14 September 2011 Surgical-P-278 v0.9
ANSYS Regional Conference: Engineering the System Mark Lanciault, Arun Venkatasubramanian
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Planar Compound Field Antennas for
Implantable Telemetry Applications 14 September 2011
‹#› 14 September 2011 Surgical-P-278 v0.9
Design Complications for Implantables
Agenda:
Compound Field Antenna Concept
1
Typical Design Specifications
Simulation Results
Conclusions and Future Work
2
3
4
5
‹#› 14 September 2011 Surgical-P-278 v0.9
Design Complications for Implantables
Agenda:
Compound Field Antenna Concept
1
Typical Design Specifications
Simulation Results
Conclusions and Future Work
2
3
4
5
‹#› 14 September 2011 Surgical-P-278 v0.9
Frequency & Power Restrictions
Frequency Range:
– Medical Implant Communication Service (MICS) (402 - 405 MHz)
– Medical Device Radiocommunications Service (MedRadio) (401 - 406 MHz) – MICS with 1 MHz sidebands for “non-listen before talk” devices
– European Telecommunications Standards Institute (ETSI) (401 - 406 MHz)
– Transceivers also now exploiting 2.400 - 2.500 GHz ISM band for wake-up signals
Power Level:
– 25 mW ERP for AFA (Automatic Frequency Agility) systems (-16 dBm)
– 100 nW ERP for non-AFA systems (-40 dBm)
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Technical Requirements & User Constraints
High energy consumption during
transmission
– Current technology: more than 99%
of the radiated energy is lost inside
the body
– Problem: limitation on device life
Irregularly distributed signal and 2
meter minimum range requirement
– Causes:
– Radiation pattern changes with
the body
size/composition/posture
– Interference of in-field objects
– Problem: reduces the feasibility
of:
– Home care applications
– Telehealth
– Remote monitoring
– Critical-life applications
‹#› 14 September 2011 Surgical-P-278 v0.9
RF Propagation Inside the Body
Magnetic antennas preferred to reduce interaction with the electric fields
– Electric fields interact with the high dielectric properties of living tissues
Reduced propagation due to two affects: reflections and direct material losses
Benefit: fat layer propagation
Muscle & organs
Fat
Skin
Fat layer Propagation
A part of th
e wave
goes through th
e skin
A part of the wave
is lost in the body
Fat layer Propagation
`Implanted Antenna
Electric
field
A part of th
e wave
is lost in
the body
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1
10
100
1000
1 10 100 1000 10000
Frequency (MHz)
Re
lati
ve
Pe
rmit
tiv
ity
Material Relative Permittivities & Conductivities
Material Rel. Permittivity Conductivity (S/m)
Air 1.0 0.00
Skin 46.8 0.69
Fat (non-infiltrated) 5.6 0.04
Cortical (compact) bone 13.2 0.09
Cancellous (spongy) bone 22.4 0.18
Muscle 57.1 0.80
Blood 64.0 1.35
Epoxy 4.4 0.00004
Glass 5.5 0.00
Alumina 9.6 0.000014
Ceramic From 10 to 30 0.00
Tissue properties at MICS frequency band*
Other inert materials
Skin Muscle
Fat
MICS
band
ISM
band
* S. Gabriel, R. W. Lau, and C. Gabriel, “The dielectric properties of biological
tissues: III. Parametric models for the dielectric spectrum of tissues,” Phys.
Med. Biol., vol. 41, no. 11, pp. 2271–2293, 1996.
‹#› 14 September 2011 Surgical-P-278 v0.9
Design Complications for Implantables
Agenda:
Compound Field Antenna Concept
1
Typical Design Specifications
Simulation Results
Conclusions and Future Work
2
3
4
5
‹#› 14 September 2011 Surgical-P-278 v0.9
Typical System Specifications
Requirement
Center frequency
Large enough frequency bandwidth
Reflected power by the antenna port
Wireless range with a 0 dB gain
base-station antenna
– For a standard waist
– For a large waist
Power efficiency
Antenna shape, size & location
Technical Specifications
Dual band - MedRadio (401 – 406 MHz) and
ISM (2.400 – 2.500 GHz)
Frequency bandwidth > 9 MHz
Return loss < -10 dB
Implanted antenna gain for 2 meter
coverage
– For a 36” waist (“healthy”)
– For a 60” waist (FDA “morbidly obese”)
Minimize losses for antenna & inside body
Case dimensions & location in body
‹#› 14 September 2011 Surgical-P-278 v0.9
Details determine the
best and worst case
antenna requirements
(folded patch design)
Typical Link Budget Worksheet
MedRadio 403.5 MHz
WakeUp 403.5 MHz
dBm
dB
-25.0
-39.0
dBm
dBm
meters
dB
dB
-25.0
-39.0
dB
dBm
dBm
dB
dB
0.8 < 3++ 2.5 < 3++ 3+ < 3++ meters
From Implanted
Antenna
to Base Station
Wireless range
Free Space loss
Units
8.0
Duplixer/spliter (Rx/Tx) -7.00
-12.5
-3.50
Tx Power
Best value:
Worst value:
ERP (best case) -17.0
Tx Antenna Gain
0
Fading Margin
ERP (worst case) -38.0
-31
2
-31
-11
Worst value:
From Base Station
to Implanted Antenna
Wake-up Signal Normal Operation
Margin (worst case)
Margin (best case)
Wireless range
(0dB margin)
6
-8
31
17
16
2
-1.50
-98Available power -83
Duplixer/spliter (Rx/Tx) -3.50
Reciever sensitivity -90 -100 -100
Rx Antenna Gain dB
0
-16.0
2
Best value:
-16.0
-11
dB
‹#› 14 September 2011 Surgical-P-278 v0.9
Cambridge Consultants 3D Body Model
Details needed to be modeled
depend on implant location
– Bone
– Lung
– Muscle
– Major blood vessels
– Fat
– Skin
36 inch waist 49 inch waist 60 inch waist
Torso
Lung volume
Heart
Sternum
Backbone
Muscle Arteries
Antenna
Fat layer
Skin layer
‹#› 14 September 2011 Surgical-P-278 v0.9
Detuning effect of fat thickness (folded patch design)
Variances in fat thickness
can drive overall bandwidth
requirements
‹#› 14 September 2011 Surgical-P-278 v0.9
Design Complications for Implantables
Agenda:
Compound Field Antenna Concept
1
Typical Design Specifications
Simulation Results
Conclusions and Future Work
2
3
4
5
‹#› 14 September 2011 Surgical-P-278 v0.9
What Is a Compound Antenna?
Compound Antennas are a class of Electrically Small Antennas (ka << 1)
Structure is a combination of two or more radiating elements in a single antenna
– One operating in TE mode (magnetic), one operating in TM mode (electric)
Adapted from Tefiku, F. and Grimes, C. A. (1999), “Coupling between elements of electrically small compound antennas”, Microwave and
Optical Technology Letters, 22: 16–21.
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Benefits of a Compound Antenna over Conventional ESA
Sources Max Gain
(in air) Min Q
Jz (or Jx, or Jy) 1.5 Chu limit
Mz (or Mx, or My) 1.5 Chu limit
Jz ± Mz 1.5 ½ of Chu limit
Jz ± My 3 ½ of Chu limit
Jz ± j My 1.5 ½ of Chu limit
Modified from table in Pozar, “New Results for Minimum Q, Maximum Gain, and Polarization Properties of Electrically Small Arbitrary
Antennas”, EuCAP 2009.
‹#› 14 September 2011 Surgical-P-278 v0.9
Benefits of a Compound Antenna over Conventional ESA
Sources Max Gain
(in air) Min Q
Jz (or Jx, or Jy) 1.5 Chu limit
Mz (or Mx, or My) 1.5 Chu limit
Jz ± Mz 1.5 ½ of Chu limit
Jz ± My 3 ½ of Chu limit
Jz ± j My 1.5 ½ of Chu limit
• High gain and radiation efficiency
Modified from table in Pozar, “New Results for Minimum Q, Maximum Gain, and Polarization Properties of Electrically Small Arbitrary
Antennas”, EuCAP 2009.
‹#› 14 September 2011 Surgical-P-278 v0.9
Benefits of a Compound Antenna over Conventional ESA
Sources Max Gain
(in air) Min Q
Jz (or Jx, or Jy) 1.5 Chu limit
Mz (or Mx, or My) 1.5 Chu limit
Jz ± Mz 1.5 ½ of Chu limit
Jz ± My 3 ½ of Chu limit
Jz ± j My 1.5 ½ of Chu limit
• High gain and radiation efficiency
• Broadband (low Q)
Modified from table in Pozar, “New Results for Minimum Q, Maximum Gain, and Polarization Properties of Electrically Small Arbitrary
Antennas”, EuCAP 2009.
‹#› 14 September 2011 Surgical-P-278 v0.9
Benefits of a Compound Antenna over Conventional ESA
Sources Max Gain
(in air) Min Q
Jz (or Jx, or Jy) 1.5 Chu limit
Mz (or Mx, or My) 1.5 Chu limit
Jz ± Mz 1.5 ½ of Chu limit
Jz ± My 3 ½ of Chu limit
Jz ± j My 1.5 ½ of Chu limit
• High gain and radiation efficiency
• Broadband (low Q)
• Small physical size (planar) Modified from table in Pozar, “New Results for Minimum Q, Maximum Gain, and Polarization Properties of Electrically Small Arbitrary
Antennas”, EuCAP 2009.
‹#› 14 September 2011 Surgical-P-278 v0.9
Design Complications for Implantables
Agenda:
Compound Field Antenna Concept
1
Typical Design Specifications
Simulation Results
Conclusions and Future Work
2
3
4
5
‹#› 14 September 2011 Surgical-P-278 v0.9
Structure of the dual band antenna
All units in mm
Material Thickness
(mm)
Skin 1.0
Fat (non-infiltrated) 1.5 to 5.5
Muscle 10
‹#› 14 September 2011 Surgical-P-278 v0.9
Return Loss vs. Fat Thickness – MedRadio band
‹#› 14 September 2011 Surgical-P-278 v0.9
Return Loss vs. Fat Thickness – ISM band
‹#› 14 September 2011 Surgical-P-278 v0.9
Surface Current Density (J)
2.400 GHz
403.5 MHz
‹#› 14 September 2011 Surgical-P-278 v0.9
Radiation Pattern – Gain vs. Theta
‹#› 14 September 2011 Surgical-P-278 v0.9
Radiation Pattern – Gain vs. Phi
‹#› 14 September 2011 Surgical-P-278 v0.9
Design Complications for Implantables
Agenda:
Compound Field Antenna Concept
1
Typical Design Specifications
Simulation Results
Conclusions and Future Work
2
3
4
5
‹#› 14 September 2011 Surgical-P-278 v0.9
Conclusions
Transcutaneous antenna design was optimized in
a small volume in the presence of living tissue
– Single planar structure 40mm x 45mm
– No passive components required
Low Q nature eliminates need for retuning for
varying body dimensions
ETSI body phantom
Future Work
Need to simulate utilizing complete body model
– Determine effect of fat layer propagation
– Locate depth of nulls
Need to build prototype antennas to compare
measured data with simulations
‹#› 14 September 2011 Surgical-P-278 v0.9
Contact details:
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