A transmit resonator is provided. The transmit resonator comprises: two inductors; a switching network electrically connected to the inductors; a plurality of capacitive electrodes electrically connected to the switching network; a detector communicatively connected to the capacitive electrodes; and a controller communicatively connected to the switching network and the detector. The detector is configured to detect impedance. The controller is configured to control the switching network to control which electrodes are connected to the inductors based on the detected impedance. The inductors and electrodes are configured to resonate to generate an electric field.