Pair Of Magnets Research Articles

Strategies for improving the force performance of a superconducting linear synchronous motor

Combined with superconducting technology, an electrodynamic suspension train can reach a higher traveling speed by taking advantage of the strong magnetic field generated by high-temperature superconducting (HTS) magnets. However, a HTS linear synchronous motor (LSM) in a propulsion system typically uses an air-core structure to reduce the normal force. As a result, excessive propulsive force ripple occurs due to magnetic circuit divergence and a large air gap, which leads to an uncomfortable ride and unexpected mechanical resonance. To reduce this ripple, this study first improves the traditional short-pitch winding structure of the stator. By staggering the double-layer coils of the stator, the ripples of the magnetic flux density generated by the upper and lower coils change from superposition to suppression. Then, the propulsive force of a pair of pole magnets of the HTS-LSM under this structure is analyzed, and its primary ripple frequency is 6 times the fundamental frequency. By installing two pairs of magnets in a bogie and staggering them by a 30° electrical angle, the peak and valley of the propulsive force of the two magnets are staggered so that the total propulsive force waveform of the bogie can be smoothed as much as possible. Concurrently, the AC loss generated by the alternating magnetic field on the HTS magnets can be reduced. Also, this study investigates the influence of the short pitch factor on the propulsive force, and the ripple can be suppressed by reducing the factor.

Bi-objective optimal design of an electromagnetic shunt damper for energy harvesting and vibration control

Owing to the electromechanical energy conversion capacity, electromagnetic shunt dampers (EMSDs) are widely applied to vibration suppression or energy harvesting from vibrating structures. Either one of the two functions can be optimized in the designs of EMSD found in the literature. In this paper, a bi-objective optimization methodology of EMSD is proposed for the simultaneous maximization of energy harvesting from the damper and the suppression of resonant vibration of a dynamic structure. An EMSD with opposing magnet pairs configuration is designed to achieve the two design objectives simultaneously in a single-degree-of-freedom (SDOF) system and a dynamic vibration absorber (DVA). It is proved analytically and experimentally that maximum energy can be harvested by the EMSD when its internal impedance equals to the external electrical resistance of the electrical circuit. Minimum resonant vibration amplitude of the primary mass can be achieved at the same resistance ratio in the DVA system by selecting the suitable number of opposing magnet pairs of the EMSD without affecting the internal resistance. An EMSD with opposing magnet pairs configuration is designed and tested in a single-degree-of-freedom (SDOF) system and a dynamic vibration absorber. Following a proper procedure, the electromechanical transduction factor of the proposed EMSD can be tuned to achieve both objectives simultaneously. The harvested energy is higher when the EMSD is deployed in the SDOF system than in the DVA system, but the frequency bandwidth for energy harvesting is much wider in the DVA system. Analyses lead to a design guideline of the EMSD for achieving the bi-objective optimization.

A fabric-based multifunctional sensor for the early detection of skin decubitus ulcers

Monitoring biosignals at the skin interface is necessary to suppress the potential for decubitus ulcers in immobile patients confined to bed. We develop conformally contacted, disposable, and breathable fabric-based electronic devices to detect skin impedance, applied pressure, and temperature, simultaneously. Based on the experimental evaluation of the multifunctional sensors, a combination of robust AgNW electrodes, soft ionogel capacitive pressure sensor, and resistive temperature sensor on fabric provides alarmed the initiation of early-stage decubitus ulcers without signal distortion under the external stimulus. For clinical verification, an animal model is established with a pair of magnets to mimic a human decubitus ulcers model in murine in vivo. The evidence of pressure-induced ischemic injury is confirmed with the naked eye and histological and molecular biomarker analyses. Our multifunctional integrated sensor detects the critical time for early-stage decubitus ulcer, establishing a robust correlation with the biophysical parameters of skin ischemia and integrity, including temperature and impedance.

A non-traditional variant nonlinear energy sink for vibration suppression and energy harvesting

In this article, an apparatus is proposed for simultaneous vibration suppression and energy harvesting in a broad frequency band. Traditionally, both the spring and the damper of a vibration absorber are directly connected to a primary system. Alternatively, a non-traditional way is to place the damper of the vibration absorber between the absorber mass and the base. A nonlinear energy sink (NES) is a type of nonlinear vibration absorber with an essential nonlinearity. When a strong nonlinear oscillator with a small linear stiffness is weakly coupled to a primary system, it behaves similarly to the NES, which is termed “variant NES”. In the proposed apparatus, a variant NES is arranged in the non-traditional way in which a cantilever beam is placed between a pair of continuous-contact blocks which force the beam to deflect nonlinearly. An electromagnetic energy harvester, which also acts as a damper in the non-traditional variant NES, is formed by attaching a pair of permanent magnets to the free end of the beam and fixing a pair of coils to the base. The transient performances of the developed apparatus are investigated in terms of vibration suppression and energy harvesting using numerical simulation and compared with those of an optimum non-traditional vibration absorber. The simulation results are validated by an experimental study. It is found that the proposed non-traditional variant NES exhibits typical NES characteristics such as 1:1 resonance, targeted energy transfer (TET), and an initial energy threshold. With the prerequisite of TET being established under high-level initial energy, the best trade-off between vibration suppression and energy harvesting is achieved when the NES’s oscillation decays slowly under low electrical damping or quickly under high electrical damping.

Single harmonic-based narrowband magnetic particle imaging

Magnetic particle imaging (MPI) quantitatively visualizes in vivo superparamagnetic iron oxide nanoparticles (SPIONs), which has shown great promises in biomedicine. In this paper, we propose a single harmonic-based narrowband MPI approach via measuring a single harmonic—3f 0 harmonic—of the SPIONs induced in an excitation magnetic field with frequency f 0 = 5 kHz. The narrowband MPI scanner is built to scan the field-free-point, generated by a pair of permanent magnets, through an imaging field-of-view, and to measure the magnetic response of the SPIONs by a narrowband receive system. The narrowband MPI approach dramatically reduces the design efforts in the transmit system and noise matching in the receive system. Phantom experiments are performed with the custom-built narrowband MPI scanner to evaluate the spatial resolution and limit of detection (LOD). Experimental results indicate that the proposed single harmonic-based narrowband MPI approach allows a spatial resolution of 0.5 mm and an LOD of 27 μg (Fe) ml−1 (254 ng Fe weight) using Perimag® SPIONs, which can significantly be improved by using optimized SPIONs and by improving the detection circuitry. We believe that the proposed narrowband MPI approach minimizes the MPI hardware efforts but still allows for good performance in terms of spatial resolution and LOD.

Design and manufacturing of the combined quadrupole and corrector magnets for the LIPAc accelerator high energy beam transport line

The International Fusion Materials Irradiation Facility (IFMIF) is a project aiming to investigate candidate materials to be used in the most exposed zones of future fusion reactors. The linear IFMIF prototype accelerator (LIPAc), presently under commissioning in Rokkasho, Japan, is a prototype of the frontend section of one of the IFMIF accelerators. Eight quadrupole magnets, six pairs of corrector magnets and one dipole are responsible for generating the magnetic fields needed for a proper beam handling along the 10 m long LIPAc high energy beam transport line, which connects the end of the superconducting radio frequency Linac with the beam dump. A novel design of combined magnets with the correctors integrated in the quadrupole poles is chosen for compactness reasons. The different stages of the production of the combined magnets, from the magnetic and mechanical design to their manufacturing and testing, including exhaustive characterization of the magnetic performance are described in this work. The results from the tests revealed the quality of the magnetic field produced. The materials selection was done carefully, to withstand the high levels of ionizing radiation expected at the magnet locations. This paper focuses on the activities performed in Europe, before sending the magnets to Japan for their installation and commissioning at the Rokkasho site.

Magnetic array for efficient and stable Flow-electrode capacitive deionization

Magnetic flow-electrode capacitive deionization (FCDI) is a promising desalination technology; however, it still faces the risk of material stability and flow channel clogging during continuous operation. In this study, a new magnetic array design was introduced in the FCDI system to achieve efficient and stable desalination. Pairs of magnets were uniformly placed on the surface of the end plates along the flow channel to create alternating magnetic and magnetic field-free zones. Core-shell magnetic carbon (MC) was used as the conductive additive to guide the flow electrodes towards the magnet sides, thus creating a high concentration electrode area on the surface of the current collectors. When the flow electrode entered the magnetic field-free zones, the concentrated flow electrode returned to a homogeneous state. The results demonstrated that the desalination rate of FCDI with a low carbon content (1.0–2.0 wt%) increased by more than 120% after the application of a magnetic field. In the magnetic array, the working surface of the current collector significantly increased due to the aggregation effect of MC particles, which improved the electron transfer efficient and shortened the ion transport distance. In addition, the operational stability of FCDI in the magnetic field array was also demonstrated in a long-term operation. When the cell voltage was 1.2 V, the average salt removal rate (ASRR) and charge efficiency of FCDI were maintained at 0.35 μmol cm−2·min−1 and greater than 95%, respectively. In summary, magnetic array design offers the potential for FCDI to break through the trade-off between desalination performance and pumping energy consumption.

Propagation of Compressional Alfvén Waves in a Magnetized Pair Plasma Medium

The reductive perturbation approach was used to explore the nonlinear propagation of fast (compressive) and slow (rarefactive) electron–positron (EP) magnetoacoustic (EPMA) modes in an EP plasma medium. The solitary wave solution of the Korteweg-de Vries (K-dV) equation is used to identify the basic properties of EP compressional Alfvén waves. It is shown that the fast (slow) EPMA mode is predicted to propagate as compressive (rarefactive) solitary waves. The basic features (i.e., speed, amplitude, and width) of the compressive (i.e., fast) EPMA waves are found to be completely different from those of rarefactive (i.e., slow) EPMA ones. It is also examined that hump (dip) shape solitary waves are found for the fast (slow) mode. The significance of our findings is in understanding the nonlinear electromagnetic wave phenomena in laboratory plasma and space environments where EP plasma may exist.

Modeling and Design of Resonant Magnetic Field Sensors in the Scheme of Differential Magnetostrictive Actuation With Compact Bias Magnetic Circuit

A type of differential resonant magnetic field sensor is developed by employing the composite elements of FeGa plates, piezoelectric quartz crystal double-ended tuning forks (DETFs) and bias permanent magnets. The model and analysis show that the differential design brings the benefits of doubled sensitivity, increased linearity and low temperature drift. Importantly, a small and compact magnetic circuit containing a pair of permanent magnets and dual FeGa plates ensures the generation of differential actuation, which not only reduces the leakage flux but also improve the field-sensitivity and resolution. The magnetic circuit model based on the “lumped parameters” method is established. As an important aid, the distribution of magnetic flux density along the longitudinal direction of the FeGa alloy is simulated by finite element analysis software. In order to avoid the prediction error caused by parameter errors, simulations in different conditions are carried out for comparative analysis. This method ensures the magnetic circuit provides qualified magnetic field. The experimental results show that the differential resonant magnetic field sensor with frequency readout has the characteristics of high sensitivity of 4.4 Hz/Oe, high resolution of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${&lt; }3.04\times 10^{-4}$ </tex-math></inline-formula> Oe, low temperature drift and excellent linear (non-linearity error of 1.3%FS) and low hysteresis (1.5%FS) over its measurement full scale (FS) of ±100Oe.

Structural and electrical dynamics of a grating-patterned triboelectric energy harvester with stick–slip oscillation and magnetic bistability

The majority of research work on triboelectric energy harvesting is on material science, manufacturing and electric circuit design. There is a lack of in-depth research into structural dynamics which is crucial for power generation in triboelectric energy harvesting. In this paper, a novel triboelectric energy harvester with a compact structure working in sliding mode is developed, which is in the form of a casing and an oscillator inside. Unlike most sliding-mode harvesters using single-unit films, the proposed harvester utilizes grating-patterned films which are much more efficient. A bistable mechanism consisting of two pairs of magnets is employed for broadening the frequency bandwidth. A theoretical model is established for the harvester, which couples the structural dynamics domain and electrical dynamics domain. This paper presents the first study about the nonlinear structural dynamics of a triboelectric energy harvester with grating-patterned films, which is also the first triboelectric energy harvester integrating grating-patterned films with a bistable magnetic system for power performance enhancement. Theoretical studies are carried out from the perspectives of both structural and electrical dynamics. Surface charge density and segment configuration of the films affect whether the electrostatic force influences the structural dynamics, which can be neglected under a low surface charge density. Differences in structural response and electrical output are found between a velocity-dependent model and Coulomb’s model for modelling the friction in the triboelectric energy harvesting system. The bistable mechanism can effectively improve the output voltage under low-frequency excitations. Additionally, the output voltage can also be obviously enhanced through increasing the number of the hollowed-out units of the grating-patterned films, which also results in a slight decrease in the optimal load resistance of the harvester. These findings enable innovative designs for triboelectric energy harvesters and provide fabrication guidelines in practical applications.

Fabrication and testing of a Hall effect based pressure sensor

PurposeThis paper aims to present the fabrication and testing of a pressure sensor integrated with Hall effect sensors and permanent magnets arranged in two configurations to measure pressure in the range of 0–1 bar. The sensor is fabricated using stainless steel (SS) and can be used in high-temperature and highly corrosive environments. The fabricated sensor is of low cost, self-packaged and the differential arrangement helps in compensating for any ambient temperature variations.Design/methodology/approachThe sensor deflects of a circular diaphragm with a simple rigid mechanical structure to convert the applied pressure to a Hall voltage output. Two sensor designs are proposed with a single pair of Hall sensors and magnets and a differential configuration with two Hall sensors and magnets. Two sensor designs are designed, fabricated and tested for their input–output characteristics and the results are compared.FindingsThe fabricated sensors are calibrated for 25 cycles of ascending and descending pressure in steps of 0.1 bar. Various static characteristics like nonlinearity, hysteresis and % error are estimated for both the sensor designs and compared with the existing Hall effect based pressure sensors. The differential arrangement design was found to have better characteristics as compared to the other design from the experimental data.Originality/valueThis paper focuses on fabricating and testing a novel differential Hall effect based pressure sensor. The differential arrangement of the sensor aids in the compensation of ambient temperature variations and the use of SS enables the sensor in high-temperature and highly corrosive applications. The proposed sensor is low cost, simple and self-packaged, and found to have high repeatability and good linearity compared to other similar Hall effect based pressure sensors available in the literature.

Real-space visualization of short-range antiferromagnetic correlations in a magnetically enhanced thermoelectric

Short-range magnetic correlations can significantly increase the thermopower of magnetic semiconductors, representing a noteworthy development in the decades-long effort to develop high-performance thermoelectric materials. Here, we reveal the nature of the thermopower-enhancing magnetic correlations in the antiferromagnetic semiconductor MnTe. Using magnetic pair distribution function analysis of neutron scattering data, we obtain a detailed, real-space view of robust, nanometer-scale, antiferromagnetic correlations that persist into the paramagnetic phase above the N\'eel temperature $T_{\mathrm{N}}$ = 307 K. The magnetic correlation length in the paramagnetic state is significantly longer along the crystallographic $c$ axis than within the $ab$ plane, pointing to anisotropic magnetic interactions. Ab initio calculations of the spin-spin correlations using density functional theory in the disordered local moment approach reproduce this result with quantitative accuracy. These findings constitute the first real-space picture of short-range spin correlations in a magnetically enhanced thermoelectric and inform future efforts to optimize thermoelectric performance by magnetic means.

Simulations of novel compact separator for extracting specific reactive ions from large plasma source

A new remote dry processing with a focusing and deflection system is proposed to accurately control the energy, flux, and arrival position of reactive particle species on the nanoscale. The trajectory simulations of the negative ion extraction and transport for designing a compact separator based on the concept are performed using the SIMION software. In the compact separator, the ion beam extracted from a plasma source can be deflected in two stages through two pairs of magnets by selecting only specific ions so that it can be laterally drawn out. It is shown from the results of the simulation that the ion beams with good focusing properties, high directivity, and a sufficient current amount can be successfully extracted from the plasma source and transported to the reactor vessel through the focusing and deflection system.

Orbital-Selective High-Temperature Cooper Pairing Developed in the Two-Dimensional Limit.

For multiband superconductors, the orbital multiplicity yields orbital differentiation in normal-state properties and can lead to orbital-selective spin-fluctuation Cooper pairing. The orbital-selective phenomenon has become increasingly pivotal in clarifying the pairing "enigma", particularly for multiband high-temperature superconductors. Meanwhile, in one-unit-cell (1-UC) FeSe/SrTiO3, since the standard electron-hole Fermi pocket nesting scenario is inapplicable, the actual pairing mechanism is subject to intense debate. Here, by measuring high-resolution Bogoliubov quasiparticle interference, we report observations of highly anisotropic magnetic Cooper pairing in 1-UC FeSe. Theoretically, it is important to incorporate orbitally selective effects of electronic correlations within a spin-fluctuation pairing calculation, where the dxy orbital becomes coherence-suppressed. The resulting pairing gap is compatible with the experimental findings, which suggests that high-Tc Cooper pairing with orbital selectivity applies to 2D-limit 1-UC FeSe. Our findings imply the general existence of orbital selectivity in iron-based superconductors and the universal significance of electron correlations in high-Tc superconductors.

Analysis of Linear Machine by Parameter Study using Equivalent Magnetic Circuit and FEA

This study proposes an analytical approach by optimum process that is generalized by number of phases, magnet, and pole-pair of linear machines based on a physical magnetic circuit model. The linear machine increases the force output of the machine due to generation of the magnetic field created by the armature winding. There is a strong attractive force between the iron-core armature and the permanent magnet. Therefore, this paper deals not only with one-phase systems by the number of magnet and pole pairs but also two-phase machines in linear machines. All this is carried out for optimum process using geometric parameters based on analytical electromagnetic field research. The best structure for optimum design is selected by a parameter study and it is accomplished with 2-D finite element analysis. The object function and design variables for this parameter study by constraints are chosen for practical and effective design of the machine. Eventually, it suggests new design rules based on optimal design through parameter study. The proposed methods allow us to draw a very important design rule, as a result it can be provided to less time of the machine design and analysis.

Design and experimental study of a piezoelectric energy harvester embedded in a rotating spindle excited by magnetic force

A piezoelectric energy harvester based on rotational motion is a promising technique to generate unlimited electrical energy. However, the necessity for an effective harvester that can be mounted on a rotating system has become an important issue as a support for self-powered wireless sensor systems. The purpose of this study is to develop a novel magnetically impelled piezoelectric rotating energy harvester integrated into a rotating spindle, which is excited by multiple magnetic pairs between symmetrically opposed stationary and spinning magnets on the surface of piezoelectric discs. The theoretical examination of the magnetic excitation on a harvester system is provided to determine magnetic the force and torque, while the voltage and power generation capability of a magnetically impelled piezoelectric rotational energy harvester under various series and parallel configurations, and spindle speed excitations were examined experimentally. The experimental results are in line with the analytical model of magnetic force, which showed that the resistance torque can be decreased significantly. A maximum instantaneous output voltage of -15–19 V and 7.5–8 V was achieved at series and parallel connection respectively. The maximum power can be obtained at parallel connection and the RMS and peak power are 870 µW and 3500 µW, respectively and a high power density of 9.67 µW/mm3. The harvester can also charge the capacitors with voltage and power saturation of 6 V and 327 µW respectively. These results showed that the suggested harvester has high durability and the potential to power wireless sensors that are integrated into spindle machines.

Investigation on the characteristics of a novel internal resonance galloping oscillator for concurrent aeroelastic and base vibratory energy harvesting

Harnessing energy from concurrent wind flow and base vibration is a prospective method to enable self-powered sensing in the circumstances where wind and base motion are coexisting, like aircrafts, bridges, railways and ocean buoys. This paper proposes a novel two-degree-of-freedom galloping energy harvester with 2:1 internal resonance for efficient dual-source energy harvesting. The harvester consists of a primary and a secondary beam with a square-sectioned bluff body attached to the free end and two pairs of magnets repulsively arranged at the beam joint. Careful tuning of the magnetic force with a quadratic nonlinear stiffness term triggers the internal resonance, leading to a remarkably superior performance compared to its linear counterpart. A fully coupled aero-electro-mechanical distributed parameter model is established based on Euler-Bernoulli beam theory and quasi-steady aerodynamic hypothesis. Explicit analytical solution for steady-stage mechanical and electrical responses is derived using harmonic balance method and validated by numerical simulation. At the wind speed of 3 m/s and base acceleration of 0.9 m/s2, the conceptual prototype achieves a 211.1% increase in the effective bandwidth and a 50% increase in the peak voltage around the first resonance. The results provide a theoretical guideline to improve the system capacity of dual-source energy harvesting.

Spin-lattice couplings in two-dimensional CrI3 from first-principles computations

Since thermal fluctuations become more important as dimensions shrink, it is expected that low-dimensional magnets are more sensitive to lattice distortions and phonons than bulk systems are. Here we present a fully relativistic first-principles study on the spin-lattice coupling, i.e. how the magnetic interactions depend on local lattice distortions, of the prototypical two-dimensional ferromagnet CrI$_3$. We extract an effective measure of the spin-lattice coupling in CrI$_3$ which is up to ten times larger than what is found for bcc Fe. The magnetic exchange interactions, including Heisenberg and relativistic Dzyaloshinskii-Moriya interactions, are sensitive both to the in-plane motion of Cr atoms and out-of-plane motion of ligand atoms. We find that significant magnetic pair interactions change sign from ferromagnetic (FM) to anti-ferromagnetic (AFM) for atomic displacements larger than 0.16 {\AA}. We explain the observed strong spin-lattice coupling by analyzing the orbital decomposition of isotropic exchange interactions, involving different crystal-field-split Cr$-3d$ orbitals. The competition between the AFM t$_{2g}$ - t$_{2g}$ and FM t$_{2g}$ - e$_{g}$ contributions depends on the bond angle formed by Cr and I atoms as well as Cr-Cr distance. In particular, if a Cr atom is displaced, the FM-AFM sign change when the I-Cr-I bond angle approaches 90$^\circ$. The obtained spin-lattice coupling constants, along with the microscopic orbital analysis can act as a guiding principle for further studies of the thermodynamic properties and combined magnon-phonon excitations in two-dimensional magnets.

Externally driven plasma models as candidates for pulsar radio emission

ABSTRACT Coherent radio emission from pulsars originates from excited plasma waves in an ultra-relativistic and strongly magnetized electron–positron pair plasma streaming along the open magnetic field lines of the pulsar. Traditional coherent radio emission models have relied on instabilities in this pair plasma. Recently, alternative models have been suggested. These models appeal to direct coupling of the external electromagnetic field to the superluminal O-mode (lt2 mode) during the time-dependent pair cascade process at the polar gap. The objective of this work is to provide generic constraints on plasma models based on lt2 mode using realistic pulsar parameters. We find that the very short time-scale associated with pair cascades does not allow lt2 mode to be excited at radio frequencies and the impulsive energy transfer can only increase the kinetic spread (‘temperature’) of the pair plasma particles. Moreover, under homogeneous plasma conditions, plasma waves on both branches of O mode (i.e. superluminal lt2 and subluminal lt1) cannot escape the plasma. In the strongly magnetized pair plasma, only the extraordinary mode (t mode) can escape freely. We show that any generic fictitious mechanisms do not result in the wave electric field of t mode to have predominant orientation either parallel or perpendicular to the magnetic field plane as observed. Such fictitious mechanisms will inevitably lead to depolarization of signals and cannot account for the highly polarized single pulses observed in pulsars. We suggest coherent curvature radiation as a promising candidate for pulsar radio emission mechanism.

Snap-through triboelectric nanogenerator with magnetic coupling buckled bistable mechanism for harvesting rotational energy

We propose a snap-through triboelectric nanogenerator with magnetic coupling and buckled bistable mechanism to harvest rotational energy (ST-RTENG). The buckled bistable beam generates convex and concave snap-through under magnetic excitation, which can significantly increase the contact force of the functional materials of triboelectric nanogenerator (TENG), thereby significantly improving the electrical output. By adopting a magnetic coupling non-contact energy transfer mechanism, the drive part and the electromechanical conversion part are easily physically separated, which improves the robustness of the system in the harsh environment. The electromechanical coupling dynamic model of the system is established and verified by experiments. The different modes and key parameters of the magnet arrangement are investigated. The ST-RTENG with two pairs of magnets with staggered poles has a maximum voltage of 1235 V at a rotating speed of 150 r/min and a maximum average power of 778 μW at a rotating speed of 800 r/min. The prototype can light up more than 1000 LEDs under low speed excitation, and realize self-powered temperature monitoring and wireless transmission. The rotational energy harvester with magnetic coupling buckled bistable mechanism proposed in this paper can be used for wind energy harvesting in the field environment, self-powered state monitoring of the pressure pipelines, and other applications that require isolation of external excitation and electromechanical conversion components.