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fm:messmethoden:mmb07:en

MMB7en Signal Processing

Module MMB7en Signal Processing
Category Messmethoden Biomechanik
Author Filip Cengic
Voraussetzung Grundlagen Biomechanik
Duration approx. XX minutes
Last edit Sept., 7th 2017
Status in processing
Course Goal

Introduction

Signals captured by biomechanical devices are often noisy and non-interpretable. Hence, post-processing environments - such as MATLAB - offer a variety of mathematical functions to reduce noise of captured signals. Noise reduction is often applied in the field of motion capturing, dynamometry and EMG capturing.



Main part

Due to the sensitive nature of biomechanical capture devices, the signal is affected from various external noises or artefacts, respectively. In order to remove the unwanted signal components, the processing part is divided into different tasks

  1. General Filtering
  2. Rectification
  3. Normalization (especially usable in EMG Measurements - MVC)
  4. Smoothing



Amplifying & Filtering

Filtering is the process of removing unwanted frequencies of the captured signal range. Frequencies can be obtained by applying a Fourier Transformation (probably more common: FFT - Fast Fourier Transformation) to the captured signal. Basically, this mean, that horizontal time line (x axis) is replaced by the frequency propertied of the signal.

The next step would be to find appropriate cutoff frequencies (s. Fig. 1). Taking EMG signal processing as an example, Henry et al. (1998, P. 34) bandpass filtered the EMG signal within the frequency range of 75-2.000 Hz.

Fig. 1: Selecting cutoff frequencies of an amplified signal

Prior to filtering they pre-amplified (x 5000-10.000) the EMG signal. The dynamics of activation takes place within the range of a few Millivolts. Hence, signal amplification should be handled with caution, in order not to amplify unwanted interference components.

As it can be seen in Fig. 1, amplification is commonly measured in decibel (dB), which is a logarithmic expression.






Conclusion

test



Fragen

test



References

Henry, S. M., Fung, J. & Horak, F. B. (1998). Control of Stance During Lateral and Anterior/Posterior Surface Translations. IEEE Transaction on Rehabilitation Engineering, 6 (1), 32-42.



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fm/messmethoden/mmb07/en.txt · Zuletzt geändert: 28.11.2022 00:58 von 127.0.0.1


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