# Skin Depth Q: Cellphone Rings in Cavity

• Thierry12

#### Thierry12

I placed a cellphone in 2 half-spheres that i closed afterwards to create a metal cavity (aliminium 1mm) and called it (with another cellphone). The phone rang even if it wasn't supposed to considering the skin effect (wavelenght were about 0,04m and i couldn't see any holes). Anyone has a clue why?

RF can get through very small gaps.
When you said you 'closed them' unless you made an airtight seal (difficult without some fancy machining) you didn't really close them.
Cell phones are designed to pick up very-very weak signals.

When you're designing enclosures for EMI/EMC, particularly at those frequencies, aluminum touching aluminum doesn't count. You have to use things like contact fingers, solder, mechanical pressure, conducting gels, and so on.
This link will give you some considerations and examples
http://www.cotsjournalonline.com/home/article.php?id=100057 [Broken]

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Next time i will close them proplerly! ty

## 1. What is skin depth?

Skin depth is a measure of the distance at which an electromagnetic wave penetrates into a material. It is defined as the depth at which the amplitude of the wave decreases to 1/e (~37%) of its original value.

## 2. How is skin depth related to cellphone rings in a cavity?

The skin depth of a material determines how much of an electromagnetic wave can penetrate into it. In the case of a cellphone ring in a cavity, the material of the cavity will affect the strength and clarity of the signal. A material with a larger skin depth will allow for more of the signal to penetrate through, resulting in a stronger and clearer ring.

## 3. What factors affect skin depth?

The factors that affect skin depth include the frequency of the electromagnetic wave, the electrical conductivity and magnetic permeability of the material, and the angle at which the wave is incident on the material.

## 4. How can skin depth be calculated?

The skin depth can be calculated using the following formula: d = (2/π) x (1/√(μσω)), where d is the skin depth, μ is the magnetic permeability, σ is the electrical conductivity, and ω is the angular frequency of the electromagnetic wave.

## 5. Why is skin depth important in the study of electromagnetic waves?

Skin depth is important because it helps us understand how electromagnetic waves interact with different materials. It also plays a crucial role in the design and function of various electronic devices, such as cellphones, where the strength and clarity of the signal are important factors.