Baù Marco, Ferrari Marco, Ferrari Vittorio
Department of Information Engineering, University of Brescia, Via Branze 38, Brescia 25123, Italy.
INO-CNR (National Research Council), Via Branze 45, Brescia 25123, Italy.
Sensors (Basel). 2017 Jun 2;17(6):1264. doi: 10.3390/s17061264.
A technique for contactless electromagnetic interrogation of AT-cut quartz piezoelectric resonator sensors is proposed based on a primary coil electromagnetically air-coupled to a secondary coil connected to the electrodes of the resonator. The interrogation technique periodically switches between interleaved excitation and detection phases. During the excitation phase, the resonator is set into vibration by a driving voltage applied to the primary coil, whereas in the detection phase, the excitation signal is turned off and the transient decaying response of the resonator is sensed without contact by measuring the voltage induced back across the primary coil. This approach ensures that the readout frequency of the sensor signal is to a first order approximation independent of the interrogation distance between the primary and secondary coils. A detailed theoretical analysis of the interrogation principle based on a lumped-element equivalent circuit is presented. The analysis has been experimentally validated on a 4.432 MHz AT-cut quartz crystal resonator, demonstrating the accurate readout of the series resonant frequency and quality factor over an interrogation distance of up to 2 cm. As an application, the technique has been applied to the measurement of liquid microdroplets deposited on a 4.8 MHz AT-cut quartz crystal. More generally, the proposed technique can be exploited for the measurement of any physical or chemical quantities affecting the resonant response of quartz resonator sensors.
提出了一种用于对AT切石英压电谐振器传感器进行非接触式电磁询问的技术，该技术基于一个初级线圈与连接到谐振器电极的次级线圈进行电磁空气耦合。该询问技术在交错的激励和检测阶段之间周期性切换。在激励阶段，通过施加到初级线圈的驱动电压使谐振器振动，而在检测阶段，激励信号关闭，通过测量初级线圈上感应的电压来非接触地感测谐振器的瞬态衰减响应。这种方法确保传感器信号的读出频率在一阶近似下与初级和次级线圈之间的询问距离无关。基于集总元件等效电路对询问原理进行了详细的理论分析。该分析已在一个4.432MHz的AT切石英晶体谐振器上进行了实验验证，证明在高达2cm的询问距离内能够准确读出串联谐振频率和品质因数。作为一种应用，该技术已应用于测量沉积在4.8MHz的AT切石英晶体上的液体微滴。更一般地说，所提出的技术可用于测量影响石英谐振器传感器谐振响应的任何物理或化学量。
