University of Hawaii

Electrical Engineering

Robert Nakata PhD Defense

Date: 2018-04-03           Add to Google Calendar
Time: 12:00pm-1:30pm
Location: iLab (building 37)
Speaker: Bob Nakata, PhD Candidate


Motion capture of human body kinematics has applications for the military, first responders, sports performance monitoring, physical therapy, movie animation and the gaming industry. Existing commercially available body motion capture sensors include fixed location camera based systems, IMU based sensors and Ultra Wide Band (UWB) sensors. Infrastructure based senors such as cameras and RF localization sensors are limited by range of coverage and require fixed location external sensors that limit the mobility of the tracked subject. Wearable IMU sensors have performance limitations due to accumulated accelerometer drift and magnetic field distortions resulting in position errors. To overcome these limitations, a stand-alone system that permits mobile motion capture has been developed using sensor fusion of RF Direction of Arrival (RFDOA) and Inertial Measurement Units (IMUs).

A proof-of-concept RFDOA prototype for motion capture was designed and built using a 16 element switched phased array antenna that measures the amplitude and phase of a RF signal emitted from tags attached to a moving appendage, simulated by a robotic arm that provides a position reference. Measured results were a position mean error of 0.1 degrees with respect to the respect to robot arm reference.

Similar techniques can be implemented for motion compensation of a mobile or handheld platform where the primary sensor payload requires a stable sensor platform. A mobile platform, such as an Unmanned Aerial Vehicle (UAV) platform is subject to unwanted motion due to aerodynamic disturbances, resulting in the corruption of phase sensitive signals of interest detected by an on-board radar sensor. Motion compensation and platform stabilization enable the deployment of a radar sensor on a UAV capable of detecting respiration vital signs on immobilized victims.

Secondary sensors, including ultrasonic and radar sensors, were evaluated for sensor fusion to mechanically stabilize the platform and to remove the platform motion effects using a phase compensation algorithm. Signal to Interference Ratio improvements ranged from 2.1 dB to 29 dB with both mechanical platform stabilization and the motion compensation algorithm enabled.