On the design of a triaxial accelerometer

Up to now, mainly uniaxial accelerometers are described in most publications concerning this subject. However, triaxial accelerometers are needed in the biomedical field. Commercially available triaxial accelerometers consisting of three orthogonally positioned uniaxial devices do not meet all specifications of the biomedical application. Therefore, a new highly symmetrical inherently triaxial accelerometer is being developed, the advantages of which are higher sensitivity and reduction of off-axis sensitivity

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

Polydimethylsiloxane as an elastic material applied in a capacitive accelerometer

Polydimethylsiloxane is a silicone rubber. It has a unique flexibility, resulting in one of the lowest glass-transition temperatures of any polymer. Furthermore, it shows a low elasticity change versus temperature, a high thermal stability, chemical inertness, dielectric stability, shear stability and high compressibility. Because of its high flexibility and the very low drift of its properties with time and temperature, polydimethylsiloxane could be well suited for mechanical sensors, such as accelerometers. A novel capacitive accelerometer with polydimethylsiloxane layers as springs has been realized. The obtained measurement results are promising and show a good correspondence with the theoretical values

Micro Coriolis Mass Flow Sensor Based on Electroplated Nickel Tubes

This paper presents a nickel plated Coriolis mass flow sensor that has been tested using water flow. The sensor consists of a free suspended tube which was fabricated by electroplating nickel on a polymer mold. The tube has a total length of 37 mm, a diameter of 280 μm and a wall thickness of 60 μm. The tube is driven into vibration by Lorentz force and the motion of the tube is detected by a laser Doppler vibrometer (LDV), a Polytec MSA-600 microsystem analyzer. The tube has a resistance of 0.1 Ω. The mass flow sensor has been tested with water over a mass flow range of 0-20 g/h and shows a linear response that corresponds well with theory. The sensor results in a pressure drop of approximately 1 bar at the maximum flow rate of 20 g/h.</p