signal transmission from sensor nodes on the body to another relies on radiation into the surrounding space. Due to obstruction by the body, the range at which a radiative signal can be intercepted is generally much larger than the separation distance between the devices. As an illustrative example, we performed full-wave simulations of radiative propagation from a transmit node on the abdomen to a receiver node on the back (FIG. 11B). The field intensity at the receiver is the same as at ~22 m in front of the subject (FIG. 11C); this eavesdropping range cannot be reduced by power control without compromising communication between the wearable devices. In contrast, metamaterial textiles localized the wireless signal within 10 cm of the body, enabling efficient transmission around the body without radiation into the surrounding space (FIG. 11B). This physical-layer security can complement cryptography and protocol-based approaches because it requires no additional computation or modification of the wireless device. [00150] Reference is now made to FIG. 12A, which is a schematic illustration of LED current as a function of frequency at an input power of 100 mW to an antenna placed above the metamaterial textiles, according to embodiments of the present disclosure, and to FIG. 12B, which is a schematic illustration of Wireless power transfer efficiency, measured as the power delivered to the LED (including nonlinear rectifier losses), as a function of input power, according to embodiments of the present disclosure. The efficient propagation of radio surface plasmons on metamaterial textiles enables wireless power transfer to many classes of lowpower sensor. As a demonstrative example, a pulse indicator was wirelessly powered on the wrist (FIG. 4A) by guiding energy along a long-sleeved sweater along the length of the arm. When powered, the pulse indicator provides a visual indication of the subject’s heartbeat because the intensity of the light-emitting diode (LED) is modulated by a resistive pressure sensor that senses pulsation on the wrist of the user. The transmitter was placed on the shoulder and the output power set to 20 dBm (100 mW, equivalent to a WiFi transmitter). Monitoring the LED brightness during wireless power transfer shows that the pulses correspond to periodic cardiac activity recorded by ECG (FIG. 4D). The transfer efficiency in this configuration is estimated to be 10.5% to the loop antenna and, including losses due to the rectifier, 3.5% to the LED (FIGS. 12A-12B). These power levels meet requirements for many low-power sensors, including temperature, pH and other physiological markers, which consume less than 1 mW. [00151] Reference is now made to FIG. 13A which is a schematic illustration of an image of the back of a sensor node integrated with a custom wireless energy harvesting unit, according to embodiments of the present disclosure. The output of the energy harvesting unit is directly connected to the power management circuit of the Bluetooth module. Reference is further made to FIG. 13B, which is a schematic illustration of an image of the sensor node placed on the wrist of a user, while