Design and Potential Analysis of an Eddy Current Sensor for Inductive Conductivity Measurement in Fluids

In the scope of this paper, a first exemplary eddy current sensor for seawater conductivity measurement is developed, based on the derived sensor theory of a previous work. By high-frequency excitation, eddy currents are induced in the fluid and are counter-fields measured with a sensing coil. The coil’s resonance point is used for amplification. The developed prototype is analyzed based on a derived transfer function and FEM simulations. The theory is validated using a prototype implementation. With conducted experiments on a sensor test bench, the characteristics are confirmed and disturbances identified. It is shown that frequencies exist where temperature influence is minimal. This work gives a perspective for a novel sensor to allow seawater conductivity measurement.

Suppression of galloping oscillations by injecting a high-frequency excitation

Galloping is an aeroelastic instability which incites oscillatory motion of elastic structures when subjected to an incident flow. Because galloping is often detrimental to the integrity of the structure, many research studies have focused on investigating methodologies to suppress these oscillations. These include using passive energy sinks, altering the surface characteristics of the structure, actively changing the shape of the boundary layer through momentum injection and using feedback control algorithms. In this paper, we demonstrate that the critical flow speed at which galloping is activated can be substantially increased by subjecting the galloping structure to a high-frequency non-resonant base excitation. The average effect of the high-frequency excitation is to produce additional linear damping in the slow response which serves to suppress the galloping instability. We study this approach theoretically and demonstrate its effectiveness using experimental tests performed on a galloping cantilevered structure. It is demonstrated that the galloping speed can be tripled in some experimental cases. This article is part of the theme issue ‘Vibrational and stochastic resonance in driven nonlinear systems (part 2)’.

On the escape of a resonantly excited couple of particles from a potential well

The escape dynamics of a damped system of two coupled particles in a truncated potential well under biharmonic excitation are investigated. It is assumed that excitation frequencies are tuned to the modal natural frequency of the relative motion and to the modal frequency of the centre of mass on the bottom of the potential well. Although the escape is essentially a non-stationary process, the critical force strongly depends on the stationary amplitude of the relative vibrations within the pair of masses. The characteristic escape curve for the critical force moves up on the frequency-escape threshold plane with increasing relative vibrations, which can be interpreted as a stabilizing effect due to the high-frequency excitation. To obtain the results, new modelling techniques are suggested, including the reduction in the effect of the high-frequency excitation using a probability density function-based convolution approach and an energy-based approach for the description of the evolution of the slow variables. To validate the method, the coupled pair of particles is investigated with various model potentials.

Empirical Expression for AC Magnetization Harmonics of Magnetic Nanoparticles under High-Frequency Excitation Field for Thermometry

The Fokker–Planck equation accurately describes AC magnetization dynamics of magnetic nanoparticles (MNPs). However, the model for describing AC magnetization dynamics of MNPs based on Fokker-Planck equation is very complicated and the numerical calculation of Fokker-Planck function is time consuming. In the stable stage of AC magnetization response, there are differences in the harmonic phase and amplitude between the stable magnetization response of MNPs described by Langevin and Fokker–Planck equation. Therefore, we proposed an empirical model for AC magnetization harmonics to compensate the attenuation of harmonics amplitude induced by a high frequency excitation field. Simulation and experimental results show that the proposed model accurately describes the AC M–H curve. Moreover, we propose a harmonic amplitude–temperature model of a magnetic nanoparticle thermometer (MNPT) in a high-frequency excitation field. The simulation results show that the temperature error is less than 0.008 K in the temperature range 310–320 K. The proposed empirical model is expected to help improve MNPT performance.

An Excitation Circuit of the Cell in Optically Pumped Magnetometer

Cell is the key component in an optically pumped magnetometer. It is necessary to light the cell before measurement and to maintain the illuminated state. The accuracy and stability of magnetic values from the instrument are closely related to the brightness and stability of the cell. The cell is also the largest power dissipation component in the sensor probe, so the overall energy consumption of the magnetometer is highly correlated with it. This paper studies the excitation circuit of cell in the magnetometer. Firstly, we demonstrate the resistivity characteristic of a cell using simulations. After that, based on the combination of signal source impedance and transmission line impedance, the matching network of excitation circuit is analyzed. We demonstrate that both T-network and Π-network can achieve the impedance matching of the transmitter circuit by a simulation experiment, under the condition of 50MHz signal, 10Ω source impedance, and 50Ω transmission line impedance. T-network shows the best performance in frequency selectivity and energy transfer. Finally, the simulation experiment also proves that a circuit composed of a self-coupled coil and an LC parallel resonant network can realize the impedance matching and the passband selection of the receiver circuit by optimizing values of the inductance and capacitance, and turns of the self-coupled coil simultaneously. The power consumption of the whole high-frequency excitation circuit of cell in the optically pumped magnetometer is only about 6W.