Terfenol-D Rod Research Articles

High sensitivity fiber optic current sensor based on Fabry–Perot interferometer manufactured by femtosecond laser

Abstract A novel fiber optic current sensor was prepared based on femtosecond laser processing technology and magnetostrictive material Terfenol-D. Its principle is to use the linear stretching of Terfenol-D material under the action of current to cause linear shift in the sensor spectrum. Firstly, we fabricated Fabry–Perot interferometer (FPI1) using femtosecond laser in a tapered few mode fiber. Then, FPI2 was prepared using the end face of FPI1, quartz capillary, and single-mode fiber. When cascading FPI1 and FPI2, by adjusting the air-cavity length of FPI2, they form a harmonic vernier effect (HVE) sensor. In HVE sensors, FPI1 forms a cantilever beam inside the capillary, which is not affected by axial strain. Therefore, when the axial strain acts on the HVE sensor, the effective length of axial strain increases to the entire length of the quartz capillary, greatly amplifying the strain sensitivity. Finally, the Terfenol-D rod is pasted onto the HVE strain sensor, and the strain change coupled to the strain sensor caused by magnetic field changes is detected by measuring the wavelength shift of the sensor. As the magnetic field strength is directly proportional to the current in the energized coil, this sensor can measure current. The experiment found that the current sensitivity of the sensor is 5.30 nm A−1 in the range of 0.5 A–3.3 A, and the linear fitting coefficient is 0.9926. Additionally, the minimum measurable current change of the sensor is 23 mA. The current sensor is of advantages of high sensitivity, stable sensing performance, compact structure, easy fabrication and low cost, meaning wide application prospect.

Dual-parameter fiber sensor based on Fabry-Pérot cavity cascaded with Terfenol-D rod integrated fiber Bragg grating

A kind of dual-parameter fiber sensor based on the Terfenol-D rod combined with the cascaded Fabry-Pérot interferometer-fiber Bragg grating (FPI-FBG) structure is demonstrated, which integrates the FBG with the Fabry-Pérot cavity made by fiber and polydimethylsiloxane (PDMS). The problem of temperature cross-sensitivity in magnetic field measurement is simply and ingeniously avoided. The experimental results show that the sensing system's temperature and magnetic field sensitivities are 121.56 pm/°C and 21.6 pm/mT, respectively. By using the dual-parameter matrix, the resolutions of temperature and magnetic field measurement are obtained to be 1.003 °C and 0.069 mT, respectively.

Magneto-mechanical-thermal coupling tunability of the topological interface state of longitudinal waves in magnetostrictive phononic crystal beams

Topological phononic crystals (PCs) have attracted increasing attention owing to their elastic wave topological transmission with high robustness, backscattering suppression, and defect immunity. However, the effective regulation of the topological interface state of elastic waves in multi-field environments remains a challenge, particularly in the magneto-mechanical-thermal coupling field. In this study, a magnetostrictive PC beam composed of Terfenol-D and aluminum rods was designed to dynamically manipulate the topological interface state of longitudinal waves when the system was subjected to magnetic, mechanical, and thermal loadings. First, the Zak phase transition of the band gap was induced by simply controlling the magnetic field distribution of a unit cell based on the nonlinear magneto-mechanical-thermal coupling constitutive characteristics of magnetostrictive materials. The frequency of the Zak point was also significantly affected by pre-stress and temperature. Subsequently, the controllable topological interface state of the longitudinal wave was successfully observed at the interface of magnetostrictive PC beams in a multi-field environment without altering the structure. The results showed that the frequency and location of the topological interface state could be dynamically tuned by magnetic, stress, and thermal loadings. The robustness of the topological interface state was also investigated. Finally, the magneto-mechanical-thermal coupling tunability of longitudinal-wave topological transport was experimentally verified for the proposed magnetostrictive PC systems. This study provides an effective method for the active modulation of elastic wave topological transmission and the development of novel tunable topological devices.

Packaged magnetic sensor based on a saddle-shape Whispering Gallery Mode microresonator

Incorporating optical Whispering Gallery Mode (WGM) microresonators in real life sensing applications is of great interest due to their tiny volumes and very high quality factors. Taper-fiber coupled microresonators, in particular, suggest high simplicity, low cost, and wide range of achievable coupling regimes. Here we apply a unique packaging method based on a tapered fiber-coupled saddle-shape microresonator (SSM), providing high mechanical stability while preserving the quality (Q) factor of the microresonator. The ability to tune the SSM's WGMs mechanically is harnessed here to detect the elongation of a magnetostrictive Terfenol-D (Ter-D) rod, and therefore to measure variations in the ambient magnetic field. As we demonstrate here, this packaging technique enables the production of tightly packaged WGM-based devices. The simplicity in manufacturing SSMs, their high Q factors, the ability to tune their WGMs mechanically/magnetically, and the high mechanical stability they provide, make them great candidates as a platform for practical miniature WGM-devices.

Energy harvesting using linear type magnetostrictive transducer for real-time application

Economic and social development of nations across the globe is demanding enormous need for energy and power resources. Energy production using safe and renewable sources can aid in mitigating the release of greenhouse gases and avoiding the devastating climate changes. In the present case, a linear type magnetostrictive transducer device is designed by employing Terfenol-D magnetostrictive rods for renewable energy harvesting application. A linear device was designed with two Terfenol-D rods, three permanent magnets (neodymium magnets), springs, and primary and secondary coils. Terfenol-D rod crystallizes in cubic Laves phase and exhibits the saturation magnetostriction value of 1242 × 10−6 at the field of 2.5 kOe. An equivalent circuit is constructed for the induced magnetic flux in the designed transducer device. Frequency and wave form dependent output voltage is examined in the designed energy harvesting device. A square wave at the applied frequency of 2200 Hz (100 mA current) produces a maximum output voltage of 4.91 V. Sine and triangle waves produce 3.38 and 2.82 V, respectively, at 1700 and 1600 Hz. The induced voltage is sufficient to ignite the light emitting diode. A linear type magnetostrictive transducer can be employed as a potential renewable energy source for real-time application with moderate output voltage.

Dynamic Characteristic Model of Giant Magnetostrictive Transducer with Double Terfenol-D Rods.

Giant magnetostrictive transducer can be widely used in active vibration control, micro-positioning mechanism, energy harvesting system, and ultrasonic machining. Hysteresis and coupling effects are present in transducer behavior. The accurate prediction of output characteristics is critical for a transducer. A dynamic characteristic model of a transducer is proposed, by providing a modeling methodology capable of characterizing the nonlinearities. To attain this objective, the output displacement, acceleration, and force are discussed, the effects of operating conditions on the performance of Terfenol-D are studied, and a magneto-mechanical model for the behavior of transducer is proposed. A prototype of the transducer is fabricated and tested to verify the proposed model. The output displacement, acceleration, and force have been theoretically and experimentally studied at different working conditions. The results show that, the displacement amplitude, acceleration amplitude, and force amplitude are about 49 μm, 1943 m/s2, and 20 N. The error between the model and experimental results are 3 μm, 57 m/s2, and 0.2 N. Calculation results and experimental results show a good agreement.

Magnetic circuit optimization design and thermal analysis of the giant magnetostrictive transducer

A giant magnetostrictive transducer was studied. The dynamic simulation analysis of the transducer was carried out, the influence of the magnetic block and the magnetic cylinder on the vibration performance of the transducer was studied, and the temperature rise of the transducer during the operation was simulated and calculated. The impedance and output amplitude of the developed transducer were tested experimentally. The results show that the axial magnetic field intensity of the Terfenol-D rod increased and then decreased, and the output amplitude increased and then decreased slightly with the increase of the thickness of the magnetic cylinder. As the thickness of the magnetic block increased, the axial magnetic field intensity of the rod increased, and the output amplitude of the transducer also increased. Compared with the transducer without magnetic cylinder, the transducer with magnetic cylinder has larger electromechanical conversion coefficient, and output amplitude, but the temperature was higher after working for the same time.

Study on high frequency magnetic energy loss of Terfenol-D rods with different structures

For the efficient application of Terfenol-D rod, six kinds of rods were studied. Finite element software was used to simulate and calculate the hysteresis loss, eddy current loss, coil resistance, and inductance of the rods at different frequencies and currents. Three kinds of rods were manufactured, the coil resistance and inductance were measured. The results showed that the hysteresis loss, eddy current loss, and coil resistance increased, and the coil inductance decreased with the increase of frequency. As the current increased, the hysteresis and eddy current losses of the rods increased, the coil resistance and inductance remain unchanged; the hysteresis loss, eddy current loss and coil resistance of the radially slit rod were the largest, whereas that of the slit rods were larger than those of the sliced rods, the coil inductance of the slit rods was less than that of the sliced rods. The numerical calculation values of coil resistance and inductance at different frequencies and currents basically agreed with the experimental test values.

Thermal Analysis of Terfenol-D Rods with Different Structures.

To reduce the heating of the Terfenol-D rod and evaluate its working efficiency, six kinds of Terfenol-D rods were designed, and the temperature field of the rods was simulated and calculated using the finite element method to obtain the temperature distribution. The results showed that the untreated rod had the highest temperature; the temperature was higher in the middle and lower at both ends; higher on the outer diameter surface; and lower on the inside. When compared to the untreated rod, the temperatures of sliced rods and slit rods decreased, and the temperature of sliced rods was lower than that of slit rods; the temperature of slit rods was higher in the middle and lower at both ends; the temperature distribution of sliced rods was more uniform relatively; the slice treatment rod had the lowest temperature and the best heat suppression effect. Three structural rods were chosen and manufactured from a total of six that were tested. It shows that the temperature of all rods was higher in the middle and lower at both ends after 30 min of operation. The actual temperature of untreated rod was 34 °C, the actual temperature of radially slit rod was 32 °C, and the actual temperature of sliced rod at both ends was 28 °C. The tested temperature distributions of three rods agreed with the calculated ones.

Core Loss Study of Different Structures of Terfenol-D Rods

the hysteresis, eddy current, and coil resistance losses of the six Terfenol-D rods. The loss factors of the rods werecalculated and analyzed. Furthermore, three structures of Terfenol-D rods were manufactured, and the loss factors of therods were measured. The results showed that an untreated rod had the largest hysteresis and eddy current losses on the outerdiameter surface, and the overall hysteresis loss of the rod was the smallest. Compared with the untreated rod, the eddycurrent and hysteresis losses on the outer diameter surface of sliced and slit rods reduced, the overall hysteresis loss of slicedand slit rods increased, and the overall eddy current loss of sliced rods reduced; the hysteresis and eddy current losses on thesurface of the sliced rods were less than that of the slit rods, and the overall eddy current loss of the sliced rods was less thanthat of the slit rods; moreover, the eddy current loss of each rod was larger than its hysteresis loss. The numerical calculationvalues of the coil resistance loss basically agreed with the theoretical calculation values. The finite element simulationcalculation values of the loss factors of the Terfenol-D rods agreed with the experimental test values.

Magnetic field sensor based on resonant cavity dispersion-frequency mapping of a multi-longitudinal mode fiber laser.

A high-sensitivity and compact-size magnetic field sensor based on a multi-longitudinal mode fiber laser is proposed and experimentally demonstrated in this paper. The resonant cavity is composed of two uniform fiber Bragg gratings (FBGs) and a length of Er-doped fiber. A Terfenol-D rod is used as a transducer to stretch the sensing FBG when applying an external magnetic field. Longitudinal mode beat frequency could be generated in the laser and would shift with the deformation of the sensing FBG caused by the external magnetic field. Experimental results show the sensitivity of the proposed sensor is -47.32k H z/m T.

Principle and Control of Active Engine Mount Based on Magnetostrictive Actuator

Engine mount system affects the automobile NVH performance. Active mounts would achieve excellent vibration isolation and relative displacement control performance in a broad frequency bandwidth by outputting controlled force to the mounting system. The actuator and control method of the active mounts determine the system performance. In this paper, an active mount based on the smart material, i.e., Terfenol-D rod, is proposed, which mainly includes three parts: rubber spring, magnetostrictive actuator (MA), and hydraulic amplification mechanism (HAM). Dynamic model of the active mount is correspondingly established. A state feedback control method based on x-LMS (Least-Mean-Square) algorithm is proposed as well. Specifically, with the consideration of the unmeasurable state parameters in the active mounting system, an x-LMS state feedback controller with the system state as the reference signal is constructed by employing Sage-Husa Kalman filter to realize the state estimation of the active mounting system. Then a detailed analysis of the proposed control method is conducted, with deriving iterative formula of tap-weight vector. Sequentially, the problem of the dependence on the excitation signal in the x-LMS algorithm is addressed. The feasibility and capability of the proposed control method are verified and evaluated by simulation of a two-degree-of-freedom active mounting system.

Magnetostrictive Vibration Harvester with a Multistage Amplifier and Its Application in Human Walking Energy Harvesting

In this paper, as a theoretical basis, a foot vibration harvester with a finite support mechanism is proposed based on the Villari effect of magnetostrictive materials and Faraday’s law of electromagnetic induction, where a rod-shaped Terfenol-D is used as a core element for energy conversion, and a multi-stage force amplification mechanism is used as a core mechanical structure. The purpose of the amplification mechanism is to amplify the input force provided to the Terfenol-D rod and increase the output electric power. Moreover, the amplification mechanism is designed based on the bridge amplification structure, microlever amplification structure, and wedge amplification mechanism. A mathematical model of the amplification mechanism was developed using the force analysis and unit stiffness matrix methods, and the size and structure were designed and optimized. The performed simulations yielded an output force amplification ratio of 18.04. Based on the optimization results, a prototype was fabricated, and experiments were conducted. Specifically, experiments on the effect of the bias magnetic field on the harvester’s harvesting capability were performed, and the operating characteristics were tested for one complete cycle. Moreover, the effects of the amplification mechanism and vibration harvester were tested for practical applications. The peak output voltage of the harvester was 397.5[Formula: see text]mV under 100 N excitation, and the output electrical power on a resistive load could reach 3.33[Formula: see text]mW. In the application of the human walking process, the voltage could reach a maximum value of 387.3[Formula: see text]mV. The results of the study initially prove that the designed vibration harvester can stably collect human walking vibration.

Design and Characteristic Analysis of Magnetostrictive Vibration Harvester with Double-Stage Rhombus Amplification Mechanism

Vibration energy harvesting is a new alternative to lithium battery power for low-power devices, attempting to recover wasted or lost vibration energy to generate electricity. Magnetostrictive-based energy harvesting exploits the coupling properties of the Villari and Faraday electromagnetic induction effects to achieve mechanical–magnetic–electric energy conversion. In order to better apply to the actual vibration environment, such as buses, and improve the ability to capture low-frequency vibration energy, a double-stage rhombus vibration energy harvesting device, based on Terfenol-D rods, was developed. By establishing an analytical model of the force amplification ratio of the harvesting device, the design is optimized using the Single-Objective Genetic Algorithm, and the safety and pre-magnetization layout methods are analyzed by Finite Element Analysis. The output characteristics of the prototype, including the output voltage frequency response under low-frequency regular excitation and random excitation, the effect of external resistance, and the vibration energy capture performance under random excitation, are investigated in detail through experiments. The results of the experiments showed that the peak output power of the fabricated prototype was 1.056 mW at 30 Hz operating frequency, the energy harvesting capability reached 41.4 μW/N, and the peak open circuit voltage and output power were 2.92 V and 266 mW, respectively, under random excitation. Practical application test results showed that the peak voltage generated was 1.06–1.51 V when the excitation level was 2.2–4.9 m/s2. The comparative study indicates that the output performance of the proposed double-stage rhombus magnetostrictive vibration energy harvesting system is a great improvement over the proposals of existing literature.

Effects of core structure on the performance of Terfenol-D rod

To improve the vibration performance of the Terfenol-D rod and make its work more efficient, six types of Terfenol-D rods were studied in this paper. The dynamic simulation analyses of the rods were carried out, and the core loss of the rods were calculated and analyzed. Three structures of rods were manufactured, and their output amplitude were tested. The results showed that an untreated rod had the highest resonance frequency, the largest mechanical quality factor, and the smallest output amplitude and outer surface stress; compared with the untreated rod, the resonant frequency and mechanical quality factor of the sliced and slit rods reduced, the output amplitude and outer surface stress of the sliced and slit rods increased; the resonant frequency and mechanical quality factor of the sliced rods were smaller than those of the slit rods; and the output amplitude and outer surface stress of the sliced rods were larger than those of the slit rods. The untreated rod had the largest core loss on the outer diameter surface; the core loss on the outer diameter surface of the sliced and slit rods reduced, and the core loss of sliced rods was less than that of slit rods. The radially slit rod had the largest overall core loss; the overall core loss of the radially cut and bonded rod and the sliced rods was less than that of the untreated rod and the radially slit rod.

Magnetic sensor based on a Whispering Gallery Mode double-tailed silica microsphere

A vector magnetometer based on a stretchable Whispering Gallery Mode (WGM) silica Microsphere with a Q-factor of 108 is reported. The used microsphere has two fiber tails enabling it to serve as a strain sensor. The Double-Tailed Microsphere (DTM) is mechanically coupled to a Terfenol-D Rod (TDR), which undergoes longitudinal strain in response to a change in the ambient magnetic field. The strain of the magnetostrictive rod induces mechanical stress on the DTM resulting in a spectral shift of the WGMs of the microsphere. The strong dependence of the magnetometer sensitivity on the sensor geometry is studied, and geometry considerations for optimizing sensor performance are discussed. By introducing and employing geometrical adjustments, applicable due to the unique structure of the magnetometer, the sensitivity improved by a factor of 33. A sensitivity of 7.73 pm/mT is reported with a detection limit of ∼1 µT. The conditions required to achieve a considerably higher sensitivity of ∼200 pm/mT are presented, suggesting an expected detection limit under 40 nT. The simplicity, low cost and lack of electrical wiring make it attractive for remote magnetic sensing. In addition, the possibility to concatenate multiple sensors to a single optical fiber makes the suggested magnetometer highly suitable for quasi-distributed vector magnetic sensing.

Design and fabrication of rotary magnetostrictvie energy harvester for knee-joint wearable applications

PurposeThis paper aims to present the design and fabrication of a rotary magnetostrictive energy generator, using to harvest the rotation energy of human knee joint.Design/methodology/approachA rotary magnetostrictive energy generator is presented in this paper. The harvester consists of six movable flat Terfenol-D rods, surround by the picked-up coils respective, and alternate permanent magnet (PM) array fixed in the upper cover of the stator. The harvester rotates like as a stepper motor, which has rotary electromagnetic power generating effect and impacted magnetostrictive power generating effect in its rotation. Modeling and simulation are used to validate the concept. A prototype of harvester is fabricated and subjected to the experimental characterization.FindingsThe size of proposed structure is control as 77 cm3, and its mass is about 0.21 kg. Huge induced voltage generated in the short-time impact situation, and that induced voltage in the harvester can up to 18.6 V at 0.32 s stepper rotation. Also, the presented harvester has good harvesting effects at low frequency human walking situation, which is suitable to be used for future researches of wearable knee joint applications.Originality/valueA new concept of magnetostrictive harvester is presneted, which will be benefit for the application of human knee joint wearable. Also, this concept will give us more idea for collection of human movement energy.

Bandgap tunability of surface acoustic waves in a two-dimensional magneto-electro-elastic phononic crystal

The propagation of surface acoustic waves in two types of tunable magneto-electro-elastic phononic crystal structures is investigated, for which Terfenol-D rods are vertically deposited on the piezoelectric substrate or embedded in the piezoelectric substrate. The bandgaps of the phononic crystal structures are analyzed by using the finite element method considering the nonlinear physical characteristics of Terfenol-D under a magnetic field and compressive pre-stress. Furthermore, through a detailed discussion of the calculated results, it is shown that the bandgaps of surface acoustic waves can be enlarged and new bandgaps will appear under an appropriate magnitude of magnetic field and compressive stress. Therefore, the present numerical model may provide relevant guidance for adjusting the bandgaps of surface acoustic waves in a two-dimensional magneto-electro-elastic phononic crystal.

Development and Test of a Two-Dimensional Stacked Terfenol-D Actuator With High Bandwidth and Large Stroke

Smart material actuators (SMAs) can provide motion with high resolution and high bandwidth, but the output stroke is relatively small. Therefore, motion amplification mechanisms for SMAs have drawn considerable attentions in recent years. However, most of existing mechanisms realize the motion amplification at the expense of working bandwidth. To achieve large stroke and high bandwidth simultaneously, a novel two-dimensional stacked magnetostrictive actuator (TSMA) was developed and tested by adopting the magnetostrictive material, i.e., the Terfenol-D in this article. The U-shaped sleeves were employed to support the axial and radial two-dimensional stacking of three Terfenol-D rods. Then, an analytical model was established based on working principle of the TSMA, and a design of experiment analysis was carried out for the sensitivity study of the TSMA's key structural parameters. Next, the involved parameters of the established analytical model were obtained via system identification. Furthermore, several experimental tests of a fabricated prototype for the TSMA were carried out. The results show that the stroke of the proposed TSMA can reach 65 μ m. The displacement amplification ratio is achieved as 2.8 and the working bandwidth is kept as 500 Hz. This proves that the proposed structure can significantly increase the displacement with a little loss of bandwidth. Finally, a set of preliminary closed-loop tests using a traditional incremental proportion-integration-differentiation (PID) control were carried out to improve the motion precision. The closed-loop tracking results of 10-100 Hz sinusoid references show that the root-mean-square errors are less than 4$\%$ using a simple PID control alone.

An improved stress-dependent model for magnetomechanical effect simulation of Terfenol-D rods

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