EXTASIS: Radio detection of cosmic rays at low frequencies

The detection of cosmic rays via the electric field (the so-called radio detection) is nowadays a fully operative technique. With the aim of exploring the low-frequency part of the emission spectrum (below 10 MHz), the EXTASIS experiment has been conceived. Located within the CODALEMA experiment at the Nancay radio-observatory, EXTASIS measures the low-frequency emission coming from the extensive air showers created by cosmic rays. Being able to calculate the electric field at low frequency is crucial in order to correctly interpret our results. We present some results from the EXTASIS experiment and discuss the calculation of the low-frequency radio signal. We also present a new formula for the electric field of a particle track within two semi-infinite media (air and soil).