Use of a multiplexed oscillator in a miniaturized electronic nose based on a multichannel quartz crystal microbalance

Acoustic sensors are generally known as high-resolution mass-sensitive transducers. They are composed of piezoelectric crystal plus at least one layer of chemically interactive material (CIM) deposited on one of their surfaces in order to infer a given chemical sensitivity. Electronic noses based on quartz crystal microbalances (QCM) are widely used in volatile organic compounds analysis. These multisensor systems typically employ a number of quartzes coated with different CIM having broad and overlapping sensitivity. Depending on the number of sensors used and taking into account the electronic units needed to drive them, the total volume of such a system may be considerable. In the present work we have shown the possibility of including four different QCM in the same quartz plate in order to reduce the overall space dedicated to the sensors, realizing the so called multichannel quartz crystal microbalance (MQCM). Moreover we have investigated the possibility of using a single oscillator circuit to drive the oscillations for all the four channels of the MQCM. The work outlines the advantages of implementing this single oscillator technique in terms of volume reduction, better homogeneity in the sensor array behavior and power saving. The overall system comprising the sensor array, the driving oscillator and the electronic interface has been built and successfully tested.