Surface acoustic wave humidity sensors: a comparison between different types of sensitive membrane

Abstract

Surface acoustic wave (SAW) sensors have been successfully exploited for the detection of both chemical and physical quantities. In this paper we report more recent results on SAW sensors for the detection of relative humidity (R.H.). Different chemical interactive materials (CIMs), of both organic and inorganic compounds, are tested and their performances in the R.H. range between 10 and 80% are reported and compared. All the devices analysed have been shown to operate in a reversible way, with a fairly good repeatibility and fast response times. The CIMs have been shown to produce a variety of different behaviours versus R.H. percentage, with respect to both the amplitude and linearity of the response. The response to R.H. has also been investigated for different orientations of both quartz and lithium niobate bare substrates. These data can be useful in order to investigate the effect of the R.H. of the surroundings on the performances of SAW based devices. In addition this test is of great importance in order to know how humidity influences the response of both chemical and physical sensors. The response of organic CIMs has also been tested toward hydroxylated molecules such as acetone and ethanol, and the relative calibration curves are reported.

Flexible Surface Acoustic Wave Based Temperature and Humidity Sensors

“…A sensitivity of 34.7 kHz/10%RH has been obtained for the device with =12 μm without surface treatment or an absorbent. This sensitivity is eight times of ~4.5 kHz/10%RH obtained from rigid SAW sensors with bare surface, 27 clearly showed the excellent performance of the flexible SAW sensors obtained, although it is smaller than ~50 kHz/10%RH obtained from the rigid SAW sensors with a polymer adsorbent. 18 18…”

SAW Sensors for Chemical Vapors and Gases

“…Similarly, humidity [9], and many organic vapors such as methanol [138], ethanol [139], acetone [31], styrene [140], dimethyl methylphosphonate (DMMP) [95] have also been detected using these sensors. With suitable polymer coating, the sensors have also been employed for detection of various explosive chemicals [141,142].…”

Influence of Humidity on the Acoustic Properties of Mushroom Mycelium Films Used as Sensitive Layers for Acoustic Humidity Sensors

“…There are a lot of humidity sensors based on various physical principles (resistive [ 1 , 2 ], conductive [ 3 ], acoustic [ 4 , 5 ], capacitive [ 6 , 7 ], etc.). As for acoustic humidity sensors, there exists a large amount of papers, suggesting the use of film bulk acoustic resonators (FBARs) [ 8 , 9 ], various types of surface acoustic waves [ 4 , 5 , 8 , 9 , 10 , 11 ], quartz crystal microbalances (QCM) [ 8 , 12 ], and plate acoustic waves [ 13 ]. Most of the acoustic humidity sensors are based on the use of specific films deposited on the surface of acoustic waveguides [ 14 ].…”

“…These, in turn, affect the acoustic wave phase velocity and/or attenuation or resonant frequency. Both organic and inorganic materials have been used as sensitive films [ 4 , 5 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ]. One of the opportunities that is poorly studied is the use of films of the mycelia from higher fungi.…”