There has been some very interesting work going on at University of Utah - I was not aware that they were doing so much work in this area. They reported what appears to be the first active cloaking method for various types of waves including microwaves and a low cost radio tomography method to image through walls.
Active Cloaking:
In recent years, scientists devised and tested various cloaking schemes. Experiments so far have been limited to certain wavelengths such as microwaves and infrared light, and every method tried so far has limitations. "We have shown that it is numerically possible to cloak objects of any shape that lie outside the cloaking devices, not just from single-frequency waves, but from actual pulses generated by a multi-frequency source," says Graeme Milton, senior author of the research and a distinguished professor of mathematics at the University of Utah.
Most previous research used interior cloaking, where the cloaking device envelops the cloaked object. Milton says the new method "is the first active, exterior cloaking" technique: cloaking devices emit signals and sit outside the cloaked object. Compared with passive cloaking by metamaterials, the new method - which involves generating waves to protect or cloak an object from other waves - can cloak from a broader band of wavelengths. The problem with metamaterials is that their behavior depends strongly on the frequency you are trying to cloak from.
This cloaking method utilizes destructive wave forms so the drawback is that you have to know the characteristics of the incoming waves before the arrive so the exact opposite wave can be transmitted as it arrives.
Here is a link to the full announcement which includes a video.
Radio Tomography:
University of Utah engineers have shown that a low cost wireless network of radio transmitters can track people moving behind solid walls. The system could help police, firefighters and others nab intruders, and rescue hostages, fire victims and elderly people who fall in their homes or even be used in retail marketing and border control.
Their method uses radio tomographic imaging (RTI), which can "see," locate and track moving people or objects in an area surrounded by inexpensive radio transceivers that send and receive signals. They used commercially available ZigBee radios which are low cost and easily available. Several studies were done by placing transmitters around an area and measuring the variations in signal strength as people moved around to demonstrate the concept.
RTI measures radio signal strengths on numerous paths as the radio waves pass through a person or other target unlike radar that measures the reflected signal so it is more like CT or X-ray imaging. The researchers developed math formulas and used them in a computer program to convert attenuated signals - which occur when someone creates "shadows" by walking through the radio signals - into a blob-like, bird's-eye-view image of that person walking. So they were able to get rough images through a wall of people and objects moving around the room.
Here is a link to the full announcement about this subject which also has a video link. Great stuff - if you find any interesting research such as these projects going on, please let us know about them.
Space Data Successfully Completes CDMA Balloon Flights
I had not heard of this company before but Space Data Corporation has announced that last month it conducted successful trials of its CDMA SkySite�, a major milestone in the development of economically practical wireless voice and data communications to large areas with sparse population. It is expected that each SkySite will be able to provide coverage over approximately 20,000 square miles. The use balloon platforms to position basestations in the sky to enable communications in remote areas that do not have coverage.
During two trial flights, a prototype miniaturized CDMA 1X-RTT base station was carried aloft over a remote area in western Utah by the SkySite balloon platform to altitudes as high as 60,000 feet. At that point, the 1900 MHz PCS band BTS was used to carry calls from, to, and between ordinary CDMA handsets located on the ground approximately 60 miles away. Call quality was excellent, with low frame error rates on both the forward and reverse channels. Backhaul was provided by a high capacity digital microwave link operating in the 2.4 GHz band. After completion of each trial, the BTS �payload� was released, parachuted to the ground and recovered intact.
The successful trial confirmed the technical feasibility of serving ordinary wireless handsets from substantial distances using the SkySite system. Applications include serving remote areas of low population densities, �fill-in� for coverage gaps in rural networks, and providing emergency communications in areas where terrestrial systems are out of service due to widespread disaster situations.
I think this is an interesting method for enabling communications in remote areas if it turns out to be as cost effective as they describe. It seems well suited for temporary situations like military operations or disaster situations in remote areas or to increase capacity temporarily in certain emergency situations. It seems like providing long term coverage would hard to justify from a cost perspective.
What do you think?
During two trial flights, a prototype miniaturized CDMA 1X-RTT base station was carried aloft over a remote area in western Utah by the SkySite balloon platform to altitudes as high as 60,000 feet. At that point, the 1900 MHz PCS band BTS was used to carry calls from, to, and between ordinary CDMA handsets located on the ground approximately 60 miles away. Call quality was excellent, with low frame error rates on both the forward and reverse channels. Backhaul was provided by a high capacity digital microwave link operating in the 2.4 GHz band. After completion of each trial, the BTS �payload� was released, parachuted to the ground and recovered intact.
The successful trial confirmed the technical feasibility of serving ordinary wireless handsets from substantial distances using the SkySite system. Applications include serving remote areas of low population densities, �fill-in� for coverage gaps in rural networks, and providing emergency communications in areas where terrestrial systems are out of service due to widespread disaster situations.
I think this is an interesting method for enabling communications in remote areas if it turns out to be as cost effective as they describe. It seems well suited for temporary situations like military operations or disaster situations in remote areas or to increase capacity temporarily in certain emergency situations. It seems like providing long term coverage would hard to justify from a cost perspective.
What do you think?
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