A novel and demonstrated surface treatment that can alter and/or control the infrared (IR) appearance of objects

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Micropit Surface TechnologyOverview

• A novel and demonstrated surface treatment that
  can alter and/or control the infrared (IR)
  appearance of objects
• U.S. Patent 6,713,774

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Micropit Surface Technology Demonstration

• Description
• Surface emissivity modified by surface
  micro-structure controls radiant energy
  independently
• Application
• Improves heat energy balance or thermal signature
  of any system Sponsor
• U.S. Department of Energy
• Developer
• Pacific Northwest National Laboratory

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Concept Fundamentals

• Hohlraum is a cavity that emits as a black-body
  
• Densely packed array can enhance heat transfer at
  a surface
• Passive array can improve thermal energy
  transport design of essentially any system
• Active array adds control of surface properties
• switchable emissivity
• camouflage of IR signature
• programmable identification

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Theoretical Thermal Emission Enhancement

• Stefan-Boltzmann relationship
• Qrad A s? (Tb4 - Ta4)
• Surface ? of 0.1 with closest practical pit
  spacing of 0.05d
• Radiant energy enhancement is 7.4

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Heat Transfer Enhancement Factors

• Temp. Difference
• Heat Transfer Mode 10K 100K 1000K
• Convection only 1 1 1
• Convection rad (? 0.1) 1.15 1.13 2.22
• Convection rad (? 1.0) 2.54 2.34 13.24
• Convection switched rad 2.21 2.07 5.96

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Design of Test Specimens

• Two plates with different hole diameter (d),
  pitch (p) and aspect ratio (AR)
• A d - 0.5mm p - 0.6mm (rectangular) AR - 3.8
• B d - 0.13mm p - 0.5mm (60 diagonal) AR - 25

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Micropit Surface Technology Demonstration

• Aluminum block containing 25 X 25 hohlraum array
  separated by slots for caps or shutters

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Block Temperature vs. Power Input
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Base and Slot Temperatures vs. Power
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25x25 Micropit Test Array Detail
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Micropit Surface Technology Demonstration

• Aluminum block containing 25 X 25 hohlraum array
  with NiTi shape memory shutters installed

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Micropit Surface Technology Demonstration

• IR image of shutters closed (left) open (right)
  as temperature changes about 5 C

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Micropit Array Block 2 Dimensions
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Micropit Array Block 2 at Room Temperature
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Micropit Array Block 2 Room Temperature Images
(Artificial Color Range About 5 ºC)
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Micropit Array Block 2 Temperature Scan by Row
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Normalized Radiance vs. Hole Number
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