Interdigitated electrode structures have applications in a myriad of fields and have become attractive for in-line electrochemical detection in lab-on-a-chip microsystems. Analytical models can replace complex and expensive numerical simulations to determine the capacitance of interdigitated electrode structures in cases where simple geometries can be assumed. Closed-form analytical expressions derived from Schwarz-Christoffel conformal mappings were used to determine the capacitance of multi-layer interdigitated electrode structures with an additional parallel continuous electrode. The partial-capacitance approach was reformulated to find the capacitance of multi-layer structures with non-monotonically changing permittivities. The analytical model was found to be in close agreement with finite-element simulations. The model is used for optimization of an insulated transducer for sensitive detection of surface processes.
In the main office building of GTZ in Eschborn, Germany a resource-oriented sanitation system containing urine diversion (UD) toilets and waterless urinals has been in operation since 2006. After 2.5 years of operating the system, a first overall evaluation of the system in terms of its acceptance amongst the users and the cleaning staff was conducted by carrying out two surveys and many interviews. The overall result is that most of the users appreciate the sanitation concept in theory but have problems with the technical design of the particular type of UD flush toilets installed here. The survey results also gave some directions towards which hygiene devices the users would appreciate in order to overcome their reluctance to sit down on the toilet seat in public buildings (the sitting being necessary for correct operation of the urine valve to separate urine from flush water). Also, it is difficult to convince the cleaning and facility maintenance staff of the necessity of special cleaning and preventative maintenance routines. Hence, before such systems can be widely used, clear cleaning routines and maintenance instruction are required as well as certain technical modifications of this type of UD flush toilets to optimise the urine/water separation and the flushing properties of the toilet.
a b s t r a c tImpedance spectroscopy has the potential for label-free integrated electrochemical detection in microfluidic lab-on-a-chip applications. Its capability to identify and discern between surface and bulk processes in solid-liquid systems finds particular use for the detection of biorecognition events or conductivity measurements. The electrochemical transducer can be in the form of interdigitated electrode structures to increase sensitivity. Experimental work was performed to characterize two different transducer designs. Applications included the monitoring of protein films on contact-less interdigitated electrode structures and conductivity detection of droplets on insulated two-electrode structures. The use of electrode passivation eliminated electrode degradation. Experimental results were compared to theoretical analytical models, and were found to closely correlate with one another. The analytical models were used to design the transducer for optimal conductivity detection. The results inform the current research efforts for the development of in-line impedance spectroscopy in digital microfluidics and confirm the use of simple analytical models for the first-order estimation of the frequency response of interdigitated electrode structures.
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