Magnetic position sensors

Magnetic position sensors are popular in industrial and automotive applications since they are robust, resistant to dust and oil and they can be cheap. However, precise magnetic position sensors can achieve 0.015 % accuracy and 10 nm resolution. The maximum achievable range is about 20 m. DC magnetic position sensors are using a permanent magnet as a field source. As a field sensor, magnetoresistors are often used instead of traditional Hall sensors. Eddy current sensors work also with non-magnetic conduction targets. Magnetostrictive sensors are based on the time-of-flight of the elastic wave excited in the magnetostrictive material. The sensors can be several meters long and their applications range from level meters to hydraulics. Magnetic trackers and long-range position sensors utilize AC field sources, which are detectable from distances up to 20 m. Compared to optical instruments magnetic trackers do not need direct view. Their applications include surgery, mixed reality, and underground and underwater navigation.

Computer Simulations of Dynamic Response of Ferrofluids on an Alternating Magnetic Field with High Amplitude

The response of ferrofluids to a high-amplitude AC magnetic field is important for several applications including magnetic hyperthermia and biodetection. In computer simulations of the dynamic susceptibility of a ferrofluid outside the linear response region, there are several problems associated with the fact that an increase in the frequency of the AC field leads to the appearance of additional computational errors, which can even lead to unphysical results. In this article, we study the dependence of the computational error arising in the computer simulation of the dynamic susceptibility on the input parameters of the numerical algorithm: the length of the time step, the total number of computer simulation periods, and averaging period. Computer simulation is carried out using the Langevin dynamics method and takes Brownian rotational relaxation of magnetic particles and interparticle interactions into account. The reference theory [Yoshida T.; Enpuku K. Jap. J. Ap. Phys. 2009] is used to estimate computational error. As a result, we give practical recommendations for choosing the optimal input parameters of the numerical algorithm, which make it possible to obtain reliable results of the dynamic susceptibility of a ferrofluid in a high-amplitude AC field in a wide frequency range.

Dielectric permittivity and relaxation process investigation of C-doped TlInS2 crystals

In this work, permittivity of TlInS2 and TlInS2 (5%[Formula: see text]C) crystals has been investigated at the AC field with 100–500 K temperatures ranges. [Formula: see text] temperature dependencies of TlInS2 and TlInS2 (5%[Formula: see text]C) crystals are studied at the frequency range of 25–106 Hz. Activation energy and ionic conductivity nature of sample were analyzed. Moreover, permittivity of these samples was studied at the perpendicular direction of axis “[Formula: see text]” of TlInS2 (5%[Formula: see text]C) crystals. The jumping process in the TlInS2 (5%[Formula: see text]C) crystals was studied using [Formula: see text] temperature dependencies.

Spark Plasma Sintering of LiFePO4: AC Field Suppressing Lithium Migration

Our work proposes a comparison between Spark Plasma Sintering of LiFePO4 carried out using an Alternating Current (AC) and Direct Current (DC). It quantifies the Li-ion migration using DC, and it validates such hypothesis using impedance spectroscopy, X-ray photoelectron spectroscopy and inductively coupled plasma optical emission spectroscopy. The use of an AC field seems effective to inhibit undesired Li-ion migration and achieve high ionic conductivity as high as 4.5 × 10−3 S/cm, which exceeds by one order of magnitude samples processed under a DC field. These results anticipate the possibility of fabricating a high-performance all-solid-state Li-ion battery by preventing undesired Li loss during SPS processing.

Microfluidic concentration enhancement of bio-analyte by temperature gradient focusing via Joule heating by DC plus AC field: A numerical approach

We present a detailed numerical analysis of electrophoresis induced concentration of a bio-analyte facilitated by temperature gradient focusing in a phosphate buffer solution via Joule heating inside a converging-diverging microchannel. The purpose is to study the effects of frequency of AC field and channel width variation on the concentration of target analyte. We tune the buffer viscosity, conductivity and electrophoretic mobility of the analyte such that the electrophoretic velocity of the analyte locally balances the electroosmotic flow of the buffer, resulting in a local build-up of the analyte concentration in a target region. An AC field is superimposed on the applied DC field within the microchannel in such a way that the back pressure effect is minimized, resulting in minimum dispersion and high concentration of the target analyte. Axial transport of fluorescein-Na in the phosphate buffer solution is controlled by inducing temperature gradient through Joule heating. The technique leverages the fact that the buffer's ionic strength and viscosity depends on temperature, which in turn guides the analyte transport. A numerical model is proposed and a finite element-based solution of the coupled electric field, mass, momentum, energy and species equations are carried out. Simulation predict peak of 670-fold concentration of fluorescein-Na is achieved. The peak concentration is found to increase sharply as the channel throat width, while the axial spread of concentrated analyte increases at lower frequency of AC field. The results of the work may improve the design of micro concentrator.

Dipole defect decay and dielectric relaxation in Na0.5Bi0.5TiO3 single crystal

Electrical properties of heat treated in air and in vacuum Na0.5Bi0.5TiO3 single crystals were measured in AC field (f=1 kHz) in the range 300–800 K. Relaxation anomaly of permittivity ε(T) is observed near 700 K for the crystal heat treated in vacuum. It is argued that processing in vacuum generates the defect dipoles, which give rise to the dielectric anomaly. The character of the ε(T) experimental dependence is quite different from the predictions of Debye model. The non-Debye behavior of ε(T) is explained by the concentration decrease of dipole defects due to their thermal destruction at high temperatures. In addition, the ε(T) anomaly could be described more precisely by taking into consideration configurational and vibrational entropy of the subsystem of dipole defects. The observed dielectric relaxation is presumably attributed to reorientations of the dipole moments of Ti3+–VO centers.