Microelectromechanical system - MEMS technology

At the heart of sensors – MEMS technology for LiDAR

“MEMS-based LiDAR sensors are usually less expensive, but they are not high-performance enough for use in autonomous vehicles.” We hear sentiments like this quite often. In this blog post we will explain how our sensors effectively invalidate this assumption, how we found the perfect mirror size for our LiDAR, and what considerations factored in to our decisions.

For use in autonomous vehicles, LiDAR sensors have to meet two basic requirements: on the one hand, they have to deliver high performance, including long range and a wide field of view. On the other hand, they must also be scalable so that millions can be produced and installed in vehicles. LiDAR manufacturers meet these challenges through various approaches. Mechanical LiDAR systems, whose beam deflection units are moved mechanically by motors, are still the most commonly used systems today. Although these devices boast a wide field of view — some up to 360° — and long range, their mechanics require regular maintenance and are large, heavy, and expensive to produce. Thus, mechanical LiDAR systems solve only the performance side of the two major demands placed on the sensor industry.

Another approach to meet these challenges is MEMS (microelectromechanical systems) technology. Here, components are produced in silicon, which has the advantage of scalability: since this technology has been tried and tested over many years, identical components can be produced in a cost-efficient manner and in large quantities. This approach is also used, among other things, in the production of microsensors.

But how do MEMS-based LiDAR systems meet the challenges of performance?

Long range with the help of the right laser source

For autonomous vehicles to be able to travel at high speeds, they must be able to “see” and perceive the world around them — not only in their immediate vicinities, but also at greater distances. This is particularly important when driving on highways, as vehicles are moving faster and therefore objects, bends, and other vehicles must be reliably detected at greater distances in order to be able to react in good time. Sensors therefore require a long range in order to enable autonomous driving at highway speeds.

In order to achieve this range with a LiDAR sensor, either the emitter or the detector needs to be optimized specifically for this application.

One possible starting point for such adjustments is the laser source. Typically, lasers with two different wavelengths are used in LiDAR sensors. Some LiDAR manufacturers rely on fiber lasers with wavelengths of 1550 nm. This wavelength cannot be focused by the human eye and can thus be used in an eye-safe manner even at high energy levels. This results in a longer range — the more energy used, the further the device “sees”. However, this type of laser source also has a decisive disadvantage: 1550 nm lasers are large and complex to manufacture, which leads to higher prices and large LiDAR housing dimensions.

Many LiDAR applications therefore use laser diodes that emit laser pulses with wavelengths of 905 nm. These have the distinct advantage of being very small and having been used for a long time in a wide variety of applications. As a result, these diodes are inexpensive and available on the market in large quantities. However, eye safety regulations require that the beam strength of the diodes be lower than that of 1550 nm lasers. The optimization on the emitter side is therefore limited.

 

Searching for the right mirror size

So how can the detector be optimized? Here the aperture plays an important role in achieving long ranges. It describes the size of the detector. In the case of our MEMS-based design, the aperture corresponds to mirror size. In order to capture as much light as possible, a large aperture — in other word as large a mirror as possible — is required. However, mirror size is also limited by certain factors – and so it is necessary to calculate the optimal mirror size while taking these into account. These factors are: photon number to be received, collimation, deflection angle, and resonance frequency.

Photon number

On the one hand, the size of the mirror used in LiDAR unit depends on how many photons have to be emitted in order for a sufficient number of photons to come back, thereby detecting an object. This minimum number of photons can be calculated accurately based on the link budget. This measure includes how many photons are lost at distance and through low reflective surfaces, homogeneous scattering of light, and detector inefficiency. In this way, it is possible to calculate how many photons must be emitted, or how large the aperture must be so that a minimum number of photons can be detected again. In addition, Blickfeld sensors have a coaxial design, which means that only the light that comes back from the same direction in which it was emitted is recaptured. This is advantageous in that it prevents other random light signals from being picked up and disturbing or falsifying the images.

Collimation

In order to obtain high-resolution data that reliably identifies even small objects, the lasers must hit objects in a collimated form. This collimation is achieved by placing a lens in front of the laser. Now the mirror size comes into play again: a mirror must be exactly large enough to deflect all the light collimated by the lens. This depends on the focal length required for optimal collimation and thus high resolution.

Resonant frequency

MEMS mirrors oscillate at a certain resonant frequency. They are triggered by integrated actuators and therefore do not require motors or any other mechanical means. This is a clear advantage because motors and moving parts quickly wear out and require regular maintenance. These problems do not arise if the oscillation is triggered by integrated actuators.

The resonant frequency at which a mirror oscillates depends on the size and mounting of the mirror. For this purpose we have developed a proprietary technique for embedding the mirrors in order to be able to use particularly large mirror sizes. Due to these unusually large diameters, a large number of photons can be directed into the surroundings and back onto the detector, which allows Blickfeld LiDAR sensors to achieve accurate a long range. In addition, thanks to their larger size, these mirrors are more robust than conventional products, which are only a few millimeters in diameter. Mirrors used in Blickfeld LiDARs also have high resonant frequencies due to their lightweight construction, which ensures that the greatest possible number of photons are returned to the detector: if the mirror oscillates too quickly or too slowly, photons will pass the detector due to the coaxial structure.

MEMS technology specifically designed for LiDAR applications

In conclusion, mirror sizes are determined by a wide array of factors. In order to build the most high-performance LiDARs based on MEMS, mirrors must have specially developed compositions, sizes, and embeddings. And only if the MEMS technology is specifically developed with LiDAR applications in mind, can the requirements of a long range, a wide field of view, and high resolutions be achieved.

 

 

 

Blickfeld Team Photo

Looking Back: This Was 2019

If we had to give 2019 a title, it would be “growth”: Our product family has grown, we have built up our production and significantly expanded our team. And an end to growth is not in sight!

Before 2019 is over, we want to take a look at some of the events of the last twelve months. This was 2019 for Blickfeld:

Turning one into two

The expansion of our product family with our long-range sensor, the Cube Range, was certainly one of the most important steps for Blickfeld this year. We can now offer a full automotive LiDAR suite: The “family eldest”, the Cube, covers the middle- and closer-range vehicle environment with a wide field of view. This is particularly important for urban driving scenarios, where many road users are involved, all of which must be detected by the sensor. The new Cube Range complements the Cube with long-range detection, which reliably detects even dark and low-reflecting objects at great distances and in high resolution.

cube and cube range


Blickfeld on Tour

The Blickfeld year started in Las Vegas. At CES 2019, Blickfeld was to be found at several booths, including Leddartech, LiteOn and Koito. We enthusiastically immersed in the CES world – our conclusion: All autonomous everything. Click here for our report on CES 2019.

But CES was not the only big fair Blickfeld was present at this year. Industry get-togethers such as AutoSens in Detroit or Brussels and the IAA in Frankfurt also were an integral part of Blickfeld’s event calendar. In addition, there were numerous other events all over the world where  Blickfeld was present with a booth or where our LiDAR experts spoke.

Blickfeld sparkles

It is always important for us to know that we are on the right track with our products and our strategy. The fact that we have won important awards and prizes this year confirms that the autonomous mobility of the future is moving ever further into focus and affects us all. We would particularly like to highlight the German Innovation Prize, the European Start-up Prize for Mobility, the Start me up Founder’s Prize and, most recently, “The Spark”, awarded under the patronage of the Federal Ministry of Economics and Energy.

start me up 2019

Blickfeld won the German Innovation Award in the startup category

Chip Production

Ready to ramp up

2019 was also an important year on the way to series production of our LiDAR sensors. We have teamed up with a production partner who has many years of experience in the manufacture of optoelectronic products in the automotive sector and with whom we have built up a highly automated production line.

Focus on vehicle design

At the end of May, we were happy to announce that we are working together with the Japanese Tier One automotive supplier Koito to integrate our solid-state LiDAR into car headlights. Together, we are working to seamlessly integrate the sensor to not disturb the vehicle design.

team

Blickfeld Team Photo

An end to growth is not in sight

Our total team size has increased by an incredible third! In January, with a total of 61 colleagues, we already had a considerable team size for a start-up less than two years old. We will end 2019 with 99 employees. It’s a good thing that we anticipated this growth and expanded our office in the heart of Munich at the end of last year.

We are ready for 2020!

We are extremely pleased with the results achieved, very grateful to our team for their tireless commitment and look forward to continuing our good cooperation with our customers and partners next year.