Hack the planet!!

The cool idea of hackerspace is growing fast:


DIY Freaks Flock to ‘Hacker Spaces’ Worldwide

A little more digging, and I find that there’s some already running in the UK, and one planned for Birmingham. Reminds me, I’ve been thinking about on organising an electronics masterclass/summer school. It would be mainly aimed at A-level students (the idea being to host it at the University as a means of attrcting students), but I guess that doesn’t necessarily have to be the case if you have a non-Uni based framework such as this in place.

Experimental Insights: The sample box

Following on from the posts about miniature circuits here and here, I thought I’d show some pictures of the sample box where the chips are housed before they are cooled down in the dilution refigerator.

As you might expect, there is more signal filtering before the DC lines enter the sample box. The filtering is again done by powder filters. These are housed in antechambers surrounding the main sample space. Here is a picture showing the coils which form the inductive component of these LC filters before they have been ‘potted’. You can also see the feedthrough capacitors entering the main sample chamber.


And here is one after showing the filters after they have been filled with stycast:


In the centre of the sample box is the sample space containing a chip carrier, the 4 filtered DC lines and 2 RF lines (which have not been connected yet here). It is important that the chip sits on a copper chip carrier which is screwed down tightly to the sample box. This is due to the physics of conductivity at low temperatures. If the chip carrier is glued down, there would not be very much thermal connection between the sample box and the chip carrier, as glues become very good thermal insulators at low temperatures. The best way to make thermal contact at low temperatures is to have two clean metal surfaces in hard contact. The sample box itself is attached to the mixing chamber of the dilution refrigerator, the part that does the cooling, so this too must be screwed down tightly.

The connectors on the outside of the box are MCX-style jacks for the DC lines and SMA jacks for the RF lines.

There is also a tapped hole on the back of the sample box where a calibrated Ruthenium Oxide thermometer is mounted.

Data mining in the twittersphere

I realised I’m spending an increasing amount of time online. The online world does seem to be developing into some form of alternate existence. I went outside for a walk, and it felt a little alien. Everyone was moving really slowly and it suddenly struck me that there wasn’t very much information coming in from my immediate surroundings…

It’s somewhat cool to spend a lot of time in information-overload mode; it makes relaxing seem easier (even in a hectic city-lifestyle).

To further my explorations, I performed a tentative investigation of Twitter. Hmmm, I really should work harder at this early adopter thing :S So I got thinking about Twitter and things you could do with it…


There is so much information available. All that information can be used… as metrics for ‘things’. For example lets think about, say, ‘Starbucks’. If twitter feed information links Starbucks with ‘good’ or ‘amazing’ or ‘:)’ then the ‘worth’ of the item can be used as a metric of public opinion based on association. You could do the same thing will politicians, banks, countries, decisions etc. A bit like an opinion-stock-market.

Also, why not try direct comparison metrics – See how many times ‘Google’ is mentioned, compared to ‘Microsoft’.

It’s also a lovely dataset for training an AI by extract information from feeds, to learn more about human behaviour and reactions.

You could use it as a metric of generally literacy / intelligence, or as a way of tracking the evolution of language. Tracking internet memes would also be fairly easy, or tracking society moods based on location (if you could also log IPs for instance). Like this recent study on well-being in European countries.

You could do all this with blogs too, but I’m guessing that the blogosphere would give a rather biased subset of the general population in several ways. In addition, blog posts tend to be longer and as such may be more difficult to mine data or trends.

It would potentially be difficult to extract absolute conclusions from this type of study, but monitoring time dependence (i.e. performing some form of normalisation) would be very interesting. If anyone knows of any studies such as this one, it would be interesting to read them.

Miniature filters II

I talked a little while ago about a prototype miniature low temperature LCR filter I made. Well I’m making the real things now, so I thought I’d share the process as they come together. Here is the first stage: The metalwork. This doesn’t actually take very long.


Each filter needs a base plate (top metal pieces with the crosses etched in) to secure the filter and provide the cryostat ground – which I’ll write about in a separate post, a flexible printed circuit board (the flat middle strips of Copper), a supporting wall with feedthrough holes (those ones are pretty obvious) and a lid (bottom metal pieces).

The walls are made just by bending the relatively thin copper plate around 4 times. The holes are made with a metal punch and are 3.18mm in diameter.

Let the mass production commence!! Well, I’m making 5 of these. I think I’ll need 4, and you always make a spare 🙂 I’m thinking of mounting them on the new fridge at 4.2K, 1.5K, 50mK and base temperature, but I haven’t quite decided yet.

Timewise this took a couple of hours (whilst I was waiting for the fridge dewar OVC to pump down – gotta love critical path analysis).

Here is a slightly more artsey photo of the same thing:


Shaping things by Bruce Sterling

shapingthings_sterling2 I’ve just been reading ‘Shaping Things’ by Bruce Sterling (2005). It’s a very interesting and cute book, I’d certainly recommend it. It’s about design, the interaction between people and objects, and how society can be catagorised into historical ‘eras’ determined by this interaction. The book talks about the SPIME – totally interactive and recyclable objects/material items, and how these items will infiltrate our future. The idea is that such objects will boast an incredible amount of information all built in to the design (how the object was made, material properties, the object’s complete history, etc.), although this is usually contained in a database external to the object (e.g. a weblink). The infrastructure for this technology is already mostly in place (barcodes/RFID) and can be extended (think micro/nanodots on each individual part of the object).

The book has some very interesting formatting – including lots of words ‘highlighted’ by the use of different fonts and paragraphs sporting background images. It takes a bit of getting used to, but I think it reinforces and enhances the main concept of the book, which is all about design.

The last few pages have a real posthumanism ‘feel good’ factor. Go read!

More cake!

I have dedicated a Condensed Matter Research page to cake.
Well, cake club to be precise (See this previous post for explanation)


Photographs of all the cakes baked so far can be seen there. I couldn’t be bothered reposting them all here. However, I will highlight my own contribution to the cake club this academic term, which was a delicious and moist coffee cake. Most people weren’t surprised that I made a coffee cake 🙂 Here is a picture of the cake. Those are chocolate covered coffee beans and pecan nuts on top. The buttercream icing is also coffee flavoured. Mmm.


Experimental Insights: Miniature filters I

For the last few weeks I have been designing and building new miniature low temperature filters. The idea of these little filter boxes is to be relatively good low pass filters (with no re-entrance of transmission at multi-GHz frequencies). The standard way to do this is to use a technology known as the powder filter. This idea was first used by Martinis et al. in the mid 1980s. They are pretty much essential for direct measurements on qubits and quantum phenomena in Josephson junctions, as they are a really good way of removing high frequency noise which causes decoherence and obscures the measurements.

Powder filters usually consist of a coil of wire with an inductance, L, and resistance, R, embedded in a powder of fine metal granules. A capacitance C can also be added to the system. The skin depth in the metal is similar to the grain size and therefore microwave frequency signals are absorbed well by the powder. Originally Copper powder was used, but stainless steel powder seems to give a better response (probably because the grains are more resistive). The result is a low pass LRC filter. LC style filters usually have problems stopping very high frequency signals, because at some frequency the inter-winding capacitance of the coil begins to look like a short, and the high frequencies jump straight across the filter. The powder helps to reduce this problem by absorbing such frequencies.

So how do you make them?

In a fully shielded system the filters must be housed in a metal enclosure. This also handily stops your powder ending up on the floor. I’m going to do a separate post on how to assemble the things. In the pictures below I haven’t put the lid on the filter yet, so you can see inside it. The filter must essentially be hermetically sealed. A rule of thumb: if it’s water-tight, it’s microwave tight 🙂 You can screw the thing together if the filter is machined, but seeing as it is handmade, and I didn’t happen to have a spare lifetime to look for all the sub-1mm screws that I would inevitably lose during this process, I soldered it together instead.

Here is the resulting filter…

The first picture below shows the little coils inside the enclosure. There are 3 filters in one here. The enclosure measures 20mm x 50mm, and the coil wire is 0.08mm thick. I don’t know exactly how many turns there are on each coil, but there’s over 100. The feedthrough capacitors are mounted on both ends of the filter coil to giv’ it some C.


Next the powder is added. This was a test run, so the powder was not permanently set in place, but was rather mixed with a solvent which allows the powder to flow (rather like cement) and then evaporates, leaving the grains tightly packed. Using this technique the powder can be removed again by adding more solvent. Here is a picture:


Once the filter has been tested, the coils can be permanently set in place. This is done with a mixture of the metal powder and an epoxy-resin known as STYCAST. Stycast sets really hard, and also does not crack at low temperatures (unlike almost every other type of glue) so it’s pretty much ideal. Here’s a picture of the finished filter.


What is the response like? Well it looks like this:


The frequency range is from 50MHz->40GHz and the reference line is -40dB with 10dB/div. Not bad for a miniature test filter. You usually chain about 3 or 4 of these in a row to get a good response. This test filter has MCX connectors to attach it to the VNA, which make it slightly larger than it should be. In the full system these will hopefully be replaced by some smaller, neater, shielded twisted pairs. I’ll write a little series of posts about other aspects of these filters, as there’s too much information to put it all in one.