Table 4.

Various liquids’ mixtures detection based on existing studies found in the literature.

Ref.	Technique	Substrate Material *	Freq (GHz)	Size (mm)	Tested Material (MUT)	Remark
[68]	ENGResonator	FR-4 ${ϵ}_r$ = 4.4 h = 1.6 mm	2.074	40 × 20	Water-glucose	The concentration range of the glucose is 20–100 mg/mL.
[67]	RF patch biosensor	N/A	17.25 and 21.09	3.3 × 2	DI water, D-glucose powder	The concentrations range of the glucose is 50–600 mg/dL. The sensitivity achieved is up to 1.13 MHz and 1.97 MHz per mg/dL, and the detection limits are 26.54 mg/dL and 15.22 mg/dL.
[70]	Broadband dielectric spectroscopy	N/A	2 to 18	N/A	N/A	The concentration is varied from 0 to 10 mg/mL. The sensitivity achieved is 0.15 dB/(mg/mL) and 0.5°/(mg/mL) at a room temperature of 25 °C.
[69]	Antenna-coupled SRR	N/A	1.9	8.3	N/A	The tested material is blood plasma with different glucose concentrations.
[71]	Antenna-driven ring	FR4 t = 35 um	2	30 × 30	DI water, glucose, NaCl solutions	A 17.5 MHz shifting of the resonance frequency is obtained with a high rate of error of 7.3%. The sensitivity achieved is 0.107 MHz/mg dL${}^{-1}$.
[72]	Transmission/reflection line method	N/A	1 to 1.20	N/A	N/A	The tested range of water-glucose concentration is from 50 mg/dL to 1000 mg/dL with a frequency range from 100 MHz to 4 GHz.
[66]	Planar MRR	FR4 Epoxy ${ϵ}_r$ = 4.4	1	108.75 × 65	Glucose percentage	The concentration of water-glucose is tested, and there is a slightly frequency shift. However, the sample is directly tested on the sensor, which increases the measurement error.
[65]	RMLresonator	N/A	9.20	2 × 0.854	Glucose percentage	The sensitivity achieved is 1.08 MHz per 1 mg dL${}^{-1}$. The detection limit is 8.01 mg dL${}^{-1}$ with a quantisation limit of 24.30 mg dL${}^{-1}$.

* h = thickness, t = copper thickness, ${ϵ}_r$ = dielectric constant, and $tan\delta$ = loss tangent. N/A = Not Available.