A new sensor for biomechanics and rehabilitation

We are evaluating a new three-dimensional magnetoresistive inclinometer with a variety of potential applications in biomechanics and rehabilitation engineering. INTRODUCTION Gait analysis methods are commonly based on a video reconstruction of the movements of body segments within a calibrated volume. W e evaluated a preliminary prototype of a new three-dimensional magnetoresistive inclinometer. Future versions of this sensor may significantly impact gait analysis and other areas of biomechanics and rehabilitation. Beauclmu Electric, Inc. (Waterford, Cl') has filed patent applications for the sensor and associated algorithms. "I 'HODS The prototype inclinometer contains two orthogonally oriented elements, mounted in a cube, 1.2 cm on edge. The orientation of the sensor was established with two marked sides and a reference coordinate system, as shown in Figure 1. The inclinometer was designed so that Sensors 1 and 2 are most sensitive to the angle between the horizontal plane and the "0 and "X" sides. respectively. The amplified and filtered output signals were recorded at 15 deg increments as the sensor was rotated in several planes and orientations, through an arc of 180 deg. Fig. 1. Representation of the inclinometer in a reference coordinate system with two sides marked for reference. RESULTS The output signals were offset to 0 at a rotation angle of 90 deg, and normalized to the most sensitive range of rotation for each sensor element. Data for two of the rotations are shown in Figure 2. Each sensor is significantly more sensitive when rotated about a horizond axis than a vertical axis. not compound movements. Evaluation of the prototype was limited by it's sensitivity to local magnetic field aberrations. According to the manufacturer, the next generation inclinometer will be accurate to -+I deg, have a frequency response from DC U) 30 Hz, and be significantly less sensitive to iocal field aberrations. hprietary algorithms will be necessary to determine the spherical coordinate angles which uniquely describe the orientation of the sensor. A gait analysis system, based on an array of inclinometers interfaced to a portabIe data acquisition system [l]. may provide near real-time measurement of body segment orientations independent of a calibrated volume. Although we have focused on the use of this sensor in gait analysis, a plethora of applications exist in biomechanics and rehabilitation. Rotation 1 Rotation 2 -Sensor 1 _c_ Sensor 1 Sensor 2 _c_ Sensor 2 0.6 8 0.4 0