Abstract
Detecting chemical species in gas phase has recently received an increasing interest mainly for security control, trying to implement new systems allowing for extended dynamics and reactivity. In this work, an open-loop interrogation strategy is proposed to use radio-frequency acoustic transducers as micro-balances for that purpose. The resulting system is dedicated to the monitoring of chemical compounds in gaseous or liquid-phase state. A 16 Hz standard deviation is demonstrated at 125 MHz, with a working frequency band in the 60 to 133 MHz range, answering the requirements for using Rayleigh- and Love-wave-based delay lines operating with 40-μm acoustic wavelength transducers. Moreover, this electronic setup was used to interrogate a high-overtone bulk acoustic wave resonator (HBAR) microbalance, a new sensor class allowing for multi-mode interrogation for gravimetric measurement improvement. The noise source still limiting the system performance is due to the analog-to-digital converter of the microcontroller, thus leaving open degrees-of-freedom for improving the obtained results by optimizing the voltage reference and board layout. The operation of the system is illustrated using a calibrated galvanic deposition at the surface of Love-wave delay lines to assess theoretical predictions of their gravimetric sensitivity and to compare them with HBAR-based sensor sensitivity.
Highlights
Current systems for detecting potentially toxic gases are in genral cumbersome and complex
The basic principle of gravimetric acoustic wave sensors is the measurement of the phase velocity variation due to the adsorbed mass density or thickness change during a chemical reaction: this phase velocity is dependent on the boundary conditions of the propagating surface acoustic wave, and is affected either by the guiding layer density and/or thickness
In order to probe gravimetric accoustic wave-based sensors we have to provide RF signals: we focus on working in the 60-133 MHz frequency range, consistent with the use of 40-μm wavelength Rayleigh wave or Love mode surface acoustic wave sensors
Summary
Current systems for detecting potentially toxic gases are in genral cumbersome and complex. In order to reach this aim, a Direct Digital Synthesizer based oscillator provides the flexible RF probe signal, while a low noise phase detector is fed by an amplitude controled signal. This low noise electronics is used in parallel with a flexible wideband I/Q demodulator for the preliminary characterization of the transfer function of each new sensor and selecting the optimum working frequency used throughout the gravimetric detection experiment
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More From: IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
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