Surface Acoustic Wave Humidity Sensor: A Review

Abstract

The Growing demands for humidity detection in commercial and industrial applications led to the rapid development of humidity sensors based on different techniques. Surface acoustic wave (SAW) technology is one of these methods that has been found to provide a powerful platform for humidity sensing owing to its intrinsic features, including small size, high sensitivity, and simple operational mechanism. Similar to other techniques, the principle of humidity sensing in SAW devices is also realized by an overlaid sensitive film, which serves as the core element whose interaction with water molecules is responsible for overall performance. Therefore, most researchers are focused on exploring different sensing materials to achieve optimum performance characteristics. This article reviews sensing materials used to develop SAW humidity sensors and their responses based on theoretical aspects and experimental outcomes. Herein the influence of overlaid sensing film on the performance parameters of the SAW device, such as quality factor, signal amplitude, insertion loss, etc., is also highlighted. Lastly, a recommendation to minimize the significant change in device characteristics is presented, which we believe will be a good step for the future development of SAW humidity sensors.

Metal Microelectromechanical Resonator Exhibiting Fast Human Activity Detection

“…This assumes that the excitation voltage V ac is much smaller than the driving voltage V dc applied to the bridge (capacitive transduction). In (2), the first term corresponds to the motional current, and the second term is the parasitic current; ∂C/∂t is the bridge-readout electrode variable capacitance, and C 0 is the static capacitance between the excitation and readout electrodes.…”

“…In parallel, high-performance humidity detection has taken an important development. Particularly, real-time humidity detection allows us to design sensors for human activity such as breath monitoring or non-contact finger movement [2][3][4][5][6][7].…”

“…In both cases, the level of humidity is changed locally due to the water vapor contents in any human exhalation during breathing, and the sharp gradient of humidity around the fingertip [2] due to skin transpiration.…”

Grooving and Absorption on Substrates to Reduce the Bulk Acoustic Wave for Surface Acoustic Wave Micro-Force Sensors

“…As a result, they hold significant potential for a wide array of future applications. The SAW sensors can be used to measure temperature [3], humidity [4], gas [5,6], force [7], and so forth.…”

SAW Humidity Sensing with rr-P3HT Polymer Films

“…Humidity measurement is critical in many branches of human activities such as industrial processes, agricultural productions, room and motor vehicles conditions, production of medicines as well the very precise research experiments. The most of the contemporary humidity sensors are based on the capacitance, resistance, impedance, acoustic and optical methods, however, their mutual drawback is often the low accuracy and hysteresis effect at the low humidity detection levels [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ]. Considerable efforts have thus been focused on the development of highly sensitive materials and novel device structures to address these issues [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ].…”