Biblio

The relative permittivity (also known as dielectric constant) is one of the physical properties that characterize a substance. The measurement of its magnitude can be useful in the analysis of several fluids, playing an important role in many industrial processes. This paper presents a method for measuring the relative permittivity of fluids, with the possibility of real-time monitoring. The method comprises the immersion of a capacitive sensor inside a tank or duct, in order to have the inspected substance as its dielectric. An electronic circuit is responsible for exciting this sensor, which will have its capacitance measured through a quick analysis of two analog signals outputted by the circuit. The developed capacitance meter presents a novel topology derived from the well-known Howland current source. One of its main advantages is the capacitance-selective behavior, which allows the system to overcome the effects of parasitic resistive and inductive elements on its readings. In addition to an adjustable current output that suits different impedance magnitudes, it exhibits a steady oscillating behavior, thus allowing continuous operation without any form of external control. This paper presents experimental results obtained from the proposed system and compares them to measurements made with proven and calibrated equipment. Two initial capacitance measurements performed with the system for evaluating the sensor's characteristics exhibited relative errors of approximately 0.07% and 0.53% in comparison to an accurate workbench LCR meter.

Securing multi-robot teams against malicious activity is crucial as these systems accelerate towards widespread societal integration. This emerging class of ``physical networks'' requires research into new methods of security that exploit their physical nature. This paper derives a theoretical framework for securing multi-agent consensus against the Sybil attack by using the physical properties of wireless transmissions. Our frame-work uses information extracted from the wireless channels to design a switching signal that stochastically excludes potentially untrustworthy transmissions from the consensus. Intuitively, this amounts to selectively ignoring incoming communications from untrustworthy agents, allowing for consensus to the true average to be recovered with high probability if initiated after a certain observation time T0 that we derive. This work is different from previous work in that it allows for arbitrary malicious node values and is insensitive to the initial topology of the network so long as a connected topology over legitimate nodes in the network is feasible. We show that our algorithm will recover consensus and the true graph over the system of legitimate agents with an error rate that vanishes exponentially with time.