Ralph Otto

Portable light-addressable potentiometric sensor (LAPS) for multisensor applications

Abstract A novel design of the light-addressable potentiometric sensor (LAPS) for realisation of a portable multisensor device is presented. Light sources and electronics including an oscillator, a multiplexer, a pre-amplifier and a high-pass filter are encapsulated in a pen-shaped case, on which the sensor plate is mounted. This sensor device is capable of measuring up to four different ion species by integrating different ion-selective materials on the sensing surface, each illuminated with an independent light source. The novel design of the sensor system is expected to make the measurement easier and to enlarge the field of practical applications.

Non-constant bias current for dc SQUID operation

The in-phase current noise of the two junctions leads to additional 1/f noise in dc SQUIDs, which is reduced by the well-known bias reversal technique (ac bias reversal). In this paper, a new idea for dc SQUID operation with ac bias reversal non-constant bias current is described. In most conventional readout electronics with constant dc bias, the dc SQUID is connected to the preamplifier by means of a transformer in order to enhance the SQUID voltage signal and thus reduce the preamplifier noise contribution. We analyse this case in ac bias condition and find that the current through the SQUID is not constant after the bias reversal. In order to solve this problem, we derived the differential equation governing the network and solved it for a constant current through the SQUID. The transient of the applied bias current is chosen to satisfy this differential equation. The time constant of the transient does not depend on the dynamic resistance of the SQUID. The bias reversal frequency could be increased without introducing additional noise to the SQUID.