Circuit for continuous motional series resonant frequency and motional resistance monitoring of quartz crystal resonators by parallel capacitance compensation

Abstract

A deep analysis of the problem associated to interface circuits for quartz-crystal-microbalance sensors reveals that the so-called static capacitance of the sensor is one of the elements which make the use of oscillators more critical for sensors applications. A phase-locked-loop based circuit designed for compensating the parallel capacitance in quartz crystal resonator sensors is presented. This circuit permits the calibration of the external circuitry to the sensor and provides a continuous measurement of the motional series resonant frequency and motional resistance. An extension and automation of the proposed system for multiple sensor characterization is introduced. Experimental results are also shown.

Probing biomechanical properties with a centrifugal force quartz crystal microbalance

“…The employed QCM driver circuit outputs Butterworth van Dyke (BvD) equivalent relative frequency Df (in hertz) and motional resistance R (in ohms). R is approximately related to the bandwidth G (half width at half maximum of the frequency response) by G ¼ R/(4pL), where L ¼ 40 mH is the motional inductance of the BvD equivalent circuit 17 . For this relationship we assume the small load approximation Df/f F o o1, where f F is the fundamental frequency 18 .…”

QCM Technology in Biosensors

“…In practice, all the QCM sensor characterization techniques provide, among other relevant parameters, the resonance frequency shift of the sensor Eichelbaum et al, 1999): network or impedance analysis is used to sweep the resonance frequency range of the resonator and determine the maximum conductance frequency (Schröder et al, 2001;Doerner et al, 2003), which is almost equivalent to the motional series resonance frequency of the resonator-sensor; impulse excitation and decay method techniques are used to determine the series-resonance or the parallel-resonance frequency depending on the measuring set-up (Rodahl & Kasemo, 1996); oscillator techniques are used for a continuous monitoring of a frequency which corresponds to a specific phase shift of the sensor in the resonance bandwidth (Ehahoun et al, 2002;Barnes, 1992;Wessendorf, 1993;Borngräber et al, 2002;Martin et al, 1997), this frequency can be used, in many applications, as reference of the resonance frequency of the sensor; and the lock-in techniques, which can be considered as sophisticated oscillators, are designed for a continuous monitoring of the motional series resonance frequency or the maximum conductance frequency of the resonator-sensor (Arnau et al, 2002(Arnau et al, , 2007Ferrari et al, 2001Ferrari et al, , 2006Jakoby et al, 2005;Riesch & Jakoby 2007). In order to assure that the frequency shift is the only parameter of interest, a second parameter providing information of the constancy of the properties of liquid medium is of interest, mainly in piezoelectric biosensors; this parameter depends on the characterization system being: the maximum conductance or the conductance bandwidth in impedance analysis, the dissipation factor in decay methods and a voltage associated with the sensor damping in oscillator techniques The different characterization methods mentioned can be classified in two types: 1) those which passively interrogate the sensor, and 2) those in which the sensor forms part of the characterization system.…”

A wireless low-range pressure sensor based on P(VDF-TrFE) piezoelectric resonance

“…The piezoelectric behavior can be characterized by the equivalent circuit of the Butterworth-Van Dyke (BVD) model [17][18][19][20][21][22][23][24][25][26] in Figure 2. C 1 , L 1 and R 1 known as the "the mechanical arm", describe the mechanical vibrations resulting from the piezoelectric effect with a finite quality factor.…”