antennae – Bean Thinking

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.

A sense of history at Lundenwic, Aldwych

Lundenwic Aldwych coffee — The bar at Lundenwic

Of all the senses, our sense of smell is probably the one that is most likely to evoke memories that can take us right back to our childhood. One whiff of something as we walk past a café can, almost magically, transport us back many years and to a quite different time and place. This aspect of our sense of smell was brought home to me a few weeks ago on a visit to Lundenwic in Aldwych.

Lundenwic was the Anglo-Saxon name for the settlement that was located between what is now Covent Garden and Aldwych. As time progressed and the population of Lundenwic decreased, the site became known as the old-settlement (Aldwic), from which we get the name Aldwych*. Lundenwic is also the name of a (relatively) new cafe that has opened up near the corner of Aldwych with Drury Lane (incidentally, originally called the Via de Aldwych*). The upstairs seating area is quite small but with Caffeine magazines on hand, and plants dotted around, as well as the bar, there is plenty to watch and to notice while savouring your coffee. The espresso based coffee is sourced from Workshop while the filter option (V60 based) features different guest beans. On the day of our visit there were two filter options available. Opting for the Kenya Kagoumoini AA, I waited for my coffee to be prepared while my cafe-physics review companion had a late lunch of a cheese and ham toasty which quickly filled this small café with the aroma of cooking cheese. The tasting notes for the coffee stated that I should expect “rhubarb and raspberry lemonade”, and while the taste was certainly of lemonade, the aroma seemed to me quite different, almost spicy.

Lundenwic coffee — Kenyan coffee, freshly brewed appealed to all five senses, but each in different ways.

The cooking cheese and the memories evoked by the smells, along with this difference between the smell and the taste of the coffee, suggested that smell ought to be the subject of this cafe-physics review. Indeed, smell turns out to be a very interesting sense. The nerve cells relating to smell are the only type of nerve cell that can regenerate†. It is this ability of these nerve cells to regenerate that recently helped a previously paralysed man to walk again. Nerve cells from his nose were transplanted into his spinal cord where they helped in the regeneration of his spinal cord (for reasons that are not yet fully understood).

But what about those smells in the coffee? That special aroma, that you breathe in and appreciate immediately after you have brewed your cup is due to a fantastic mix of over 1000 volatile aroma chemicals. If you let your coffee stand, those chemicals evaporate off, which means that the just-brewed aroma starts to change. One of the most important chemicals for this coffee aroma is called 2-furfurylthiol. It has been shown that the concentration of 2-furfurylthiol in the coffee decreases by a factor of 4 over the course of an hour‡. Even after as little as twenty minutes or so, the concentration of these complex aroma molecules starts to decrease significantly and so if you, (horror of horrors), were to let your coffee cool overnight and then zap it in the microwave in the morning, you would no longer regain that freshly-brewed smell that may have attracted you to the coffee in the first place.

durian skins and seeds — What was left after a session eating durian on a durian farm in Penang, Malaysia

This may also be the reason that the coffee at Lundenwic tasted differently to how it smelled. By inhaling the aroma and then tasting the coffee without exhaling (and so pushing the aroma back through the nose), our nerves are sensitive to different sensations. Although we may experience this while tasting many foods, occasionally it is crucial. A few years ago, Hasbean coffee were selling a very unusual coffee. The coffee, from Indonesia was called “Sidikalang”. Looking back at Hasbean’s “Inmymug” video, it is clear that it was very difficult for Hasbean’s Stephen Leighton to come up with tasting notes for the coffee which, in the end was compared with “durian”. The aroma of durian has been described as “turpentine and onions garnished with a gym sock” and yet in South East Asia it is known as the King of Fruits and is highly sought after for its taste. The aroma chemicals found in durian have recently been analysed (by the same group as studied the aroma of coffee). Nonetheless, the inclusion of “durian” in the tasting notes was extremely accurate (and did result in an amusing, if unconventional, attempt at opening one of the fruits in the video). It was accurate not only in terms of the experience of the taste/smell combination of that coffee. The actual taste and smell of the coffee was very similar to that of durian. A very unusual and interesting coffee that I have never yet had the opportunity to experience again.

However, to return to Lundenwic, how do the (lovely and inviting) smells that emanate from that café compare with the smells of the area that had been Aldwych before 1905 (when Aldwych was built, demolishing the slums that had existed there)? Some museums, such as the Canterbury Tales (in Canterbury), use the aromas (odours?) of medieval life to give visitors some idea as to what life was like in years gone by. Recalling a childhood visit to that museum, I would suggest that the smell of freshly brewed coffee and melting cheese is an almost unquantifiable improvement.

Truly we could say that at Lundenwic, it is time to wake up and smell the coffee.

Lundenwic is at 45 Aldwych, WC2B 4DR

*The London Encyclopaedia, 3rd Ed, MacMillan publishers, 2008.

†”On Food and Cooking: The science and lore of the kitchen”, Harold McGee, George Allen & Unwin publishers, 1988.

‡The coffee had been held at 80C in a thermos flask for the duration of the experiment. It may be expected that as your coffee cooled down, the volatile aroma molecules would evaporate more slowly than the time indicated in this study.