Metrological Characterisation of Movella DOT Wearable Sensors for Measuring Induced and Transmitted Vibrations

The research focuses on the dynamic calibration of off-the-shelf inertial measurement unit (IMU) triaxial accelerometers, sensors generally used for kinematic analyses in sport and biomedical engineering. The assessment of Xsens Movella DOT sensors’ performance, reliability, and limitations is presented, providing a metrological basis for their application in wearable monitoring systems. The metrological characterisation was performed to quantify the sensors’ dynamic response, their bandwidth, and measurement repeatability and reproducibility within the range of interest. Three units from the same batch were tested along three orthogonal axes under controlled excitation conditions, using a laser Doppler vibrometer as reference. The experimental protocol included harmonic excitations in the 10–45 Hz range, harmonic excitation up to 130 Hz to quantify limitations and potential errors of the sensors when measuring signals out of the nominal bandwidth, and random excitation, limited in the frequency range up to about 40 Hz, to validate their applicability in a generic dynamic environment. Thus, the acquired signals were analysed in both the time and frequency domains: in particular, the Frequency Response Function (FRF) between the IMU accelerometers and the reference system was measured, along all three measurement directions, and the corresponding Power Spectral Densities (PSDs) were computed. A numerical optimisation procedure was then applied to model the acquired FRF, providing an estimation of the FRF complex function, allowing for correction in general dynamic applications. One major result was that dynamic compensation is mandatory within the nominal bandwidth, given the attenuation of the measured amplitude of about 25% at the maximum frequency of the bandwidth; moreover, aliasing error occurs if the excitation frequency is above the Nyquist frequency, introducing frequency-dependent errors and misleading results. Thus, the proposed methodology and correction model, together with the highlighted instrumental effects, allow for accurate acceleration measurements by using the tested Xsens Movella DOT sensors (Xsens, Enschede, The Netherlands) in an induced and transmitted vibration scenario, although the defined methodology can be more generally extended to similar devices and instruments, aiming for proper dynamic characterisation.