Planar Compound Field Antennas for Implantable Telemetry ... · Details determine the best and...

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


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)


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


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


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.



Agenda:


1


Simulation Results


2

3

4

5


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


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


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


Detuning effect of fat thickness (folded patch design)

Variances in fat thickness

can drive overall bandwidth

requirements



Agenda:


1


Simulation Results


2

3

4

5


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.


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.



Sources Max Gain

(in air) Min Q






• High gain and radiation efficiency





Sources Max Gain

(in air) Min Q







• Broadband (low Q)





Sources Max Gain

(in air) Min Q







• 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




Agenda:


1


Simulation Results


2

3

4

5


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


Return Loss vs. Fat Thickness – MedRadio band


Return Loss vs. Fat Thickness – ISM band


Surface Current Density (J)

2.400 GHz

403.5 MHz


Radiation Pattern – Gain vs. Theta


Radiation Pattern – Gain vs. Phi



Agenda:


1


Simulation Results


2

3

4

5


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


Contact details:

Cambridge Consultants Ltd Cambridge Consultants Inc

Science Park, Milton Road 101 Main Street

Cambridge, CB4 0DW Cambridge MA 02142

England USA

Tel: +44(0)1223 420024 Tel: +1 617 532 4700

Fax: +44(0)1223 423373 Fax: +1 617 532 4747

Registered No. 1036298 England

[email protected]

www.CambridgeConsultants.com

Cambridge Consultants is part of the Altran group, the

European leader in Innovation Consulting. www.Altran.com

© 2011 Cambridge Consultants Ltd, Cambridge Consultants Inc. All rights reserved.

Commercially Confidential This Presentation contains ideas and information which are proprietary to Cambridge

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