Fig. 1

 A When the coil is placed on the head, the primary magnetic field (black) generates looping eddy currents within the target (purple). These eddy currents generate a counteracting magnetic field (blue) which causes a measurable change in coil resistance, resonant frequency, and impedance. B When a more conductive hemorrhage is present, more eddy currents are generated, and a larger counteracting magnetic field is produced. Image created using Biorender.com