Friday, June 11, 2010

It's Electric

The funny thing about “energy” is that it is neither created nor destroyed; it only changes form. So when coal is burned at a power plant the coal’s chemical energy is ultimately converted into electricity. This process is typically only 35% efficient ; wasting approximately 65% of coal’s energy when converting its chemical energy into electricity. Basically the heat from the fire is used to boil water, which is used to turn a turbine, which turns a magnet inside a coil of wires to produce electricity. So heat from burning (considered chemical energy) is converted into mechanical energy by turning the turbine which is then converted into electrical energy simply by moving a magnet through a coil, losing energy at each step along the way.

As the world becomes more energy conscious, we are seeing new technologies that convert mechanical energy into electricity. It’s pretty simple to convert mechanical energy into electricity so I encourage you to use your imaginations and invent stuff. Wind farms already exists (many on the Tug Hill Plateau west of here) that convert steady wind into electricity as do hybrid vehicles that use the rolling wheels while breaking to produce electricity. You can sort of think of a coal-fired power plant as a fancy way to create a steady wind that will turn a turbine to produce electricity.

Solar energy conversion does not rely on mechanically moving a magnet through a coil of wires as with many other electricity producing methodologies. It relies on the sun to induce electron motion inside a semiconductor device. Solar energy conversion is very attractive since it is passive and does not rely on burning carbon. However, it’s relatively expensive and requires sunlight. I’m still amazed at the magic of solar power. Think about what we are asking a solar cell to accomplish. We want to create electrical energy from a piece of semiconductor that has no moving parts and we want it to last more than 20 years being blasted by the sun daily and we want it to be cheap and reliable. I would not last 20 years if you put me in the sun everyday and asked me to reliably produce and I think I’m a pretty sophisticated machine, as far as humans go.

How does a solar cell do it? There are two key components to solar cells, the semiconductor material from which it is made and the special junction between two semiconductor materials which acts as an electrical one-way sign. I will leave detailed physics and electrical engineering explanations of solar technology to other more eloquent sources. Instead I will opt to explain it through interpretative dance…. of course.

Imagine a dark stage with dancers on the floor in fetal positions; this is our un-illuminated solar cell. As you watch the motionless dancers in dark silence you notice a line that divides the stage in half and the line has a large one-way symbol pointing to the right. As the stage lights come up, our dancers awaken and begin to randomly walk around the stage. This represents the motion of electrons in a solar cell once the sun is shining. You marvel at the dancers’ movements under the bright lights of the stage and notice something curious. Although each dancer (a.k.a. electron) has a random motion, they are all beginning to congregate on the right hand side of the stage because after they cross the center line, the one-way (P/N junction) does not let them randomly walk stage left. So the stage is loaded with flying dancers on the right while only a few remain on the left. This represents a charge separation and will produce electricity if “released”. So, the last step in our geek-fest interpretive dance of the solar cell is to picture a tube (representing an electrically conducting wire) placed on the stage that allows the dancers on the right to crawl through and get back to the left where there is more space. Many of them crawl through the tube and as they do, you realize that they represent electricity flowing through a wire and are awestruck by the simple elegance that is a solar cell. As the curtain closes you clap, cheer and exhale greenhouse gases to show your appreciation.

Hope this helps to explain how things work. I figure there is never a wrong time to invoke an interpretive dance analogy when explaining complex physics processes.

Wednesday, June 2, 2010

Oil and Water

You may have heard that oil has been leaking in the Gulf of Mexico for weeks as a result of a rig accident and is causing an environmental nightmare. News about global warming and the effects of burning fossil fuels are all over the news. We are bombarded by dire predictions that we are running out of energy and that we need to reduce our dependence on carbon-based fuels. Why is it so difficult to get energy from other sources? To understand why this is tough we need to first understand energy and all its forms.

Energy is an illusive thing. From a physics standpoint it is the ability to do work on a system. Translated into English this means we can use energy to do stuff like propel our cars, heat our homes, power the refrigerator, send a baseball flying over the left field fence, etc. Carbon happens to be a very nice way to store energy. When you burn carbon, it produces heat, a form of energy (as well as water and carbon dioxide a.k.a. a “green-house” gas). Even cavemen knew that fire was good because it can be used to warm the cave. What they may not have realized is that energy is easily stored in the form of wood, oil or other chemical forms. They just knew: “fire good”. Long after the cavemen, electricity was discovered and quickly became popular because it is easy to transport from a central location and can be used to power up many devices that make life easier like toasters, fans, lights, etc. I’ll speak more about electricity later.

Getting back to the Gulf oil leak, the reason oil is so nice is because it can be refined into gasoline to power our cars. Like most chemical sources of energy, this is a very convenient form to store energy in for use at a later time. Have you ever run out of gas and tried to push a car down the road? It requires a lot of energy to move a car. Gasoline packs a lot of energy in a relatively cheap, easy-to-use, liquid form that stores well. Simply stated, it requires energy to move an object like a car from point A to point B. And while gasoline is the most convenient energy source for this task, there are many environmental drawbacks.

It has been difficult to find an alternative power source for automobiles despite all the scientific research. One alternative is Ethanol from corn, sugar cane and other sources. Although there is no chance of a catastrophic oil-leak-type disaster from a corn field, it has other drawbacks and still produces “green house” gasses when burned to power your car. Battery powered cars seem pretty cool. A battery is a nice way to convert chemical energy into electricity without any moving parts but they don’t last very long and currently are really heavy. Don’t be fooled into thinking that batteries don’t contribute to green house gases either as they are typically charged by plugging them into the wall. The electrical energy from the wall socket might come from coal-fired power plants. So I say, just bike it! Remember however that when you bike, you are burning (in the biological sense) calories and producing greenhouse gases each time you exhale.

In summary, chemical energy in the form of fossil fuels are particularly easy to store, use and extract from the ground. The typical way to release the energy from a chemical source is by burning them but remember this produces greenhouse gasses. I’ll consider other energy sources like electrical, nuclear, wind, etc later. Right now though, I have to go chop some wood so I can use it to heat my ‘man cave’ next winter.

Monday, May 10, 2010

Why are vampire movies so popular?

It’s well known that LEDs produce a single color of light, like green, blue, red and amber. Mixtures of colors like purple (red and blue) or even white (full color spectrum) are possible only when the LED is used in conjunction with a phosphor. A phosphor is a material that emits light when it is excited by light. So a phosphor takes in one color of light, say blue, and reemits another color or typically a variety of colors. Sort of like the game you used to play in elementary school called “telephone”. Remember, you give your neighbor a message and then it gets translated into an entire spectrum of messages by the time it makes it around the circle. Phosphors do the same sort of thing with light so they are useful at converting a blue LED into a white LED for example.

The phosphors that are typically used in LEDs are similar to those found in fluorescent light tubes. In fact, if you’ve ever seen a broken fluorescent tube there is a white powder on the inside of the glass. That powder is the phosphor that converts the inherent UV light of the fluorescent tube into white-ish looking light. A fluorescent light tube without this phosphor layer is the ever-popular “black light”. Anyway, the light produced using phosphors is not really “white” light. In fact, the light is largely void of any red light component. Hence, you look like a vampire when you see yourself illuminated with a fluorescent light or white LED light. Without a red component, your skin looks like it is without blood since there is no reflected red light to show your true rosy color. Researchers around the world are looking for better phosphors to improve the color of LED light but it is a difficult challenge because current phosphor technologies are inexpensive, long-lasting and efficient. For now, we have to be content with white-ish light from these efficient light sources but someday LEDs and fluorescent lights will have better color quality because of a new phosphor technology or other discovery.

I’m not really into that whole vampire phenomenon that has swept the nation and I don’t understand the wild popularity of pasty-white teens biting each other. Sure some feel it is because Edward is so handsome. From a scientific standpoint, the popularity may be driven by the fact that people are replacing incandescent (full-spectrum white) bulbs with LEDs and fluorescent bulbs that make you look like a vampire. Under the white-ish glow of today’s light sources, perhaps today’s teens see a bit of themselves in the characters on screen. Just a thought.

Wednesday, April 28, 2010

You can’t melt an action figure with an LED

When I was a kid, my brother and I were playing with our action figures; G. I. Joes to be exact. We got distracted and turned our attention elsewhere for a while until we started smelling burning plastic. My mother’s keen nose helped her quickly sniff out the problem. My (not very bright) brother stuck his action figure in the lamp as a hiding place and the heat from the light bulb was melting poor Joe’s backside. Childhood tales like this will soon no longer be possible, not because G.I. Joe is no longer popular, but because of the heat source that melted his nether-regions. The goal of a “light bulb” is to produce light, not heat. Any heat production is an unwanted byproduct and represents conspicuous inefficiency. Australia has already banned the sale of incandescent light bulbs because of their inherent inefficiency and other countries, including the US, are following suit.

The two big alternatives to incandescent bulbs are compact fluorescent lamps (CFLs) and light emitting diodes (LEDs). You can read a lot online about the pros and cons of each. Since we are stuck with these technologies for the foreseeable future, we might as well understand how they work. As I’m a big fan of beating a dead horse, I’ll explain their operation in the same context as my last blog – through dance!

In my last blog, I talked about semiconductor physics and how they generally do not conduct electricity until they are given a stimulus. When stimulated, the electrons can move in the semiconductor but after the stimulus is removed the electrons transition back down to their natural non-conductive state. When electrons transition from “conductive” to “insulating” states, light is often emitted in the process. Now picture the semiconductor dancer from my previous blog. When stimulated with the spot light, she dances freely, but when the light turns off she falls to the floor as an insulator. In a dramatic move right before collapsing to the floor, she gives off a burst of light (radiative recombination to physics folk) – this is basically how a light emitting diode works. Taking this analogy way beyond its limit, her heritage determines the color of light that she emits. For example, a Latin dancer will produce a red light, a Russian dancer a blue light, an Asian dancer a green light. Translated from the stage back to semiconductor reality, this means that the color of light emitted from an LED depends on what materials are used (amaze your friends by saying, “an LED’s wavelength is determined by the material’s electronic band structure”). I often joke that LEDs come in any color you want as long as it’s red, amber, green or blue. These colors happen to correspond to semiconductor materials that are readily mass producible and illustrates the point that LEDs emit one color only. Next time you look at multi-color LED Christmas lights, you will notice the aforementioned LED colors because they are the least expensive to produce.

Anyway, since the light from LEDs is produced by electrons transitioning between states, there is very little waste energy, therefore they generally do not get “hot” like a light bulb and are more energy efficient. I know what you are thinking; because the light in an LED is produced through radiative recombination events it is inherently monochromatic, so how do you explain white LEDs? More on this later…..

Wednesday, April 21, 2010

Interpretive Dance and Semiconductor Physics

Greetings! I am beginning this blog to help explain some of the mysteries of technology because it is difficult to keep pace with all of today’s advances. I want to provide an understanding of the esoteric scientific underpinnings that surround our everyday life. I’ll take on hard-hitting topics from nanotechnology and chip fabs to Mentos and Diet Coke. I will try to explain seemingly unrelated topics from Hudsons voyages to the latest lyrics, all from a scientific viewpoint. As humans, we all see the world differently. Scientists see the world as simply reflected electromagnetic radiation with wavelengths between approximately 400 nm and 750 nm. This blog will explain ideas from this point of view without boring you with scientific jargon and long-winded descriptions. It will hopefully be fun, relevant and educational “info”tainment.

For my very first post, I thought it might be useful to explain some of the science behind semiconductors as the Capital Region is arguably becoming a major hub of semiconductor activity. To me, a semiconductor is one of the most misunderstood materials. The mention of the word ‘semiconductor’ often conjures up images of computers; the two always seem to be intertwined. But why? While semiconductors are used in computers, they are also used in LEDs, solar cells, sensors, and zillions of other electronic gadgets.

A scientific explanation of semiconductors involves looking at the electronic band structure and noticing a characteristic band-gap between conduction and valance band. However, explanations like this are tough stuff. As such, I’ve come up with my own analogy to explain semiconductor behavior through interpretive dance. That’s right, interpretive dance. I figure this explanation will stick with you and you can use it at your next cocktail party to look like a genius.

Imagine a stage with a dancer laying motionless on the floor. This motionless dancer is ‘the insulator’. Glass, plastic and ceramics are all traditional insulators because they don’t pass heat or electricity very easily. Now picture a hyper-active dancer jumping all over the stage with a flowing ribbon in tow. This dancer is ‘the conductor’ and simulates the behavior of electrons in a conductor. When most people think of conductors, they think of metals because they conduct electricity and heat very well - that’s why we make frying pans and wires from them. So we have one dancer laying motionless on the stage (‘the insulator’), one dancer leaping across the stage with flowing ribbon (‘the conductor’), and now enters ‘the semiconductor’ as a third dancer. Picture a dancer, motionless on the floor like ‘the insulator’, until a laser spotlight shines on her and she starts leaping around like ‘the conductor’. Once the laser spotlight moves away from her, she falls motionless to the floor again. She remains motionless until the laser shines upon her to excite her once more into dancing. This is ‘The Dance of the Semiconductor’. A semiconductor is inherently an insulator but can be made into a conductor given a stimulation; hence the name ‘semi’ conductor. The stimulation can come as an applied voltage, as heat, or in this case via laser excitation.

Which is what makes a semiconductor such an interesting material; they conduct like wire but without stimulation revert back to being an insulator. Because of this ability, they make really good on-off switches. A fancy version of an on-off switch is called a transistor, one of the key building blocks for computer logic which is why people map semiconductor materials to computers. Now, however, we have learned ‘The Dance of the Semiconductor’ and understand this “Dancing Queen” can be used in many ways. I think ABBA summed up the potential of semiconductors best, “See that girl, watch that scene, dig in the dancing queen”.

There are several resources online that explain more about semiconductor applications:

and my favorite site which explains nano-sized semiconductor particles:

Full-Disclosure, I’m the founder and CEO of Evident Technologies so I’m a bit biased.