above the textile surface with 2 mm step size. The surface modes were excited using a dipole with 1 cm length placed 2 mm above the input position, driven by a signal generator (Model 835, Berkeley Nucleonics). 

[00133] According to some embodiments, transmission was measured as | $_{2i}$| between two identical l-inch short antennas (2.4 GHz, RN-SMA-S-RP, Microchip Technologies) connected to a vector network analyser (PicoVNA 106, Pico Technology) using coaxial cables (SMA-SMA, 50 Ω , Amphenol). The spacing between the antennas and the textile surface was set to 2 mm using foam separators. 

[00134] According to some embodiments, wireless communication was performed using the Bluetooth low energy (BLE) protocol. Sensor nodes made use of single-mode Bluetooth v4.0 modules (BL600, Laird Technologies) configured with an integrated antenna, a coin cell battery adapter (BA600, Laird Technologies) and a 3 V lithium battery (CR1632, Energizer). Sensors transmitted to a central hub consisting of an Android smartphone running a connectivity application (nRL Connect, Nordic Semiconductor) that recorded the signal strength from each sensor. Latency measurements were performed using connectivity testing software (UwTerminalX, Laird Technologies) run from a laptop connected to a hub device (BL620, Laird Technologies) wirelessly connected to the sensor nodes. 

[00135] According to some embodiments, wireless power transfer used a l-inch short antenna (RN- SMA-S-RP, Microchip Technologies) placed on the textile surface for power transmission. The antenna was driven by a 2.4 GHz signal input directly from a signal generator (SMB100A, Rohde and Schwarz) at 20 dBm (100 mW). The wireless energy harvesting unit was implemented using flexible printed circuit boards (PCBs) integrating the loop antenna and interconnection traces, fabricated commercially (O.l-mm-thick polyimide, 0.5 oz Cu, Gold Phoenix Printed Circuit Board). The rectifier was assembled on a rigid PCB (R4-TG130 substrate, 1 oz Ag, Interhorizon Corporation Pte) by microsoldering (NAE-2A, JBC) the following components: (1) 10 p capacitor (Johanson Technology, 250R05L100GV4T), (2) 10 n capacitor (Murata Electronics, GRM0335C 1HR20WA01D), (3) 0.2 p capacitor (Murata Electronics, GRM0335C1ER50BA01D) and (4) Schottky diode (Skyworks, SMS762 1-060). The PCBs were integrated together with a red LED chip (Lumex, SML-LX0603SRW-TR) by microsoldering. The pressure sensor was connected in parallel with the LED by copper wire to yield the wireless pulse sensor device. 

[00136] According to some embodiments, evaluation of wireless sensor networks on the body was performed with six healthy subjects (three females and three males), aged 20 to 40 years. Subjects wore an athletic shirt integrated with metamaterial textiles with sensors attached on the back and 

