Abstract Dielectric elastomers (DE) are regarded as a potential alternative to conventional actuator technologies. They feature low weight, high strains and low material costs. Their scope of application ranges from sensors, energy generators, smart textiles to biomimetic robots and much more. A few concepts of loudspeakers using DE have been demonstrated by the research community. One of the disadvantages of previously concepts was the need for mechanical bias (e.g. by air pressure). This work proposes a new concept of loudspeaker, which does not need prestretch or other means of mechanical bias. Buckling dielectric elastomer transducers (BDET) use the area expansion of actuated DE to buckle up. This mechanism is used to construct a millimeter-scale loudspeaker with good frequency response in the upper frequency range. The concept is implemented using automatically fabricated multi-layer membranes. The multilayer structure allows to generate more force and has higher flexural rigidity than a single-layer setup. Samples with different amount of layers are fabricated and an analytical model is derived. Measurements of the static deflection, the frequency response and the total harmonic distortion validate the model. The small scale of the speaker allows it to be installed in large arrays and thus might offer a hardware platform for high-resolution beam forming or wave field synthesis.

This article presents the experimental validation of a Direct Adaptive Control for angular position regulation of a lightweight robotic arm. The robotic arm is single degree-of-freedom (DOF) system, actuated by two Shape Memory Alloy (SMA) wires. The proposed adaptive control is capable of adapting itself to the hysteretic behavior of SMA wires and update its behavior to deal with the changing parameters of the material over time. The closed-loop approach is tested experimentally showing its effectiveness to deal with the highly nonlinear dynamics of the SMA wires. These results are discussed and compared with a classical control approach. The updated design and hardware development and modeling of the robotic arm are shown.

The reduction of low-frequency noise transmission through thin-walled structures is a topic of research for many years now. Due to large wavelengths and the mass law, passive solutions usually gain low performance in the frequency range below 500 Hz. Active systems promised to fill the gap and to achieve significant reductions of transmitted sound. Nevertheless, experiments showed the outstanding performance of such specialized systems, but also demonstrated the computational and hardware effort of such solutions. The upcoming additive manufacturing technology enabled new multi-material designs of complex structures. Based on this technology, acoustic metamaterials emerged in the laboratories and in literature. Arrays of miniaturized locally resonant structures are able to change the noise transmission of thin walled structures beyond the limits of the given mass law in certain frequency bands. For future aircraft contra-rotating open rotor (CROR) engines are a promising technology to reduce their CO 2 footprint. Since the contribution of CROR engines to the cabin noise is higher than for jet engines, new strategies for the reduction of noise transmissions for frequency bands below 200 Hz are necessary. For the tonal noise of the CROR engines, acoustic metamaterials seem to be an appropriate solution. In this paper a 110 × 110 × 1 mm 3 thin-walled sample plate is presented. It is covered with a 5 × 5 array of multi-material resonant structures, which are printed as mass on a beam. The rubber-like beam material combines a low Young’s modulus with a high material damping, leading to a low eigenfrequency of the resonators. The design of the resonators using simulations and experimental data is shown. To explore the potential of the design, an acoustic test box is manufactured. Starting with all resonators unblocked the emitted sound intensity of the plate is measured. Sequential blocking of selected resonators proves the concept. Additional laser scanning vibrometer measurements give insights into the vibration behavior of single resonators.

Since its inception by Richard Feynman in 1982, quantum computing has provided an intriguing opportunity to advance computational capabilities over classical computing. Classical computers use bits to process information in terms of zeros and ones. Quantum computers use the complex world of quantum mechanics to carry out calculations using qubits (the quantum analog of a classical bit). The qubit can be in a superposition of the zero and one state simultaneously unlike a classical bit. The true power of quantum computing comes from the complexity of entanglement between many qubits. When entanglement is realized, quantum algorithms for problems such as factoring numbers and solving linear algebra problems show exponential speed-up relative to any known classical algorithm. Linear algebra problems are of particular interest in engineering application for solving problems that use finite element and finite difference methods. Here, we explore quantum linear algebra problems where we design and implement a quantum circuit that can be tested on IBM’s quantum computing hardware. A set of quantum gates are assimilated into a circuit and implemented on the IBM Q system to demonstrate its algorithm capabilities and its measurement methodology.

Compared to clinic-based systems, rehabilitation robots designed for home use could enable increased accessibility and intensity of therapy for stroke survivors. To move upper extremity rehabilitation robots from the clinic to the home, the designs must become smaller, lighter, and less complex. One path to reducing the size of the robot’s hardware is to replace conventional actuators with smaller designs utilizing the unique properties of smart materials. As a first step towards reducing the size of upper extremity rehabilitation robots, this paper presents results from a characterization study of a prototype electrorheological fluid. The fluid’s dynamic yield stress was first measured using a modified controlled stress rheometer. A testbed was then developed to analyze the mechanical performance of a custom brake filled with the fluid. System parameters measured included braking torque at varying electric field strengths as well as the fluid’s speed of response. Maximum torque output was 4.80 N-m at an electric field strength of 3 kV/mm. Experimental results also indicate that the fluid’s activation and relaxation times will enable sufficient control bandwidth for the desired application. However, non-linear effects, such as field-dependent hysteresis, are significant and may require compensation from the controller supervising interaction between the robot and patient.

The availability of low-cost, readily programmable digital hardware offers numerous opportunities for novel modeling and control approaches. One such opportunity is the realization of hardware modeling of distributed dynamic systems. Such models could be useful for control algorithms that require high-fidelity models operating in real-time. The ultimate goal is to utilize digital systems with programmable hardware. As a proof-of-concept, multiple discrete microcontrollers have been used to emulate how programmable hardware devices may be used to simulate a distributed vibrating system. Specifically, each microcontroller is treated as a single vibrating mass with stiffness and damping coupling between the masses. Each microcontroller has associated position and velocity variables. The only additional knowledge required to compute the acceleration of each “mass” is thus the position and velocity of each immediate neighboring mass/microcontroller. The computation time is independent of the number of nodes; adding nodes results in no reduction in processing speed. Consequently, the computational approach will be applicable to very high order models. Practical implementation of such models will require digitally programmable hardware such as field-programmable gate arrays (FPGA), however an added benefit will be a still greater reduction in cost, as multiple microcontrollers are replaced by a single FPGA. It is expected that the hardware modeling approach described in this work will have application not only in the field of vibration modeling and control, but also in other fields where control of distributed dynamic systems is desired.

Additive manufacturing ( i.e. 3D printing) has only recently be shown as a well-established technology to create complex shapes and porous structures from different biocompatible metal powder such as titanium, nitinol, and stainless steel alloys. This allows for manufacturing bone fixation hardware with patient-specific geometry and properties (e.g. density and mechanical properties) directly from CAD files. Superelastic NiTi is one of the most biocompatible alloys with high shock absorption and biomimetic hysteresis behavior. More importantly, NiTi has the lowest stiffness (36–68 GPa) among all biocompatible alloys [1]. The stiffness of NiTi can further be reduced, to the level of the cortical bone (10–31.2 GPa), by introducing engineered porosity using additive manufacturing [2–4]. The low level of fixation stiffness allows for bone to receive a stress profile close to that of healthy bone during the healing period. This enhances the bone remodeling process (Wolf’s Law) which primarily driven by the pattern of stress. Also, this match in the stiffness of bone and fixation mitigates the problem of stress shielding and detrimental stress concentrations. Stress shielding is a known problem for the currently in-use Ti-6Al-4V fixation hardware. The high stiffness of Ti-6Al-4V (112 GPa) compared to bone results in the absence of mechanical loading on the adjacent bone that causes loss of bone mass and density and subsequently bone/implant failure. We have proposed additively manufactured porous NiTi fixation hardware with a patient-specific stiffness to be used for the mandibular reconstructive surgery (MRS). In MRS, the use of metallic fixation hardware and double barrel fibula graft is the standard methodology to restore the mandible functionality and aesthetic. A validated finite element model was developed from a dried cadaveric mandible using CT scan data. The model simulated a patient’s mandible after mandibular reconstructive surgery to compare the performance of the conventional Ti-6Al-4V fixation hardware with the proposed one (porous superelastic NiTi fixation plates). An optimized level of porosity was determined to match the NiTi equivalent stiffness to that of a resected bone, then it was imposed to the simulated fixation plates. Moreover, the material property of superelastic NiTi was simulated by using a validated customized code. The code was calibrated by using DSC analysis and mechanical tests on several prepared bulk samples of Ni-rich NiTi. The model was run under common activities such as chewing by considering different levels of the applied fastening torques on screws. The results show a higher level of stress distribution on mandible cortical bone in the case of using NiTi fixation plates. Based on wolf’s law it can lead to a lower level of stress shielding on the grafted bone and over time bone can remodel itself. Moreover, the results suggest an optimum fastening torque for fastening the screws for the superelastic fixations causes more normal distribution of stress on the bone similar to that for the healthy mandible. Finally, we successfully fabricated the stiffness-matched porous NiTi fixation plates using selective laser melting technique, and they were mounted on the dried cadaveric mandible used to create the finite element model.

This contribution focuses on the application potential of active fiber reinforced polymer (FRP) structures with integrated shape memory alloy (SMA) elements for new aerodynamic functions. The advantages of hybrid SMA FRP structures are highlighted and promising application concepts are discussed. Main focus is the development of an active aerodynamic airfoil. Beginning with the idea of an adaptive airfoil, able to bear an application relevant down force at a relatively high deflection, the design process starts with an evaluation of different airfoil actuation concepts. A SMA powered bending beam is a part of the airfoil itself. Applying the finite element method with a suitable model for the active hybrid material, an effective selection of material and design is possible. After manufacturing and assembling of the active hybrid airfoil a comparison of experimental results and simulation is the first proof of success. Finally, the installation of an integrated hardware setup with power source, control and the active airfoil, demonstrating actuation on demand, verifies the potential of the new approach.

This conceptual research focuses on identifying damage precursors in carbon fiber reinforced polymer laminates. By coupling integrated in situ sensing elements (magnetostrictive particles) and multi-scale ultrasonic inspection (Quantitative Ultrasonic Imaging) with minimum hardware the authors are able to capture and gain an understanding of damage precursors. Preliminary damage precursors can be identified and quantified and correlated to a particular failure mode(s) and/or fabrication process accelerating the need for a sensing/repair strategy that could be implemented to capture the specific precursor prior to the onset of cracks. Capturing and mitigating damage precursors ahead of micro-crack formulation will slow the evolution of the damage precursors to micro-cracks, mitigate adverse loading environment, and develop techniques to reduce stress and loading below the endurance limit to keep it from being fatigued.

Shape memory alloy (SMA) actuators have recently been developed in the form of torsional tubes that can undergo large twisting deformations. Wing twisting has been investigated as a means to reduce induced drag in cruise conditions in small aircraft, but the actuation hardware required to generate wing twist at larger scales is prohibitively cumbersome. Replacing conventional actuators with SMA torque tubes provides a way to minimize weight of the twisting system but wing structural design then becomes more challenging. This analysis-driven design study examines an SMA torque tube as applied to the twisting wing design problem. A composite skin is considered to maximize wing performance under combined twist and aerodynamic loads. The SMA has been analyzed using a 3-D thermo-mechanical constitutive model while a preliminary study was performed to determine a composite lamina with appropriate unidirectional properties. An optimization was then completed to find an ideal composite layup. This optimization also included the design of a passive torque tube used to properly balance the twist generated by the SMA against that required in the wing. Localized buckling in the twisted wing was also considered and avoided. The product of this optimization was a composite wing that twisted while considering constraints of stress on the SMA. To validate the controllable use of SMA actuators, testing was completed on a scaled wing model fitted with a rapid prototype shell.

Mandibular segmental defect reconstruction is most often necessitated by tumor resection, trauma, infection, or osteoradionecrosis. The standard of care treatment for mandibular segmental defect repair involves using metallic plates to immobilize fibula grafts, which replace the resected portion of mandible. Surgical grade 5 titanium (Ti-6Al-4V) is commonly used to fabricate the fixture plate due to its low density, high strength, and high biocompatibility. One of the potential problems with mandibular reconstruction is stress shielding caused by a stiffness mismatch between the Titanium fixation plate and the remaining mandible bone and the bone grafts. A highly stiff fixture carries a large portion of the load (e.g., muscle loading and bite force), therefore the surrounding mandible would undergo reduced stress. As a result the area receiving less strain would remodel and may undergo significant resorption. This process may continue until the implant fails. To avoid stress shielding it is ideal to use fixtures with stiffness similar to that of the surrounding bone. Although Ti-6Al-4V has a lower stiffness (110 GPa) than other common materials (e.g., stainless steel, tantalum), it is still much stiffer than the cancellous (1.5–4.5 GPa) and cortical portions of the mandible (17.6–31.2 GPa). As a solution, we offer a nitinol in order to reduce stiffness of the fixation hardware to the level of mandible. To this end, we performed a finite element analysis to look at strain distribution in a human mandible in three different cases: I) healthy mandible, II) resected mandible treated with a Ti-6Al-4V bone plate, III) resected mandible treated with a nitinol bone plate. In order to predict the implant’s success, it is useful to simulate the stress-strain trajectories through the treated mandible. This work covers a modeling approach to confirm superiority of nitinol for mandibular reconstruction. Our results show that the stress-strain trajectories of the mandibular reconstruction using nitinol fixation is closer to normal than if grade 5 surgical titanium fixation is used.

This paper presents design and testing of a haptic keypad system using an array of haptic actuators. The research goals are to construct a prototype haptic keypad system using haptic actuators and to evaluate the performance of the prototype keypad for haptic rendering. To this end, an MR haptic actuator was designed and fabricated such that it can convey realistic force feedback to users. To demonstrate haptic applications of the MR actuator, a haptic keypad system was constructed, which consists of following components: (1) 3 × 3 array of haptic actuators, (2) 3 × 3 array of force sensing resistors (FSR), (3) a controller including a micro-processor, a current amplifier and a wireless communication module, (4) a graphic display unit with PC. After constructing a prototype keypad system, a haptic rendering technology was employed to interface the hardware keypad system with test software (virtual environment). The prototype system enabled human operators to interact with the target contents in a virtual environment more intuitively. The evaluation results show a feasibility of applications of MR fluids-based haptic actuators in real-world mobile applications.

The NASA Ames Research Center (NASA Ames) Center Chief Technologist (CCT) Office sponsors the Advanced Digital Materials and Manufacturing for Space (ADMMS) Initiative, which focuses on advanced manufacturing technologies for space, including identifying several target products, areas and applications, approaches for advanced manufacturing, mechanisms for collaboration, and complementary facilities. The pilot project for this initiative is the Multi-Purpose Avionics Core Element (M-PACE). The primary goal of M-PACE is to demonstrate advanced manufacturing techniques, such as additive manufacturing and Digital Materials, to minimize the cost of cube satellites and increase their modularity. M-PACE will be designed and built at the NASA Ames’ SpaceShop, which is a state-of-the-art advanced manufacturing facility built for NASA researchers to formulate ideas for projects. The final products of M-PACE are several completed side panels of a one-unit (1U) (10 cm cube) cube satellite prototype built using commercial off-the-shelf (COTS) components, which will show the basic functionality of the internal payload by connecting it to the side panels for power and other subsystem capabilities. Within the structure, we are investigating the use of Digital Materials, which are universal building materials with the ability to increase precision and ease of assembly and disassembly of three dimensional (3D) objects. M-PACE will use COTS power systems and open-source hardware and software to distribute data through Ethernet through the use of snap-fit card connectors. Similar to Peripheral Component Interconnect (PCI) Express cards, we envision the spacecraft subsystems and payloads to be on a PC104-like board that will slide into the side panel connectors to enable distribution of power and data. This design has the potential to greatly reduce the cost of Cube Satellite testing and integration due to the absence of wires and ease of access to internal boards for any necessary modifications.

Shape Memory Alloys (SMAs) have many promising applications in the aerospace, automotive, and energy industries. However, due to a lack of understanding of their actuation fatigue, applications are sometimes limited to non-structural or non-critical components. This paper addresses the actuation fatigue characteristics of a specific SMA, equiatomic Nickel-Titanium (NiTi), with varying heat treatments, as well as different methods for assessing actuation fatigue response, including improved testing procedures and distributed extension measurement methods. Heat treatments ranged from 350°C to 400°C for one to three hours. Dogbone specimens processed from heat treated NiTi sheets were mechanically loaded on test frames which provided resistive heating and forced convective cooling with dry air via vortex tubes. Two mechanical loading schemes were utilized: constant uniaxial load (initial stress of 200MPa) and a linear or spring load centered at 200MPa (and ranging from approximately 150MPa to 250MPa). Linear loading schemes were introduced in order to better simulate actuation in an aerospace application, such as the morphing of semi-rigid surfaces. Specimens were thermally cycled to full actuation with a time-based control scheme developed in LabVIEW. Fatigue responses varied widely as a result of different heat treatments and loading schemes. Due to the main failure mechanism being high localized extension (necking) for the constant loading schemes, additional hardware and software were developed to visually capture extension distribution over specimen length. By analyzing actuation characteristics (e.g. transformation strain) and fatigue mechanisms, the ideal post-processing for actuator applications was determined. Utilizing the local extension distribution evolution over the fatigue life of NiTi specimens as well as postmortem analysis of the failure surfaces allowed for the failure modes to be determined for each heat treatment.

In many applications, the detection of changing gaseous or liquid concentration within an environment is accomplished by monitoring the shift in resonance frequency of a microelectromechanical system designed to adsorb the target analyte. Recently, mass sensing using the onset and crossing of a dynamic bifurcation has been shown to reduce the mass threshold which may be detected. This approach effectively replaces detection of an analog quantity resolved by hardware capability (phase shift or resonant frequency) with a digital quantity having fundamental resolution restricted by system noise (crossing the bifurcation). While promising, successful sensing with oscillators continually excited near a system bifurcation is practically limited in performance by repeatable characteristics close to the critical crossing frequency and the passive detection ability of the sensors has not yet extended to mass quantization over a period of time. In this research, we explore an alternative method to exploit bifurcation for mass sensing by utilizing a new sensor system composed of a small bistable element within a primary linear host sensor that helps alleviate these concerns. The proposed system design provides adjustable control of the rate at which the bifurcation is crossed, helping to tailor the sensitivities of the system encountered in the transition region, introduces new bifurcations to exploit, and lends the opportunity to utilize the numerous bifurcation phenomena sequentially to denote mass accumulation quantity occurring between consecutive jump events. The conceptual underpinnings of the method are presented in detail and example operational trials are demonstrated by simulation to expound its operation and adjustability. Discussion is provided to evaluate the system in terms of existing bifurcation-based mass sensing approaches and to outline remaining goals.

Pneumatic artificial muscles (PAMs) are lightweight, flexible actuators capable of higher specific work than comparably-sized hydraulic actuators at the same pressure and electric motors. PAMs are composed of an elastomeric bladder surrounded by a helically braided sleeve. Lightweight, compliant actuators are particularly desirable in portable, heavy-lift robotic systems intended for interaction with humans, such as those envisioned for patient assistance in hospitals and battlefield casualty extraction. However, smooth and precise control remains difficult because of nonlinearities in the dynamic response. The objective of this paper is to develop a control algorithm that satisfies accuracy and smooth motion requirements for a two degree-of-freedom manipulator actuated by pneumatic artificial muscles and intended for interaction with humans, such as lifting a human. This control strategy must be capable of responding to large, abrupt variations in payload weight over a high range of motion. In previous work, the authors detailed the design and construction of a proof-of-concept PAM-based manipulator. The present work investigates the feasibility of combining output feedback using proportional-integral-derivative control or fuzzy logic control with model-based feedforward compensation to achieve improved closed-loop performance. The model upon which the controller is based incorporates the internal airflow dynamics, the geometric parameters of the pneumatic actuators, and the arm dynamics. Simulations were performed in order to validate the control algorithm, guide controller design, and predict optimal gains. Using real-time interface software and hardware, the controller was implemented and experimentally tested on the manipulator. Performance was evaluated for several trajectories, and different payload weights. The effect of varying the feedforward gain was also analyzed. Model refinement further improved performance.

The paper presents the design, development, and assembly of Structural Health Monitoring (SHM) experiments intended to be launch in space on a sub-orbital rocket flight as well as a high altitude balloon flight. The experiments designed investigate the use of both piezoelectric sensing hardware in a wave propagation experiment and piezoelectric wafer active sensors (PWAS) in an electromechanical impedance experiment as active elements of spacecraft SHM systems. The list of PWAS experiments includes a bolted-joint test and an experiment to monitor PWAS condition during spaceflight. Electromechanical impedances of piezoelectric sensors will be recorded in-flight at varying input frequencies using an onboard data acquisition system. The wave propagation experiment will utilize the sensing hardware of the Metis Design MD7 Digital SHM system. The payload will employ a triggering system that will begin experiment data acquisition upon sufficient saturation of g-loading. The experiment designs must be able to withstand the harsh environment of space, intense vibrations from the rocket launch, and large shock loading upon re-entry. The paper discusses issues encountered during design, development, and assembly of the payload and aspects central to successful demonstration of the SHM system during both the sub-orbital space flight and balloon launch.

Wireless ultrasound inspections using Piezoelectric Wafer Active Sensors (PWAS) are attractive for Structural Health Monitoring (SHM). However, the impedance mismatch between the PWAS and the wireless transponder reduces the wirelessly transmitted signal strength. Electrical Impedance Matching (EIM) circuit can be introduced to maximize the power transmission between the PWAS and the wireless transponder. This paper discusses the wireless excitation of ultrasound as well as the design, simulation, and characterization of the EIM networks for PWAS. To maximize power transmission, a two port EIM network was developed using a computerized smith chart. The equivalent circuit of the PWAS and the EIM network were then combined to establish the equivalent circuit of the matched transducer. Computer simulations were carried out to evaluate the gain, the bandwidth, and the sensitivity of the EIM networks. Two-port EIM networks were implemented for both the actuator and the sensor in an ultrasound pitch-catch inspection system. The performance of the pitch-catch systems with and without the EIM networks was compared. Detailed analysis, simulation, hardware implementation, and measurement results are presented.

Due to their ability to change into a previously imprinted actual shape through the means of thermal and electrical activation, shape memory alloys (SMA) are suitable as actuators. To apply these smart materials to a wide range of high-speed applications like valves or safety systems, an analysis of the application potential is required. The detection of inner electrical resistance of SMA actuators allows gauging the actuator’s stroke. By usage of a microcontroller a smart system without any hardware sensors can be realized which protects the system from overheating during high-current activation. The publication concentrates on different experimental data on high-speed actuation under 20ms and the potentials in the field of industrial applications. The paper gives an overview about different controlling methods for SMA-actuators, experiments concerning the resistance behavior of SMA and the development of systems using a resistance control feedback signal during high-speed activation.

An ankle foot orthosis (AFO) is a device that provides a controlled force to compensate for the muscle deficiencies in the ankle and helps normalize the gait of the patient. Evidence has indicated that there exists an optimal match correlating the patient’s gait related problems and the AFO stiffness. AFO ankle stiffness is measured by the moment around the ankle joint exerted by the AFO per degree of ankle joint rotation. To date, several testing devices and procedures have been developed to assess the stiffness characteristics of AFOs. Most of the devices are manually driven and may not exactly replicate human leg motion. Objective of developing an automated testing assembly is to identify stiffness characteristics of passive AFOs so as to develop an active AFO with shape memory alloy. We have developed an assembly using aluminum T-slotted profiles, single flange linear bearings, and living hinges from 80/20 Inc. Angle measurement was done by mounting Digital Protractor on the shank segment. The whole assembly was mounted on BOSE ElectroForce 3330 test instrument. dSPACE hardware-in-the-loop solution was used for real time data capture of force and angle sensor output. After assessing the characteristics of passive AFO we incorporated SMA wire in the AFO. Similar tests were conducted to evaluate effect of SMA wires on the overall stiffness of an AFO. The results confirm that SMA wires provide stiffness variation such a way that AAFO can be developed to achieve stiffness variation close to normal ankle stiffness.