Reflectors for far infrared (human body temperature range)

[aelis]

Some opinions needed about practical reflectors for infrared spectrum originating from human body for use in garments:

 

Is is possible to reflect infrared of human body with a mesh type reflector? Lets say perforated aluminum or mylar?

 

Question is the effect of the holes in the reflective material and their effect.

 

I have seen and experienced in many wood burning fireplaces a solid metal screen with round holes the size of 2-4mm effectively blocking the heat radiation.

 

I have read about far-IR- metal mesh filters, where cross shaped perforations in the scale of the wavelengt desired to filter. But for the purposes of use in clothing, the micron-size-scale is not possible.

 

In theory would a perforated mylar, with round holes of X size and Y repeat, reflect body heat and effectively allow air/moisture out without condensation on the material surface?

 

 

[Klaynos]

If the mesh has length scales much larger than the wavelength then your reflectivity will greatly reduce. If you have 50% material fraction then you'll reflect of the order 50% (assuming a perfect reflector).

 

Mesh of a similar length scale with have strange effects, such as spoof surface plasmon modes etc...

 

Guessing at your purpose then layers of 30% metal fill fraction to air might work. You'd need to ensure connected air gaps exist.

 

Depending of purpose, the issue you'll have is the material heating from conduction from the skin and just moving the IR source out a bit.

[swansont]

How much heat from a fire is radiation vs convection? The screen may also be blocking the latter.

 

The peak wavelength of thermal radiation at ~35-40 ºC is around 10 microns, so as Klaynos notes, you'd need holes around this size to effectively block radiation from a human.

[studiot]

Some more detailed indication of the intended use is needed.

 

Is this for real life or for a story?

 

Are you thinking of a cloaking fabric against IR detectors for military or quasi military purposes?

 

Infrared devices with reflectors are used in surveying and navigationover distances of several kilometres.

The reflectors are of the corner reflector type.

So I suppose you could consider microbead corner reflectors coating the fabric, like sequins.

Some more detailed indication of the intended use is needed.

 

Is this for real life or for a story?

 

Are you thinking of a cloaking fabric against IR detectors for military or quasi military purposes?

 

Infrared devices with reflectors are used in surveying and navigationover distances of several kilometres.

The reflectors are of the corner reflector type.

So I suppose you could consider microbead corner reflectors coating the fabric, like sequins.

[swansont]

If the person is wearing the mesh, it's going to heat up and radiate on its own.

[aelis]

The question was to speculate whether clothing in real life could have considerable benefit from reflective layer, most likely between inner insulation and outer layer against wind and water, and if it would still be usable as a clothing item considering the moisture permeability.

 

The self-radiance of the reflective layer is a good point, unless the layer is behind a reasonable insulation.

[Klaynos]

The question was to speculate whether clothing in real life could have considerable benefit from reflective layer, most likely between inner insulation and outer layer against wind and water, and if it would still be usable as a clothing item considering the moisture permeability.

 

The self-radiance of the reflective layer is a good point, unless the layer is behind a reasonable insulation.

There's a reason that aluminium emergency blankets exist.

[aelis]

There's a reason that aluminium emergency blankets exist.

That is the starting point.

 

Wearing one sewn onto one's jacket would not be the most comfortable experience, thus the need to know about a mesh or a screen layer.

 

My thought was, that let's say there is a layer of perforated what-ever-emergency-blanket, the small holes, which are not in the radiation wavelength scale, but what is possible to achieve with everyday techniques (about 0,1mm), the layer will breathe in a way, but would collect considerable amount of condensation water, when close to the outside layer of the clothing, in order to not to heat up much and thus radiate heat away. Sounds right?

 

On the other hand if the holes are larger and the reflective layer covers less area, if I understood correctly earlier posts also point to, the amount of reflection is relative the amount of area covered by the reflective material. The the question is, what is then the optimal hole size - total perforated area relation, where no longer moisture condenses on the reflective material.

 

I recon the big boys would go with some kind of fabric coating technique in order to achieve breathable yet radiation blocking fabric, like mentioned previously.

[Sensei]

When I was playing with 120 FPS IR camera, I could see myself (in IR range), reflected by Aluminium metal sheet.