[SI-LIST] Re: dielectric loss question
- From: Jim G Roberts <jgroberts@xxxxxxxxxx>
- To: milabont@xxxxxxxxx
- Date: Wed, 12 Feb 2003 15:23:08 +0100
Mike, Peter,
It is also interesting that since data rate are in the 10GHz rates that
the
surface roughness begins to give a large percentage of the losses.
These are also very frequency sensitive.
If of interest I have a PPT file.
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Mike LaBonte wrote:
> I don't have any info specific to moisture in PCBs. 2.45GHz
> is where the dielectric permittivity of water begins to decrease
> significantly, but it is not a peak absorption frequency. Peak
> dielectric loss for water occurs in the range of 10GHz to 160GHz,
> depending on the temperature. The peak frequency is higher for
> higher temperatures. At 25degC the peak is near 40GHz.
>
> At DesignCon 2000 Howard Johnson presented "Multi-Level Signaling",
> in which he gave the rate of change for signal degradation due to
> skin effect and dielectric loss at 20dB/decade near 1-2GHz. At
> least half of that is dielectric loss. But the paper also shows
> noise increasing at 20dB/decade, and SNR falling to zero under 10GHz.
>
> My take on it is that water will not be the main cause of signal
> loss.
>
> http://www.sbu.ac.uk/water/microwave.html
> http://signalintegrity.com/Pubs/misc/mls.htm
>
> Mike LaBonte
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Peter Arnold
> Sent: Tuesday, February 11, 2003 2:35 PM
> To: 'Si-List' (E-mail)
> Subject: [SI-LIST] dielectric loss question
>
> All,
>
> A question from the curious - in high-speed signaling environments we may
> create time-varying electric fields that have components close to the
> frequency used to heat water in microwave ovens, somewhere around 2.45GHz.
> This suggests a portion of dielectric loss at these frequencies might be due
> to dielectric heating of any moisture that might be present in the
> fiberglass.
>
> Is this in fact the case, and what magnitude is the effect at normal
> humidities? Does loss increase in real multi-GHZ signaling systems as
> dielectric moisture content increases?
>
> Thank you,
> peter arnold.
>
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