Non-contact monitoring of kiwifruit ripening using a high-sensitivity multi-frequency inductive sensor

A wireless multifrequency resonator (WMFR) based on an original combination of several flexible passive radiofrequency transmission-line resonators, is used as an inductive multi-sensor for the non-contact monitoring of kiwifruit ripening. In this paper, the complex dielectric property changes of a kiwifruit sample were monitored during a two-week ripening period, with a three-frequency WMFR in the 100 MHz-300 MHz bandwidth. Thanks to an equivalent electrical circuit modelling the coupling between the WMFR and the monitored fruit, three sensor output parameters were defined and assessed at each frequency, to efficiently monitor the dielectric changes induced by the structural and biochemical modifications of the fruit during ripening.