Synthesis of a Zobel “M-Derived Half Section” and “Constant K” Filter
(A Human-Competitive Result Produced by Genetic Programming)
Genetic programming evolved a Zobel “M-derived half section” and “constant K” filter circuit as described in Section 25.15.2 of Genetic Programming III: Darwinian Invention and Problem Solving (Koza, Bennett, Andre, and Keane 1999). The “M-derived half section” in this figure is the vertical shunt containing capacitor C3 and inductor L11.
The circuit in the figure has the recognizable features of the circuit for which Otto Zobel of American Telephone and Telegraph received U.S. patent1,538,964 (Zobel 1925). Zobel invented the idea of adding an "M-derived half section" to one or more "constant K" sections. As he explains in U.S. patent 1,538,964 (Zobel 1925),
“The principal object of my invention is to provide a new and improved network for the purpose of transmitting electric currents having their frequency within a certain range and attenuating currents of frequency within a different range. . . . Another object of my invention is to provide a wave-filter with recurrent sections not all of which are alike, and having certain advantages over a wave-filter with all its sections alike.”
The advantage of Zobel's approach is a "sharper transition" in the frequency domain behavior of the filter. Claim 1 of Zobel's 1925 patent covers
“A wave-filter having one or more half-sections of a certain kind and one or more other half-sections that are M-types thereof, M being different from unity.”
Claim 2 covers
“A wave-filter having its sections and half-sections so related that they comprise different M-types of a common prototype, M having several values for respectively different sections and half-sections.”
Claim 3 goes on to cover
“A wave-filter having one or more half-sections of a certain kind and one or more half-sections introduced from a different wave-filter having the same characteristic and the same critical frequencies and a different attenuation characteristic outside the free transmitting range.”
Viewed as a whole, the differences between the teachings of Zobel's 1925 patent and the evolved circuit are minor and unsubstantial. Thus, under the "doctrine of equivalences," the evolved circuit infringes on the claims of the now-expired Zobel patent.
Referring to the eight criteria in chapter 1 of Genetic Programming III: Darwinian Invention and Problem Solving (Koza, Bennett, Andre, and Keane 1999) for establishing that an automatically created result is competitive with a human-produced result, the automatic synthesis of the Zobel “M-derived half section” filter circuit satisfies the following two criteria:
(A) The result was patented as an invention in the past, is an improvement over a patented invention, or would qualify today as a patentable new invention.
(F) The result is equal to or better than a result that was considered an achievement in its field at the time it was first discovered.
Johnson, Walter C. 1950. Transmission Lines and Networks. New York: McGraw-Hill.
Koza, John R., Bennett III, Forrest H, Andre, David, and Keane, Martin A. 1999a. Genetic Programming III: Darwinian Invention and Problem Solving. San Francisco, CA: Morgan Kaufmann.
Zobel, Otto Julius. 1925. Wave Filter. U.S. Patent 1,538,964. Filed January 15, 1921. Issued May 26, 1925.
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Last updated on December 28, 2003