Sensor Technology - Trends
Superhuman Senses
Sensors can detect a vast range of microscopic particles and identify odorless gases. Destined to become smaller and smarter, they will one day even be able to recognize one another and form networks.
Siemens researcher Dr. Maximilian Fleischer presents a new gas sensor that measures the amount of carbon dioxide in the air. CO2, which is used in today`s air-conditioning systems, is an odorless gas that can cause unconsciousness and even death when present in excessive concentrations
As any child who has ever touched the burner on a stove knows only too well, our fingers are pretty poor temperature sensors. High speeds, too, can pose problems for our senses. Above a certain velocity, the human eye is incapable of recognizing even the closest of friends in a train rushing by. Not to mention our sense of smell. We cant even detect the odor of many of the gases that are dangerous to us.
By contrast, highly developed artificial sense organs are able to feel, see and smell as much as 1,000 times more precisely than any human. Whats more, they can do so in the most adverse conditions. Today, sensors are an integral part of our everyday life. A modern car, for example, is equipped with around 100 of these tiny components. Of increasing importance here are so-called MEMS (Micro-Electro-Mechanical Systems), sensors which combine microelectronics with micromechanics and other technologies to form new systems. Sensors also play an important role in manufacturing, quality assurance, environmental technology and healthcare. Today, the companies gathered in the German trade association for sensor technology market 100 different types of sensor systems, and the industry is booming. In fact, the world market for civilian sensor systems is forecast to grow to a volume of around $50 billion a year by 2008 (see Facts and Forecasts).
Sensitive Textiles
Technology from ElekSen makes it possible to manufacture flexible sensors and switches that can be integrated into everyday objects such as cell phones, toys and car seats.
According to Ray Sangster, CEO of Britains ElekSen, digging around in your bag to find that ringing cell phone or to skip a track on your MP3 player might soon be a thing or the past. "One of the most promising applications for our technology is clothing that can be used to operate electronic devices," says Sangster, pointing out that ElekSen has developed textile sensors that can be integrated into all types of "soft" materials and could enable users to operate cell phones, PDAs and MP3 players by simply touching their sleeves.
These sensors possess a sandwich structure in which the external layers consist of conductive nylon sheets that are glued together with an adhesive. A layer located between the external layers contains individual conductive fibers, which are incorporated into an insulating material. The system works as follows: A low measuring-circuit voltage is applied to the layers by the device (for example, an MP3 player) or by a battery. If the sensor is touched, the pressure establishes a connection between the conductive layers, making it possible to measure where the sensor is being touched. The strength with which the sensor is pressed can also be determined. As the pressure increases, more conductive fibers touch each other. The result is a stronger electrical current.
This technology could be used, for example, to produce "smart" toys. A doll with a built-in foldable sensor could burp when patted on the back, cry if it is hugged too strongly or laugh when it is tickled. However, the foldable sensors can not only detect pressure, but also humidity. As they are washable and very robust, they would be ideally suited for the healthcare sector, where they could, for example, determine if an incontinent patient needed new bed linen or if a patient has left his or her bed. Car seats that adapt themselves to accommodate different drivers backs are another possible application. One of the main strengths of ElekSens textile sensors is their versatility. But this versatility also presents a challenge. "The wide range of potential uses is forcing us to focus on certain areas," says Dr. Uwe Albrecht, Head of Corporate Funding at Siemens Venture Capital GmbH, an important investor in ElekSen.
A further developmentindividual sensor fibers that can be woven into textilesmay well also contribute to market success. Sangster is hoping for big opportunities, especially since development of the sensors has already taken four years. "ElekSen is now working together with 82 different companies," says Sangster. "To raise that figure, well have to make people aware of potential new applications." Examples of such applications include flexible keypads for mobile phones and automotive controls that are integrated into car seats. In fact, the only limit to their application is imagination.
Stefanie Hense
Cutting Fuel Consumption, Emissions and Noise
A piezo sensor developed by Siemens VDO can be integrated into a glow plug to directly monitor combustion in diesel engine cylinders. The sensor could be ready by 2006.
The more precisely the combustion processes in an engine can be monitored, the better the engine can be managed by adjustment of the amounts of fuel injected and the ignition points. This in turn can reduce fuel consumption and exhaust emissions, as well as lowering noise levels, according to Gérard Troy and Dr. Bernd Last, who are responsible for Business Development and Pre-Development Activities at Siemens VDO in Toulouse, France.
Current monitoring methods use measurements from the engines periphery, such as coolant temperature, amount of manifold air, or engine r.p.m. It would be more effective, however, to measure pressure changes directly in cylinder, since they are closely related to the thermodynamics of the combustion process. "This kind of information is important because it will help us meet new emission limits for diesel enginessuch as Euro Vthat will go into effect in the next few years," says Troy. "But its also useful for gasoline direct injection." The best way to measure combustion pressure is to use a sensor installed directly on or in the combustion chamber. However, the space available for such a sensor is very limited in modern engines, with their multi-valve technology.
It is often necessary to bore additional holes for the sensors. With this in mind, Siemens VDO in Toulouse developed a sensor that can be directly installed in a diesel engine glow plug. "What were doing is using a combustion chamber access point thats already there, which means its very easy to equip existing engines with the sensor," Last explains. The glow plug facilitates cold starts in diesel engines, where air is sucked in and compressed so strongly in the combustion chamber that it heats up to 900 °C. The diesel fuel that is then injected immediately ignites when it makes contact with the hot air. Because its integrated into the glow plug, the sensor membrane is not directly exposed to the heat and pressure that develop in the combustion chamber. The sensor therefore lasts longer and its measurements are more precise. The innovative sensor element is made of a heat-resistant ceramic and functions using the piezoelectric effect.
Under pressure, the ceramic material changes its atomic structure within a few milliseconds, displacing electric charges in the material itself. The sensor thus emits electric signals that the control electronics use to monitor pressure changes in the cylinder. "Mass production of the glow plug sensor is scheduled to begin in 2006," says Troy. " We have already established a partnership with Federal Mogul to jointly develop and market glow plug sensors".
Sylvia Trage
Operating at around 1,500 °C. Siemens has also placed a high priority on sensor technology as a field that cuts across many areas at Corporate Technology (CT). Indeed, Siemens has pioneered the development of sensor systems, and today the tiny devices are entering areas into which no human could ever venture. For example:
A new type of sensor is now being used to analyze gas concentrations in combustion chambers and dusty factory chimneysat temperatures of up to 1,500 °C (see Gas Sensors).
Sensors inside industrial gas turbines monitor the huge turbine blades as they rotate at 3,600 r.p.m. (see Defying the Inferno).
Sensors inspect the overhead lines of rail vehicles and are able to detect tiny traces of wear and tear in the wires at a speed of 80 km/h and in complete darkness (see Facts and Forecasts).
X-ray sensors scan tiny computer chips for defects and enable a virtual 3D flight through the layers of the component, even detecting flaws on the nanometer scale (see Optical Sensors).
Destined to become smaller, more versatile and more accurate, tomorrows sensors will be able to take on even more complex tasks. The drive toward smaller and cheaper components is one of the major trends in sensor development, as manufacturers move toward miniaturization in order to simplify production and reduce costs. At the same time, smaller dimensions generate new applications in the sensor market. Potential examples here include a healthcare diagnostics system the size of a check card (see Biosensors) and minuscule sensors which, when mixed with paint and applied to interior walls, will monitor the climate in buildings (see MEMS).
Closer to market launch is an astonishing development from the Fraunhofer Institute for Silicon Technology in Itzehoe, Germany. A disposable sensor in the form of a pill enables athletes to determine lactic acid levels, thus helping them to determine their current fitness. "The athlete puts the pill in his or her mouth and then starts the training program," explains Institute Director Prof. Anton Heuberger. "During the training session, the sensor continuously measures lactic acid levels and transmits the data via Bluetooth to a reader unit." This saves on blood tests and provides continual monitoring. The pill sensor is due to come on the market in 2006.
Electronic Doctor. According to Heuberger, however, there are limits to miniaturization: "Sensors of a few millimeters in length are realistic," explains the Professor of Microsystems Technology. "Anything much smaller is certainly technically feasible but still illusory from a financial aspect." Ultimately, he emphasizes, to be successful, technology must be affordable. "A sensor component that is extremely small but still costs over 10 is just too expensive."
A further trend is to integrate a number of sensors in one system, which can then measure a number of variables at the same time. Such applications could have a big future in the field of healthcare. "Our vision is to combine a number of chips in one package, which will be able to provide rapid and early diagnosis of a whole range of diseases," says Prof. Bernhard Boser, a Director at the Sensor & Actuator Center at the University of California in Berkeley. "This could radically change the face of healthcare." The Swiss scientist and his team have already developed a biosensor that is capable of accurately identifying one conditiondengue fever, a serious viral disease found in the tropics, which strikes 100 million people every year. The test for dengue fever merely involves putting a drop of blood on a sensor chip one square millimeter in size and inserting the latter into a laptopa simple, flexible procedure that could conceivably, at some later date, be used by anyone. In the long term, Boser explains, "people who suspect they have the flu, for instance, should be able to buy a test, just like a pregnancy testing kit, and then go to a physician if it proves positive."
Dr. Walter Gumbrecht from Siemens CT has developed a similar biosensor. Quicklab, a mini-laboratory in check card format, examines a persons drop of blood within the space of an hour for traces of pathogens. Using quicklab, physicians would be able to diagnose an infection on the spot and therefore prescribe the right medication much more rapidly than today (see Biosensors).
However, while high-tech sensors are often much more powerful than the human senses, our eyes, ears, noses and hands do have one advantage over technology: They are connected with a brain and can thus benefit from a unique source of know-how. For example, some sensors have problems distinguishing certain things. "For a long time, natural gas sensors would react not only to carbon monoxide but also to the vapor of any naphtha cleaning agent in the air," explains Dr. Udo Weimar, a specialist for biosensors and chemosensors at the University of Tübingen. "We therefore need to come up with sensors that are highly selectivein other words, sensors that react to only one substance." (see interview)
Sensor Networks. Moreover, as Michael Staudt from Siemens Automation and Drives explains, the intelligent sensors of the future will be able not only to transmit signals but also to interpret events. In fact, this is exactly what CS10, an optical sensor developed by Staudt, does when it reads complex color patterns (see Optical Sensors and picture below). The sensor is designed for use in environments such as filling plants, where it can monitor colored labels on bottles every 30 ms and sound the alarm in the event of an error.
Histogram produced by an optical sensor which is capable of interpreting highly complex color patterns in milliseconds
A further trend is the attempt to make sensors work independently in a similar fashion to highly complex biological systems such as the human brain or immune system. The aim is that sensors should become autonomous and self-organizing, and that they should be able to independently determine their precise location, communicate with one another via radio, and establish and maintain a network without any outside support (see Pictures of the Future, Spring 2003, Sensor Networks). Dr. Rudolf Sollacher from Siemens CT is working on just such a project. For example, his sensor network would be able to guide a fire crew to the source of the blaze inside a building and also provide information on the ambient temperature (see Sensor Networks).
"Self-organizing sensor networks are already technically feasible," says Sollacher. He identifies further applications in agriculture or in areas at risk from forest fires or avalanches, where sensor networks could provide early warning of an impending catastrophe. Here, sensors located throughout the risk area would independently gather all the data required. "But thats still some way off," admits Sollacher.
Continual Tire Monitoring
A new sensor measures tire pressure and temperature. Although minuscule, it could make a big contribution to road safety.Defective tires are a common cause of serious road accidents. A frequent problem is insufficient tire pressure. In extreme cases, the resulting deformation to the tire makes it heat up so much that it melts and bursts. Regularor, ideally, continuousmonitoring of tire pressure is the only way to avoid this. Indeed, millions of vehicles are already equipped with pressure sensors designed to warn drivers that tires are dangerously short of air. In the U.S., there are even moves to make such sensors compulsory from 2006 onward. The battery-powered sensors are mounted on the valve, inside the wheel rim. Once the vehicle has traveled a certain distance, they start to register tire pressure and temperature, and transmit this data to a central receiver unit.
Unfortunately, such sensors are complicated to install. Moreover, if the brakes significantly heat up, this can cause the wheel rims to become hot, thereby falsifying the temperature reading. Together with Goodyear, Siemens VDO has now unveiled a new generation of tire-pressure sensors that really deserves to be called a diagnostic system. The electronics, which are the size of a fingernail, are mounted on a sturdy, heat-resistant ceramic base and consist essentially of so-called bare diesin other words semiconductors without the standard black plastic packagingonly a few square millimeters in size. Using this type of construction, Siemens engineers were able to integrate pressure and temperature sensors, along with evaluation electronics and a memory, in a very small space. The memory, which also marks a new advance, records pressure and temperature data, tire operating life and changes to tire pressure over time. In addition, it communicates with the onboard electronics, providing the systems responsible for vehicle stability (ABS, ESP, ASR) with up-to-date information on tire condition.
Researchers have developed a sensor that constantly monitors tire pressures and temperature. The sensor and its associated electronics are so compact that they can be built into tires. Sensor data is transmitted to receivers in the wheel arches
The complete sensor system is mounted on a rubber ring, which runs around the whole tire and also incorporates the antenna. The ring, which is not heavy enough to affect the running properties of the tire, is joined inseparably to one of the side walls. As a result, the electronics no longer have to be mounted to the wheel rim in addition to the tire and then transferred to another wheel whenever a tire is changed. Similarly, the new system automatically communicates all the details of the type of tire, thereby obviating the need to reset the onboard electronic systems following a tire change. A transmitter-receiver unit mounted in each wheel arch receives data from the sensor, provides it with control pulses and feeds it with energy. As both data and energy transmission take place inductively via coils in the chip and the wheel arch, a battery is no longer required. Whats more, the sensor registers the tire pressureor a flatas soon as the driver turns the ignition key, and not, as in the past, only after the vehicle has traveled a certain distance. Dieter Wagner, Project Manager at Siemens VDO, says that this is only the first step toward the truly intelligent tire. "Before long, sensors will be able to detect defects in tires. Theyll be able to measure tread depth, slip on wet roads and the forces inside the tire."
Bernhard Gerl