Environment-Independent Miniature Antennas

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2 April 9, 2010 Environment-Independent Miniature Antennas Hubregt J. Visser

3 Presentation overview Introduction Curved Microstrip Patch Antenna Design CPW Printed Monopole Antenna Design Conclusions

4 Holst Centre 4 Antenna Matching Example: Communication between two transceivers at 2.45 GHz antenna antenna radio feeding & data Γ distance R radio feeding & data Transmitter Receiver Average polarization and gain efficiency Antenna matching determines R max

5 Holst Centre Antenna Matching (ctd.) PT=0dBm PT=-6dBm PT=-12dBm PT=-18dBm 70 Distanc ce (m) Matching especially important for low-power, body-worn applications Antenna Reflection Coefficient (db)

6 Presentation overview Introduction Curved Microstrip Patch Antenna Design CPW Printed Monopole Antenna Design Conclusions

7 Holst Centre 7 Antenna Requirements Bracelet type antenna S 11 <-7.5dB 2.45GHz Nordic nrf24l01 radio P T =0dBm FR4 based Size as small as possible Design for P T <0dBm

8 Holst Centre 8 Antenna Design (ctd.) Metal (Cu) Thickness 0.070mm R=25mm RO4003B, ε r =3.38, tanδ= Thickness 1.254mm Ground plane:60mm X 20mm Antenna: Patch: 30mm X 14mm, gaps: 21mm X 0.4mm Microstrip: 3mm width Resonance: 2.40GHz

9 Holst Centre 9 Antenna Design (ctd.)

10 Presentation overview Introduction Curved Microstrip Patch Antenna Design CPW Printed Monopole Antenna Design Conclusions

11 Holst Centre 11 Antenna Requirements S11 < -10dB in free space S11 < -10dB close to head S11 < -10dB in contact with head Connected to coaxial cable FR4 based Size as small as possible Choose antenna concept Model human head Avoid common mode currents Auricularis muscle region Design antenna using CSTMWS Henry Gray, Gray s Anatomy: The Classic Collector s Edition, Granercy, 1988.

12 Holst Centre 12 Antenna concept Printed monopole antenna in CPW technology

13 Holst Centre 13 Human head model Skin Fat Muscle Cancellous bone Dura CSF Auricularis muscle region Brain (average white and grey matter) Tissue Thickness (mm) skin 1.5 fat 1.5 muscle 2.5 skull 4.25 dura 1.0 CSF 1 Antonios Drossos, Veli Santomaa and Niels Kuster, The Dependence of Electromagnetic Energy Absorption Upon Human Head Tissue Composition in the Frequency Range of MHz, IEEE Transactions on Microwave Theory and Techniques, Vol. 48, No. 11, November 2000, pp brain

14 Holst Centre 14 Human head model (ctd.) ε ( ω) ε = σ ωε α ( ) ( ) ( ) ( ) 1 α α ωτ 1 ωτ 1 ωτ 1 α j + j + j + jωτ j 0 1 ε 2 r = ε ' r j ε" r Dielectric f=2.00ghz f=2.25ghz f=2.45ghz f=2.65ghz f=2.90ghz ε r ε r ε r ε r ε r ε r ε r ε r ε r ε r dry skin fat muscle skull dura CSF brain Camelia Gabriel and Sami Gabriel, Compilation of the Dielectric Properties of Body Tissues at RF and Microwave Frequencies, Final report, AFB DC , Physics Department, King s College London, June

15 Holst Centre 15 Human head model (ctd.) Use a spherical, layered human head model Use Auricularis muscle region characteristics for the whole sphere Keep complex permittivity constant over frequency range R=120mm Use delta-gap excited dipole to test feasibility

16 Holst Centre 16 Human head model (ctd.) Feasible

17 Holst Centre 17 Human head model (ctd.) Save

18 Holst Centre 18 Common Mode Currents S11 (db) Linel length = 05mm Line length = 15mm Line length = 25mm Line length = 35mm Frequency (GHz)

19 Holst Centre 19 Common Mode Currents (ctd.) Blocking slots

20 Holst Centre 20 Antenna Design encapsulated in resin S11(dB) offset = 0mm offset = 5mm Frequency (GHz)

21 Holst Centre 21 Prototype Measurement Return loss vs. frequency Free standing Holding outer coaxial conductor Against skin S11 (db B) Frequency (GHz)

22 Presentation overview Introduction Curved Microstrip Patch Antenna Design CPW Printed Monopole Antenna Design Conclusions

23 Holst Centre 23 Common mode current suppression leads to small ground planes and thus small printed monopole antennas Environment-independence may be obtained through shielding or encapsulating the antenna within a dielectric A balanced combination of physical reasoning, analytic models and CSTMWS leads to time-efficient antenna design

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