## Facts

- Walker owned patents covering apparatus and methods for locating fluid levels and obstructions in oil wells using acoustic pulses and returning echoes.
- The apparatus claims described a combination including: (1) a wave source at the well head, (2) an echo detector, (3) a tuned acoustical resonator to emphasize a selected frequency component of the echo, and (4) timing/recording means to compute depth from the echo’s return interval.
- Halliburton used an echo-based measuring system that performed the same general task but used an electrical filter, rather than an acoustical tuned resonator, to select the desired frequency component of the returned signal.
- Walker and licensees sued Halliburton for patent infringement involving three patents.
- The district court held two patents valid and infringed (including specified apparatus claims) and held a third “method” patent invalid for lack of invention.
- Halliburton appealed the validity and infringement findings; Walker sought reversal of the method patent’s invalidity ruling.

## Issues

1. Whether Halliburton infringed Walker’s apparatus claims when Halliburton substituted an electrical filter for the claimed acoustical tuned resonator (doctrine of equivalents).
2. Whether the asserted apparatus claims were valid over the prior art or were merely an unpatentable aggregation of known elements.
3. Whether the separate method patent, directed to determining depth by applying an equation to echo timing data, stated patentable invention.

## Decision

- The Ninth Circuit affirmed the judgment that Halliburton infringed specified apparatus claims, holding the electrical filter was equivalent to the acoustical tuned resonator within the claimed combination.
- The Ninth Circuit upheld the validity of the litigated apparatus claims, treating Walker’s arrangement as a patentable combination producing a new and useful result in oil-well depth measurement.
- The Ninth Circuit affirmed the invalidity of the method patent for lack of invention, concluding it amounted to a mathematical relationship applied through routine calculation.

## Legal Principles

- Infringement may be found when an accused device substitutes an element that performs substantially the same function in substantially the same way to achieve substantially the same result as the claimed element (equivalents).
- A combination of known components may be patentable when the arrangement yields a new and useful result not taught by the prior art, rather than a mere aggregation of known parts.
- A claimed “method” that chiefly recites a mathematical relationship or principle applied through routine computation, without an additional inventive contribution, is not patentable invention under the standards applied.

## Conclusion

The Ninth Circuit held that Walker’s echo-measurement apparatus claims were valid and infringed because Halliburton’s electrical filter was an equivalent substitute for the claimed tuned resonator, but it affirmed that Walker’s separate formula-based method claim was invalid for lack of invention.


Halliburton Oil Well Cementing Co. v. Walker, 146 F.2d 817 (9th Cir. 1944)