RADIOMEASURING GAS CONCENTRATION TRANSDUCER BASED ON TRANSISTOR STRUCTURE WITH NDR FOR THE DIAGNOSIS OF STRAINS OF THE BACTERIUM HELICOBACTER PYLORI

Abstract

The article discusses a radiomeasuring gas concentration transducer for the diagnosis of strains of the bacterium Helicobacter pylori. One of the promising directions in the construction of gas concentration transducers for respiratory diagnostics is the use of gas concentration frequency transducers based on the reactive properties of transistor structures with negative differential resistance (NDR). This type of transducers allows you to solve the problem of using analog-to-digital converters, because it implements the method of converting "informative signal - frequency", which is one of the best for further processing on a computer. Theoretical and practical studies have shown that using the reactive properties of semiconductor devices and transistor structures in which there is a negative differential resistance, it is possible to significantly increase the sensitivity and accuracy of measuring gas concentration, in particular NH3. The authors proposed and studied a gas concentration measuring transducer, which is built on the basis of a transistor structure with negative differential resistance and a gas-sensitive element to NH3. With a change in gas concentration, the conductivity of the sensitive element changes, which adsorbs NH3 molecules, which in turn changes the active and reactive components of the impedance of the transistors structure. The reactive component of the impedance of the transistors structure is capacitive in nature. This capacitance is part of the total capacitance that occurs at the electrodes of the drain of a double-gate MOS transistor and collector of a bipolar transistor, which together with the inductance L form a resonant oscillatory circuit. A dynamic mathematical model of the frequency transducer of gas concentration by the method of variable states is developed. The dynamic model of the self-generating secondary transducer of gas concentration allows you to determine the value of the frequency of the output signal depending on the change in gas concentration at any time. Analytical expressions of the transformation function and sensitivity equations are obtained. The sensitivity of the developed device for the diagnosis of strains of the bacterium Helicobacter pylori ranges from 2.1 kHz/ppm to 3.4 kHz/ppm.