Theoretical and experimental determination of cell constants of planar-interdigitated electrolyte conductivity sensors

In this paper, an analytical expression is presented for the cell constant of planar-interdigitated electrodes used as electrolyte conductivity sensors. The result of this expression is compared with results of measurement carried out with several differently shaped planar probes provided with a thin Ta2O5 insulating film, showing good agreement. More than 10 different devices have been fabricated with predicted cell constants ranging from 0.14 to 4.44 cm¿1. The measured cell constants are typically 10¿20% smaller, possibly due to fringing effects

Gas bubbles electrolytically generated at microcavity electrodes used for the measurement of the dynamic surface tension in liquids

A new method is proposed for the measurement of dynamic surface tension in aqueous solutions. The advantage of this method with respect to the classical method based on sparging is that the use of gas pumps is avoided, resulting in a miniaturized system. This method is based on the in situ generation of gas bubbles by means of electrolysis at microcavity electrodes (MCEs). As a consequence of electrode surface shaping, a single nucleation site for gas bubbles is created. The MCE is used simultaneously as a bubble actuator (generator) and as a bubble size and/or frequency sensor. Measurement results prove the suitability of the electrolytic method for the monitoring of the dynamic surface tension in aqueous solutions

On the mechanical behaviour of thin perforated plates and their application in silicon condenser microphones

In this paper an alternative approach to the modelling of plates with a large number of holes is presented. By means of plate theory, it is shown that perforated plates can be modelled by conventional orthotropic plates with modified elastic properties. The modification of the elastic constants is derived by equalizing the strain-energy of the perforated and the orthotropic plate. The model obtained is then compared with previous methods and applied in the electrochemical simulation of a silicon micromachined microphone structure. The microphone structures are simulated numerically, using an algorithm based on finite differences

The application of silicon dioxide as an electret material

The authors have investigated silicon dioxide for its electret properties. It appears that thermally grown silicon dioxide has a large lateral surface conductivity, resulting in poor electret behavior. This can be adequately reduced by chemical surface modification, resulting in an excellent silicon dioxide electret. Experiments have shown that corona-charged SiO2 layers are much more resistant to high temperatures than Teflon-FEP electrets. A 1.1-¿m-thick SiO2 layer, charged up to 150 V, yields a time constant of the charge decay in excess of 400 yr at ambient laboratory condition

Gas Bubbles Electrolytically Generated At Microcavity Electrodes (MCE) Used For The Measurement Of The Dynamic Surface Tension In Liquids

A new method is proposed for the measurement of dynamic surface tension in aqueous solutions. The advantage of this method with respect to the classical method based on sparging is that the use (of gas pumps is avoided, resulting in a miniaturised system. This method is based on the in-situ generation of gas bubbles by means of electrolysis at Microcavity Electrodes (MCE). As a consequence of electrode surface shaiping, a single nucleation site for gas bubbles is created. The MCE is used simultaneously as a bubble actuator (generator) and as a bubble size andlor frequency sensor. Measurement results prove the suitability of the electrolytical method for the monitoring of the dynamic surface tension in aqueous\ud solutions

A drift free nernstian iridium oxide PH sensor

A novel way of eliminating drift problems in metal oxide pH sensors is presented. The method employs a FET-structure under the electrode that uses the metal oxide as a gate contact. In addition to the enhanced drift properties, the new sensor has an almost ideal nernstian response. First a theoretical explanation is given, which is then confirmed by measurement

Characterization of proteins by means of their buffer capacity, measured with an ISFET-based coulometric sensor-actuator system

Proteins form the specific selector in many biochemical sensors. A change in one of the properties of such a protein has to be detected by an appropriate transducer, which completes the biochemical sensor. One of these properties is the buffer capacity of a protein. If the binding of a substance to a protein can significantly change the proton binding, which accounts for the buffer capacity of proteins, the detection of this changed buffer capacity enables the construction of a new type of biosensor.\ud \ud It will be shown that the buffer capacity can be measured with an ISFET-based sensor—actuator device. The alternating generation of protons and hydroxyl ions by alternating current coulometry at a porous noble metal actuator electrode causes an associated small pH perturbation, which is detected by the underlying pH-sensitive ISFET. The amplitude of the measured signal is a function of the buffer capacity of the solute, in which proteins can be present (or these proteins can be adsorbed in the porous actuator electrode of the device). A model describing the transfer function from the electrical input signal of the actuator to the resulting chemical output, which is subsequently detected by the ISFET pH sensor, is presented. Preliminary results of the measured buffer capacity of ribonuclease and lysozyme are presented