A biometric monitoring system comprises a substrate with a first surface having a length and a width. A first transmitting antenna is coupled to the first surface at a first end of the length of the first surface. A second transmitting antenna is coupled to the first surface at a second end of the length of the first surface. The first and second transmitting antennas extend across the width of the first surface. A plurality of receiving antennas are coupled to the first surface, each of which extends across the width of the substrate and is spaced apart from an adjacent receiving antenna along the length by a predetermined distance. A controller is configured to supply a first signal to the first transmitting antenna and sequentially measure a transmission coefficient or voltage of the first signal at the plurality of receiving antennas until an attenuation in the transmission coefficient or voltage exceeds a threshold.
