In this first stage of the project (2022) our team has carried out the design, construction and testing of the functional laboratory model - automatic installation for disinfection of hands (palms) with cold plasma.
The installation is based on a high-voltage generator circuit that provides the signal that initiates and maintains the electrical discharge (plasma) in an applicator. The electric discharge (plasma) is generated between the internal electrode of the applicator and the hand (palm) of the user, which the high voltage circuit "sees" as a ground plane.
The high voltage source is a radio frequency generator having an output frequency in the range of MHz. This frequency range was chosen for reasons of electroprotection of the user: at frequencies in the radio range, the skin effect occurs, thus the high-frequency currents flow on the outer contour of the surface exposed to the plasma - the user's palm in the present case. Also for reasons of electroprotection of the user, the power supply of the high voltage source is carried out by means of a special circuit that separates the entire installation from the 220V~ network, during the treatment.
The operation of the entire cold plasma disinfection plant is controlled by a central control module based on a microcontroller. This central control module activates the peripherals of the installation by means of relays according to the command given by the user.
For the protection of the high voltage source (and implicitly the user), the supply line is supervised by a protection circuit that monitors the current intensity to the high voltage source with the help of a current transformer. In case of exceeding a value considered maximum, the protection circuit provides a fault signal to the central control module, which thus stops the supply of the high voltage source.
The cold plasma disinfection test consisted in exposing the surfaces of some bacteria cultures to the effect of electric discharge, for an output power of 50W (limited in the circuit) and different exposure times, from 5 to 15 seconds.
To study the surface morphology of the bacterial cultures, SEM electron microscopy image captures were also performed.
Under the effect of the ion bombardment generated in the volume of the electric discharge, the bacteria are destroyed by an "explosion" effect of the cell membrane. The diameter of the bacteria before treatment is approx. 1.77±0.37 µm, and after the plasma exposure we observe the diameter reduction to 0.88±0.11 µm (fragments of the exploded bacteria) (values measured on SEM images).
Thus, for a plasma treatment duration of 15...20 seconds, we achieved the complete destruction of bacteria/fungi colonies.
The following images show the laboratory prototype of an automatic installation for the disinfection of hands (palms) with cold plasma, designed, made and tested at INCDTIM Cluj-Napoca.