Design, realization and characterization of a symmetrical triaxial capacitive accelerometer for medical applications

Small triaxial accelerometers are needed in the medical field for the monitoring of mobility. For this purpose, a new highly symmetrical inherently triaxial capacitive accelerometer has been designed. The basic structure of the device consists of six capacitors surrounding a central mass which is suspended by springs made of the rubber elastic polymer polydimethylsiloxane. The advantages of the design are a low off-axis sensitivity, an equal sensitivity in all axes and a reduction of the sensor's dimensions. In order to show the practical feasibility of the design, a number of manually assembled prototypes of the triaxial accelerometers have been realized with dimensions down to 2 mm × 2 mm × 2 mm. The prototypes are capable of detecting accelerations in three directions with unfortunately unequal sensitivities per axis (e.g., from 0.8 to 1.1 V (m s2) 1) and a maximum off-axis sensitivity of 3% in the well-assembled devices. Clinical measurements have been carried out with the prototypes. The measurement results indicate that the triaxial accelerometer is sensitive enough to register the kind of movements that occur in healthy persons during normal standing.