For over 30 years, Barry Fox has trawled the world’s weird and wonderful patent applications each week, digging out the most exciting, intriguing and even terrifying new ideas. His column, Invention, is available exclusively online.

Read previous Invention round-ups:

Eyeball electronics, phone jolts, Personal crash alarm, Talking tooth, Shark shocker, Midnight call-foiler, Burning bullets, A music lover’s dream, Magic wand for gamers, The phantom car, Phone-bomb hijacking, Shocking airport scans, Old tyres to printer ink and Eye-tracking displays.

Wall-beating bugging

With half a century’s experience of listening to feeble radio signals from space, NASA is helping US security services squeeze super-weak bugging data from Earth-bound buildings.


It is easy to defeat ordinary audio eavesdropping, just by sound-proofing a room. And simply drawing the curtains can defeat newer systems, which shine a laser beam onto a glass window and decode any modulation of the reflected beam caused by sound vibrations in the room.

So the new “through-the-wall audio surveillance system” uses a powerful beam of very high frequency radio waves instead of light. Radio can penetrate walls – if they didn’t, portable radios wouldn’t work inside a house.

The system uses a horn antenna to radiate a beam of microwave energy –between 30 and 100 gigahertz – through a building wall. If people are speaking inside the room, any flimsy surface, such as clothing, will be vibrating. This modulates the radio beam reflected from the surface.

Although the radio reflection that passes back through the wall is extremely faint, the kind of electronic extraction and signal cleaning tricks used by NASA to decode signals in space can be used to extract speech.

Read how to eavesdrop through a wall, here.

Backlit prints

Imagine wallpaper that switches on to brighten the room, or floor tiles that glow underfoot, or even a photo album with pictures that glow on demand.

Kodak researchers in Rochester, New York, US, have been doing a lot more than imagining. Recently filed patents reveal how photographic prints, or inkjet printing paper, can be made to self-illuminate.

Kodak’s new paper has a backing sheet made from a three-layer sandwich. A thin metallic sheet is coated with a smooth layer of white-light phosphor, similar to that used in a black and white TV tube, and the phosphor layer is topped with a transparent metal film.

The backing sandwich is then either coated with the silver halide chemicals used to make conventional photo prints, or the dye absorbing layers used for inkjet printing paper. Polymer glues hold the layers together, add strength and seal against atmospheric damp.

When electrical current flows from one metal layer, through the phosphor powder, to the other metal layer, a glow is produced. This provides a uniform backlighting for the images printed over the top.

The effect requires about 100 volts at several hundred hertz but very low current – similar to a pocket LCD screen. A transparent polymer coating acts as an insulator to protect against any tingle if touched.

Kodak has made the backlit paper thin enough to pass through a conventional printer and flexible enough to fit in a photo album.

Get full details of what Kodak is hatching, here.

Reflections on sea rescue

Finding people lost at sea could soon be lot easier, thanks to work done for the US air force by an inventor in Stamford, Connecticut, US. Although Gerald Falbel’s patent was filed to help search for downed military pilots, it can be used equally well for finding shipwrecked sailors or airline passengers in life-rafts.

The downed pilot wears a helmet that carries a large glass hemisphere, similar to a camera fisheye lens, on the top. This sits over a reflector, which catches light from every direction and reflects it back in the direction it came from – much like a cats-eye road marker.

A spotter plane flying high over the rescue area – at about 10,000 feet – sweeps a laser beam across the water, say East to West. It then rapidly retraces the beam’s path, before starting a new sweep slightly to the North. Each sweep takes just 1 second, meaning a path tens of miles long can be scanned in just a few minutes.

If the beam hits a cats-eye helmet it bounces straight back, to be registered by a camera sensor and recorded as a hit. Although there will inevitably be false reflections, from stones or water glints, they will not show up from the same place on a retraced beam sweep, so can be safely ignored.

The laser is also pulsed to help the sensor distinguish a genuine hit from reflected sunlight – sunlight has no pulses.

More detail on the high-speed air sea search system is available here.