Shape memory polymers (SMPs) are smart materials capable of “remembering” and reverting to a pre-set shape upon exposure to specific stimuli like heat or light, even after substantial deformation. When combined with flexible electronics, SMPs enable innovative morphing structures for space applications. These structures, such as adaptive satellite antennas and solar arrays, possess the capability to reconfigure themselves dynamically, thereby optimizing signal reception, energy harvesting, and spacecraft aerodynamics in accordance with the unique demands of each mission. This research merges material extrusion (MEX) and fused filament deposition techniques to advance the additive manufacturing of SMP-based morphing structures, which feature conductive silver traces encased in a shape memory polylactic acid/thermoplastic matrix. Thermo-mechanical material properties of the printed SMP, including the maximum recoverable strain and glass transition temperature, were first characterized. Subsequently, a series of SMP-based structures were prototyped to demonstrate their morphing capabilities in response to light, thermal, or electrical stimuli. These results confirmed the feasibility of on-demand manufacturing of morphing structures, reducing the constraints of Earth-based pre-launch design limits and ensuring sustainability for future deep-space exploration missions.
Inflatable structures present an efficient solution for deep space habitats, enabling compact storage during launch and providing a large operational volume once deployed in space. However, their lightweight and thin-walled design makes them susceptible to Micro-Meteoroids and Orbital Debris (MMODs), as well as the cumulative effects of creep strain. To ensure the safety of these inflatable habitats, this study used a commercial material extrusion system to prototype a flexible and multifunctional sensor for non-destructive structural health monitoring. This unique sensor consists of a piezoelectric polyvinylidene fluoride-trifluoroethylene (PVDF-trFE) film sandwiched between a pair of electrodes. The piezoelectric layer detects dynamic impact force due to MMODs and the electrodes printed into piezoresistive strain gauges are capable of measuring creep strain. In this study, a comprehensive sensor fabrication technique, including piezoelectric ink synthesis, printer settings, and material post-processing method, was first developed. Subsequent experiments using a mechanical load frame and impact hammer quantified the sensor sensitivity in piezoresistive and piezoelectric mode, respectively. The printed sensor achieved a gauge factor exceeding 8 in piezoresistive mode. An additional machine learning model predicted impact magnitude and impact width with linear correlation coefficients of 0.99 and 0.89, respectively, when compared to the tested values. These promising results underscore the potential for in-situ manufacturing of such multifunctional sensors, paving the way for sustainable deep space missions that not only minimize launch mass but also diminish reliance on exhaustive pre-launch designs.
Heat-driven shape memory polymers (SMPs) can revert to a memorized geometry once they reach the phase-transformation temperature. This work merges the fused filament three-dimensional (3D) printing and nScrypt microdispensing to create morphing and flexible electronics that could result in innovations in antennas and sensors for biomedical and aerospace applications. Polyurethane and polylactide will first be printed simultaneously on a 3D printer to form SMPs. The thermomechanical properties of the printed SMPs will then be characterized for different TPU/PLA ratios. By nScrypt printing silver electrodes on the SMPs, a morphing antenna will eventually be prototyped and characterized.
Piezoelectric poly(vinylidene fluoride-co-trifluoroethylene), or PVDF-trFE, has enabled unprecedented flexible and dynamic force sensors due to its mechanical robustness and biocompatibility. This study focuses on additive manufacturing of PVDF-trFE thin film sensors using an nScrypt micro-dispenser. PVDF-trFE ink composition, substrate treatment, and printer settings were first investigated to ensure consistent and uniform printing. Post-processing procedures, including curing and electrical poling, were then analyzed experimentally. The effectiveness of the manufacturing procedure was quantified in terms of piezoelectric coefficients. By using commercially-available electrically conductive silver inks, a force sensor consisting of a PVDF-trFE film sandwiched by silver electrodes were prototyped.
Surface acoustic wave (SAW) devices consisting of interdigitated transducers printed on piezoelectric substrates have resulted in low-cost, low-power, and small-footprint thermometers for high temperature and radioactive environments. This study developed temperature-dependent finite element models in both time- and frequencydomain. Modeling accuracy was evaluated using an aerosol-jet printed SAW thermometer measured from room temperature to 200 Celsius. Time-domain simulation results enabled acoustic wave propagation visualization and successfully guided the signal denoising of measured scattering parameters. Frequency-domain simulation accurately predicted the temperature-driven natural frequency drift in SAW transducers while maintaining high computational efficiency. The models developed in this study will facilitate computer-aided design of future SAW transducers and expand their applications in harsh environments.
The sense of touch, also known as tactile recognition, is crucial for modern robotics to explore and understand ambient environments. This study used a commercial inkjet printer to additively manufacture a flexible and passive tactile sensor consisting of a piezoelectric P(VDF-trFE) thin film sandwiched by a pair of electrodes. Consistent and reliable printing of piezoelectric thin films is achieved by investigating ink preparation procedures, printer settings, and substrate surface treatment. Post-processing procedures, including drying and curing, are studied to ensure thin film uniformity and functionality. Eventually, in-situ signal processing and wireless data transmission circuits are developed and validated. The printed piezoelectric tactile sensor can be potentially used for human health monitoring and soft robotics due to its high flexibility and biocompatibility.
Shape memory nickel-titanium (NiTi) thin films have demonstrated superior capabilities in microelectromechanical systems and biomedical implants due to its corrosion resistance, large work output per unit mass, radiation resistance, and biocompatibility. The goal of this project is to additively manufacture NiTi thin film devices with micrometer resolution. NiTi colloid inks for 3D printing applications were developed and characterized. NiTi thin films were then printed onto a ceramic substrate using an aerosol jet printer, subsequently, sintering and heat treatment procedures were developed. Damping capability and output power density of the printed NiTi thin films were eventually characterized.
Advanced sensor network in aircraft can enable in-situ structural health monitoring, reduce unscheduled groundings, and consequently decrease maintenance expenses. This research aims to fabricate lightweight, flexible, wireless, and passive thin film sensors consisting of magnetostrictive thin films, a sensing coil, and yttria-stabilized zirconia substrates. External stress variation changes the magnetic permeability of the magnetostrictive thin films, resulting in an electrical impedance shift on the sensing coil, and thus can be detected wirelessly using a secondary excitation coil. Specifics for the additive manufacturing procedures, experimental data characterized, and theoretical numerical simulations for the magnetostrictive thin film sensors are presented.
A novel mechanism called the vibration ring is being developed to enable energy conversion elements to be incorporated into the driveline of a helicopter or other rotating machines. Unwanted vibration is transduced into electrical energy, which provides a damping effect on the driveline. The generated electrical energy may also be used to power other devices (e.g., health monitoring sensors). PZT (‘piezoceramic’) and PMN-30%PT (‘single crystal’) stacks, as well as a Tb0.3Dy0.7Fe1.92 (‘Terfenol-D’) rod with a bias magnet array and a pickup coil, were tested as alternative energy conversion elements to use within the vibration ring. They were tuned for broadband damping using shunt resistors, and dynamic compression testing was conducted in a high-speed load frame. Energy conversion was experimentally optimized at 750Hz by tuning the applied bias stress and resistance values. Dynamic testing was conducted up to 1000Hz to determine the effective compressive modulus, shunt loss factor, internal loss factor, and total loss factor. Some of the trends of modulus and internal loss factor versus frequency were unexplained. The single crystal device exhibited the greatest shunt loss factor
whereas the Terfenol-D device had the highest internal and total loss factors. Simulations revealed that internal losses in the Terfenol-D device were elevated by eddy current effects, and an improved magnetic circuit could enhance its shunt damping capabilities. Alternatively, the Terfenol-D device may be simplified to utilize only the eddy current dissipation mechanism (no pickup coil or shunt) to create broadband damping.
A novel and precise characterization of the constitutive behavior of solid and laminated research-grade, polycrystalline Galfenol (Fe81:6Ga18:4) under under quasi-static (1 Hz) and dynamic (4 to 1000 Hz) stress loadings was recently conducted by the authors. This paper summarizes the characterization by focusing on the experimental design and the dynamic sensing response of the solid Galfenol specimen. Mechanical loads are applied using a high frequency load frame. The dynamic stress amplitude for minor and major loops is 2.88 and 31.4 MPa, respectively. Dynamic minor and major loops are measured for the bias condition resulting in maximum, quasi-static sensitivity. Three key sources of error in the dynamic measurements are accounted for: (1) electromagnetic noise in strain signals due to Galfenol's magnetic response, (2) error in load signals due to the inertial force of fixturing, and (3) time delays imposed by conditioning electronics. For dynamic characterization, strain error is kept below 1.2 % of full scale by wiring two collocated gauges in series (noise cancellation) and through lead wire weaving. Inertial force error is kept below 0.41 % by measuring the dynamic force in the specimen using a nearly collocated piezoelectric load washer. The phase response of all conditioning electronics is explicitly measured and corrected for. In general, as frequency increases, the sensing response becomes more linear due to an increase in eddy currents. The location of positive and negative saturation is the same at all frequencies. As frequency increases above about 100 Hz, the elbow in the strain versus stress response disappears as the active (soft) regime stiffens toward the passive (hard) regime.
Vibrations generated by machine driveline components can cause excessive noise and structural dam- age. Magnetostrictive materials, including Galfenol (iron-gallium alloys) and Terfenol-D (terbium-iron- dysprosium alloys), are able to convert mechanical energy to magnetic energy. A magnetostrictive vibration ring is proposed, which generates electrical energy and dampens vibration, when installed in a machine driveline. A 2D axisymmetric finite element (FE) model incorporating magnetic, mechanical, and electrical dynamics is constructed in COMSOL Multiphysics. Based on the model, a parametric study considering magnetostrictive material geometry, pickup coil size, bias magnet strength, flux path design, and electrical load is conducted to maximize loss factor and average electrical output power. By connecting various resistive loads to the pickup coil, the maximum loss factors for Galfenol and Terfenol-D due to electrical energy loss are identified as 0.14 and 0.34, respectively. The maximum av- erage electrical output power for Galfenol and Terfenol-D is 0.21 W and 0.58 W, respectively. The loss factors for Galfenol and Terfenol-D are increased to 0.59 and 1.83, respectively, by using an L-C resonant circuit.
KEYWORDS: Energy conversion efficiency, Resistors, Finite element methods, Resistance, Magnetism, Capacitors, 3D modeling, Magnetostrictive materials, Energy harvesting, Instrument modeling
Iron-gallium alloys, known as Galfenol, are a class of magnetostrictive materials that convert mechanical energy to magnetic energy and vice versa. Galfenol devices especially unimorph consisting of a Galfenol beam bonded to a passive substrate, have great potential in energy harvesting applications, but advanced multiphysics models are lacking for these smart devices. This study presents a comprehensive finite element model for Galfenol unimorph harvesters which incorporates magnetic, mechanical, and electrical dynamics. Experiments considering impulsive tip excitations under purely resistive or resistive-capacitive electrical loads are conducted to validate the proposed model. The energy conversion efficiency and peak power density of a unimorph beam with a natural frequency of 139.5 Hz are analyzed experimentally. The maximum energy conversion efficiency is 5.93% when a 74 Ω resistor and a 2 μF capacitor are connected in parallel to the pickup coil in parallel. The maximum power density observed in experiments is 10.72 mW/cm3 when load resistance is 74 Ω. This performance may be optimized in the future utilizing the proposed finite element model.
Magnetostrictive iron-gallium alloys, known as Galfenol, are a recent class of smart materials with potential in energy harvesting applications. Unimorph energy harvesters consisting of a Galfenol beam bonded to a passive substrate are simple and effective, but advanced models are lacking for these smart devices. This study presents a finite element model for Galfenol unimorph harvester systems. Experiments considering various design parameters such as pick up coil size, load resistance, beam thickness ratio, and bias magnetic field strength are conducted to guide and validate the modeling effort. If the free length of the Galfenol unimorph beam is considered as the effective length, the maximum average power density, peak power density, and open-circuit voltage amplitude achieved in experiments are 13.97 mW/cm3, 35.51 mW/cm3, and 0.66 V, respectively. By only considering the length of Galfenol surrounded by the pickup coil, the maximum average power density and peak power density are 23.66 mW/cm3 and 60.14 mW/cm3, respectively.
This paper focuses on the development of a three-dimensional (3D) hysteretic Galfenol model which is implemented using the finite element method (FEM) in COMSOL Multiphysics. The model describes Galfenol responses and those of passive components including flux return path, coils and surrounding air. A key contribution of this work is that it lifts the limitations of symmetric geometry utilized in the previous literature and demonstrates the implementation of the approach for more complex systems than before. Unlike anhysteretic FEM models, the proposed model can simulate minor loops which are essential for both Galfenol sensor and actuator design. A group of stress-flux density loops for different bias currents is used to verify the accuracy of the model in the quasi-static regime.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.