In the loop at Coffee is my cup of tea

exterior coffee is my cup of tea, cimcot, coffee Hackney

Coffee is my cup of tea on Dalston Lane. The colour of the exterior matches the crockery used inside.

There is a lot of truth in the name of this café. “Coffee is my cup of tea” in Hackney is a lovely retreat, a place where you can take time to enjoy whatever drink is your cup of tea. Walking through the door, you are presented with a few wooden tables and a cocktail menu on the wall. A breath of calm on an otherwise busy road. Together with the bench just outside, there is plenty of seating inside. There’s even a long table along the window where you can sit if you would like to enjoy your coffee while gazing at the passers-by. There were the usual range of coffees on offer along with fresh juices, other drinks together with a range of food. When we went in the late afternoon, there didn’t seem to be many cakes on offer but maybe we were just unlucky. Coffee only this time. The coffee is roasted by Assembly and there is of course tap water available at the end of the bar.

Facing the bar, glued to the wall, were a circle of stiletto shoes. Forming what seemed to  be a “shoe star”, they were one of a number of art works around the shop. The café is also quite spacious, the window at the front providing plenty of light and contributing to the relaxed space. When my long black arrived, the light coming in from the windows produced great interference patterns on the bubbles of the coffee, an irresistible piece of coffee physics. The cocktail menu provided quite a distraction, again making the point that it was a shame we visited on an afternoon: an evening of coffee and cocktails would make a lovely night. However, a sunny afternoon was a great time to sip and enjoy a long black. While the long black started off very fruity, the taste changed (matured?) as the temperature of the coffee decreased. In the background to this all though, something so subtle as to be almost un-noticeable caught my attention. Completely surrounding the window was a very thin piece of copper wire. Were there tiny little lights on it to make the café more attractive (romantic even?) in the evening? I couldn’t see any. From our table, it seemed as if it was just a thin, closed loop of copper wire forming a loop around the window.

coffee cimcot

Fantastic interference patterns on the bubbles of the coffee at Coffee is my cup of tea

Such a loop could be used as a radio antenna, a “loop antenna”. Indeed, when Heinrich Hertz (1857-1894) first discovered radio waves in 1887-8, he used a (gapped) loop antenna as the receiver. Hertz had been trying to test James Clerk Maxwell’s theory that visible light was part of a much broader spectrum of electromagnetic waves, particularly, that there should exist very low frequency waves far beyond the visible region of the spectrum, waves that we now know as “radio waves”. Radio, TV, wifi, all things that seem so obvious now but were really only predicted and discovered relatively recently. Working in his laboratory in Karlsruhe, Hertz set up a radio generator which consisted of two brass balls that were charged until a spark flashed between them. Sitting a few metres away, a gapped loop of wire, the ‘loop antenna’ suddenly showed a spark over the gap. The spark that Hertz had generated in one part of the room had been mysteriously transmitted, as if through an aether, to be picked up by the antenna a few metres away. Clearly it was consistent with Maxwell’s predictions. The electric spark had generated a low frequency electromagnetic wave that had been picked up with the loop antenna. With further experiments, Hertz showed that this wave was indeed reflected and refracted in the same way as ordinary, visible, light and even determined its wavelength (which for Hertz’s experiment was about 66cm)¹.

loop antenna at cimcot, Dalston Lane

It is probably easiest if you visit the cafe but look very very closely at the frame of the window. There is a copper wire surrounding it.

Although Hertz did not immediately see any practical application of his result (beyond the fact that it was a test of Maxwell’s theory of light), ‘radio’ soon started to be developed. Marconi and others worked with wavelengths of 200-600 m to transmit radio waves across the Atlantic Ocean¹. As amateur radio enthusiasts got hold of radio sets in the 1920s they started working with wavelengths that were initially considered impractical for applications (much shorter than the hundreds of metres used by Marconi). These enthusiasts soon realised that they could communicate with other enthusiasts in distant countries through the reflection of the radio waves off of the (until then unknown) ionosphere¹. Gradually our understanding of radio waves and antennae design developed, leading to further, unexpected applications. Depending on the design of the antennae, radio waves (and microwaves, which have a slightly shorter wavelength of the order of 0.1-100cm*) could be made to be directional. So antennae could be made that transmitted waves only in set directions (or conversely could detect the direction from which radio/microwaves originated). This understanding of antennae design would lead to advances in Radar technology.

Which brings us back to the loop antenna at Coffee is my cup of tea. Loop antennae are grouped into two types, “small” and “large”. It is fair to say that it is a large window at Coffee is my cup of tea and so the loop antenna there would fit into the “large” category. These antenna are ‘resonant’ (meaning that they respond most) to wavelengths equal in length to the circumference of the antenna. From memory, I’d guess that the window was roughly 2m high and 3 m across, meaning it had a circumference of 10 m. We can calculate the frequency of the radio waves that would be resonant with this by using the fact that the frequency (f) is just the speed of light (c) divided by the wavelength (λ) (ie. f=c/λ). The speed of light is 3×10^8 m/s, so the frequency would be (3×10^8)/10 = 30 MHz. There are two last things to notice about this result. First, the name of Hertz lives on in the unit of frequency (Hz). Secondly, the loop antenna around the window at Coffee is my cup of tea is resonant with approximately the frequency of Citizens Band radio (CB radio operates at ~27 MHz). Which may make us question once more what this loop of wire is doing at this friendly little café on Dalston Lane.

Coffee is my cup of tea can be found at 103B Dalston Lane, E8 1NH

¹Britain’s shield radar and the defeat of the Luftwaffe, David Zimmerman, Amberley publishers (2001, 2010)

*Technically Hertz discovered microwaves rather than radio waves. However, given neither were named at the time and they are both of longer wavelength than visible light, it is perhaps too pedantic a point.


Diamonds are forever at Violet, Hackney

the outside of Violet

Violet in Hackney

Violet is not quite where I expected it to be. I had expected it to be in a row of shops on a main street, instead it is tucked away, a little cafe in a back street in Hackney. Despite the relative anonymity, Violet has won awards for the quality of its cakes. Award winning cakes are hard to resist and so, a few weeks ago I went along to Violet to try the coffee. With a couple of seats outside and a large room upstairs with seating, it is very easy to enjoy a good coffee and a cake while taking in the surroundings. The cakes certainly do not disappoint and, importantly for Bean Thinking, they know exactly what goes in them, meaning that if you are allergic to nuts or have other food allergies or intolerances, they are incredibly helpful. They definitely get a tick in the “cafe with good nut knowledge” category.

As it had been raining when we tried Violet, we decided to take a seat upstairs. Stacked in one corner of the room were a set of wooden chairs, reminiscent of those chairs that we had to stack at school. Each chair fitted almost exactly onto the previous one. At the top of the stack of chairs however, the uppermost chair did not fit exactly onto the previous chair, it was as if there was a defect in the stack.

stack of chairs, Violet

The chair stack in Violet.

The diagonal legs of the chairs resembled the multiple strata in a layered substance such as graphite. Each layer of graphite features a hexagonal arrangement of carbon atoms forming a structure very much like the chair legs in the chair stack. Graphene, a material of which there is currently a lot of hype, is a single layer of graphite. The carbon equivalent of one chair leg on its own. Carbon is a fascinating element. If, rather than being arranged in layers, it is arranged into a more 3D crystal structure, then you get diamond, a colourless, extremely hard crystal structure, very different from graphite. It is in diamond that defects in the stacking structure (such as with the uppermost chair) can cause spectacular effects.

If the carbon atoms are arranged into a perfect crystal structure, (the equivalent to the chairs being perfectly stacked), then diamond is colourless. If on the other hand, something happens to disrupt the structure, perhaps there is one carbon atom missing in the structure or maybe another, impurity element, such as nitrogen, has got in, the way that the electrons in the diamond react to light changes. This means that it can take on a colour. The introduction of nitrogen for example, in concentrations of only 0.1% will make the diamonds more yellow or orange. Red diamonds are a consequence not of impurities but simply defects in the crystal arrangement. The equivalent to that one last chair in the chair stack changing the properties of the stack completely. Knowing that the colour of a diamond is a result of a defect in the arrangement of carbon atoms in the structure offers us two possible viewpoints. Either people who buy red diamonds are paying a premium for defective goods, or, beauty takes many forms and what is beautiful is not necessarily what is regular and perfect. I know which view of the world I prefer to take.

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Violet is at 47 Wilton Way, E8 3ED