Patent GB-1203126-A (GB)
Title: Electronic olfactory detector
Inventor: MEINHARD JAMES EDGAR
IPC: G01N30/64
Filed: 1968-10-31
Abstract: 1,203,126. Semi-conductor gas -detectors. J. E. MEINHARD. 31 Oct., 1968, No. 51597/68. Heading H1K. [Also in Division G1] A sensor for detecting the molecular components of a smell consists of at least one organic rectifying diode with its junction exposed to the olfactory agent and with means for monitoring the junction characteristic. The diode has two layers of different organic materials in contact and can be of PP<SP>+</SP>, PN or NN<SP>+</SP> form. Many Lewis bases are N-type conductors and many Lewis acids are P-type conductors. Examples of N- and P-type materials are given. Specific diode combinations are: phenazine vs the charge transfer complex (CTC) of chloranil and p-phenylenediamine; indigo vs chloranil; indigo vs CTC chloranil and p-phenylenediamine; chloranil vs CTC chloranil and p-phenylenediamine; indigo vs fluorescein; phenazine vs CTC tetracyanoquinodimethane and triethylamine; phenazine vs fluorescein; phenazine vs indigo; phenazine vs CTC chloranil and 2: 5-dimethoxyaniline; and indigo vs CTC tetracyanoquinodimethane and triethylamine. The two superposed layers may be sandwiched between planar electrodes or between coaxial cylindrical electrodes; one of the electrodes and the organic body is multiply apertured to allow access of the olfactory agent to the junction. With the cylindrical device the olfactory agent may be fed through the central tube. Manufacture of the diodes is described with detail relevant to formation of the electrodes, the body, and to the formation of the apertures to expose the junction. Response of the sensor is dependent on concentration of the molecular entities detected, different junction combinations respond differently to different molecular entities, and sensors with identical junction combinations may respond differently to molecular entities if the sensors are differentially heated or illuminated. Fig. 5 shows an arrangement of different sensors held at the same temperature and exposed to the same " atmosphere " (liquid or gaseous). The current measured by ammeter 20 gives an indication of the total content of material detected whereas the components present are identified by comparing the responses of each diode with a diode 25 chosen as a reference. The reference diode may, as shown, be covered with semipermeable material 36 so that it cannot respond to certain entities. Diode 29 is shown illuminated to respond most strongly to particular molecular entities by suitable choice of wavelength of illumination. A diode may be made more responsive to certain materials by immersing itin a liquid which selectively removes these materials from a multicomponent gas stream. Alternatively particular materials may be selectively applied by freezing out or by gas chromatography. The sensor array is calibrated with known quantities of known materials. In modified circuits a bridge with backing potentials may be used to give more linear response or the circuit illustrated may be modified by the use of individual potentiometers to replace resistors 30-34. In advanced systems analogue to digital conversion may be used to feed information to pattern recognition units and display systems or to operate alarms.