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Implantable Antennas for Biomedical Applications: An Overview on Alternative Antenna Design Methods and Challenges

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Implanted biomedical devices are witnessing great attention in finding solutions to complex medical conditions. Many challenges face the design of implantable biomedical devices including designing and implanting antennas within hostile environment due to the surrounding tissues of human body. Implanted antennas must be compact in size, efficient, safe, and can effectively work within adequate medical frequency bands. This paper presents an overview of the major aspects related to the design and challenges of in body implanted antennas. The review includes surveying the applications, design methods, challenges, simulation tools, and testing and manufacturing of implantable biomedical antennas.
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Implantable Antennas for Biomedical Applications:
An Overview on Alternative Antenna Design
Methods and Challenges
Adel Damaj, Hilal M. El Misilmani, and Soubhi Abou Chahine
Electrical and Computer Engineering Department
Beirut Arab University
Beirut, Lebanon
adelwd@gmail.com, hilal.elmisilmani@ieee.org, achahine@bau.edu.lb
AbstractImplanted biomedical devices are witnessing great
attention in finding solutions to complex medical conditions. Many
challenges face the design of implantable biomedical devices
including designing and implanting antennas within hostile
environment due to the surrounding tissues of human body.
Implanted antennas must be compact in size, efficient, safe, and
can effectively work within adequate medical frequency bands.
This paper presents an overview of the major aspects related to the
design and challenges of in body implanted antennas. The review
includes surveying the applications, design methods, challenges,
simulation tools, and testing and manufacturing of implantable
biomedical antennas.
KeywordsImplantable antennas, biomedical applications,
biomedical telemetry.
I. INTRODUCTION
Implantable medical devices are implanted devices capable
of communicating with an external device using wireless
technology. The electromagnetism has been used in medical
applications since the last century and has been converted to
radio frequency. Implanted devices are taking important interest
in the field of biomedical applications. Typically, links that are
used for biomedical communication are radio frequency (RF)
and inductive links. Inductive link, which uses coil antennas, is
a shortrange communication channel that suffers from low data
rates ranging from 1 to 30 kbps [1], and a restrained transmission
of less than 10 cm [2]. To get rid of such problems, studies
nowadays are directed towards RF-linked implantable medical
devices, which offer the advantage of longer range and higher
data rates.
Several frequency ranges have been suggested and currently
tested to be used in different medical implant applications. In
1998, the ITU-R Recommendation SA.1346 suggested to use the
401 to 406 MHz band for Medical Implant Communications
Services (MICS) [3]. Other recommended frequency bands for
biomedical applications range from 433.1 to 434.8 MHz, 608 to
614 MHz, 868 to 868.6 MHz, 902.8 to 928 MHz, 1395 to 1400
MHz, 1427 to 1432 MHz and 2.4 GHz to 2.5 GHz, known as the
Industrial, Scientific, and Medical (ISM) bands, and the
Wireless Medical Telemetry Service (WMTS) [4].
Nowadays, implanted biomedical devices have become very
essential in many fields and they are currently proposed and used
in a large range of medical applications such as: intracranial
pressure monitoring, radiometer/heating, dental antenna for
remote health care applications, continuous real-time pressure
measurements, sugar level check, pacemaker connection, insulin
push out, endoscopy, and blood pressure measurements. In fact,
they are important in humans’ medical diagnosis, treatment, and
prevention. The role of implanted antennas in diagnosis includes
a wide range of applications, such as magnetic resonance
imaging (MRI). In MRI, the antenna transmits electromagnetic
vibrations to the human body, and as a feedback, it receives the
nuclear magnetic resonant frequency signals radiated from the
nuclei that create the human body [4]. The role of implanted
antennas in treatment includes a pacemaker that helps monitor
and control heartbeat, and swallow-able capsule with sensing
facility. To get the benefits of such a medical system, a telemetry
device must communicate with an external receiver using an
integrated antenna.
Working in a suitable biomedical band requires an efficient
compact antenna that fits either inside or around implanted
device [5]. There is an urge for installing an implantable antenna
capable of allowing multi or broadband data transmission, taking
into consideration the attenuation due to body heterogeneous
tissues [6] which cause reduction in both efficiency and
bandwidth. The major challenge is that the implanted antenna is
heavily miniaturized which leads to an electrically small size
antenna, thus suffering from decreasing of its radiation
performance. The solution to such a problem is to achieve a good
compromise between size and radiation characteristics.
Other challenges facing communication system include the base
station and the sensitivity of the receiver, channel propagation
related to path propagation of the radiated EM waves, the
scattering due to the close objects, and the human body and its
lost characteristics effect. A care should be also taken to ensure
a well maintained biocompatible insulation to avoid safety
issues. Another challenge is found in the power supply used with
the implanted antenna that often has the largest volume size.
In this paper, a literature review on the design of antennas for
biomedical applications is presented. Starting with a brief
description of implanted antenna systems, an extensive review
of several antennas used in various biomedical applications is
Figure 1. Wireless implantable system [7]
presented. The design challenges facing such antennas are
discussed while investigating the different techniques that can be
used to reduce the size of the antenna for proper insertion inside
the body. The different simulation tools, in addition to the typical
measurements techniques, in vitro and in vivo, are also
presented. The biocompatibility issues and safety precautions
concerned in the design of implanted antennas for biomedical
applications are also discussed.
II. IMPLANTED ANTENNA SYSTEM
Wireless implantable system for biomedical telemetry
includes the sensor, power supply, implantable antenna and the
insulation, as shown in Fig. 1. The main target is to transmit
information from internal part of the body to an external base of
operation, thus the physiological signals are obtained by means
of a suitable transducer, then transmitted by the operator through
implanted antenna [7].
To design a biomedical antenna for an implanted
communication system, one must consider all the surrounding
environment aspects referring to [8]. These aspects are
simplified into circular stratum representing the working habitat.
The first stratum is air which contains the origin. The second is
the bio-compatible padding, and the following is made up of
several layers representing the human body, as shown in Fig. 2.
4
4
3
2
1
1- Air.
2- Insulation.
3-Human tissue layer.
4-Human tissue layer.
5-Free space.
5
Figure 2. Body sample: muscle, skin and fat
III. IMPLANTED ANTENNAS FOR BIOMEDICAL APPLICATIONS
A small three-dimensional spiral antenna has been presented
in [5] for biomedical applications. The presented antenna
operates in the MICS band. At a frequency of 405 MHz, the
attained bandwidth is 225.5 MHz (55.7 %). The dimensions of
the proposed antenna are 14×14×15 mm3. To achieve such
dimensions, an optimization process is performed by analyzing
several spiral configurations then choosing the most appropriate
dielectric material. The investigation concluded that the use of
the higher relative permittivity material leads to a smaller and
efficient antenna. Another optimization technique has been
presented using grounding pins Planar Inverted-F Antennas
(PIFA). One of the major achievements is reducing the volume
by 55%, while only losing 1.4 dB of antenna gain and
maintaining the attained bandwidth. The developed antenna
enjoys a stable behavior in several homogeneous phantoms. To
obtain the power absorbed by the body model, the Specific
Absorption Rate (SAR) in the homogeneous muscle equivalent
phantom has been also computed showing that the power
received at the antenna should be leveled at 7.4 mW.
The construction of a triple-band inserted miniaturized-slot
PIFA has been presented in [6]. The antenna can operate in the
MICS band at 433MHz, WMTS band at 1430 MHz and ISM
band at 2.4 GHz. The presented antenna has a volume of less
than 1 cm3 of dimensions 19×30×1.6 mm3, with a minimized
size of about 50% more than that of standard E-shaped patch
antennas. This has been achieved through settling the
corresponding places of the feed, and the use of shorting pins.
An adjustable folded dipole implantable antenna, operating
in the ISM band at 2.45 GHz, has been presented in [9]. The
resulting bandwidth of the antenna is around 50.2%, with
dimensions of 8.5×25.9×3.2 mm3. A superstrate and a substrate
of Polydimethylsiloxane (PDMS) have been used in the
optimization process of the antenna dimensions. To mimic the
human muscles tissue, a specific liquid has been used. The
antenna has an acceptable SAR value, but suffers from a large
size that restricts an immediate implant. The developed antenna
can be used for observing blood pressure and temperature, and
pursue defenseless people and pets.
Two antennas, PIFA antennas and annular slot antennas,
have been presented in [10]. The PIFA antenna can operate at
2.4 GHz, to be used for intracranial pressure monitoring (ICP).
The slot antenna can operate at 915 MHz and 1.5 to 2 GHz,
suitable for heating and radiometry, respectively. The SAR
profile, the tissue loss, and the thickness of the silicone
biocompatible highly have been shown to affect the gain and the
radiation characteristics of the antenna. Concerning the PIFA
antenna presented [10], the SAR decay profile has similar results
using different thicknesses. For a thicker coating, the SAR was
seen to decay less while going in depth in the tissue using the
slot antenna. As for the slot antenna, it was observed that it
demonstrated a larger bandwidth than that of the PIFA antenna,
with higher radiation efficiency (4.9 to 8.0 dB).
A dual folded dipole antenna has been presented in [11],
operating in the ISM band and WMTS. In addition, the compact
dimensions of the proposed antenna are 25×34×2.5 mm3, shown
in Fig. 3. The feeding structure of the dual folded dipole antenna
is comprised of a 50 Coplanar Waveguide (CPW). The
antenna can operate with a good impedance matching in the 1.42
GHz and 2.4 GHz, with bandwidths of 10.52% and 23%,
respectively.
A combination between Hilbert-type fractal and
Archimedean Spirals has been presented in [12] for implanted
dental antenna applications. The antenna can be used for remote
health care applications, and can operate within the medical
radio band. Moreover, the compact area is less than 245 mm2,
11.5×8 mm3, as shown in Fig. 4. The line spacing and width
have been optimized to expand the bandwidth by 346%. The
antenna has been tested in vitro using an imitation cubic oral
cavity, and in vivo close to the molar of a 25-year-old man. The
results showed that the antenna radiation characteristics have
been severely affected when used in an actual human mouth. As
a result of mouth closing and opening, it has been observed that
the 400 MHz operating frequency shifted by 80 to 120 MHz for
this, it was concluded that a larger bandwidth is recommended.
A fully implantable wireless sensor attached to a helical
antenna with dimensions of 15×4.5 mm2 has been presented in
[13]. The antenna can be used as continuous blood pressure
monitoring system through continuous real-time pressure
measurements. The antenna is twisted along a nylon screw, and
a Polydimethylsiloxane material (PDMS) is used for insulation.
A phantom close to the properties of the human body has been
used to test the antenna in vitro, using a sensor and a patch
antenna, connected to the interrogator and a digital scope. An
animal has been also used to test the antenna in vivo. The results
showed acceptable similarities between the results of both tests.
An implantable CPW fed monopole antenna with a
rectangular patch element of dimension of 18×24×0.65 mm3 has
been presented in [14]. The antenna can operate at a frequency
of 2.45 GHz, with a bandwidth of 320 MHz, covering the ISM
band. The antenna is intended to be used for several applications,
endoscopy, glucose and blood pressure monitoring, insulin
pumps, pacemaker communication and retinal prosthesis. The
antenna has been tested in vitro using a mixture of sugar and salts
in an ultra-pure water. It was noticed that with the increase of
sugar concentration, the permittivity (𝜀) decreases, with slight
increase in the value of the conductivity (σ), whereas, with an
increase of salt concentration, the permittivity decreases, with a
significant increase of the conductivity. The antenna radiation
characteristics has been also compared with other implanted
antennas, for which it was concluded in [14] that the proposed
antenna has good VSWR and impedance matching, with low
return loss and high gain.
A PIFA Omni directional antenna, suitable for long-range
communication for medical application with dimensions of
65×40 mm2 has been presented in [15]. The antenna operates at
441 MHz with a bandwidth of 14.55%. Several methods have
been also presented in order to enlarge and tune the bandwidth,
as in replacing the radiator element with a plate, or changing the
size of the ground plane. In addition, several inserted slits in the
ground plane have been used to decrease the quality factor and
further improve the bandwidth.
An electrically small and efficient implanted antenna, using
MEMS on-chip technology, has been presented in [16]. The chip
area is 1.5×1.5 mm2, and the entire system dimensions are
5×3×1.5 mm3. To place this instrument near the nervous system,
wafer level encase has been used to entirely combine the antenna
within the micro device. Increasing the substrate dielectric
permittivity and antenna folding have been also suggested to
decrease the size of the antenna. The proposed MEMS antenna
has been tested as a receiver at a frequency of 10 MHz, and
showed an important size reduction compared to a standard
miniaturized antenna.
Figure 3. Dual folded dipole antenna [11].
Figure 4. Hilbert-type fractal and Archimedean Spirals Antenna [12].
An implantable slot dipole antenna operating in the 2.4 to
2.48 GHz band has been also presented in [17]. The antenna has
the dimensions of 18.5×25.9 mm2. Using a PDMS as a
homogeneous tissue, a deviation of the operating frequency has
been observed when placing the antenna in various tissues. The
antenna showed to be applicable for biomedical implantable
applications with an ohmic loss of 2.5%. The antenna has been
also tested in a heterogeneous stratum using a model of a 6-year
old male child. The results showed that the path loss model in
the heterogeneous medium the required power of implanted
antennas at a frequency of 2.45 GHz.
The design of an electrically small antennas using the
Integrated Passive Devices (IPD) design has been presented in
[18]. Two antennas have been proposed. The first is a planer
antenna with dimensions of 18×50 mm2, while the second is a
monopole antenna with dimensions of 5.3×3.25 mm2. The
meandered monopoles fed using microstrip and Coplanar
Waveguide (CPW) transmission lines have been also discussed.
Small-bumps have been used to link the planner antenna to the
RF front-edge. The inserted system includes batteries and a
microphone, and it is enveloped by a capsule. For monopole
antenna, the arm has been easily meandered to minimize it. The
results of both antennas showed a good efficiency at 1.9 GHz
with quality factor of 9.4 and 10.9.
A loop antenna has been presented in [19] for energy
harvesting, using a CMOS RF technology. The antenna part
compromises the loop antenna with an inductor, with
dimensions of 3×3 mm2. To increase the harvested energy, five
stages have been used in the rectifier structure. Simulation
results showed that an efficiency of 60% has been obtained with
a 100 kΩ load. The measured results at 4 GHz, using a +20 dBm
RF source at a 7 cm distance, showed that the proposed system
is capable of collecting a power of 0.5 µW with a 500 kΩ load,
which makes it suitable to be used to power low-power
biomedical systems, such as a health monitoring implant via
temperature sensors.
IV. ANTENNA DESIGN CONSIDERATIONS
In order to design an antenna suitable for implanted
biomedical applications, the antenna must be compact, for
optimal case, of a diameter of 5 to 10 mm, with 30 to 55 mm
length [20]. Many steps should be followed to achieve a compact
implanted antenna suitable for biomedical applications. These
steps include using miniaturization techniques, obeying
biocompatibility issues, using an effective simulation tools,
launching in-vitro and in-vivo measurements, and not to forget
safety issues.
A. Miniaturization techniques
Implantable antennas miniaturization techniques are
becoming more challenging for researchers nowadays.
Generally speaking, the design of such antennas require the
study of the following:
1) Dielectric Materials
Choosing high dielectric substrate/superstrate is the simplest
way to achieve antenna size reduction. This can decrease the
useful wavelength and lead to smaller resonance frequencies
[21]. Rogers 4003 and FR4 [10], [22]with permittivity of 3.55
and 4.7 respectively are widely used with implanted antennas to
decrease the overall size. Higher permittivity materials such as
Alumina ceramic(𝜀𝑟= 9.9) , Glass wafer (𝜀𝑟=10), Roger
(𝜀𝑟=10.2),Teflon (𝜀𝑟=11), and Zirconium dioxide (Zro2)
(𝜀𝑟=21), can cause remarkable size decreasing. Table I lists
the different dielectric materials used in the referenced papers in
this work with their corresponding dielectric constants.
2) Antenna structures
Different antenna structures have been proposed for
biomedical applications, such as helical antenna, CPW fed
monopole, PIFA, MEMS, flexible folded slot dipole, slot PIFA,
rectangular patch, On-chip antenna, IPD, Hilbert-type fractal
and Archimedean spirals. The PIFA design is the most common
antenna type used for implantable antenna applications [6, 10,
15]. The resonant length of a microstrip patch antenna is half
the wavelength at the resonance frequency. PIFA antenna is
known for its quarter-wavelength length, which make it suitable
for such applications requiring small antenna size [4]. MEMs
antennas are considered the smallest antennas to be used in these
application [16].
Inspecting Table II and comparing some antenna design
structures at the same resonance frequency, it is seen that MEMs
possess the smallest size, followed by patch, monopole, spiral,
and slot dipole antennas.
1) Stretching the Current way of the Radiator
Elongating the current path of the radiator can be considered
as an effective way for size reduction. This lengthening shifts the
resonance frequency to lower frequencies and hence achieving
size reduction. Several design techniques can be used for this
purpose, as in the use of line, loop, helical, meandered, and slot
antennas.
TABLE I. MATERIALS AND RELATIVE DIELECTRIC CONSTANT FOR
REFERENCE PAPERS.
Ref.
Materials
Relative dielectric constant
𝜺𝒓
[5]
Teflon, HIK500,
11
[10]
Rogers 4003
3.55
[11]
material
2.2
[12]
ZrO2
21
[14]
ceramic
9.8
[15]
material
4
[16]
Glass wafer
3.7 - 10
[20]
Rogers 3210
10.2
[22]
FR4
4.7
[23]
Roger
10.2
[24]
alumina ceramic (Al2O3)
9.9
TABLE II. COMPARISON BETWEEN DIFFERENT ANTENNA STRUCTURES
AND FREQUENCY BANDS USED IN REFERENCE PAPERS
Ref.
Design Type
Frequency Band
[5]
Spiral
MICS
[6]
Slot PIFA
ISM,
MICS,WMTS
[9]
Folded slot dipole
ISM
[10]
PIFA
ISM
[11]
Dual folded
ISM,WMTS
[12]
Fractal Arc. spirals
MICS
[13]
Helical
868 MHz
[14]
Inverted L- shaped slot ,
ainverted U- shaped slot
ISM
[15]
PIFA
MICS
[16]
MEMS
1 MHz
[17]
Slot Dipole
ISM
[18]
Meandered PIFA
ISM
[19]
Loop antenna
4 GHz
[20]
L- Shaped fed spiral
ISM, MICS
[23]
Dual - spiral
ISM
[24]
Magnetic-type loop
MICS
[25]
Patch
MICS
Table II lists the different miniaturization techniques used in
the papers referenced here, along with the total dimensions of
each antenna. In [13], a fully implantable wireless sensor
attached to a helical antenna achieved a dimension of 15×4.5
mm2. A small three-dimensional spiral antenna, with
dimensions 14×14×15 mm3, has been proposed in [5]. A
monopole antenna having a meandered arm has been presented
in [18]. In [12], it was noticed that the combination of Hilbert-
type fractal and Archimedean spirals optimizes the line spacing
and width, and leads to a bandwidth expansion of 346% over a
compact area less than 8×11.5×8 mm3.
2) Impedance Matching
An effective method for size reduction is the inductance and
capacitive loading methods. This helps in improving the
impedance matching at the desired frequency band. In [15], a
capacitive loading produced by a parallel plate capacitor has
been used with a PIFA antenna and resulted in a decrease of the
total length from λ/4 to less than λ/8. Moreover, impedance
matching has been obtained in [11] by adjusting the distance
between the path as well as the width of feeding structure for a
dual folded dipole antenna. Furthermore, impedance matching
and size reduction is achieved for an RF energy collecting circuit
with an on chip antenna in [19].
Figure. 5 In vitro measurement system, (1) Network analyzer, (2) Antenna, (3)
Muscle tissue liquid
3) Frequency bands
One of the major constraints for a system to be used in
biomedical applications is to operate in approved bands. It is
well known that higher operating frequencies have shorter
wavelengths which leads to decreasing the size of the
antennas. Higher frequencies with wide bandwidth are also
better for data communication, however they suffer from
higher tissue attenuation than at lower frequencies [26]. Table
ΙΙ also lists the different operating frequencies for the studied
antennas, where [6, 9, 10, 11, 14, 17, 18, 20, 27] are operating
in the ISM band, [12, 15, 20, 22, 23, 24] are operating in the
MICS band, while [5, 13] are operating in WMTS band.
Hence, a care should be taken in the design of the antenna at a
desired operating frequency and application requirements,
taking into account the device dimensions and transmit
distance.
V. SIMULATIONS AND TESTING
A. Simulation tools
Several software packages can be used for designing and
simulating antennas for biomedical applications. The most
commonly used are: High Frequency Structure Simulator
(HFSS), a commercial finite element method solver for
electromagnetic structures; CST Microwave Suite, a
computational solution for electromagnetic design and analysis;
Finite-Difference Time-Domain (FDTD) or Yee's method, a
numerical analysis technique used for modeling computational
electrodynamics; IE3D software used in the analysis and design
of 3D and planar microwave circuits; FEKO software used in
field calculations involving bodies of arbitrary shape. Table III
lists some of the papers on antenna design for biomedical
applications with the corresponding simulation software used in
each paper.
B. Measurments
Two types of measurements are used for implanted devices,
in vitro measurements and in vivo measurements, Correlations
between in vitro and in vivo data must be used during
development to reduce design time and optimize the results.
1) In Vitro Measurements
In this type of measurements, the fabricated antenna is
inserted into a body like sample liquid/solid, as shown in Fig. 5.
This phantom liquid/solid is typically a bowl contain a liquid or
gel material that is similar to the electrical properties of the
biological tissue for which the fabricated antenna is proposed to
be inserted in. The measured results are then compared to the
simulated ones for validation. Testing inside sample is almost
simple and more practical to use. Different phantoms have been
proposed and used in the literature, such as: a liquid similar to
the dielectric typical feature of muscle tissue [9, 11], an
equivalent body medium [28], Polyacrylamide scalp phantom
and saline [10], dental model [12], a tissue-emulating material
consisting of ultra-pure water, sugar, and salt [14], a
heterogeneous sample of a male child from a virtual family [17],
and pork skin phantom [6]. Table ΙΙΙ lists different phantoms
liquid/solid that were used in the referenced papers.
2) In Vivo Measurements
In this type of measurements, the effect of the live tissues on
antenna performance is investigated. The measurements can be
done through either using a phantom that mimic the tissue, or by
implanting the antenna inside the body of the animal, as shown
in Fig. 6. In [12], a high-gain dental antenna made up of Hilbert-
type fractal and Archimedean spirals has been inserted in the
mouth of an Asian volunteer man, close to his molar, by which
measurements were launched in different positions (open and
close). An animal experiment has been presented in [13], where
the sensor and the antenna have been placed inside the chest of
a pig.
VI. BIOCOMPATIBILITY ISSUES AND SAFETY CONSIDERATION
A. Biocompatibility issues
In order to insure the patient's safety, implantable device
must be biocompatible for long life operation. Accordingly, we
have two ways to apply biocompatible issues. The first one is
to utilize biocompatible components directly in the construction
of the antennas, as shown in Fig. 7(a). The materials used are
Teflon, alumina and macor. While the second way is to
envelope the antenna with a slim layer of biocompatible
material, as shown in Fig. 7(b), it should be taken into attention
that the thickness of the biocompatible material could influence
the antenna act. In some cases, certain biocompatible materials
can’t be found in some laboratories, thus other dielectric
materials can be chosen with same electrical properties for
fabrication.
In [9], a superstrate and a substrate of PDMS have been used
in the design of an antenna embedded in silicone. In [11], an
implantable CPW fed dual folded dipole antenna inserted in
PDMS has been also presented. It was shown in [12] that metal
should be prevented in the denture material. Therefore, ceramic
is most suitable material for use. Accordingly, the two most
used materials are: alumina (Al2O3) of a relative dielectric
constant 𝜖𝑟 of 9, and zirconium dioxide ZrO2 of 𝜖𝑟 of 21.
B. Saftey
Specific Absorption Rate (SAR) is the amount of the
electromagnetic energy delivered to human tissue. SAR is a
function of the electrical conductivity, the induced E-field from
the radiated energy, and the mass density of the tissue. The SAR
is calculated by averaging over a 10 g or 2 g of tissue in the
shape of a cube. The FCC limit for public exposure of RF
signals is an SAR level of 1.6 W/kg. In Europe it is typically
(2)
(1)
(3)
TABLE III. SIMULATION SOFTWARES AND MEASUREMENTS USED IN
REFERENCE PAPERS
Ref.
Simulation
tool
In Vitro Measurements
In Vivo
Measurements
[5]
HFSS
Equivalent body
NO
[6]
FEKO
Pork skin phantom
NO
[9]
2.5 field
simulator
Liquid mimicking tissue
NO
[10]
HFSS
Polyacrylamide, scalp
phantom, saline,
NO
[11]
IE3D
Liquid mimicking tissue
NO
[12]
HFSS
dental model
Human body
model
[13]
NA
Testing rig
Animal
[14]
IE3D
Water, sugar, and salt
NO
[15]
IE3D
NO
NO
[17]
NA
Child, Virtual Family
NO
[19]
HFSS
Anechoic chamber
NO
[20]
HFSS
Three layered lossy human
tissue model
NO
[23]
CST
human body phantom
NO
[25]
IE3D
NO
NO
Figure 6. Animal experiment [27]
(1)
(2)
(3)
(4)
(5)
(6)
(a)
(b)
Figure 7. (a) Biocompatible metal, (b) Biocompatible coating, (1)
Biocompatible superstrate, (2) Biocompatible substrate, (3) Biocompatible
metal, (4) Metal, (5) Substrate, (6) Biocompatible coating
taken to be less than 2 W/kg [29]. An SAR of 0.079W/Kg
averaged over 1-g is presented in [9].
VII. CONCLUSION
In this paper, a literature review of the design of antennas for
biomedical applications been investigated. Starting with a brief
description of implanted antenna systems, an extensive review
of several antennas used in various biomedical applications
have been presented. The design challenges facing such
antennas have been discussed while investigating the different
techniques that can be used to reduce the size of the antenna for
proper insertion inside the body. The different simulation tools,
in addition to the typical measurements techniques, in vitro and
in vivo, have been presented. The biocompatibility issues and
safety precautions concerned in the design of implanted
antennas for biomedical applications have been also discussed.
It is very clear that the design of implanted antennas requires an
important investigation of the different challenges and
techniques discussed in this paper.
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[1]
A. k Skrivervik and F. Merli., "Design Strategies for Implantable
Antennas," in In Antennas and Propagation Conference (LAPC),
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[2]
K. Asimina and K. S. Nikita, "A review of implantable patch antennas
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Propagation Magazine, vol. 54, no. 3, pp. 210-228, 2012.
[3]
Recommendation ITU-R RS.1346, 1998.
[4]
K. Gurveer, A. Kaur, G.t Kaur Toor, B. S. Dhaliwal, and S. Sundar
Pattnaik, "Antennas for biomedical applications," Biomedical
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[5]
J. Abadia, F. Merli, and J.-F. Zurcher, "3D-Spiral Small Antenna Design
and Realization for Biomedical Telemetry in the MICS band,"
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... There are four universal microwave frequency bands for wireless communications in the health and medical domains: the Medical Implant Communication System (MICS, 401-406 MHz); the Wireless Medical Telemetry Service (WMTS, 1427-1432 MHz); the Wireless Body Area Network (WBAN, 2360-2400 MHz); and the Industrial, Scientific and Medical (ISM) bands (2.4-2.5 GHz) [8][9][10]. In practice, medically implantable and/or ingestible antennas should be small, operable at the medical frequency bands, and harmless to humans. ...
... The simulated impedance matching (|S11| ≤ −10 dB) was achieved at 400-406 MHz and at 2.41-2.47 GHz, as shown in Figure 4. Figure [10,18]. In the simulation, the six layers of the lossy multilayer spherical body-parts model represented human internal organs and body parts with varying dielectric constants (Table 3) [28]: layer 1 was air, layer 2 was the glass pod, layer 3 was the stomach, layer 4 was the bone, layer 5 was the muscle, and layer 6 was free space. ...
... The dielectric plays a crucial role in the data-transmission performance of the antenna. [10,18]. In the simulation, the six layers of the lossy multilayer spherical body-parts model represented human internal organs and body parts with varying dielectric constants (Table 3) [28]: layer 1 was air, layer 2 was the glass pod, layer 3 was the stomach, layer 4 was the bone, layer 5 was the muscle, and layer 6 was free space. ...
Article
Full-text available
In light of the growth in demand for multiband antennas for medical applications, this research proposes a MICS/ISM meander-line microstrip antenna encapsulated in an oblong-shaped pod for use in diagnoses of the gastrointestinal tract. The proposed antenna is operable in the Medical Implant Communication System (MICS) and the Industrial, Scientific and Medical (ISM) bands. The antenna structure consists of a meander-line radiating patch, a flipped-L defected ground plane, and a loading resistor for antenna miniaturization. The MICS/ISM microstrip antenna encapsulated in an oblong-shaped pod was simulated in various lossy-material environments. In addition, the specific absorption rate (SAR) was calculated and compared against the IEEE C95.1 standard. For verification, an antenna prototype was fabricated and experiments carried out in equivalent liquid mixtures, the dielectric constants of which resembled human tissue. The measured impedance bandwidths (|S11| ≤ −10 dB) for the MICS and ISM bands were 398–407 MHz and 2.41–2.48 GHz. The measured antenna gains were −38 dBi and −13 dBi, with a quasi-omnidirectional radiation pattern. The measured SAR was substantially below the maximum safety limits. As a result, the described MICS/ISM microstrip antenna encapsulated in an oblong-shaped pod can be used for real-time gastrointestinal tract diagnosis. The novelty of this work lies in the use of a meander-line microstrip, flipped-L defected ground plane, and loading resistor to miniaturize the antenna and realize the MICS and ISM bands.
... The importance of implantable devices can quickly be figured, a tremendous number of people use such tools, by which they are used to improve the conditions and the quality of their lives [1]. Implantable devices are currently taking a considerable interest in biomedical applications, ranging from human's treatment to medical diagnosis and prevention, such as sugar level check, blood pressure measurements, pacemaker connection, insulin push out, real-time pressure measurements, and dental system for health care applications [2]. In such applications, sensors can also be implemented to collect and transmit information needed into a nearby receiver connected to a computer, which simulates the required data by doctors [3]. ...
... In general, miniaturization techniques might include choosing a suitable dielectric material, so a high dielectric substrate leads to smaller resonance frequencies, and optimizing the antenna structure itself, e.g., stretching the current way of the radiator or using meander line antenna. A thorough investigation of different designs suitable for implantable biomedical application has been done in [2]. It is seen that all the investigated antennas possess overall dimensions ranging between 30 to 55 mm in length, and 5 to 10 mm in width. ...
... Upon extensive research, scientists approved certain microwave frequency bands for safe biomedical application on human body, in particular microstrip antennas were found to be most advantageous among other technologies [1,2]. Examples to some recent achievements are the breast cancer detector at its early stages, the on-body antenna and the implanted antenna inside the human body that detect the vital signs [3][4][5][6]. Until recently, no globally accepted frequency band had been dedicated to biotelemetry for implantable medical devices. The ITU-R Recommendation SA. 1346 [7] outlined the use of the 402 -405 MHZ frequency band for Medical Implant Communication Systems (MICS). ...
... Another challenge is found in the power supply used with implanted antenna that often has the largest volume size.' On the other hand, noninvasive technology of antennas are easier to apply yet more difficult to achieve due to the need to breakthrough multiple body layers that have different dielectric constants and thus interact differently with the waves, and moreover differ from one person to another [6]. Of course, the aforementioned factors affect the antenna characteristics and performance mainly; its radiation efficiency, its directivity, its radiation pattern, and the frequencies that it serves. ...
... erefore, a more efficient, noninvasive, safe, and nonionized radiation method is required for detecting bone fractures [2]. Microwaves [3,4]. Since the human body is made up of layers with different dielectric constants, an antenna resonating at lower frequencies will have a greater depth of penetration. ...
Article
Full-text available
In this study, the design of a compact narrowband monopole antenna for bone crack detection is presented. The proposed antenna consists of a modified hexagon-shaped radiator with six triangular slits integrated on its bottom periphery, a rectangular-shaped ground plane, and a microstrip feed line of 50 Ω. The antenna is fabricated on the FR-4 substrate with a thickness of 1.6 mm, an overall size of 32 mm × 30 mm, and electrical dimensions of 0.13λ0 × 0.122λ0, where λ0 is the free space wavelength at 2.45 GHz. The resonant frequency of the designed antenna is 2.45 GHz. The antenna offers a gain of 1.68 dB and an efficiency of 85.3%. The presence of a crack in the bone is detected by observing the shift in the peak resonating frequency of the antenna. This method can detect bone fractures in a noninvasive manner. The human arm model is constructed, and the effect of bone cracks of different lengths on the resonating frequency is investigated. The pig bone and tissues are used to validate the simulated results. The simulated results are in agreement with the measured outcomes. Also, the specific absorption rate (SAR) of the antenna is calculated and found to be less than 0.57 W/kg. The designed monopole antenna has several advantages, including a small footprint, straightforward design, low cost, and easy integration with other devices. The proposed method is suitable for primary-level bone crack diagnosis.
... Implantable devices have a vital role in healthcare applications such as glucose monitoring [1][2][3]. The implant is composed of different components that sense, process and send the bio-signals to body worn or external receivers around the human body [4][5][6]. The location of the implantable device -whether it is in the bone, deep in the muscle or just beneath the skin -is mainly influenced by the application [7]. ...
... An implant may require establishing a wireless link with an onbody or an off-body device. This wireless link is commonly referred to as an in-body link [7]. It must be noted that establishing a reliable and high-quality in-body link is a challenging task. ...
Article
Matching media are used in various applications to increase the power transmitted into the human body. The selection of the optimum matching medium permittivity is not a straightforward task, as the optimum value maximizing the transmitted power depends on the thickness of the matching medium and the electromagnetic properties of the target tissue. In this paper, a computationally heavy empirical approach and a machine learning-based approach are utilized for the selection of the matching medium. The empirical approach demonstrates that the matching medium can increase the |S21| values up to 8 dB, which is validated with measurements. Next, a machine learning-based tool is proposed to predict the optimum matching medium permittivity for any target tissue and any matching medium thickness. A one-dimensional convolutional neural network followed by a multi-layer perceptron is trained with the simulated average Poynting vector magnitudes for muscle and fat as target tissues. The average Poynting vector magnitude and the dipole length for given system parameters are predicted by the trained artificial neural network. The accuracy is calculated by comparison with the results of the empirical analysis and found to be 1% and 12.3% mean absolute percentage error for dipole length and average Poynting vector magnitude, respectively. The proposed tool decreases the time required to milliseconds.
... The characteristics of the tissues, in terms of relative permittivity and conductivity, are frequency-dependent, so their values were accordingly modified in the simulation model [33]. The antenna was designed on a 30-mil thick Rogers4003 substrate, a widely employed substrate for biomedical applications [34,35], with a relative permittivity ε ′ r =3.38 and a dissipation factor tan δ=0.0027. A plated hole of 1-mm diameter was drilled to perform the short circuit between the substrate layers. ...
Article
A pseudo-correlation type radiometer based on astrophysical instrumentation is proposed for biomedical applications. The working frequency band is centred at 3.5 GHz. The prototype performance and functionality are assessed. The theoretical analysis of the receiver topology is described, as well as the subsystems employed in its configuration, such as a customized on-body antenna and microwave circuitry based on off-the-shelf devices. Experimental characterization of the individual subsystems and preliminary measurements of the radiometer prototype are presented. Furthermore, customized phantoms, based on polyvinyl alcohol cryogel, are employed for the characterization of the on-body antenna, as well as the radiometer.
Article
While implantable medical devices offer tremendous potential for treating a myriad of diseases and disorders, there are many situations in which such devices are only needed for short time periods, with extended presence or surgical removal leading to a host of undesired complications. To address this concern, researchers are working to develop implantable circuitry that eventually disintegrates. Prior work in this area leveraged known bioresorbable materials, but the lifetime of circuits formed from such materials is determined upon fabrication, and on‐demand, triggered disintegration is not possible. To better match the lifetime of an implanted device to the status of the condition it is monitoring or treating, it would be advantageous to be able to noninvasively trigger disintegration at a particular time, avoiding situations in which the device lifetime is either too short or too long. Thus, to enable implantable circuitry with wireless capabilities that can disintegrate upon external stimuli, thermoresponsive transient RF antennas are formed that exhibit stable wireless response in warm aqueous environments but disintegrate and irreversibly lose functionality when cooled below a critical temperature. Antennas are formed by embedding patterned networks of silver nanowires in a thermoresponsive polymeric binder, which maintains network conductivity in warm solution but disintegrates and releases the nanowires when solution temperature drops. Mild sintering enhances electrical properties of the conductive nanowire network and antenna response while maintaining the capability for disintegration. To reduce the undesired effects of swelling, devices are sandwiched between two parylene films. These thermoresponsive transient devices represent an important step toward the realization of wireless medical implants whose disintegration can be triggered at any time by an external cooling stimulus.
Article
Full-text available
Ageing population and a multitude of neurological and cardiovascular illnesses that cannot be mitigated by medication alone have resulted in a significant growth in the number of patients that require implantable electronic devices. These range from sensors, gastric and cardiac pacemakers, cardioverter defibrillators, to deep brain, nerve, and bone stimulators. Long-term implants present specific engineering challenges, including low energy consumption and stable performance. Resorbable electronics may offer excellent short-term performance without the need for surgical removal. However, most electronic materials have poor bio- and cytocompatibility, resulting in immune reactions and infections. This paper reviews the current situation and highlights challenges for future advancements.
Conference Paper
Full-text available
A implantable CPW fed dual folded dipole antenna operating in the ISM band (2.4-2.48 GHz) and WMTS (1.4-1.43 GHz) for biomedical applications. The proposed antenna is made compatible for implantation by embedding it in a biocompatible Poly Dimethyl Siloxane (PDMS). A study of sensitivity of the antenna performance as a function of the dielectric parameters of the environment in which it is immersed was performed. The proposed antenna is simulated using the method of moment's software IE3D by assuming the predetermined dielectric constant for the human muscle tissue, fat and skin and the parameters of the antenna such as return loss, radiation pattern, and VSWR are plotted.
Article
A compact dual-band bioimplantable antenna with novel resonator geometry is designed for dual-band wireless biotelemetry applications in MICS and ISM bands. The radiating element geometry is based on an Lshaped transmission line fed anti-spiral resonator structure, which is loaded with the spiral resonator at the end to increase the effective electrical length. The effect of resonator geometric parameters on the return loss is discussed with the inclusion of three layered lossy human model in the numerical calculations. The footprint size of the optimized bioimplantable antenna is 15 × 15 × 1.92 mm³, having the total surface area of λ0/20 × λ0/20, where λ0 is the free space wavelength at 403 MHz in MICS band. The compact dual-band antenna has the impedance bandwidth of 24.81% at 403 MHz and 14.7% at 2.45 GHz with the gain values -12.25 dBi and -12.4 dBi in MICS and ISM bands, respectively. The average SAR values at the resonance frequencies are numerically computed to find out the input power delivered to the antenna for the reliable operation. The radiation parameters and 3D radiation patterns indicate the potential use of the proposed implantable antenna with the permissible gain in dual-band wireless biotelemetry applications.
Article
The objective of this paper is to design a miniaturized dual-spiral antenna for implantable bio-medical application in the frequency range 2.41 GHz of ISM band. A parametric model of a skin, fat and muscle implantable antenna is designed and analysed their parameters such as return loss, impedance matching, gain, VSWR and radiation patterns etc. The total size of the proposed antenna is 30 mm and the thickness is 1.6 mm. To make the proposed antenna is suitable for implantation and the proposed antenna is made up of alumina (Al2O3) substrate. The proposed antenna is fed by coplanar waveguide method for high frequency response. It shows the lower return loss, good impedance matching and high gain compared to other antennas. The proposed antenna design methodology can be applied to optimize antenna for several implantation scenarios and ISM band applications.
Article
The emerging techniques in the medical field include the use of bio implantable antennas to diagnose the diseases. The major disadvantage of these techniques is the side-effects caused by the radiations in the human body. There have been a lot of advancements in this area to reduce the radiation emitted. One among them is the use of PIFA antenna inside an indestructible capsule (Polyetheretherketones) which is helpful in both short and long range communications. The work includes the design of PIFA antenna using IE3D and MATLAB software. The characteristics of the antenna are analyzed with the aim to reduce the size and radiation effect of antenna and to increase the gain, efficiency and data rate.
Conference Paper
Biocompatibility is one of the most important aspects that need to be taken into account when it comes to implantable antennas. However, very few studies have addressed the effects that biocompatibility considerations might have on the design and performance of implantable antennas. This study addresses the conversion of non-biocompatible implantable antennas into their biocompatible equivalents, exploring the difficulties and proposing solutions. Two methods are suggested for ensuring the biocompatibility of implantable antennas, and these are further investigated and compared. The proposed biocompatible antennas are finally evaluated within an anatomical head model for intra-cranial pressure (ICP) monitoring applications.
Article
Biomedical engineering today holds a prominent place as a means of improving medical diagnosis and treatment, and as an academic discipline. Today glucose monitoring, insulin pumps, deep brain simulations and endoscopy are a few examples of the medical applications that can take advantage of remote monitoring system and body implantable unit. Body implantable devices are widely researched for humans, in the applications such as monitoring blood pressure and temperature, tracking dependent people or lost pets, wirelessly transferring diagnostic information from an electronic device implanted in the human body for human care and safety, such as a pacemaker, to an external RF receiver. Antennas can be implanted into human bodies or can just be mounted over the torso (skin-fat-muscle) to form a bio-communication system between medical devices and exterior instruments for short range biotelemetry applications. In addition to the clear benefits to the healthcare system provided by body implanted devices, economical aspects are also relevant. Remote monitoring systems facilitate the diagnosis of diseases and favor the hospital at home by reducing the hospitalization period. © 2015, Korean Society of Medical and Biological Engineering and Springer.
Conference Paper
This paper presents the design of a triple-band implantable miniaturised slot PIFA antenna for Medical Implant Communication Service (MICS) band at 433MHz, Wireless Medical Telemetry Service (WMTS) band at 1430 MHz and Industrial, Scientific, and Medical (ISM) band at 2.4GHz. Simulations based on homogeneous and inhomogeneous phantoms are employed to design the proposed small antenna suitable for implanting in the arm or under the chest. The measured results are obtained by immersing a prototype of the proposed antenna in a phantom. The antenna occupies a volume less than 1cm3 and its size reduction is about 50% compared to the standard E-shaped patch antenna reported in the literature.
Conference Paper
Because of the large real permittivity and significant conductivity of biological tissues at microwave frequencies, the performance of microwave antennas loaded with the tissues is very different from that in air. Moreover, for performing heating and radiometry inside the tissues, the specific absorption rate (SAR) profile generated in the near-field of the antennas is the quantity of interest rather than the radiation pattern. On the other hand, for medical implants, the SAR profile and the tissue loss are undesired effects, but are unavoidable and greatly impact the radiation property and the gain of the antennas. This paper highlights some of these mentioned issues. It presents planar antennas utilized for an intracranial pressure monitoring (ICP) implant and radiometer/heating antennas applied for the measurement of blood perfusion. Measurement setups and/or procedures for the characterization of the antennas will be discussed as well.