Once again, the inventors showed remarkable creativity," comments jury chairman Prof. Dr. Andreas Schütze. "And the selection was no easy task this year either." This is also reflected in the fact that fourinstead of three of the 35 applications were shortlisted.

For the AMA jury, made up of representatives from science and industry, what counts when awarding the prize is not only the level of innovation and originality of the solutions, but also their market relevance and timely implementation in competitive products. The award goes to the developers themselves, not to their companies or institutes. The final winner of the €10,000 prize - either a single winner or several winners - will be announced at the opening event of Sensor+Test on June 26, 2018 in Nuremberg.

Miniaturized environmental sensor

The BME680 sensor measures four environmental variables simultaneously.

© SystemPlus Consulting

Dr. Richard Fix from Bosch Sensortec impressed the jury with an environmental sensor that records four different measured variables in parallel: Ambient temperature, air pressure, relative humidity and air quality. The BME680 uses the concentration of certain trace gases, in particular volatile organic compounds (VOCs), which often evaporate from plastic parts, furniture and cleaning agents and can have an adverse effect on well-being, as a measured variable for the latter.

This requires a sensitivity down to the ppb range. The sensor uses a metal oxide thin film for measurement, which is heated to 200 to 400 °C and thus becomes semi-conductive. Its electrical resistance changes depending on the gas concentration. A special surface coating ensures that the sensor only reacts to a single or a few target gases. The temperature measurement of the BME680 is not affected, as the air quality is measured with a separate chip in the same housing.

A silicon diode measures the temperature. Humidity is determined using a polymer whose dielectric constant changes depending on the proportion of water in the air. For pressure measurement, the BME680 uses piezoresistive elements on a thin membrane. With a resolution of just 12 Pa corresponding to a height difference of 1 m, this makes height localization much more precise than using GPS satellite signals. The system uses an app to query the local air pressure on the ground. The difference to this, which the sensor determines, is a measure of the height above the ground, such as the floor in a building. A device worn by an athlete can use this to determine whether they are running uphill or downhill on level ground, which in turn can provide information about calorie consumption.

Each unit is calibrated at the factory and has a long service life thanks to internal compensation algorithms. The sensor is particularly suitable for smartphones, wearables and home automation.

Highly accurate flow measurement

Coriolis mass flow sensor with drastically reduced measuring error thanks to multi-frequency technology.

© Endress + Hauser Flowtec AG

The flow of liquids and gases can be measured in various ways, for example using the Coriolis effect. This involves setting a U-shaped pipe into mechanical vibration. If a medium moves in a radial direction, the vibration begins to wobble, so to speak. Acceleration sensors at two different measuring points evaluate the signals, between which a phase difference is now formed that is proportional to the mass flowing through per unit of time. To save energy, the control electronics excite the pipe with a mechanical resonance frequency. This frequency depends on the density of the medium flowing through and is determined by the control electronics.

Such sensors have been manufactured in large quantities and in many different designs for decades. They work very accurately with homogeneous media, their measurement uncertainty is only 0.1 %. However, problems arise with liquids with trapped gas bubbles. These include crude oil, which often contains natural gas, and carbonated drinks. Such liquids are compressible, which means that the gas bubbles are compressed on one side of the measuring tube and expanded on the other; the measurement becomes inaccurate.

Wolfgang Drahm's team at Endress+Hauser Flowtec AG in Freising has found a solution to this problem. Their Promass Q sensor works with multi-frequency technology: an exciter causes the pipe to vibrate simultaneously at two different natural resonance frequencies, usually around 200 to 300 Hz and around 1,000 Hz. Each frequency provides its own measurement signal. Both are initially subject to errors, with the deviation being greater at the higher frequency.

An algorithm developed for this purpose calculates a much more accurate final value from these two "incorrect" values. The flow here passes through the outer curved tube, which contains two inner tubes that are excited in antiphase. This keeps the vibration largely inside. The straight tube in the middle is only used for mechanical stability; nothing flows through here. While conventional Coriolis sensors deliver errors in the order of 10% even with gas contents of just 1 to 2% of the volume, the Promass Q still works accurately to within a few parts per thousand at 10%.

This is particularly useful in the chemical industry for oils and waste water, in the food industry for beverages, but also for more viscous media such as ice cream - nobody gets the wrong quantity delivered.

Siloxane-resistant multi-pixel gas sensor

Long-term stability thanks to resistance to siloxanes: the SGP-MOXSens gas sensor.

© Sensirion

Metal oxide-based gas sensors are widely used, not only as individual elements but also in the form of arrays. If the individual pixels in these are given different characteristics, different gases can be measured simultaneously using pattern recognition - down to the sub-ppm range. Such sensor arrays are well suited to monitoring breathing air quality indoors, especially in offices. Here you often have to deal with vapors from equipment, furniture and carpets - the volatile organic compounds (VOCs) mentioned at the beginning.

However, the metal oxide sensors degrade over time; their sensitivity decreases and they display readings that are too low. A laborious recalibration or replacement is then unavoidable. This is caused by so-called siloxanes - chain molecules consisting of alternating silicon and oxygen atoms with hydrogen atoms or hydrocarbon groups attached to them. They are often found in workplaces because IT devices with plastic housings, such as cell phones and laptops, release them. In practice, there are many different variants of this group of substances. Their concentrations are usually in the ppb range.

The Sensirion working group led by Dr. Felix Hoehne has now succeeded in developing a type of gas sensor that is particularly resistant to these siloxanes and has significantly improved long-term stability. The SGP-MOXSens (Fig. 3) contains the complete sensor system on one chip, including analog and digital signal pre-processing, temperature and humidity compensation and storage of calibration data.

The small housing contains four different metal oxide elements (pixels) in the form of porous nanoparticle films on a micro-heating plate, together with the associated ASIC on a chip. By offsetting the individual signals, selectivity is improved and several gases can be measured simultaneously. Thanks to a very small thermal mass, the response time is 50 ms and controlled temperature profiles can be run over a range of several 100 °C.

Thermometer with automatic in-situ calibration function

Simple self-calibration with permanently installed, stable reference element: iTHERM TrustSens TM37x temperature sensor.

© Endress + Hauser Wetzer, curve diagram: Landolt-Börnstein

In the chemical, pharmaceutical or food industry, there are technical processes in which the prescribed temperature must be maintained with very high accuracy. As the usual temperature sensors are not completely free from long-term drift, they must be checked and calibrated at regular intervals, approximately every few months.

Phase transitions of certain substances are used as reliably reproducible fixed points. These are often melting or boiling temperatures, for example a high-purity water-ice mixture for the temperature 0 °C. However, the calibration process is very complex and time-consuming; the sensor has to be removed and inserted into the calibration apparatus, during which time production comes to a standstill. With hundreds to thousands of thermometers in a large company, this results in high costs and loss of revenue.

Alfred Umkehrer from Endress + Hauser Wetzer in Nesselwang developed a pioneering sensor with self-calibration in cooperation with Innovative Sensor Technology IST. The necessary basic research had previously been carried out at Ilmenau Technical University. In the iTHERM TrustSens TM37x product, an element with a physically constant temperature reference is permanently installed. As the melting or boiling points of substances are difficult to handle, self-calibrating thermometers use a different type of fixed point: a phase transition between two different states of a solid.

Umkehrer chose a ferroelectric ceramic material with a material-specific Curie temperature of 118 °C for his thermometer. If the temperature exceeds this value, the polarization disappears. At this point, the dielectric constant is very high, and it also changes by several hundred percent with minimal temperature fluctuations. The iTherm exploits this effect. The temperature at which the dielectric constant has a very specific value serves as the reference temperature.

The reference element is hermetically encapsulated and permanently installed in the sensor, together with the associated electronics. This means that uncomplicated self-calibration is now possible without having to remove the sensor from the system.

Support for young entrepreneurs

In addition to the main prize itself, special prizes will also be awarded to young entrepreneurs in the form of a free exhibition stand at Sensor+Test. The condition is that the start-ups have been on the market for no longer than five years, have fewer than 50 employees and generate an annual turnover of less than 10 million euros. This year there are three.

• Dr. Matthäus Langosch (CeLaGo Sensors, Saarbrücken, and Saarland University of Applied Sciences): Thin-film film strain gage, which makes it possible to use flexible, highly sensitive and application-specific strain gage shapes for sensitive, energy-saving and robust sensor systems.
• Houssam El Moutaouakil (Senvisys, Saarbrücken): Efficient wireless safety of railroad crossings through vibration analysis supported by artificial intelligence.
• Theresa Ebeling (HygNova, Berlin): HygNova Advance helps medical institutions reduce hospital infections by increasing hand disinfection rates