CED Patent #3842194: Information records and recording/playback systems therefor

Featured CED Patent No. 3,842,194

US03842194: Information records and recording/playback systems therefor

This patent was applied for on March 22, 1971, ten years to the day before RCA's nationwide introduction of the CED system. This application along with two other patents filed the same day represents the first detailed description of the CED system external to RCA. As illustrated in perspective (Fig. 1) and cut-away transverse (Fig. 2) views above, the system as conceived in 1971 was quite similar to what hit the market in 1981, i.e. a stylus (20) rides in a groove (14) of a vinyl disc (10) recovering capacitance variations from the modulation elements (18) in the bottom of the groove. Despite the overall similarity in appearance, a reading of the patent reveals some notable differences from the marketed CED system:

The 1971 system had a density of 1000 grooves/inch and a disc rotation rate of 360 RPM. The marketed system had 9541 grooves/inch and rotated at 450 RPM.
This patent describes a three layer disc consisting of a vinyl substrate (10) coated with a thin layer of conductive aluminum (11) followed by a thin dielectric layer of polystyrene (12). The final system used conductive vinyl (doped with minute carbon black particles) for the entire disc.
The stylus (20) shown above was made of sapphire, and had a tantalum electrode (23) embedded inside. The marketed system used a diamond stylus, and the electrode material was titanium sputtered directly on the trailing edge of the diamond stylus rather than being embedded. A later illustration in this patent shows that RCA was also experimenting with the direct sputtering of tantalum on the trailing edge of the stylus in 1971.
This patent mentions electron beam mastering as the preferred method. Electromechanical mastering was used in the final product and is mentioned as an alternative method in this patent.
The disc player described in the patent is a top load design similar to audio turntables of the period in which the operator places an uncovered disc on the turntable by hand.

Of the three patents filed on March 22, 1971, this one is the most detailed and is mentioned in hundreds of the CED patents that followed over the years. The credited inventor of this patent is Jon Kaufmann Clemens who developed the CED concept during his early days at RCA and can rightly be considered "The Father of the CED." The other two CED patents filed on March 22, 1971 are:

US03711641: Velocity adjusting system
US03783196: High-density capacitive information records and playback apparatus therefor

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