Perturbation, sensor signals

The flow of electrical current in a circuit with an electrolyte causes ionic transport between the electrodes, which affects the electrode reaction. The application of a small perturbation in a potentiometric sensor has been shown to improve the sensor performance in what is referred to as the current reversal method [24—26]. An analysis of the response to such a perturbation can also be used as a diagnostic tool to evaluate sensor performance during operation [27, 28]. Similarly, the application of a bias voltage to a potentiometric sensor can be used to affect the performance of the sensor, such as the relative responses to NO and NO2 gases [29—31]. The response to voltage or current perturbations can also be used as the sensor signal. 

Burst signals (supemovae) have been the primary target for the resonant mass detectors. The minimum detectable perturbation of the metric sensor caused by a burst of GW of duration r is ... 

It should be noted that GC mode experiments with amperometric tips may contain a feedback component to the current if the electrochemical process at the tip is reversible and the tip-to-specimen distance is less than about 5a. However, at greater distances or when employing a potentiometric tip, the tip acts approximately as a passive sensor, i.e., one that does not perturb the local concentration. This situation is quite distinct from feedback mode, where the product of the electrolysis at the tip is an essential reactant in the process at the specimen surface. This interdependence of tip and specimen reactions in feedback mode ensures that the biochemical process is confined to an area under the tip defined by the tip radius and diffusional spreading of the various reagents (20). In contrast, the biochemical process in GC mode is independent of the presence of the tip and may therefore occur simultaneously across the whole surface. In addition, the tip signal often does not directly provide information on the height of the tip above the surface methods to overcome this limitation are described in Sec. I.D. Finally, since the tip process and the biochemical reaction at the specimen are independent, a wide range of microsensors may be employed as the tip, e.g., ion-selective microelectrodes, which are not applicable in feedback experiments. 

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