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TEMJournal.Volume11,Issue3,pages1352-1356,ISSN2217-8309,DOI:10.18421/TEM113-45,August2022.
1352 TEMJournal–Volume11/Number3/2022.
Analysis of Four Coils by Inductive Powering
Links for Powering Bio-implantable Sensor
Mokhalad Alghrairi
1,3
, Nasri Sulaiman
1
, Wan Zuha Wan Hasan
1
,
Haslina Jaafar
1
, Saad Mutashar
2
1Department of Electrical and Electronic Engineering, Faculty of Engineering, Universiti Putra Malaysia,
Serdang 43400, Selangor, Malaysia
2Department of Electrical Engineering, University of Technology- Iraq
3Department of Computer Techniques Engineering, Imam Al Kadhim College (IKC), Baghdad, Iraq
Abstract – The inductive coupling link technique is
popularly used for transmitting power in many
biomedical applications, where it helps in transferring
power to numerous implanted biomedical devices like a
wireless pressure sensor system. It has also been noted
that the inductive coupling variables significantly
affect the coupling efficiency. In this study, the
researchers have investigated the inductive coupling
link variables for 3 transmitter coils and one receiver
coil. They used a resonant frequency of 27 MHz as the
operating frequency, based on the Industrial, Scientific
and Medical (ISM) band. The experimental results
indicated that the Voltage gain (i.e., Vgain) value of the
inductive links was dependent on the Coupling Factor
(K) existing between every coil and load resistance (i.e.,
Rload). It was also noted that the value of the Voltage
gain increased with an increase in the implanted
resistance, based on a constant coupling factor.
Furthermore, the simulation results indicated that if
the Rload=1000, the Vgain value would be maximal,
whereas if Rload = 200Ω, the Vgain value would be
minimal and ≈ 5V.
DOI:10.18421/TEM113-45
https://doi.org/10.18421/TEM113-45
Correspondingauthor:MokhaladAlghrairi,
Department of Electrical and Electronic Engineering,
FacultyofEngineering,UniversitiPutraMalaysia,Serdang
43400,Selangor,Malaysia.
Email:mokhalad.khalel@alkadhum‐col.edu.iq
Received:13March2022.
Revised:09August2022.
Accepted:15August2022.
Published:29August2022.
©2022MokhaladAlghrairietal;published
byUIKTEN.ThisworkislicensedundertheCreative
CommonsAttribution‐NonCommercial‐NoDerivs4.0
License.
The article is published with Open Access at
https://www.temjournal.com/
These results indicated that the operating system
could satisfy all the requirements for powering the
implanted sensor biodevices.
Keywords – low band frequency (ISM), energy
harvesting, in-stent restenosis, four inductive coupling
links
1. Introduction
In the past few years, the inductive link technique
has been used in many Implantable Medical Devices
(IMDs) like brine implants, pacemakers, retinal
implants, cochlear implants and in-stent restenosis
coronary artery systems, for transmitting power to
the pressure sensors. Additionally, these devices help
in recording, measuring and sensing the various
physiological signals present in the body [1], [2]. A
majority of these devices are implanted in the body
for the long term. Hence, owing to the long life-spans
of the implanted batteries, occupied area and the
resulting chemical effects, the inductive coupling
links are regarded as a suitable choice for powering
the implanted medical devices for a short-range [3].
Generally, the inductive coupling links are made of
two resonating RLC parts [4], wherein Part 1 is
operated by the Power amplifier that is placed
outside the body and is known as a primary part,
external component or in vitro part. On the other
hand, Part 2 is integrated and placed within the body
and is known as a secondary component, internal part
or in vivo part. The secondary part is supplied power
inductively with the help of the primary part based
on the magnetic flux, wherein it acts as the antenna.
However, this technique cannot satisfy the power
requirements of the device if the distance between
the receiver and transmitter components is large.
Furthermore, the researcher designed a device that
included two RLC circuits within the transmitter
component while one RLC component was included
in the receiver component for improving the power
transfer efficiency when the two components of the
TEMJournal.Volume11,Issue3,pages1352‐1356,ISSN2217‐8309,DOI:10.18421/TEM113‐45,August2022.
TEMJournal–Volume11/Number3/2022.1353
link were tuned to the same resonant frequency [5],
[6]. It was noted that the fragile coupling link present
between the transmitter and receiver coils led to the
ineffective power transfer between the sides [7]. In a
majority of the cases, the primary coils were tuned in
a series resonant for offering a low impedance load,
whereas the secondary circuit was invariably parallel
[8]. For transmitting the power to the implanted
biodevices at a narrow band, the researchers selected
a resonant frequency based on the Industrial,
Scientific and Medical (ISM) band, as it could not
heat or damage the human tissues [9]. The inductive
coupling link variables are as follows: Transmitter
coil inductance, i.e., L1, L2, L3; Receiver coil
inductance (L4); Mutual inductance (Mij); Resonant
frequency (f0); and Coupling factor of Kij (where Kij
must range between 0 and 1 i.e., 0< Kij <1). These
inductive coupling link variables directly affect the
coupling link efficiency. Out of all the above factors,
the coupling factor (Kij) is a major parameter that
helps in determining the quantity of power that is
transmitted to the implanted sensor biodevices [10].
In this study, the researchers have determined and
analysed the relationship between Voltage gain
(Vgain) and other variables like coupling coefficient
(Kij) and load resistance (Rload) for the 3 RLC
circuits at the transmitter end and one RLC Circuit at
the receiver end. They have assumed the implanted
load resistance variables to be 200, 400, 600 and
1000 while the variable coupling factors were
presumed to be 0.3, 0.5, 0.7, 0.9.
2. Method and Theoretical Model for Inductive
Coupling Link
In this study, the researchers implemented a
wireless inductive coupling link that used a magnetic
flux for transferring power between the transmitter
and receiver coils. Figure 1. presents the inductive
link that consists of the L1, L2 and L3 coils at the
transmitter end and the L4 coil at the receiver end.
For improving and maximizing the power transfer
efficiency, the researchers tuned the transmitter coils
in a series resonance, while the receiver coil was
tuned in parallel resonance.
Figure 1. Structure of Inductive Coupling Circuit
Physically, it was seen that the coupling factor
(Kij) was equal to the fraction of magnetic flux that
was generated by L1, which then passed through coil
2, i.e., L2, and then to the third and fourth coils, i.e.,
L3 and L4. Also, the mutual inductance (Mij) was
the reciprocal property of 2 coils, i.e., M12, M23 and
M34, respectively. On the other hand, the coupling
coefficient (Kij) ranged from 0 to 1, which indicates
the electrical coupling level between the different
inductor pairs.
𝐾
(1)
This was seen to be the primary factor that
determined the maximal distance (Dij) which helped
in accurately operating the implant and determining
the amount of power that could be transmitted to the
implanted biomedical devices. The researchers
calculated the inductive parameters depending on the
shape of the different coils, i.e., the transmitter end
coils were rectangular, while the coils at the receiver
end were helical [11]
𝐿.
𝑙𝑛.
∅0.18∅0.13∅ (2)
𝐿
(3)
Furthermore, the parasitic resistance values, i.e.,
RL1, RL2, RL3 and RL4 for the L1, L2, L3 and L4
coils that were calculated using Eqs. (4-7) were small
as shown in Table 1. These values could be used for
inductive powering based on various factors like the
type of coils, resistive load and coupling links
𝑅,, 𝑅
(4)
𝑅 𝜌
.
(5)
𝑙4𝑁
𝑑 4𝑁𝑤2𝑁
1𝑠𝑤 (6)
𝑅
(7)
The capacitance for circuit can be calculated from
equations (8-11)[8].
𝐶𝐶
.
1 .
. (8)
𝐶.
(9)
𝐶.
(10)
𝐶
(11)
Wherein Rload indicates the implanted resistance,
which is > 2ꞶL4
For estimating the Voltage gain (Vgain) between
Coils 1 and 2, Coils 2 and 3, and Coils 3 and 4, the
researchers determined the Quality Factor (Qn) for
every coil. This was dependent on the Resonant
Frequency (f0), coil inductance, and parasitic
resistance for the pair of coils, as shown in Eqs (2, 3)
and (8-11).
TEMJournal.Volume11,Issue3,pages1352‐1356,ISSN2217‐8309,DOI:10.18421/TEM113‐45,August2022.
1354TEMJournal–Volume11/Number3/2022.
𝑄
(12)
Wherein; n =No. of coils; parasitic resistance. The
Vgain value was estimated using Eq. 13.
𝑣 𝑘
𝑄2 (13)
𝑣 𝑘
𝑄3 (14)
𝑣 𝑘
𝑄 (15)
𝑄
//
(16)
Table 1. Presents the values of the various parameters
used in this inductive coupling system
Parameter Symbol Value
Coil Inductance
1,2,3 L1, L2, L3 44.80µH
Coil Inductance 4 L4 0.355 µH
Parasitic
Resistance 1,2,3 R1, R2, R3 14.98 ꭥ
Capacitance 1 C1 0.80 PF
Capacitance 2 C2 0.557 PF
Capacitance 3 C3 0.557 PF
Capacitance 4 C4 97.41 PF
Resonance
Frequency F0 27MHz
3. Result and Discussion
Many researchers have realized the significance of
developing effective IMDs since these devices can
directly impact the safety and the lives of the users.
The inductive coupling link is regarded as the most
effective technique that helps in transmitting power
to the battery-less, implanted devices [12]. In this
study, the researchers have used a series-to-parallel
inductive coupling topology, where they tuned 3
primary coils (reader) in a series resonance for
decreasing the impedance load and operating the
transmitter coils. They improved the link efficiency
by tuning both the receiver and transmitter RLC
circuits so that the inductive link showed a similar
resonance frequency of 27 MHz.
The researchers used the Pspice OrCad software
tool for simulating the proposed system. Figure 2.
presents the relationship between the Voltage gain
(Vgain) and Coupling factor (Kij) for Coils 1 and 2
when the coupling factor value was variable (K12 =
0.3, 0.5, 0.7 and 0.9, respectively). The simulation
results indicated that the Vgain value at K12=0.9 was
smaller compared to its value when K12= 0.5; while
it was higher than its value when K12 = 0.3. This
was based on the reflected magnetic flux occurring
between the 4 coils. This was believed to increase if
the distance between Coils 1 and 2 was higher but
within the limited range; however, the Vgain value
would decrease if K12 = 0.3. A similar scenario was
noted for Coils 2 and 3 when the K12 value between
Coils 1 and 2 was fixed at 0.5, as described in Figure
3. On the other hand, the Vgain value between Coils
3 and 4 would be higher if k= 0.9, instead of a
different K34 value when the load resistance value
was fixed at 400ꭥ, as presented in Figure 4.
Figure 2. Shows the relation between voltage gain and
coupling factor for first coil and second coil
Figure 3. Shows the relation between voltage gain and
coupling factor for third coil and fourth coil
Figure 4. Shows the relation between voltage gain and
coupling factor for third coil and fourth coil
For validating the model, the researchers used the
MATLAB software and highlighted the relationship
between the variation in the coupling factor values
between the different coils, as it increased the
variation in the distance between the coils. Figure 5.
describes the variation between the coupling factors,
i.e., K12 with K23 at 0.5 and K34 at 0.5. It was noted
that the efficiency was low if K12 = 0.9, compared to
TEMJournal.Volume11,Issue3,pages1352‐1356,ISSN2217‐8309,DOI:10.18421/TEM113‐45,August2022.
TEMJournal–Volume11/Number3/2022. 1355
the efficiency if K12 = 0.5. This explained the data
presented in Figure 2. Based on a similar scenario, it
was noted that for K23, the efficiency decreased
when the Coils 2 and 3 were closer to each other, as
presented in Figure 6.
Figure 5. Variation of efficiency with Coupling factor K12
at K23 =0.5
Figure 6. Variation of efficiency with Coupling factor
K23 at K12 =0.5
Figure 7. highlights the relationship between
Vgain, constant coupling factor value (k12=0.5,
k23=0.5, k34= 0.5), and the load resistance, i.e.,
Rload= (200, 400, 600, 1000). The results indicated
that the Vgain value was maximal if the load
resistance value was maximised (Rload = 1000),
while it was the lowest if the load resistance value
was the least (Rload = 200).
Figure 7. Shows the relationship between voltage gain
with constant coupling factor
Figures 2.-4. indicated that the inductive links at
maximal Vgain value behaved like a passband filter
when the central frequency was maintained at 27
MHz. Figure 8. and Figure 9. indicated the input and
output sinusoidal signals with a fixed coupling factor,
i.e., K34= 0.5 and constant load resistance, i.e.,
Rload = 400. Thus, the output signal that was
transmitted to the IMDs was decreased in
comparison to the output signal generated from the
primary coil. It was noted that the output signal also
transferred power and also satisfied the power
requirements for different components of the
implanted biosensor.
Figure 8. Shows the input sinusoidal signal to the first
transmitter coil
Figure 9. Shows the output sinusoidal signal from the load
resistance
4. Conclusion
In this study, the researcher simulated the design of
the inductive coupling link for the wireless power
transmission using the Pspice Orcad software. They
highlighted the relationship between different
parameters like Voltage gain, coupling factor and
load resistance. The mathematical module and
simulation results indicated that at a constant load
value, i.e., Rload and varying coupling factor (Kij)
values, the coupling link behaved like a passband
filter at the selected central frequency of 27 MHz.
The Vgain value increased with an increase in the
load resistance at a constant coupling factor. Table 1.
presents the values of all parameters used in the
system, which could satisfy the requirements of the
IMDs and also transmitted power to the internal
component.
TEMJournal.Volume11,Issue3,pages1352‐1356,ISSN2217‐8309,DOI:10.18421/TEM113‐45,August2022.
1356 TEMJournal–Volume11/Number3/2022.
Acknowledgements
This work is supported by University Putra Malaysia
through the project under title A high efficient RLC
inductive transmission coupling to monitor in-stent
restenosis coronary artery under Grant Inisiatif Putra
Siswazah (GP-IPS) 9712900.
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