EE322 -- Homework 4: Engineering Principles
Wireless Charger
Group Leader:
Jiuxiang Liu #10377574
Group Members:
Shan Jiang #10377573
Qing Zhao #10377569
We pledge our honor that we have abided by the Stevens Honor System!
Section 1 – Team Member Contribution
For the first group report, every group member contributes for the principle researching
work. As discussed in the group meeting, each member were supposed to find at least three
effective resources related to our project. In order to avoid overlapping resources, the group
assigned each member a particular direction for the researching job. Jingxiang was assigned to
search the relative principles which might be applied on the project. Shan was allocated to find
out the current research on this topic. And Qing was asked to search and compare the companies
which have released their wireless charger product. Finally, the group had another meeting to
exchange our research gains with each other.
Below is a table of team member contribution.
Jingxiang Liu
Shan Jiang
Qing Zhao
33.3%
33.3 %
33.3 %
Percentage of
effort towards this
assignment
Section 2 – Project Initial Research
2.1 Project Initial Idea
The possibility of charging devices wirelessly has been an eye-catching research topic in
recent years. The existing technology, and the corresponding product as well, so far for wireless
power transmission is to transmit power through magnetic field using two coils based on
resonance theory. This can be regarded as an evolutionary change of the way people used to
charge their electric devices. With such product, people can just leave their cell phones or tablets
on the charging pad and let the charger do anything else automatically.
However, although people can get rid of the trouble caused by the tangled charger wires
with such a wireless charger pad, it still doesn’t release people thoroughly. Because people can
only operate the charging devices without moving the devices away from the charger.
Therefore, the group generate the idea of designing a more powerful and convenient
wireless charger, which can realize the function of short-distance wireless charging. The detailed
discussion will be presented in the following report.
2.2 Project-Related Principles
The project is based on the inductive charging technology – the process of transferring
energy between two objects through the use of induction coils. Simply put, these coils produce a
magnetic field which sends energy from a charging base station (transmitter) to a coil on a
portable device (receiver) via a process called inductive coupling. The figure shows the working
principle of a typical wireless charger.
Firstly, a wireless charger sends an AC power signal to the transmitting coil. When the
current is transferred through the coil, an electromagnetic field is created around the coils. Then,
if a receiving coil is placed in range of this induction coil, the oscillating magnetic field will
create an AC current, which after A/D (AC signal to DC signal) converting by additional
circuitry, can be used to charge the electric devices.
Since power can be transferred through solid objects such as walls, house hold furniture
and human tissues. For our project, introducing a third coil can extend the range of the wireless
power transfer so that the charger’s distance limitation can be extended.
2.3 Current Product Analysis
In the current market, a few wireless charger have been released. The group compare and
analyze some of the mature product include Nokia wireless charger, Powermat and Proxi
wireless charger. The table below shows the specifications of each product.
Brand
Nokia
Powermat
Proxi
Max # of Devices Charged
1
3
3
Output Voltage (V)
12
18
18
Operational Frequency (kHz)
130
125
128.9
Full Charge Shutoff
No
Yes
Yes
Although these product are on sale on the market, they are not perfect solutions for the
idea of wireless charging. Due to the distance limitation of the wireless charger, it is still hard for
people to operate their devices while charging. Therefore, the group would like to improve the
design of the current wireless charger.
2.4 Relative Research on This Topic
The group tried to learn more technical details about our topic by reading the relative
researches.
In the paper, Characteristic Analysis of Double Spiral Resonator for Wireless Power
Transmission, the group got a basic understanding of a unique resonator pattern, named “double
spiral resonator” in wireless power transmission (WPT) via resonance coupling. The paper also
introduces the exploiting electromagnetic (EM) field calculation method to obtain the coupling
coefficient of two double spiral resonators at different distances via the parasitic parameters of
the resonators.
In the article, Rectangular coils optimization for wireless power transmission, the group
find out an alternative way to implement the magnetic coils. This paper presents a method of
characterizing and optimizing rectangular coils used in inductively coupled systems. After
setting up a lumped component model for inductive coils, the efficiency can be expressed in
terms of geometrical parameters of the coils. Subsequently, the power efficiency can be plotted
versus these parameters in Matlab, thus getting the desired coils for optimum power transfer.
With this design procedure from mathematical optimization, the author eventually designed two
rectangular coils spaced 10 mm apart, which achieves a power transmission efficiency of 46.4%
at a frequency of 3 MHz.
In the paper, Principle Elaboration and System Structure Validation of Wireless Power
Transfer via Strongly Coupled Magnetic Resonances, the group learned the method to increase
the resonance efficiency. The author talk about this topic from theoretical analysis of wireless
power transfer (WPT) via strongly coupled magnetic resonances (SCMR).
Section 3 – Reference
1. "Wireless Power." Wikipedia. Wikimedia Foundation, 16 Feb. 2014. Web.
2. "Inductive Power Transmission." - Wireless Power Consortium. N.p., n.d. Web.
3. "Inductive Charging." Wikipedia. Wikimedia Foundation, 15 Feb. 2014. Web.
4. "Wireless Charging." PowerbyProxi. N.p., n.d. Web.
5. “Wireless Power User Guide” http://cds.linear.com/docs/en/applicationnote/AN138fa.pdf
6. http://www.nokia.com/global/innovation/wireless-charging/wireless-charging/
7. "Principle Elaboration and System Structure Validation of Wireless Power Transfer via Strongly
Coupled Magnetic Resonances." IEEE Xplore. N.p., n.d. Web.
8. "Characteristic Analysis of Double Spiral Resonator for Wireless Power Transmission." IEEE
Xplore. N.p., n.d. Web.
9.
Duan, Z., Y.-X. Guo, and D.-L. Kwong (2012), Rectangular coils optimization for wireless power
transmission, Radio Sci., 47, RS3012, doi:10.1029/2011RS004970.