Evaluation of antenna-integrated 315MHz transmitter for smart microsensors

This paper presents the evaluation of the prototype of an integrated smart microsensor system that has been developed to monitor the motion and vital signs of humans in various environments. Integration of radio frequency transmitter (RF) technology with complementary metal-oxide-semiconductor/micro electro mechanical systems (CMOS/ MEMS) microsensors is required to realize the wireless smart microsensors system. The essential RF components such as a voltage controlled RF-CMOS oscillator (VCO), spiral inductors and an integrated antenna have been fabricated and evaluated experimentally. The fabricated RF transmitter and integrated antenna were packaged with subminiature series A (SMA) connectors, respectively. For the impedance (50 Omega) matching, a bond-wire type inductor was developed. Integrated techniques for the RF transmitter by CMOS compatible processes have been successfully developed. After matching, the measured emission power at distance of 5 m from RF transmitter was -37 dBm (76.1 dB muV/m). The radiation patterns for the prototype of smart microsensor is close approximately an isotropic antenna. Also, for the 300-MHz band application, the prototype of smart microsensor has been successfully demonstrated.