Very low-frequency IEPE accelerometer calibration and application to a wind energy structure

In this work, we present an experimental setup for very low-frequency calibration measurements of low-noise Integrated Electronics Piezo Electric (IEPE) accelerometers and a customised signal conditioner design for using IEPE sensor down to 0.05Hz. AC-response IEPE accelerometer and signal conditioners have amplitude and phase deviations at low frequencies. As the standard calibration procedure in the low-frequency range is technically challenging, IEPE accelerometers with standard signal conditioners are usually used in frequency ranges above 1 Hz. Vibrations on structures with low eigenfrequencies like wind turbines are thus often monitored using DC-coupled micro-electro-mechanical systems (MEMS) capacitive accelerometers. This sensor type suffers from higher noise levels compared to IEPE sensors. To apply IEPE sensors instead of MEMS sensors, in this work the calibration of the entire measurement chain of three different IEPE sensors with the customised signal conditioner is performed with a low-frequency centrifuge. The IEPE sensors are modelled using IIR filters to apply the calibration to time-domain measurement data of a wind turbine support structure. This procedure enables an amplitude and phase-accurate vibration analysis with IEPE sensors in the low-frequency range down to 0.05 Hz.

Lead-substituted barium hexaferrite for tunable terahertz optoelectronics

In recent years, due to their outstanding dielectric and magnetic properties, hexagonal ferrites (hexaferrites) have attracted considerable interest for developing electronic components of next-generation communication systems. The complex crystal structure of hexaferrites and critical dependences of their electric and magnetic properties on external factors, like magnetic or electric fields, pressure or doping, open ample opportunities for targeted tuning of these properties when designing specific devices. To that end, we explored the electromagnetic properties of the Pb-substituted barium hexaferrite, Ba1-xPbxFe12O19, a compound featuring an extremely rich set of physical phenomena that are inherent in the dielectric and magnetic subsystems of the material and are expected to have significant effect on its electromagnetic response at radio and terahertz frequencies. We performed the first detailed measurements of the AC response of single-crystalline Ba1-xPbxFe12O19 in an extremely broad spectral range from 1 Hz to 240 THz down to temperatures as low as 5 K. We fully characterized numerous microscopic phenomena that determine the broad-band dielectric response of the compound, and we analyzed their nature. This includes temperature-activated radiofrequency relaxations that were attributed to the dynamic response of magnetic/dielectric domains. The terahertz response is dominated by a ferroelectric-like soft mode with an unusual temperature behavior that we explain by means of a microscopic model. Several narrower terahertz excitations are associated with electronic transitions between the fine-structure components of the Fe2+ground state. Narrow resonances detected in the gigahertz region are presumably of magneto-electric origin. The obtained data on diverse but controllable electromagnetic properties of Ba1-xPbxFe12O19 compounds provides the researchers with information that makes the entire class of hexaferrites materials attractive for manufacturing electronic devices for the radiofrequency and terahertz ranges, such as absorbing coatings, anti-reflective coatings, absorbers, electromagnetic shields, antennas, phase shifters, filters, resonators, modulators, etc.

The effect of temperature on the structural, dielectric and magnetic properties of cobalt ferrites synthesized via hydrothermal method

A series of cobalt ferrite nanoparticles were prepared using hydrothermal process by varying the reaction temperature. The structural, magnetic and dielectric properties have been studied with the help of X-ray diffractometer (XRD), vibrating sample magnetometer (VSM) and impedance analyzer respectively. XRD spectra of all samples confirmed the formation of cobalt ferrite (CoFe2O4) nanoparticles (NPs). The lattice constant ‘a’ for temperature series samples is averaged around 8.4023 Å. Crystallite size of temperature series is calculated by Debye–Scherer formula that lies in the range of 15.04–20.49 nm. Its values increase because the chance of coalescence increases by increasing temperature. The maximum packing factor is obtained for the sample with highest reaction temperature. From VSM data, we get the M–H hysteresis curves for complete temperature series which confirms the magnetic nature. The maximum saturation magnetization 150.67 emu/g is obtained for the sample prepared at highest temperature. Different magnetic parameter such as saturation magnetization, coercivity, retentivity, squareness ratio, anisotropy constant and magneton number has been calculated from VSM data. AC response of all prepared ferrites was studied with impedance analyzer of frequency range 20 Hz to 20 MHz. Ferrites are the insulating materials, so, eddy current does not induce in transformer cores made of ferrite materials. In the medical field cobalt ferrite is used for drug delivery, as a biosensor and in MRI.

The Effect of Fatigue Loading on Electrical Impedance in Open-Hole Carbon Nanofiber-Modified Glass Fiber/Epoxy Composites

Composite materials are ideal for many weight-conscious applications such as aerospace and automotive structures because of their exceptionally high specific properties. However, composite materials are susceptible to complex damage and difficult-to-predict damage growth. This necessitates the application of structural health monitoring (SHM) for in-operation monitoring of damage formation and accumulation. Self-sensing materials are strong candidates for composite SHM because they do not suffer from limitations associated with traditional, point-based sensors. A common approach to self-sensing is the piezoresistive effect in nanofiller-modified materials. To date, work in the area of self-sensing via the piezoresistive effect has focused overwhelmingly on the direct current (DC) response of these materials. This is an important limitation because alternating current (AC) effects inherently provide more information by relating both impedance and phase to damage. Therefore, this work explores the effect of high-cycle fatigue loading on the AC response of carbon nanofiber (CNF)-modified glass fiber/epoxy laminates. Specifically, impedance magnitude and phase angle are both measured through the thickness and along the length of a tension-tension fatigue-loaded specimen with an open-hole stress concentration as a function of load cycle and up to 10 MHz. The collected impedance data is then fit to an equivalent circuit model and correlated to stiffness changes. This means that changes in equivalent circuit behavior can be used to track fatigue-induced softening in self-sensing composites. In light of these promising preliminary results, AC effects appear to have considerable potential for real-time tracking of damage accumulation.

AC Analysis of Differential Active Balun Topology

The current manuscript aimed to study a differential active balun circuit in terms of the small-signal analysis, implemented in a standard 90-nm complementary metal-oxide semiconductor (CMOS) technology. Small-signal or alternating current (AC) response or frequency response of the active balun determines the maximum frequency of operation and the effective bandwidth of the circuit. With the analysis, the active balun circuit could be modeled and designed to achieve gain or attenuation at the desired frequency of operation. Design tradeoffs are inevitable and are carefully considered in the analysis and design. Eventually, the differential active balun design achieved a gain difference better than 1 dB and a phase difference of 180°±10° or better at the frequency of operation of 5.8 GHz, comparable to previous designs and researches.