**Abstract**

This chapter presents novel passive and active wearable sensors for biomedical systems, energy harvesting, and communication devices. Design tradeoffs, simulation, and measured results of compact efficient sensors for communication, energy harvesting, IoT, and healthcare systems are discussed in this chapter. The new sensors are green sensors with an energy harvesting unit. The sensor electrical parameters near the human body were evaluated by employing RF CAD software. The sensors are flexible passive and active devices with high efficiency and low cost. Low-cost sensor may be developed by printing the printed antenna with the antenna feed network and the active components on the same board. Efficient metamaterial sensors were developed to improve the system electrical performance. The resonant frequency range of the sensors, with Circular Split-Ring Resonators CSRRs, is lower by 5% to 11% than the sensors with CSRRs. The directivity and gain of the sensors with CSRRs are higher by 2.5dB than the sensors without CSRRs. For S11 lower than –6 dB, the bandwidth of the novel metamaterial sensors may be around 15 to 55%. The directivity and gain of the new metamaterial sensors are around 5 dBi to 7.5 dBi. The receiving active sensor gain is 12 3 dB. The transmitting active sensor gain is 13 3 dB.

**Keywords:** wearable devices, wearable resonators, healthcare applications, IoT, metamaterial resonators, active antennas, communication, RF energy harvesting, self-powered devices
