TCT testbed

RF Testbed for TCT

D Fallon - Electronics Research IncL Yan, G Hanson, S Patch - UWM

TCT testbedGoal - controlled illumination for large FOV imaging

- illuminate with high-power, broadband (short) pulse w/108 MHz carrier freq

- control polarization of E field

- quantify

Pinc, both power and envelope

Ptrans,

Pinc - Ptrans - Pbaseline = power loss in object

Feng et al ‘01 Wisc ‘07

optimized m

atch ~10ns

uncontrolled E-field & loss

?match?

TCT testbed

TCT Wave Eq Model

+ homog ICs

€

1

c2 (x)

∂ 2

∂t 2− Δ

⎛

⎝ ⎜

⎞

⎠ ⎟p x, t( ) =

βB( )(x)

C(x)σ x,ω( )

∂ E(x, t)2

∂t

€

p x, t( ) =∂

∂t

Rf (x,ct)

ct

⎛

⎝ ⎜

⎞

⎠ ⎟

€

f x( ) =−1

8π 2

1

t 2

∂

∂tt 2 p u, t( )[ ]

t=x−u

cu∈S 2

∫ du

for I(t)= (t)

thermal mechanical

electrical

€

=2βBρ( )(x)

C(x)

σ x,ω( ) ∂∂t E(x, t)

2

( )

2ρ(x)

€

~ f (x)∂I (t)

∂t

TCT testbed

Quantitative Imaging Challenges

• partial scan data - iterative recon

• transducer aperture size - integrating detectors

• acoustic attenuation - corr. for aphysical model

• variable soundspeed

• E field pattern/optical fluence corr.

• broadband data required, including low freqs

• unwanted EM coupling to US measurements

• transducer response - freq dependent & has limited sensitivity - anisotropic

TCT testbed

E-field pattern & Acoustic Source

€

1

c 2(x)

∂ 2

∂t 2− Δ

⎛

⎝ ⎜

⎞

⎠ ⎟p x, t( ) =

βB( )(x)

C(x)σ x,ω( )

∂E(x, t)2

∂t

€

=βBσ E

2

C

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟ x( )

∂I(t)

∂t quasi − static

SOP to solve in frequency domain near carrier frequency.

€

−k2(x)+ Δ( ) ˆ p x,ω( ) =βB

C

⎛

⎝ ⎜

⎞

⎠ ⎟(x) σ E

2

( ) x,ω( )

1) E is wave-like. At 100 MHz, air~300cm, H20 ~33cm, fat~70cm, muscle~40cm

2) tangential BCs force continuity of E x n

Solve Helmholtz in frequency domain

TCT testbed

E-field in TCT Testbed

Power in

Very nearly TE103

Aluminum walls & DI water not lossy, waves resonate

I(t) ~ H(t).

acoustic window

E-field on central plane inside Surface current

add output port

E ~ 0.9 TE10 + 0.1 TE103

I(t) ~ (t)

TCT testbed

TCT Testbed - hardware

Translators - Sherry Yan, George Hanson, UWM-EE.

Port design - & duck - courtesy Dan Fallon, ERI, Inc.

S21 power from port 1 out port 2

S21 =-0.5593 dB or Pout = 0.88 Pin

S11 =-27.598 dB or Prefl= 0.002 Pin

T = Maine springtime room temp

TCT testbed

System

Signal Generator - Rohde&Schwarz (SML01)

Pulsed Amplifier - QEI Corp

50kWpulsed amp-QEI Corp

tunable carrier freq

carrier freq 108MHz

TCT testbed

Pulse profiles - time & freq

Remove carrier frequency (108 MHz) - 2.25 MHz transducers do badly with 500ns pulse- 5 MHz transducers do well with 500ns pulse

TCT testbed

S-parametersMeasure - incident & reflected power at each port: Pinc, Pref, Ptrans, Pload - for carrier freqs 70:130 MHz, w/4 microsec pulses (Eckhart)

Compute (in dB scale) - S11, power reflected, ideal - dB - S21, power transmitted, ideal 0 dB

€

S11 k( ) =10 log10 Pref / Pinc( ) = 20 log10 Vref L2/ Vinc L2( )

S21 k( ) =10 log10 Ptrans / Pinc( ) = 20 log10 Vtrans L2 / Vinc L2( )

TCT testbed

S-parameters

€

S11 k( ) =10 log10 Pref / Pinc( ) = 20 log10 Vref L2/ Vinc L2( )

S21 k( ) =10 log10 Ptrans / Pinc( ) = 20 log10 Vtrans L2 / Vinc L2( )

S11 S21

MHz MHz

TCT testbed

E-field measurements

€

TE10 z( ) ∝ e−γz where γ =α + jβ

TE103 reflections modeled as ρeiθ

v z, t( ) = ARe e−γz + ρeiθe−γ 2 L−z( )[ ]e

iωot( )

Slotted top & monopole antenna fabricated at UWM G. Becker, M Rhodes

€

at 22oC,

γ 2 = 0.0729 + j14.6( )2

fit for A, ρ , θ

TCT testbed

Can see a balloon

qualitative

TCT testbed

ConclusionsTestbed performs essentially as a transmission line, preserving short temporal pulse shape.

Bandwidth of testbed greater than bandwidth of QEI pulses.

Chimney shields effectively

TCT testbed

Thanks

• WUWM for lending dir coupler line sections• Tom May (WUWM Chief Engineer) for system setup• Andrew Eckhart for collecting S-param data• Mike Schrauth for developing positioners • Mark Rhodes & Jerry Becker for slotted top &

antenna