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Performance of wireless sensor systems are evaluated on the basis of the quality of data communication and efficiency of power transmission. This work presents the design methodology of a miniaturized tag antenna for remote powering of wireless sensor systems at 2.45 GHz ISM band. Accurate simulations of the rectifier input impedance aimed at the maximization of transmitted power are presented. Simulation results combined with simple transmitting antenna scattering parameters and cable loss measurements provide straightforward characterization of the fabricated tag antenna. The experimental measurements on a 12x10mm miniaturized antenna designed with the proposed approach show a gain of -5.9 dB close by 0.8 dB to the simulation results.

The design of a wearable antenna for UHF band at 900 MHz with an integrated front-end for a wireless sensor system targeting remote patient monitoring is presented. A wearable antenna for human body with-7.2 dB gain is demonstrated using five layer torso model. The antenna can deliver 25 µW of power to the rectifier at 4.6 meters distance from the base station emitting PEIRP =4 W. Local power management circuitry consumes a total power of 4 µW while delivering 10 µW of power for the sensors of the wireless sensor system. The system designed with 0.18µm CMOS process demonstrates the performance of the frontend together with 3D electromagnetic simulation results of the wearable antenna.

Optimal matching between tag antenna and integrated circuit is crucial for maximizing delivered power in remotely-powered sensor systems. The method maximizes conjugate matching between antenna with inductive reactive impedance and an integrated circuit with capacitive reactive impedance. Obtaining the desired conjugate impedance by the intrinsic antenna impedance excludes the need of an impedance matching network. This enables fully integrated sensor systems with further miniaturization. In this study the design of a meandered slot antenna with genetic algorithm optimization for an operation frequency of 2.45 GHz is proposed. Investigations on constraints limiting the power link efficiency between reader and tag antenna at system level outline possible design actions and give rise to the design flow of the antenna. Simulation results on the proposed architecture verify the performance of the designed miniaturized antenna.

The design methodology of a miniaturized tag antenna and an integrated rectifier for remote powering of wireless sensor systems operating at 2.45 GHz ISM band is presented. To maximize the power transfer the antenna input impedance is matched to the conjugate of the rectifier impedance. The overall efficiency of the rectenna is evaluated through the combination of the simulations and experimental results with the antenna-rectifier chain (rectenna) and the radiating source antenna (transmitter) respectively. A 16x8mm 2 tag antenna placed 12 cm apart from a transmitter having 2 of provides maximum output power of 560 . The efficiency of rectenna is analyzed considering CMOS process variations affecting the rectifier.