Electrical signals from biomedical devices are often small in amplitude and can be easily distorted by noise sources, the most common of which comes from the power grid and is called 60 hertz main noise (60 Hz noise). Diagnosing this noise in biological signals and filtering it out of your signals to the greatest extent possible is essential for the success of your instrumentation designs. Watch the video below and answer the corresponding questions to better understand 60 Hz noise and remove it from your measurements.
Self-Assessment Questions:
Click here to test your understanding of 60 Hz noise and how to filter it.
Discussion Questions:
- Can you get rid of 60 Hz noise solely through amplification of your signal? If so, how? If not, why not?
- How would the order and type of filter used affect the attenuation of 60 Hz noise? Compare and contrast Chebyshev, Butterworth, and Bessel filters of 1st, 2nd, and 3rd order filters and postulate an application for each using this study by Roland et al. as a guide.
- Find at least three different biological signals that can be successfully differentiated from 60 Hz noise using a high pass filter, a low pass filter, or a band stop filter (one signal for each filter type). What are the frequency ranges of each signal (use the articles by Vale-Cardoso et al. and Roland et al. as a starting point)?
- How will the cutoff frequency of 60 Hz noise filters affect your signal amplitude? How can you combine filtering and amplification to prevent this? How can you design your filters to minimize this effect?
- Consider a hospital room in which a patient is getting a 12 lead ECG taken by a nurse. List possible sources of noise due to the hospital room layout and surroundings and specify what effect this will have on the output ECG signal measured.
- Consider a signal whose frequency range contains 60 Hz. What are some limitations of using notch filters to filter out 60 Hz main noise (use Wesson et al. as a starting point)?
Continue Reading:
- A. S. Vale-Cardoso and H. N. Guimarães, “The effect of 50/60 Hz notch filter application on human and rat ECG recordings,” Physiol. Meas., vol. 31, no. 1, pp. 45–58, 2010. Read the article here.
- This article compares raw ECG notch filtering with human ECG notch filtering of 60 Hz noise. It demonstrates attenuation of rat QRS waves in notch filtering of 60 Hz noise, which is an important consideration in research settings.
- T. Roland, S. Amsuess, M. F. Russold, and W. Baumgartner, “Ultra-low-power digital filtering for insulated EMG sensing,” Sensors (Basel), vol. 19, no. 4, p. 959, 2019. Read the article here.
- This article explains the measuring principles of an EMG device for amputees. It discusses filtering strategies for 50/60 Hz main noise in different countries and low frequency noise associated with muscular movement.
- K. D. Wesson, R. M. Ochshorn, and B. R. Land, “Low-cost, high-fidelity, adaptive cancellation of periodic 60 Hz noise,” J. Neurosci. Methods, vol. 185, no. 1, pp. 50–55, 2009. Read the article here.
- Although more advanced in its methods, this article explains the limitations of notch filters in 60 Hz noise filtering and describes a method for adaptive noise cancellation in microcontrollers.
Be First to Comment