Bachelor Thesis. Analogue Phase-Shifter Circuit for 7-Tesla Magnetic Resonance Tomograph (MRT)

Transcription

1 Bachelor Thesis Analogue Phase-Shifter Circuit for 7-Tesla Magnetic Resonance Tomograph (MRT) by Poh Seng Pua Supervised by Prof. Dr. Ing Klaus Solbach Department of Microwave and RF- Technology University of Duisburg-Essen Duisburg, 08-December-2008

2 Outlines Problem Introduction Aim of the Thesis Design Details Simulation & Test Results Conclusions 2

3 Problem Introduction Why are we interested in designing phase shifters in MRTsystem? Inhomogeneous materials such as tissues, bones, fat and etc in the body RF signals are diffracted and the phase is shifted when RF signals are applied The inhomogeneous field distributions are occurred inside the patient s body due to the superposition effect of all the RF signals 3

4 Aim of the Thesis To design a 90 and 180 bits of the phase shifter by using PIN diodes and other SMD components at 300MHz operating frequency in order to compensate the inhomogeneous field distributions inside thepatient s thepatients body. 4

5 Design Details Phase Shifters Ferrite Phase Shifters change the ferrite permeability to obtain a required phase shift Semiconductor Device Phase Shifters PIN Diodes GaAs FET Schottky Diodes used aselectronics switches 5

6 Design Details Phase Shifters PIN Diode Phase Shifters Advantages are: low losses high power resist low temperature drift fast switching speed low cost of production 6

7 Design Details Phase Shifters PIN Diode Phase Shifters Switched line Loaded line High pass low pass 7

8 Design Details Phase Shifters PIN Diode Phase Shifters Series PIN diode switched line phase shifter Shunt PIN Diode switched line phase shifter 8

9 Design Details PIN Diode Phase Shifters MSub Term Term1 Num=1 Z=50 Ohm MSUB MSub1 H=0.508 mm Er=3.38 Mur=1 Cond=1.0E+50 Hu=1.0e+033 mm T=35 um TanD=0.003 Rough=2.4 um S-PARAMETERS S_Param SP1 Start=200 MHz Stop=400 MHz Step=1.0 MHz R R1 R=1 Ohm R C R3 C1 R=400 kohm C=0.2 pf MLIN TL1 Subst="MSub1" W=1.14 mm L=70.53 mm MLIN TL2 Subst="MSub1" W= mm L= mm R R2 R=1 Ohm R R4 R=400 kohm C C2 C=0.2 pf Term Term2 Num=2 Z=50 Ohm Series PIN diode switched line phase shifter Term Term3 Num=3 Z=50 Ohm MLIN TL3 Subst="MSub1" W=1.14 mm L=154 mm MLIN TL7 Subst="MSub1" W=1.14 mm L=154 mm R R5 R=1 Ohm MLIN TL6 Subst="MSub1" W=1.14 mm L= mm MLIN TL5 Subst="MSub1" C W=1.14 mm C3 L=70.53 mm C=0.2 pf R R7 R=400 kohm R R6 R=1 Ohm MLIN TL4 Subst="MSub1" W=1.14 mm L=154 mm MLIN TL8 Subst="MSub1" C W=1.14 mm C4 L=154 mm C=0.2 pf R R8 R=400 kohm Term Term4 Num=4 Z=50 Ohm Shunt PIN Diode switched line phase shifter m1 freq= 300.0MHz db(s(2,1))= m1 m2 m2 freq= 300.0MHz db(s(4,3))= m3 m4 freq= 300.0MHz freq= 300.0MHz db(s(6,5))= db(s(8,7))= m3 m4 db(s(4,3)) db(s(2,1)) db(s(8,7)) db(s(6,5)) Forward transmission coefficient for reference line, state Forward transmission coefficient for 90 phase shift line, state2 9

10 Design Details PIN Diode and SMD Components BAR63 03W PIN Diode SMD 0603 Kemet Capacitor 680pF SMD 0805 EPCOS Inductor 1uH SMD 0805 Resistor 1kΩ 10

11 Design Details Printed Circuit Test Board Bias Circuit TL2=237.5mm DC Blocking DC Power Supply, 10V forward bias & 20V reverse bias TL2=404.3mm RF in RF out TL1=73.4mm TL1=74.5mm 90 bit Phase Shifter 180 bit Phase Shifter 11

12 Simulation & Test Results 90 bit Phase Shifter PCB vs EM co simulation Reference line length, state 1 90 phase shift line length, state db(s(1,1)) db(s(1,1)) db(s(2,1)) db(s(2,1))

13 Simulation & Test Results 90 bit Phase Shifter PCB vs EM co simulation Reference line length, state 1 90 phase shift line length, state e(s(2,1)) phas phase e(s(2,1))

14 Simulation & Test Results 90 bit Phase Shifter PCB s phase error at frequency range between 290MHz and 310MHz Frequency 90 Degree MHz Δθ 12 Δθ 21 δ(δθ 21 )

15 Simulation & Test Results 180 bit Phase Shifter PCB vs EM co simulation Reference line length, state phase shift line length, state db(s(1,1)) db(s(1,1)) db(s(2,1)) db(s(2,1))

16 Simulation & Test Results 180 bit Phase Shifter PCB vs EM co simulation Reference line length, state phase shift line length, state phas se(s(2,1)) phas se(s(2,1))

17 Simulation & Test Results 180 bit Phase Shifter PCB s phase error at frequency range between 290MHz and 310MHz Frequency 180 Degree MHz Δθ 12 Δθ 21 δ(δθ 21 )

18 Simulation & Test Results Cascaded 2 bits Phase Shifter PCB vs EM co simulation Reference line length 90 phase shift line length db(s(1,1)) db(s(1,1)) db(s(2,1)) db(s(2,1))

19 Simulation & Test Results Cascaded 2 bits Phase Shifter PCB vs EM co simulation phase shift line length 270 phase shift line length db(s(1,1)) db(s(1,1)) db(s(2,1)) db(s(2,1))

20 Simulation & Test Results Cascaded 2 bits Phase Shifter PCB s phase error at frequency range between 290MHz and 310MHz Phase Shift Frequency 90 Degree 180 Degree 270 Degree MHz Δθ 12 Δθ 21 δ(δθ 21 ) Δθ 12 Δθ 21 δ(δθ 21 ) Δθ 12 Δθ 21 δ(δθ 21 )

21 Simulation & Test Results Cascaded 2 bits Phase Shifter Forward Bias Voltage at 8V and 12V )) All States db(s(1, s )) All States db(s(2,

22 Simulation & Test Results Cascaded 2 bits Phase Shifter PCB s phase error at 8V and 12V Forward Bias Voltage for 300MHz operating frequency Forward Bias Voltage Phase Shift 90 Degree 180 Degree 270 Degree Δθ 12 Δθ 21 δ(δθ 21 ) Δθ 12 Δθ 21 δ(δθ 21 ) Δθ 12 Δθ 21 δ(δθ 21 )

23 90 bit Phase Shifter Conclusions Specifications of the Phase Shifter Insertion loss < 0.5dB Phase error < 1 at 300MHz Forward bias Voltage, 180 bit Phase Shifter Insertion loss < 0.6dB 06dB Phase error < 1 at 300MHz Forward bias Voltage, 23

24 Conclusions Cascaded 2 bits Phase Shifter Insertion loss < 1.1dB 11dB Phase error < 2 at 300MHz Forward bias Voltage, 24

25 End Thank You For Your Attention! 25