Antenna Near-field for Distance Sensing Applications

Antennas are increasingly being used for sensing applications due to their simple construction and ability to perform both sensing and communication functions which can reduce device construction requirements and cost. In this research, an antenna based distancing method is proposed. Unlike other antenna-based sensing techniques that utilize resonant frequency shift for sensing, this method uses the attenuation of the transmission coefficient magnitudes for distance sensing. This was verified through measurements done in air. The resonance frequency remained constant (and therefore could still be used for communication) while the transmission coefficient varied with the distance between and transmit and receive LTCC antenna (and therefore could be used for sensing). For a fixed frequency, the distance was estimated using the transmission coefficient attenuation and the Friis equation modified for a link in the near field. Further still the experiments were repeated in water. It was found that in the high dielectric constant and lossy medium, a cut-off frequency was identified above which the transmission coefficient was very severe. The cut off frequency correspondingly varied with antenna separation. The shift of this cut off frequency was used to estimate distance by identifying intercept points on exponential plots of the power ratio versus normalized frequency. The setup can be used for highly sensitive distance sensing in applications such as under water mechanical alignment.