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- All Subjects: Materials Science
The two general categories of structural health monitoring (SHM) systems include passive and active monitoring. Active SHM systems utilize an input of energy to monitor the health of a structure (such as sound waves in ultrasonics), while passive systems do not. As such, passive SHM tends to be more desirable. A system could be permanently fixed to a critical location, passively accepting signals until it records a damage event, then localize and characterize the damage. This is the goal of acoustic emissions testing.
When certain types of damage occur, such as matrix cracking or delamination in composites, the corresponding release of energy creates sound waves, or acoustic emissions, that propagate through the material. Audio sensors fixed to the surface can pick up data from both the time and frequency domains of the wave. With proper data analysis, a time of arrival (TOA) can be calculated for each sensor allowing for localization of the damage event. The frequency data can be used to characterize the damage.
In traditional acoustic emissions testing, the TOA combined with wave velocity and information about signal attenuation in the material is used to localize events. However, in instances of complex geometries or anisotropic materials (such as carbon fibre composites), velocity and attenuation can vary wildly based on the direction of interest. In these cases, localization can be based off of the time of arrival distances for each sensor pair. This technique is called Delta T mapping, and is the main focus of this study.
Perturbation-based Training on Compliant Surfaces to Improve Balance in Children with Cerebral Palsy
Children with cerebral palsy suffer from balance deficits that may greatly reduce their quality of life. However, recent advancements in robotics allow for balance rehabilitation paradigms that provide greater control of the training environment and more robust measurement techniques. Previous works have shown functional balance improvement using standing surface perturbations and compliant surface balancing. Visual feedback during balance training has also been shown to improve postural balance control. However, the combined effect of these interventions has not been evaluated. This paper presents a robot-aided rehabilitation study for two children with cerebral palsy on a side-specific performance-adaptive compliant surface with perturbations. Visual feedback of the participant’s center of pressure and weight distribution were used to evaluate successful balance and trigger perturbations after a period of successful balancing. The platform compliance increased relative to the amount of successful balance during each training interval. Participants trained for 6 weeks including 10, less than 2 hours long, training sessions. Improvements in functional balance as assessed by the Pediatric Balance Scale, the Timed 10 Meter Walk Test, and the 5 Times Sit-to-Stand Test were observed for both participants. There was a reduction in fall risk as evidenced by increased Virtual Time to Contact and an increase in dynamic postural balance supported by a faster Time to Perturb, Time to Stabilize, and Percent Stabilized. A mixed improvement in static postural balance was also observed. This paper highlights the efficacy of robot-aided rehabilitation interventions as a method of balance therapy for children with cerebral palsy.