A method of purifying substances is described herein, particularly suitable for purifying silica and forming it into silicon oxide sheets or ribbons, or silicon sheets or ribbons. Alternatively or in conjunction, the directional antenna array includes a balun structure that is configured to couple the driven element to at least one of an electromagnetic energy source and an electromagnetic sink, and the balun structure includes a dipole structure, a first feed point extending from the dipole structure and a second feed point extending from the first parasitic element. According to the invention the sensor head is physically separated from the electronic module and is combined, at least with the core, to form a single-piece structural unit which is surrounded by a common anti-corrosion layer. In one configuration, the circuit input is applied to the gate of the transistor via the resistor, and the output is taken from the source of the transistor.