Eight channel embedded electronic open loop interrogation for multi sensor measurement

Abstract

One strategy in addressing the issue of selectivity in direct detection gas sensors - and specifically when using piezoelectric acoustic transducers - is to use multichannel measurement approaches in which each sensor is functionalized with a different chemical layer and provides different responses when exposed to a given mixture of gasses. Within this context, an 8-channel open loop embedded electronics operating as a transmission-mode radiofrequency network analyzer has been developed. The frequency ranges generated by the synthesizer is 50 to 160 MHz or 200 to 500 MHz. A low noise phase detection scheme was implemented, in addition to magnitude measurement. This instrument is used with Surface Acoustic Wave (SAW) and High-overtone Bulk Acoustic Resonator (HBAR) transducers: in the former case, the open-loop approach allows for an improved measurement dynamics, while in the latter case multiple resonances can be probed sequentially, yielding different acoustic penetration depths in the sensing layer. Demonstration of measurement in liquid phase is provided by characterizing the gravimetric sensitivity of HBARs using copper electrodeposition. Values ranging from 2.2 to 13.1 cm2/g are observed, emphasizing a departure from a perturbative Sauerbrey-like relationship.