**8. Conclusions**

The active and passive sensors and metamaterials antennas presented in this chapter are wideband, efficient, compact, and low-cost. RF energy harvesting modules are connected to the antennas and sensors. Electromagnetic waves propagating in the air can be collected by the antennas and converted to DC power that may recharge the healthcare, computing system batteries, wearable sensors, and other RF modules. Evaluation of efficient active and passive wearable antennas and sensors is one of the most significant goals in the evaluation of wearable healthcare devices, medical sensors, IoT, wireless communication and medical systems. Passive and active metamaterial compact antennas and sensors characteristics such as gain, matching, noise figure, efficiency, bandwidth, and radiation pattern are presented in this chapter. The directivity and gain of the sensors with CSRRs are higher by 2.5 dB 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 passive sensors are around 5 to 7.5 dBi. The receiving active sensor gain is 12 3 dB. The transmitting active sensor gain is 13 3 dB.

The metamaterial antennas and sensors discussed in this research may be used in wireless communication devices, computing networks, IoT devices, sport, and medical applications. Metamaterial technology is employed to design compact, efficient antennas and sensors. The receiving dual-polarized antenna network with the energy harvesting module, size is 21.54.5 cm. The printed slot antenna is vertically polarized. The printed dipole is horizontally polarized. The resonant frequency of the dipole with CSRR is around 0.33 GHz, which is lower by 15% than the resonant frequency of the printed dipole without CSRR. The measured antenna bandwidth is around 45% for S11 lower than -6 dB. The measured directivity and gain of the antenna with CSRR are around 5.5 dBi. The S11 of the optimized receiving metamaterial antenna is lower than -6 dB in the frequency range from 0.18 to 0.4 GHz, around 60% bandwidth. The receiving active sensor gain with TAV541 LNA is 12 3 dB, and the noise figure is better than 1 dB, for frequencies from 0.1 to 1GHz.

The active computed and measured transmitting antenna gain with HPA VNA25, is 13 3 dB 1 for frequencies from 0.1 to 0.8 GHz. The transmitting sensor output power is around 19.5 dBm.

Electromagnetic power amount in public centers, stadiums, hospitals, and malls may range from 1 μW/cm<sup>2</sup> to 5 mW/cm<sup>2</sup> . The harvesting system efficiency increases as function of the RF power collected by the harvesting system. The efficiency of the harvesting system is around 50% for 0 dBm input power. However, the efficiency of the harvesting system is around 60% for 10 dBm input power.

The antennas and sensors presented in this chapter may be used in medical devices that improve the daily health of patients. Wearable antennas and healthcare devices are an important choice for healthcare organizations, hospitals, and patients. The wearable sensors presented in this chapter support the development of personal healthcare systems with online immediate medical staff responses to treat and improve patients' health.
