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Surface acoustic wave resonators are widely applied in electronics, communication, and other engineering fields. However, the spurious modes generally present in resonators can cause deterioration in device performance. Therefore, this paper proposes a hexagonal weighted structure to suppress them. With the construction of a finite element resonator model, the parameters of the interdigital transducer (IDT) and the area of the dummy finger weighting are determined. The spurious waves are confined within the dummy finger area, whereas the main mode is less affected by this structure. To verify the suppression effect of the simulation, resonators with conventional and hexagonal weighted structures are fabricated using the micro-electromechanical systems (MEMS) process. After the S-parameter test of the prepared resonators, the hexagonal weighted resonators achieve a high level of spurious mode suppression. Their properties are superior to those of the conventional structure, with a higher Q value (10,406), a higher minimum return loss (25.7 dB), and a lower ratio of peak sidelobe (19%). This work provides a feasible solution for the design of SAW resonators to suppress spurious modes. [ABSTRACT FROM AUTHOR]

A separate-stator modular machine with biased flux is proposed in this paper. In this machine, the windings and the permanent magnets are located in two separate parts of the stator, which favors the heat dissipation and magnetic saturation reduction of the machine. With the specially designed stator structure, a biased flux can be introduced to flexibly regulate the excitation field by injecting a zero-sequence current into the phase windings, so that a wide operation speed range can be achieved. Moreover, a modular structure is adopted to simplify the automated manufacture assembly. In this paper, the machine configuration and the working principle are first illustrated. The effect of the design parameters on its torque capability is then investigated. A coupled electromagnetic-thermal optimization method based on the genetic algorithm and finite-element method is proposed to improve the torque performance of the machine. [ABSTRACT FROM AUTHOR]

In this paper, a new permanent magnet (PM) linear motor is proposed. This motor has a special structure with complementary stator flux, which helps to reduce the flux leakage and improve the utilization of the PM. The PMs are installed in a leaning manner, which increases the effective area of the PMs and enhances the field excitation. Hence, the force density of the motor can be improved and it will be, especially suitable for applications within a limited space. The motor structure and working principle are first explained. The design of the motor is then comprehensively investigated. An electromagnetic optimization method based on tabu search algorithm and finite-element method is proposed for the motor to improve its force density. [ABSTRACT FROM AUTHOR]

This paper presents a shoe-sole-embedded power harvester which can extract power from walking to charge portable or mobile electronic devices. The core component of the design is a combination of a trans-rotary magnetic gear (TRMG) and a disk-type axial-flux permanent magnet (AFPM) generator. The key idea is to convert linear foot motion into rotation using the TRMG, so that the AFPM can be driven to generate electric power. The proposed energy harvester has a high power density due to its electromagnetic nature. Moreover, by integrating a TRMG, it eliminates the mechanical problems caused by the conventional transmission mechanisms, which also makes it compact in size. Besides introducing its structure and working principle, the design procedure is presented and its performance is analyzed using the finite-element method. [ABSTRACT FROM PUBLISHER]

A novel gearless and brushless power-split transmission system is proposed for a variable speed constant frequency wind power generation application. The key is to design a special hybrid axial–radial flux focusing structure, which has an improved utilization of permanent magnet (PM) materials. This design integrates the merits of two popular concepts—the direct-drive PM generator and the doubly fed induction generator. It is direct driven, with high torque density and in the meanwhile, it needs only a partial-scale converter. To improve the stability of the system, five phase currents are used for the control winding. A time stepping finite-element method is used to analyze the dynamic performance of the proposed system. [ABSTRACT FROM AUTHOR]

This paper presents a novel gearless and brushless power split transmission system for variable-speed constant-frequency wind power generation application. The core element of this system is a novel axial-flux doubly fed dual-rotor permanent magnet machine. The key of the design is to utilize the flux modulation principle to modulate the magnetic flux in an axial-flux machine and use doubly fed stator winding to control the rotor rotation. This design combines the merits of direct-drive machines and doubly fed generators. As the mechanical problems related to brushes, slip rings, and gear boxes are successfully overcome, the operational reliability of the system is improved. The stator winding of the proposed system can be directly connected to the power grid, and the power rating of its associated frequency converter is reduced. Time-stepping finite-element method is used to analyze the dynamic performance of the proposed system. [ABSTRACT FROM AUTHOR]

Compared with mechanical gears, a magnetic gear (MG) has many merits by virtue of its contactless feature, high efficiency and inherent overload protection. In this paper, a novel MG with intersecting shaft axes based on the flux modulation effect is proposed. Compared with previous MGs, the transmission direction of the novel MG can be designed very flexibly and it also has good competitive edge in relation to the use of permanent magnets, which enables it to have a relatively high-torque density. The working principle and performance are validated by an example design using finite element method. The effects of the dimensional parameters on the torque performance are analyzed. It is also verified that the torque density can be further improved by adopting a flux concentration configuration in its rotor design. It is concluded from the torque per unit volume density performance that the novel MG is very promising as a substitute to conventional gears. [ABSTRACT FROM AUTHOR]

Coal macrolithotypes control the heterogeneity of coal physical properties in coalbed methane (CBM) reservoirs and have a significant effect on the success of hydraulic fracturing stimulation. However, only a few studies have focused on this heterogeneity, and the propagation mechanism of hydraulic fractures related to the coal macrolithotype is not well understood. In this study, we considered the Hancheng area, Ordos Basin, China, as an example to understand macrolithotype differences, establish finite element numerical models of the cohesive zone, and evaluated the hydraulic fracture initiation and vertical propagation behavior of laminated coal reservoirs. We used physical experiments, such as direct shear test and Digital Image Correlation (DIC), along with finite element simulation and a finite element model; the results show that the tensile strength of bright coal is the lowest and that of dull coal is the greatest; the average cohesion and shear strength of the bright-dull coal interface are 0.418 MPa and 1.3778 MPa (σ = 3 MPa), respectively. Notably, behavioral differences are likely to impact the geometric evolution of hydraulic fractures. In the numerical models of hydraulic fracturing for a laminated coal reservoir, the hydraulic fracture propagates predominantly vertically as the interlayer has a lower elastic modulus and higher tensile strength. Because the interfacial shear strength is weak, the fractures can easily penetrate and propagate into the bedded interface between layers, and often, the distance of lateral slip increases into the interlayer interface. Thus, when dull coal is fractured, the geometry of the hydraulic fracture is often characterized as an isolated fracture distribution. The fracture then, rapidly propagates into the interlayer, activating the natural fractures in the bright coal reservoir, thus improving the fracture scale in the interlayers (model 2). However, as bright coal is a productive strata, the geometry of the hydraulic fracture is also dominated by crisscross network structures, and the fractures preferentially propagate along the interface (model 1). • The differences of mechanical properties that linked to the macrolithotype contribution were investigated systematically. •The impact of these sensitivity factors on hydraulic fracture geometry evolution was evaluated. •The influences of coal macrolithotype on hydraulic fracture geometry evolution were investigated. [ABSTRACT FROM AUTHOR]

In this paper, a permanent magnet (PM) linear memory machine is proposed for ocean wave power generation. A notable feature of this machine is its online tunable mnemonic flux. This enables it to operate efficiently in a wide speed range and makes it suitable for the variable-speed wave-power generation. Moreover, this machine has both the PMs and the windings arranged in its stator so that it does not need slip rings or brushes. The proposed machine is also robust and cost-effective because it has a simple translator of slotted steel. In this paper, the configuration and working principle of the linear memory machine are firstly introduced. The results of a parametric analysis are presented to investigate the effects of the proposed machine's geometric parameters. The performance of the proposed machine is then analyzed using time-stepping finite element method (TS-FEM). [ABSTRACT FROM AUTHOR]

With the continuous development of machines, various structures emerge endlessly. In this paper, a novel 6-stator-coils/17-rotor-teeth (6/17) E-shaped stator tooth flux switching permanent magnet (FSPM) machine is introduced, which has magnets added in the dummy slots of the stator teeth. This proposed machine is parametrically designed and then compared with the conventional 6/17 E-shaped stator tooth FSPM machine through finite element method (FEM) analysis. Then, combined with the results of FEM, the performance of two machines is evaluated, such as electromagnetic torque, efficiency, back electromotive force (back-EMF). The final results show that this novel 6/17 FSPM machine has greater output torque and smaller torque ripple. [ABSTRACT FROM AUTHOR]