As described in a forthcoming paper,* NIST researchers conducted tests in downtown Denver, Colo., to measure precisely the clustering of signal reflections from radio waves bouncing off one or more multi-story buildings multiple times before reaching a distant receiver. The researchers replicated this environment indoors using a “reverberation chamber,” a room with highly reflective surfaces and a big, slowly rotating paddle that automatically alters signal paths.
First, researchers feed a wireless transmitter’s signal into a device called a fading simulator, which is adjusted to re-create the timing and strength of the reflections of an outdoor urban area. The output then is fed into the reverberation chamber, where signal reflections decay exponentially over time, creating a cluster of signals similar to that observed in the field tests.
Industry certification of cell phones currently requires tests of parameters such as total radiated power using the opposite of a reverberation chamber, a room called an anechoic chamber that is lined with materials that absorb radio waves and reflect as little as possible. This testing takes about a day, requiring dozens of measurements of cell phone directional power from multiple angles. By contrast, an equivalent set of tests could be performed in about an hour in a reverberation chamber, according to NIST engineer Kate Remley, a senior author of the new paper. Reverberation chambers also could be used to measure cell phone receiver sensitivity, although currently there would be no time savings for this test, Remley says. Many industry testing practices are established by CTIA-The Wireless Association, the trade group representing the wireless industry.
NIST is studying new applications for reverberation chambers, which have typically been used to measure electronic equipment’s immunity to radio-frequency interference. By adjusting the reflectivity of the chamber through selective use of signal-absorbing material, researchers have found they can “tune” the signal decay time to simulate the conditions found in real-world environments. NIST researchers expect the new method will be useful for test and design of wireless devices such as cell phones, notebook computers equipped with wireless links, as well as new technology such as wireless beacons being developed for the emergency responder community.
The Denver tests were conducted in 2009. NIST researchers measured the power delays between a transmitter and a distant receiver positioned on streets lined with buildings three floors high or taller and a flat, single-layer parking lot. Most buildings were constructed of glass, steel, and concrete.
* H. Fielitz, K.A. Remley, C.L. Holloway, Q. Zhang, Q. Wu and D.W. Matolak. Reverberation-chamber test environment for outdoor urban wireless propagation studies. IEEE Antennas and Wireless Propagation Letters. Forthcoming.
Laura Ost, email@example.com, (303) 497-4880
Laura Ost | Newswise Science News
New Technologies for A/V Analysis and Search
13.04.2017 | Fraunhofer-Institut für Digitale Medientechnologie IDMT
On patrol in social networks
25.01.2017 | Fraunhofer-Institut für Arbeitswirtschaft und Organisation IAO
At the productronica trade fair in Munich this November, the Fraunhofer Institute for Laser Technology ILT will be presenting Laser-Based Tape-Automated Bonding, LaserTAB for short. The experts from Aachen will be demonstrating how new battery cells and power electronics can be micro-welded more efficiently and precisely than ever before thanks to new optics and robot support.
Fraunhofer ILT from Aachen relies on a clever combination of robotics and a laser scanner with new optics as well as process monitoring, which it has developed...
Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.
A warming planet
Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.
The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...
Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...
Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!
When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...
19.09.2017 | Event News
12.09.2017 | Event News
06.09.2017 | Event News
25.09.2017 | Physics and Astronomy
25.09.2017 | Life Sciences
25.09.2017 | Physics and Astronomy