A high sensitivity open loop electronics for gravimetric acoustic wave-based sensors

In order to use radiofrequency acoustic transducers as gravimetric sensors for detecting chemical species in gas phase, we propose an openloop interrogation strategy. As opposed to the closed loop - oscillator - strategy whose performance is strongly dependent on the environment of the acoustic transducer and might yield to a lack of oscillation if the damping of the acoustic wave is not compensated for by the amplifier, an openloop strategy provides, beyond the actual acoustic parameters, the data needed for the diagnostics of a poorly performing transducer. Indeed, in an openloop strategy, the large dynamics of the I/Q demodulator needed to extract the phase and magnitude information at each frequency yields improved robustness of the measurement system - transducer and associated electronics - with respect to the closed loop strategy. However, reaching comparable noise levels with the former strategy is challenging: we propose an embedded frequency-sweep network analyzer dedicated to gas-phase monitoring of chemical compounds with improved sensitivity with respect to commercially available integrated circuits or general purpose network analyzers. We demonstrate a 16 Hz standard deviation at 125 MHz, with a working frequency band in the 60 to 133 MHz range, answering the requirements of using Rayleigh and Love-mode acoustic 40 μm wavelength transducers as classically found in the literature. The remaining noise source is solely due to the Analog-to-Digital Converter of the microcontroller, so room is left for improving this result by optimizing the voltage reference and board layout.