset while monitoring the electrical output — i.e., claim 1's continuous slope-based detection.

Confidence: MEDIUM–HIGH. The combination is well-supported; the residual uncertainty is whether "motional resistance" is construed so narrowly that Granstedt's "electrical impedance" is held not to disclose it. Even then, the recited change in magnitude of an output signal is squarely disclosed by all three.

GROUND 3 — Mecea 1993 + Granstedt 2001 (+ known QCM constant-current oscillator art) renders claims 8–15 obvious

Claim 15 (d ≈ λ/2 … 50λ): Granstedt uses 1.5λ; Mecea uses integer half-wavelengths; the description itself maps the range to "the first resonance peak to the 100th resonance peak." A recited numerical range that the primary references already bracket (and that the specification justifies only by convenience) is an obvious design choice under In re Aller / KSR.

Claim 6 (micrometer or piezoelectric actuator): movable reflectors driven by micrometer screws are the standard construction of ultrasonic interferometers (Griffiths; and in the examiner-cited interferometer/velocimeter family US 2,536,025 / US 3,482,647), and the piezoelectric-actuator alternative is the routine substitution of a known linear actuator.

Confidence: MEDIUM–HIGH for 8a–8e; HIGH for 8f and 15.

GROUND 4 — Dependent claims

4. Motivation-to-combine synthesis (KSR / Graham)

1. Identical field of endeavor and problem. Griffiths, Mecea, and Granstedt are all directed to measuring gas composition via sound velocity in a resonant cavity bounded by a reflector. The claimed invention is not a new field; it is a performance optimization of a 1926-class instrument.
2. Predictable results. Every recited function — resonance, wavelength-dependence on gas, temperature-dependence of sound speed, output-signal readout — was known and characterized (Griffiths: resonance reaction on the circuit; Mecea: temperature laws for cavity dilatation and sound velocity; Granstedt: linear impedance response vs. concentration).
3. A finite number of identified, predictable solutions. Choose the transducer (quartz/piezo), choose the drive (constant-current oscillator or impedance measurement), choose the operating point (on the slope), choose the gap. Each was known and each is claimed as a discrete choice.
4. Known technique, predictable improvement. Temperature compensation by adjusting the acoustic path length was the standard technique for high-Q acoustic cavities (Mecea 1993 by design; US 3,482,647 "precise sound path"; US 5,557,047/US 6,094,987 ultrasonic-with-temperature-compensation). Applying it to Griffiths'/Granstedt's cavity is the application of a known technique for its known purpose.
5. Explicit teaching in the art linking the elements. Granstedt 2001 literally states that changing the reflector distance produces the same impedance effect as changing the gas, i.e., it teaches the equivalence that the patent's claim 1 relies upon.

5. Secondary considerations and anticipated rebuttals

• Unexpected results — not supported. The patent touts a ~40 ppm He-in-air detection limit. Mecea 1993 reports 10.8 ppm O₂ in N₂ and catalyst-free sub-second H₂-in-air response, and Granstedt reports 0.7 vol% CO₂/He discrimination plus linear impedance response. The patent's performance is not superior to the art and is arguably inferior on the reported figures — a strong reason an "unexpected results" argument would fail.
• Long-felt, unmet need — not supported. Acoustic sound-velocity gas analysis is a 1926 technology; Mecea 1993 and Granstedt 2001 show sustained, successful development through 2001.
• Teaching away — the opposite is present. The patent's BACKGROUND says prior methods "cannot be used for measurements of low gas concentration," but the same record's Mecea 1993 teaches the opposite. Granstedt 2001's statement that its setup "does not represent an optimized solution" invites, rather than discourages, optimization.
• Possible patent-owner counter-argument (strongest). That the granted claims recite a "continuous process" at a fixedly arranged gap (claim 8) with motional-resistance-based detection, whereas Griffiths/standard interferometers move the reflector to null the output and read wavelength. Rebuttal: Mecea 1993 and Granstedt both set the gap and operate; the "fixed" limitation is disclosed or an obvious operating choice, and "motional resistance" is the routine QCM term for the loss that all three references describe functionally (energy absorbed by the gas changing the resonator's electrical response).

6. Bottom line

Overall: U.S. 9,267,924 faces a substantial, well-documented § 103 vulnerability, primarily because its own inventor's 1993 publication (cited in the European search report for this patent family) and the Granstedt 2001 paper (also cited in the ESR) collectively disclose the resonant-cavity, single-transducer, sound-velocity-based gas-detection architecture, gas-dependent output-signal change, slope/reference-gas tuning, and temperature compensation by adjusting the cavity gap. The single most likely ground to succeed is Mecea 1993 as the primary reference, with Griffiths 1926 and Granstedt 2001 as corroborating art and the ultrasonic-interferometer patents (US 2,536,025; US 3,482,647) supplying the actuator/micrometer setting of d.

Confidence statement. The NPL-based conclusions rest on quoted full text and are held with high confidence. Conclusions resting on the U.S.-patent citations (US 2,536,025; US 3,482,647; US 3,697,936; US 5,557,047; US 6,094,987; US 6,260,408) are provisional and should be confirmed against full texts before any validity opinion is finalized — particularly to confirm that these references disclose path-length/temperature compensation as I have inferred from their titles.