Principles of Very Low Power Electrochemical Control Devices

A new technology util izing electrochemical phenomena has been developed, from which it is possible to design detection and control devices requir ing extremely low power consumption, in the order of 100-1000 times smaller than that of transistors. As an example, an electrochemical detector for acoustic energy operates on 10 gw in the quiescent state, delivering 300-500 t,w when ful ly excited. Development work to date has been limited to low frequencies (0-200 cps). Reversible redox systems and working d-c electrodes are used in conjunction with such electrochemical phenomena s concentration polariza-tion, electrokinetic effects, and the electrocapillary curve of mercury. Use of Concentration Polarization for Flow Detection The use of Pt wire micro-electrodes and the dif-fusion current for the analysis of electrolyt ical ly reducible or oxidizable substances is wel l known (1). A great deal of in format ion on the effects of st i rr ing (as, for example, with rotat ing Pt elec-trodes) has also been publ ished in the chemical l i terature (2). That these phenomena can be used for detecting and measur ing fluid flows wil l be im-mediate ly apparent o the reader. That the type of funct ion obtainable from an electrochemical un i t operat ing on this pr inc ip le may be made to vary over a considerable range by changing the electrode design is not quite so obvious. A typical flow detector is shown in Fig. 1. Elec-trodes may be of any metal which is inert to the electrolytic system used. In this part icu lar example Pt electrodes are used in an electrolytic system of Is and KI in water. The cathodic reduct ion of Is is made the control l ing react ion by using a low con-centrat ion of iodine (10-~N) and a high KI (sup-port ing electrolyte) concentrat ion (0.5N). Other electrolyte systems may be used, as, for example, ferr icyanide- ferrocyanide, bromine-bromide, ceric-cerous, ferr ic- ferrous, etc. It is only necessary that they be reversible redox systems