Porous silica material and optical microphone
View Patent ↗A porous silica material disclosed in the present application is a porous silica material in which a plurality of silica particles are connected to one another three-dimensionally, wherein: a density of the porous silica material is less than 220 kg/m 3 ; a particle diameter of the silica particles is 3.5 nm or more; and the water content of the porous silica material is 8 wt % or less.
1. A porous silica material in which a plurality of silica particles are connected to one another three-dimensionally, wherein:
a density of the porous silica material is less than 220 kg/m 3 ;
a particle diameter of the silica particles is 3.5 nm or more; and
a water content of the porous silica material is 8 wt % or less; and wherein
a plurality of pores are provided between the plurality of silica particles, and the pores include a plurality of cavity portions and constriction portions located between the plurality of cavity portions; and
an inner diameter of the constriction portion is smaller than an inner diameter of the cavity portion and is smaller than a mean free path of an air.
2. The porous silica material according to claim 1 , wherein the particle diameter the plurality of silica particles is 3.5 nm or more and 20 nm or less.
3. The porous silica material according to claim 2 , wherein the particle diameter of the plurality of silica particles is 8 nm or more and 20 nm or less.
4. The porous silica material according to claim 1 , wherein the plurality of silica particles do not form secondary particles but form a skeleton of the porous silica material.
5. The porous silica material according to claim 1 , wherein the density is 57 kg/m 3 or more and less than 220 kg/m 3 .
6. The porous silica material according to claim 5 , wherein the water content is 0.79 wt % or more and 8 wt % or less.
7. An optical microphone comprising:
a reception section including acousto-optic propagation medium portion formed by a porous silica material in which a plurality of silica particles are connected to one another three-dimensionally, wherein:
a density of the porous silica material is less than 220 kg/m 3 ;
a particle diameter of the silica particles is 3.5 nm or more; and
a water content of the porous silica material is 8 wt % or less,
wherein a sound wave enters the reception section from a space around the reception section and propagates through the acousto-optic propagation medium portion;
a detection section for outputting light of a wavelength that passes through the porous silica material, wherein the light passes through the acousto-optic propagation medium portion through which the sound wave is being propagated so as to detect the light which has been modulated by the sound wave, thereby outputting a detection signal; and
a conversion section for converting the detection signal to a sound pressure to output a received signal.
8. The optical microphone according to claim 7 , wherein the detection section is a laser Doppler vibrometer.
9. The optical microphone according to claim 7 , wherein
the porous silica material includes a plurality of pores provided between the plurality of silica particles, and the pores include a plurality of cavity portions and constriction portions located between the plurality of cavity portions; and
an inner diameter of the constriction portion is smaller than an inner diameter of the cavity portion and is smaller than a mean free path of an air.