Thermal Junction Rectification Artifact

The thermal junction rectification artifact is the alternative explanation offered by Harry F. Breckel in 1927 for the apparent rectification produced by Palmer H. Craig's stacked bismuth plates.

The finding

Breckel tested the device at Craig's Macon, Georgia laboratory and at a large commercial laboratory, with the inventor supervising. He found that the apparent rectification arose from lead and copper contacts on the bismuth films producing a small unidirectional transverse current — of the order of a few millivolts — when heated by the current. The output-to-input efficiency was very low.

Two further artifacts were identified in the same tests:

• Inductive meter artifact. Current and voltage readings were largely due to wires and meters sitting in the strong magnetic field; readings fell to absolute zero when the meters were moved away.
• Capacity/"feed-through" artifact. The assembled plates acted as a condenser, feeding antenna current through to conventional vacuum tubes that did the actual work. Radio reception results were zero.

Breckel concluded that the Hall effect principle as applied to radio was "entirely without merit at this time."

General lesson

The artifact illustrates a recurring problem in low-level electrical measurement: a genuine but unwanted thermoelectric or inductive effect can mimic the phenomenon under test. The standard control — reversing the magnetic field and averaging, since the Hall emf reverses with the field while thermal effects do not — is the same control C. W. Heaps recommended for Craig's low-field measurements.

See also

Hall-Effect Rectification, Anomalous Low-Field Hall Coefficient in Bismuth, comparisons/comparison-craig-hall-effect-claims-vs-evidence.