**2. Problem-solving techniques: methods for removing EMI in practical use-case scenarios**

With the significant advancements in sensor technology over the past 10 years, EMI is less of an issue as in the past. That being said, there are additional variables beyond the measurement instrument itself which determines the quality of bioelectric signal obtained. One of these variables is the increasing level of EMI in our environment.

## **2.1 Obtaining quality signals: Practical examples**

Described below are practical examples demonstrating methods of reducing or eliminating EMI in actual practice.

#### *2.1.1 Practical example 1: The CT angiogram and ECG*

The author was required to have a CT Angiogram, and arrived for the exam with my own pack of ECG electrodes. At the time, the CT was timed based upon the ECG, and without a clean ECG signal, the test could not be performed.

After looking at the electrodes they were using, I asked the nurse if they had difficulty obtaining a stable ECG signal. She acknowledged that they were having significant challenges with the ECG, and did not know why. They had the ECG serviced, but the difficulties continued. What was wrong?

The hospital-supplied electrodes had a very high viscosity "gummy bear" type conductive medium. The author-supplied electrodes had a low viscosity gel form of conductive medium. Having the most high-tech ECG would not matter, as the weakness in this system was in the \$5.00 pack of electrodes.

To obtain a clean signal, the skin-electrode interface has to have a low enough impedance that the ECG amplifiers would be capable of acquiring the ECG signal without being "saturated" with EMI from all the other electronics in the room. I explained that the hospital supplied electrodes may work if given enough time for the conductive medium to heat up enough to permeate the skin. The gel-type medium on the author supplied electrodes instantly permeated the skin due to its low viscosity.

### *2.1.2 Tools for evaluating and reducing EMI*

These first two devices are crucial in detecting EMI/EMF issues at the physical location of data collection. The inverse square law applies to EMI. In other words, by moving a few feet away from the source of the EMI may resolve the problem. Therefore, you must test for EMI at the location where you will be performing the data collection. You will see the manufacturer and model number of the devices used in troubleshooting.


A demonstrative method of eliminating EMI was in resolving an EMI issue with one of the most popular, commercially available microphones (Blue Microphones model: Yeti). The popularity of this microphone is based upon its simplicity and

excellent sound quality (once EMI is removed). It is USB-powered and does not rely upon a separate amplification system.

The approach to resolving EMI issues with a microphone is identical to resolving EMI issues with SEMG or any low-level bioelectric signal. The microphone is a perfect example, as the process for eliminating EMI is the same for the microphone for bioelectric signals. There is no need to learn to operate an oscilloscope as the human ear can hear the change in sound quality when the EMI issue is resolved.

Upon plugging the device into my computer, and attempting to record, I immediately noticed a problem with a low-frequency" hum". In an online search, I found every expert on the microphone recommending the use of audio editing software with a noise reduction algorithm.

The resultant processed audio demonstrates the exact problem with digital signal filtering: The digital noise reduction definitively removed the hum, but concomitant with this approach was the removal of the subtle, rich, and warm qualities of the human voice heard in the original recording. The use of sound as an analogy demonstrates the impact digital signal processing may have on biologic signals, as sound has much of the same spectral and amplitude characteristics.

In a google search, the experts on this microphone almost unanimously recommended using audio editing software filters and equalizers to recover the unique vocal attributes removed during the noise reduction processing. In following this approach, the resultant output although improved lacked all the qualities of the original recording, degrading the sound quality along with removing the hum. Is there a better way than to use software to filter out the EMI?

Ideally, if we could remove the source of EMI, there would be no need for postrecording filtering. The problem-solving process presented below applies to any bioelectric signal contaminated by EMI (e.g. SEMG, EMG, ECG etc.) As with all problem-solving, it is essential to change one variable at a time (**Figures 1**–**5**).

These are the steps I followed in resolving the EMI issue:

1.Use an electrical ground tester (Klein Tools Model RT 310) to confirm that all electrical outlets are tied to earth ground. Although this issue is more likely to occur in an older residential home, it is still possible the location was not properly wired. An ungrounded AC circuit is a source of EMI and needs to be

**Figure 1.** *Grounded 3 prong AC adapter.*

*Protecting Bioelectric Signals from Electromagnetic Interference in a Wireless World DOI: http://dx.doi.org/10.5772/intechopen.105951*

**Figure 2.** *Ungrounded AC adapter.*

**Figure 3.** *The Inverse Square law.*

resolved immediately. The ground appeared good in all outlets throughout my office setting.


**Figure 4.** *Faraday cage concept.*

a location with severe EMI issues, the lab room was painted with a commercially available shielding paint designed with a grounding plate (e.g. Gigahertz Solutions Manufacturer number 863–091 with grounding plate 863–138). It is recommended that a professional perform the installation of such paint. Also, there are manufacturers who provide cloth that can be used to build a Faraday Cage (JJ Care part FF44x20), but the process of building a proper Faraday cage is more complex than it appears [6], and without proper understanding of the principles it is the position of the author that these should be limited to use in clinic or lab settings. The Faraday cage I built for the microphone was unsuccessful.

4.Testing the microphone/computer system at a different location was done to eliminate any source of EMI not obvious. Changing locations has exposed issues for other offices, but did not eliminate the EMI issue with the microphone. In one scenario the dry cleaner next door was using industrial size washers

and dryers generating so much EMI that the only solution was to move the entire SEMG system to the opposite end of the office. The good news is that the inverse square law applies to EMI (the impact of EMI drops off rapidly the further you move away from the source of interference).


stalled and grounded (Smart Meter Guard, Model SMG1). The smart meter still functioned properly, but the microphone EMI issue was not resolved.

11.I decided to take an inventory of the system disconnected to evaluate possible sources of EMI that were inherent in the design. What I immediately noticed was that the USB A cable to Mini USB cable (which powered and transmitted data from the microphone to the PC) was a standard cable without a ferrite core. I purchased a male USB-2.0 A to male Mini USB cable (Monoprice model 105,447), manufactured with a ferrite core wrapped around the Mini-USB end of the cable. The problem was resolved, and this wonderful microphone was now usable without any digital filtering. Attenuating EMI at the source will always lead to a cleaner, more clinically valuable signal and reduce the need for as much signal processing. The process above applies to any EMI issue with any device.
