Search Results (57)

This study investigates the feasibility of using a wearable system with full-wave alternating current (AC) excitation to measure electrodermal activity (EDA). Typically measured using direct current (DC) excitation, EDA is often affected by signal drift due to electrode–skin polarisation. To address this, a portable device was developed that applies fixed-amplitude, full-wave AC signals and records EDA under controlled conditions. The electrical behaviour of the skin was also simulated using a multilayer model to analyse current propagation at different frequencies. The experimental procedure was conducted with ten healthy participants under controlled conditions. Two stages were carried out: the first compared the similarity of the skin conductance level (SCL) between DC and half-wave alternating current (AC) signals; the second analysed signal stability and skin response at full-wave AC excitation. Compared to DC, full-wave AC excitation demonstrated reduced signal drift, greater temporal stability, and enhanced measurement of the skin’s capacitive response. These findings support the adoption of AC excitation for EDA measurement, especially in ambulatory and real-time biomechanical applications where signal reliability and stability are essential. Full article

A mononuclear complex [Dy(phenN₆)(HL′)₂]PF₆·CH₂Cl₂ (H₂L′ = R/S-1,1′-binaphthyl-2,2′-diphenol) with local D_6h symmetry was synthesized. Structural determination shows that Dy³⁺ was encapsulated within the coordination cavity of the neutral hexaaza macrocyclic ligand phenN₆, forming a non-planar coordination environment. The axial positions are occupied by two phenoxy groups of binaphthol in the trans form. The local geometry of Dy³⁺ closely resembles a regular hexagonal bipyramid D_6h configuration. The axial Dy-O_phenoxy distances are 2.189(5) and 2.145(5) Å, respectively, while the Dy-N bond lengths in the equatorial plane are in the range of 2.524(7)–2.717(5) Å. The axial O_phthalmoxy-Dy-O_phthalmoxy bond angle is 162.91(17)°, which deviates from the ideal linearity. Under the excitation at 320 nm, the complex exhibits a characteristic emission peak at 360 nm, corresponding to the naphthalene ring. The AC susceptibility measurements under an applied DC field of 1800 Oe show distinct temperature-dependent and frequency-dependent AC magnetic susceptibility, typical of single-molecule magnetic behavior. The Cole–Cole plot in the temperature range of 6.0–28.0 K was fitted using a model incorporating Orbach and Raman relaxation mechanisms, giving an effective energy barrier of U_eff = 300.2 K. Theoretical calculations on complex 1 reveal that the magnetization relaxation proceeds through the first excited Kramers doublets with a calculated magnetization blocking barrier of 404.1 cm⁻¹ (581.4 K). Full article

During operation, converter transformers enter a saturation state, leading to phenomena such as magnetising inrush currents. Accurately measuring the excitation characteristic curve of an iron core under deep-saturation conditions is essential for analysing low-frequency transient phenomena in transformers. This paper presents a method for calculating the excitation characteristics of a converter transformer under deep iron core saturation. The method involves establishing an improved T model for the converter transformer and conducting open-circuit experiments in the linear working region to obtain the excitation characteristic curve and knee point parameters. AC-DC hybrid excitation is used to achieve deep saturation, and measurements of saturated inductance at different levels of saturation at the transformer terminals are taken. The mathematical relationship between saturated inductance and magnetic impedance is derived, allowing deduction of the magnetising characteristic curve of the converter transformer under deep-saturation conditions based on measured saturated inductance values. A finite element simulation analysis was performed on a single-phase four-column converter transformer with a capacity of 250 MVA. Additionally, a test platform for toroidal transformers and dry-type transformers has been set up to carry out excitation characteristic measurement and verification. Experimental results demonstrate that errors are maintained within 10% or less, validating this approach’s effectiveness. Full article

This study presents a novel, coil-only magnetostrictive ultrasonic detection method that operates effectively without permanent magnets, introducing a simpler alternative to conventional designs. The system configuration is streamlined, consisting of a single meander coil, an excitation source, and a nickel sheet, with both the bias magnetic field and ultrasonic excitation achieved by a composite excitation containing both DC and AC components. This design offers significant advantages, enabling high-frequency Lamb wave generation in nickel sheets for ultrasonic detection while reducing device complexity. Experimental validation demonstrated that an S0-mode Lamb wave at a frequency of 2.625 MHz could be effectively excited in a 0.2 mm nickel sheet using a double-layer meander coil. The experimentally measured wave velocity was 4.9946 m/s, with a deviation of only 0.4985% from the theoretical value, confirming the accuracy of the method. Additionally, this work provides a theoretical basis for future development of flexible MEMS-based magnetostrictive ultrasonic transducers, expanding the potential for miniaturized magnetostrictive patch transducers. Full article

The reliability of components of industrial electrical assets fed by power electronics might be at risk due to the type and extent of electrothermal stresses. The move of power electronics toward higher levels of voltage, switching frequency, slew rate, and specific power increases the risk of partial discharge inception and thus of accelerated extrinsic aging and premature failure. The reaction to this challenge is to embrace the concept of partial discharge-free (PD-free) design and operation. This paper presents a PD-free approach to the design of laminated busbars, considering both AC and DC insulation subsystems, and focusing on surface insulation. The availability of a recently proposed model to estimate the inception field is a key tool. The model is validated through PD measurements performed on a laminated busbar, using new automatic software that can identify the type of source generating PD. Combined with electric field calculations, the model provides estimates of the PD inception voltage which are almost coincident with the measurement results. Inception voltages in the order of 10 kV and 20 kV have been observed for AC and DC excitation, respectively. In the case of DC supply, tests at different ambient temperatures, 25 °C and 60 °C, indicate that the inception voltage does not change significantly with temperature. Disposability, scalability to any voltage/power, and capability to work, potentially, for any other type of insulation system, are interesting features of the proposed approach, which are discussed in the paper. Full article

Existing magnetic tracer detection systems primarily rely on fundamental wave signal acquisition using non-differential sensor configurations. These sensors are highly susceptible to external interference and lack tomographic localization capabilities, hindering their clinical application. To address these limitations, this paper presents a novel method for achieving the deep spatial localization of tracers. The method exploits second harmonic signal detection at non-zero field points. By considering the combined nonlinear characteristics of the coil’s axial spatial magnetic field distribution and the Langevin function, a correlation model linking the signal peak and bias field is established. This model enables the determination of the tracer’s precise spatial location. Building on this framework, a handheld device for localizing magnetic nanoparticle tracers was developed. The device harnesses the second harmonic response generated by coupling an AC excitation field with a DC bias field. Our findings demonstrate that under conditions of reduced coil turns and weak excitation fields, the DC bias field exhibits exclusive dependence on the axial distance of the detection point, independent of particle concentration. This implies that the saturated DC bias field corresponding to the second harmonic signal can be used to determine the magnetic nanoparticle sample detection depth. The experimental results validated the method’s high accuracy, with axial detection distance and concentration reduction errors of only 4.8% and 4.1%, respectively. This research paves the way for handheld probes capable of tomographic tracer detection, offering a novel approach for advancing magnetically sensitive biomedical detection technologies. Full article

This article introduces a novel regenerative suspension system designed for active seat suspension, to reduce vibrations while recovering energy. The system employs a four-quadrant electric actuator operation model and utilizes a brushless DC motor as an actuator and an energy harvester. This motor, a permanent magnet synchronous type, transforms DC into three-phase AC power, serving dual purposes of vibration energy recovery and active power generation. The system’s advanced vibration control is achieved through the switching of MOSFET transistors, ensuring the suspension system meets operational criteria that contrast with traditional vibro-isolation systems, thereby reducing the negative effects of mechanical vibrations on the human body, while also lowering energy consumption. Comparative studies of the regenerative system dynamics against passive and active systems under random vibrations demonstrated its effectiveness. This research assessed the system’s performance through power spectral density and transmissibility functions, highlighting its potential to enhance energy efficiency and the psychophysical well-being of individuals subjected to mechanical vibrations. The effectiveness of the energy regeneration process under the chosen early excitation vibrations was investigated. Measurements of the motor torque in the active mode and during regenerative braking mode, and the corresponding phase currents of the motor, are presented. Full article

Inspired by the fact that flying insects improve their power conversion efficiency through resonance, many soft robots driven by dielectric elastomer actuators (DEAs) have achieved optimal performance via first-order modal resonance. Besides first-order resonance, DEAs contribute to multiple innovative functions such as pumps that can make sounds when using multimodal resonances. This study presents the multimodal resonance of a rectangular planar DEA (RPDEA) with a central mass bias. Using a combination of experiments and finite element modeling (FEM), it was discerned that under a prestretch of 1.0 × 1.1, the first-, second-, and third-order resonances corresponded to vertical vibration, rotation along the long axis, and rotation along the short axis, respectively. In first-order resonance, superharmonic, harmonic, and subharmonic responses were activated, while only harmonic and subharmonic responses were observed in the second- and third-order resonances. Further investigations revealed that prestretching tended to inhibit third-order resonance but could elevate the resonance frequencies of the first and second orders. Conveniently, both the experimental and FEM results showed that the frequencies and amplitudes of the multimodal resonances could be tuned by adjusting the amplitudes of the excitation signals, referring to the direct current (DC) amplitude and alternating current (AC) amplitude, respectively. Moreover, instead of linear vibration, we found another novel approach that used rotation vibration to drive a robot with soft bristles via hopping locomotion, showcasing a higher speed compared to the first-order resonance in our robot. Full article

Transcranial electrical brain stimulation techniques like transcranial direct current (tDCS) and transcranial alternating current (tACS) have emerged as potential tools for treating neurological diseases by modulating cortical excitability. These techniques deliver small electric currents to the brain non-invasively through electrodes on the scalp. tDCS uses constant direct current which weakly alters the membrane voltage of cortical neurons, while tACS utilizes alternating current to target and enhance cortical oscillations, though the underlying mechanisms are not fully understood more specifically. To elucidate how tACS perturbs endogenous network dynamics, we simulated spiking neuron network models. We identified distinct roles of the depolarizing and hyperpolarizing phases in driving network activity towards and away from the strong nonlinearity provided by pyramidal neurons. Exploring resonance effects, we found matching tACS frequency to the network’s endogenous resonance frequency creates greater entrainment. Based on this, we developed an algorithm to determine the network’s endogenous frequency, phase, and amplitude, then deliver optimized tACS to entrain network oscillations. Together, these computational results provide mechanistic insight into the effects of tACS on network dynamics and could inform future closed-loop tACS systems that dynamically tune stimulation parameters to ongoing brain activity. Full article

Among the different techniques for monitoring the flow rate of various fluids, thermal flow sensors stand out for their straightforward measurement technique. However, the main drawback of these types of sensors is their dependency on the thermal properties of the medium, i.e., thermal conductivity (k), and volumetric heat capacity ($\rho c_p$). They require calibration whenever the fluid in the system changes. In this paper, we present a single hot wire suspended above a V-groove cavity that is used to measure k and $\rho c_p$ through DC and AC excitation for both pure gases and binary gas mixtures, respectively. The unique characteristic of the proposed sensor is its independence of the flow velocity, which makes it possible to detect the medium properties while the fluid flows over the sensor chip. The measured error due to fluctuations in flow velocity is less than ±0.5% for all test gases except for He, where it is ±6% due to the limitations of the measurement setup. The working principle and measurement results are discussed. Full article

This paper studies the stability of a real-world wind farm, Bison Wind Generation System (BWGS) in the state of North Dakota in the United States. BWGS uses an AC collector grid rated at 34.5 kV and a symmetrical bipolar high-voltage DC (HVDC) transmission grid rated at ±250 kV. The HVDC line transfers a total power of 0.5 GW, while both the HVDC rectifier and inverter substations use line-commuted converters (LCCs). The LCC-based rectifier adopts constant DC current control to regulate HVDC current, while the inverter operates in constant extinction angle control mode to maintain a fixed HVDC voltage. This paper proposes a frequency scan-based approach to obtain the d–q impedance model of (i) BWGS AC collector grids with Type 4 wind turbines that use permanent magnet synchronous generators (PMSGs) and two fully rated converters, and (ii) an LCC-HVDC system. The impedance frequency response of the BWGS is acquired by exciting the AC collector grid and LCC-HVDC with multi-sine voltage perturbations during its steady-state operation. The resulting voltage and current signals are subjected to a fast Fourier transform (FFT) to extract frequency components. By analyzing the impedance frequency response measurement of BWGS, a linear time–invariant (LTI) representation of its dynamics is obtained using the vector fitting (VF) technique. Finally, a Bode plot is applied, considering the impedance of the BWGS and grid to perform stability analyses. This study examines the influence of the short circuit ratio (SCR) of the grid and the phase lock loop (PLL) frequency bandwidth on the stability of the overall system. The findings provide valuable insights for the design and verification of an AC collector and LCC-based HVDC transmission systems. The findings suggest that the extraction of the impedance model of a real-world wind farm, achieved through frequency scanning and subsequent representation as an LTI system using VF, is regarded as a robust, suitable, and accurate methodology for investigating the dynamics, unstable operating conditions, and control interaction of the wind farm and LCC-HVDC system with the AC grid. Full article

This paper provides a proof of concept for a linear electric generator that can be used to harvest energy from various sources of linear motion, such as vibrations, free-piston engines and wave energy. The generator can be used to power small electronic devices, such as sensors, or charge household batteries. The literature was reviewed to develop an understanding about the applications, control methods, excitation methods and mechanics of rotating and linear electric machines. A bidirectional, two-sided linear machine was designed with two stator cores and a single mover core. The stator windings and mover winding can be independently excited, allowing for three modes: no mover excitation, a DC excited mover, and an AC excited mover. Simulation results showed that the magnetic flux generated by DC excited stator cores were concentrated in the centre of the mover core. The use of two stator cores eliminates lateral flux in the mover core when it is not excited, minimising attraction and repulsion forces. Parametric analysis showed that flux cutting occurred in all operation modes, verifying that the generator will produce power when operating. Hardware tests produced an output current when the machine was electrically and mechanically excited, verifying the proposed design. Full article

In a high-voltage direct current (HVDC) transmission system, commutation failure at the receiving end may lead to transient overvoltage at the sending end converter bus of the weak alterative current (AC) system. Firstly, the principle calculation method of overvoltage generation at the sending end after commutation failure is analyzed. Combined with the output characteristics of the hydroelectric excitation system, a coordinated control strategy for hydroelectric and DC systems is proposed. Since the voltage and current values at the DC outlet of the rectifier side change first after a fault occurs at the receiving end, the relationship equation between DC voltage and AC bus voltage is derived and it is used as an input signal to construct additional excitation control for hydropower stations. The proposed strategy is verified by establishing a simulation hydrogen–wind–solar model bundled via a DC sending system in PSCAD/EMTDC. The simulation results illustrate that the transient overvoltage suppression rates are all more than 35%, and the maximum is 38.53%. The proposed strategy can reduce the overvoltage by 0.126 p.u. compared with the International Council on Large Electric Systems (CIGRE) standard control strategy. Full article

The spectral quality of magnetic resonance spectroscopic imaging (MRSI) can be affected by strong magnetic field inhomogeneities, posing a challenge for 3D-MRSI’s widespread clinical use with standard scanner-equipped 2nd-order shim coils. To overcome this, we designed an empirical unified shim–RF head coil (32-ch RF receive and 51-ch shim) for 3D-MRSI improvement. We compared its shimming performance and 3D-MRSI brain coverages against the standard scanner shim (2nd-order spherical harmonic (SH) shim coils) and integrated parallel reception, excitation, and shimming (iPRES) 32-ch AC/DC head coil. We also simulated a theoretical 3rd-, 4th-, and 5th-order SH shim as a benchmark to assess the UNIfied shim–RF coil (UNIC) improvements. In this preliminary study, the whole-brain coverage was simulated by using B₀ field maps of twenty-four healthy human subjects (n = 24). Our results demonstrated that UNIC substantially improves brain field homogeneity, reducing whole-brain frequency standard deviations by 27% compared to the standard 2nd-order scanner shim and 17% compared to the iPRES shim. Moreover, UNIC enhances whole-brain coverage of 3D-MRSI by up to 34% compared to the standard 2nd-order scanner shim and up to 13% compared to the iPRES shim. UNIC markedly increases coverage in the prefrontal cortex by 147% and 47% and in the medial temporal lobe and temporal pole by 29% and 13%, respectively, at voxel resolutions of 1.4 cc and 0.09 cc for 3D-MRSI. Furthermore, UNIC effectively reduces variations in shim quality and brain coverage among different subjects compared to scanner shim and iPRES shim. Anticipated advancements in higher-order shimming (beyond 6th order) are expected via optimized designs using dimensionality reduction methods. Full article

Brushless synchronous machines (BSMs) are replacing conventional synchronous machines with static excitation in generation facilities due to the absence of sparking and lower maintenance. However, this excitation system makes measuring electric parameters in the rotor challenging. It is highly difficult to detect ground faults, which are the most common type of electrical fault in electric machines. In this paper, a ground fault detection method for BSMs is proposed. It is based on an inductive AC/DC rotating current sensor installed in the shaft. In the case of a ground fault in the rotating parts of the BSM, a fault current will flow through the rotor’s sensor, inducing voltage in its stator. By analyzing the frequency components of the induced voltage, the detection of a ground fault in the rotating elements is possible. The ground faults detection method proposed covers the whole rotor and discerns between DC and AC sides. This method does not need any additional power source, slip ring, or brush, which is an important advantage in comparison with the existing methods. To corroborate the detection method, experimental tests have been performed using a prototype of this sensor connected to laboratory synchronous machines, achieving satisfactory results. Full article