International Journal of Engineering Trends and Technology (IJETT) – Volume 8 Number 3- Feb 2014
Design and Control of a Transcutaneous Power
Regulator for Artificial Heart
Ms. R. Kasthuri#1, Mr N. Lekshmanan*2
#1
PG student, #2 Assistant Professor, Dept. of Biomedical Engineering, Anna University,
Udaya School of Engineering, Ammandivilai, Kanyakumari, Tamil Nadu, India.
Abstract— In medical implant systems high efficiency and
improving the patient’s mobility. Artificial organs and
monitoring devices to be implanted into human body for the
extension and the improvement of human lives. The implants
must operate inside the body for the considerable period of time
and communicate with outside world wirelessly for exchange of
medical data and commands. Rechargeable batteries are
recharged remotely through the human skin via inductive links.
In my project transformer model a remote power supply for use
in the artificial hearts for easy controllability and high efficiency,
which can monitor the charging level of the battery has been
designed and implemented. In order to recharge the battery the
electro-magnetic coupling between primary coil and secondary
coil has been used. Primary and secondary windings of the
transformer are positioned outside and inside the human body
respectively. In such a transformer, the alignment and gap may
change with external positioning. The coupling coefficient of the
transformer is also varying, and so are the tool to large leakage
inductances and the mutual inductance. Resonance-tank circuits
with varying resonance frequency are formed from the
transformer inductors and external capacitors. A control method
is proposed to lock the switching frequency at just above the load
insensitive frequency for optimized efficiency at heavy loads.
Specifically operation at above resonant of the resonance circuits
is maintained under varying coupling coefficient. A
transcutaneous power regulator is built and found to perform
excellently with high efficiency and tight regulation under
variations of the alignment or gap of the transcutaneous
transformer load and input voltage.
Keywords— IM-SOC (implantable system on chip), Artificial
heart (AF), Transcutaneous energy transfer (TET).
I. INTRODUCTION
Now a days artificial organs and implant devices
are good role to play in the medical field. Artificial
heart (FIG.1.1) and monitoring devices to be
implanted into human body for the extension and
improvement of human life. The implants must
operate inside the body for a considerable period of
time and communicate outside world wirelessly for
exchange of medical data and commands. Among
difference forms of power sources, chemical
rechargeable batteries are by far the safest and most
popular form of power for implants. Rechargeable
ISSN: 2231-5381
batteries are recharged remotely through the human
skin via inductive links. Totally implantable
systems minimize the risk of infection and improve
the patient’s mobility. Reliable and safe methods of
providing power to the implants are the key factors
in achieving totally implantable systems. Inductive
link technology is widely used for powering
different kinds of implants. Air core type
transformers have been used and studied in and in
particular the work in class E power converters for
low power applications and for achieving space
saving [4].
II. DESIGN METHODS OF TRANSFORMER COIL
A transformer is a static electrical device that
transfers energy by inductive coupling between its
winding circuits. A varying current in the primary
winding creates a varying magnetic flux in the
transformer's core and thus a varying magnetic flux
through the secondary winding. This varying
magnetic flux induces a varying electromotive force
(emf) or voltage in the secondary winding.
Transformers can be used to vary the relative
voltage of circuits or isolate them, or both.
Transformers range in size from thumbnail-sized
used in microphones to units weighing hundreds of
tons interconnecting the power grid. A wide range
of transformer designs are used in electronic and
electric power applications. Transformers are
essential for the transmission, distribution, and
utilization of electrical energy [11]. Transformers
for use at power or audio frequencies typically have
cores made of high permeability silicon steel. The
steel has a permeability many times that of free
space and the core thus serves to greatly reduce the
magnetizing current and confine the flux to a path
which closely couples the windings [7]. Early
transformer developers soon realized that cores
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International Journal of Engineering Trends and Technology (IJETT) – Volume 8 Number 3- Feb 2014
constructed from solid iron resulted in prohibitive
eddy current losses, and their designs mitigated this
effect with cores consisting of bundles of insulated
iron wires. Later designs constructed the core by
stacking layers of thin steel laminations, a principle
that has remained in use. Each lamination is
insulated from its neighbours by a thin nonconducting layer of insulation. The universal
transformer equation indicates a minimum crosssectional area for the core to avoid saturation. The
effect of laminations is to confine eddy currents to
highly elliptical paths that enclose little flux, and so
reduce their magnitude. Thinner laminations reduce
losses, but are more laborious and expensive to
construct. Thin laminations are generally used on
high-frequency transformers, with some of very
thin steel laminations able to operate up to 10 kHz
[20]. The conducting material used for the windings
depends upon the application, but in all cases the
individual turns must be electrically insulated from
each other to ensure that the current travels
throughout every turn.
method are easy to understand. A DC source
provides power to an oscillator, which energizes a
primary coil. Magnetic flux is linked through the
implanted secondary coil, which is energized [12].
The induced current and voltage are then modified
as needed by a rectifier and regulator, to provide the
particular power requirements of the implanted
device. In nearly every practical TETS application,
the primary coil is worn against the skin, above the
implanted secondary coil [9]. Depending on the
design, the secondary coil will be implanted
anywhere from several millimetres to several
centimetres beneath the surface of the skin.
Although the coils are not linked through a fixed
common core, and although they can become
displaced during movement by the test subject, the
two coils form a loosely-coupled transformer. Thus,
the terms “primary” and “secondary” are carried
over from transformer theory.
A. Transmitter Section
III. BATTERY CHARGING PRINCIPLES
The most general rule for charging a battery is to
supply constant current to it at a rate of 0.1C, where
C is the capacity of the battery in mAh. So a 1000
mAh battery would be charged at 100 mA,
following the 0.1C rule. This method is referred to
as slow charging, and theoretically requires at least
10 hours to fully charging the battery. Again,
whether a 10 h charge time is practical for a clinical
device depends on the application. Another
technique for charging batteries is fast charging,
where charge times are less than 3 h. This charge
time is much more practical for an implanted device P/Y TMTR-Primary transmitter
application. The ability to fast charge a battery
Fig. 1 Block diagram of transmitter section
depends very much on the chemistry of the battery
[14].
Tuned circuit, any electrically conducting pathway
containing both inductive and capacitive elements.
IV. TRANSCUTANEOUS ENERGY TRANSFER
If these elements are connected in series, the total
A system capable of wireless power delivery is
voltage V across the open terminals is simply the
now commonly referred to as a transcutaneous
sum of the voltage across the inductor and the
energy transfer system (TETS). This method allows
voltage across the capacitor. The current i flowing
an implanted system to be continually powered,
into the positive terminal of the circuit is equal to
without the constraints presented by implanted
the current flowing through both the capacitor and
batteries. Although TETS design can be quite
the inductor. Inductive reactance magnitude
complex, the principles behind this power delivery
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International Journal of Engineering Trends and Technology (IJETT) – Volume 8 Number 3- Feb 2014
increases as frequency increases while capacitive performance microcontroller. In this one is a fast
reactance magnitude decreases with the increase in programming time and static operation.
frequency. At a particular frequency these two
reactance’s are equal in magnitude but opposite in
sign. Power driver ckt usually used to regulate
current flowing through a circuit or is used to
control the other factors such as other components,
some devices in the circuit. The term is often used,
for example, for a specialized integrated circuit that
controls high-power switches in switched-mode
power converters. A regulated power supply is one
that controls the output voltage or current to a
specific value; the controlled value is held nearly
constant despite variations in either load current or
the voltage supplied by the power supply's energy
source.
B. Receiver Section
Fig. 3 Buzzer circuit
S/Y RCVR-Secondary Receiver
Fig. 2 Block diagram of receiver section
The secondary coil receiving the corresponding
voltage from the transmitter side. bridge rectifier
which converts AC to DC. which provides the same
output polarity for either input polarity. A voltage
regulator is designed to automatically maintain a
constant voltage level. A voltage regulator may be a
simple "feed-forward" design or may include
negative feedback control loops. Charge control
circuit is control the voltage depends on the battery
level. Then the ADC which converts analog to
digital signal. AT89S52 Is a low power, high
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A buzzer or beeper is a signalling device, The
word "buzzer" comes from the rasping noise that
buzzers made when they were electromechanical
devices, operated from stepped-down AC line
voltage at 50 or 60 cycles. Other sounds commonly
used to indicate that a button has been pressed are a
ring or a beep. The buzzer circuit also present in the
receiver circuit. It indicates the low voltage of the
battery. A simple electromagnetic relay consists of
a coil of wire surrounding a soft iron core, an iron
yoke, which provides a low reluctance path for
magnetic flux, a moveable iron armature, and a set,
or sets, of contacts; two in the relay pictured. The
armature is hinged to the yoke and mechanically
linked to a moving contact or contacts. It is held in
place by a spring so that when the relay is deenergised there is an air gap in the magnetic circuit.
In this condition, one of the two sets of contacts in
the relay pictured is closed, and the other set is open.
Other relays may have more or fewer sets of
contacts depending on their function. The relay in
the picture also has a wire connecting the armature
to the yoke. This ensures continuity of the circuit
between the moving contacts on the armature, and
the circuit track on the Printed Circuit Board (PCB)
via the yoke, which is soldered to the PCB.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 8 Number 3- Feb 2014
V. RESULTS
Fig. 4 LCD Module Interfacing With
The main aim of this project is to eliminate the
need for periodic surgery for battery replacements
in artificial heart. This can be achieved by using RF
coupling technique for energy transmission to
regulate the power supply and control method for
artificial heart. The lithium carbon monofluoride
battery has a high density when compared with the
lithium battery that is used today. In this project for
demo purpose a POT is used instead of a battery
and the expected output of charging using RF
coupling technique is achieved. The controlling
applications such as monitoring the battery status is
obtained successfully using a microcontroller and it
is displayed in the LCD display is used.
Microcontroller
The AT89S52 is a low-power, high-performance
CMOS 8-bit microcontroller with 8K bytes of insystem programmable Flash memory. The device is
manufactured using Atmel’s high-density nonvolatile memory technology and is compatible with
the industry-standard 80C51 instruction set and pin
out. The on-chip Flash allows the program memory
to be reprogrammed in-system or by a conventional
non-volatile memory programmer. By combining a
versatile 8-bit CPU with in-system programmable
Flash on a monolithic chip, the Atmel AT89S52 is a
powerful microcontroller which provides a highlyflexible and cost-effective solution to many
embedded control applications. The AT89S52
provides the following standard features: 8K bytes
of Flash, 256 bytes of RAM, 32 I/O lines,
Watchdog timer, two data pointers, three 16-bit
timer/counters, a six-vector two-level interrupt
architecture, a full duplex serial port, on-chip
oscillator, and clock circuitry. In addition, the
AT89S52 is designed with static logic for operation
down to zero frequency and supports two software
selectable power saving modes. The Idle Mode
stops the CPU while allowing the RAM,
timer/counters, serial port, and interrupt system to
continue functioning. The Power-down mode saves
the RAM contents but freezes the oscillator,
disabling all other chip functions until the next
interrupt or hardware reset.
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VI. CONCLUSION
An implantable micro-stimulator SOC (IMSOC)
is designed as artificial heart for remote delivery of
power by means of coupled coils supplying power
to a bio-implanted rechargeable battery. The
IMSOC consist of a smart control circuit for power
management, an RF-coupling power system for
battery charging and two ultra-small rechargeable
batteries as power supplies. Which can monitoring
the charging level of the battery using LCD display.
Stimulus parameters, such as pulse width,
amplitude, and frequency can be programmed from
the remote controller. Hence by using method of RF
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International Journal of Engineering Trends and Technology (IJETT) – Volume 8 Number 3- Feb 2014
coupling in recharging the artificial hearts battery,
loading variations and improper device shutdown
can be prevented and also we can eliminate the
need for periodic surgery for battery replacement,
therefore improving the quality of patient’s life.
[9]
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