Embodiments relate to a sensor for use in a magnetic resonance tomography unit and to a system including of a magnetic resonance tomography unit and a sensor. The sensor includes an energy supply device, a data transmission device and a first resonant antenna. The first resonant antenna includes a signal connection to the data transmission device and/or the energy supply device. A significant mismatch of the first resonant antenna exists between the impedance of the signal connection and the impedance of the first resonant antenna in free space at a first resonant frequency.