Enhanced Sensitivity of FeGa Thin-Film Coated SAW Current Sensor

A surface acoustic wave (SAW) device is proposed for sensing current by employing the patterned FeGa thin film as the sensitive interface. The layered media structure of FeGa/SiO2/LiNbO3 was established to reveal the working principle of the sensors, and an SAW chip patterned by delay-line and operating at 150 MHz was fabricated photolithographically on 128° YX LiNbO3 substrate. The FeGa thin film with a larger magnetostrictive coefficient was sputtered onto the acoustic propagation path of the SAW chip to build the sensing device. The prepared device was connected into the differential oscillation loop to construct the current sensor. The FeGa thin film produces magnetostrictive strain and so-called ΔE effect at the magnetic field generated by the applied current, which modulates the SAW propagation velocity accordingly. The differential frequency signal was collected to characterize the measurand. Larger sensitivity of 37.9 kHz/A, low hysteresis error of 0.81%, excellent repeatability and stability were achieved in the experiments from the developed sensing device.

The emergence of high room temperature in-plane and out-of-plane magnetostriction in polycrystalline CoFe2O4 film

The polycrystalline CoFe2O4 (CFO) film on cantilever substrate of silicon was grown using pulsed laser deposition (PLD) method and investigated its in-plane and out-of-plane magnetostrictive strain at room temperature (300 K) using the indigenous optical Cantilever Beam Magnetometer (CBM). The film shows a high compressive magnetostrictive strain of ‒ 387 ppm and ‒ 708 ppm for in-plane and out-of-plane configurations, respectively. Considerably, the magnetostrictive strain loops (λ‒H) possess a certain degree of hysteresis with a symmetric butterfly shape. The origin of large compressive magnetostriction of CFO film is attributed to the non-180° domain wall motion followed by 90° domain rotation. The large values of saturation magnetostrictive strain make CFO film a suitable candidate in sensor design for different purposes.

The Study of Magnetoimpedance Effect for Magnetoelectric Laminate Composites with Different Magnetostrictive Layers

The rectangular magnetoelectric (ME) composites of Metglas/PZT and Terfenol-D/PZT are prepared, and the effects of a magnetostrictive layer’s material characteristics on the magnetoimpedance of ME composite are discussed and experimentally investigated. The theoretical analyses show that the impedance is not only dependent on Young’s modulus and the magnetostrictive strain of magnetostrictive material but is also influenced by its relative permeability. Compared with Terfenol-D, Metglas possesses significantly higher magnetic permeability and larger magnetostrictive strain at quite low Hdc due to the small saturation field, resulting in the larger magnetoimpedance ratio. The experimental results demonstrate that the maximum magnetoimpedance ratios (i.e., ΔZ/Z) of Metglas/PZT composite are about 605.24% and 239.98% at the antiresonance and resonance, respectively. Specifically, the maximum ΔZ/Z of Metglas/PZT is 8.6 times as high as that of Terfenol-D/PZT at the antiresonance. Such results provide the fundamental guidance in the design and fabrication of novel multifunction devices based on the magnetoimpedance effect of ME composites.

Computational Design of Microstructures With Stochastic Property Closures

The present work addresses a stochastic computational solution to define the property closures of polycrystalline materials under uncertainty. The uncertainty in material systems arises from the natural stochasticity of the microstructures as a result of the fluctuations in deformation processes. The microstructural uncertainty impacts the performance of engineering components by causing unanticipated anisotropy in properties. We utilize an analytical uncertainty quantification algorithm to describe the microstructural stochasticity and model its propagation on the volume-averaged material properties. The stochastic solution will be integrated into linear programming to generate the property closure that shows all possible values of the volume-averaged material properties under the uncertainty. We demonstrate example applications for stiffness parameters of α-Titanium, and multi-physics parameters (stiffness, yield strength, magnetostrictive strain) of Galfenol. Significant differences observed between stochastic and deterministic closures imply the importance of considering the microstructural uncertainty when modeling and designing materials.

Characteristic investigation of a magnetostrictive fast switching valve for digital hydraulic converter

In order to adapt the frequency requirements of fast switching valve applied to the digital hydraulic converter, a 2/2 way fast switching valve driven by giant magnetostrictive material was performed in this article. The finite element simulation of the fast switching valve’s electromagnetic field and flow field was carried out. In addition, the integrated analytical model of giant magnetostrictive material–fast switching valve coupling with enhanced transmission line method was built in MATLAB/Simulink. The displacement and pressure-flowrate characteristics of giant magnetostrictive material–fast switching valve were discussed and validated in the experiments. The results indicated that the nonlinearity magnetization presents a positive relationship with the driving current before it reaches the saturated state, and the hydraulic force at the expected opening is far less than output force caused by magnetostrictive strain. The experimental valve displacements are in good agreement with obtained results from analytical model, which reveals that the analytical model is accurate enough to predict the main performances of the fast switching valve. The maximum valve displacement without supply pressure is up to 68 µm, which attenuates moderately with the growth of supply pressure. The experimental responses of the displacement and the pressure of giant magnetostrictive material–fast switching valve are less than 1 ms. The amplitude of output flowrate is 8.1 L/min at the frequency of 100 Hz when the pressure drop across giant magnetostrictive material–fast switching valve is 6 MPa theoretically. Similarly, the maximum transient flowrate derived from experiments reaches 8.2 L/min at pressure drop across giant magnetostrictive material–fast switching valve of 5.9 MPa, which is basically consistent with that predicted by analytical model. These reveal that the giant magnetostrictive material–fast switching valve can be utilized in the digital hydraulic converter to improve the system’s efficiency.

A concise and accurate model for the magnetomechanical effect

Stress concentration and microscopic defects inside a component can cause the failure of equipment and mechanical structures, and traditional non-destructive testing (NDT) methods are not able to completely solve this problem. The magnetomechanical effect organically combines the magnetic field and stress, making it an important approach for detecting stress concentration and microscopic defects in a component. The magnetomechanical model proposed by Jiles can explain the non-linear relationship between stress and magnetic induction, but it fails to explain the asymmetry in the change of magnetisation under the conditions of tensile and compressive stress. A general nonlinear magnetomechanical model proposed by Shi can more precisely explain the magnetomechanical effect, but with complex equations. Using a more precise equation for magnetostrictive strain and taking into account the effects of the demagnetising field and a linear stress-dependent term on the magnetomechanical effect, this paper proposes a concise and accurate model based on the merits of the two methods. This theoretical model can demonstrate the magnetomechanical effect more accurately than Jiles' model and is easier to solve and apply than Shi's model. This model offers the possibility of quantitative measurement of stress concentration by magnetic measurements.

Computational Design of Microstructures With Stochastic Property Closures

The present work addresses a stochastic computational solution to define the property closures of polycrystalline materials under uncertainty. The uncertainty in material systems arises from the natural stochasticity of the microstructures and the variations in deformation processes, and impacts the performance of engineering components by causing unanticipated anisotropy in properties. We utilize an analytical uncertainty quantification algorithm to describe the microstructural stochasticity and model its propagation to the volume-averaged material properties. The stochastic solution will be integrated into linear programming to generate the property closure that shows all possible values of the volume-averaged material properties under the uncertainty. We demonstrate example applications for stiffness parameters of a-Titanium, and multi-physics parameters (stiffness, yield strength, magnetostrictive strain) of Galfenol. Significant differences observed between stochastic and deterministic closures imply the importance of considering the microstructural uncertainty when modeling and designing materials.