This Small Business Innovation Research (SBIR) Phase I project aims at developing a key sensor component in a wireless wearable system for weight and physical activity management in everyday life. The unique advantage of the proposed wearable system is its ability to monitor and provide feedback regarding body weight, physical activity levels and caloric energy expenditure throughout a waking day (not just exercise) while being virtually imperceptible by the user and others. The main research objective of this SBIR project is development of a novel method for seamless weight measurement by a capacitive sensor embedded in the shoe insole. The research will involve design of the sensor plate topology, characterization of the sensor in loading experiments, and implementation of software methods for real-time capacitive measurements focused on lowering the total cost of the sensor system. The anticipated technical result is a durable and low-cost sensor that will enable creation of the wireless biofeedback device for weight and physical activity management.
The broader impact/commercial potential of this project can potentially involve a large portion of the U.S. population. Most Americans and many adults worldwide (over 1 billion people) are overweight or obese. Studies show that the effects of overweight and obesity on public health are comparable to those of cancer. Since physical activity is one of the best methods to prevent weight gain and maintain weight loss, there is an urgent need to develop tools that assist in increasing physical activity and promote wide-scale modification of lifestyle behaviors. The proposed wireless wearable system will facilitate bringing a new kind of a physical activity monitoring device to market. This wireless system can be used by individuals interested in weight management, active adults and athletes. The system will facilitate weight loss and help to prevent weight gain by encouraging small and sustainable changes in daily physical activity via an interactive electronic interface. In the long run, the proposed system may contribute to lowering the nation?s spending on obesity-related healthcare expenses, currently estimated at $147 billion a year. The technology will have numerous markets: Health & Fitness, Athletics, Consumer Fitness, Medical Rehab, Research, and even computer games.
Research accomplishments of the Phase I project A number of tasks have been completed for this Phase I project to accomplish the initial objectives. All objectives have been fully met with satisfactory results: A capacitive pressure sensor topology in which user’s foot is one of the plates and capacitance is proportional to applied force was developed; The capability of such sensor to detect the wearer even if no force is applied to the sensor was confirmed; A cost-saving microcontroller-based algorithm for measuring of capacitance was designed; Several sensor configurations were characterized and the best configuration with accuracy of approximately ±1% in weight measurement was chosen based on the results of loading tests; An analytical model for the sensor was developed; A Bluetooth-based wireless datalogger was designed and capacitive sensor data from a real human foot were acquired in real time. Overall, the work in Phase I resulted in a successful design of the key component of the novel activity monitoring system (Fit Companion) and prepared the project for moving into Phase II. The results of this Phase I grant indicate the robustness of the proposed approach to in-shoe pressure measurements using a capacitive sensor of a in which the foot is one of the plates. Advantages of the designed wireless pressure sensor include: Ability to detect user wearing the shoes even if no pressure is applied to the insole (for example, in a sitting posture). This capability is critical for detecting compliance in wearing the wireless physical activity monitor and saving battery life by switching the device into a sleep mode when the shoe is not worn. Ability to accurately estimate weight. While the shoe cannot be a direct replacement of a floor scale, achieved 1% accuracy in weight estimation will allow for greatly increased accuracy in energy expenditure prediction. As an example, the shoe will be able to detect when the user carries an additional load (for example, a mother carrying a newborn) and thus expends more energy than usual. We expect that through further statistical processing, the shoe will be able to provide reliable weight trends over past weeks and months. The weight measurement capability can also be used to detect and warn the user of potentially harmful peak loads during physical activity and prevent trauma. Low cost. The designed configuration of the sensor has a substantially lower manufacturing cost not only compared to that of a force sensitive resistor but also other types of capacitive sensors available on the market. The key contributors here are use of the foot as one of the sensor plates (and thus avoiding the cost of force sensitive resistors and the cost of the manufacturing a layered capacitive sensor) and extremely simple measurement circuit that can be implemented virtually on any microcontroller, including the cheapest models on the market today. Potential high reliability. While the reliability was not assessed in this study, the body of existing research convincingly suggests much higher reliability of a capacitive sensor compared to force sensitive resistors. Since the developed capacitive sensor also has only a single plate (the foot is another plate), the reliability should even be higher than that of traditional two-plate sensors.
