Q & A/Mulligan: Solar Panels

In response to my post the other day about photovoltaic cells, I received a number of responses indicating I had done an inadequate job explaining the technology. One dear friend wrote:

okay, I believe you because I trust you, but I don't totally comprehend the concept of how PV cells generate energy. It seems like scientists are trying to fool me into believing some gobbledygook they made up.

So here goes a more complete-- and hopefully better-- explanation:

The most basic idea with a solar cell is that it works by using energy from the sun, in the form of photons, to create electricity. In order to do this, engineers start off by putting two layers of "doped" silicon in contact with each other-- one of these layers is positively-charged; the other is negatively-charged.

The positively-charged layer (p-layer) has a lot of "holes"-- places where electrons could be if there were electrons available. The n-layer, on the other hand, has a lot of electrons that are extra-- you can think of them like a bunch of understudies on an acting set (they have a role, but they're really just waiting around to jump into a more stable, more important role).

When the two layers come together, the extra electrons on the n-side, close to the barrier, rush to fill the "holes" on the p-side. On the p-side, the holes migrate over to the n-side. This happens really fast, until equilibrium is reached, right at the boundary between the two sides (called the p-n junction):



Because the n-layer now has this positive charge right by the barrier, it takes too much energy for more electrons to move from the n-side to the p-side. However, electrons can move easily from the p-side to the n-side.

Of course, once the equilibrium is reached when the two layers are put together, electrons aren't going to keep moving around on their own-- they need energy to push them. Here's where photons come into play: photons are a form of energy, and when they strike the layers of silicon, they transfer that energy to electrons and dislodge them from their place. Electrons on the p-side cross the barrier to the n-side, but the electrons on the n-side can't cross to the p-side, so they get knocked around the n-side, looking for somewhere to go.



In a solar cell, some of those electrons end up in metal conducting strips (remember those thin silver lines on the PV cell on your calculator?) in the solar panel, which move the electrons out of the cell and into a wire-- generating electricity!



The solar panel is a closed-loop system, meaning that the electrons that are lost through the metal conducting strips and into the wire travel aren't lost forever-- after doing their job generating electricity, they travel back through the wire and are picked up by a conductive metal backing on the back of the solar panel, where they transfer back to the p-layer.

The whole solar panel has a number of parts-- we've mentioned the two layers of silicon, the metal conducting bands, and the metal backing. The top of the panel is also covered in an anti-reflective coating so that the panel can absorb as much light as possible, and the whole thing is covered in a layer of protective glass:



If you're with me to this point, you can see why solar panels are fairly inefficient producers of energy, even though the sun is so powerful. Only certain levels of energy from the sun knock the electrons in the silicon out of place; also, of the electrons that do start to fly around, only a few of them make it into the metal conducting strips.

Does this Ring a Bell?

My friend Will e-mailed me this today!

GBW: IKEA cometh to Brooklyn

I have a hate/love/(hate again) relationship with IKEA. I hate the light-birch color of their furniture, because it reminds me of the flesh in a freshly-axed tree, which makes me feel guilty. I love IKEA because it has supplied me with almost all of my furniture (mostly via craigslist). And I hate IKEA again because the entire store is set up to make customers disoriented and lost, so that they come back to the same sections over and over until they decide to buy the merchandise they didn’t think they wanted, like trick answers on a multiple-choice test.

That said, many of our city-dwelling, carless lives have been eased significantly by the opening of an IKEA in Brooklyn this past June. And although it’s located in transportationally-challenged Red Hook, IKEA makes itself accessible to visitors with free shuttles from the F and G trains, a free water taxi to Manhattan, and direct service on two Brooklyn bus lines. In addition, you can rent a UHAUL right out of the parking garage to drive large purchases home.

The Brooklyn IKEA is also pleading its case as a social/environmentally responsible superstore by applying for a silver LEED certificate. The most significant green feature of IKEA is the huge photovoltaic array on its roof, which provides the building with somewhere between 5 and 10 percent of its energy needs.

Put simply, photovoltaic cells work by converting light (photo) energy into electric (voltaic) energy. Although it seems like people are talking about “solar energy” as a relatively new idea, the roots of photovoltaic (PV) technology goes back about 170 years to a French physicist named Alexandre Edmond Becquerel. Becquerel was the first to observe (or at least get credit for observing) that electricity could be created by shining light on to certain chemical solutions. One century and several brilliant minds later, Bell Labs introduced the first high-powered PV silicon cell, and the NY Times predicted that solar cells would lead to a source of “limitless energy” (If I had a nickel for every time...).

PV technology is not only pretty old, but it’s also fairly ubiquitous. Unless you went to school before the 1980’s, your first memory of PV cells probably dates back to your first calculator. And unless you were an exceptionally engaged student, you probably spent some time in math class covering the light sensor with your finger and watching the numbers fade gradually from the display screen, only to reappear when your finger was removed. Voila-- your first tactile experience with semiconductors!

A photovoltaic cell works by using a semiconductor—a material that has some qualities of an insulator and some qualities of a conductor. The most common semiconductor is silicon. In it’s pure state, silicon is stable, meaning that it has neither too many nor too few electrons. However, another trace element can be added to silicon to disturb this balance. This process is called doping, and people use it to create sheets of negatively-charged (n) and positively-charged (p) silicon.

To create a PV cell, the two sheets of semiconductor-- one with extra electrons (n-silicon) and one missing electrons (p-silicon)-- are placed together. When the sun's energy, in the form of photons, strikes the negatively-charged layer, electrons are knocked loose and move toward the p-silicon. This movement of electons creates an electric field, generating electricity.

Bonus: How to Potty In Space

I'm feeling a little bad about having missed Friday's post, so here's a little addendum to today's:

One of the exhibits in the Brooklyn's Children's Museum is called "Living in Space." It was created in collaboration with NASA and inspired by the International Space Station. According to the Museum's press pack, kids can "experience sleeping, dressing, and working like astronauts-- becomeing ISS crewmembers for a day."

Noticeably absent from the Press Pack's description of "Living in Space" is the part of the exhibition called "How to Potty in Space." Here, there is sort of a replica of a little space station bathroom. It looks just like an airplane lavatory, except that the toilet is covered in a piece of clear plastic with a target painted on it. Next to the toilet there is a plaque with these instructions:

How to Potty in Space:
1. Attach the target to your backside
2. Using the monitor try to line up that target to the one on the toilet.

Next to these instructions is this picture:


Attached to the wall there is a blue felt target with a strap attached to it, next to a computer monitor.

While I was standing there, trying to figure everything out, a little boy came in and almost pushed me out of the way to strap the target around his waist and sit down on the toilet.

I admire the frankness of this exhibit, but I have to admit that the display left me with more questions than answers: How do targets and computer monitors really come into play when astronauts use the restroom? Is the felt pad represented here strictly anecdotal, or do astronauts employ some sort of motion-sensored bullseye to help line things up?

If I haven't wondered how to potty in space before, I certainly do now.

Anyone? Anyone?

Life, Color, Energy at The Brooklyn Children's Museum

I rode my bike down to the Brooklyn Children’s Museum yesterday. It was a rainy fall day and the sounds of the city were damped by the white noise swoosh of tires on wet streets, and the grey light gathered the colors from buildings and signs into a single, deadened hue, and everyone seemed to wrap themselves up in the blanket of their own thoughts.

I was content on doing this, too, until I turned the corner onto St. Marks Avenue and the Museum blotted brightly onto the sepia world in front of me like yellow paint spilled on newsprint. Riding up to the entrance of the Museum, I felt like Dorothy in the scene in The Wizard of Oz, after the tornado, when she opens the door of her displaced house and finds herself in a world of color.

Inside, the Museum was swarming with the frenetic motion of children, and the collection of sounds captured the whole range of human emotion—inside this place, kids were confronting the world and reacting to it vocally with joy, surprise, fear, excitement, and despair.

Next to the ticket counter, one little boy stood under the Welcome sign, his face turned against the wall. He had apparently been notified that it was time to go home and was fighting it out, will versus fate. When fate presented itself physically in the form of his winter jacket, the little boy launched into a wail woeful and prolonged and barely broken by the half-hearted spanking delivered by his father.

Throughout the Museum, children were being frightened by praying mantises and puppets, repulsed by an obese Burmese Python, and thrilled by the exhilaration of indulged curiosities. If the building's exterior implies some wild promise of the wonders to be found within, I think-- judging by the expressions on these kids' faces-- that it delivers.

The Brooklyn Children’s Museum originally opened in 1899. In 2005 it underwent major renovations, becoming both literally yellow and figuratively green. When the building re-opened this fall, it boasted a number of green features. Motion and carbon dioxide sensors adjust lighting and ventilation to fit the current number of museum visitors, ensuring both clean air and energy-savings. Other green attributes of the museum include recycled materials, solar paneling, and waterless no-flush urinals (yuck?).

The feature that sets the Museum apart from most other green buildings in NYC, however, is the use of geothermal wells for heating and cooling. You may have heard of people harnessing geothermal energy in places where there is intense heat under the Earth’s surface. New York, of course, is nowhere near a volcano, so when we talk about using “geothermal” energy here, we’re talking about taking advantage of the relatively stable temperature of the ground below our feet.

Because the earth absorbs and releases heat from the sun much more slowly than the air, temperatures several feet below the Earth’s surface remain relatively constant, at around 50 degrees Fahrenheit, year-round. During the winter, warmth from underground can be used to heat the inside of buildings; during the summer, heat can be sunk back into the ground, thus keeping the inside of the building cool.

The geothermal system used at the Brooklyn Children’s Museum is called an open-loop system. An open-loop system works by removing water from underground, circulating it throughout the building (and through a mechanical heat pump, which we'll have to get into later), and then returning it to the ground below. Two wells-- one for uptake and one for return-- reach down to tap an aquifer, an underground region where water collects in the small spaces in rock.


Open-loop systems are nice because they retain a lot of heat energy, but they have some major problems. For example, water generally seeps into underground aquifers over a long period of time, like water through a drip coffee machine. If you attempted to pour all of the water into your coffee filter at once, rather than drop-by-drop, you would end up with a giant, pooling mess and no water at all making it’s way though the filter. The same thing happens often with open-loop geothermal systems, making them a somewhat risky investment.

More commonly, people invest in close-loop geothermal systems. Here, a metal coil filled with water or refrigerant runs underground, absorbs heat, and carries it into a heat pump in the building above.

As with all forms of newer, "cleaner" energies, we're likely to realize some very exciting possibilities, as well as some serious limitations, to geothermal energy in the years to come. In our exploration of this energy, it is my hope that we proceed like the kids at the Brooklyn Children's Museum-- with tireless, joyful curiosity guided by a respectful caution for the vast unknown.

Photo credits:
Brooklyn Museum: Chuck Choi
Fantasia With Children: Bruce Cotler

Green Building Week: Sick of Work? Here's Why.

The opening scene in Joe Versus the Volcano (above) is a brilliant depiction of the classic soul-sucking office job. The main character, Joe, works at the American Panascope Corporation (“Home of the Rectal Probe”), in an office dominated by the buzz of flickering fluorescent lights, the automatic-artillery sound of a typewriter, and the high-strung, one-sided ranting of a boss on the telephone.

Joe does not feel good, and the other people in the office don’t look like they feel good. The secretary, Dede, pauses her work every few seconds to take a hit off of her inhaler and wipe her nose with the back of her hand. When Joe tells his boss that he doesn’t feel good, the boss dismisses everyone’s substandard health as “a fact of life.” “Do you think I feel good?” He asks Joe. “I feel rotten. So what? I don’t let it bother me…”

The film is replete with hyperbole, but I think this first scene gets the dismal office-job reality just right. While we tend to think of job-related health risks as a strictly blue-collar or unskilled worker issue, studies have shown that conditions in many office buildings pose risks to human health. Sick-building-syndrome, once thought to be synonymous with mere malingering, is now understood to be a real result of poor air quality, indoor pollutants, and biological contamination.

A study conducted in 2000 estimated that improved indoor environments in the U.S. could save $20 billion to $160 billion from direct improvement in worker performance, as well as billions of dollars per year in health care costs associated with asthma and other respiratory illnesses.

It’s no wonder, then, that the U.S. Green Building Council considers human health issues as part of their standards for sustainable building. The Council has developed a Green Building Rating System called LEED (Leadership in Energy and Environmental Design) through which buildings can become certified as Officially Green. The System works by granting points for various building aspects, such as sustainable site development, energy efficiency, water savings, material selection, and indoor environmental quality. Buildings can be certified on a number of different levels, from Certified to Platinum.

In New York City, the new 7 World Trade Center (the old building was the third to fall, after the twin towers, on 9/11) was the first building in NYC to attain LEED Gold certification. The building opened in May 2007 with sustainable features including 30% recycled steel, ultra-clear glass for improved natural light and energy efficiency, and high-efficiency heating and cooling systems.

The skyscraper pulls in clean air from above to circulate around the building, and uses technology like carbon dioxide detectors to monitor the level of ventilation and circulation needed-- the more people in a room, the more air circulation. The Trade Center's developer, Larry A. Silverstein, said that air quality was a personal issue for him: "I'm an asthmatic," he said. "When you have asthma, you realize how important it is to have clean air to breathe."

Of course, Mr. Silverstein was probably motivated by more than a sense of altruism prompted by personal health issues in his decision to go green (clean energy considerations and materials cost about $35 million out of the $700 million project). From an economic standpoint, it is advantageous for developers to build green buildings and seek LEED certification because, in the end, it saves them money in energy costs (30 to 70 percent), and it attracts tenants who are interested in keeping their employees healthy and productive.

While buildings like 7 WTC and Hearst Tower have likely set a standard precedent for all future commercial building in NYC, it's probably going to be a while before the average American workplace can offer clean air and natural light to working Americans.

If you ask me, the solution is to stay out of the office.

Green Building Week: Habana Outpost

Why not start with something fun?

This bar is in my neighborhood in Brooklyn. To be honest, I’ve always kind of avoided it because I found the bright green fence disconcerting. But now, after learning about all of its greenery, I’m totally going back for some Cuban-style corn on the cob.

This establishment has gone to some pretty impressive eco-friendly lengths. For starters, it’s run on solar energy produced by this photovoltaic roof. The panels produce more than enough energy to provide electricity to the bar, and the owner sells the surplus to Con Edison (when was the last time you heard of anyone getting a check from ConEd?). The garden area also boasts two rain-water collection systems that route rainwater from the roof and solar panels and use it to flush the toilets and water the plants.

Pretty much all of the materials at Habana Outpost are recycled, reclaimed, sustainable, or otherwise Earth-friendly. The cutlery is made out of potato starch and the cups are composed of corn-- both fully compostable. The picnic tables are made out of a material called TREX, which is a mixture of recycled plastic bottles and sawdust. The outdoor kitchen is a reclaimed mail truck; the wooden doors were taken from an old monastery in South America.

The two least-significant measures at the Outpost also happen to be my favorites: a bike-powered blender and a sunlight chandelier. At the blender, you can make yourself a margarita by hopping on the bike and pedaling for a few minutes, shaving off a dollar off of your drink (as well as four or five calories).

Inside Habana Outpost, there's a chandelier that looks like something out of The Abyss. The chandelier works by using outdoor sensors to channel sunlight into fiber optic cables, which carry the light inside and through the chandelier. You have probably heard of fiber optic cables in association with transmitting information—they are well-known for being faster and more efficient than wire cables-- but did you know that they can carry solar energy for zero-use lighting? I didn't. These fiber optic cables have a wider diameter than the ones used in communications, but they work essentially the same way-- by internally-reflecting all of the light that passes through them. Apparently, this method is becoming increasingly popular in both commercial spaces and residences. Not only does it reduce energy costs; it also brings natural light into spaces that would otherwise be restricted to harsh artificial light.

While we are talking on a national scale about an "energy revolution," Habana Outpost is a great reminder that clean energy doesn't have to be such a big deal. After all, this place is just a bar with a green fence and delicious corn.

Clean Energy Week! (or how i learned to stop worrying and love the little picture)

It’s been a week since the election, and I keep thinking about Harry Truman who, upon assuming the Presidency on April 12, 1945, told reporters that he felt “like the moon, the stars, and all the planets had fallen” on him. Truman came into the Presidency after 82 days as VP to Franklin Roosevelt, who hadn’t exactly kept Truman abreast of domestic and foreign affairs. One of the first secrets Truman learned of when he took office was the existence of the Manhattan Project, and one of the first decisions he had to make was whether or not to employ nuclear warfare. Very heavy indeed.

While President-elect Obama doesn’t look as bewildered as Truman reported feeling, I have to imagine that he’s had the same elevated experience of his own gravity. He has the weight of two wars, a ponderously sagging economy, and a potential energy crisis-- not to mention 300 million Americans watching to see what he’ll do.

While energy issues didn’t rank highly at the exit polls (compared especially to the economy), the President-elect’s economic plan appears increasingly to be tied to the promotion of green technology and the creation of green jobs. Obama’s energy platform proposes investing $150 billion in clean energy technology over the next decade to create five million new green collar jobs. And at her post-election press conference last week, Speaker Nancy Pelosi spoke of a stimulus package that would “grow our economy by creating jobs and to do it in a newer, greener way.”

There is some debate about the validity of tying the economy to energy policy. Some, like David Brooks, view the economic crisis as an opportunity to transform the way we supply and manage energy in the U.S.—something he says we could have done in the 1970’s. Critics argue that Obama’s green investment/job creation plan ignores the jobs that would be lost in the fossil fuel industry.

And there are some who scoff at the perceived potential of alternative energies in general, which is something I can't quite understand. Perhaps part of that sentiment stems from a knee-jerk reaction to the fact that environmentalists are often grounded in neither reality nor science, but only politics. I can understand that. I can also understand (and share) a healthy skepticism of anything being touted as the Next Great Thing. On the other hand, it strikes me as dangerously myopic to view energy alternatives in terms of either politics or fads. Some alternative energies are new, but they're here, and people are using them.

But these are big issues. Because I am not required to shoulder the weight of the solar system or the world or the drooping economy or the depleting ice caps (yes, they are. yes, it's us), I'd rather not. I'd rather walk around New York City and check out some of the green building they're doing around here. So for the next week or so, look forward to a feature each day on a building in NYC. I'll focus on a different type of energy (wind, solar, etc.) with each post.

Though I'll start with those tomorrow, I'll leave you with something to wet your recycled, sustainable, Earth-friendly whistle today...it's Big and Green and really Bizarre...

It's a building designed by architect David Foster for Dubai, called Dynamic Tower. Each floor is designed to rotate 360 degrees, and the building will generate all of it's own electricity through inter-floor, horizontal wind turbines and solar panels on the roof of each floor. Weird? Definitely. Possible? Maybe.

NANOBAMA!

John Hart, a Mechanical Engineering Professor at University of Michigan (go blue!) might be making the tiniest art ever.

These mini sculptures are made out of carbon nanotubes, which are spectacular little structures made entirely of carbon, each with a diameter tens of thousands of times smaller than a human hair. Carbon nanotubes are all the rage at the moment because of their unique properties —for instance, they are extremely lightweight but about 100 times stronger than steel, which makes them potentially useful for paper batteries (and theoretically useful in the creation of a space elevator…).

Each of the Obama faces above is composed of about 150 million nanotubes, stacked parallel to each other, for a total width of about .5 millimeters (10 times the diameter of a human hair). The sculptures themselves are so small that they are barely visible to the human eye—it takes an electron microscope to obtain a photograph like the one you see here. I suppose it’s a weird hobby, making art too small to see, but I think I like it.

Check out more nano-art here.

Man, Magician, Machine

There are a lot of reasons to hate getting your hair cut when you’re a kid. Reason #1: sitting still sucks. Reason #2: Sharp scissors + ears = pain. Reason #3: it’s scary going to school with a new look, especially when that look is the result of a tearful afternoon spent with your mother and a pair of scissors, in which mom keeps muttering “oh, now that side’s shorter!” and, at the end of which you are told coaxingly that you look like Ramona Quimby, and “isn’t that fitting?”.

Before self-consciousness kicks in, I think Reasons #1 and 2 are enough to instill an early hatred of the barber shop. But this was not so for my siblings and I. When we were little and living in Ann Arbor—before the west coast, before the first grade, before my mother took the shears into her own hands*—we had Fantastic Sam’s. And Fantastic Sam’s meant magic.

The basic idea was this: after the haircut (provided you were good—no crying, no fidgeting), the hairdresser would take a lock of your hair and go behind a curtain, where the hair would magically transform into a toy, which would magically appear at the bottom of the curtain. The trick was nearly flawless and, save for the sharp disappointment brought on by the appearance of a human hand, I was enthralled.

Looking back, I’m not sure if the premise of the trick really included a transformation of hair-to-toy, but that’s the way I liked to think about it. Those were the days, after all, when lost teeth turned into quarters, and magic seemed an appropriate way to account for the private mysteries of the world.

I am reminded of the magic trick at Fantastic Sam’s every time I use a vending machine-- primarily because, in the years that have elapsed since early childhood, I have gained little insight into the workings of technology. I am no longer tempted to use magic to make sense of things, which is perhaps why I have largely stopped trying to make sense of things at all.

But science has a way of calling back our curious natures, however repressed by the constraints of experience. And so, recently, when someone asked how the MetroCard vending machines worked, I set out to find the answer…

We can account for most of the details using EVERY OTHER post I’ve written this week about MetroCards: the cards in the machine come encoded with certain information (serial number, expiration date), and a magnetic read head inside of the vending machine writes the rest of the information to the card when you buy it. If you pay by credit card, the same technology is at work: a magnetic read head reads your card, communicates with your bank electronically, and debits your account for the amount paid. The question that’s left to us, then, is how the machine reads cash and coins.

There are several ways that machines test the validity of cash. First, bills are printed with magnetic ink, and different bills generate different magnetic fields (magnetic read heads again, my friends!). Second, denominations have different fluorescent properties that can be detected using an ultraviolet scanner. Third, each bill is slightly electrically conductive, and its conductivity can be used to identify it. Fourth, and finally, digital cameras can measure the different optical qualities of a bill to determine whether it is counterfeit.

Although there are some fancy ways to read coins, most change is judged based on its physical characteristics alone: diameter, thickness, and the ridges that run along the edge. While this might seem like a security measure just waiting for a bored scam artist, the physical properties are difficult to replicate, and machines are picky—they measure each coin to the thousandth of an inch.

And how does your MetroCard get physically pushed out to you while you stand in front of the machine? Well, for starters, there’s a hairdresser…

*While these are true stories, I think it’s only fair to mention that my mother has given me plenty of good haircuts over the years. In fact, most of the time I got a professional cut, I’d come home and beg her to alter it. Most notably, I came home from Bumble and Bumble a few years ago looking like a Republican, and my mom fixed it. Thanks again, Mom.



The photo at right was taken during the Ann Arbor days. The haircut was courtesy of my older brother Gabe, who I mistakenly and unfortunately believed had my best interest at heart.

Broken Laws, Bent MetroCards

I broke a law on Halloween. (Okay, so it’s conceivable that I broke several laws on Halloween, but I’m talking about something I really shouldn’t, in retrospect, have done.) It was the end of a very long day full of transportation-related debacle that included ten hours on the Fung Wah bus, a flat tire on my bicycle in Cambridge, and an outrageously expensive taxi ride from Cambridge to Boston.

Back in New York, I decided to spring for a cab home to Brooklyn, and was turned away by six consecutive drivers-- some of whom had legitimate excuses, some of whom just didn’t want to cross the bridge.

So I walked to the F train and, descending the stairs, felt the old sense of hurry and rush that everyone always feels when they get underground and hear the train coming and decide to break into a run. Except. The LED display at the turnstile informed me that my MetroCard had insufficient funds. And just as that occurred, a couple of mechanics were opening the gate and entering the station-- and this thing happened that I can’t really explain. I grabbed the door behind them, opened it, and walked through. Then I ran down the stairs and made my train.

Why did I do it, knowing that the NYPD arrests thousands of people a year for the crime? I’d like to say I was acting on instinct. I’d like to say it was the same thing that happened to Wesley Autrey last New Year’s, when he jumped onto the tracks in front of a speeding train and lay down on top of a stranger, saving his life.

I guess mine was just a less heroic instinct.

The MTA loses millions of dollars annually to fare evasion (16 million as of 2005). Mostly, people hop turnstiles, but there are also plenty of cheap scams involving unlimited MetroCards or station agents. When MetroCards were first introduced and the technology was lousier, it was easier to fool the system, and tech-geeks (and anyone who learned from them) were getting free rides all over the city.

My personal favorite of these early scams is the bent MetroCard. The idea was to take an empty card and bend it in the place on the magnetic stripe where fare deduction is encoded. This worked because, when you swipe a MetroCard, the data is read and rewritten by a series of magnetic “read heads” that perform different jobs. Magnetic read heads are these little pea-sized machines that convert the magnetic information on your card into electrical signals, and vice-versa. In fact, this technology works just like tape and video players, except that instead of the tape moving from spool to spool across the read head, your hand moves the magnetic stripe along as you swipe. This read head is a version of a simple electromagnet:

When you pass your card through the machine, an electrical pulse travels through the coiled wire and creates a magnetic field in the iron core. When the magnetic field reaches the gap in the core, a fringe pattern is created in order to bridge the gap. This fringe pattern interacts with the magnetic stripe on your card to write new information on it. The opposite process also occurs to read your card—the microscopic magnets on the stripe create a magnetic field in the iron core, which travels to the wire and sends electrical signals back through the wire.

The whole process, with different read heads performing different jobs, takes only about one-tenth of a second.

In 2005, the MTA changed the read-head technology and drove the card-bending trick into extinction. The change involved making the technology more sensitive, thus promoting MetroCard swiping to a low-level art form involving, if not beauty, a delicate combination of grace and speed.

The Transit Trail: Using MetroCards to Solve Crime (and why we know where you are right now…)

Since the MTA completed its transition from token to MetroCard in 1997, the electronic fare cards have been used on many occasions to help solve criminal cases. In 2001, a transit worker named Christopher Stewart was accused of stabbing an ex-girlfriend to death in Staten Island. His alibi placed him on a ferry to Manhattan, but the trail left by his MetroCard told a different story—he’d swiped it on a bus near the scene of the murder twelve minutes after the crime took place. The new evidence won the case for the prosecution, and Stewart was convicted of second-degree murder.

MetroCards have been used to exonerate as well as condemn. In 1998, for example, a Brooklyn high-school student filed a federal civil rights case after being arrested for allegedly hopping a turnstile. The student had been on his way to the library to work on a school project, and ended up spending nineteen hours in custody instead. Two years after the incident, electronic records from the MTA showed that the kid had, in fact, swiped his card right before being picked up by the cops.

So, how is it possible to trace one MetroCard out of five million? The third track (see Monday's Post) on a MetroCard is encoded with a unique serial number when the card is manufactured. When a MetroCard is swiped at a station or on a bus, the data on the card is both read and rewritten by a magnetic read/write head (see tomorrow’s post), and all data from the transaction is conveyed to the Automatic Fare Collection Database—a central computer database where all electronic transit histories are stored.

What does this mean for you, assuming you aren’t a public-transit-reliant criminal? If you buy your MetroCards in cash, your transit history trail can be traced only for as far back as the card in your wallet goes. If, on the other hand, you use a credit or debit card each time you purchase a new transit ticket, the Automatic Fare Collection Database knows who you are and where you’ve been going since you first stepped through a turnstile.

A Naked Card and an Old Subway Car

I stumbled upon this article on the web last night called “The MTA Exposed!” It was written by a self-described “hobbyist” who has apparently committed himself to decoding the MetroCard and, though it is still a “work-in-progress,” writing his own (free) electronic ticket. Despite the exciting title, the author’s investigative efforts hadn’t uncovered anything particularly incriminating about the MTA, though he was able to glean an impressive amount of information about MetroCard code using just some receipts and an old tape recorder.

I mention the hobbyist and his website because I found, at the bottom of the page, the above photograph. Here you can actually see the data tracks on the MetroCard, thanks to some magnetic developer fluid (the fluid makes data recorded on tape or other magnetic material visible to the naked eye). The top strip contains tracks one and two, where information about your card's expiration date, remaining fare, etc. is stored. The bottom strip is track three, and is encoded with the card's serial number.

In other news, I visited the Transit Museum today in my own investigative effort, and recommend a field trip if you are in the area. There are a lot of very cool artifacts, including a display of old turnstiles going back all the way to the original, pre-automated ticket-chopper machine used when the subway first opened in 1904. At one point, before World War II, the turnstiles were wooden, which suggested to me a time (probably fictional) when things were more beautiful and more natural, and made with more care than they are now. I hate feeling nostalgic for times I never experienced—whenever it happens, I try to walk around imagining the present through the soft-focus, simplifying lens of time. I imagine someone standing in the Transit Museum fifty years from now, marveling at the old stainless steel turnstile, wishing she could have lived in a time when commonplace things were made out of natural materials rather than thick antibacterial plastic. And it works, kind of.

The Transit Museum is located in an old subway station, and you can go down to the tracks and walk through some of the antique cars. On a day like today, there isn’t much traffic through there, and the old upholstered seats in car R10 are a good place to sit and think.

This Magnetic Moment: An Introduction to the MetroCard

If you live in New York City, you are familiar with the MetroCard: it is your key to the city’s public transportation system, your eighty-dollar-a-month unlimited pass or dwindling pay-per-ride card or fleeting single fare. It is the thing you take for granted until you find yourself without it in a station with no agent and a broken vending machine, standing sadly by the turnstile as a stream of people swipe their cards and pass through the gate and board the train without giving you so much as a sympathetic smile. It is the thing you take for granted knowing how to use until you are caught behind a group of tourists who approach the turnstile uncertainly in front of you, as one would approach a large and unfriendly and perhaps rabid dog. You watch as, after some discussion and a few false starts, they drag their collective card slowly through the machine, failing to notice the screen reading “please swipe your card again at this turnstile” until after they’ve given the unyielding iron bar a few sincere pushes. Meanwhile, you hear your train come, and you hear it go, but the good part inside of you swallows your fury and provides the tourists with a friendly tutorial on the speed with which a MetroCard should be swiped.

But as common as the MetroCard is to us, and as familiar the anecdotes, few of us have any idea how the thing actually works. Because I didn't know either when a friend asked me a few weeks ago, I began researching it. And because I had so much fun learning about it, I'm going to devote a few blog entries to the workings of the MetroCard, our key to the city...

The technology on the card itself—the magnetic stripe—is actually fairly uncomplicated. Magnetic stripes are made out of thousands of tiny particles of iron oxide, each about 20 millionths of an inch long. Because iron oxide is a magnetic material, all of these little particles are oriented in one of two directions-- you can think of them like arrows pointing north or south. When the card is blank, all of these little magnetic particles are oriented in the same direction, and by switching some of the particles around, the stripe becomes “encoded.” Just like binary code (0’s and 1’s) can be interpreted as characters and words and whole computer applications, the magnetic orientation of these particles can be read as information regarding your card’s serial number, balance, expiration, and so on.

The magnetic stripe on a MetroCard contains information in exactly the same format as virtually all other cards with magnetic stripes. Though you can’t see it, the stripe carries three different “tracks,” each with a different type of data. Track one on a driver’s license holds information about your name and address, along with the location the card was issued. On a MetroCard, tracks one and two hold information about the card type, expiration date, times used and remaining card value, while track three is encoded with a unique serial number. One inch of one of these tracks holds 210 bits of data, which translates to about 70 characters. Each time you swipe, your card is both read and rewritten to reflect your new balance. And how does that work? I'll tell you later this week.

(I created the handy drawing above using Microsoft Paint, an application that I don't believe has been updated with a new version since I was in elementary school. Speaking of simple technology...)