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Get Ready For Atomic Radio (technologyreview.com)
An anonymous reader quotes a report from MIT Technology Review: David Anderson at Rydberg Technologies in Ann Arbor, Michigan, and a couple of colleagues, have reinvented the antenna from scratch. Their new device works in an entirely different way from conventional antennas, using a laser to measure the way radio signals interact with certain types of atoms. The secret sauce in the new device is Rydberg atoms. These are cesium atoms in which the outer electrons are so excited that they orbit the nucleus at great distance. At these distances, the electrons' potential energy levels are extremely closely spaced, and this gives them special properties. Indeed, any small electric field can nudge them from one level to another. Radio waves consist of alternating electric fields that readily interact with any Rydberg atoms they come across. This makes them potential sensors.
But how to detect this interaction? A gas made of Rydberg atoms has another property that turns out to be useful -- it can be made transparent by a laser tuned to a specific frequency. This laser essentially saturates the gas's ability to absorb light, allowing another laser beam to pass through it. However, the critical frequency at which this happens depends crucially on the properties of the Rydberg atoms in the gas. When these atoms interact with radio waves, the critical frequency changes in response. That's the basis of the radio detection. Anderson and co create a gas of cesium atoms excited into Rydberg states. They then use a laser tuned to a specific frequency to make the gas transparent. Finally, they shine a second laser through the gas and measure how much light is absorbed, to see how the transparency varies with ambient radio waves. The signal from a simple light-sensitive photodiode then reveals the way the radio signals are frequency modulated or amplitude modulated. The atomic radio can detect a huge range of signals -- over four octaves from the C band to the Q band, or wavelengths from 2.5 to 15 centimeters. It also should be less insensitive to electromagnetic interference due to its lack of conventional radio circuitry. "The atomic radio wave receiver operates by direct real-time optical detection of the atomic response to AM and FM baseband signals, precluding the need for traditional de-modulation and signal-conditioning electronics," say Anderson and co.
But how to detect this interaction? A gas made of Rydberg atoms has another property that turns out to be useful -- it can be made transparent by a laser tuned to a specific frequency. This laser essentially saturates the gas's ability to absorb light, allowing another laser beam to pass through it. However, the critical frequency at which this happens depends crucially on the properties of the Rydberg atoms in the gas. When these atoms interact with radio waves, the critical frequency changes in response. That's the basis of the radio detection. Anderson and co create a gas of cesium atoms excited into Rydberg states. They then use a laser tuned to a specific frequency to make the gas transparent. Finally, they shine a second laser through the gas and measure how much light is absorbed, to see how the transparency varies with ambient radio waves. The signal from a simple light-sensitive photodiode then reveals the way the radio signals are frequency modulated or amplitude modulated. The atomic radio can detect a huge range of signals -- over four octaves from the C band to the Q band, or wavelengths from 2.5 to 15 centimeters. It also should be less insensitive to electromagnetic interference due to its lack of conventional radio circuitry. "The atomic radio wave receiver operates by direct real-time optical detection of the atomic response to AM and FM baseband signals, precluding the need for traditional de-modulation and signal-conditioning electronics," say Anderson and co.
That should be "more or less insensitive", not "more insensitive".
Have you read my blog lately?
reinvented the antenna from scratch
The battery was reinvented, due to it's first development, in what is now modern day Iran, being lost over time. The antenna, however, has not been forgotten so could not have been "reinvented". Redesigned, perhaps, or a new type of antenna may have been invented, but the antenna on my roof is still there, and is still a variation of the first dipole antenna invented by Heinrich Hertz. This seems to be a variation of the phased array, just on a molecular scale, who's development has been filtered through the marketing department.
--- Keep the choice with the user..
highly radioactive
No.
Highly REactive: Add water and it burns. Not an issue when it's a trace of gas in, say, a "gassy vacuum tube" the size of a grain of rice.
The isotope you mine is the (only) stable one. You can get radioactive isotopes from reactor waste - but you can get radioactive isotopes of just about ANY element from reactor waste.
Lasers are often small diodes these days. Shining two through a glass capsule - then into an absorber in one case and a photodetector in the other - is no big deal.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
Why is this better than current radio?
Replace an antenna the size of your hand, your arm, rabbit ears, a tower, ... with something you can mount on a chip in a tiny package on a PC board.
Get rid of the noise, intermodulation, and other pathologies in the high gain amplification and filtering of the tiny amount of energy picked up by that antenna, substituting a direct quantum-mechanical readout of the field, with high signal strength, only competing with noise from variations in the lasers' output as your starting point, feeding a strong signal to a more ordinary amplifier.
If it works out it could be a big deal in a tiny package.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
It can only receive signals.
Good for broadcast, not so good for anything requiring two way communication,
Transmitting with a tiny antenna is easy. You use the same amount of energy as with a big antenna, but with a little antenna the energy density is much higher. As long as you make the impedance match properly, so all the energy is launched, you're fine, regardless of the area of the antenna.
One antenna I'm working with currently is for BLE - on the 2.4G band. The quarter-wavelength there is about 1 1/4 ". But the antenna is mostly a chip of ceramic, with some horrendously high permittivity. (Ceramics can get to 6k or so, though I haven't computed the scale of this thing to estimate its permittivity.) So the quarter-wavelength, in and immediately around the chip, is scaled down in proportion, making the antenna about the same length as a surface-mount capacitor, though substantially narrower. The energy density is also scaled up (in proportion squared), and by the time the wave has expanded to the size of a free-air quarter-wavelength antenna the energy density is down to just that of the larger antenna.
On the receiving side it still works - sort of. But the energy density of the incoming wave doesn't scale up at all when the antenna shrinks. So it intercepts only the tiny amount of energy that passes within a scaled-down quarter-wavelength around the scaled-down antenna, rather than that passing withing a free-air quarter wavelength of a free-air quarter wavelength metallic conductor.
So one of these for transmitting and one of the invention for receiving (if it also works at such a tiny size) and you have your ultraminiaturized two-way system.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way