“A good example of these physical laws is the operation of a microwave. If the appliance is connected to a socket with mains voltage, an electric field is present. As soon as the microwave is switched on and current flows, in other words, electrically charged particles move through the current-carrying conductor, this movement produces a magnetic field. The interaction of these two fields results in an electromagnetic field that expands through space like a wave. This phenomenon is like when a stone falls into water. Electromagnetic fields behave in space like the waves that result on the surface of water from a stone. These fields also expand in a wave-like form and can, to stay with the example of a microwave, interfere with the Wi-Fi reception of a smartphone or tablet,” explains Dominik Schröder, research scientist and doctoral candidate in the “Smart Wireless Systems” department who works with electromagnetic fields at Fraunhofer ENAS in the Paderborn office.
Omnipresent: surrounded by electromagnetic fields
The appearance of electromagnetic fields is not limited to residential environments alone, however. We are surrounded by them every day and everywhere: “At the office, we naturally use Wi-Fi to search for information quickly in the internet or to communicate with colleagues via web conferences. When we are on the go, we can be reached by telephone at all times or listen to music via Bluetooth headphones thanks to our mobile companion, the smartphone. In the medical field, magnetic resonance imaging (MRI) is used to visualize internal structures of the human body and detect diseases. Electromagnetic fields also occur within our own four walls – regardless of whether we are doing laundry, listening to the radio or using the microwave,” says the scientist.
Electromagnetic fields are not limited to anthropogenic sources, in other words, sources artificially created by people, though. These physical force fields also occur in nature. If an electric discharge happens during a storm, for example, the resulting lightning creates an electromagnetic pulse that spreads out in the form of a wave. The earth’s magnetic field is another typical example of such a naturally occurring field that protects from cosmic radiation from outer space.
“Electromagnetic fields not only occur in large dimensions but also on a very small scale. Several billion transistors are installed on a single semiconductor chip, for example. Our modern, technologized world would not be able to function without them. If their individual electromagnetic fields do not interact harmoniously but interfere with each other, it produces a dilemma,” explains the Fraunhofer researcher.
Invisible but real: detecting interfering electronic fields with measurement technology
This is precisely one of the greatest challenges when using state-of-the-art technologies: When the expanding electromagnetic waves of a component meet the waves of other electric or electronic devices and thus further electromagnetic fields, superposition can cause an increased interference pulse. This interference pulse, which is also referred to as unwanted electromagnetic coupling or interference, makes itself known as static on the radio, on tablets or in headphones, for example.
It becomes dangerous when such interference sources limit the functioning of entire systems or cause them to fail completely. “In vehicles, for example, a multitude of components interact to ensure our safety and that of pedestrians via driver assistance systems. If a malfunction occurs due to unwanted electromagnetic interferences, the function of braking assistants could be affected, preventing a braking operation from being properly initiated – with fatal consequences for other road users. A similar phenomenon is also known from aviation: Mobile phones have to be turned off during starting and landing maneuvers in order to prevent unwanted interferences with the sensitive onboard electronics, such as navigation systems, and thus risks to passengers,” explains the researcher.
To prevent exactly that from happening, the scientists at Fraunhofer ENAS at the office in Paderborn are detecting such error sources that can lead to risky interference pulses. In doing so, they have an eye on interference factors between different electric and electronic objects as well as within a closed system. The reason for this is because the increasing miniaturization of systems means that more and more components are being arranged in smaller and smaller spaces. This growing density and complexity increase the susceptibility of the overall system to errors due to unfavorable interferences.
The detection work of the researchers is supported by the near-field scanner developed in Paderborn. It is able to detect above all strong, but also weak and inconspicuous interference fields, contactlessly, automatically and extremely precisely in the direct vicinity of the interference source, in the so-called near field, and to present them in a structured and clear manner.
In this way, the scientists overcome the barriers of existing investigation methods: “Established test methods and solutions for identifying interference sources frequently work according to the principle of trial and error and are very tedious, expensive and time-consuming. In the end, it remains unclear whether searching for causes using functional experiments leads to a meaningful result. A product has to be continually redesigned in the development and design phase of technologies in order to eliminate errors as the source of undesirable force fields. The resulting new geometries or arrangements of individual components in turn harbor the potential for new unintended errors – this unnecessarily costs time and poses a major obstacle when launching products on the market,” explains Dr. Christian Hedayat, head of the “Smart Wireless Systems” department at Fraunhofer ENAS.
This process is considerably accelerated by the near-field scanner technology of the Fraunhofer researchers: With the help of this technology, error sources can be precisely determined and exactly localized in a component. For this purpose, the researchers rely on the near-field scanner NFS3000 developed at the institute. This makes it possible to visualize electromagnetic fields in the range of 0 Hz to 90 GHz and thus low-frequency as well as high-frequency fields locally resolved from a few millimeters to centimeters above the test object. The positioning system of the NFS3000 with its spatial measuring range of 50 centimeters x 80 centimeters x 50 centimeters makes it possible to study measuring objects on the wafer level and component level as well as to measure complete electronic devices as well as antenna and radio technologies.
“For these measurements, we use specialized near-field probes. They are moved above the measuring object with a positioning accuracy of one micrometer and scan the component to be tested with high precision and in every spatial direction (x, y and z direction). If an even more specialized probe is required for the measuring object, a special application case or frequency range, we also develop this together with our customers,” explains Christian Hedayat.
Fraunhofer Institute for Electronic Nano Systems
