Maxwell bridge

About: Maxwell bridge is a research topic. Over the lifetime, 22 publications have been published within this topic receiving 169 citations.

Apparatus and method for the detection and measurement of liquid water and ice layers on the surfaces of solid materials

Abstract: An embodiment of the present invention is a roadway sensor for surface installation in a hole such that a thin ceramic contact sensor may be used to measure and cross-compare fundamental physical antenna parameters of the space immediately above a roadway or bridge surface. Measurements are combined by a microprocessor to discriminate between dry pavement, water (rain), snow and ice above the sensor head. Ambient surface temperature, water depth and ice/slush conditions are determined to estimate any hydroplaning hazard and ice/antifreeze/water mixtures. The sensor comprises an antenna that exhibits a resonant frequency and an input admittance including a real term; a Maxwell bridge coupled to the antenna for detecting the resonant frequency, input admittance and real term; and a frequency sweeping oscillator for driving the antenna at a plurality of frequencies proximate in frequency to the resonant frequency. A phase sensitive detector determines an attenuation rate and phase and thereby is able to extract a conductivity (σ) and a dielectric (e) measurement. The microprocessor relates the conductivity and dielectric measurements to yield, for example, a pair of estimates for ice and water content and layer thickness.

Modification of the Maxwell–Wien Bridge for Accurate Measurement of a Process Variable by an Inductive Transducer

Abstract: The small inductance of an inductive transducer generally linearly changes with a process variable, but their measurement by the usual inductive bridge circuit like the Maxwell bridge, the Maxwell-Wien Bridge, the Hay bridge, etc., suffers from errors due to the effect of the stray capacitance between bridge nodal points and the ground and the stray inductance on the inductive coil, respectively. The conventional Wagner-Earth technique is not suitable for continuous measurement. In this paper, a modified operational-amplifier-based Maxwell-Wien bridge measurement technique has been proposed in which the effect of stray capacitance and inductance is minimized. In the first phase of the experiment, the bridge performance has been studied with a known variable inductor, and in the second phase, the same experimentation was done by replacing the variable inductor with an inductive coil having an adjustable core position for the measurement of displacement. The linear characteristics over a wide range of displacement with good repeatability, linearity, and variable sensitivity have been described.

Design and signal processing of a magnetic sensor array for train wheel detection

Abstract: This paper proposes a train wheel detection system based on the use of an inductive sensor array. It allows multiple detection points and uses coded signals in order to work with low signal to noise ratios. The sensor array consists of pairs of sensor coils placed at every detection point. In this work, unlike previous work about this matter, the coils are interconnected in series as a part of a Maxwell bridge that is used to excite the coils and to receive the unbalance signal when there is a perturbation caused by the train pass over the detection point. Furthermore, the signal used is encoded with complementary sequences, allowing a single process of many detection points. Finally, the gain of the process allows placing the signal-processing module far away of the detection point, which makes it possible to work with a detector system without electronics near the railways.

Design of Quadrature Directional Couplers with Continuously Variable Coupling Ratios

Abstract: This paper presents a systematic approach for the design of directional couplers with tunable coupling strength, which maintain the properties of perfect impedance match and isolation over the whole tuning range. The devised method is based on eigenreflections and requires the synthesis of one-ports. This can be carried out with the help of graphical presentations in the Smith chart, thus fostering intuition in finding new circuit structures. The method is theoretically demonstrated by the development of a novel tunable LC-coupler or Maxwell bridge and a tunable proximity coupler. An experimental realization of the Maxwell bridge yields a tunable coupling ratio between 2 dB and 20 dB while maintaining excellent return loss and isolation.

Lossless current sensing and its application in current mode control

Abstract: In this paper, it is revealed that the lossless current sensing structure is very similar to the well known Maxwell bridge. The matching condition in lossless current sensing is the same as the balance equation in Maxwell bridge. In practice, it is difficult to meet the matching condition due to the parameter value variations. However, it is shown that in current mode control, at certain time constant mismatching situations, the circuit dynamic response actually could be improved. Furthermore, a "speedy capacitor" could be added to the lossless current sensing circuitry to significantly improve the sensed current signal to noise ratio and avoid jittery operation in wide DC-DC conversion ratio applications.