L. Rodriguez-Pardo

A biosensor for detection of DNA sequences based on a 50MHz QCM electronic oscillator circuit

This work deals with the development of a high sensibility DNA biosensor based on a 50MHz Quartz Crystal Microbalance (QCM) Oscillator Electronic Circuit. The designed QCM oscillator sensor is able to detect the presence of complementary DNAs in a solution that match the sequence on a given strand in function of the changes in the output frequency of the oscillator. The design is adapted so that the Barkhausen condition is satisfied even when the quartz is immerged in liquid media. Also a comparative study of the developed 50MHz biosensor in front of a QCM oscillator with smaller frequency is carried out, with object of checking if the sensibility of the oscillator increases, allowing to detect smaller concentrations of the complementary DNA.

Density and viscosity measurements in lead acid batteries by QCM sensor

In automotive applications, submarines and remote communication systems it is necessary to know the state of charge (SOC) of the batteries in order to manage them efficiently. Due to the acid concentration dependence of SOC, traditionally, density measurements are done in order to estimate it. But other parameters like electrolyte viscosity have highest changes with SOC than density. In this paper, a QCM (Quartz Crystal Microbalance) oscillator sensor for monitoring density and viscosity changes in lead-acid batteries is presented. The frequency shift is monitoring in solutions with H2SO4 concentration in the battery electrolyte range and the sensitivity and resolution of the sensor are determining for the application. Then, successful experiments are carried out by placing the quartz crystal inside the battery cell.

Noise and resolution in 2 MHz, 6 MHz, 9 MHz and 27 MHz QCM sensors in liquid media

In this paper, a comparative study of noise and resolution is presented with respect to the frequency and the quality factor. The study has been made using four oscillators designed to be used in quartz crystal microbalance sensors in damping media. The four circuits have been designed at increasing frequencies in order to improve the sensitivity. Also, a calibration of the sensors was made. On the other hand, the current resolution limit of a microbalance oscillator is determined using an AT resonator, since this does not depend on the frequency. However, when working in liquid, the damping of the resonator makes the resolution diminish due to a worsening the quality factor. The relationship between the resolution limit and the frequency and characteristics of the liquid medium has been determined. The resolution worsens when the density and viscosity of the liquid is increased. However, in this case, the increase in frequency implies a small increase in the resolution. Therefore, when working below the maximum quality factor, for similar values, the resolution can be improved by elevating the work frequency.

OptiMiller: a CAD tool for the design and optimization of Miller electronic oscillator circuits for QCM sensors

Despite the long history of the quartz crystal oscillators, for their use as mass sensors in damping media, the success of a design still depends strongly on the designers ability and experience. The large reduction that the quality factor of the quartz experiences in those media implies the necessity to adapt the designs so that the oscillation remains in spite of this reduction. In this paper, a CAD tool to help users in the design and optimization of Miller oscillators for the realization of quartz crystal microbalance sensors (QCM) for liquid media is presented.

Simultaneously measurement of frequency shift and series resistance changes of a quartz resonator using a miller QCM oscillator

In this work it is shown that a Miller quartz crystal microbalance (QCM) electronic oscillator circuit can be used to simultaneously measurement of the resonant frequency shifts and changes in the motional resistance of the resonator. In order to calibrate the sensitivity to variations in the series resistance of the resonator, an experiment was carried out with the resonator immersed in liquids at different concentrations of glycerol. Also the sensor system has been applied to control the series resistance during the water uptake in a cataphoretic organic coating. It was observed that the series resistance remains constant during the experiment in the absence of changes in the damping of the resonator (there are no viscoelastic changes in the coating). Moreover, we have studied amplitude fluctuations of the sensor system, determining the sensor resolution in the resistance measurements.

Passive QCM sensor system for monitoring of water absorption and drying in Nafion® polymer membranes

This work deals with the development of a Passive Quartz Crystal Microbalance (QCM) Sensor system for liquid environment to follow the water uptake and drying characteristics of Nafion® polymer membranes. An automated system for the electro-acoustic characterization of a quartz crystal resonator using an impedance analyzer was designed and implemented. The developed system allows carrying out in situ and real time measurements of the equivalent circuit and resonance frequency of the resonator in highly damping media where QCM oscillator sensors (active way sensors) present operation problems with low resonator quality factors. The sensor was used to observe the hydrate and drying properties of Nafion® polymer membranes. Also, a study of noise and resolution of the sensor was carried out. 9MHz commercial quartz crystals provided by Maxtek were used, with a deposition area of 0.2 cm2. A resolution of 25 ng / cm2 was obtained.

A New Simulation Tool for the Design of TSM Acoustic Wave Sensors

This paper describes a new simulation tool aimed at helping engineers design TSM acoustic wave sensors for liquid media. It helps to adapt the design to the application environment, so that the oscillation remains in spite of the large reduction of the quality factor that the quartz experiences in those media