A sand control screen assembly is operably positionable within a wellbore. The electronic unit comprises a mechanical part, a circuit board attached to the mechanical part and an electronic component connected to the circuit board. For example, the surface-oxidized areas are one or more lowly-surface-oxidized areas and one or more highly-surface-oxidized areas. This also allows the end portions to be reduced in thickness, thus decreasing the dimensions of the connector. The microwave is supplied into the reaction vessel through a radial-slot antenna. The control unit is designed to synchronize the operation of the spectrum determination unit as a function of the time intervals allocated to the transmitters for the determination of the spectrum of the incoming signal in the predetermined frequency band.