like butta

Cold you please test ninja turtle ooze and report back. It's some kind of guar gum/vinyl acetate and borate gelatin:

We've got excellent results with micro-coax on pot cores.

Are you doing a reverse convolution to beautify the step waveform? You can tolerate a really ugly TDR if you can make a FIR filter to pound it flat.

Nah, Western religious art, particularly Italian Renaissance stuff, leaves me cold. Cute little cupids representing the glorious cherubim, Madonnas modeled after artists’ paramours, corrupt prelates and donors painted into biblical scenes, blech.

Cheers

Phil Hobbs

Right well I don't know if pizza's dielectric properties have been studied thoroughly but there's been a lot of work done on Jell-O, it seems pretty customizable. There's always room for Jell-O

Have you considered using a mechanical low pass filter on your slide hammer, a pad on either the hammer or anvil striking surfaces? Rawhide faced iron hammers are very good at driving stakes into very hard soil without the severe impulse of a metal on metal impact, and while rawhide might not be good for 1E6 cycles you could try rubber sheet or heavy gasket material, tune the response by changing thickness and hardness to suit. Presumably the same slide hammer is used for removal, so you would want to pad the upper surface also.

Between padding the hammer and compliant mounting of your circuit (two series low pass filters) you should be able to keep the acceleration of your circuit module to something reasonable.

Hard epoxy potting compounds can put a lot of stress on parts from differential thermal expansion, sometimes a compliant layer of a more flexible material is used over sensitive components before potting with hard epoxy.

Glen

Thanks, that’s interesting. We’ve thought about a pad, but haven’t done any studies yet. The problem of hard epoxy ripping things apart is pretty well known, I think—as you say, the fix is a thin layer of RTV or something like that.

I didn’t know about rawhide-faced hammers, which sound cool. With hard materials, the pulse width equals the length of the impactor divided by the speed of sound in the material, which in this case is just about 20us. The force is the change of momentum divided by the pulse width.

If the pad compresses by 1 mm when the slide hammer arrives at 2 m/s, the pulse width is about 500us, so the peak acceleration would be more like

Cheers

Phil Hobbs

Just for future reference if you want a material much more rigid than butter at room temperature you could try cocoa butter. If you make chocolates it is probably already in your pantry :-). It's a mix of triglycerides that melt between about 90 and 100 F so melting it to cast in place or paint it on or clean it back off would be pretty easy. I found one online reference using Brave search that listed dielectric constants for some fatty acids and trglycerides similar to those in cocoa butter. They were between about 3 and 3.4 so right in the range you were lookng for. Anyway, I was curious and bored ...

Regards, Carl

There are also "Dead-Blow Hammers" used for automotive bodywork. They spread the strike over a longer period, often by being hollow and filled with steel shot.

I had one of those back at IBM. They seem a bit on the wimpy side for pounding stakes into hardpan, no?

Thanks

Phil Hobbs

White chocolate is clearly the future of RF design. ;)

Cheers

Phil Hobbs

It’s been used for making edible lasers.

Cheers

Phil Hobbs

I have that one in my tricks file, for sure.

We’re using two ferrite sleeves as a 1:1 balun, which is the sideways version.

The step is actually very nice-looking—clean edges, flat pulse tops, no worries. We did have to make a couple of layout adjustments to get there, but the result shows TDR edges surprisingly similar to the SD-24’s.

Ours is much less fancy, and needs a few pulses per delay value to get good convergence in the sampling loop, but in a not-too-scientific comparison on a 24-inch RG-188 cable, both the SD-24 and our gizmo showed 60-ps TDR edges (10-90%). Of course the SD-24 is more like 30 ps on a less lossy cable, but for $16 per completed board, including MCU and data converters, I’m pretty happy with it.

Cheers

Phil Hobbs

Rawhide faced iron hammers would certainly work.

These are too soft to drive a steel rod.

Not to worry, help is coming ...

.

.

There are smaller options.

.

Joe

Butter seems to be pretty lossy at RF, but I don't know whether that matters.

It was only an inch or two of propagation distance, and we were mostly interested in the performance of the mode-matching structures.

Cheers

Phil Hobbs