The Bridge - Issue 2, 2022 - 24

Feature
Mitigating Self-generated EMI
for Wireless Devices
Dr. Chulsoon Hwang, IEEE Senior Member, Missouri University of Science and Technology, Gamma Theta 2019
Wireless connection is the cornerstone for the
Internet of things, a network allowing distant devices
I. Introduction
and sensors to communicate wirelessly with each
other. The maximum physical distance across which
two devices can communicate is called the " radio
range. " Although a long radio range is essential for
the connectivity and portability of wireless devices,
designers are finding that digital circuits within the
same system often create sufficient electromagnetic
interference (EMI) that decreases receivers'
sensitivity; thereby, substantially degrading the radio
range. This article discusses an electromagnetic
(EM) framework to model the noise radiation from
digital circuits and its coupling to on-board radio
frequency (RF) antennas. A new approach, based
on the EM framework to mitigate the self-generated
EMI in wireless devices is introduced. The approach
does not require absorbers/shielding cans and it
does not compromise signal integrity. The success
of the mitigation concept introduced in this article is
demonstrated by applying it to a practical RF device,
namely, the smart speaker.
THE BRIDGE
A fundamental requirement of wireless devices
is a long RF range. Radio range is a function of
multiple factors: transmitter power, antenna gain,
path loss, and receiver sensitivity. Transmitter power
and antenna gain are typically regulated by federal
law. For instance, the Federal Communications
Commission limits the specific absorption rate
(SAR), the rate at which the body absorbs energy
when exposed to an RF field, to 1.6 W/kg for cellular
telephones [1]. Transmitters with higher power also
consume more energy, whereas low power is critical
for portable devices. Therefore, increasing the RF
range of wireless devices by increasing transmitter
power or antenna gain is not advisable. Because
path loss is an environmental feature that is usually
unmanageable, the only practical and feasible
approach to increase RF range is improving receiver
sensitivity. Increasing the receiver sensitivity can
increase the radio range as much as transmitter
power, without increasing the power consumption or
causing harm to the human body.

The Bridge - Issue 2, 2022

Table of Contents for the Digital Edition of The Bridge - Issue 2, 2022