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Vol. 71, Issue 9, September 2006, pp. 711-720




Modelling and Experiments on a Quartz Crystal Resonator Sensor for Conductivity Measurements

  of Low-Concentration Ionic Solutions


Alexsandro Cesar DE PAULA1a, Marco FERRARI2a,
David Mendes SOARES1b, Vittorio FERRARI2b


1Depto Física Aplicada, Universidade Estadual de Campinas, Cidade Universitária “Zeferino Vaz” 

sn – 13083-970 Campinas, Brazil. Tel.:+55 19 3788 5309, fax:+55 19 3788 5376

E-mail: a alexcp@ceb.unicamp.br, b soares@ifi.unicamp.br


2Dip. Elettronica per l’Automazione, Università degli Studi di Brescia, Via Branze, 38,

25123 Brescia, Italy. Tel.:+39 030 3715899, fax:+39 030 380014

E-mail: a marco.ferrari@ing.unibs.it, b vittorio.ferrari@ing.unibs.it



Received: 7 September 2006   /Accepted: 20 September 2006   /Published: 25 September 2006


Abstract: The monitoring and control of the electrical parameters of ionic solutions have different applications in industry and are particularly important in medical and biochemical studies, where ionic solutions are commonly used. This paper analyzes the effect of the conductivity of a low-concentration ionic solution on the resonant response of a Quartz Crystal Resonator (QCR) sensor with asymmetric electrodes put in contact with the solution. A model of the QCR sensor is presented, and experimental results obtained with a 6-MHz sensor exposed to low-concentration solutions of NaCl in water are reported. The model and experimental results are in very good agreement throughout the explored conductivity range between around 10 and 200 mS/m.


Keywords: Conductivity, low-concentration ionic solution, Quartz Crystal Resonator (QCR) sensor, impedance analysis


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