Research

Magnetostrictive materials deform in response to a magnetic field or exhibit changes in magnetization when stressed. Our group focuses on certain magnetostrictive materials, including terbium–iron–dysprosium (Terfenol-D), iron–gallium (Galfenol), iron–cobalt–vanadium (Remendur), and cobalt ferrites. Leveraging their unique properties, we have pursued applications such as:

1. Magnetically-activated bioscaffolds for bone tissue engineering (NSF CAREER)
2. Acoustic transducers for pipeline structural health monitoring (DOE CINR)
3. Ultrasonic waveguide thermometers for nuclear power plants (DOE ASI program)

Piezoelectric materials undergo significant deformation instantaneously when subjected to an electrical field. Conversely, they generate electric charges on their surfaces when exposed to mechanical stress. Our group focuses on certain piezoelectric materials, including polyvinylidene fluoride polymer (PVDF), poly(vinylidene fluoride-co-trifluoroethylene) polymer (PVDF-trFE), aluminum nitride (AlN), lithium niobate (LNO), and barium titanate (BTO). We have explored applications such as

1. Dual-mode sensors for structural health monitoring in inflatable habitats (NASA EPSCoR)
2. Flexible and stretchable tactile senor arrays for human health monitoring (NASA ISGC Fellowship & NIH COBRE RPL)
3. Surface acoustic wave thermometers for nuclear power plants (DOE ASI)

Shape memory materials can recover a predetermined permanent shape after being deformed into a temporary shape. This shape memory effect can be triggered by external stimuli including heat, light, or electricity.  Our group focuses on PLA/TPU composites and biocompatible TATATO/TMTMP-based polymers. We have investigated applications such as:

1. Flexible and morphing electronics for deep space exploration (NASA EPSCoR)
2. Self-activated neural stimulators (Boise State)

Aerosol jet printing (AJP) involves atomizing a nanoparticle colloid ink into a fine aerosol, which is carried by a gas stream (typically nitrogen) through a nozzle and precisely deposited onto a substrate. This technique enables high-resolution printing of complex patterns on both flat and three-dimensional surfaces without requiring masks. In addition to passive electronic materials such as silver, gold, and nickel, our group has successfully used AJP to print the following smart materials:

1. Terfenol-D
2. Galfenol
3. Lithium Niobate

Coupled with a pulsed light sintering system (Xenon S2100) or a helium plasma sintering system, we have achieved room-temperature sintering of smart materials, enabling AJP on temperature-sensitive substrates such as human skin and plastics.

Material extrusion (MEX) is an additive manufacturing process in which viscous pastes or molten filaments are extruded through a nozzle, layer by layer, to build three-dimensional structures. This technique enables the fabrication of complex geometries with precise control over material placement. Our lab operates a custom fused filament fabrication system capable of printing metal filaments (e.g., stainless steel 17-4 and copper), two Hyrel MEX systems, and has access to an nScrypt MEX system for high-precision ink deposition. Using these platforms, we have successfully printed the following smart materials:

1. Cobalt ferrite
2. Terfenol-D
3. Galfenol
4. PVDF-trFE
5. Barium titanate/PDMS composites
6. Terfenol-D/PVDF composites
7. PLA/TPU shape memory composites

Each Hyrel system is equipped with five docking stations that support interchangeable extrusion and processing heads—including fused filament, pneumatic, stepper-motor-driven, and laser heads—enabling versatile multi-material printing. This capability allows us to integrate printed smart materials with flexible electronic components made from liquid metals, laser-induced graphene, silver pastes, PEDOT:PSS, and liquid metal composites.

Acoustic droplet ejection (ADE) is a non-contact printing and dispensing technique that uses focused acoustic energy to eject precise droplets of liquid from a source reservoir onto a target surface. By tuning the acoustic wave frequency and energy, ADE can generate droplets ranging from picoliters to nanoliters without the need for nozzles or physical contact. This eliminates risks of clogging, contamination, or mechanical wear, making it especially advantageous for handling viscous, delicate, or biologically sensitive fluids. Our group has customized an ADE system and is exploring its capabilities in printing magnetostrictive thin films.

Printed smart materials, particularly metals and ceramics, demand intensive multiscale modeling to accurately describe their behavior. The figure below illustrates a typical microstructure of a magnetostrictive acoustic transducer. A robust constitutive model must capture phenomena across multiple length scales, including magnetic domain rotation at the nanoscale, crystal deformation and porosity at the microscale, and multiphysics interactions at the millimeter to meter scale. While individual models targeting each scale exist in the literature, developing a comprehensive framework that bridges these scales remains a significant challenge. Leveraging the Mori–Tanaka homogenization method and representative volume element concepts, our group has developed efficient and accurate constitutive models for the following printed smart materials:

1. Terfenol-D composites
2. Terfenol-D/PVDF composites
3. Monolithic Terfenol-D

Smart materials and systems are multiphysics in nature. For instance, the linear variable differential transformer (LVDT) used in nuclear reactors involves electrical dynamics, magnetic dynamics, mechanical dynamics, and thermal dynamics. A comprehensive system-level model needs to account for individual dynamics and their coupling. Our team has successfully developed and validated the following multiphysics models for smart materials and systems:

1. Magnetostrictive waveguide thermometers
2. Piezoelectric surface acoustic wave thermometers
3. Linear variable differential transformers
4. PLA/TPU-based shape memory morphing electronics
5. Magnetostrictive unimorph actuators

We aim to revolutionize bone defect treatment by developing a transformative magnetoelectric biomaterial replicating the complex mechanobiological environments in human bones. This functional biomaterial, made of magnetostrictive Terfenol-D nanoparticles dispersed in a piezoelectric PVDF polymer matrix, can generate precise, nonintrusive mechanical cues through two unique mechanisms: the Delta-E effect, mimicking elasticity variations during bone growth, and the magnetoelectric effect, mimicking mechanical vibrations and piezoelectric stimuli found in bones.

A 2016 report revealed that 80% of operational nuclear power plants in the U.S. experienced financial challenges or faced early retirement, primarily because their maintenance costs are three to four times higher than those of coal or natural gas plants. Among the most vulnerable components are reactor piping systems, which undergo significant wear and degradation from environmental stressors, requiring timely maintenance. To address these challenges and close existing research gaps, we are developing a novel magnetostrictive structural health monitoring (SHM) system specifically designed for in-pile applications. The figure below highlights our recent progress in room-temperature printing of magnetostrictive thin films.

Another figure illustrates the configuration of the magnetostrictive Lamb wave transducer and demonstrates that its performance is comparable to commercial PZT transducers.

Inflatable reentry vehicles and habitats are attractive for NASA’s Moon to Mars Exploration campaign and the next-generation space station, because of their high volume-to-mass ratio and packaging efficiency. Since inflatable structures are usually thin-walled, ionizing radiation and micro-meteoroid orbital debris pose considerable threats to their integrity. To meet this urgent structural health monitoring needs, we aim to combine smart materials development and On-Demand Manufacturing of Electronics (ODME) techniques to deliver a wireless, flexible, self-sustaining, and multifunctional SHM system. We have first developed a sensor features a PVDF-trFE film sandwiched between two electrodes, enabling dual-mode operation. In piezoresistive mode, resistance changes in the printed meandering electrode reflect accumulated strain. In piezoelectric mode, the PVDF-TrFE film generates voltage in response to dynamic impacts.

Our group has successfully printed magnetostrictive composites on top of passive substrates to form cantilever actuators, also known as unimorph actuators, as shown in the figure below. 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.

Furthermore, we have printed PLA/TPU composites into morphing structures (see figure below) that can be activated by external heating. By integrating these composites with electrically conductive traces, we achieved electrical activation of the shape memory structures. In addition, by adjusting the composite color, we enabled light-based activation.

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. The figure below 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.

In collaboration with National Cheng Kung University, we developed a mathematical model for magnetostrictive composites made of Terfenol-D particles embedded in a polymer matrix. The model accounts for particle orientation, size, and volume fraction, as well as mechanical loads and magnetic fields. Unlike most existing models, which only consider particle orientation at the composite level, our approach incorporates it directly at the particle level. This makes the framework both more efficient and equally accurate, as confirmed by comparisons with published experimental data.