LEDs for Fitness Tracking & Health Monitoring

The OSRAM Podcast: Episode #6 with Christoph Göltner

Welcome to the Photonstudio, the OSRAM Podcast. My name is Dieter Schierer, I am an OSRAM employee working in the field of digital communication and I am pleased to present the new episode on biomonitoring with light. It is impossible to imagine everyday fitness life without them: Smartwatches and Fitness Trackers that record the pulse, calories burned, oxygen saturation in the blood and many other biological measurements during and after the training. What was reserved for the professional sport in the last decades has arrived in our everyday life.

The individual biomonitoring. The striving for performance and self-optimization is as old as mankind itself. Whether it is the Olympic motto "higher, faster, further" or the desire for beauty. And as in all our podcasts, light plays a crucial role when it comes to measuring vital signs. How and which light is used in the fitness trackers and which trends we can expect in the future will be revealed by my guest in the photon studio today: Dr. Christoph Göltner, Marketing Engineer for Vital Sign Monitoring at OSRAM's Opto Semiconductors business unit. Today he joined us from Sunnyvale in California.

Dieter: Christoph, I am very pleased that you are our guest in the Photonstudio today!

Christoph: Dieter, thank you very much for giving me the opportunity to advertise for the Sensor Group at OSRAM OS.

Dieter: Christoph, you are working for OSRAM Opto Semiconductors, one of our business units in America. You are a Marketing Engineer for Vital Sign Monitoring. But what exactly does it mean when we talk about Vital Sign Monitoring?

Christoph: Originally this market segment was called Wearables and it goes back to Fitbit Trackers and Smartwatches, which were launched about five years ago and have been a great success. It is one of the largest growing markets in consumer electronics. Optical sensors are important here because they can give much simpler and much more accurate readings of body condition. The best example is certainly the heartbeat. Previously, the pulse rate was measured electrically with chest straps and electrodes. Of course, it is much more uncomfortable to run around with a chest strap than with a watch on your wrist. OSRAM is very well positioned here in Silicon Valley. The main impulses for innovations come from this region.

Dieter: All top models of the Smartwatches and the so-called Fitness Trackers are equipped with optical sensors. These are mostly green shining LED's, which you can see on the backside. Could you briefly explain to us what exactly these LED's do?

Christoph: The principle is based on the fact that blood absorbs light. This means that the higher the blood volume, the more light is absorbed. In this case, a green LED brings the light signal into the skin. A part of this light is reflected back and received by a photo diode, which sits directly next to the LED. With very precise measuring electronics a pulse signal can then be derived. With today's electronics and amplification factors it is possible to measure even the smallest signals. However, the challenge is that I have a lot of interference, for example when I move my hand. I then have to make sure that I compensate for these through the software algorithm, so that I can get good information about the target quantity.

Dieter: I would like to know how this works. I also wear a watch like this and it is fascinating how much information the watch can provide. The watch measures my pulse, communicate the anaerobic threshold, measure the oxygen saturation in the blood and measures the length of sleep. I have read that the process of measuring is related to systole and diastole. You will have to explain this to me in more detail. And why do you need a light as a measuring instrument and not just an electrode in the fitness tracker?

Christoph: The optical sensor has the great advantage that it is non-invasive. Green is the color that is absorbed most by the blood. The concept is based on the principle of PPG (Photoplethysmography). This is a principle that ultimately measures the absorption of blood based on blood volume. You have an expansion of the arteries due to the pulse wave that passes through the body. The LED sends a light signal into the skin and the photodiode measures what is reflected back. The minimal difference due to the expansion of the arteries is then evaluated to measure the heartbeat and heart rhythm. The same applies to derived variables. For the oxygen content you use the difference between red and infrared, because the hemoglobin absorbs infrared and red differently. Based on this difference I can then measure the blood oxygen content. So, it is not only green what is used, but green is the most popular wavelength for heartbeat measurement. But the wrist is actually the most unsuitable place on the body. Here you have tendons and bones and actually not so much tissue that is supplied with blood. Therefore, the challenge of measuring on the wrist is particularly great. But thanks to the experience and refinement of the corresponding algorithms, this can be done very reliably today.

Dieter: What influences the accuracy of the measurement? What is particularly important? And what if there are differences in the measurement?

Christoph: Derived are things like the so-called heartbeat variability. What is crucial here is how to measure the pulse curve over time. For this it is very important that I am very precise. Even though I am talking about heartbeat variability, it is about finding the peak of the pulse wave. If I don't find it, small deviations lead to bad results. Therefore, the demands on the optical sensor are immense. This is one aspect where OSRAM stands out from the competition! We have a much deeper system knowledge here and our optical fundamentals are also very solid.

Dieter: The optical modules are constantly being further developed. Two years ago, I read a press release that we at OSRAM had increased the efficiency of green LEDs by 40 percent, thereby reducing the effects of the so-called green gap phenomenon. What does this Green Gap phenomenon mean and what challenges still exist today in the development of new chips for fitness trackers?

Christoph: In my role, I am often asked by the relevant strategy departments how the market and prices for sensors are developing. We expect a typical price reduction per year for almost all components. I then always say exactly the opposite. People then ask me, why is this the case? And I then explain that optical sensors are becoming more and more complicated and costly. The first sensors only had an LED and a photodiode. This means that if the watch wobbles on my wrist, I lose my signal because the contact to my skin is gone. Today, when I take one of the leading Smartwatches apart, I find that there are eight photodiodes and a number of LEDs inside. The principle here is called Multipath. Now I have several light paths from the emitter to the photodiode. The algorithm then compares which signal is best and can derive much better results from 3-4 different signals. The challenge for us is to be able to offer and build such ever more complex sensors in a cost-effective and efficient way.

Dieter: And the green light? What challenges do we find here? And what points are important for customers here?

Christoph: Green light can be generated by various methods. The problem is that no semiconductor combination can be ideally optimized for green. One is always at the end of the spectrum of one or the other material generation. What is also tried in the meantime is to cause a change of light frequency with so-called quantum dots. These are all topics that are being further developed and where OSRAM is also a leader. What is really crucial for the customer is another topic, namely the forward voltage of green LEDs. The Smart Watches will all be battery-powered, and a lithium-ion battery supplies about 3.3 volts. If I have an LED that needs a higher forward voltage, like the green LEDs originally, I either need two batteries or I have to install a voltage pump. So there is a shortening of the battery life time. With our new green LED's, we are able to provide the customer with a product that works without a voltage pump. This is one of the main reasons why more than two thirds of the world market use our green LEDs.

Dieter: Currently, the Corona crisis dominates the reporting to a large extent. I can imagine that the Vital Sign Monitoring applications are now becoming even more important and are helping to monitor patients or people at risk, for example. Do you already have any projects or what is the current state of affairs?

Christoph: The pandemic is an economic and human disaster for the whole world. But of course, there are also positive aspects and in this case, it is true, since the peak of the pandemic I certainly have more than five new projects dealing with Sp02, i.e. the blood oxygen content. The problem here is that such devices all have to be certified accordingly by the FDA (Food and Drug Administration). This sometimes takes half a year or even years. These are issues that most people do not even know about. The main aspect is actually when the big Smartwatch manufacturers talk about how their products help. This refers more to aspects that my health behaviour and the parameters, how my heartbeat changes. And here I can use AI algorithms to detect changes in the processes and then give a warning. In many cases, as a person affected, only notice the symptoms after a certain time. With the appropriate sensors I can recognize in advance that something is going on and make preparations to contain it.

Dieter: The possible applications of optical sensors in the field of Vital Sign Monitoring go far beyond Fitness Trackers and Smartwatches. A few years ago I already talked to a colleague about the topic of measuring water content in the body. He described it to me in such a way that you can measure the water content in the body with a chip, which is built into the ring on the finger. But now I want to know what applications you think will be possible in the near future with optical modules?

Christoph: The forecast is more than bright. It's only been a few years since these fitness trackers with optical heartbeat measurement came on the market. Meanwhile they are standard and have established themselves. I'm always happy when luxury watches from Switzerland incorporate them. Because when I give a CEO a watch and it looks so plastic, I know that he will never wear it. But meanwhile these luxury watches also use these sensors. When it comes to future usecases, optical brainwave measurement is my favorite topic. I am always fascinated when I go to trade fairs and you get a band around your forehead and then you can control things with your concentration.

Of course this is still absolutely inaccurate today. But I am fascinated that I can give mental caused control signals and then evaluate them. One of the really big technology companies has a team here that deals with topics that traditionally all work with EEG. Here you stick electrical contacts on the skin to measure brain waves. The problem, of course, is that I lose my signal if it slips or falls away. Now there are already approaches to do this partly optically, that I can derive the brain wave activities algorithmically similar to the Sp02 measurement. But you had mentioned several other applications. Some are very difficult to implement, water content is certainly one of them. Some start-ups have tried this, but haven't gotten to the point where it is ready for a product. What is clear is that it is physically and physiologically possible. It is actually always just a question of time and whether there is enough business case behind it to finance such a product development. What often appears in the press is the blood sugar content. Diabetics, who have to prick their finger every day, would surely switch immediately to an optical, non-invasive method. I have talked to 5-6 companies over the last three years about this, who claim that they can do it. In some cases, you notice immediately that the physiological basis is not there. But I have met at least one company that has plausibly shown me that it is optically possible. It is only a matter of time until it is brought into a form that is more manageable for the patient and until the cost level is reached to bring the product to market. I would say that within the next five years such devices will be on the market. In today's world, five years is an eternity, but there will also be many new sensor applications that we may not even be aware of.

Dieter: Do you have a concrete example for that?

Christoph: A start-up company in the USA is now measuring the amount of infusion fluid that enters the tissue instead of the bloodstream, where it leads to complications. This is measured with yellow light wavelengths, for example. This is now a marginal example and there are many of these examples. Some of them manage to make it to the mass market. Another example comes from space travel. Astronauts lose muscle mass because they are exposed to gravity.

A small company in Northern Europe uses our photodiode and our emitters to determine muscle mass spectroscopically with two wavelengths. These are all starting points that show how optical sensors are being used for a constantly growing number of applications. This is absolutely fascinating!

Dieter: Christoph, I think you have a really exciting job! But what do you enjoy most about it?

Christoph: A very important aspect is how fast and flexible we are to serve customer requests. We had an inquiry for our sensors with a very large Asian smartphone manufacturer. We had to deliver a concept and a prototype in a very short time. In no less than two weeks, we had delivered the first photodiodes with the corresponding custom configuration. At OSRAM we are able to react really quickly if the team sticks together and can react accordingly. If you can work with the elite of the technology and be respected, I would say it is fun, which you certainly don't have in normal business life in most companies. I can only congratulate anyone who gets into a similar situation!

Dieter: Thank you very much, you have explained a lot to me and with your forecast we can be really curious what is coming up in the area of Vital Sign Monitoring.

Christoph: Thanks Dieter, it was a lot of fun and I hope that the podcast will be heard by many people.

In today's episode of the Photonstudio, Christoph explained to me how the acquisition of vital signs with optical sensors works and which applications and products we will see in the near future besides the widely used smartwatches and fitness trackers. You can listen to this episode and all other episodes of our podcast on iTunes, Spotify, Soundcloud and Google Podcast. Enjoy it and see you next episode of the Photonstudio.

Photonics is THE key technology in every OSRAM solution