FRidh's blog

Today I was searching the web if there was anything about thermoacoustic speakers. You might ask yourself ‘Why, Freddy, whyare you searching the web for thermoacoustic speakers?’ The biggest reason is because thermoacoustics is simply cool. But also, because it could be a method to create sound waves without using mechanic vibrations, and thus no moving parts. And the biggest advantage actually has to do with impedance matching. Let me explain that a little further.

Air has a certain characteristic impedance (frequency dependent). The acoustic impedance of a loudspeaker however is different, especially at lower frequencies. At high frequencies it doesn’t really matter, simply because air is a gas and thus soft. But for low frequency vibrations air is more solid which hinders the transfer of vibrations as sound waves. Thermoacoustic speakers wouldn’t have this problem, since there would be no moving part and thus no impedance mismatching.

When searching the web this afternoon I came upon this article from 2008. Chinese researchers had managed to create sound thermoacoustically using carbon nanotubes. The principle is actually quite simple. The temperature of an electric carrier depends on the electric current flowing through it and a higher current means a higher temperature. If the carrier is really small and thin, like nanotubes, the change in temperature can be quite rapid. So if we put an AC current of say 100 Hz through the nanotube, the temperature will oscillate with 100 Hz as well.

These nanotubes are put in direct thermal contact with the air. Since the temperature of the tubes oscillate with 100 Hz, every period the temperature will be higher than that of air, and half a period later it will be lower than the surrounding air. When a temperature difference occurs, heat will be adiabatically transferred to the air causing a pressure oscillation as well. And this pressure oscillation is indeed a sound wave of 100 Hz.

Now if you don’t believe me, see and listen yourself.

Last Thursday it was finally made clear, I am admitted to the Sound & Vibration Master programme at Chalmers University of Technology in Gothenburg, Sweden! I thought this would be the ideal news to blog about so here it is and, since I lately haven’t really looked at this blog anymore, I decided that from now on I will maintain it again. Yay!

Anyway, the 23th of August is the Welcome day for all the new students, and the 29th of August will be my first day. I decided to take Swedish lessons this summer so I booked a full-time course for foreign students which takes place from the 8th till the 26th of August. According to the website it also includes trips making me even more eager to start with it! Since I of course have to move in first,  I will be moving to Gothenburg the last week of July. That should give me enough time to prepare and arrange everything, like getting a Swedish ID number and card, bank account, mobile phone subscription, etcetera.

But besides arranging those things in Sweden there is plenty to arrange here as well. For instance, since I won’t be having a Dutch address anymore my Dutch ID number will be deactivated. This has a consequence for my social health insurance since normally an ID number is required. Now I know my insurer will only need to be informed about it, and for this kind of case, emigration, they make an exception, but still, I better not forget it! I must note that as soon as I am registered at the Gothenburg tax office, I won’t need a Dutch health insurance anymore, but that registration can take a while.

I will also need to apply for study support and loan again. But since I will study abroad, I need to apply for the support and loan at least 3 months ahead, so they can check whether the programme is accredited. And of course I will have to find an apartment in Gothenburg, and move out of my current one. Luckily I still have lots of my stuff packed from last time I moved