Design, realization and measurement of micro-magnetic radiators inside pipes filled with water

The paper presents the design, realization and measurement of micro magnetic antennas for the construction of wireless sensors and active RFID components. Small magnetic antennas are suitable for applications requiring the transmission through a dissipative medium. Furthermore, they exhibit a good omnidirectional radiation diagram and, especially for sensing applications, small antennas are necessary to reduce space occupation. Unfortunately, small antennas are characterized by light efficiency and high mismatch. This manuscript introduces an efficient way to reduce the overall antenna dimensions by selecting an efficient geometrical shape and embedding the matching circuit inside the antenna. The return loss has a 0.6% bandwidth at -10 dB, larger in comparison to other realizations than can be found in the literature. Although several realizations at different frequencies have been carried out, two solutions, at 433 MHz and 900 MHz, with simulations and measurements, are presented.