Xiaoning Jiang

The proposed research aims to understand the relationship between the domain configuration of ferroelectric (FE) materials and macroscopic properties, which will lead to an optimal microstructure tuning strategy for enhanced properties and new material development. Despite the significant amount of reports on domain engineering techniques for FE properties enhancement, understanding of the associated fundamental mechanism remains inconclusive. It is still unclear whether it is preferable to decrease the domain size or increase the density of the domain walls. There has still been a lack of knowledge on the domain size dependence in the intrinsic (i.e., domain) and the extrinsic (i.e., domain wall) contribution to the macroscopic material behavior due to the limitations in the conventional experimental techniques (e.g., XRD and PFM). We propose a novel approach utilizing X-ray photon correlation spectroscopy (XPCS) based on the coherent synchrotron source to investigate the effects of domain/domain wall contributions to the in-situ piezoelectric behaviors. Our preliminary results indicate that XPCS can detect the dynamic fluctuation in the Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) single crystal samples varied by the domain wall density or the domain size. We also demonstrated the feasibility of controlling domain size and domain wall density by electric poling and creating domain heterogeneity using composite nanoelectrodes. These preliminary results encouraged us to search for answers to the following research questions: What are the domain scaling effects on the intrinsic and extrinsic contributions to piezoelectricity? How does the large piezoelectricity emerge from the heterogeneous domain configuration? To address those questions, three objectives are proposed: 1) To distinguish the intrinsic and extrinsic response signals using the ���two-field��� decorrelation approach, 2) To investigate the effect of the intrinsic and extrinsic responses varied by the domain configuration on the macroscopic piezoelectricity and 3) To reveal the role of local heterogeneities in determining the overall material response in consideration of both the intrinsic and extrinsic contributions.

Assistive devices such as functional electrical stimulation (FES) and powered exoskeletons promote independence and recovery after a spinal cord injury or a cerebrovascular accident such as stroke. Substantial gains in recovery hinges on designing assistance synchronous with a user's impaired motor intent and actively encouraging them to bear effort. Including the intent or user's effort in their closed-loop control mostly relies on electromyography (EMG)-based models of limb force. However, EMG is a poor surrogate for modeling impaired muscle force generation as it fails to capture complex interaction between muscle's contractile behavior and the motor intent signals. Our recent preliminary data showed that a predictive model that fuses EMG with ultrasound predicts muscle forces with higher fidelity than an EMG-based approach. The combination allows incorporating ultrasound-derived mechanical measures of the muscle's contractile behavior, such as pennation angle, fascicle length, strain, strain rate, etc. Ultrasound-derived muscle strain measures also significantly correlated with the muscle force changes due to FES-induced muscle fatigue. Potentially, using ultrasound enables highly accurate monitoring of muscle force in real-time, which in turn facilitates symbiotic adjustment of exoskeleton assistance. Despite this intriguing proposition, a lack of wearable ultrasound sensors hinders the practical integration of ultrasound with an exoskeleton or FES. Although wearable single ultrasound transducers and EMG electrodes exist, wearable multiple US transducers embedded in an array for smart health applications are non-existent. If successfully translated to practice, an ultrasound-based sensing array would help visualize spatially distributed muscle fibers' contractile behavior and muscle force production, preferably in more than one imaging plane. When merged with EMG and stimulation electrodes, the array would capture descending volitional neural signals and multiple muscles' stimulation. Acoustically matched ultrasound transducers and stimulation electrodes permit simultaneous monitoring and actuation (via FES) of spatially distributed muscle fibers. This unique merger of technologies is also motivated to abate muscle fatigue effects due to FES, which, if unaddressed, could potentially cause falls or unstable control of an exoskeleton and its integrated FES system. Our objective here is to create a new wearable novel multimodal muscle-machine interface that combines dynamic in vivo ultrasound imaging with EMG signals. The innovative combined use of ultrasound and EMG in the muscle-machine interface provides objective in vivo visualization, and muscle action measurement caused volitionally by neural signals from the spinal cord or artificially via FES. The main objectives of the proposal are 1) development of a flexible and stretchable, body-conforming sensing array composed of EMG electrodes and ultrasound transducers, 2) use the feedback from the sensing arrays to synchronize exoskeleton assistance with a user's impaired motor intent, and 3) validate the sensing array to measure muscle force changes due to a new FES technique that uses a spatially distributed sequential stimulation (SDSS) method, and 4) use the feedback from the sensing array to coordinate the SDSS method with an exoskeleton.

The research goal is to understand how thermal conductivity of ferroelectric materials can be switched with external electric fields and how this switching behavior can be engineered through the reconfigurable ferroelectric domains. This is motivated by the possible new paradigm of energy regulation for harvesting, saving, and management if dynamic control of thermal energy transport can be achieved. Seeking solutions for thermal control in materials are limited by the traditional toolkit of linear, static, and passive thermal components, such as thermal resistors and thermal capacitors. This paucity of thermal options pales in comparison to the rich selection of highly nonlinear, switchable, and active components in the electrical domain. Since switchable and nonlinear thermal components are not nearly as mature as their electrical counterparts, the pursuit of these thermal components remains a motivating interdisciplinary challenge to researchers for years. In this project, we will measure the thermal conductivity- domain structure correlation to reveal the effects of domain walls and domain engineering. The studies on the manipulation of domain walls using domain engineering has translational implications for a range of applications, such as infrared imaging, solid-state cooling, and waste-heat energy conversion due to pyroelectric and electrocaloric effects, and sensors based piezoelectric effects.

In this project, a dual mode ultrasound array will be developed for thermal strain imaging.

Over 11 million people in the United States are affected by unintentional and uncontrollable rhythmic movements due to parkinsonian tremor, essential tremor, and cerebellar tremor. Individuals experiencing tremors in the hands and arms face difficulty performing activities of daily living. Electrical stimulation that works by stimulating motor (efferent) nerves of antagonistic muscles is a potential wearable option for tremor suppression when medication is ineffective, but prior to the pursuit of effective yet invasive (and costly) brain surgery. However, the two significant drawbacks of electrical stimulation are stimulation-induced muscle fatigue and discomfort due to high levels of stimulation. An intriguing new method of stimulation targets afferent nerve fibers to inhibit tremor in antagonistic muscles. These fibers relay sensory information on muscle position and velocity back to the spinal cord. By stimulating these fibers, spinal neural circuitry can be modulated that in turn inhibits muscle activity due to the descending tremor inputs from the brain. The new method uses low stimulation intensity levels, which is comfortable and fatigue resistant. However, determining the stimulation parameters that can effectively disrupt tremors remains challenging, largely due to the numerous interactions that can occur between stimulated afferent nerves and the descending tremorgenic neural inputs. These interactions occur through a complex neural circuitry whose modeling is difficult and computationally intensive for determining stimulation parameters in real-time. Direct measurements of muscle velocity and length changes with ultrasound can help create a data-driven model of afferent stimulation and help design individual-specific afferent stimulation parameters. However, ultrasound has never been used for tremor suppression control. Real-time algorithms and models that map ultrasound-derived muscle activity to oscillating limb displacement will be established. These algorithms and models will automate individual-specific stimulation parameters for tremor suppression. Lastly, for future clinical translation wearable ultrasound arrays that monitor multiple muscles will be developed.

In this project, alternating currenting poling of ternary relaxor-PT piezoelectric single crystals will be investigated for enhanced properties.

In this project, we propose to optimize a miniaturized multidirectional ultrasound transducer prototype and simulate the energy deposition profiles generated by this prototype.

In this project, a forward-viewing catheter delivered microbubble assisted sonothrombolysis system will be developed for rapid and effective treatment of deep vein thrombus. Intravascular transducers will be designed, fabricated and characterized, followed by in-vitro, ex-vivo and in-vivo thrombolysis tests.

In this pilot project, small aperture high intensity ultrasound transducers will be devloped and integrated into catheters, followed by in-vitro, ex-vivo and in-vivo intratumoral therpy tests.

A customized aixACCT piezoelectric system will be purchased for extensive characterizations of relaxor-PT single crystals with engineered nanodomains.