In the 22nd issue of the *Journal of Electrical Engineering* in 2017, researchers Xu Guizhi, Li Chenxi, Zhao Jun, and Zhang Xian from the Provincial Key Laboratory of Reliability and Intelligentization of Electrical Equipment at Hebei University of Technology, as well as the Tianjin Key Laboratory of Advanced Electrical and Electronic Technology, discussed the growing application of wireless energy transmission technology. One of its most notable uses is in electric vehicle (EV) charging.
To assess the safety of human exposure to electromagnetic fields during wireless charging, three-dimensional finite element-based simulation software was used to create a detailed model of the human body under such conditions. The study focused on analyzing the electromagnetic exposure of major organs, aiming to evaluate potential health risks.
The results showed that different tissues and organs absorb electromagnetic waves differently due to their varying electromagnetic properties. The maximum current density reached 20.058 mA/m², while the peak power density was 1.22×10â»âµ W/m², and the highest specific absorption rate (SAR) was 4.37×10â»â· W/kg. All these values were found to be significantly below the safety limits set by the International Commission on Non-Ionizing Radiation Protection (ICNIRP), indicating that the electromagnetic environment created by wireless EV charging is generally safe for humans.
With global concerns over climate change, dwindling fossil fuel reserves, and environmental pollution from vehicle emissions, electric vehicles have gained significant traction due to their eco-friendly and zero-emission characteristics. However, traditional plug-in charging methods come with several drawbacks, including limited flexibility, spark generation during connection, wear and tear, and safety issues related to long cables affecting aesthetics.
The introduction of Wireless Power Transfer (WPT) technology has offered a promising alternative. This method provides advantages such as waterproofing, reduced mechanical wear, and lower maintenance needs, making it a safer and more convenient option for EV charging. As a result, wireless charging technology is seen as having great potential for future applications.
As the adoption of wireless charging increases, so does the attention on its electromagnetic safety. In 2007, MIT introduced a medium-range magnetically coupled resonant wireless power transfer system, which operates with magnetic field strengths comparable to Earth’s geomagnetic field, posing minimal risk to human health. However, for EVs, where higher power levels are required, careful assessment of electromagnetic radiation is essential to ensure safety.
Currently, the widely accepted measure for assessing electromagnetic exposure is the Specific Absorption Rate (SAR). Since direct measurement of SAR and current density in human tissues is challenging, numerical simulations using tools like COMSOL Multiphysics are employed to estimate the electromagnetic energy absorbed by the body.
By constructing models of the resonator, a seated human body, and an electric vehicle, this study simulated and calculated the electromagnetic exposure of various organs. The findings were compared against ICNIRP guidelines to determine whether the exposure levels fell within acceptable safety limits.
Figure 1 illustrates the field structure of the radio energy transmission system used in the study.
In conclusion, the research demonstrated that while different organs and individuals may experience varying levels of electromagnetic exposure, all measured values remained well below the safety thresholds set by international standards. These findings help alleviate public concerns about the safety of wireless EV charging, supporting the broader adoption of wireless energy transfer technology in the automotive industry.
Speaker
Speakers are one of the most common output devices used with computer systems. Some speakers are designed to work
specifically with computers, while others can be hooked up to any type
of sound system. Regardless of their design, the purpose of speakers is
to produce audio output that can be heard by the listener.
Speakers are transducers that convert electromagnetic waves into sound waves. The speakers receive audio input from a device such as a computer or an audio receiver. This input may be either in analog or digital form. Analog speakers simply amplify the analog electromagnetic waves
into sound waves. Since sound waves are produced in analog form,
digital speakers must first convert the digital input to an analog
signal, then generate the sound waves.
The sound produced by speakers is defined by frequency and amplitude.
The frequency determines how high or low the pitch of the sound is. For
example, a soprano singer's voice produces high frequency sound waves,
while a bass guitar or kick drum generates sounds in the low frequency
range. A speaker system's ability to accurately reproduce sound
frequencies is a good indicator of how clear the audio will be. Many
speakers include multiple speaker cones for different frequency ranges,
which helps produce more accurate sounds for each range. Two-way
speakers typically have a tweeter and a mid-range speaker, while
three-way speakers have a tweeter, mid-range speaker, and subwoofer.
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