Table 3.

Comparison of developed SAW sensors for relative humidity sensing with other strategies reported in literature, adapted with permission from [173].

fo	Substrate	Surface Morphology	RH Range (%)	Max Response of Frequency Shift	Recovery & Response Time	Max Difference of Δf (kHz)	Ref.
1.54 GHz	128° YX LiNbO3	NiO nanoparticles	11–85	−5.81 MHz	4 s, 23 s	478	This work
1.54 GHz	128° YX LiNbO3	NSOH nanobelts	11–85	−2.95 MHz	10 s, 21 s	130	This work
395 MHz	ZnO/poly-imide (PI)	Graphene oxide	11–85	−1.5 MHz	5 s, 22 s	-	[174]
199 MHz	ST quartz	SiO2 films	30–93	−520 kHz	<10 s, <10 s	-	[175]
126 MHz	AlN/Si	Ga doped ZnO films	10–90	−400 kHz	-	20	[176]
433 MHz	ST quartz	Silicon-containing polyelectrolyte	10–95	−30 kHz	~10 s, ~10 s	-	[177]