Metal detectors

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Empty your pockets and step through, please. We’re going to get an inside look at metal detectors, today on Engineering Works!

More and more places are guarded by metal detectors these days – airports, courthouses; even some schools. Here’s how that frame in the doorway finds that pocketful of change you forgot to put into the tray.

It starts with electricity and a coil of wire. You might remember from your high school physics that when you run an electric current through a coil, you get a magnetic field. Turn it off and the magnetic field goes away.

In the coils in airport metal detectors, the electricity comes in very short, very powerful pulses, usually about a hundred every second. When one of these pulses ends, you get an electrical spike, or sudden jump in the electricity. Then another pulse zaps through the coil. It’s called pulse induction, or PI.

Special instruments measure how much time passes between these pulses. As long as the time between them stays the same, nothing happens. But when you walk through this magnetic field with something metal, like a handful of change or a gun in your pocket, it makes a little magnetic field of its own. This magnetic field slows down the pulses in the metal detector enough for the instruments to see the difference. And an alarm goes off. Everybody knows what happens then.

Time to go. Aw, you forgot about your pen!

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Remote controls

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Grab the popcorn out of the microwave and get comfortable on the couch – we’re going to watch TV. Today. On Engineering Works!

For most of us, the first step in watching TV is finding the remote control. No more getting up to change channels or turn up the volume for us. But how does that little wand get the channel you want from the couch across the room to the television?

Like so many other things these days, it starts with an engineer and a microchip. The chip and other electronic stuff – transistors, resistors, diodes – are what makes the remote control work. Also in there is a set of contacts that has the same layout as the remote control keypad. When you press a key, that closes a tiny switch that tells the chip which key you pressed.

When the chip detects what key you pressed, it translates the pressure into a signal. Each key has a different sequence. Like Morse code. The chip sends that sequence to the transistor, which amplifies, or strengthens, the signal.

Then it zips to a tiny infrared device, an LED, or light-emitting diode. You can’t see infrared light, but a receptor in your television can. The receptor translates the infrared signal back to an electric signal. And the receiver changes the channel from Channel 5 to Channel 4, or whatever.

Sit down and have some popcorn. It’s time for that Seinfeld rerun.

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On, off, on, off, on, off …

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Get out your magnifiers. We’re going to take a look at the tiny beginnings of the Information Age: transistors. Today, on Engineering Works!

Transistors might be the Rodney Dangerfields of the Information Age. They do the work, but the microchips get the credit. As Rodney might say, microchips wouldn’t be nothin’ without transistors.

Engineers at Bell Laboratories built the first one in 1947. Transistors act as both on-off switches, stopping or starting the flow of electricity, and as modulators or amplifiers, increasing the electrical signal. Think of the dimmer switch in your living room. It turns a light on and off, and dims and brightens it.

In a microchip, engineers put together millions of transistors in a particular pattern that does whatever task the chip is intended to do. Arrange the transistors one way, and you get processors that make calculators calculate and computers compute. A different pattern gives you the chip that keeps time in your digital watch or microwave oven. Maybe you need a sensor to monitor temperatures or detect intruders: design a different pattern and it’s yours.

By themselves, transistors can’t do much. But put together enough of them in the right patterns and you can do big jobs and complex calculations; fast, too. Each transistor switches on and off 100 million times a second.

It’s about time to switch off this week’s Engineering Works! See you next time.

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Earthquake!

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We’re going to shake things up today! Earthquakes. On Engineering Works!

Here in Texas, earthquakes are something you see in the news; almost never in real life. But around the world, earthquakes are actually pretty common — more than a thousand every day. But they’re so small that nobody notices except for the scientists looking for them.

Earthquakes happen when rock deep underground breaks along what’s known as a fault line. Kind of like when you break a cracker, but bigger. This break releases energy – a lot of energy. And that makes the ground shake. Just one earthquake can release ten-thousand times the energy of the first atomic bomb.

The problem is that all that shaking stresses everything on the ground above the place where the rocks break. Buildings and bridges fall down and people are hurt or killed.

The biggest recorded earthquake so far was in Chile in 1960. A smaller quake in Mexico in 1985 sloshed water out of swimming pools in Tucson, Arizona – more than a thousand miles away.

Engineers are working on ways to strengthen older buildings, bridges and other structures so earthquakes cause less damage when they happen. It’s called retrofitting. They’re also developing new kinds of construction that will make buildings in places where earthquakes are common less likely to be damaged.

So don’t get all shook up.

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