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FLEXIBLE ANTENNAS

Riaz Ahmed Liyakath

Department of Electrical Engineering

University of South Florida

Tampa, FL-33620

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PRESENTATION OVER-VIEW:

Introduction to flexible electronicsWhy we go for flexible antennas?Materials used for making flexible antennasExamples to explain the working of various types of

flexible antennasMy current research Challenges and future scope

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REASONS TO MAKE ANTENNAS FLEXIBLE:

Flexible antennas are robust light weight antennas which

are withstand mechanical strain upto a certain extent.

Fig 1. Scope of flexible electronics

Flexible antennas

Polymer based antennas

Carbon nano-tube antennas

Textile antennas Micro fluidic antennas

Fig 2. Antennas for air-crafts

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MATERIALS USED FOR FLEXIBLE ANTENNAS:

i) Silicone elastomers: Polydimethyl Siloxane (PDMS):

Reasons to opt for PDMS:PDMS an inexpensive, flexible polymerCan withstand mechanical strainCan be mixed and cured at room temperatureDielectric properties can be tuned.

FABRICTION PROCESS:

Fig 1. Various silicone elastomers

Fig 2. Patch antenna made from PDMS- ceramic composite

1. Polymer based antennas:

ii) PDMS- ceramic composites:

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4. Micro fluidics/ Liquid metals:

Liquid metals are filled in micro-fluidic cavities in an silicone elastomer.

The liquid metal prevents loss of electrical connectivity when the antenna is deformed.

Liquid metal antennas on the other hand, can conform to any shape without strain and can be reversibly deformed.

5. Textiles:

FlecTron

fleece fabric

Conductive textiles coated with Carbon nanotubes(CNTs) and gold

3. Compressed Nano tubes:

APPLICATIONS:High gain-beamforming antennas for wireless systems

Fig 1. CNT based antenna

Fig 2. Twisted liquid metal antenna

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LIQUID METAL PLANAR INVERTED CONE ANTENNA (PICA):

The antenna is manufactured by

injecting liquid metal into micro-

structured channels in the elastic

PDMS material.

The antenna has a good return loss

of 10 dB in the operating frequency

and the radiation efficiency was also

observed to be greater than 70%

which is considered good.

The produced antenna allows

stretching up to 40%.

It is a highly broadband antenna

Fig. 3: Photographs of the stretchable PICA: (a) and (c) non-stretched antenna, (b) stretched antenna with 40% y-axis elongation, (d) stretched antenna with 40% -axis elongation, (e) folded antenna, and (f) twisted antenna.

The planar inverted cone antenna (PICA) operates in the Ultra wide band (UWB) of frequency 3.1 to 10.6 GHz

Fig. 1: Sketch of feed cable connection to the antenna

Shi Cheng, Zhigang Wu, Paul Hallbjörner, Klas Hjort, Anders Rydberg, “Foldable and Stretchable Liquid Metal Planar Inverted Cone Antenna”, IEEE Transactions on Antennas and Propogation, Vol. 57, No. 12, Dec 2009

Fig. 2: Feed cable

Fig. 3: Return loss and efficiency

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REVERSIBLY DEFORMABLE AND MECHANICALLY TUNABLE FLUIDIC ANTENNAS :

The antenna consist of a fluid metal alloy ( eutectic gallium indium - EGaIn) injected into micro fluidic channels comprising a silicone elastomer (PDMS).

FLUIDIC DIPOLE FEATURES:

Withstand mechanical deformation (stretching, bending, rolling, and twisting)Resonant frequency can be tuned mechanically by elongating the antenna Resonates at 1962 MHzEfficiency is around 90%(approx.) at a broad frequency range (1910–1990 MHz)The size of antenna is 54 mmSimple to fabricate

Fabrication Process:

Ju-Hee So, Jacob Thelen, Amit Qusba, Gerard J. Hayes, Gianluca Lazzi,and Michael D. Dickey, ‘Reversibly Deformable and Mechanically Tunable Fluidic Antennas’ , Adv. Funct. Mater. 2009, 19, 3632–3637

Fig 1. prototype antenna being stretched

Fig 2. prototype antenna being rolled (left) and antenna self-heals in response to sharp cuts

Fig,.3: Measured reflection coefficient of the dipole both inits ‘‘relaxed’’ position (54mm length) and mechanically elongated positions (58, 62, and 66mm length) as a function of frequency. The ability to stretch the antenna allows the frequency to be tuned mechanically.

Figure 4. Resonance frequency of a fluidic dipole antenna as a function of the length of the antenna as modulated by stretching

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ELASTIC ANTENNAS BY METALLISED ELASTOMERS:

Fig 1: Elastic coplanar waveguide:

Fig 2: Normal coplanar waveguide:

The objective of this is to investigate Elastic antennas made by metallised elastomers at RF frequencies for microwave transmission lines and antennas applications

Both give radiation patterns as expected for a normal monopole antenna

Fig 5: Simulated return loss of ultra-wideband antennas

Fig 3. Ultra-wideband monopole antennaFig 4. Radiation patterns

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The below table shows that the conductor thickness is important for designing an efficient antenna

Fig 7: Simulated return loss after stretching

Fig.6 : Self-compensating antenna

Table 1: Conductor thickness vs. Efficiency

Qing Liu, Kenneth Lee Ford, Richard Langley,”Elastic Antennas by Metallised Elastomers”, 2010 Loughborough Antennas & Propagation Conference, Nov 2010

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A MILLIMETER-WAVE MICROSTRIP ANTENNA ARRAY ON ULTRA-FLEXIBLE MICRO MACHINED POLYDIMETHYLSILOXANE (PDMS) POLYMER:

As bulk PDMS is demonstrated to be lossy at millimeter waves, membrane-supported devices are considered.

A new reliable and robust technological process has been developed to micro machine membrane-supported transmission lines and microstrip antenna arrays.

Transmission lines

Fig. 1. (a) Schematic view of 50- ohm transmission lines printed on bulk PDMS and PDMS membranes . (b) Bulk PDMS transmission line in the impedance measurement setup based on an Anritsu Universal test fixture 3680 V. (c) 50-ohm transmission line on a PDMS membrane d) Measured and computed insertion loss of 50-ohm transmission lines printed on bulk PDMS and 20-m-thick PDMS membranes

Antenna array

A 4 X 2-element microstrip antenna array supported by a 20- micro meter-thick PDMS membrane is designed.

The insertion loss of microstrip lines fabricated on 20- m-thick membranes is about 0.5 dB/cm at 60 GHz.

Fig. 3(below). Measured and computed radiation patterns of the membrane supported microstrip antenna array at 55 GHz. (a) H-plane. (b) E-plane

Fig. 3. (a) Reflection coefficient and (b) input impedance of the antenna array.

Fig. 2. (a) Layout of the microstrip antenna array supported by a PDMS membraneand zoom to see rounded angles. (b) 3-D schematic of theantenna array. (c) Photograph of the fabricated prototype

Sami Hage-Ali, Nicolas Tiercelin, Philippe Coquet, Ronan Sauleau, Hiroyuki Fujita, Vladimir Preobrazhensky, and Philippe Pernodm,’ A Millimeter-Wave Microstrip Antenna Array on Ultra-Flexible Micromachined Polydimethylsiloxane (PDMS) Polymer’ , IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 8, 2009

DESIGN AND MANUFACTURING OF STRETCHABLE HIGH-FREQUENCY INTERCONNECTS:

Meander-shaped conductors in a coplanar waveguide topology.

They are produced based on laser-ablation of a copper foil, which is then embedded in a highly stretchable bio-compatible silicone material - Silastic MDX4-4210 .

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Fig 3. Horse-shaped CPWMaximal magnitude of -14 dB for the reflection coefficient and a minimal magnitude of -4 dB for the transmission coefficient in the frequency band up to 3 GHz. Neither magnitude nor the phase of the transmission coefficient was influenced by elongations up to 20%.

Fig. 6 Close up of the horseshoe-shaped CPW

Fig. 7 Prototype stretchable high-frequency interconnect

Fig. 5 Tapered interconnection between the pads and the CPW

Fig 4. Structure of the flexible link

Fig. 2 Comparative simulation of the magnitude of the reflection coefficient of a straight and horseshoe-shaped CPW

Fig. 5 Close up of the horseshoe-shaped CPW

Fig. 1 Structure of the entire external interconnection

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ROBUST PLANAR TEXTILE ANTENNA FOR WIRELESS BODY LANS OPERATING IN 2.45 GHZ ISM BAND:

A single-feed rectangular-ring textile

antenna is proposed for wireless body

area networks operating in the 2.45

GHz ISM band.

Conductive part - FlecTronNon-conductive antenna substrate -fleece fabric

Fig. 1 Geometry of rectangular-ring microstrip textile antenna

Fig. 2 Measured and simulated return loss (S11) Fig. 3 Measured antenna gain along broadside

Fig. 4 Simulated antenna gain at 2.45 GHza xz-planeb yz-plane

ADVANATGES:Highly efficient Flexible Wearable

A. Tronquo, H. Rogier, C. Hertleer and L. Van Langenhove, ‘Robust planar textile antenna for wireless body LANs operating in 2.45 GHz ISM band’ , ELECTRONICS LETTERS 2nd February 2006 .

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DUAL-BAND TEXTILE ANTENNA USING AN EBG STRUCTURE:

The antenna is fully characterized in free space and on the body model, with and without an electromagnetic band gap (EBG) substrate. The bandgap array consists of 3 × 3 elements and is used to reduce the interaction with human tissues. With the EBG back reflector, the radiation into the body is reduced by more than 15 dB.Increases of 5.2 dB and 3 dB gain are noticed at 2.45 GHz and 5.5 GHz, respectively.

Dual-band coplanar antenna.

EBG geometry

Antenna on EBG geometry

The efficiency of the antenna combined with the EBGstructure and placed 1 mm above the homogeneous phantom,significantly increases (83% at 2.45 GHz and 86% at 5.5GHz).

Nacer Chahat1, Maxim Zhadobov, Ronan Sauleau, Kouroch Mahdjoubi, ‘Improvement of the On-Body Performance of a Dual-Band Textile Antenna Using an EBG structure ’, 2010 Loughborough Antennas & Propagation Conference

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A FLEXIBLE MONOPOLE ANTENNA WITH BAND-NOTCH FUNCTION FOR UWB SYSTEMS:

A flexible monopole antenna for UWB systems which can cover the frequency band 3.1 - 10.6 GHz is proposed and fabricated on PET film having the flexible characteristic.

To obtain the wide bandwidth, the stepped CPW feed line and the declined shape of the ground plane is used.

It has a band-notch function of 5 GHz WLAN band using two slits. Thisis used to reject 5 GHz band, which includes the limited band by IEEE802. 1 la and HIPERLAN/2.

Fig 2. Rolled type flexible antenna

Fig 1. Rolled type flexible antenna

Fig 3. The parameter study of the length of the slit of the flexible UWB antenna

Su Won Bae, Hyung Kuk Yoon, Woo Suk Kang, Young Joong Yoon and Cheon-Hee Lee, ‘A Flexible Monopole Antenna with Band-notch Function for UWB Systems’ , Proceedings of Asia-Pacific Microwave Conference 2007

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OPTICALLY TRANSPARENT ULTRA-WIDEBAND ANTENNA:

Optically transparent ultra-wideband (UWB) disc monopole using AgHT-4 transparent film is designed. The antenna is fed by a 50 V coplanar waveguideIts operational bandwidth is measured from 1 to 8.5 GHz.

Fig. 1 UWB transparent antennaFig. 2 Measured and simulated return loss

Fig. 3 Gain sweep for transparent and aluminum UWB antenna using coaxial and optical fibre

Fig. 4 H (left) and E-plane radiation patterns for transparent and aluminium UWB

APPLICATIONS:Vehicles,Building windows,Computer video monitors Solar photovoltaic panels

A. Katsounaros, Y. Hao, N. Collings and W.A. Crossland, ‘Optically transparent ultra-wideband antenna’, ELECTRONICS LETTERS 2nd July 2009 Vol. 45 No. 14

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MY RESEARCH:

We plan to make a planar antenna on a flexible substrate that can be tuned to work over a range of frequencies by stretching the substrate.

1.5 2.0 2.5 3.0 3.5 4.0 4.51.0 5.0

-20

-15

-10

-5

-25

0

Frequency

Mag.

[dB

]

Readout

m1

S11

m1freq=dB(newstlen5per_mom_a..S(1,1))=-23.646Min

2.427GHz

5% stretch

1.5 2.0 2.5 3.0 3.5 4.0 4.51.0 5.0

-30

-20

-10

-40

0

Frequency

Mag. [d

B]

Readout

m1

S11m1freq=dB(newstlen25per_mom_a..S(1,1))=-31.789Min

2.057GHz

25% stretch

1.5 2.0 2.5 3.0 3.5 4.0 4.51.0 5.0

-40

-30

-20

-10

-50

0

Frequency

Mag. [d

B]

Readout

m1

S11

m1freq=dB(newstwid5per_mom_a..S(1,1))=-41.608Min

2.537GHz

10% stretch

STRETCH ALONG LENGTH:

STRETCH ALONG WIDTH:

Fig 1.Fundamental idea

Fig 2. 4-probe measurementSet-up (left) and fabricated PDMS film (right)

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WHAT FUTURE HOLDS FOR THESE ANTENNAS:

Flexible antennas

Medicine

E-Textiles

Military

Air-planes

Flexible RFID tags

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THANK YOU!