Patent GB-1076180-A (GB)
Title: Electrochemical logic elements
IPC: H03K19/02
Filed: 1964-11-30
Abstract: 1,076,180. Electrochemical logic elements. SPACE-GENERAL CORPORATION. Nov. 30, 1964 [Jan. 10, 1964], No. 48632/64. Heading H3B. Logic elements which may have learning properties use the Lillie nerve model comprising a soft iron wire immersed in nitric acid, a signal being propagated along the passivated surface of the wire in response to electrical stimulation at one end. A dilution of about 70% by weight of nitric acid in water is used, and when the soft iron is immersed an unstable, passivated, poorly conducting coating is formed on its surface. This coating is locally disturbed by the adjacent application of a positive potential at one end of the wire, and the local reaction then proceeds as a wave to the other end of the wire, the coating being re-established as the wave proceeds. As shown in Fig. 1, an electrode 16, 22, 25 is provided for each input and output of the logic element, each electrode consisting of a soft iron excitable portion 20 j oined with a thinner inexcitable portion 21 of a conductive metal, e.g. gold, silver, platinum or aluminium, which is chemically inactive in the diluted nitric acid. When the coating on the soft iron portion is locally disturbed by the adjacent application of a positive potential at a pin 30, 31, 32, a primary cell is formed by the exposed soft iron, the diluted nitric acid electrolyte and that part of the inexcitable portion 21 adjacent the soft iron portion 20. The primary cell current flows for the duration of the local reaction as it proceeds from one end of the iron wire to the other, this current tending to stabilize the disturbed coating. The logic element shown comprises two compartments 13, 14, each filled with diluted nitric acid, a dielectric partition 15 through which the inexcitable portions 21 of the electrodes extend separating the two compartments. The pins 30, 31, 32 and their associated electrodes 16, 22, 25 are respectively coupled to an input pulse source 33, an output circuit 34 and an inhibit pulse source 35. When the input pin 30 is pulsed a travelling wave current is set up in portion 20 of electrode 16 which circulates from compartment 14 to compartment 13 through electrode 22. Provided this current exceeds a threshold value a local travelling wave reaction is set up in portion 23 of electrode 22 which produces an output voltage. If, however, pin 32 alone is pulsed from the inhibit source no output is set up in electrodes 20 or 23 as the direction of current from compartment 13 to 14 through the electrodes is such as to stabilize the coatings on iron wire portions 20 and 23. If both input and inhibit pulse sources act together, simultaneous travelling waves of local reaction are produced in portions 20 and 26 which act as cells in series assisting and provide a short circuit path for the current produced. No output is then obtained from electrode 22. A modification is described, Fig. 4 (not shown), consisting essentially of two Fig. 1 elements in combination, each compartment 40, 41 housing three excitable iron portions 39a, 43a, 60a and 42a, 62a, 64a of a total of six electrodes 39, 42, 43, 60, 62 and 64. The input electrode 39 of the first element is continuously excited, the inhibit electrode 42 is coupled to a " b " pulse source and the output electrode is coupled by an elongated excitable conductor 61 to the inhibit electrode 60 of the second element. Consequently, the input electrode 60 is energized under NOT "b" conditions. An "a" pulse source is coupled to the input electrode 62 of the second element and the arrangement consequently produces an "a" AND " b " output from electrode 64. An alternative AND logical element is described, Fig. 5 (not shown), in which two input electrodes 71, 72 and one output electrode 73 have their excitable portions 71a, 72a, 73a in one compartment and the inexcitable portions 71b, 72b, 73b in the other compartment. The inexcitable portions 71b, 72b of the input electrodes are each dimensionally insufficient to enable a current to flow sufficient to stimulate the output electrode, and the threshold value of stimulating current is obtained only by energizing both inputs simultaneously. Alternatively, with larger inexcitable portions the logic OR operation is obtained. An exclusive OR arrangement is described with reference to Fig. 6 (not shown), in which each compartment has a respective excitable portion of input electrodes 80, 81 and an excitable portion of an output electrode 93 is common to both compartments. A modification of Fig. 1 having adaptive properties is shown in Fig. 7. In this embodiment each compartment is filled with an electrolyte comprising 54% nitric acid, 0À1% gold chloride and 46% water, gold being used as the material for the inexcitable portions of the electrodes 112, 114, 115. Field electrodes 122, 123 connected to a reversible D.C. source 125 are provided one for each compartment. When a positive potential is applied to one of the field electrodes shortly after a pulse is applied to one of the electrodes 112, 114, the flow of current through the excitable and inexcitable portions of a recently fired electrode will cause the growth of minute dendritic gold whiskers on the inexcitable portion. This growth will extend with successive pulsing, each pulse increasing the conductance of that input electrode. At the same time the negative potential in the other field electrode will diminish the dendritic growth on the other input electrode. By reversing the field electrode potentials the converse effect is obtained. Consequently, when sufficient pulses are applied to one electrode, the relative conductances become such that the other electrode when pulsed is unable to influence the output. Thus, if the input on electrode 112 is "a" and on electrode 114 is NOT "b," the output with sufficient training is either "a" or "O" depending on the polarity of the field electrodes. A two electrode element having adaptive properties is described, Fig. 8 (not shown), in which the excitable portions are irregular masses 133, 134 supported by glass balls 130 of various sizes packed in a single compartment. The balls reduce the bulk conductivity of the electrolyte and replace the dielectric partition of the previous embodiments. A more complex adaptive logic element using a poorly conducting membrane and also involving dendritic growths is described, Fig. 8 (not shown).