Titanium Enclosure Question - RF Cafe Forums

 Post subject: Titanium Enclosure Question

Posted: Mon Aug 23, 2010 11:19 am 

Hi, Industrial Designer with little RF knowledge in need of help here...

I need to design a Titanium enclosure for a device that receives GPRS Data, meaning, the signal should not be weakened by the enclosure (much). The antenna would be inside, protected by the Titanium cover, much like in a celphone.

Knowing that Titanium is not (slightly?) magnetic, would a signal in the 850-1900 Mhz Range travel through a thin sheet (ie 0.5mm) of pure Titanium?

I have read elsewhere about "RF permeable" or "RF transparent" but it sounds too good to be true.

As an alternative, would perforation help (i.e. hole pattern) on the aeras covering the actual antennas?

I've been having trouble to figure out any specs on this, the only leads I found where about coatings of antennae and such....

Thanks for your advice to a layperson,it would be highly appreciated!

Cheers,

Enzo

 Post subject: Re: Titanium Enclosure Question

Posted: Wed Aug 25, 2010 12:54 pm 

A six-sided box made of 0.5mm titanium (or indeed any metal) will be an excellent Faraday cage - almost no RF signal of any frequency will make it through. Cellphones are mostly not metal (injection-molded plastic, perhaps coated with a conductive material in areas which are intended to be shielded) - and in any case, the antenna is outside the shielded part of the cellphone.

The recent debacle with the Apple iPhone was due to their clever solution to this problem - they placed the antenna on the outer rim, where it could be contacted by the user's hand, and if held so that the hand bridged one of the gaps, signal dropped. Still, it was in some ways a good solution to the dilemma of not enclosing your antenna with a shield, when you box your product.

Antenna design for portable electronics is often a very difficult field.

The antenna must be outside the metallic enclosure, somehow. If you cut a window in the metallic box, of the right size, you will get some signal - but the antenna and box combination will almost certainly be very directional. "Directional" means "almost deaf in some directions".

How do I know that you can't put the antenna inside? The "skin depth" is how far an electromagnetic field ("radio wave") can penetrate into a conductor (like metal). The formula is d=sqrt(f*pi*mu*sigma), where f is the frequency in Hertz, mu is the magnetic permeability of the material, and sigma is the conductivity of the material. I don't have the numbers for titanium at my fingertips, but for copper at 900 MHz the depth is 2.2 microns. If the wave can't make it through the metal, it doesn't reach the inside.

So what can you do? "Slot antennas" are a possibility, as is the Apple iPhone idea.

Good Luck!

 Post subject: Re: Titanium Enclosure Question

Posted: Wed Jan 05, 2011 11:35 pm 

I believe that a Titanium enclosure is compatible with an iphone. The issues cover a lot of speculations and they made alternative solution for the problem. I insist it can be a good Apple iphone idea.

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iArissa
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