The induced current is produced because of the induced magnetic field and is passing through the coil (which generates the external magnetic field). Radio frequencies from the sample are emitted to return to its ground state after the external radiofrequency pulse excited its nuclei. So, both of them exist, but I don't understand what happened with the detector? Is induced current passes through the coil to the detector then it sends the signal to the software as FID? OR the radio frequencies that are emitted then the detector collects them and sends them directly to the software? and if any of them happen what do we use the other?