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Magnetostrictive Materials

Magnetostrictive materials exhibit mechanical deformation when driven by a magnetic field or vice versa. These unique properties make them highly versatile, with applications ranging from actuation and sensing to energy harvesting. While the magnetostrictive effect is inherent to all ferromagnetic materials, only specific alloys—such as those combining iron with rare earth elements, gallium, or aluminum, as well as certain amorphous metals—offer sufficiently high levels of magnetostriction to be commercially viable. Magnetostrictive materials are suitable for harsh environments (i.e., high temperature, radiation) and biomedical applications.

Ultrasonic waveguide thermometer (Active)

Sponsor: DOE Advanced Sensors & Instrumentation (ASI) Program

Ultrasonic thermometry has the potential to improve upon temperature sensors currently used for in-core temperature measurements. Ultrasonic thermometers (UTs) work on the principle that the speed at which sound travels through a material (acoustic velocity) is dependent on the temperature of the material. Temperature may be derived by introducing a short acoustic pulse to the sensor and measuring the time delay of acoustic reflections generated at acoustic discontinuities along the length of the sensor. UT temperature measurements may be made near the melting point of the sensor material, allowing monitoring of temperatures potentially in excess of 3000 °C.

Magnetostrictive waveguide thermometer: (a) assembly, (b) wave visualization using PSV-400 laser doppler vibrometer, (c) COMSOL simulation result, and (d) time-of-flight results at various temperatures.

The figure above shows a typical UT design based on iron-gallium alloys or Galfenol. We have developed an accurate and efficient multiphysics model that is able to capture the acoustic wave propagation in the waveguide.

Additive manufacturing of magnetostrictive materials (Active)

Sponsor: NASA Established Program to Stimulate Competitive Research (EPSCoR)
Previous Sponsors: NASA Idaho Space Grant Consortium (ISGC) grant

(a) Configuration of magnetostrictive beam actuator, (b) magnetostrictive cobalt-ferrite beam printed by nScrupt SmartPump; and (c) Tip deflection of the cobalt ferrite beam under varying magnetic field.

Our group has successfully printed magnetically-active composites by dispersing magnetostrictive particles in polymeric matrices. By printing magnetostrictive composites on top of passive substrates, we further developed cantilever actuators, also known as unimorph actuators, as shown in the figure on the left. When a magnetic field is applied along the longitudinal direction of the beam, the magnetostrictive layer deforms while the passive substrate tends to maintain flat. Therefore, the unimorph actuator outputs micro-scale and butterfly-shape tip deflection. This actuator can be potentially used for precision drug delivery or optical instrument control.

Piezoelectric Materials

Piezoelectric materials can output significant deformation instantaneously when subjected to an electrical field. Therefore, they have been widely used as high frequency and large power density actuators. On the other hand, electric charges accumulate on the surface of piezoelectric materials when they are subjected to mechanical loadings. Therefore, piezoelectric materials have also been utilized as structural vibration energy harvesters and sensors. Our lab focuses on piezoelectric ceramics (e.g., PZT, barium titanate) and piezoelectric polymers (e.g., PVDF, PVDF-trFE).

All-printed tactile sensor (Active)

Sponsor: NASA EPSCoR
Previous Sponsor: SEMI FlexTech

piezo tactile sensor
(a) Configuration of a P(VDF-trFE) piezoelectric tactile sensor; (b) all-printed piezoelectric tactile sensor.

A typical piezoelectric tactile sensor consists of a piezoelectric layer (e.g., PVDF-trFE) sandwiched by a pair of electrodes, as shown in the figure on the left. Our group has printed the PVDF-trFE layer and top silver electrode. In collaboration with Dr. Benjamin Johnson (Boise State), our group has developed signal processing and wireless data transmission circuits for piezoelectric sensors for the purpose of measuring carotid pulses.

Printed surface acoustic wave (SAW) sensors

Previous Sponsor: DOE Advanced Sensors & Instrumentation (ASI) Program
(a) Optical image and (b) temperature-varying natural frequencies of the surface acoustic wave transducer printed by aerosol jet printing.
Surface acoustic wave (SAW) devices are a subclass of micro-electromechanical systems (MEMS) that generate an acoustic emission when electrically stimulated. These transducers also work as detectors, converting surface strain into readable electrical signals. Physical properties of the generated SAW are material dependent and influenced by external factors like temperature. By monitoring temperature-dependent scattering parameters a SAW device can function as a thermometer to elucidate substrate temperature. Traditional fabrication of SAW sensors requires labor- and cost- intensive subtractive processes that produce large volumes of hazardous waste. This study utilizes an innovative aerosol jet printer to directly write consistent, high-resolution, silver comb electrodes onto a Y-cut LiNbO3 substrate. The printed, two-port, 20 MHz SAW sensor exhibited excellent linearity and repeatability while being verified as a thermometer from 25 to 200 C. Sensitivities of the printed SAW thermometer are -96.9 × 10-6 C−1 when operating in pulse-echo mode and pulse-receiver mode, respectively. These results highlight a repeatable path to the additive fabrication of compact high-frequency SAW thermometers.

Shape Memory Materials

Shape memory materials exhibit coupling between thermal and mechanical energies. Specifically, our group focuses on shape memory polymers that can return from a deformed shape (temporary shape) to the memorized shape (permanent shape) when they are heat up beyond the transformation temperature. This unique property has enabled innovations in morphing structures, actuators, and self-healing structures.

Morphing Electronics (Active)

Sponsor: NASA EPSCoR

printed shape memory polymer
Printed shape memory polymers morphing between a 3D rose shape and a 2D Bronco logo.

Our group has printed shape memory polymer structures that exhibit more than 60% deformation at a transformation temperature of around 70 °C. The figure on the left shows a printed morphing structure transforming between 2D Bronco logo and 3D rose shape. The video below shows a morphing electrical circuit printed on top of shape memory polymers.

Multiphysics Modeling

Multiphysics Modeling of Surface Acoustic Wave Transducers

Previous Sponsor: DOE Advanced Sensors & Instrumentation (ASI) Program
Our team developed a series of temperature-dependent finite element models for a SAW transducer consisting of printed silver interdigitated transducers (IDTs) deposited onto piezoelectric lithium niobate. Modeling accuracy was evaluated experimentally from room temperature to 200 °C using an aerosol-jet-printed SAW thermometer. A time-domain study enabled visualization of the wave propagation and successfully guided the denoising of the scattering parameter measurement. Additionally, frequency-domain models using traditional modal analysis or the unique port boundary condition feature in COMSOL Multiphysics accurately predicted the temperature-driven natural frequency drift in the SAW thermometer. The finite element models developed in this study serve to facilitate the computer-aided design of future SAW transducers for applications in harsh environments.

Constitutive model for Terfenol-D Composites

MsM microstructures: magnetic domain (grey dot-dashed line) and grain (blue dashed line).

In collaboration with National Cheng Kung University, we developed a mathematical framework for two-phase magnetostrictive composites composed of oriented or non-oriented magnetostrictive Terfenol-D particles embedded in passive polymer matrices. The phase constitutive behavior of the monolithic Terfenol-D with arbitrary crystal orientations is represented by a recently developed discrete energy averaged model. This unique Terfenol-D constitutive model results in close-form and linear algebraic equations accurately describing the nonlinear magnetostriction and magnetization in magnetostrictive composites subjected to a given loading or magnetic field increment. The effectiveness of this new mathematical framework in capturing magnetostrictive particle size orientation, phase volume fractions, mechanical loading conditions, and magnetic field excitations are validated using a series of experimental data available in literature. Compared to existing models that prevalently addressed particle orientation in composite constitutive level, the model framework in this study directly handles particle orientation in the phase constitutive level, and therefore achieves enhanced efficiency while maintaining comparable accuracy.

Finite element model for LVDT (Active)

Sponsor: DOE Advanced Sensors & Instrumentation (ASI) Program

Linear Variable Differential Transformers (LVDT) sensors
(a) A CT image showing the cross section of a Halden LVDT sensor. (b) 2D axisymmetric model configuration in COMSOL Mutiphysics. (c) Magnitude of magnetic flux density in Tesla when the core is 1 mm away from the null position.

Linear Variable Differential Transformers (LVDT) sensors, known for superior in-pile performance under irradiation, are available to provide micron-scale resolution data enabling the evaluation of fuel performance. Such a high resolution measurement requires a careful understanding of not only sensor itself, but also the complete implementation strategy, including thermal conditions, hardware selection and design, and data processing. To evaluate sensor performance, reduce sensor size, and optimize sensor configurations, this study first develops a finite element model in COMSOL Multiphysics for commercial LVDT sensors in order to investigate the impact of each component’s dimensions and material properties. This study then establish a finite element model including a through hole at the LVDT core to allow for instrumentation pass-through, such as a fiber optic cable.

Sponsors and Collaborators

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