Microfluidically Loaded Highly Reconfigurable

Compact Antennas & RF Devices

Gokhan Mumcu

Associate ProfessorCenter for Wireless and Microwave Information Systems (WAMI)

Department of Electrical EngineeringUniversity of South Florida

4202 E. Fowler Ave., Tampa, FL, 33620

IEEE MTT/AP Orlando Chapter MeetingNovember 30th, 2016

Forum for Electromagnetic Research Methods and Application Techniques

(FERMAT)

Copyright

2

© The use of this work is restricted solely for academic purposes.

The author of this work owns the copyright and no reproduction

in any form is permitted without written permission by the

author.

Abstract

3

Reconfigurable radio frequency (RF) antennas and filters have drawn growing interest to enable compact and light-weight multifunctional systems for wireless communications, sensor networks, biomedical imaging, and remote sensing. Existing reconfigurable RF device design approaches that are based on material loadings, semiconductor and ferroelectric varactors, micromechanical systems (MEMS) switches and capacitors are today well-recognized to offer compact and cost-effective device implementations with high reconfiguration speeds. However, these technologies continue to exhibit limited performance in terms of key RF metrics such as power handling, frequency tunability bandwidth, pattern scanning range, efficiency, and frequency-agile capability. Consequently, novel alternative techniques that address the overall performance needs of reconfigurable RF devices are highly desirable to advance their capabilities and use into mainstream technologies.

This presentation focuses on novel reconfigurable RF antennas, filters, and imaging systems realized by resorting to innovative microfluidic based reconfiguration techniques. The operational principles of these devices rely on continuously movable microfluidic loads consisting of metal (in liquid or solid form) and dielectric solution volumes. The realization of the devices are carried out by utilizing microfluidics and microfabrication techniques with multilayered ultra-thin substrates to maximize the parasitic loading effect of the microfluidic loads for achieving high reconfiguration performances. It will be shown that the proposed microfluidic reconfiguration techniques offer significantly improved frequency tuning range (>4:1 and >2:1 in monopole antenna and filter topologies, respectively) without suffering from excessive loss factors and high power handling issues observed in conventional semiconductor based implementations. Another example design will demonstrate that the microfluidic reconfiguration techniques lead to low-cost mm-wave (30GHz) beam-scanning high-gain antenna arrays without necessitating the use of costly and lossy phase shifters.

Keywords: Reconfigurable antenna, filter, mm-wave, antenna array, microfluidics, liquid metal;

Biography

4

Gokhan Mumcu (S’03–M’09–SM’15) was born in Bursa, Turkey, on March 30, 1982. He

received the B.S. degree in electrical engineering from Bilkent University, Ankara, Turkey, in

2003, and the M.S. and Ph.D. degrees in electrical and computer engineering from The Ohio

State University, Columbus, in 2005 and 2008, respectively.

He is currently an Associate Professor at the Electrical Engineering Department of

University of South Florida, Tampa, FL. From 2009 to 2015, he was an Assistant Professor at

the Electrical Engineering Department of University of South Florida. His research interests

are small antennas, engineered materials, THz technologies, and reconfigurable RF devices,

antennas and arrays using microfluidic reconfiguration techniques.

Dr. Mumcu is the recipient of the 2014 CAREER award from the U.S. National Science

Foundation. He is also recipient of 2014 faculty outstanding research award from the

University of South Florida. He ranked first on the national university entrance exam taken

annually by over 1.5 million Turkish students in 1999. He received the 1999 international

education fellowship of the Turkish Ministry of Education. He was the recipient of a best

paper award at 2008 URSI National Radio Science Meeting, and the 2008 outstanding

dissertation award at The Ohio State University, ElectroScience Laboratory. He served as the

technical program committee co-chair of the 2013 IEEE International Symposium on

Antennas and Propagation and USNC/URSI National Radio Science Meeting and 2016

International Workshop on Antenna Technology (iWAT).

Reconfigurable RF Components for

Emerging Multifunctional Miniature Systems5

Passive RF components (such as filters and antennas) occupy a

significant footprint in wireless communication devices and system-

on-chip components.

Recent technology trends that pack many capabilities into small

platforms suffer from the size limitations of RF components.

Reconfigurable RF components hold promise to enable

consolidation of multiple RF front-ends (each serving for a

distinct sensing/communication functionality) into a single

multifunctional RF front-end.

More than 50% of a system-on-a-chip

consists of passive RF devices

Compact communication

systems with higher data rates

State-of-the-art Technologies for Implementing Reconfigurable RF Components

6

Semiconductor Technologies

Varactor Diodes: Variable capacitors that can be controlled with bias voltage.

PIN Diodes: ON/OFF RF switching functionality controlled with bias voltage.

Transistors: ON/OFF RF switches controlled with gate voltage.

Material Loadings

Magnetic materials: Permeability variation controlled with external magnetic field (e.g. yttrium iron garnet).

Ferroelectrics: Permittivity variation controlled with external electric field (e.g. barium strontium titanate).

Polymers: Physical size control with mechanical setups (e.g. stretching) or heat (e.g. shape shifting alloys).

Micro Electro Mechanical Systems (MEMS)

MEMS capacitors: Variable capacitors with bias voltage.

MEMS switches: ON/OFF RF switches controlled with bias voltage.

Advantages

Cost effective, high reconfiguration speed (except mechanical actuation of polymers), compact, low loss and

RF isolation (especially with MEMS technology)

Disadvantages

Power handling is limited due to intermodulation products, harmonics, and device construction.

Limited continuous frequency tunability bandwidth or frequency tuning in discrete steps.

Loss is still high for achieving high radiation efficiency.

Design complexity and high cost for systems that need many reconfigurable RF devices (e.g. beam-steering

arrays)

Microfluidics for Reconfigurable RF Components

7

Microfluidic Loading of RF devices with:

• Continuously movable metals (in liquid or solid form)

• Dielectric solutions

• Fluidic channels utilizing ultra-thin walls

offers new possibilities & degrees of freedom for RF design:

Miniaturization

Large Frequency Tuning Range

High Power Handling

Low Cost Beam-Steering

Low Loss

Filled

Location

Ground

PlaneSubstrate of the Feed

Network

Liquid Crystalline

Polymer (LCP)

Polydimethylsiloxane

(PDMS)

Rexolite

Feed

Network

Microfluidic

Channels

Complex Material Development

Interdisciplinary projects & Collaboration of different departments

Fundamental Understanding

Applied Mathematics, Physics

Electrical Engineering

Prototype Development &

Device Testing

EM & RF Engineers

Material Production

Material Science, Mechanical

Engineering

Presentation Highlights –Microfluidically Loaded Reconfigurable Compact RF Antennas and Filters

8

Wideband Frequency Tunable Monopole Antennas

Concept: Harnessing liquid metals for varying length of a monopole

Technique: Ultra-thin low-loss microfluidic channel walls to enable a stationary RF antenna

feed through strong capacitive coupling

Performance: >4:1 frequency tuning (1.2 – 5.2 GHz) with >80% radiation efficiency

Path for reliability and high power handling: Replacing liquid metals with metalized plates

(15W @ 3.3GHz)

Frequency-agile Bandpass Filters

Concept: Metalized plates within channels to tune printed open loop resonators

Technique: Ultra-thin low-loss channel walls to maximize capacitance variation

Performance: ~2:1 frequency tuning (0.8 – 1.5 GHz) with low insertion loss

High power handling: ~10W, limited by maximum temperature handling considerations

MM-Wave Beam-Scanning Arrays

Concept: Moving metalized plate acting as a patch antenna feed behind a microwave lens

Technique: Stationary RF feed networks to accommodate the location of feed antenna

Performance: Comparable or better in radiation efficiency. Very low cost due to no active RF

devices and simplified fabrication procedure.

Path for larger arrays: Utilizing metalized plates as switches within feed network

RF In

Liquid

metal

Liquid

out

Liquid

in PDMS

LCP

RT5880

Ground

plane50W microstrip

line

Microfluidic

connectors

Non-radiating

lengthRadiating

Length (l/4)

1.29GHz

2.48GHz

5.17GHz

3.53GHz

Fabrication Techniques

9

Fabrication:

1) Pattern the printed circuit board (PCB) with

photolithography.

2) Benzocyclobutene (BCB) is spun on the substrate

and cured in convection oven.

3) Microfluidic channels are prepared within

Polydimethylsiloxane (PDMS) polymers using

soft lithography and micromolding

4) PDMS and BCB are bonded by plasma

activation.

5) In this process, BCB (or LCP) is treated with 4%

APTES (3-aminopropyl triethoxysilane) solution.

Notes:

• BCB allows very thin channel walls (<<10um) –

suitable over a large frequency range including

mm-waves

• Our earlier devices (<10GHz) used Liquid Crystal

Polymers (LCP) instead of BCB (with >25.4um

thickness).

• Channels can contain liquid metals (earlier work),

or metalized plates (current work)

• Metalized plates and metallization patterns can

take non-uniform shapes for increased speed and

controlling multiple components/functionalities

Vertical Movement

Horizontal Movement

Liquid Metal Wideband Frequency Tunable Monopole Antenna

– Operation Principle10

RF In

Liquid

metal

Liquid

out

Liquid

in PDMS

LCP

RT5880

Ground

plane50W microstrip

line

Microfluidic

connectors

Concept:

• Liquid metal is inside the microfluidic channel.

• Liquid metal can overlap with the microstrip feed line

and its ground Non-radiating length

• Liquid metal volume that does not overlap with ground

plane radiates Radiating length

• Controlling the radiating length using micro-pumps, the

antenna can be tuned to the desired resonant frequency.

Challenges:

• Feeding/Packaging – Feeding the antenna with direct

electrical connection is not practical. Ultra-thin channel

walls solves this by enabling feeding through RF

coupling.

• Movement – the ability to move a liquid metal volume

inside a microchannel without formation of any

discontinuities.

• Precise flow control – controlling the flow of the liquid

metal precisely to tune to a desired resonant frequency.

LRad=l1/4@fLOW

LRad=l2/4@fHIGH

LO

Liquid Metal Flow Characterization for

Maximum Antenna Length

Fabricated microfluidic

channels

LCP

To ensure proper working of the antenna the liquid metal has to stay as

a connected volume and flow without any disruption.

Longer liquid metal slugs are needed to operate at the lowest possible

frequency and attain the largest frequency tuning range

Channel width controls the instantaneous bandwidth – needs to be

practically large.

The effect of channel width and height on the maximum length of

liquid metal slugs were experimentally characterized using mercury

and Teflon solution

11

Mask for

microfluidic channels

0.5mm

50mm

3mm

1mm

2mm

4mm

5mm

22mm

18mm

6mm

Ch

ann

el w

idth

(w

)

Channel

Width (w)

Channel Height (H)

100mm 150mm 200mm 250mm 300mm

0.5mm 11mm 25mm 36mm 50mm 45mm

1mm 8mm 12mm 17mm 22mm 21mm

2mm 5mm 8mm 15mm 18mm 15mm

3mm 2mm 2mm 3mm 6mm 3mm

Liquid Metal Flow Characterization for

Widest Feed Overlap & Feed/Antenna Transition

12

WO

Wantenna

The wider the overlap area with the microstrip

line feed, the larger the tuning range (due to the

coupled line resonance issue)

Total volume of liquid metal in antenna section:

50mm x 0.5mm x 0.25mm=6.25mm3

From the characterization table, widest channel

that can accommodate the antenna volume is

2mm

( 2mm x 18mm x 0.25mm=9mm3)

Second set of experiments were performed to determine

the junction shape that would provide a reliable inter-

transition between the 2mm and 0.5mm wide channel.

The rounded junction was observed to provide a reliable

operation without disrupting the continuous slug nature

of the liquid metal.

Channel

Width (w)

Channel Height (H)

100mm 150mm 200mm 250mm 300mm

0.5mm 11mm 25mm 36mm 50mm 45mm

1mm 8mm 12mm 17mm 22mm 21mm

2mm 5mm 8mm 15mm 18mm 15mm

3mm 2mm 2mm 3mm 6mm 3mm

Liquid Metal Wideband Frequency Tunable Monopole Antenna – Design & Simulations

13

Wantenna

WO

LO LRad

LG

WG

LO(min)

Y

X

1 2 3 4 51

1.5

2

2.5

3

1 2 3 4 584

86

88

90

92

50mm

25mm

20mm

10mm

Frequency (GHz)

Rea

lize

d p

eak

gai

n(d

B)

Efficien

cy (%

)|S11| (

dB

)

Frequency (GHz)

1.2GHz

2.3GHz

3.3GHz

4.8GHz

50-10-20-30

-40dB

030

60

90

120

150

0-30

-60

-90

-120

-150180

50-10-20-30

-40dB

030

60

90

120

150

0-30

-60

-90

-120

-150180

Frequency tuning range = 1.2GHz to 4.8GHz (4:1)

HLCP

HPDMS

WOWms

Lo

1mm

2mm

5mm

10mm

Frequency (GHz)

|S21| (

dB

)

Antenna Top View

Feed/Monopole RF Transition Design

HLCP

HPDMS

WOWms

RF Port 1 RF Port 2

Top View

Side View

RF Port 2RF Port 1

Minimum overlap length needed = 5mm

(<0.5dB insertion loss @1.2GHz)

Liquid Metal Wideband Frequency Tunable Monopole Antenna – Experimental Verification

14

Liquid

in

Liquid

in

Liquid

metalMicrostrip

feed lineGround

plane

Top view

Bottom view

Non-radiating

lengthRadiating

Length (l/4)

1.29GHz

2.48GHz

5.17GHz

3.53GHz

(i)

(ii)

(iii)(iv)

|S11| (

dB

)

50-10-20-30

-40dB

030

60

90

120

150

0-30

-60

-90

-120

-150180

50-10-20-30

-40dB

030

60

90

120

150

0-30

-60

-90

-120

-150180

1.29GHz

2.48GHz

3.53GHz

5.17GHz

mp-x control

unit

Uni-directional

Micro-pumps

Liquid metal

antenna

Antenna was integrated with piezoelectric micro-pumps and controller unit.

Reconfiguration speed = 252MHz/sec (16s to cover the whole tuning range)

Good agreement with simulations – 4:1 frequency tuning range

High radiation efficiency (>80%) with stable radiation pattern

Liquid Metal Wideband Frequency Tunable Monopole Antenna – Extension to Antenna Arrays

15

The liquid metal monopole antenna can be used to

construct high gain frequency tunable antenna

arrays.

The array is operated with single pump by

resorting to meandered and/or interconnected

microfluidic channels.

Specifically, a 4 element array was demonstrated.

The inter-element spacing was small to prevent

grating lobes but large enough to reduce mutual

coupling between the antenna elements.

Frequency tuning range of the array (2:1): 2.5

to 5GHz

Measured broadside gain: 6.2dB @ 2.5 GHz,

8dB @ 5GHz

d b=0

P1 P2 P3 P4

25mm

Liquid

outLiquid

in

2.5GHz

5GHz

50-10-20-30

-40dB

030

60

90

120

150

0-30

-60

-90

-120

-150180

mp6-OEM

driver circuit

Micro-pumps

Microcontroller

Y

Z

50-10-20-30

-40dB

030

60

90

120

150

0-30

-60

-90

-120

-150180 2.5GHz

5GHz

Transitioning to Liquid Metal Free RF Components

16

Liquid metals are either toxic (e.g. mercury) or suffer from excessive oxidization (e.g. Galinstan) that causes

them to wet the surfaces they come in contact with (i.e. sticking)

Several research groups are working on reliable actuation of non-toxic liquid metals (such as encapsulating

liquid metal in carrier fluid, using electrolytes to continuously remove oxide layer, electrowetting, etc.).

However, there is still no established reliable technique available.

Even though the liquid metal actuation issues are solved, their conductivity is 10 to 20 times lower. Hence, the

high power handling and loss performance of the devices will be limited with this conductivity layer

Our Solution: Utilize metalized plates within microfluidic channels to achieve low loss and high power

handling RF devices.

Metalized plate (quartz, PCB, glass, etc) in

microfluidic channel

LCP is also replaced in certain implementations with lower

loss dielectric polymer BCB (Benzocyclobutene).

BCB offers thinner layers (< 25µm), higher power handling,

and a more convenient PDMS/PCB bonding procedure.

Wideband Tunable Monopole Antenna – Extension to High Power RF Applications

17

Operation principle is identical with liquid

metal monopole.

Liquid metal is replaced with metalized

plate.

2:1 frequency tuning range (1.2 – 3.3 GHz

simulated).

12 µm thick BCB is used as the channel wall.

Minimum feed overlap area is designed

similarly to the liquid metal monopole antenna

in a way to provide RF short at the lowest

frequency.

Feed board is Rogers 4003C: a better

thermally conductive substrate.

Metalized plate is also from Rogers 4003C

PCB material for convenient implementation.

Wideband Tunable Monopole Antenna – Experimental Verification

18

2:1 measured frequency tuning range from 1.7 to 3.5 GHz

Measured and simulated radiation gain patterns agree

well.

A more compact bi-directional pumping unit was

developed using on chip mp6-OEM drivers (Bartels).

Reconfiguration speed: 1550MHz/s (1.15s for entire

tuning range). Significantly faster as compared to liquid

metal since a low viscosity dielectric liquid FC-40 was

satisfactory for plate movement.

Wideband Tunable Monopole Antenna – Power Handling

19

First experimental demonstration of high power

handling capability of a microfludically

reconfigurable antenna.

Steady state thermal simulations carried out with

ANSYS Multiphysics Workbench compared well

with thermal profiles acquired from thermal

imaging camera.

Power handling capability goes down with higher

operation frequency due to decreasing radiation

efficiency.

The antenna temperature rises from 20oC to 60oC

at 3.3 GHz with 15W of RF power.

The antenna construction ideally can withstand up

to 165oC (boiling temperature of FC-40).

Micropump manufacturer limits maximum

temperature with 70oC

Frequency-Agile Bandpass Filters– Initial Work with Liquid Metals & Tubes

20

Microfluidics For Reconfigurable Filters:

• Liquid Metals: Can dynamically change shape of resonators

• Metalized Plates: Maximized capacitance variation (from 0pF!)

• High power handling

• Large frequency tuning range

• Lower loss as compared to semiconductor/ferroelectric varactors

d=d1 d3 d4 d5

Frequency (GHz)

dB

(S11

) &

dB

(S2

1)

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

0.50

1.00

-25

-20

-15

-10

-5

-30

0

freq, GHz

dB

(S

(2,1))

dB

(S

(1,1))

dB

(S

(4,3))

dB

(S

(3,3))

dB

(S

(6,5))

dB

(S

(5,5))

dB

(S

(8,7))

dB

(S

(7,7))

• Limited tunability due to thick tube walls and

rounded shape: 650 – 870 MHz (29%)

• < 3dB insertion loss with 5% fractional bandwidth

• Not reliable due to the liquid metals and tubed

construction

Increase tuning range and decrease loss with

ultra-thin microfluidic channel walls (LCP)

Replace liquid metal with metalized plate

Open Loop Resonators Loaded with Microfluidically Controlled Metalized Plates

21

• Simulated frequency tuning range: 0.6 GHz to 1.5 GHz

• Simulate quality factor (Q) : 72 to 160

• Hybrid (circuit + full wave) model for reducing the full wave

simulation requirements. Faster design of high order filters

• 6mm displacement needed to cover the tuning range. Can be

miniaturized further with thinner insulator.

0.6 0.8 1.0 1.2 1.4 1.60.4 1.8

-4

-3

-2

-1

-5

0

freq, GHz

dB

(C

apacitanceextraction5..S

(2,2))

dB

(C

apacitanceextraction5..S

(1,1))

dB

(C

apacitanceextraction4..S

(2,2))

dB

(C

apacitanceextraction4..S

(1,1))

dB

(C

apacitanceextraction3..S

(2,2))

dB

(C

apacitanceextraction3..S

(1,1))

dB

(C

apacitanceextraction2..S

(1,1))

dB

(C

apacitanceextraction2..S

(2,2))

dB

(C

apacitanceextraction..S

(1,1))

dB

(C

apacitanceextraction..S

(2,2))

Frequency (GHz)

S11

(dB

)

C5

C4

C3C2

C1

C

L

r

C1 C2

PDMS

Channel

LCP

Resonator

Roger

6010.2

Ground

Metallized plate

Represents moving plate

RF Port 1

Example 2-pole filter design with 10% FBW

22• To have constant FBW, the external quality factor (Qe) and coupling coefficient (k) must be kept

constant across the entire frequency tuning range of 0.6 GHz to 1.5 GHz.

• Qe was stabilized by adding series lumped inductors to the tapping lines. The tapping location and

lumped inductor value was optimized to achieve desired Qe value.

• k was stabilized by selecting a resonator arrangement that relies on mixed magnetic and electric

coupling. The coupling gap was selected to achieve the desired k value.

• Further stabilization in Qe and k variation is possible with rectangular resonator shapes but this was not

pursued for the example filter demonstrations.

Coupling Gap

Tapping

location

2-pole filter implementation

23

24.4mm

12

.4m

m

Input

Output

• A meandered microfluidic channel was designed to

operate the filter with a single pumping unit.

• The resonators were slightly misaligned vertically

with respect to each other to accommodate metalized

plate movement.

• Metalized glass plates were initially prepared by

dicing saw and sputtering. Later implementations

used PCB for manufacturing ease and lower density.

• 12mm long plates can provide the 0.6 – 1.5 GHz

tuning range.

• Experiments used 10mm plates for initial testing

which resulted in 0.9 – 1.5 GHz tuning range (50%)

Experimental verification of the 2-pole filter

24

1.0 1.50.5 2.0

-30

-20

-10

-40

0

freq, GHz

dB(S

(2,1

))dB

(S(4

,3))

dB(S

(6,5

))dB

(S(1

0,9)

)dB

(S(1

2,11

))dB

(S(1

,1))

dB(S

(3,3

))dB

(S(5

,5))

dB(S

(9,9

))dB

(S(1

1,11

))

S2

1(d

B)

Frequency (GHz)

Simulated

1.0 1.50.5 2.0

-30

-20

-10

-40

0

freq, GHz

dB(S

(4,3

))dB

(S(1

0,9)

)dB

(S(1

6,15

))dB

(S(2

2,21

))dB

(S(2

,1))

dB(S

(3,3

))dB

(S(9

,9))

dB(S

(15,

15))

dB(S

(21,

21))

dB(S

(1,1

))

MeasuredS

21

(dB

)

Frequency (GHz)

Tuning range 1.5 GHz to 0.9 GHz (50%)

Insertion loss is better than 1.7 dB (Liquid metal implementation was 29% tuning, 3 dB IL)

Fractional Bandwidth varies from 8% to 10% (1.5 GHz to 0.9 GHz)

Tuning speed of 7.96ms per MHz (125.52 MHz/s) with Teflon Solution

Issues that addressed next:

o Synchronizing movement of 2 distinct plates is challenging – Reliability is low.

o Higher order filters with better selectivity, out of band rejection, and different

footprint arrangements (linear vs. square footprints).

4-pole Filters &Selectively Metallized Plates

25

Qe and k design follows the same procedures. Simulated tuning range is 1.5 GHz to 0.6 GHz.

Fractional bandwidth is 5% +/-1%.

Insertion loss is < 4.7dB

>40dB out of band rejection.

A selectively metalized plate is utilized to remove the synchronization issues.

Channel and plate is modified to take Z-shape to increase tuning speed (7x).

Metallized

Areas

Liquid In Liquid Out

RF In

RF Out

RCl

RPl

RP

w

RC

w

MicrochannelRoger 5880 plate

Metallized

Areas

Liquid In

Liquid Out

RF In

RF Out

ZCl

ZPl

RP

w

RC

w

Microchannel

Zin

Roger 5880

plate

Frequency (GHz)S

21

(dB

)

Z-shaped plate and channel

Straight rectangular plate and channel

4-pole Filters: Experimental Verification

26

Liquid In

Liquid Out

ZPl

ZPl

ZP

l

ZP

l

ZC

l

ZC

l

Roff

Roff

RF In

RF Out

g12

g12

g23

Alternative

Footprint Design

Frequency (GHz)

S2

1(d

B)

Frequency (GHz)

S2

1(d

B)

Frequency (GHz)

S2

1(d

B)

Measured tuning range is 1.5 GHz to 0.8 GHz

Fractional bandwidth is 5% +/-1%.

Insertion loss is < 4.7dB

>40dB out of band rejection.

2MHz per ms (300ms for 6mm motion range)

51.5 × 14 mm2

37.6 × 34.2 mm2

6mm

34

.2m

m

37.58mm

Ba

rtels MP

-6

Micro

pu

mp

s

Inp

ut

Ou

tpu

t

PDMS

Selectively Metallized Plate

LCP

PCB with Printed Resonators

Ground

4th order 2:1 Frequency-Agile Bandpass Filter

Pad to Ground

S0 S1S2 S3

S4

Sg

RL

RW

Plate

R

Combline Filters for Wider Tuning Range and High Power Handling(publication pending)

27

Microfluidic

Channel

Metallized

Plate

PD

MS

Rogers 6010.2

Gro

un

dH

alf

Wavele

ngth

Reso

nato

rP

ad

to

Gro

un

d

BCB

1

1.5

2

2.5

3

3.5

4

4.5

185

190

195

200

205

210

215

0 2 4 6 8 10 12

Un

loaded

Qu

ali

ty F

acto

r (Q

u)

Fre

qu

ency (G

Hz)

Plate Displacement (mm)

Frequency tuning is based on “length variation” and moderate

capacitive loading.

6um thick BCB is used to maximize capacitive coupling between

metalized plate and the printed resonator.

Quality factor (resonator loss) remains constant over large tuning

range (1.5 – 4 GHz).

11.5 mm movement range for entire tuning range

Substrate Stack-up View Top View

4th order Combline Filter Performance(publication pending)

28

CL

PL

PO

CO

PW

PL

PI

PO 3

8.0

1 m

m

34.975 mm

Barte

ls MP

-6

Mic

rop

um

ps

Inp

ut

Ou

tpu

t

0.5 2.0 4.0 6.0 8.0 10.0 12.0

0

-30

-20

-10

-40

Frequency (GHz)

S11

& S

21

(dB

)

-5

-15

-25

-35

Design utilizes a capacitive coupling and stub loading mechanism and input/output ports to maintain external quality

factor constant across the wide frequency tuning range (1.5 – 4 GHz, 2.7:1).

Fractional bandwidth is ~5% +/- 2%.

Insertion loss is < 3 dB.

Footprint, 34 x 38 mm2

2.5 MHz per ms.

Printed Resonators & Grounding Pads

Metalized Plate

Filter PrototypeMeasured Response

4th order Combline Filter Power Handling(publication pending)

29

From the correlation between simulation and

experiments, we expect that the maximum power

handling is ~30W (780C) without heat sink.

Highest tuning range and power handling capability

among the microfluidically reconfigurable RF filters

despite its higher order design.

Future work: Replace PDMS with Quartz/Glass.

Thermal simulation for 15 W input power

level at 2.5 GHz.

480C is the highest expected temperature.

Mini-circuit

High Power Amp

ZHL-16W-43-S+

Attenuator

Isolator

ENA

`

Experiment 15 W input power level at 2.5 GHz.

460C is the highest temperature.

MM-Wave Beam-Scanning Arrays

30

Metalized plate can act as a repositionable radiating element (100µm channel walls)

Metalized plates can be used as variable capacitors to build phase shifters (<10µm channel walls)

Metalized plates can be used as switches within a feed network (<<10µm channel walls)

Low loss and cost

Scanning with microfluidics is compact and potentially high speed.

Beam-Scanning Focal Plane Array Concept: Microfluidic channel with the metalized plate is placed at the focal plane of a microwave lens.

Each antenna (i.e. metalized plate) location generates a beam towards a different direction (i.e. beam-

scanning when antenna location is reconfigured).

Design Challenges:

o Stationary feed network that can accommodate location variation of the patch antenna feed

o Trade-offs between efficiency, bandwidth, and gain

Filled

Location

Ground

PlaneSubstrate of the Feed

Network

Liquid Crystalline

Polymer (LCP)

Polydimethylsiloxane

(PDMS)

Rexolite

Feed

Network

Microfluidic

Channels

Number beams depends on lens

diameter. Scan range is typically

± 3 0.

80mm diameter was used to

generate 8 beams with 70 half

power beam width (~29dB

directivity @ 30GHz).

Microfluidic FPA Resonant Corporate Feed Network

31

λg /2

O.C

λg

λg /2

λg

O.C

λg /2

O.C

λg

λg /2

O.C

λg/2 λg/2

O.C

Line of Symmetry

O.C O.C

𝝀𝒈 separation guarantees 3dB HPBW intersection

between beams as they are scanned.

Resonant feed network directs the RF energy from the feed point to antenna element by making use of

open-circuit conditions.

It consists of multiples of λg microstrip lines

Can take different forms: corporate, straight, edge vs. center fed.

Resonant Corporate Feed Network Current Distributions

32

Simulated current distribution agrees with expectations and clearly shows the resonances on the

feed network

Resonant Corporate Feed Network: Analytical Model

33

1) Design the 𝝀𝒈/𝟐 resonator

28 29 30 31 32-40

-30

-20

-10

0

Frequency [GHz]

|S1

1| [d

B]

Antenna

Equivalent Circuit

2) Extract equivalent circuit model for

a stub loaded with antenna

𝑄𝑠𝑡𝑢𝑏 = 𝑓0 𝐵𝑊, 𝛽 = 𝜋 𝑙𝑠𝑡𝑢𝑏, 𝛼 = 𝛽 2𝑄𝑠𝑡𝑢𝑏

3) Use the antenna circuit model and TL equations

in the feed network’s equivalent circuit model

Bandwidth is limited by N (i.e. number of antenna

locations)

N=8 2.7% bandwidth

Resonant Corporate Feed Network: Radiation Performance

34

-90 -60 -30 0 30 60 90-20

-15

-10

-5

0

[degree]

[dB

]

Location

0 5 10 15 20 25 30-5

-4

-3

-2

-1

0

[degrees]

[dB

]

4 3 2 1

-90 -60 -30 0 30 60 90-20

-15

-10

-5

0

[degree]

[dB

]

Radiation patterns are calculated through a ray

tracing code utilizing currents computed by

Keysight ADS Momentum Suite

Excellent bandwidth agreement between

analytical model and simulations (2.6% vs.

2.7%)

High Side Lobe Level (only 10dB) Implies

strong radiation leakage from the corporate

feed network

All antenna locations see same feed network

loss (2.5dB). Superior or comparible to state-

of-the art implementations.

±300 field of view (FoV). Beams overlap at the

3dB point.

70 beamwidth (i.e., 29dB directivity)

Improve SLL with alternative feed network

29 29.5 30 30.5 31-20

-15

-10

-5

0

Frequency [GHz]

|S1

1| [d

B]

28 29 30 31 32-20

-15

-10

-5

0

Frequency [GHz]

S11

[d

B]

Antenna in location #1

Antenna in location #2

Antenna in location #3

Antenna in location #4

High SLL

Feed Network

Loss

Only the performance of patches #1 – #4 are

shown due to feed network symmetry.

Resonant Straight Feed Networks for Better SLL Performance

35

λg

𝝀𝒈 separation guarantees 3dB HPBW intersection between beams as they are scanned.

λg

λg

Antenna locations closer to feed point see longer resonant stubs Limits bandwidth for large N

λg

O.Cλg

O.Cλg

O.C𝒁𝟎λg

λg

𝒁𝟎

1) Schematic

Resonant Straight Feed Networks for Better SLL Performance

36

2) Antenna Design

3) Equivalent Circuit

Straight feed network minimizes radiation leakage due to being shorter and bend-free

Bandwidth is limited by N and determined by the antenna closes to the feed point.

N=8 3% bandwidth (5.3% for center-fed)

Feed network loss is dependent on antenna location. Average loss is 2.8dB (1.45dB for center fed).

Side lobe levels are less than 20dB of the main beam.

4 6 8 10 12 14 160

2

4

6

8

10

N

B.W

[%

]

Center Fed

Edge Fed

Experimental Verification (with Edge fed Straight Feed Network)

37

-90 -60 -30 0 30 60 90-20

-15

-10

-5

0

[degree]

[dB

]

0 5 10 15 20 25 30-5

-4

-3

-2

-1

0

[degree]-90 -60 -30 0 30 60 90

-20

-15

-10

-5

0

[degree]

[dB

]

Location4 3 2 1

As expected, a very good impedance match at 30GHz is achieved.

The measured bandwidth is 4% and higher than the 3% expected due

to the different reference plane location used in the experimental setup.

The normalized radiation patterns exhibit 70 HPBW.

Microfluidically Reconfigurable Selectively Metallized Plates:Switched Feed Networks

38

1) Switching Schematic

2) Microfluidic Switching Operation Via Selectively

Metallized Plate

To improve the bandwidth, loss

performance, and scanning speed of the

array; a selectively metalized plate approach

is employed to realize a switched feed

network

The required plate motion is reduced from

around 40mm to 4.2mm.

Having switches on the feed network

removes the need for resonances and

bandwidth becomes independent of array

size.

Experimental Verification of the Microfluidically Switched Transmission Line(publication pending)

39

Switch loss is near zero,

showing no difference

between a continuous

line and a switch line

when connectors are

taken into account.

Connector loss is at ~1

dB (0.5 dB per

connector).Fluid

IN/OUT

Fluid

IN/OUT

Microfluidically Switched Feed Network Operational Concept

40

0.6

mm

4.2

mm

𝝀𝒈/𝟐 𝝀𝒈/𝟐 𝝀𝒈/𝟐

0.8mm 1.8mm

O.C.

O.C.

2) Switched Array Bandwidth Performance

1) Feed Network Response

Microfluidically Switched Feed Network Performance

41

A very good impedance matching is achieved – suitable for larger arrays without bandwidth

compromise.

Insertion loss is <2 dB for the complete band (superior to other techniques).

The bandwidth depends on the antenna choice.

5%

6%

7%

8%

9%

1 2 3 4 5 6 7 8

BW

[%

]

Position

Feed Network

Loss

Fabricated Prototype and Characterization (Underway)(publication pending)

42

Array impedance is matched for different switch

positions (i.e. antenna excitations)

Larger S11 ripples in measurements are likely

due to connector – de-embedding is in progress.

Gain measurements are currently in progress.

Integrated Actuation with Piezoelectric Disks(publication pending)

43 MM-Wave devices (phase shifters, filters, and FPAs) require a small amount of metalized plate

displacement.

This motivates for integrating/packaging an actuation mechanism with the device.

Currently, we are investigating achieving actuation with piezoelectric disks – Initial experiment

is done for controlling resonance frequency of an X-band open loop resonator:

1) Piezo electric actuation on a microfluidic channel

Piezo disk actuator

BCB Bonding

Layer

APTES-Treated

LCP Membrane

Silver Epoxy

Microfluidic

Channel

PDMS Chip

Rogers RO6010Moving

Plate

Deflection

Voltage

AppliedDeflection

Increase

Voltage

Increased

Initial PositionPlate MovesFinal Position

2) Experimental Setup

On-Going Work on Other Possible Microfluidically Reconfigurable RF Devices –Textile Antennas (OSU Collaboration)

44

0.0254 mm

LCP

0.012 mm

BCB

2 mm

PDMS

0.51 mm

RT5880

LG

WG

LA

0.9 GHz 0.96 GHz 1.12 GHz 1.28 GHz 1.40 GHz

S1 S2 S3 S4possible locations of

the shorting plate

within the channel

Frequency (GHz)

|S11| (d

B)

S1

S2

S3

S4

Micropumps

Embroidered conductive fibers on

polymer substrates have been found

promising for novel flexible and

conformal electronics.

Goal: Introduce microfluidic based

reconfiguration into the textile

antennas

Technique: The method of using

metalized plates within the

microfluidic channel will be examined

to create microfluidically controlled

varactors and/or switches.

Frequency tunability of 0.9GHz to

1.4GHz is demonstrated with LCP

based antenna prototypes

Integration with textile antenna is

completed by developing the

fabrication procedures – similar

frequency tuning performance is

obtained.

Concluding Remarks

45

Microfluidic Loading of RF devices with:

• Continuously movable metals (in liquid or solid form)

• Dielectric solutions

• Fluidic channels utilizing ultra-thin walls

offers new possibilities & degrees of freedom for RF design:• Miniaturization• Large frequency tuning range• High power handling• Low cost beam-steering• Low loss

Realized wideband frequency tunable monopole antennas with

high radiation efficiencies and high RF power handling

capabilities.

Introduced a new microfluidically controlled metalized plate

technique to alleviate reliability and low conductivity issues of

liquid metals.

Realized frequency-agile bandpass filters with 2:1 frequency

tuning range and high power handling capability.

Introduced a novel technique for low cost and efficient

realization of high gain mm-wave beam-scanning arrays.

Metallized

Areas

Liquid In

Liquid Out

RF In

RF Out

ZCl

ZPl

RP

w

RC

w

Microchannel

Zin

Roger 5880

plate

Journal Publications Related to the Presented Work

46

1. G. Mumcu, A. Dey, and T. Palomo, “Frequency-Agile Bandpass Filters Using Liquid Metal Tunable Broadside Coupled Split Ring

Resonators,” IEEE Microwave and Wireless Components Letters, vol. 23, no. 4, pp. 187 – 189, April 2013.

2. A. Gheethan, M. C. Jo, R. Guldiken, and G. Mumcu, “Microfluidic Based Ka-Band Beam Scanning Focal Plane Array,” IEEE

Antennas and Wireless Propagation Letters, vol. 12, pp. 1638 – 1641, 2013.

3. A. A. Gheethan, A. Dey, and G. Mumcu, “Passive Feed Network Designs for Microfluidic Beam-Scanning Focal Plane Arrays and

Their Performance Evaluation,” IEEE Transactions on Antennas and Propagation, vol. 63, no. 8, pp. 3452 – 3464, Aug. 2015.

4. A. Dey and G. Mumcu, “Microfluidically Controlled Frequency Tunable Monopole Antenna for High Power RF Applications,” IEEE

Antennas and Wireless Propagation Letters, vol. 15, pp. 226 – 229, 2016.

5. T. Palomo and G. Mumcu, “Microfluidically Reconfigurable Metallized Plate Loaded Frequency-Agile RF Bandpass Filters,” IEEE

Transactions on Microwave Theory and Techniques, vol.64, no.1, pp. 158 – 165, Jan. 2016.

6. A. Dey, R. Guldiken, and G. Mumcu, “Microfluidically Reconfigured Wideband Frequency Tunable Liquid Metal Monopole

Antenna,” IEEE Transactions on Antennas and Propagation, vol. 6, no. 6, pp. 2572 – 2576, June 2016.

Conference Publications & Presentations

47

1. A. Gheethan, R. Guldiken, and G. Mumcu, “Microfluidic Enabled Beam Scanning Focal Plane Arrays,” IEEE Antennas and Propagation

Society Symposium, pp. 1 – 4, Orlando, FL, USA, July 2013.

2. A. Dey, R. Guldiken, and G. Mumcu, “Wideband Frequency Tunable Liquid Metal Monopole Antenna,” IEEE Antennas and Propagation

Society Symposium, pp. 1 – 4, Orlando, FL, USA, July 2013 (student paper competition finalist – selected to be among the top 15 out of 141

competing papers).

3. A. Gheethan and G. Mumcu, “MM-Wave Beam Scanning Focal Plane Arrays Using Microfluidic Reconfiguration Techniques,” presented

in URSI - National Radio Science Meeting, Boulder, CO, USA, Jan. 2014.

4. T. Palomo and G. Mumcu, “Highly reconfigurable Bandpass Filters Using Microfluidically Controlled Metalized Glass Plates,” IEEE

International Microwave Symposium (IMS), pp. 1 – 3, Tampa, FL, USA, June 2014.

5. A. Gheethan and G. Mumcu, “2D Beam Scanning Focal Plane Arrays Using Microfluidic Reconfiguration Techniques,” IEEE Antennas

and Propagation Society Symposium, pp. 1 – 4, Memphis, TN, USA, July 2014 (student paper competition honorable mention – selected to

be among the top ~30 out of 149 competing papers).

6. A. Dey and G. Mumcu, “High Resolution Surface Imaging Arrays Interrogated with Microfluidically Controlled Metalized Plates,” IEEE

Antennas and Propagation Society Symposium, pp. 1 – 4, Memphis, TN, USA, July 2014.

7. A. Dey, A. Kiourti, G. Mumcu, and J. L. Volakis, “Microfluidically Reconfigured Frequency Tunable Dipole Antenna,” 9th European

Conference on Antennas and Propagation (EuCAP 2015), pp. 1 – 3, Lisbon, Portugal, Apr. 12–17, 2015.

8. A. Dey and G. Mumcu, “Microfluidically Controlled Metalized Plate Based Frequency Reconfigurable Monopole for High Power RF

applications,” IEEE Antennas and Propagation Society Symposium, pp. 1 – 4, Vancouver, BC, Canada, July 2015.

9. G. Mumcu, “Microfluidic Based High Gain Beam-Scanning Antenna Arrays for MM-Waves and Beyond,” presented in URSI - National

Radio Science Meeting, Boulder, CO, USA, Jan 2016 (invited).

10. A. Dey and G. Mumcu, “Small Microfluidically Tunable Top Loaded Monopole,” IEEE International Workshop on Antenna Technology

(IWAT), pp. 1 – 2, Cocoa Beach, FL, March 2016.

11. E. Gonzalez and G. Mumcu, “A Microfluidically Switched Feed Network for Beam-Scanning Focal Plane Arrays,” IEEE International

Workshop on Antenna Technology (IWAT), pp. 1 – 2, Cocoa Beach, FL, March 2016.

Conference Publications & Presentations (continued)

48

12. A. Dey and G. Mumcu, “Microfluidic Based High Resolution Microwave Imaging System,” IEEE Antennas and Propagation Society

Symposium, pp. 1 – 2, Fajardo, Puerto Rico, Jun. 26 – Jul. 1 2016.

13. E. Gonzalez and G. Mumcu, “Low-Loss Wideband Feed Networks for High Gain Microfluidic Beam-Scanning Focal Plane Arrays,” IEEE

Antennas and Propagation Society Symposium, pp. 1 – 2, Fajardo, Puerto Rico, Jun. 26 – Jul. 1 2016.

14. E. Gonzalez and G. Mumcu, “MM-Wave High Gain Beam-Scanning Focal Plane Arrays with Microfluidically Switched Feed Networks,”

URSI - National Radio Science Meeting, Boulder, CO, USA, Jan. 2017 (invited).

15. T. Palomo and G. Mumcu, “Frequency-Agile RF Filters Using Microfluidically Reconfigurable Selectively Metallized Plates,” IEEE Radio

and Wireless Symposium, Phoenix, AZ, USA, Jan. 2017 (invited).