Table 5.

Comparison of recently reported work on microwave planar resonators in detecting the material properties in terms of sensitivity, detection range and complex permittivity.

Ref.	Source Title	Sensor	Sample Containers	Bare Sensor ${\mathit{f}}_{\mathit{o}}$ (GHz)	${\mathit{f}}_{\mathbf{empty}}$ (GHz)	${\mathit{f}}_{\mathbf{water}}$ (GHz)	Sensitivity (MHz/$\mathbf{\Delta }\mathit{ϵ}$)	Normalized Sensitivity (%)	Detection Range (${\mathit{ϵ}}^{\prime }$/${\mathit{ϵ}}^{\prime \prime }$)	Complex Permittivity
[16]	Sensors Actuators A: Physical	SRR	PET film microfluidic channel	2.1	2	1.85	1.83	0.091	9–83/6–15	Real/imaginary
[11]	IEEE Sensors Journal	CSRR	PDMS microfluidic channel	2.4	2	1.52	6.11	0.31	9–79.5/9–15.6	Real/imaginary
[55]	IEEE Trans. Microw. Theory Techn.,	SRR	Capillary microfluidic	≈3	3.1035	3.042	0.805	0.026	1.893–77.42/0.001–12.49	Real/imaginary
[109]	Sensors, 2016	SIW	PDMS microfluidic channel	18	17.08	14.95	27.31	0.16	2.3–79/-	Real
[110]	IEEE trans.antennas propagation	SIW	Microfluidic channel (etched on the PMMA substrate using a laser)	5.06	4.69	4.2	6.24	0.13	-	-
[45]	Microw. Opt. Tech. Lett.	Double SRR	Micro-capillary	2.1	2.1213	2.0402	1.03	0.048	24.49–80.1/-	Real
[111]	J. Applied Physics	Dual-gap SRR	PDMS microfluidic channel	3.24	3.23	2.98	3.27	0.1	8–77.5/8.8–16.6	Real/imaginary
[59]	IEEE Microw. Wirel. Compon. Lett	Bridge SRR	Micro-capillary	2.35	2.27034	2.20220	0.861	0.038	24.5–80.1/-	Real/-
[54]	IEEE Sensors Journal	Splitter/combiner SRRs	PDMS microfluidic channel	1	0.978	0.87	1.35	0.138	27.86–80.86/3.04–10	Real/Imaginary
[102]	J.Electrochemical Soc.	Single CSRR	Fluid	4.078	4.078	3.897	2.33	0.057	8.96–8.64/5.22–11.34	Real/imaginary
[103]	IEEE Microw. Wirel. Compon. Lett.,	SIW	Glass pipe	2.52	2.51	2.391	1.56	0.062	5.25–77.50/-	Real
[112]	IEEE Microw. Wirel. Compon. Lett.	PMR	3D printed microfluidic channels	5.8	5.77	5.31	5.86	0.1	9–79.5/-	Real
[99]	Sensors Actuators A	RCRR	Container	0.90	0.810	0.639	0.002	0.27	1–78.5/2.45–9.5	Real/imaginary
[113]	Sensors	Quarter-Mode SIW	PDMS channels	5.81	5.791	5.321	6.53	0.11	5.08–73/-	Real
[114]	Sensors	SIW	PDMS microfluidic channel	≈8	8.26	7.60	10	0.12	5–67/-	Real
[115]	Sensors	3D SRR	Teflon tube	2.56	2.559	2.350	2.79	0.11	6–76/-	Real
[15]	IEEE Sensors Journal	CSRR	Glass capillary	2.4	2.365	2.302	0.808	0.034	9–79/8.1–17.1	Real/imaginary
[95]	IEEE Trans. Microw. Theory Techn.	Microwave sensor	PTFE Tube	2.5	2.6	≈2.07	7.02	0.27	1–140/76.7	Real/loss tangent
[100]	Int. J. RF Microw. Computer-Aided Eng.	CSIWwith DMS	Micro-capillary channel	4.40	4.3392	4.1850	1.95	0.045	24.5–80.1	Real
[116]	IEEE Sensors Journal	Multi-layered mushroom HIS	Tube coiled within the sensor	4.455	4.340	4.018	4.18	0.096	1–78/0.00058–17.16	Real/imaginary
[101]	Scientific Reports	CSIW	Micro-capillary channel	4.4	4.4035	4.2510	1.93	0.044	24.5–80.1/0–22.99	Real
[12]	IEEE Trans. Microw. Theory Techn.	LC resonator	PDMS microfluidic channel	≈ 2.2	1.91	1.27	8.14	0.43	30–79.6/4–11.5	Real/imaginary
[75]	Measurement	SRR	Droplet on the sensor	5.7	5.76	4.80	12.5	0.22	24–78/-	Real
				7.8	7.85	6.35	19.74	0.251
[80]	IEEE Trans. Microw. Theory Techn.	SIW	Embedded micropipe	≈3.82	3.8267	3.4077	5.62	0.15	4–75.6/	Real/loss tangent