Table 3.

Comparison of other recently published works and this work.

Ref.	Resonator Type	Operating Frequency	$\mathit{Sensitivity} (\%/{\mathit{\epsilon }}_{\mathit{r}}^{\prime })$	Relative Size †	Structure	Measurement Type	Maximum Error
[14]	Cylindrical dielectric resonator	10.5 GHz	0.0628	NA	Non-planar	Non-invasive and contactless	13.4%
[43]	SIW cavity resonator	8.96 GHz	0.0188	(0.46${\lambda }_0\times$~$\times$0.047${\lambda }_0$) §	Planar	Non-invasive and contactless	2.93%
[44]	Complementary SRR-loaded quarter mode SIW resonator	3.82 GHz	0.407	NR	Planar	Non-invasive and contactless	NR
[45]-1	Microstrip SRR	3.1035 GHz	0.026	0.37${\mathsf{\lambda }}_0\times$0.37${\mathsf{\lambda }}_0\times$0.016${\mathsf{\lambda }}_0$	Planar	Non-invasive and contactless	2.3%
[45]-2		3.1114 GHz	0.00655				2.9%
[46]	Coupled impedance resonator	1.37 GHz	0.13	(0.23${\lambda }_0\times$~$\times$0.002${\lambda }_0$) †	Planar	Non-invasive and contactless	NR
[47]	Coupled ring resonator	2.29 GHz	0.222	NR	Planar	Non-invasive and contactless	NR
[48]	SIW cavity resonator	17.08 GHz	0.16	1.7${\lambda }_0\times$1.99${\lambda }_0\times$0.147${\lambda }_0$	Planar	Non-invasive and contactless	NR
[49]	SIW cavity resonator	5.8513 GHz	0.00683	1.46${\mathsf{\lambda }}_0\times$0.64${\mathsf{\lambda }}_0\times$0.019${\lambda }_0$	Planar	Invasive	5%
This work	Square SIW re-entrant cavity resonator	2.18875 GHz	0.366	0.4${\lambda }_0\times$0.36${\lambda }_0\times$0.041${\lambda }_0$	Planar	Non-invasive and contactless	3.24%

^†${\mathsf{\lambda }}_0$ is the free space wavelength at operating frequency; ^§ Length of the sensor is not mentioned in [43]; ^† The overall width of the sensor is not given in [46].