Smart sensors with impact
Professor Kofi Makinwa builds sensors based on chip technology. One of his achievements is a wind sensor without moving parts. He would like to combine one of these wind sensors with other sensors to build affordable, hard-wearing weather stations for Africa, as the continent currently only produces a limited amount of meteorological data. We need global weather and climate models, but we still know far too little about a third of the world, explains the TU Delft Professor of Microelectronics.
What exactly are sensors based on chip technology?
Sensors form the connection between the real world and computers. My field involves designing smart sensors: microchips that combine sensors and signal processing. I build chips that can ‘feel’ their environment, as it were, that can process this information and subsequently transfer it to a computer, all in one. Chip technology means that we can produce them very cheaply. Tyre pressure sensors in cars are one example of such a sensor. They measure the pressure in a rotating tyre and communicate the information wirelessly to the dashboard. Or the temperature sensors that can be found everywhere nowadays: in your smartphone, your car, your household appliances. Sensors that I developed at TU Delft are now in production at companies including SiTime, AMS and NXP, and are being used in Apple’s latest gadgets, for example. But I started to ask myself what use they had outside of the Western world.
And so you arrived at the idea of a wind sensor?
This wasn't my idea, but came from my predecessor and promotor, Professor Huijsing. He devised a sensor that measures wind just like people do, based on temperature. If you put your finger in the air, wind blows past it. You feel one side of your finger becoming slightly colder than the other and based on this information, you can estimate how hard the wind is blowing and in which direction. During my doctoral research, I dramatically simplified the electronics required for this. It all now fits on a 4x4 mm chip. The major benefit of measuring wind in this way is that there are no moving parts, as in traditional anemometers. That makes these chips hard-wearing.
But one sensor does not make a weather station…
Indeed, but a hard-wearing rain sensor has already been developed. Over at the department of Nick van de Giesen (Professor of Water Management), they devised an acoustic rain sensor, the Disdro. It works using a really cheap piezo element, like in musical greetings cards. You can use it to measure the number of drops that land on it. It always reminds me of my youth in Nigeria. There's something very reassuring about the sound of tropical rain beating down on a steel roof, it's perfect to fall asleep to.
The rest of the necessary sensors are actually already commonplace. For example, your smartphone contains temperature and atmospheric pressure sensors. A simplified camera can be used to measure the intensity of sunlight, so that is also already available. Sensors such as these cost just a few cents. If you connect these sensors to a microprocessor, it can use a mobile phone connection to transmit their information every so often. A weather station doesn't have a high data rate. Temperature, humidity and a few other variables: that can all be reported in just a single text message. A solar panel can produce enough electricity to run the entire station; after all, there is plenty of sun in Africa.
It always reminds me of my youth in Nigeria. There's something very reassuring about the sound of tropical rain beating down on a steel roof, it's perfect to fall asleep to.
So the weather stations will soon be installed in Africa?
With his TAHMO project, Nick van de Giesen is investing heavily in a network in Africa. That is important, as projects in Africa often fail due to a lack of ownership. Organisations install things with the best of intentions, but then return home, under the assumption that the problem has been solved. More often than not, nobody has been trained to maintain the device or use it correctly. And if you install an expensive bit of kit, it often ends up on the black market. Weather stations are now being offered to schools, including an educational package. This creates ownership, as people then think: ‘that is for our children, we will leave it be’. But if you want to install a weather station at thirty-kilometre intervals, you will need several tens of thousands of them. That means that as well as being hard-wearing, they also need to be cheap, ideally under €100 apiece. And that will only be possible if they also contain the cheap rain and wind sensors we spoke of earlier.
What still needs to happen to achieve that goal?
The final major hurdle is finding an affordable means of calibrating the rain and wind sensors. For a temperature sensor, you only have to warm something small up and cool it down again. But it gets more complicated with a wind sensor. To measure wind speed, you need to get a certain volume of air moving, and that is where we are experiencing difficulties. It also needs to be in a wind tunnel, and that takes time. You also need to calibrate each sensor individually, due to a range of manufacturing tolerances that vary from sensor to sensor. The longer it takes, the more expensive it obviously gets. Moving forward, I now have two ideas. You could standardise the design and production in such a way that each sensor has a specified accuracy as standard. Another option is to look into whether we can systematically recreate the effect of wind by strategically positioning heat sources. That would allow us to calibrate in much smaller set-ups. There is a similar issue with the rain sensor. Exactly how many millimetres of rain have fallen per surface? To calibrate that, you would need a very precise shower.
And yet we really do need these weather stations…
Absolutely, for starters, for Africa itself. Weather forecasts are extremely important to farmers, especially in these times of extreme weather. In Nigeria, where I was born, I see that the weather is changing. There was always an interruption in the rainy season – known as the August break – but instead of that, the dry season now starts earlier. That is disastrous for farmers who sow their seeds based on the traditional growing season. I recently visited South Africa, and there – in Cape Town – they were in the midst of two years of unprecedented drought. One of the reasons why we have so many refugees is that the situation in their native country is so difficult. People are desperate. The climate and weather patterns are changing. Governments are failing. We need to offer these people hope. We need to sketch a future in which hard work and dedication is rewarded with a better life – even if it is only a little bit better.
So, we need more weather and climate data. That is also in our own interest. The better we can chart the changing climate, the better it is for us all. Satellite observations are not enough, we need data from down on the ground in order to verify our models.
If it is also in our interest, why haven’t the weather stations already been installed?
Thanks to smartphones and cars, we already have several sensors of sufficient quality. The principles have also already been established for wind and rain, but the production methods are still too expensive. That problem can be solved, but we need money and dedication to crack it. The market is not massive, and the added value for the consumer is negligible. You will not become the next Bill Gates or Mark Zuckerberg by investing in this. We apparently attach much more importance to things like our mobility than to weather stations in Africa.