This presentation focuses on the future of wireless medical technology and discusses the key requirements for developing and connecting medical implants to wireless networks. The presentation highlights the importance of wave propagation, antenna design, and sensor development in this field. These slides are designed to serve as a comprehensive tutorial on the topic, providing valuable insights and practical guidance for researchers and professionals interested in the latest developments in wireless medical technology. This is presented at EUCAP2023, Florence, Italy

1. Overview of
Medical Implant
Antennas
Ali Khaleghi 1,2
1 Norwegian University of Science and Technology (NTNU), Trondheim, Norway, ali.khaleghi@ntnu.no
2Intervention Center, Oslo University Hospital (OUS), Oslo, Norway

2. Outline
• Medical Implant: key engineering challenges and factors
• Implant sensor technology
• Implants with wireless Technology
Introduction
• Application: Sensing, Powering, Communication
• Design steps and parameters
Implant Antenna
• Frequency allocation
• Electromagnetic simulation of biologically integrated antennas
• Tissue material properties
• Human organ and tissue models
Simulation and Modeling
•Application in cardiac, gastric, and brain implants
Miniaturized Implant Antennas and
examples
•Importance of antenna miniaturization for implantable devices
•Potential for further development and improvement.
Future directions and Conclusion

3. Medical implants
• First electronic implant: Cardiac pacemaker
(1958)
• Key Engineering challenges:
Materials, battery power, functionality, electrical power
consumption, size shrinkage, system delivery, and wireless
communication
• Key factors:
Electrical connectivity and communication, corrosion,
robustness, and hermeticity during the development stage

4. Implantable sensor technology
Cardiac: Cardiac
pacemakers, implant ECGs,
Cardiac accelerometer
sensors, ICDs
Neural: Neurostimulators
for pain management, Brain
signal sensing for amputees,
Brain-machine interface
(BMI) devices
Musculoskeletal:
Orthopedic implants and
sensors
Gastric: Stomach bleeding
sensors, Gastric sensors,
Capsule endoscopy
Hearing aid: Cochlear
implants for hearing loss,
Visual: Retinal implants for
vision loss,
Drug delivery: Drug pumps
for targeted drug delivery,
Glucose sensors for diabetic
patients
Pressure: Implantable
pressure sensors for bladder
control, Intracranial
pressure sensors in patients
with traumatic brain injuries

5. Implants with Wireless Tech.
Wireless technology integration with implants:
• Removing wires: Greater Mobility, Remote Monitoring, Reduced Risk of
Infection, Longevity, Smaller Size
• Real-time monitoring of biomarkers for preventive medicine.
• Wireless connectivity provides data fusion to smart networks for more rapid
and accurate communication between the implant and external devices (for
telemetry and command).
• Use of Artificial Intelligence and Deep learning algorithms allowing for the
development smarter and more personalized treatments for patients
A conceptual drawing of a person with multiple
implants and on-body hubs interconnected to a
communication network.
Challenges
• Remote powering
• Wireless routing
• Required data rates (100s bps to 10s of Mbps)
• Multi-source aggregation and the protocol exchange
• Considerations: frequency, tissue loss, radiation safety, and encapsulation.
• Device: Security, reliability, battery life, compatibility, interference, cost, and
ethical considerations

6. Implant Antenna Design:
Application
Application:
• Sensing
• Dielectric properties, Impedance,
Movement
• Wireless Powering
• Inductive, resonance, capacitive,
conductive, radiative or a combination of
all
• Wireless Communication
• Implant to on-body
• Implant to implant
• On-body (via fat channel)
• Body area communication (over air)
• Near-field, mid-field and far-field

7. Implant Antenna Design:
Considerations
Size and shape
governed by use case
(micro to cm)
Operating frequency
specified by standards
Surrounding tissues
implant location
Subsequent biological
tissues: implant depth
Encapsulation
material type: longevity,
location
Nearby Electronics and
Metal objects
integration effects
Implant depth
superficial, in-depth
Impedance matching
source or sink
impedance
Bandwidth
data rate, sensitivity
Antenna nearfield
necessary to manage
overall efficiency
Far-field radiation
pattern
targeted for in-distance
communication or on-
body
Efficiency and gain
embedded antenna
Specific absorption
rate Safety

8. Frequency
Allocation
for Med.
Radio
• FCC, ETSI, ITU
National and International Agencies for Frequency Allocation
• MICS: 402-405 MHz for low-power, short-range wireless connection
• WMTS: 1.395-1.4 GHz for wider coverage area
• ISM: 433-434 MHz, 868-868.6 MHz, 902-908 MHz, 2.4-2.48 GHz, and 5.715-5.875 GHz for
high data rates and wide coverage
• UWB: 3.1-10.6 GHz for high-quality transmission in some regions
Frequently Used Operating Frequencies for Implantable Antennas
• Resonant frequencies of 1, 5, 10, 24, and 49 MHz for small data transmission in surface-
level implants (< 40 mm) like retinal and cochlear devices.
Inductive:
• Communication between devices on/in the human body uses frequencies < 60 MHz.
Galvanic coupling with a center frequency of 21 MHz is the standard for HBC (IEEE
802.15.6).
HBC:
• The conductivity of the tissues is the main factor that helps to establish the connection
link.
Galvanic Conductivity:

9. Electromagnetic
Simulation of
Biologically
Integrated
Antennas
• FEM, FDTD, or dyadic Green's function
(DGF) are suitable for human EM
models.
• Tissues can be modeled as
homogenous or heterogeneous
materials produced by CT, MRI, or
Visible Human Project (VHP®) data.
• SEMCAD®, CST MWS®, ANSYS
HFSS ®, and REMCOM XFDTD ® are
useful EM tools for simulating
biologically integrated antennas.

10. Material Properties
of Tissues
Dielectric properties highly
depend on the water contents of
the tissues
- Conductivity
- Permittivity
- Dispersion
- Permeability (unity for tissues)
http://niremf.ifac.cnr.it/docs/DIELECTRIC/Report.ht
ml
Gabriel et al 1996, 4-Cole-Cole model

11. Human models
Human models: IT’IS Found. Switzerland (CAD and
Voxel), CST AG (Voxel), REMCOM (Voxel), etc
• Voxel-based models:
• Suitable for FD at low freq. and FDTD
rectangular grids at high freq. Subgridding
techniques and use of GPU computations.
• CAD-based human model:
• FD and FEM (HFSS, Maxwell, COMSOL) with
tetrahedral mesh. Allows for solving
resonances and is suitable for small antennas,
narrowband, low frequency, and can consider
the antenna detailed geometry using layered
human models

12. Small Implant
Antennas
Effective power delivery for both TX and RX
Impedance: not necessarily 50 ohms, can be complex or low impedance
Important to protect transmitter and reduce heat generation
Antenna
matching
Small antenna naturally is high Q
Detuning and sensitivity to variable tissues
Sensitive to encapsulation loss, coating metal surrounding electronics
High SAR close by antenna if electric or high structural loss if electric loop
Poor performance
Low loss
High-Q
Trade-off: Bandwidth, Efficiency, Sensitivity and impedance matching
Applied loss: Local material loss (add thermal to antenna structure) or local tissue
added loss (add thermal to biological tissues- increase efficiency)
Usually, the TX power is low: SAR will be less concern
Lossy
antenna
Tissues become a part of the radiating element
Antenna effective size is much larger than the real size (up to 10 times) depending
on the tissue type
Important to manage the antenna near field to reduce proximity loss: with coating,
gap, or local field type
Antenna
virtual size

13. Antenna types prefered for
implants
• Electric loop antenna
• Limited near-field loss and lesser influence from the
medium
• Can be high Q and less sensitive to medium
• Antenna matching is an issue
• Possible interference to implant electronics
• Electric loop antenna with a ferromagnetic core improves
impedance and excites magnetic dipoles (
• Magnetoelectric antennas (mechanical resonance based)
[1] T. Yousefi and R. E. Diaz, “Pushing the limits of radiofrequency (RF) neuronal telemetry,” Sci. Rep., vol. 5, pp. 1–16, 2015, doi: 10.1038/srep10588.
[2] M. Ramzan, X. Fang, Q. Wang, N. Neumann, and D. Plettemeier, “Miniaturized Planar Implanted Spiral Antenna Inside the Heart Muscle at MICS Band for Future Leadless Pacemakers,” Int. Symp. Med. Inf. Commun. Technol. ISMICT, vol. 2019-May, May 2019, doi:
10.1109/ISMICT.2019.8743709
[3] M. Zaeimbashi et al., “Ultra-compact dual-band smart NEMS magnetoelectric antennas for simultaneous wireless energy harvesting and magnetic field sensing,” Nat. Commun. 2021 121, vol. 12, no. 1, pp. 1–11, May 2021, doi: 10.1038/s41467-021-23256-z.
[1]
[2]
[3]

14. Generic antenna
forms in tissues
Muscle embedded antenna
• Dipole
• Loop
• Electrode with a capacitive gap
For any given size of implant and depth, an optimum
frequency governs maximum power efficiency.

15. Wireless Capsule Endoscopy Antenna
Designs
A swallowable capsule with an embedded
camera for capturing images through the
gastrointestinal tract
Challenges:
Proximity to lossy tissues, polarization mismatch, and orientation.
Integration: Outer shell of capsule can be used to integrate antenna
Miniaturization:
- Meander-shaped conformal antenna (433 MHz)
- A Wideband electrode antenna with insulation gap
- Three orthogonal current paths are realized with a meander-shaped
geometry at 2.4 GHz ISM band to make the capsule orientation
independent
- A wideband conformal antenna is proposed to operate at 650 to 3600 MHz
with less sensitivity to the environment.
- Galvanic or conductive communication is also a power-efficient option for
WCE video transmission that needs direct contact of electrodes with tissues

16. Antenna Design for
Pacemaker Devices
• Pacemakers are used to treat cardiac
arrhythmia
• Conventional pacemakers (CP) and
leadless pacemakers (LP) both require
communication antennas for programming
and monitoring
• CPs use magnetic coupling and newer
models have Bluetooth connections
• LPs are deeper in the heart and require
connection to a reader for programming
and reporting
• Antenna design must consider size,
encapsulation, medium, and integration

17. Simultaneous wireless charging and high
data rate BMI communication
- High data rate Backscatter comm. Up to 64 Mbps
- Dual polarized dual port near field reader antenna
- Magnetic coupling for powering 30 mW
- Resonance coupling for powering
- Low data rate (NFC) for Telemetry Telecommand
- Magnetic coupling
https://www.b-cratos.eu/

18. Future directions for
Implant antennas
• Magnetoelectric antenna
• Material-based layered structure using
magnetostrictive and piezoelectric
properties (Metglass, FeGaB, AlN)
• Multiphysics COMSOL-based simulations
• Manufacturing and test process is not
straightforward
• MRI compatibility
• MagnetoElectric Coreshell
• Can be used as a sensor antenna or
stimulation system for neurons
• MagnetoElectric Backscatter antenna
• Can have sub-mm size and used for WPT
and backscattering
• Antenna as sensing