Arduino lover. Interesting physics. Metal detector

Friends! I posted this video in order to reveal the essence of the principle of operation of the metal detector induction type. This experiment uses a homemade metal detector on the Arduino UNO. The natural frequency of the oscillating circuit, which consists of a search coil and a capacitor is about 62 kHz. In the presentation aluminum disk ( I used a paper disk covered with aluminum tape ), we see an increase in the frequency on the oscilloscope I think it’s a certain alloy has a diamagnetic properties fo