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.