Template Matching and Matrix Profile for Signal Quality Assessment of Carotid and Femoral Laser Doppler Vibrometer Signals

Background: Laser-Doppler Vibrometry (LDV) is a laser-based technique that allows measuring the motion of moving targets with high spatial and temporal resolution. To demonstrate its use for the measurement of carotid-femoral pulse wave velocity, a prototype system was employed in a clinical feasibility study. Data were acquired for analysis without prior quality control. Real-time application, however, will require a real-time assessment of signal quality. In this study, we (1) use template matching and matrix profile for assessing the quality of these previously acquired signals; (2) analyze the nature and achievable quality of acquired signals at the carotid and femoral measuring site; (3) explore models for automated classification of signal quality.Methods: Laser-Doppler Vibrometry data were acquired in 100 subjects (50M/50F) and consisted of 4–5 sequences of 20-s recordings of skin displacement, differentiated two times to yield acceleration. Each recording consisted of data from 12 laser beams, yielding 410 carotid-femoral and 407 carotid-carotid recordings. Data quality was visually assessed on a 1–5 scale, and a subset of best quality data was used to construct an acceleration template for both measuring sites. The time-varying cross-correlation of the acceleration signals with the template was computed. A quality metric constructed on several features of this template matching was derived. Next, the matrix-profile technique was applied to identify recurring features in the measured time series and derived a similar quality metric. The statistical distribution of the metrics, and their correlates with basic clinical data were assessed. Finally, logistic-regression-based classifiers were developed and their ability to automatically classify LDV-signal quality was assessed.Results: Automated quality metrics correlated well with visual scores. Signal quality was negatively correlated with BMI for femoral recordings but not for carotid recordings. Logistic regression models based on both methods yielded an accuracy of minimally 80% for our carotid and femoral recording data, reaching 87% for the femoral data.Conclusion: Both template matching and matrix profile were found suitable methods for automated grading of LDV signal quality and were able to generate a quality metric that was on par with the signal quality assessment of the expert. The classifiers, developed with both quality metrics, showed their potential for future real-time implementation.

Analysis of frequency response sensor of MEMS gyroscope in vacuum chamber

This article presents a study of the frequency response of a MEMS gyroscope in a vacuum chamber. On the basis of experimental studies by the method of laser Doppler vibrometry, the dependences of the amplitude of oscillations of the inertial mass in the vertical plane at various pressures are obtained. The bandwidth of the MEMS sensor was also measured.As a result of the experiments, the damping factors were determined to compose a more complete mathematical model and for more accurate finite element modeling in ANSYS, and refined parameters of the electrostatic drive and the amplitude of oscillations along the axis of the drive were obtained. These studies will be useful for determining the residual degree of vacuum in the case for further frequency tuning of the device.

Use of Laser Doppler Vibrometry for Measuring Flow-Induced Vibration of a Thermowell in a Pipe Flow

Thermowells with helical strakes are becoming promising to prevent them from fatigue fracture by Kármán vortex street. Many studies suggest various kinds of measurement techniques, including strain rate measurement, acceleration measurement, and high-speed visualization to evaluate the role of Kármán vortex street to the flow-induced vibration. Nevertheless, use of laser Doppler vibrometry has not yet been reported in the literature. This study compared the tip deflection of a thermowell due to the flow-induced vibration by using the laser Doppler vibrometry and the strain rate measurement. The laser Doppler vibrometry could measure the tip deflection directly. On the other hand, the strain rate measurement had to convert the strain rate into the tip deflection through the Euler-Bernoulli beam theory. Measurement equivalence between the laser Doppler vibrometry and the strain rate measurement was discussed with the results of tip deflections of the thermowell.

Vibration Analysis for NDE of Ceramic Components

In this contribution we study vibration testing for ceramic parts on the example of an electrolyte cup, used in a prospective power cells design. An adapted experimental arrangement for the vibration excitation and the acoustic measurements was built and tested. In parallel, extensive numerical modal analysis simulations were performed using ANSYS. The resonance spectra obtained by modelling agree with the experimentally determined spectra in such a way that the experimentally determined eigenfrequencies can be assigned to the cup modes. The correctness of this identification was verified by direct mode visualization with scanning laser doppler vibrometry. A much faster and potentially in-line capable method for experimental mode identification is the simultaneous measurement at several points using a microphone array and subsequent signal evaluation with operational modal analysis. This procedure was successfully tested. Features in the spectra connected with the presence of flaws are discussed. These features include the drop of some eigenfrequencies and the splitting of degenerated modes.