Abstract
This paper presents an optimal design for a new humidity sensor composed of a dual-resonator oscillator configuration with an operation frequency of 300 MHz, and a polyaniline (PANI) coating deposited along the resonation cavity of the sensing device. To improve the corrosion resistance of the sensor chip, Al/Au electrodes were used to form the SAW resonator. Prior to device fabrication, the coupling of modes (COM) model was used for the performance prediction and optimal design parameters determination. Two SAW resonators with Al/Au electrodes were fabricated on an ST-X quartz substrate, and used as the frequency control element in the feedback path of an oscillator circuit. A PANI thin coating was deposited onto the resonator cavity of the sensing device by a spinning approach as the sensor material for relative humidity (RH) detection. High detection sensitivity, quick response, good repeatability and stability were observed from the sensor experiments at room temperature.
Highlights
IntroductionHumidity detection has been attracting increasing interest over the past years in the fields of industrial and agricultural production, food storage, meteorology, environment protection, etc. [1].Recently, surface acoustic wave (SAW)-based humidity sensors have attracted much attention sinceSensors 2013, 13 they exhibit the advantages of very fast response (several seconds), high sensitivity, small size, integrated electronic circuitry, and easy to realize wireless communication over the current impedance-type or capacitance type humidity sensors [2,3,4], and the optical sensors coated with chiral sculptured thin films or thin dielectric waveguide [5,6]
Humidity detection has been attracting increasing interest over the past years in the fields of industrial and agricultural production, food storage, meteorology, environment protection, etc. [1].Recently, surface acoustic wave (SAW)-based humidity sensors have attracted much attention sinceSensors 2013, 13 they exhibit the advantages of very fast response, high sensitivity, small size, integrated electronic circuitry, and easy to realize wireless communication over the current impedance-type or capacitance type humidity sensors [2,3,4], and the optical sensors coated with chiral sculptured thin films or thin dielectric waveguide [5,6]
The schematic and working principle of a typical SAW-based humidity sensor with a dual-oscillator configuration is shown in Figure 1, where the SAW devices are used as frequency control elements in the feedback path of an oscillator circuit
Summary
Humidity detection has been attracting increasing interest over the past years in the fields of industrial and agricultural production, food storage, meteorology, environment protection, etc. [1].Recently, surface acoustic wave (SAW)-based humidity sensors have attracted much attention sinceSensors 2013, 13 they exhibit the advantages of very fast response (several seconds), high sensitivity, small size, integrated electronic circuitry, and easy to realize wireless communication over the current impedance-type or capacitance type humidity sensors [2,3,4], and the optical sensors coated with chiral sculptured thin films or thin dielectric waveguide [5,6]. Surface acoustic wave (SAW)-based humidity sensors have attracted much attention since. The schematic and working principle of a typical SAW-based humidity sensor with a dual-oscillator configuration is shown, where the SAW devices are used as frequency control elements in the feedback path of an oscillator circuit. A sensitive interface allowing analytes to be sorbed onto the device surface was deposited along the acoustic wave propagation path of the sensing device. The physical adsorption between the sensing film and the target water vapor species modulates the phase velocity of the SAW propagating along the SAW device, and the target relative humidity can be characterized by the oscillation frequency shift.
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