microwave absorbent adhesive polymer?


Neil Smith G4DBN
 

Are there any secret sources of microwave absorbant material which will work from 2.5 to 10 GHz with good reflection loss and bulk loss, around 1mm thick and self-adhesive?

For the F6BVA 3cm to UHF transverters, we need a bit about 150 x 50 mm.

I see RF Microwave has some at around £330 for a 600 mm square sheet of silicone 1mm carbonyl/iron, which makes 48 pieces at around £8.50 per piece including VAT etc.  The price from Mouser etc for similar stuff works out about the same. Is that the right sort of price or is there some low cost magic stuff of which I am unaware? The gap above the PCB is only 7mm, and some of the components are a few mm tall, so 1/16" or about 1.5 mm is the max I can fit in.

Neil G4DBN


Pete - GM4BYF
 

Not self stick, but microwave plate warmers do the trick for absorption.

e.g. https://www.lakeland.co.uk/13008/Microwave-Plate-Warmers

73
Pete GM4BYF

On 02/03/21 23:27, Neil Smith G4DBN wrote:
Are there any secret sources of microwave absorbant material which will work from 2.5 to 10 GHz with good reflection loss and bulk loss, around 1mm thick and self-adhesive?

For the F6BVA 3cm to UHF transverters, we need a bit about 150 x 50 mm.

I see RF Microwave has some at around £330 for a 600 mm square sheet of silicone 1mm carbonyl/iron, which makes 48 pieces at around £8.50 per piece including VAT etc.  The price from Mouser etc for similar stuff works out about the same. Is that the right sort of price or is there some low cost magic stuff of which I am unaware? The gap above the PCB is only 7mm, and some of the components are a few mm tall, so 1/16" or about 1.5 mm is the max I can fit in.

Neil G4DBN



--
vry 73
Pete GM4BYF


John E. Beech
 

Don't laugh, but has anyone tried a thin strip of balsa wood or plywood for the absorber? ( Perhaps covered in
graphite pencil lead?) I once made an effective waveguide dummy load for 10 GHz out of wood - a specially shaped
wedge. I don't know where the design came from but I got it from G8MWR (SK).

de John G8SEQ

-------Original Message-------
From: Neil Smith G4DBN <neil@g4dbn.uk>
To: BVA-transverters-uk@groups.io <BVA-transverters-uk@groups.io>, UKMicrowaves@groups.io
<UKMicrowaves@groups.io>
Subject: [UKMicrowaves] microwave absorbent adhesive polymer?
Sent: Mar 02 '21 23:27

Are there any secret sources of microwave absorbant material which will
work from 2.5 to 10 GHz with good reflection loss and bulk loss, around
1mm thick and self-adhesive?

For the F6BVA 3cm to UHF transverters, we need a bit about 150 x 50 mm.

I see RF Microwave has some at around £330 for a 600 mm square sheet of
silicone 1mm carbonyl/iron, which makes 48 pieces at around £8.50 per
piece including VAT etc.  The price from Mouser etc for similar stuff
works out about the same. Is that the right sort of price or is there
some low cost magic stuff of which I am unaware? The gap above the PCB
is only 7mm, and some of the components are a few mm tall, so 1/16" or
about 1.5 mm is the max I can fit in.

Neil G4DBN






Mike Willis
 

I could say something about spiders being good RF absorbers in 10 GHz waveguides but perhaps some graphite loaded materials would be useful, or indeed graphite powder mixed with glue and painted on.
--
Mike G0MJW


John Fell
 

RSGB VHF Manual - Microwave section .Wood in guide dummy load .

John
G0API

On Wed, 3 Mar 2021 at 10:11, John E. Beech <john@...> wrote:
Don't laugh, but has anyone tried a thin strip of balsa wood or plywood for the absorber? ( Perhaps covered in
graphite pencil lead?) I once made an effective waveguide dummy load for 10 GHz out of wood - a specially shaped
wedge. I don't know where the design came from but I got it from G8MWR (SK).

de John G8SEQ

>  -------Original Message-------
>  From: Neil Smith G4DBN <neil@...>
>  To: BVA-transverters-uk@groups.io <BVA-transverters-uk@groups.io>, UKMicrowaves@groups.io
<UKMicrowaves@groups.io>
>  Subject: [UKMicrowaves] microwave absorbent adhesive polymer?
>  Sent: Mar 02 '21 23:27

>  Are there any secret sources of microwave absorbant material which will
>  work from 2.5 to 10 GHz with good reflection loss and bulk loss, around
>  1mm thick and self-adhesive?

>  For the F6BVA 3cm to UHF transverters, we need a bit about 150 x 50 mm.

>  I see RF Microwave has some at around £330 for a 600 mm square sheet of
>  silicone 1mm carbonyl/iron, which makes 48 pieces at around £8.50 per
>  piece including VAT etc.  The price from Mouser etc for similar stuff
>  works out about the same. Is that the right sort of price or is there
>  some low cost magic stuff of which I am unaware? The gap above the PCB
>  is only 7mm, and some of the components are a few mm tall, so 1/16" or
>  about 1.5 mm is the max I can fit in.

>  Neil G4DBN












Neil Smith G4DBN
 

I certainly made a wedge load in WG16 from a well-seasoned bit of oak in 1974, it was  made by planing long tapers on each face down to a point over about 4 inches. I had a 5 mW Gunn, slotted line and a cavity wavemeter that my dad made. The match was as good as I could measure. At those power levels, there was no danger of a smoke test becoming literally smoky.

The expensive silicone stuff has metal flakes and a sharp onset of absorption at somewhere around  4-8 GHz, but more importantly, it has a reduced reflectance, so any standing waves in the cavity are suppressed.  The foam materials and flexible ferrites are probably wider bandwidth.

I think dried spiders in epoxy might work and perhaps cheap lino or MDF sheet covered in pencil graphite woudl be fine, so long as it was painted to prevent any bits falling on to the PCB...

What I'm aiming for is a 100% reproducible performance to ensure that every one of these transverters that gets built is going to work without special bodging, so I think we are going to go with a purpose-made product.  It doesn't sound like the price from Franco is unreasonable, but I thought I'd check to see if there was someone with a vast hoard of Laird/Eccosorb or similar material somewhere in the UK.

Neil G4DBN

On 03/03/2021 10:37, Mike Willis wrote:
I could say something about spiders being good RF absorbers in 10 GHz waveguides but perhaps some graphite loaded materials would be useful, or indeed graphite powder mixed with glue and painted on.
--


Mike Willis
 

Have you considered resonant lines terminated in resistors?
--
Mike G0MJW


John E. Beech
 

Hi Neil,
I can understand you wanting something that is going to give reproducible results.

Not microwave but I was involved professionally in designing "antennas" that didn't radiate. They were operated at VLF (
usually 82 kHz) & designed to produce an oscillating electric field at high voltage which decayed rapidly away from the
"antenna". One particular installation was required to have an antenna in the ground which people could walk over so we
made a lid out of exterior grade plywood. It didn't work! We had to resort to chipboard or MDF for the lid. I never was
sure why plywood was NBG - I guessed it was something to do with the layers of glue between the wooden laminates.
BTW these "antennas" could light up a neon screwdriver from ten inches away when fully tuned ie about 3 kV on
them - driven by a 20 W audio amplifier.

de John G8SEQ

-------Original Message-------
From: Neil Smith G4DBN <neil@g4dbn.uk>
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] microwave absorbent adhesive polymer?
Sent: Mar 03 '21 11:00

I certainly made a wedge load in WG16 from a well-seasoned bit of oak in
1974, it was  made by planing long tapers on each face down to a point
over about 4 inches. I had a 5 mW Gunn, slotted line and a cavity
wavemeter that my dad made. The match was as good as I could measure. At
those power levels, there was no danger of a smoke test becoming
literally smoky.

The expensive silicone stuff has metal flakes and a sharp onset of
absorption at somewhere around  4-8 GHz, but more importantly, it has a
reduced reflectance, so any standing waves in the cavity are
suppressed.  The foam materials and flexible ferrites are probably wider
bandwidth.

I think dried spiders in epoxy might work and perhaps cheap lino or MDF
sheet covered in pencil graphite woudl be fine, so long as it was
painted to prevent any bits falling on to the PCB...

What I'm aiming for is a 100% reproducible performance to ensure that
every one of these transverters that gets built is going to work without
special bodging, so I think we are going to go with a purpose-made
product.  It doesn't sound like the price from Franco is unreasonable,
but I thought I'd check to see if there was someone with a vast hoard of
Laird/Eccosorb or similar material somewhere in the UK.

Neil G4DBN

On 03/03/2021 10:37, Mike Willis wrote:
> I could say something about spiders being good RF absorbers in 10 GHz
> waveguides but perhaps some graphite loaded materials would be useful,
> or indeed graphite powder mixed with glue and painted on.
> --







KENT BRITAIN
 

One fairly good absorber is the sheet magnets often put on frig magnets and the backs of business cards.

I put it around the edges of my reference horn antennas to reduce sidelobes.   It's Iron particle loaded rubber!
I get mine from a local office supply house.  It already has adhesive on one side.     Kent G8EMY/W5



On Wednesday, March 3, 2021, 04:11:43 AM CST, John E. Beech <john@...> wrote:


Don't laugh, but has anyone tried a thin strip of balsa wood or plywood for the absorber? ( Perhaps covered in
graphite pencil lead?) I once made an effective waveguide dummy load for 10 GHz out of wood - a specially shaped
wedge. I don't know where the design came from but I got it from G8MWR (SK).

de John G8SEQ

>  -------Original Message-------
>  From: Neil Smith G4DBN <neil@...>
>  To: BVA-transverters-uk@groups.io <BVA-transverters-uk@groups.io>, UKMicrowaves@groups.io
<UKMicrowaves@groups.io>
>  Subject: [UKMicrowaves] microwave absorbent adhesive polymer?
>  Sent: Mar 02 '21 23:27

>  Are there any secret sources of microwave absorbant material which will
>  work from 2.5 to 10 GHz with good reflection loss and bulk loss, around
>  1mm thick and self-adhesive?

>  For the F6BVA 3cm to UHF transverters, we need a bit about 150 x 50 mm.

>  I see RF Microwave has some at around £330 for a 600 mm square sheet of
>  silicone 1mm carbonyl/iron, which makes 48 pieces at around £8.50 per
>  piece including VAT etc.  The price from Mouser etc for similar stuff
>  works out about the same. Is that the right sort of price or is there
>  some low cost magic stuff of which I am unaware? The gap above the PCB
>  is only 7mm, and some of the components are a few mm tall, so 1/16" or
>  about 1.5 mm is the max I can fit in.

>  Neil G4DBN












KENT BRITAIN
 

You will need enough carbon/graphite to make the glue electrically conductive.  You have to get your glue to were it reads a few hundred Ohms on your Ohm meter before it will do any significant absorbing.  Kent

On Wednesday, March 3, 2021, 04:37:32 AM CST, Mike Willis <willis.mj@...> wrote:


I could say something about spiders being good RF absorbers in 10 GHz waveguides but perhaps some graphite loaded materials would be useful, or indeed graphite powder mixed with glue and painted on.
--
Mike G0MJW


Dave (G1OGY)
 

Neil
You could try layers of Ofcom staff.
They appear to be overly concerned with RF absorption.

Dave, G1OGY


On Tue, 2 Mar 2021 at 23:27, Neil Smith G4DBN <neil@...> wrote:
Are there any secret sources of microwave absorbant material which will
work from 2.5 to 10 GHz with good reflection loss and bulk loss, around
1mm thick and self-adhesive?

For the F6BVA 3cm to UHF transverters, we need a bit about 150 x 50 mm.

I see RF Microwave has some at around £330 for a 600 mm square sheet of
silicone 1mm carbonyl/iron, which makes 48 pieces at around £8.50 per
piece including VAT etc.  The price from Mouser etc for similar stuff
works out about the same. Is that the right sort of price or is there
some low cost magic stuff of which I am unaware? The gap above the PCB
is only 7mm, and some of the components are a few mm tall, so 1/16" or
about 1.5 mm is the max I can fit in.

Neil G4DBN






Peter Burgess
 

You could try Hitek in Scunthorpe, the company I used to work for used them for RAM, the products they had worked well enough for us to damp down resonances to over 10GHz, and while not cheap were cheaper than Eccosorb.
I don't have any contacts there, the web page for their current offering is https://www.hitek-ltd.co.uk/cho-mute

Osco also do foam and silicon absorers. I've not dealt with them.

Peter
G4BCH


Neil Smith G4DBN
 

https://www.amazon.co.uk/Self-Adhesive-Magnetic-Approx-Thickness-Magnet/dp/B017UR081Q

is an example of that sort of thing, £4.75 for an A4 sheet, so about £0.60 instead of £8.50 for the real thing.

I am semi-tempted to give it a try, as it represents a significant saving. It is likely to have consistent and repeatable results and is *probably* far enough from the relay to avoid problems.  It *might* be sufficiently absorbent. In the worst case, I'd have to buy some of the real deal sheet from Franco or Mouser and ship it out separately.

I'm happy to take the group opinion on this as I really don't know.  From a project risk perspective, if the things hoot or misbehave, that's a pretty big disaster for the sake of saving less than £8, although recovery just involves paying for the material and shipping and VAT, plus me filling and addressing 70 envelopes and buying a pile of stamps.  However, we might get away with it.

I am generally risk-averse about this sort of value engineering in a large project without serious testing being done.

Neil G4DBN


On 03/03/2021 15:49, KENT BRITAIN wrote:
One fairly good absorber is the sheet magnets often put on frig magnets and the backs of business cards.

I put it around the edges of my reference horn antennas to reduce sidelobes.   It's Iron particle loaded rubber!
I get mine from a local office supply house.  It already has adhesive on one side.     Kent G8EMY/W5



Neil Smith G4DBN
 

Thanks Peter, I've asked them for a quote for two sheets of CHO-MUTE 9025 self-adhesive 0.8mm

Neil

On 03/03/2021 16:49, Peter Burgess via groups.io wrote:
You could try Hitek in Scunthorpe, the company I used to work for used them for RAM, the products they had worked well enough for us to damp down resonances to over 10GHz, and while not cheap were cheaper than Eccosorb.
I don't have any contacts there, the web page for their current offering is https://www.hitek-ltd.co.uk/cho-mute

Osco also do foam and silicon absorers. I've not dealt with them.

Peter
G4BCH
_._,_._,_


Gordon REASON <gordonj.reason@...>
 

I did give Mike , at the uWave store , some absorber , some time ago , but it was'nt a large sheet .......

On 03 March 2021 at 16:55 Neil Smith G4DBN <neil@...> wrote:

https://www.amazon.co.uk/Self-Adhesive-Magnetic-Approx-Thickness-Magnet/dp/B017UR081Q

is an example of that sort of thing, £4.75 for an A4 sheet, so about £0.60 instead of £8.50 for the real thing.

I am semi-tempted to give it a try, as it represents a significant saving. It is likely to have consistent and repeatable results and is *probably* far enough from the relay to avoid problems.  It *might* be sufficiently absorbent. In the worst case, I'd have to buy some of the real deal sheet from Franco or Mouser and ship it out separately.

I'm happy to take the group opinion on this as I really don't know.  From a project risk perspective, if the things hoot or misbehave, that's a pretty big disaster for the sake of saving less than £8, although recovery just involves paying for the material and shipping and VAT, plus me filling and addressing 70 envelopes and buying a pile of stamps.  However, we might get away with it.

I am generally risk-averse about this sort of value engineering in a large project without serious testing being done.

Neil G4DBN


On 03/03/2021 15:49, KENT BRITAIN wrote:
One fairly good absorber is the sheet magnets often put on frig magnets and the backs of business cards.

I put it around the edges of my reference horn antennas to reduce sidelobes.   It's Iron particle loaded rubber!
I get mine from a local office supply house.  It already has adhesive on one side.     Kent G8EMY/W5



 


 


Dave G8KHU
 

Personaly I'd go for Eccosorb MCS, it's almost 80dB/cm absorbtion at 10 GHz cf the < 20 dB/cm of the chomerics CHO-MUTE

(digikey 903-1498-ND)


Neil Smith G4DBN
 

Thanks Dave, Mouser have Eccosorb MCS 1mm in 12 x 12 inch sheets for £89.51 in 5-off, part number 739-21109145, a bit cheaper than Digikey at £104.

Assume 2 x 6 inch sections, that means 12 units per sheet. With the VAT, that is £8.95 per transverter for the full-fat high-end proper material, and free carriage, no carrier fees.

I did buy a couple of A4 sheets of fridge magnet material, but I'll probably use them to fix things to whiteboards and tin cupboards and maybe even fridges.

Neil G4DBN

On 03/03/2021 20:33, Dave G8KHU wrote:
Personaly I'd go for Eccosorb MCS, it's almost 80dB/cm absorbtion at 10 GHz cf the < 20 dB/cm of the chomerics CHO-MUTE

(digikey 903-1498-ND)
_._,_._,_



Dave G8KHU
 

Neil
Before you order check with Mouser that their material has the pressure sensitive adhesisve tape option - the Mouser description just says mounting is "adhesive". Does that mean it's got the adhesive film or that you need adhesive to glue it in place? The Digikey version does at least says that the adhesive is non-conductive single sided so I'm assuming that this is the factory fitted adhesive sheet . The base number just referes to the material and the laird site lists the psa as an option - https://www.laird.com/products/microwave-absorbers/microwave-absorbing-elastomers-and-films/eccosorb-mcs/21109145
The non-adhesive stuff is a pig for amateur use as nothing seems to stick it reliably, carpet tape falls off and superglue / rtv fail rapidly. The proper adhesive is a two part mix that's fiendishly expensive, comes in a one litre can which has very limited shelf life and has enough skull and crossbones warning symbols to sink a pirate ship. I had to use it once and swore never, ever, again.
HTH Dave G8KHU


Andy G4JNT
 

I had that stuff once - nothing would stick it.
I just taped it on with magic tape, completely overlapping the absorber piece.

Good stuff , Magic Tape.   Sticks forever.



On Thu, 4 Mar 2021 at 08:18, Dave G8KHU <david@...> wrote:
Neil
Before you order check with Mouser that their material has the pressure sensitive adhesisve tape option - the Mouser description just says mounting is "adhesive". Does that mean it's got the adhesive film or that you need adhesive to glue it in place? The Digikey version does at least says that the adhesive is non-conductive single sided so I'm assuming that this is the factory fitted adhesive sheet . The base number just referes to the material and the laird site lists the psa as an option - https://www.laird.com/products/microwave-absorbers/microwave-absorbing-elastomers-and-films/eccosorb-mcs/21109145
The non-adhesive stuff is a pig for amateur use as nothing seems to stick it reliably, carpet tape falls off and superglue / rtv fail rapidly. The proper adhesive is a two part mix that's fiendishly expensive, comes in a one litre can which has very limited shelf life and has enough skull and crossbones warning symbols to sink a pirate ship. I had to use it once and swore never, ever, again.
HTH Dave G8KHU


Neil Smith G4DBN
 

I've sent them a tech query

Thanks Dave

Neil

On 04/03/2021 08:18, Dave G8KHU wrote:
Neil
Before you order check with Mouser that their material has the pressure sensitive adhesisve tape option - the Mouser description just says mounting is "adhesive". Does that mean it's got the adhesive film or that you need adhesive to glue it in place? The Digikey version does at least says that the adhesive is non-conductive single sided so I'm assuming that this is the factory fitted adhesive sheet . The base number just referes to the material and the laird site lists the psa as an option - https://www.laird.com/products/microwave-absorbers/microwave-absorbing-elastomers-and-films/eccosorb-mcs/21109145
The non-adhesive stuff is a pig for amateur use as nothing seems to stick it reliably, carpet tape falls off and superglue / rtv fail rapidly. The proper adhesive is a two part mix that's fiendishly expensive, comes in a one litre can which has very limited shelf life and has enough skull and crossbones warning symbols to sink a pirate ship. I had to use it once and swore never, ever, again.
HTH Dave G8KHU
_._,_._,_