Using analytical signals and synchronous detection to obtain signals of skin galvanic activity on alternating current

The interest in the skin galvanic channel for obtaining information about a person's condition is related to the fact that these signals mainly arise as a result of higher nervous activity. This makes them interesting in a number of practical applications, such as lie detectors, devices for monitoring the ability of operators, etc. The aim of this work was to improve the method for measuring the parameters of the GSR in order to increase the accuracy, noise immunity and reliability of measurements. For this purpose, measurements on alternating current were used. To increase the accuracy and noise immunity, the known principle of synchronous detection in combination with the mathematical apparatus of analyzing analytical signals was used. The experiments were conducted on 6 subjects. As a result of the experiments, the records of signals from the object of study and from the excitation signal generator were obtained. These signals had a sinusoidal shape, but they had different amplitudes and relative phase shifts. To obtain the parameters of the measured impedance, an approach based on the use of analytical signals was used. Measurements on alternating current allow obtaining, in addition to the active component of the impedance, also a reactive component – capacitance. It is shown that when using a sinusoidal signal as a probing voltage, as well as when using a mathematical apparatus for analyzing analytical signals and synchronous detection, it is possible to obtain high-quality parameters of the GSR signals, both their real and imaginary parts. It turned out that the relative value of fluctuations on the dependence of the active part of the impedance was about 7‧10–5, while the relative value of fluctuations of the imaginary part, measured in the same way, was close to 6‧10–5. Thus, the question of what better and more accurately characterizes the GSR remains open. As a result of the work performed, an improvement of the method for measuring the parameters of the galvanic skin response with probing alternating voltage of a sinusoidal shape using a mathematical apparatus for analyzing analytical signals and synchronous detection was proposed and implemented. It is shown that in this way it is possible to measure the parameters of the GSR with a relative accuracy of about 10–4 or 0.01%. This fully satisfies the requirements of the practice known to us, where the GSR signals are usually recorded with a minimum value of 0.2%. The analysis also showed that the improved method has a higher noise immunity compared to traditional recording on direct current. This made it possible to use significantly lower values of the probing voltage than on direct current, usually amounting to 1 V – 1.5 V. On alternating current, the above-mentioned recording accuracy (about 10–4 or 0.01%) is realized with an effective value of the exciting signal of about 0.1 V, which made it possible to eliminate the influence of nonlinear effects during GSR measurements.