A method is provided that includes setting up a composite material structure under test (SUT) between a transmit coil and a receive coil. The transmit coil is driven with a RF signal over a plurality of frequencies, thereby causing the transmit coil to produce a magnetic field that by magnetic coupling through the SUT induces a voltage in the receive coil. The voltage in the receive coil is measured, and from the voltage, a measurement of attenuation of the RF signal caused by the SUT between the transmit coil and receive coil is produced. And an effective conductivity of the SUT is calculated from the measurement of attenuation.