Wireless power and data transfer through carbon composite using a common inductive link

International Journal of Power Electronics and Drive System (IJPEDS)
Vol. 11, No. 3, September 2020, pp. 1441∼1448
ISSN: 2088-8694, DOI: 10.11591/ijpeds.v11.i3.pp1441-1448 r 1441
Wireless power and data transfer through carbon
composite using a common inductive link
Tuan Anh Vu1
, Chi Van Pham2
, William Tran3
, Anh-Vu Pham4
, Christopher S. Gardner5
1,2,3,4
Department of Electrical and Computer Engineering, University of California, United State
5
Lawrence Livermore National Laboratory, United State
1
VNU University of Engineering and Technology, Vietnam
Article Info
Article history:
Received Apr 21, 2019
Revised Mar 21, 2020
Accepted May 6, 2020
Keywords:
Energy harvesting
Inductive coupling
Through carbon composite
Wireless data transfer
Wireless power transfer
ABSTRACT
This paper presents the design and development of an integrated wireless power
transfer and data communication system. The power and data transfer share a
common inductive link that consists of two identical Helical coils placed on both sides
of a carbon composite barrier. Power and data are transferred simultaneously through
a 5-mm thick carbon composite barrier without any physical penetration or contact.
Power transfer measurements show that the system can deliver 9.7 AC power to the
receiving coil with a power transfer efficiency of 36% through the carbon composite
barrier. The system achieves a bidirectional half-duplex data communication with the
data rate of unit 1.2kbit/s.
This is an open access article under the CC BY-SA license.
Corresponding Author:
Tuan Anh Vu,
VNU University of Engineering and Technology,
144 Xuan Thuy Rd., Cau Giay Dist., Hanoi, Vietnam.
Email: tanhvu@vnu.edu.vn
1. INTRODUCTION
Design and optimization of wireless power transfer (WPT) systems have been well studied over the
last decades to charge cell phones and electric vehicles as well as to power up sensors over a short distance
[1–6]. In recent years, there has been a great demand for wirelessly powered sensors to support structural
health monitoring (SHM) for industrial applications containing carbon composite barriers and enclosures (e.g.,
naval vessel, aircraft and chemical vat). Drilling holes for feeding wires reduces the integrity of the structure.
Specifically, practical issues include higher probabilities for the leakage of toxic chemicals and the loss of
pressure or vacuum. The SHM systems typically require embedded sensors for data acquisition inside a sealed
container, wireless communication, and energy harvesting. The sensors need to be powered and controlled
wirelessly through a barrier without any physical penetration through mechanical structures.
Several methods have been proposed to transfer power and data wirelessly using a common inductive
link. The concept of inductive power transfer (IPT) is similar to the principle of transformers in which an
alternating magnetic field in the primary coil induces a load voltage on the secondary coil when the two coils
are tightly coupled [7-9]. In low-power applications, the inductive link for power transfer is also used for data
transmission, where the data is directly modulated on the power carrier [10-14]. However, these techniques
have low data rates and low power transfers.
Several methods using multiple inductive links with multiple carriers have been proposed to increase
the data rate while maintaining the power transfer efficiency [15, 16]. In these methods, power and data
are transferred via independent physical channels, where the power signal is delivered through one inductive
Journal homepage: http://ijpeds.iaescore.com

1442 r ISSN: 2088-8694
link and the data signal is transmitted through another. However, multiple links will cause extra magnetic
interferences between the two channels, thereby decreasing the signal-to-noise ratio (SNR) in a communication
channel. Multiple inductive links also lead to larger device size, which is undesirable for confined space
applications. The method with multiple carriers in a single inductive link is another candidate for WPT systems.
Conventional systems feed both power and data signals through two terminals of the inductive coil [17, 18] or
use strong couple inductors to mix them before driving those signals to the coil [19]. However, these approaches
cause direct interference of high power leakage into the data communication band at multiple harmonics. As
a result, sharp-response filtering circuits or high power data transmission (well above harmonics levels) is
required for a successful data communication. The main challenge of this approach is to achieve a reliable
communication link in the presence of a strong interference from the power link.
In this paper, a novel system for simultaneous power and data transfer through a 5-mm thick carbon
composite barrier using a common inductive link will be presented [20, 21]. The block diagram of the proposed
system is shown in Figure 1. In this system, power is applied two terminals of the transmitting coil while the
data is fed through the coil’s center tap. By doing this, the power and data signals are isolated by means of the
half-coil impedance. This feeding configuration can help to reduce the data signal power being transmitted to
only 1.5. Consequently, it significantly releases the amount of power that needs to be harvested on the sensing
side for sensing and communication operation. A complete system prototype is built to demonstrate that it can
deliver 9.7 AC power to the sensing side and achieve wireless communication at the data rate of 1.2.
2. SYSTEM OVERVIEW
As demonstrated in Figure 1, the system is divided into two parts: the primary side and the sensing
side. On the primary side, a power amplifier (PA) delivers power to two terminals of the transmitting coil
while the data is applied via the coil’s center tap. The power and data mixed signals are captured across two
terminals of the receiving coils. A rectifier is employed on the sensing side to convert the harvested energy into
DC power. This DC power is then used for sensing and communication operation on the sensing side, which
does not have any batteries. The frequency of the power carrier is set at 300 while the data carrier is set at 8.
The data-carrier frequency should be at least an order of magnitude higher than the power-carrier frequency so
that the crosstalk interference of data communication from power transfer is suppressed. This facilitates the
design of demodulation circuit and guarantees the reliability of communication. Low frequency was chosen for
the wireless power transfer to isolate high power leakage at multiple harmonics into the data communication
band. Conversely, for the wireless data transfer, high frequency had to be chosen to have large bandwidth for
high data rate. However, the frequency of data carrier cannot be too high because data signals may experience
significant loss through the inductive link.
Figure 1. Proposed system for power and data transfer through carbon composite
Int J Pow Elec & Dri Syst, Vol. 11, No. 3, September 2020 : 1441 – 1448

Int J Pow Elec & Dri Syst ISSN: 2088-8694 r 1443
2.1. ASK transceiver
In the proposed system, bidirectional half-duplex communication between the primary side and the
sensing side is implemented using amplitude-shift keying (ASK) modulation. The proposed ASK transceiver
shown in Figure 2, is adopted in both sides. In forward communication, the primary side is set to a transmitter
mode while the sensing side is set to a receiver mode. In backward communication, the primary side is set
to a receiver mode while the sensing side is set to a transmitter mode. The ASK transceiver can operate in
two modes: transmitter mode and receiver mode, which are controlled by a bidirectional electronics switch
TPS2080 from Texas Instruments. On the transmitter mode, digital data from an Arduino microcontroller (uC)
is mixed with an 8-kHz carrier frequency generated by a local oscillator (LO) on a printed circuit board (PCB).
The ASK modulated signal is then amplified by a commercial audio PA TDA7391 from STMicroelectronics
and employed as a signal source to transmit data. On the receiver mode, the incoming data is demodulated and
read by the same Arduino microcontroller. The ASK demodulator includes an active high-pass filter (HPF), a
squarer, a low-pass filter (LPF) and a comparator. The active HPF consists of a second-order RC HPF followed
by an op-amp amplifier. The strong power carrier signal and its harmonics that may interfere with the baseband
data signal are suppressed by 40 by the active HPF. The filtered signals are then amplified and demodulated by
the following sub-blocks in the receiver chain.
Figure 2. Proposed ASK transceiver, (a) ASK modulator, (b) ASK demodulator
2.2. Class-E power amplifier
A class-E PA is co-designed with the inductive link for power transfer. Class-E PAs achieve signif-
icantly higher efficiency than their conventional class-B or -C counterparts. The efficiency is maximized by
minimizing power dissipation, while still maintaining a desired output power. The insulated-gate bipolar tran-
sistor (IGBT) STGW15S120DF3 from STMicroelectronics was used as the power transistor. This IGBT family
has been specifically optimized for low switching frequencies. The complete circuit of the 300 class-E PA with
all component values are given in Figure 3. The PA design is obtained by the Sokal-Raab approach [22, 23] is
the coupling capacitor at the input of the PA. R1 and R2 form a voltage divider for gate biasing. The DC-feed
choke, L0 provides the connection to the DC power supply. L1 and L2 represent the coil inductances. In this
design, the IGBT operates as an on/off switch and the load network shapes the voltage and current waveforms
to prevent simultaneous high voltage and high current in the transistor. The load network is designed consider-
ing effects of the inductive link. The inductances of the transmitting and receiving coils become a part of the
load network. C1 and C2 ensure that the collector voltage and collector current switching transitions are time-
displaced from each other. Consequently, the power dissipation is minimized, especially during the switching
transitions. L2 and C3 form a series-parallel resonant circuit. The IGBT is driven with a gate voltage of 8 and
a supply voltage of 15. Measurement results show that the designed PA achieves a high collector efficiency of
54.2% when delivers 27 power at 300 to the transmitting coil.
Wireless power and data transfer through carbon composite... (Tuan Anh Vu)

1444 r ISSN: 2088-8694
Figure 3. Schematic diagram of the class-E power amplifier
2.3. Power management
The power management module consists of an impedance transformer followed by several voltage
regulators. Since the impedance of the coil is approximately 1 at 300, the AC power is harvested on the
receiving coil in form of low voltage and high current. The series-L parallel-C impedance transformer is used
to boost up the harvested AC voltage. The AC voltage is then converted into the DC voltage by a full-bridge
rectifier GBPC3502W from ON Semiconductor followed by several smoothing capacitors. The DC voltage is
distributed to several voltage regulators to generate stable voltage supplies for powering different sub-blocks of
the ASK transceiver and sensors on the sensing side.
2.4. Helical coil
The power and data carrier share a common inductive link using a pair of identical Helical coils
whose inductances are 0.45. Analysis and design of Helical coil were presented in [24-27] By co-axially align-
ing a pair of coils, the wireless IPT channel is formed without any physical penetration through the carbon
composite barrier. The Helical circular geometry results in a more uniform magnetic field distribution that sig-
nificantly improves the efficiency of energy transfer compared to that of the conventional Solenoid counterpart.
The Helical coils are constructed using American Wire Gauge (AWG) 16 magnet wire. They have 63 turns with
inner and outer radius of 22 and 108, respectively. Measurement results demonstrate that the power transfer
efficiency is 36% for transfering power at 300 through the 5-mm thick carbon composite barrier.
3. EXPERIMENTAL RESULTS
A complete prototype was built to demonstrate the effectiveness of the proposed system.
Figure 4 illustrates the measurement setup for power and data transfer through a 400×400×5 carbon com-
posite barrier. The other Helical coil cannot be seen in the figure since it is covered by the carbon composite
barrier. For the practical demonstration of the proposed system, the prototype performances were verified in
two experiments as shown in Figure 5. The first experiment verifies backward communication in which the
sensing side sends data to the primary side. A temperature sensor TMP36 connected to the Arduino microcon-
troller on the sensing side continuously collects information on the temperature of the surrounding environment.
The Arduino microcontroller is programmed to read this data and then the ASK transceiver sends the data to the
primary side at a rate of 1.2. The temperature values are displayed on the monitor of a computer connected to
the Arduino microcontroller board for further verification. In the second experiment, bidirectional half-duplex
data communication is established when two ASK transceivers exchange one thousand bytes of data. The
data is enclosed by the user-defined start and stop bytes. The ASK transceiver on the sensing side starts the
communication at a data rate of 1.2 by sending the start byte followed by one thousand bytes of data and then
the stop byte. After sending the stop byte, the transceiver is switched to receiver mode. On the primary side,
as soon as the ASK transceiver detects the start byte, it is switched to the receiver mode and starts receiving the
data in the backward communication. Alternatively, whenever the ASK transceiver on the primary side detects
the stop byte, it is switched to the transmitter mode and starts sending the data in the forward communication.
For both experiments, the ASK transceiver on the sensing side was powered by the rectified AC power that was
harvested simultaneously while the data was received properly without any bit error.

Figure 4. Measurement setup
Figure 5. Experiment setups: (a) Real-time measurement of environment temperature; (b) Bidirectional
half-duplex data communication.
Figure 6 (a) shows a typical spectrum of measured power and data mixed signals in the frequency
domain captured by a vector signal analyzer. As seen in this figure, the modulated data signals exhibit lower side
band (LSB) and upper side band (USB) symmetrically at the data-carrier frequency of 8. At this data rate, the
channel bandwidth needed for data communication is 2.4. The power of the data signal at the carrier frequency
and LSB/USB are 14.6 and 6.1, respectively. At the fundamental frequency of 300, the power of transmitted
signal is 30.3 while the second and third harmonics are 22.6 and 11.2, respectively. Although the power signal
is much higher than the data signal, they are still separated when the data-carrier frequency is chosen to be
much higher than the power-carrier frequency. Consequently, the modulated signal is not interfered with the
high-order harmonics of the power-carrier signal. Figure 6 (b) shows the mixed signals in the time domain
captured by an oscilloscope. The low frequency corresponds to the power-carrier signal of 300, which is used
to transfer power to the sensing side. The high frequency signal corresponds to the data-carrier signal of 8,
which is used for ASK modulation.
Figure 7 shows a measured signal waveforms in backward communication at a data rate of 1.2.
The backward communication is more challenging due to the limited power budget that can be harvested on
the sensing side. The demodulation of the weak reception data signals on the primary side is critical to have data
received properly. Figure 7 (a) and 7 (b) show the transmitted digital data from the Arduino microcontroller
and the ASK modulated signal after the data signal is mixed with the 8-kHz carrier frequency generated by the
local oscillator, respectively. The strong power-carrier signal at 300 and its harmonics are suppressed by the
active HPF; thus, only data signals are available for demodulation. Figure 7c plots the baseband signals after
downconversion and low-pass filtering. Depending on the received signal strength, the reference voltage of the
following comparator is set accordingly. The digital data coming out from the ASK demodulator is plotted in
Figure 7 (d). Comparing Figure 7 (a) with Figura 7 (d), it is demonstrated that the transmitted and received
data are exactly the same with 0.24 delay time in transmission. The received digital data is read by the Arduino
microcontroller on the primary side and displayed on a computer monitor for verification. The signal-to-noise

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ratio (SNR) of approximately 18 for a bandwidth of 2.4 could be obtained. Using the proposed system, sensors
and communication circuits enclosed in sealed containers can be powered up and communicate with exterior
devices without any physical penetration for wire feed-throughs.
Figure 6. Measured transmitting mixed signals in, (a) frequency domain and (b) time domain
Figure 7. Measured signal waveforms in backward communication at data rate of 1.2, (a) Transmitted digital
data, (b) ASK modulated signals before power amplification, (c) Received signal after low-pass filtering and
(d) Received digital data after thresholding
4. CONCLUSION
In this paper, we have presented a novel system using multiple carriers in a single inductive link
for wireless power and data transfer through the 5-mm thick carbon composite barrier. The proposed system
exploits the center tap architecture enabling high power transfer and data communication at the same time.
Measurement results demonstrate that the system could achieve wireless communication at a data rate of 1.2
while the sensing side was powered up using 9.7 AC power that was harvested simultaneously.

ACKNOWLEDGMENT
This work has been supported by Lawrence Livermore National Laboratory under the project number
B620352.
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