Dr. Nicholas J. Jones Profile

Dr. Nicholas J. Jones

at Naval Surface Warfare Ctr Carderock Div

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Proceedings Article | 22 March 2021 Presentation + Paper

Experimental study on dynamic load line for magnetostrictive actuator

Jin-Hyeong Yoo, Nicholas Jones

Proceedings Volume 11591, 115911H (2021) https://doi.org/10.1117/12.2585005

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Magnetostrictive materials show a dimensional change in response to changes in their magnetization. Terfenol-D (Tb_xDy_1−xFe₂ x ~ 0.3) is one of well-known magnetostrictive material which shows giant magnetostriction (>1000ppm), and the high magnetostriction is beneficial for actuator applications. In order to implement a magnetostrictive actuator in a real application, the maximum stroke and maximum force output of the actuator should be defined. One way to define actuator performance is to measure the load line performance, allowing the user to determine the suitability of the actuator for a particular application. Actuator load line is defined in terms of two key parameters, blocked force and free displacement. However, magnetostrictive materials have a highly nonlinear strain response, which is a function of both applied magnetic field and applied stress. Within a certain stress region, the strain response of Terfenol-D at a constant bias magnetic field may actually increase with increasing applied compressive stress, which is not the normal behavior of a linear actuator. In this study, the empirical dynamic load line performance of a Terfenol-D actuator with various driving conditions is evaluated. The load line performances are measured up to 204 kg of additional mass and the actuation frequency range of 0.5 Hz to 20 Hz. The trend of the load line is compared with simulation results based on static characterization of a separate Terfenol-D rod.

Proceedings Article | 27 March 2019 Paper

Performance of a water level sensor using magnetostrictive materials

JinHyeong Yoo, Nicholas Jones, Kyle Flynn, Rachel Jacobs

Proceedings Volume 10970, 109700K (2019) https://doi.org/10.1117/12.2514282

KEYWORDS: Sensors, Magnetic sensors, Magnetostrictive materials, Temperature metrology, Environmental sensing, Oscilloscopes, Iron

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FeGa-based alloys (Fe_1-xGa_x, Galfenol) belong to a branch of magnetic materials called “magnetostrictive” materials, in which their dimensions change in response to changes in the magnetization. Magnetostrictive materials also experience an inverse effect, called the Villari effect, where magnetization and permeability changes occur in response to changes in applied stress/strain. In this study, an active mode water level sensor has been developed. The sensor has been designed to work when the water is both in motion and still. A Galfenol-brass unimorph beam has been constructed, with Galfenol as the active layer. The beam is clamped at one end, and, when it is flexed, there will be a stress concentration near the clamped region. This change in stress can be measured by a magnetic field sensor, which can detect local fluctuations in magnetic field due to the Villari effect. Two magnetic coils are used, one for alternating current (AC) magnetic field generation and the other for measuring the magnetic field response of the strip. The resonance frequency of the beam in air is higher than in water. By choosing an operating vibrational frequency higher than the resonance frequency in air, we can separate the pick-up coil impedance responses when the beam is surrounded by air or water, or even by sediment. The vertical response of the beam has also been measured; as the beam is covered by more water, its resonance frequency should incrementally change. The experimental results are compared with a simulation using a theoretical vibration model for a cantilever beam under water. The beam was tested both as the water level increased and decreased, showing a 10% increase from not submerged to fully submerged and the results were verified by the simulation. The relative sensor impedance between air and water was also evaluated from room temperature (25°C) to 80 °C to verify signal differentiation.

Proceedings Article | 22 March 2018 Presentation + Paper

Performance prediction for a magnetostrictive actuator using a simplified model

Jin-Hyeong Yoo, Nicholas Jones

Proceedings Volume 10596, 105961G (2018) https://doi.org/10.1117/12.2297039

KEYWORDS: Magnetism, Magnetostrictive materials, Performance modeling, Actuators, Magnetic sensors, Sensors, Solids

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Iron-Gallium alloys (Galfenol) are promising transducer materials that combine high magnetostriction, desirable mechanical properties, high permeability, and a wide operational temperature range. Most of all, the material is capable of operating under tensile stress, and is relatively resistant to shock. These materials are generally characterized using a solid, cylindrically-shaped specimen under controlled compressive stress and magnetization conditions. Because the magnetostriction strongly depends on both the applied stress and magnetization, the characterization of the material is usually conducted under controlled conditions so each parameter is varied independently of the other. However, in a real application the applied stress and magnetization will not be maintained constant during operation. Even though the controlled characterization measurement gives insight into standard material properties, usage of this data in an application, while possible, is not straight forward. This study presents an engineering modeling methodology for magnetostrictive materials based on a piezo-electric governing equation. This model suggests phenomenological, nonlinear, three-dimensional functions for strain and magnetic flux density responses as functions of applied stress and magnetic field. Load line performances as a function of maximum magnetic field input were simulated based on the model. To verify the modeling performance, a polycrystalline magnetostrictive rod (Fe-Ga alloy, Galfenol) was characterized under compressive loads using a dead-weight test setup, with strain gages on the rod and a magnetic field driving coil around the sample. The magnetic flux density through the Galfenol rod was measured with a sensing coil; the compressive loads were measured using a load cell on the bottom of the Galfenol rod. The experimental results are compared with the simulation results using the suggested model, showing good agreement.

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