Sensor Technology - Building Technologies

What might sound like science fiction is already an everyday reality for Dr. Osman Ahmed, Senior Principal Engineer with the Building Automation unit (BAU) of Siemens Building Technologies (SBT) in Buffalo Grove, Illinois. His department studies the practicality of such ideas. At the core of these systems is MEMS (Micro-Electro-Mechanical Systems) technology—tiny silicon building blocks which can ideally serve as sensors, processors and actuators all in one, and also have radio modules for communication with other devices. As a result, these systems can not only measure environmental conditions and process signals; they can even take action on their own. The first MEMS sensors already exist, carrying out tasks such as measuring the pressure in car tires and transmitting this information via radio to the vehicle (see  Continual Tire Monitoring).

Ahmed is convinced that MEMS sensors’ wireless communication is their greatest advantage. Today’s systems measure the conditions inside a building using sensors and devices mounted on the walls, he says. "All of these devices have two things in common: They need wires to supply them with electricity and wires to transmit signals to a central control unit." But that drives up costs because installation and any fault-finding required are immensely time-consuming. MEMS sensors, on the other hand, do not require wiring and can transmit their signals via radio. Besides reporting climate data, they can also be used to transmit information from fire alarms or even images taken by tiny MEMS cameras. They are also less susceptible to faults. The result is cost-effective, intelligent building automation. "Such tiny sensors could form the backbone of next generation of building systems," says Ahmed. However, alongside easily installable sensors, a new breed of even more powerful computers will be required to process and convert the volume of data from the large number of sensors. "Thanks to the wide range of its activities, and the work of Corporate Technology (CT)—in microsystems, for instance—Siemens has fulfilled all of the requirements for offering the best solutions," says Ahmed.

Monolithic MEMS. One of the goals MEMS researchers are currently pursuing is to create a so-called monolithic MEMS chip that is made from a single piece of silicon instead of using the established practice of transplanting different components onto a silicon substrate. Such systems would have a great advantage—they could be produced relatively inexpensively by using standard semiconductor methods. Researchers hope that these silicon components will function just as reliably as conventional microprocessors. Using exposure and etching techniques, for example, it would be possible to etch tiny arms capable of detecting airflows in the monolithic MEMS, which also contain a microprocessor. The microprocessor would register the vibration signals as a change in voltage. Such a chip could sense and process environmental stimuli, take on control functions and pass on the information.

Here, according to Ahmed, the biggest challenge faced by MEMS engineers is the packaging of the various technical components. The difficulty lies also in protecting the electronics against damage while ensuring that the sensors remain in contact with their surroundings. Because standard miniature housings do not yet exist, Siemens Building Technologies is actively tracking professional organizations such as Memsnet (? www.memsnet.org), a forum that brings developers and users together. The forum’s aim is to develop solutions that would make further miniaturization and new applications possible. Experts at Memsnet expect that the first monolithic MEMS will reach maturity in about five years. In five to ten years the sensors could be ready for use on walls. However, no one can predict the practical value of this development.

But no monolithic silicon MEMS chip is available today that provides all the functionality SBT is looking for. Nevertheless, the alternative to a single MEMS chip that can do it all is no less exciting. It consists of a micro-system platform that integrates a MEMS chip, a wireless module, a microprocessor and an efficient power management system. The advantage of the microsystem is that it can also be produced by using standard semiconductor methods that are matured, stable, and extremely cost-effective. SBT is currently using one-centimeter-square, multiple-component MEMS from Siemens Corporate Technology in a cooperative project with the University of Florida. The sensors will be used to monitor relatively small houses—mouse cages—rather than buildings. Testing of the prototypes will begin in the university’s labs at the end of the year. "Although this application may raise a few eyebrows at first, the underlying aim is actually quite serious," reports Ahmed. Scientists conducting experiments with mice want to make sure the animals’ reactions really are caused by a certain medication or treatment, and are not due to changes in temperature or muggy air. The MEMS measure airborne carbon dioxide and ammonia levels. High levels indicate a risk of suffocation and the need for changing the straw.

These MEMS consist of a silicon substrate with integrated components such as gas sensors or heating elements that measure airflows. Weak electric currents flow through these elements to heat them. When air flows past, it cools them. The researchers plan to further miniaturize the unit and increase its user friendliness before its market launch. They expect to be able to significantly reduce the price of their MEMS unit through suitable packaging and adding wireless data communications. Following a preliminary market assessment, SBT estimates that in the U.S. alone there are about 4–5 million cages. The success of the project could thus give the company a head start in the development of further building management systems in microchip format.

Tim Schröder