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Measuring vibration without a touch

Like I said last post, I found a paper about a new type of non contact sensor for ground vibration tests.

The sensor replaces the accelerometers that need to be placed on the airplane. It’s called a NIRV (noncontact inertia reference velocity) sensor, internally it is the combination of a laser displacement sensor and an accelerometer.


The sensors are mounted on large stands that surround the airplane, the laser displacement sensors in the NIRV sensors determine the distance between the sensor and the airplane. Because the stands are very big, they will wobble a bit themselves. To compensate this wobble of the sensor, he uses the accelerometer and makes the distance measurement more accurate.

During the GVT’s, the displacement of the airplane is registered and is expressed in terms of velocity per unit force, just like the data that the normal accelerometers produce. Because the data is expressed in the same unit, the NIRV measurements can then be compared to the results of normal accelerometers, they concluded that the 2 types give an equally good result.

The NIRV sensors have a big advantage, because the sensors are mounted on the stands, these can be used on most airplanes, so this will make you save time in the setup of a measurement. This because there is no tear down or build up needed between 2 measurements, like with the normal accelerometers.


So guys, see you later and hope you understood everything.

Sensing vibration

There is already a post about ground vibration tests (GVT).

In these tests they normally use accelerometers, so I think this is a good thing to blog about.

There are 2 types of accelerometers, first you have the AC – and secondly the DC – coupled devices. The AC – coupled device can’t measure static acceleration, so it doesn’t register the gravity. While a DC device can measure starting from zero Hertz.

An AC device isn’t suited to follow slow motions, because of the limitations by its RC time constant which defines its high-pass characteristics. The DC on the other hand has no problem tracking a slow motion.

A typical AC sensor is a piezoelectric accelerometer. While a typical DC-accelerometer is the capacitive (used in air-bags and mobile devices) or a piezoresistive one.

I have found a good paper about this, it gives a lot of info and a good comparison.

In GVT they use AC and DC sensors, also force and temperature sensors. The fact they also use temperature sensors is because DC piezoresistive sensors are very temperature dependent.


But of course the technology isn’t standing still so there is a new kind of sensor they are testing for the GVT. So stay tuned for my next post if you want to know more about it.


See you next time followers.


Using a single sensor delivers a limited amount of information. Sensors almost always appears in networks. If you look back at previous blogposts most applications use a network of sensors to achieve their goal. For example, a single Tile node would be of limited use. You only gain full advantage of the functions when there is a large number of nodes connected through a network. Thus a large part of the development process of a sensor application is the network connecting the sensors and their driving electronics.


(image by Vector)


A very important and widely adopted interface is the CAN (controller area network) messaging protocol. Originally developed by Robert Bosch GmbH for use in the automotive industry the CAN bus has huge economic importance. Over 100 million of nodes are connected each year using the CAN protocol. Nowadays the CAN bus is widespread across different industries and continues to gain  importance in aerospace industry. Air-conditioning, door management, fire detection, cabin management and the aircraft galley electronics are typically connected using a CAN bus under the ARINC standards. This makes the CAN bus suitable as the network to connect our sensors.

You can read more about the economically  importance of the CAN protocol on this site. The CAN bus is even used in livestock facilities. If you are interested in the CAN implementation you can read this introduction guide (for beginners).

Ground vibration testing

As stated in my last post this one is providing some details about ground vibration testing (GVT). These tests are performed at the end of the development process. The main goal is to collect vibration data. This data is used to validate the aircraft structure and is helpful to predict the flutter behavior of the plane. Due to their huge importance in safety-critical flight tests multiple configurations must be tested. This causes an extreme time pressure for the engineers. The GVT is economically important for aircraft manufacturers. The video below is displaying some of the GVT tests of the solar impulse airplane. Shakers excite the airplane and accelerometers placed all over the airplane collect the responses. It’s important the exact position of all the accelerometers is known accurately. An entire GVT cycles can be done in just under a month which is rather fast for placing 700 accelerometers and over 25km of wiring. (EADS-CASA completes large-scale Airbus A400M ground vibration test in less than a month’s time

You can find more information about GVT on the LMS site

You can also check out these interesting papers about GVT:

Advanced systems and services for Ground Vibration Testing –  Application for a research test on an Airbus A340-600 aircraft

Ground Vibration Testing of Large Aircraft – State-of-the-Art and Future Perspectives

flutter testing

The main application of our thesis is in aerospace industry. This industry is under continuous pressure and has to develop aircrafts in shorter timeframes and at lower costs than ever before. A large part of aircraft development time is used for testing. This means if testing time can be reduced significantly  a shorter time to market can be achieved.

An aircraft has to be flutter certified. This is a certification at maximum flight speed to determine structural integrity and safety of the airplane. The first formal flutter test was carried out by Von Schlippe in 1935 in Germany. His approach was to vibrate the aircraft at resonant frequencies at progressively higher speeds and plot amplitude as a function of airspeed. This approach was sufficient untill a Junkers JU90 crashed in 1938 during flutter tests. Next a more advanced approach was used. The typical test procedure is visible in the figure. The full explanation is available in this NASA-report. It’s still based on the Von Schlippe methods. Firstly, structural excitation of the plane. The second part is the response measurement. This is done using hundreds of accelerometers. The last part is the data analysis.


Before these tests can be started a ground vibration testing(GVT) is done to predict analytically the flutter behaviour. My next post will provide more details on ground vibration testing. You can also watch the flutter test of the A380 in the youtube video.



Detecting raindrops

I was driving in my car and it started to rain. My windscreen wipers automatically started to work and I was wondering how it works. So after searching I found a good blog post that explains how it works. Here you see a schematic representation of its internals:

01-rain-sensor-working-principle-reflection-of-infrared-light-electro-luminescent-diodeSo, on the left you have a LED that sends out a beam of light and depending on the amount of light that is received on the right side, the output gives a certain value. When a raindrop lies on top of the windscreen above the sensor, a portion of the LED light beam is deflected to the outside and therefore the receiver receives less light and this difference is visible at the output. This is then used to adjust the speed of the windscreen wipers.

So this can make the live of a driver easier. There can be a lot of possibilities to use this sensor for, like closing the roof of a convertible or turning on the lights during heavy rainfall.

Are there other possibilities to use the sensor for, that you can think of, which can ease the job a driver?





Extra! Extra! Read all about it!:
A new innovation in the automotive industry was recently announced, McLaren are going to use Ultrasonic waves to clear the windscreens of their super- and hypercars.


These Ultrasonic Waves have multiple advantages like, they don’t distract the driver and it is more aerodynamic than the standard windscreen wipers. The Sunday Times was the first to publish article about this topic so if you have an account I would certainly recommend you all to read it.

This new development shows another application of Ultrasonic waves than the distance measurement we do in our Thesis.

Privacy at festivals

Hey you guys,

Let’s talk about how ‘free’ you are at a festival.

I read a paper about how they track people at ‘Rock Werchter’ using Bluetooth, they started the first experiments already during the edition of 2009.

They use Bluetooth to track the movement of groups of festival goers, because nowadays every cell phone has this feature. Most people don’t even turn it off because they use it in their car to call handsfree. Every cell phone has a unique MAC address, so by placing a lot of Bluetooth scanners. You can see how cell phones move around all day. They will not know your phone number so don’t be afraid of that, they can only see what trajectory a certain cell phone has followed.

The retrieved data can be used to optimise the infrastructure of the next year. Like, what is the optimal position of drink shops or toilets? But like you all know, they not only organise it for fun. They want to make money out of it. I think that the data is also used to determine at which spots on the festival grounds, the most festival goers pass by. The spot where the most people pass a day will have a high value to place a publicity stand on. And sponsors will pay big money for big advertisement.


Which would be the primary reason for this tracking according to you? The upgrading of the festival experience every year or will it be the money of publicity?

What do you think, is it a violation of the privacy?

When I hear tracking and violation of privacy, I immediately think about the location tracking that was in the Apples IOS4 maybe some of you still know it . That was a big hype at that moment, because it was a real privacy violation. And Apple was obligated by court to change this in their operating system.



For the Flemish students there was also a little TV interview with the students of the University of Ghent who realised it:


Automotive sensors

One of the most known applications using ultrasound sensors is the park assist. Or if we take it one step further the automatic parking system. Park assist systems mostly use ultrasound sensors or cameras to scan the road in 2 dimensions to gather accurate distance information. This system simplifies life especially for people who have problems with parking cars. However with these system the drivers abilities to park himself will drop considerably.  The automotive sector is increasingly relying on sensors to improve safety and comfort. At low speed ultrasound sensors and cameras are used. At high speed most systems rely on RADAR-systems. For more information about the different systems you can read this paper.


Also these systems are used to provide information on the display about the surroundings making it possible to detect objects in otherwise invisible regions. This gives the possibility to designers to change the normal view of a car. For example improving the aerodynamics by replacing the mirrors with cameras.


Sensor based cars will eventually lead to self-driving cars available for consumers. In today’s world smartphone and tablet makers turn out new models every year because the consumers became tech-hungry. Will the same phenomenon apply to cars as well in the future? What do you think? I think consumers will expect the latest technology and newest systems in their cars. This means a new automotive landscape and probably new business models in the automotive world.

What if a touchscreen isn’t good enough anymore?

Here is the new innovation in interactive computing:

The LEAP motion.

It is a small device that can be connected to your laptop by a simple USB plug, next you install the added software and you can start controlling your pc with hand gestures. You can download a lot of applications and games from their own app store to get the full benefit of the Leap.

It uses two monochromatic IR cameras and three infrared LEDs. The LEDs send out a dotted pattern of invisible IR light and then the cameras take pictures (over 200 frames per second) to detect movement.

Here you see a HP laptop with the leap build-in, it looks very nice and is already for sale in the United States of America. Now just hope they will sell it in Belgium soon.

So apart from the huge ‘wow’ factor, I think it can introduce a revolution in the computer industry. The first thing I think of is the medical sector; they are already using robots during some operations. How great would it be if a surgeon could control a robot that executes all his motions which were captured by a Leap? This could make it possible to perform a surgery over internet. Nowadays when you have a rare condition, you need to travel miles and miles to be treated by a specialist. Then you could get this treatment in your local hospital.


What do you guys think about my idea of surgery over internet? Or better yet, who of you could give me another example how a Leap can improve our life?



Tile, the world’s largest lost and found.

Tile is a sensor application for the localization of lost things. It’s an example of sensor localization appearing in our nowadays lives. Tile will influence the life of the people using it. Connecting a Tile to your keys and you never have to search them again… unless you lost your smartphone. Tile is using an application on your smartphone to visualize the localization of your lost object. You can even play lost and found with sound guidance when you come closer to your object.

Using Tile basically makes you more dependent on technology. Without it you still have to remember where you left your keys which is a basic brain activity. Using Tile this brain activity is going to happen less, influencing the way our brain develops.  Already over 2,6 billion us dollars of tiles are pre-ordered.

Did I mention other people with Tile can help you find your lost objects by just passing close to them? Check out the video below and let me know what you think of Tile!