Minimizing the reflection of electromagnetic waves - the basics of STEALTH

That paper has little to do with stealth. EM field intensity may decrease a s 1/r due to atmospheric loss, but you neglect the fact that real signals a re propagated by antennae with finite aperture with finite solid angle. Thi s means the power intercepted by the target, for purposes of reflection, is in the ratio of the target area to the area subtended by the solid angle, which degrades by 1/r^2, a very large loss. Stealth is all about geometrical design to reduce reflection/eliminate reso nators:

Am 20.05.2019 um 00:22 schrieb snipped-for-privacy@gmail.com:

The basis of STEALTH is a total reflection by appropriate means, such as special paint coating, to attenuate 6 dB, which is physically achievable.

se as 1/r due to atmospheric loss, but you neglect the fact that real signa ls are propagated by antennae with finite aperture with finite solid angle. This means the power intercepted by the target, for purposes of reflection , is in the ratio of the target area to the area subtended by the solid ang le, which degrades by 1/r^2, a very large loss.

resonators:

Read the wiki article. There's a history there. No one started out by looki ng at paint schemes.

Am 20.05.2019 um 01:11 schrieb Winfield Hill:

Am 20.05.2019 um 01:11 schrieb Winfield Hill:

I'm guessing that if your coating has a resistance of 300 ohms per square (or some other magic number) performance is significantly better, it's a matter of making the coating black to radar frequencies.

se as 1/r due to atmospheric loss, but you neglect the fact that real signa ls are propagated by antennae with finite aperture with finite solid angle. This means the power intercepted by the target, for purposes of reflection , is in the ratio of the target area to the area subtended by the solid ang le, which degrades by 1/r^2, a very large loss.

resonators:

This fall into the category of RAM, and it's not easy to do. Major limitati ons to effectiveness are bandwidth and angle of impingement dependency. And this is not cheap. Looks like it's mainly used to augment the geometric sh aping of the airframe to further reduce reflection from those areas known t o be vulnerable. One summary: "Essentially, RAM absorbs the incident EM energy and converts it into heat, thereby reducing the scattered energy towards the radar. RAM is known to be quite effective in controlling the backscattering than forward scattering (Hiatt et al. 1960). RAMs have relat ively high values of imaginary part of permittivity and permeability. Such coatings result in ch ange in polarisation of the scattered waves. Narrowband RAM coatings, such as the Salisbury screen and Dallenbach layer, have been used since 1950s. However, modern radar systems span a wide range of freque ncy. Hence, the need for wideband RAMs is apparent. A typical RAM employed on aircraft coul d be a ferritebased paint or a composite. However, there are significant im plications of using RAM. Firstly, most of them are toxic. Secondly, RAM coatings require precise application techniques, as the coating thickness and smoothness must be uniform across the platform. Ideally a RAM should not impose weight penalty due to speed and pay load co nsiderations. It should possess high mechanical strength and should be anticorrosive, che mically stable and should not get charged at high temperature. It must have a wideband RCSR. L astly, it should be effective in all directions (Vinoy and Jha 1996). The RAM application pr ocess typically involves robotic sprayers that can accurately control the coating thickness . Furthermore, these coatings require strict constitutive parameter tolerances as well as unifor mity in order to achieve the desired result. Therefore, the cost of implementation of RAM is often t oo high. Another issue is that RAM also increases the weight of the platform. This may have notable impact on the vehicle performance aerodynamically. For different platforms, RAM coatings have been developed with appropriate combination of rubber, cotton-glass, epoxy and mica. Other possibilities are graphite f ibres, Kevlar and ferrites. The materials can be of different forms such as sheets, honeycomb s, laminates, etc. Ferrite materials in forms of flakes, wires or microspheres can be loaded i nto glass?epoxy or silicon rubber. The inks and coatings can be applied on kapton film or epox y honeycombs. Radar-absorbing paints are also coated over the surface of the vehicles. Th ese paints consist of small ferrite particles that are polarised towards the impinging wave. S uch paints are prepared by mixing solid iron oxides with various polymer resins, such as e poxy and plastics. The constitutive parameters including thickness of the paint, fix the reson ance frequency for maximum absorption. "

Am 20.05.2019 um 15:09 schrieb snipped-for-privacy@gmail.com:

There is only a minimum thickness of the color. The parameters are determined by the cut-off frequency, the conductivity and the relative dielectricity (see paper).

That's a common misperception, but dB attenuation in power and intensity are one and the same number. If you have a quantity X for which the power is proportional to X^2 then 20LOG(X)= 10LOG(X^2) or dB(intensity)=dB(power).

Am 20.05.2019 um 16:31 schrieb snipped-for-privacy@gmail.com:

no

Power reflection attentuation is 10LOG(P2=1/P1=2)=-3.01 dB electric field attenuation is 20LOG(E2/E1)=-6.02 dB

Am 20.05.2019 um 16:31 schrieb snipped-for-privacy@gmail.com:

Decibels are always logarithms of power ratios.

Cheers

Phil Hobbs

Am 20.05.2019 um 16:31 schrieb snipped-for-privacy@gmail.com:

... but I know what You mean :)

Did you miss the part about P ~ E^2 ???

Your answers to the comments explain a lot.

Am 20.05.2019 um 17:47 schrieb snipped-for-privacy@gmail.com:

I know what You mean. I made a mistake in E, H and Power.

It is 10LOG(P2/P1)=10LOG(1/2)=-3.01 dB