The inertial sensing technologies, including accelerometers and gyroscopes, have demonstrated invaluable importance in clinical practices. They allow a precise measurement of human beings’ motion behavior, having built the foundation of gait analysis, monitoring of physical activities, and prosthesis of human balance disorders. The miniaturization of the device enabled by micro-electro-mechanical system (MEMS) technology is expected to elevate the clinical motion measurement to a new level.
In the present work, the principle, design and testing of a microscale liquid state inertial sensing system, different from traditional inertial sensors using silicon based solid materials, for the human body motion measurement is demonstrated. The sensing technology uses a comparable structure as the natural motion sensing organ, the human vestibular system, and is expected to provide a new paradigm for the sensing of human body motion. The system uses a liquid droplet as the inertial component. Its movement inside the sensor configuration is detected by an array of addressable electrodes. The relative movement of the droplet to its frame indicates the direction and magnitude of the external acceleration.
In order to realize the sensing technology, the work starts with the investigation of surface science leading to a superhydrophobic surface, which enables sensitive droplet motion. Afterwards, the dynamic response of the liquid droplet to various external stimuli is studied using both theoretical and experimental tools. The on-chip electrical measurement by the addressable electrode array is obtained with the assistance of a data Acquisition (DAQ) circuitry system. Characterization of the sensing system shows that the system can sensitively detect motion behaviors in the low frequency range, 0-20Hz, which covers the frequency range of daily human body movement. This technology exhibits promising potential for clinical motion measurement, especially for the prosthesis of human balance disorders.
The bio-inspired inertial sensor is expected to partially or entirely accomplish the motion sensing task for vestibular disordered patients. Therefore, it can be applied in the engineering prosthesis system to restore their balance function. The sensing system possesses advantages of simple structure, low cost, low power consumption and immunity to external electromagnetic noises, which holds the potential for mass application in medical practices.
In addition, the research in surface wettability regulation, droplet dynamics and electrical measuring methods also contribute technology foundations for digital microfluidic devices.