Abstract: An intelligent radiofrequency measuring device is presented. It contains a section of a TEM transmission line as a sensor, which is short-circuited at one end, along with an electronic unit based on a PIC microcontroller. The device provides temperature error compensation and enhanced functionality. It can be used for detecting hidden metal objects as well as for contactless counting of moving metal objects. We present an intelligent radiofrequency (RF) measuring device that uses a section of a TEM transmission line, short-circuited at one end, as a resonant sensor. A compact electronic unit built around a PIC microcontroller measures the sensor’s resonance and performs temperature-drift compensation by computing the digital frequency difference between a periodically captured background resonance F_0 and the current resonance F. The device supports two operating modes: (i) metal detection with audible feedback proportional to ∆f=|F-F_o | and (ii) contactless counting of moving metal objects using a programmable decision threshold. Compared with conventional beat-frequency oscillator (BFO) metal detectors, the proposed architecture avoids parasitic phase locking of dual oscillators, simplifies tuning, and improves robustness to environmental variations (e.g., soil and nearby structures). A prototype with a ring-shaped aluminum sensor (D=90 cm,d=18 mm) achieved detection depths up to 115cm for large metallic targets and reliably counted metal objects passing through the sensor’s field. These results indicate that low-cost, microcontroller-assisted resonant sensing can deliver practical sensitivity while enabling additional functionality, such as target discrimination via the sign of ∆f.

Keywords: radiofrequency sensor, short-circuited stub, resonant frequency, metal detection, contactless counting, temperature compensation, microcontroller

Pages: 120-124

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