  This work presents a triboelectric nanogenerator-based (TENG) therapeutic
stress ball to provide gesture monitoring and physiological data on patients
requiring physical therapy of various degrees. The device utilizes a 5-layer
stack of silicone and braided silver-coated nylon rope electrodes to create a
sensor network that monitors 40-points across the surface of a semi-spherical
prototype. A modified version of a standard ECG circuit was utilized to provide
proper loading, noise rejection, filtering, and phase of the TENG signals along
with multiplexing of the many electrodes. All system components were selected
with a final embedded system in mind. Testing of the device was conducted
utilizing an Arduino Uno and an EVAL-AD5940BIOZ evaluation board for
electrodermal activity for stress and/or pain after exercise. An accelerometer
was included for device activation and hand tremor detection. Upon testing, the
self-powered TENG sensors produce positive impulses upon contact and negative
impulses upon release of contact from the surface of the ball. Furthermore,
finger removal detection was demonstrated by capturing the associated negative
impulse by maintaining the bipolar signal in our conditioning circuit. EDA
results indicate silver-coated nylon as a potentially good dry-electrode which
can be used with even more electrodes for bio-impedance or ECG capture to
further expand the device functionality. A MATLAB-based GUI was designed to
provide the user with data tracking and visual monitoring of the data via
serial communication from the microcontrollers. Finally, it should be noted
that this provides a means for low-cost low-power gesture tracking without the
use of flexible capacitive grid arrays and provides the user with a pleasant
tactile experience that one expects form a stress ball due to its unique
material design.
