Gas sensing properties of Langmuir-Blodgett polypyrrole film investigated by surface acoustic waves

Abstract

The gas sensing properties of organic polypyrrole (PPS) film, deposited onto LiNbO(3) substrate by Langmuir-Blodgett (LB) technique, have been monitored by surface acoustic wave (SAW) delay lines and studied with respect to sensitivity, selectivity, response time, stability, repeatability, and aging. The SAW PPy elements demonstrate high sensitivity toward NH(3) gas with high selectivity against CH(4), CO, H(2), and O(2). The detectable threshold concentration has been estimated as 20 ppm NH(3) in air; the response time is in the 10s range, and the recovery time is about 15 min; the repeatability of the SAW response toward eight sequential NH(3) gas exposures is within 6%; the aging of the PPy film is within 4% over a month; and the effect of humidity on SAW NH(3) gas response is negligible for the typical conditions at room ambient air. Partially reversible SAW response recognizing NH(3) gas as one component of an interfering gases-mixture has been observed. Simultaneous chemoresponses of SAW phase and insertion loss have been performed in order to investigate the sensing mechanisms. By merging with electrical conductivity gas response, the dominant SAW sensing effects for NH(3 ) gas detection are defined as elastic loading.

Origin and role of elasticity in the enhanced DMMP detection by ZnO/SAW sensor

“…Hence mass loading, acoustoelectric interaction, and elastic changes are the main perturbation effects which are expected to contribute to the observed sensing response characteristics of ZnO/SAW sensor. It is known that the mass loading effect causes a decrease in the frequency of SAW sensor oscillator and therefore differential frequency is expected to increase (i.e., + f) [28]. On the other side, an increase in the elasticity of the sensing layer increases the frequency and hence differential frequency decreases (− f).…”

“…The effect of acousto-electric interaction on the velocity and hence frequency of the SAW device is given by [28]:…”

Development of a portable electronic nose based on chemical surface acoustic wave array with multiplexed oscillator and readout electronics

“…Considering the effects of perturbation by mass loading including elastic loading and electric loading, the propagation characteristics of the surface wave are affected as follows [16,17]:…”

Langasite surface acoustic wave gas sensors: modeling and verification

“…SAW gas sensing can be accomplished using either gas-induced conductivity [11] or mass changes to the sensing layer covering the acoustic path [12]. Changes in the electrical conductivity or the mass density change the velocity of the surface acoustic wave, which can be detected in transient or steadystate measurements.…”

“…We consider here a SAW device with a gas sensing layer [10,11,12]. SAW gas sensing can be accomplished using either gas-induced conductivity [11] or mass changes to the sensing layer covering the acoustic path [12].…”