Radio wave absorber, radio wave absorption structure including radio wave absorber, and composition for radio wave absorber

1 . A radio wave absorber, comprising:

a resin; and

a carbon fiber selected from a pitch-based carbon fiber and a PAN-based carbon fiber,

wherein 60 to 90% by volume of the total carbon fiber is present in a region from the first surface of the radio wave absorber to half of the total thickness of the radio wave absorber.

2 . The radio wave absorber according to claim 1 , wherein the content of the carbon fiber is 2% by volume or less of the total volume of the radio wave absorber.

3 . The radio wave absorber according to claim 1 , further comprising:

a hollow particle in an amount of 10% by volume or less of the total volume of the radio wave absorber.

4 . The radio wave absorber according to claim 1 , wherein the carbon fiber has a mean length within a range of 100 to 4000 μm.

5 . The radio wave absorber according to claim 1 , wherein the resin has an organosiloxane structure represented by the following formula (1):

in the formula, R 1 and R 2 represent independently, a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

6 . The radio wave absorber according to claim 1 , further comprising:

a carbon particle in an amount of 10% by volume or less of the total volume of the radio wave absorber.

7 . The radio wave absorber according to claim 1 , which absorbs radio wave over the entire frequency range of 75 GHz to 105 GHz in an amount of 30% or more.

8 . A radio wave absorption structure, comprising:

the radio wave absorber of claim 1 , and

a radio wave reflector stacked on the surface side of the radio wave absorber in which the carbon fiber is lopsidedly distributed,

wherein the radio wave absorber has a thickness of 200 to 500 μm.

9 . The radio wave absorption structure according to claim 8 , which absorbs radio wave over the entire frequency range of 75 GHz to 105 GHz in an amount of 30% or more.

10 . The radio wave absorber according to claim 2 , further comprising:

a hollow particle in an amount of 10% by volume or less of the total volume of the radio wave absorber.

11 . The radio wave absorber according to claim 2 , wherein the carbon fiber has a mean length within a range of 100 to 4000 μm.

12 . The radio wave absorber according to claim 2 , wherein the resin has an organosiloxane structure represented by the following formula (1):

in the formula, R 1 and R 2 represent independently, a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

13 . The radio wave absorber according to claim 2 , further comprising:

a carbon particle in an amount of 10% by volume or less of the total volume of the radio wave absorber.

14 . The radio wave absorber according to claim 2 , which absorbs radio wave over the entire frequency range of 75 GHz to 105 GHz in an amount of 30% or more.

15 . The radio wave absorber according to claim 3 , wherein the carbon fiber has a mean length within a range of 100 to 4000 μm.

16 . The radio wave absorber according to claim 3 , wherein the resin has an organosiloxane structure represented by the following formula (1):

in the formula, R 1 and R 2 represent independently, a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

17 . The radio wave absorber according to claim 3 , further comprising:

a carbon particle in an amount of 10% by volume or less of the total volume of the radio wave absorber.

18 . The radio wave absorber according to claim 3 , which absorbs radio wave over the entire frequency range of 75 GHz to 105 GHz in an amount of 30% or more.

19 . The radio wave absorber according to claim 4 , wherein the resin has an organosiloxane structure represented by the following formula (1):

in the formula, R 1 and R 2 represent independently, a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms.