![]() ![]() ![]() Besides the solid-state sensors, many innovative microscale technologies that are not based on solid state materials also provide promising solutions for body motion sensing. Basically, a micro-gyroscope is composed of two sets of mass-spring-damper systems, one for driving and the other for sensing. The rotational motion is measured by micromachined gyroscopes, which can be categorized mainly in two groups, linear vibratory gyroscope and torsional gyroscopes. Each accelerometer includes a mass-spring-damper system where the linear acceleration can be derived from the displacement of the proof mass. Cantilever based accelerometers have attracted tremendous interest during the past decades, and are widely available for motion sensing. Among the engineering modalities, linear motion and rotational motion are detected by accelerometers and gyroscopes, respectively. The human vestibular system possesses a simple but delicate structure that can simultaneously and accurately detect the six independent variables, which are subsequently interpreted by the central and peripheral neural systems to keep body balance and maintain gaze stability. ![]() The six independent variables fully describing the motion characteristics of an object. In order to accurately measure the motion characteristics of an object, a sensing system with six degree-of-freedom (DOF) sensing capability is required. As schematized in Figure 1, sway, heave and surge are linear motions along the three perpendicular coordinate axes in the space roll, pitch and yaw are rotational movements with respect to the three perpendicular directions. Generally speaking, the motion characteristics of an object, such as a human subject, an organ, or a tissue (e.g., solid tumor), can be described by six independent variables. Over the past two decades, research on microscale motion sensors has received extensive attention, and continues to be an active domain. In particular, rapid development of micro-electro-mechanical-systems (MEMS) with high accuracy, high reliability and multiple functionalities has provided a powerful tool set for body motion sensing. Recently, microscale motion sensing technologies have gained dramatic advances, which have significantly propelled the development of human balance prosthesis, sports medicine, radiotherapy, and biomechanical research. It is also difficult to be integrated into a modern medical system, such as portable medical device and point-of-care (POC) medication. Although effective, this technique is obtrusive and expensive. The current clinical solution for motion sensing is to use a camera based motion capture system, where the body motion is derived from the movement of multiple feature points attached on the body. For instance, head rotation and body orientation are the input signals for human balance prosthesis the movement of chest wall needs to be precisely monitored when a ventilation machine is used to support human breath the body motion characteristics also need to be evaluated during the rehabilitation process of disabled people. Motion sensing is a critical sensing modality that plays an important role in medical practice. ![]()
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