Microwave Induced Thermoacoustic Imaging Power Requirements

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Microwave Induced Thermoacoustic ImagingPower
Requirements

• By Zaid Al-Husseini

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Sections

• General Power Information
• Amp Systems Microwave Generator
• IEEE RF standards for Human Exposure
• Wang et al. Power levels in their MITI
• Kruger et al. Power levels in their MITI
• Problems and Future Plans

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General Power Information

• Found Wang et als paper entitled Scanning
  Thermoacoustic Tomography in Biological Tissue
  describing in detail through several equations
  the minimum power requirements needed to induce
  thermoacoustic waves in biological tissue e.g..
  Breasts and Tumors
• Both Kruger and Wang used high end microwave
  generators operating between 10kW-50kW
• There is some uncertainty onto whether Krugers
  use of 50kW with certain pulse width complies
  with IEEE safety standards for RF human exposure.
• In order for us to induce microwaves however we
  will need a microwave generator to operate on the
  order of several kW.

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Amp Systems Microwave Generator

• The Company Amp Systems in CA, designs and
  constructs high power pulsating microwaves that
  operate at Power of up to 50kW.
• This is the same company Kruger used to design
  his Microwave generator.
• It will cost approximately 35,000 and will
  require approx. 12-16 weeks for construction and
  delivery.
• It can pulsate up to a max width of 10ms with no
  minimum pulse width restrictions
• Depending on which generator is bough it will be
  able to output a max power of anywhere between
  25-50kW.
• It weighs approx. 200 lbs

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IEEE RF standards for Human Exposure
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Wang et al. Power levels in their MITI

• At 3 GHz Wang used a 0.025s (40 Hz) Repetition
  Rate with a 0.5 µs pulse width. Thus the Duty
  Cycle is 0.5 µs/0.025s 0.00002
• At a 3 GHz, P10 kW with an outlet of 7.2 cm x
  3.4 cm 24.48 cm2.
• Thus the average power 0.00002 x 10kW 0.2 W
• Pavg0.2 W / 24.48 cm2 8.16 mW/cm2
• The upper limit at this level for Partial Body
  Body exposure is 10-20 mW/cm2
• At 9 GHz Wang used a 0.5s (2 Hz) Repetition Rate
  with a 0.5 µs pulse width. Thus the Duty Cycle is
  0.5 µs/0.5s 0.000001
• At a 3 GHz, P10 kW with an outlet of 2.3 cm x
  1.0 cm 2.3 cm2.
• Thus the average power 0.000001 x 25kW 0.025
  W
• Pavg0.2 W / 24.48 cm2 10.86 mW/cm2
• The upper limit at this level for Partial Body
  Body exposure is 10-22.1 mW/cm2

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Kruger et al. Power levels in their MITI

• It takes 38 seconds for a complete sweep of 8192
  pulses.
• At 434 GHz this gave Kruger a 38 s/ 8192 p
  0.0046 s/p (217 Hz) Repetition Rate with a 0.7 µs
  pulse width. Thus the Duty Cycle is 0.7
  µs/0.0046s 0.00015
• At a 434 MHz, P50 kW with 8 circular waveguides
  of 2.7 cm giving an area of 22.9 cm2
• Thus the average power 0.00015 x 50kW 7.5 W
• Pavg7.5 W / 183.2 cm2 40.9 mW/cm2
• The upper limit at this level for Partial Body
  Body exposure is 1.45 mW/cm2

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Problems and Future Plans

• Need a lot of money for Microwave Generator (must
  ask for grant)
• Helping John with MWI multiplexers and apparatus.