Hizook

Roland Piquepaille had an interesting write-up on an Israeli teams' efforts to create a miniature, inductive-powered robot to explore the inside of the human body (blood vessels in particular).

At first, I thought the above image was the actual prototype, in which case I would have been very impressed. Then, I read on...

You can see above "an artist's rendition of what the tiny submarine robot would look like." (Credit: Unknown, via the Jerusalem Post)

"Artist's rendition," indeed.

The researchers stress that the project is an "interesting development, but it has a long way to go before it is used in medicine." Solomon says that the tiny robot could be controlled for an unlimited amount of time to carry out any necessary medical procedure. The power source is an external magnetic field created near the patient that does not cause any harm to humans but supplies an endless supply of power for it to function. The robot's special structure enables it to move while being controlled by the operator using the magnetic field.

Yep, makes sense to use inductive/magnetic coupling for power, create the smallest such robot (that I know of), and claim great aspirations about fighting cancer and malignant tumors, but where is the functional prototype? "A long way to go," no doubt. I think there needs to be a little more substantiation when making such extreme claims. Publications are always good, as are active project websites.

Anyway, I've have seen a fair number of actual gastrointestinal robots for endoscopies (aka, "inside the human body") that use a similar idea. Most use peristaltic (undulating) motions to prevent tearing, lacerations, and punctures. However, some designs still use "gripping" feet mechanisms. One great example is a hybrid design from Carnegie Mellon (project homepage here and press release here). Most importantly, they are already performing testing in plastic tubing and pig intestines.

	This prototype shows a "six-legged" (actually, they apply pressure to the gastrointestinal tract walls) robot.
	This is another prototype (apparently 3-legged?) robot in an actual capsule.
	An overview of the CMU approach. Click on the image to enlarge.

Another great example comes from a New Scientist article entitled "Worm-inspired robot crawls through intestines." It features work performed by a multi-national European research team, and again, this research has produced working prototypes (with videos)!

	A prototype crawling through a pig intestine. Be sure to check out the video here.   (Local copy of the video here)
	A more recent prototype being held in a researcher's hand. Check out the video of the legs actuating here.   (Local copy of the video here)

I'd like to take a moment to rant about what seems to be "bad" journalism. First, I'd like to pardon Roland Piquepaille, as he represents a fair amount of skepticism in his article. However, the remainder of the blogosphere is taking this "advancement" on dogmatic faith as an absolute truth. Maybe the Israeli team's work is a huge advancement, but maybe it isn't (there just isn't enough data at this point to make a clear distinction). Either way, the blogosphere isn't helping science by disseminating (mis)information. This is just plain wrong, and I hypothesize (along with some colleagues) that this may be true of several other recent "advancements" featured on many blogs.

I make a pledge to represent anything I post as accurately as possible, and to the best of my knowledge (what little I have). Hopefully the other blogs will too.

This is a cool idea (from PopSci):

Never Lose Another Memo -- Soon, staples won’t just keep papers together—they’ll make sure you keep them, period. As RFID tags shrink in price and size, Swingline wants to embed them in staples so that lost documents can radio their location to a tracking device.

I think the idea is really great, and would have been useful to me, except for one fact...

I bought a Tablet PC (a great Fujitsu Lifebook) so that I don't need to worry about print materials anymore. My homeworks are written (literally) on the tablet, then printed for submission, and almost all handouts are provided in electronic form. My organizational skills are two orders of magnitude more advanced in the electronic realm than they ever were in the physical realm.

A similar concept to the RFID staples might still be useful for my textbooks though, at least until I can get them in PDF form. Speaking of which, they should really offer reduced-priced textbooks in PDF form. They'd save a bundle on distribution. I guess they're just reluctant to do so without DRM

[Via OhGizmo]

This is a follow-up (actually, a response to criticisms) regarding a previous post, called: Why Nuclear Byproducts Could Be a *GOOD* Thing: Making Yucca Mountain Profitable.

First, I'd like to address the comment from "Anonymous" about Pu-238. You are right. Not having a purely-alpha-emitting material is a big problem. The mass of beta and gamma emitters is small (or non-existent). They would effectively contribute nothing to thermal heating, thus contribute nothing to the thermoelectric generator's (TEG) output power. However, you should consider the depleted uranium (DU) decay chain seen below (most of the waste for Yucca Mountain is going to be DU, I believe).

What this shows is that all decay steps involve the transmission of either a alpha particle or beta particle, accompanied (optionally) by a gamma particle. Looking at the process, we can see that the ratio of beta-to-alpha decay is about 50-50. Thus, our power efficiencies should effectively be halved due to this fact!

Now I'd like to address the comment by "Anonymous" about efficiencies (and a few other topics). Again, you are also correct. The efficiencies of TEGs are very low! There is a company called "ThermoLife" that makes the product shown below. In their academic paper, they accurately describe the efficiency (with a temperature difference of 5°C) to be on the order of 0.2% to 0.8%. Even though the efficiency is VERY low (especially for low temperatures), they can still generate a usable amount of electrical power. In fact, it is enough to drive a wristwatch (among other applications)!

The fundamental limit of the amount of energy obtained from a temperature difference is given by the Carnot cycle. The Carnot efficiency is an ideal thermodynamic value expressed by (T_H - T_C)/T_H = ΔT/T_H. where T_H and T_L represent the high and low temperatures of the thermodynamic cycle. According to this quotation, the Carnot efficiency gets smaller with decreasing of temperature difference, e. g. from room temperature (20°C) to human body temperature (37°C) the Carnot efficiency is limited to 5.5% and a temperature gradient of 5°C leads to a Carnot efficiency of only 1.6%. Furthermore the best thermoelectric materials achieve maximum efficiency values up to about 17% of Carnot efficiency in the range of small temperature gradients [5]. Considering this limitation a conservative estimation of the efficiency for standard thermoelectric materials lies in the range from 0.2 to 0.8% for temperature differences from 5°C to 20°C [14].

Before I calculate the "actual" efficiencies of my proposed system, I'd like to address the other two criticisms in this comment. First, please note that we are NOT driving steam with the heat! A TEG uses a heat difference across across solid conductors. The TEG would consist of a layer of devices that would sit between the nuclear material's inner protective jacket and the outer radiation shield (I think both are being made of stainless steel, but I could be mistaken). This actually forms one solid "chunk" of metal with the TEG and depleted uranium sitting at the center. TEGs require zero moving parts, and that is one of the beauties of the system. There is little-to-no mechanical wear or system degradation, no pumps, no valves, and no radioactive water! If you'd like to see what I'm talking about, the NASA ones are a good example (here and here). Otherwise, take a look at ones that are being attached to the exhaust pipes of military vehicles (from this source, or here locally). Imagine (like the NASA ones mentioned above) that the depleted uranium is stored where it says "Exhaust" and that the outer radiation shielding acts as the heat sink ("Heat Exchangers").

The second criticism regards the heat gradient that would be created. The TEGs built by NASA had an inner temperature of 600°C. Because of the alpha-beta argument above, lets make a conservative estimate of the core temperature of 250°C. This heat is being dissipated through a large, outer radiation shield. I'd like to point out that this temperature will exist regardless of the existence of the TEG. Lets assume that the temperature drop across the TEG is 50°C, and the remaining temperature drop is through the outer radiation shield. The outer temperature (of the radiation shield) would be that of ambient air. Since the facility is deep underground, I think it is safe to assume (even with Nevada heat raging on the surface), that a background temperature in the tunnels could be about room temperature, or 20°C. Some forced-convection air flow may be necessary to augment heat conduction through the air, but this can be solved using an ionic wind "fan" (much like the commercially available air purifiers). This would again have no moving parts, and again, it would be necessary regardless of the existence of the TEG. We're putting the TEG in place to "scavenge" power from this heat gradient; in fact, the TEG could be used to generate the power to (at least) create this air flow! That's the whole idea of this proposal: Use the inherent "problems" with the Yucca Mountain site to make it more "green."

To prove that I'm not making up the power generation numbers, take a look at the efficiency calculations below... I'm not going to work through the device physics, if you're interested in that aspect, look at this paper. Instead, I'll use the NASA TEGs as a base-line, then extrapolate. First, lets look at my assumptions:

The NASA numbers come from this previous post. I'm assuming that the efficiency of the NASA TEGs was 15% of the Carnot efficiency (a bit lower than that mentioned in the article above, but considered a safe estimate given 30-year-old technology). For our efficiency, I've selected 25% of the Carnot efficiency. The reason for the increase is that new quantum well thermoelectric generators have shown a power-factor increase of at least 50% over "traditional" TEGs. Thus, I have underestimated the efficiency of ours (to be safe). The "Relative" efficiency (called "rel") is used to compare the number of alpha emitters in each case. We saw earlier that we expect about half the amount of alpha decay compared to Pu-238, thus a "Rel" value of 0.5 for our device. Now lets set up the relative comparison and see what sort of power we can expect...

As you can see, we're still talking about 400 MegaWatts of electrical power! This still equates to a small nuclear reactor!

Every year, the United States (and the rest of the world) suffers financial losses in the billions due to nuclear byproducts from power generation, weapons decommissioning, etc. There are problems in transportation, short-term storage, long-term storage, safety, etc. Unfortunately, we cannot eliminate these problems, but we can make them as palatable as possible. For instance, the Yucca Mountain facility is a huge botched opportunity!

If you're curious about the technical details of Yucca Mountain, look at the Nuclear Energy Institute's website. To save you some trouble, I'll summarize a few key facts. The facility has the capacity for 120,000 metric tons of nuclear byproducts, though a limit has been set by policy at 70,000 metric tons. The costs associated with this project are huge.

[Because of disposal costs] Congress imposed a fee of one-tenth of a cent per kilowatt-hour of nuclear-generated electricity upon consumers. This fee generates about $750 million a year, and balances in the fund accrue interest.

[To build the facility] Assuming that the government eventually meets this obligation, each additional year of delay costs taxpayers an estimated $1 billion, according to the Department of Energy.

Essentially, the "extra" costs for nuclear power are being handed to tax-payers. Split evenly over the ≈300 million taxpayers, this equates to about $5.83 per taxpayer. I'm sick of paying that unnecessary $5.83 each year. I previously promised a *BIG* insight into Radioisotope Thermoelectric Generators (RTGs), so here it is:

Solve the world's nuclear waste woes by scavenging power from its byproduct radioisotopes!

I've written extensively about RTGs being used in NASA Space programs. There were the RTGs on the Voyager crafts, and also on the Apollo moon missions (shown above). The documentation for the Apollo ones is quite good; they generated 70 Watts from 3.8 kg (about 8-pounds) of Plutonium-238. Additionally, after 30 years of operation, the Voyager RTGs are still functioning without a single RTG failure! Keeping all this in mind, take a look at the "quick-calcs" below.

Using the 70,000 metric tons measure, the facility could be generating $1.2 Billion per year (assuming an average energy price of 10.65 cents/kWh, which is determined annually, here). The amount of power generated would be ≈ 1.3 GigaWatts, which matches the output of some of the world's largest nuclear power plants. Combine that with the fact that an RTG power plants' expected lifetime (duration of power generation from the radioisotopes) is on the order of hundreds-to-thousands of years (one of the purported "downsides" of nuclear byproducts), and you have a facility that will continue to produce power for a very, very long time (and still be relatively safe)!

Not only can we save the $-billions required each year in taxes & losses, the facility could be self-sufficient and recuperate its already staggering losses. It would also provide an effective "extra" nuclear power-plant for the region, benefiting its surrounding communities. It would continue to be operational as long as there are radioisotopes present, which will be for a very, very long time. If nothing is done, it will be a supreme waste.

I'm sure there are a number of astute readers will note that RTGs at Yucca Mountain could not operate using Plutonium-238 as did the Apollo missions. Nor could they be operated at the extreme temperature differences achievable in space (reducing the Carnot efficiency of the process). Not to mention the fact that you'd need to spend a fair amount of the generated power to manage (cooling and general electrical power) the facility.

You'd be correct; all of those things reduce the overall efficiency of the system. However, there have been some advances in thermoelectric power generation in the last 30 years. Consider the MEMS units shown above (and actually used in wristwatches, as described by a previous post here). Couple that with the still very "new" quantum well thermoelectric generators (local copy here), which appear to offer an order of magnitude better efficiency (shown below). Also, the calculations above only considered 70,000 metric tons, versus the 120,000 metric ton capacity. This increases the power generation by almost a factor of 2. All things considered, you can still achieve a "usable" amount of electricity from the system for a very long time.

A few closing remarks: As far as I can tell, the idea to use the Yucca Mountain (or any nuclear waste storage facility) for power generation is an untapped resource. I'm not entirely sure of the efficacy of this idea, and I'm sure there are many un-addressed engineering issues associated with such a project. I'm releasing the idea because I'm sick of the wasted opportunity, the untapped resource that is otherwise a detriment to our environment, and in general to "help the world." I ask two things. First, tell everyone you can -- I want this to get enough press to bring it to the attention of those "in charge." Don't let the opportunity be wasted. Second, remember that the idea originated here, by Travis Deyle.

** This article has been submitted to both Digg and Reddit.

For small robots (in particular), jumping is an efficient means of locomotion. The only energy loss you suffer is from slippage at the jump surface and drag while in flight. This is why so many small animals (such as fleas, grasshoppers, etc) use jumping as their main method of locomotion. Well, consider the image below.

That bug isn't a robot, but it is the inspiration for microrobot vehicles. If you incorporate scavenged energy, electronic brains, micro-scale actuators, and swarm capabilities, you have a very functional system (and possible base platform for large robotic swarms)! Enter Sarah Bergbreiter from UC Berkeley.

For me, mobile autonomous microrobots are defined as millimeter-sized mobile robots with power and control on board. These robots offer numerous advantages due to their size and low power requirements. For example, millimeter-sized microrobots could be used to add mobility to sensors in large-scale sensor networks as the size of those integrated sensors shrink as shown in the Berkeley Smart Dust Project.

At the millimeter size scale, jumping can offer numerous advantages for efficient locomotion, including dealing with obstacles and potentially latching onto larger mobile hosts (larger robots, animals, vehicles, etc).

Sarah and team have been developing a jumping actuator for microrobots. The actuator uses electrostatic "inchworm" motors to add tension to a custom-made silicone (elastomer) micro-rubber band. The rubber band is released, driving a foot/leg which performs the jump. There isn't anything particularly novel about the MEMS techniques, but the use of actuation on a microrobot or sensor platform is a very cool research area (and one that I plan to pursue for my PhD!).

She has two research papers about this device:

• Bergbreiter, S.; Pister, K.S.J. "Design of an Autonomous Jumping Microrobot," accepted to ICRA 2007. (paper pdf)

• Bergbreiter, S.; Pister, K.S.J. “An Elastomer-Based Micromechanical Energy Storage System,” ASME 2006, Chicago, IL, November 5-9, 2006. (paper pdf)

She also has two very cool movies:

Demonstrating the quick release capabilities of the energy storage system. The leg is first held in place by large electrostatic clamps before release and shot an 0402-sized capacitor ~1.5cm along a glass slide.

Inchworm motor pulling an assembled micro rubber band. Watch the parallel flexures on each side to see the 30um of motion. Approximately 5nJ of energy is stored and released.

If you'd like more technical details, I'd check out her papers (above), website, or the MIT Technology Review article on the subject. (I also have local copies of the papers here and here as well as the videos here and here, all for posterity).

Recently I've written a lot about Thermo-Electric Generators (TEGs) and Radioisotope TEGs (called RTGs). I've written posts about micro TEGs, and RTGs used during the Apollo moon missions.

Well, it turns out that RTGs have been used for a long time in space missions. They were even used on the Voyager spacecraft, launched in the 1970s! In fact, Voyager 1 is the most distant man-made object from Earth. Despite the fact that it was launched almost 30 years ago (it was launched Sept. 5, 1977), the RTG has kept it powered and operational. You can see a picture of the Voyager RTG above. To quote:

"After a quarter of a billion device hours, not one of the 1,200 thermoelectric generators on each Voyager has failed," says Vining, who used to work at the Jet Propulsion Laboratory in Pasadena, Calif.

Curious... Stay tuned for a *BIG* insight regarding RTGs...

Imagine having sunglasses which can change color or opacity on-demand with the flick of a switch! This is the goal of Chunye Xu (and team) at the University of Washington. In the image below, the lenses block 55% of incident light (on the left) and 95% (on the right). There is also a video of the lenses in action (locally here).

The sunglasses use a thin-film of electrochromatic material. Wikipedia has a decent page that discusses the effect. It is also described in the news release as follows.

Researchers made the glasses using electrochromic materials that change transparency depending on the electric current. Many groups, including the UW, are developing such materials for so-called "smart windows" that could soon be used in energy-efficient homes and offices. Most smart windows use liquid-crystal technology or inorganic oxides. Those materials are expensive to produce and require a constant or frequent injection of power to hold their tint. The UW glasses are based on a new type of smart window using organic, rather than inorganic, oxides. These are cheaper to manufacture and require less power.

The prototype glasses are powered by a watch battery that attaches to the glasses frame, and the wearer spins a tiny dial on the arm of the glasses to change color or shade. The lenses were created by sandwiching a gel between two layers of electrochromic material. Applying a small voltage moves charged particles from one layer to another, and changes the transparency. Once the glasses are a certain tint they will stay that way without power for about 30 days. A single watch battery is able to power thousands of transitions, Xu said.

Also, the prototype shown above only produced blue hues. This isn't exactly "new," as viologens (another electrochromatic material) produces a bluish hue. However, the big breakthrough comes in the ability to create red and green hues, which Xu and colleagues have done, as discussed in their academic paper (or here locally). This opens the technology to some new applications (from another news release).

By combining the polymers of different colors into multiple layers and supplying different levels of current from the batteries in the sunglasses, a wide variety of different colors can be produced in the lenses, Xu says.

If the power consumption is low enough, this technology could be used (instead of the magnetic bead technology) for the next generation of electronic-ink (or E-Ink) and electronic-paper. Electronic-paper is already being touted as one of the "next big things" for smart materials. In fact, we've already seen commercial products, such as the Sony Reader pictured. Electrochromatic electronic-paper would allow for color rendering yet still boast the very low power consumption required for prolonged operation. Further, the electronic-paper would be read (much the same as "normal" paper) in lit conditions. If thin-film solar cells can be integrated into the electrochromatic layers, the electronic-paper could be entirely self-powered!

So a question that could be posed is "How is this better than the lenses that change transparency when you go from indoors to outdoors?" Well, those lenses use the photochromatic effect, where the lenses change color/opacity based on the amount of incident light. In this case, the lenses are sensitive to UltraViolet (UV) light. When outdoors the lenses become darker in the presence of UV, and when indoors the lenses become lighter as the UV is no longer present. There are 2 or 3 problems with photochromatic lenses (compared to these new electrochromatic lenses).

• When you're in the car, the car's windshield blocks much of the UV light, causing the lenses to become more transparent. Since people spend most of their outdoor-time inside their car (well, at least I do), the lenses' ability to turn dark is useless.

• You can't adjust the lens settings to be brighter or darker based on your personal lighting preference. My threshold for bright light is much less than most other peoples'. This might have something to do with too much time in front of a computer monitor...

• For those who care about fashion, you can't change the color of photochromatic lenses to match your attire. (I personally don't care about this though.)

I'm spending (part of) my spring break visiting the Smithsonian Museums in Washington DC. Naturally, my favorite one is the National Air and Space Museum. While there, I came across many very cool historical items. One was particularly interesting. Recall my post about a MEMS Thermo-Electric Generator (TEG). Well, it turns out the same technology was used during the Apollo missions to power their Apollo Lunar Surface Experiments Package (ALSEP), only on a macro scale.

The Thermo-Electric Generator on the ALSEP was called the Systems Nuclear Auxiliary Power (SNAP-27), and was a Radioisotope Thermo-Electric Generator (or RTG). The RTG that powered the ALSEP was actually powered off a canister containing 3.8 kilograms (over 8 pounds) of Plutonium-238. As the Plutonium went through radioactive decay, the particles emitted would collide with the container walls, heating it up to 600°C (1100°F). The TEG sat between this container and some heat-fins, which radiated heat to keep the cold side of the TEG at around 275°C (530°F). It produced about 70 Watts of power (via 442 thermoelectric elements). Even after 10 years, it still output 90% of its original capacity. The image shown is actually Alan Shepard's shadow in front of the RTG during an Apollo 14 moon walk.

I've included a few pictures below. The first is the Plutonium container, while the other two are diagrams of the SNAP-27.

So what do you do with ≈70 Watts for 10 years? Well, the ALSEP was designed (across several Apollo missions) to perform many experiments, illustrated below.

The image shows a variety of experiments (from this site):

1. ASE Mortar Package Assembly
2. Heat Flow Experiment electronics box
3. Solar Wind Spectrometer
4. Suprathermal Ion Detector/Cold Cathode Ion Gauge
5. Lunar Surface Magnetometer
6. Charged Particle Lunar Environment
7. Passive Siesmic Experiment
8. Laser Ranging Retroreflector
9. Lunar Ejecta and Meteorites Experiment
10. Lunar Atmosperic Composition Experiment
11. Lunar Surface Gravimeter

I suppose the RTG is a well-suited power supply for space-based robots. I wonder (given the abundance of nuclear waste) why doesn't NASA use RTGs more frequently for robotic exploration... Why not power Martian rovers by RTGs instead of solar (or as a long-term companion to solar)? I mean, the RTG was designed to be "safe" for re-entry. In fact, the Apollo 13 RTG was scuttled along with the lunar module due to difficulties during the mission; it is currently lying in the Tonga Trench.

OK, this post is a bit long, but that's because the topic is really revolutionary (and fits nicely into several of my personal interests). First, I'll go over an abridged version with pictures and videos, then get into a little more scientific discussion.

Basically, the idea is that you place a diode in a liquid (or on its surface), and then apply an alternating current (simple AC) signal across the liquid. The diode will then be propelled through the liquid. Don't believe me, check out this video. You can then hook up the diodes in a large ring, and it will spin like a gear (video). Use a LED and the circuit can light up. Use a zener diode, and you get constant velocity. Use a photodiode, and you get light-controlled velocity. Make the diodes stationary, and you can pump the liquid (even at the micro scale). Use multiple diodes to make a (micro) mixer. Use lots of diodes to make micro robots (not done yet, but conceivable). It's all quite interesting, and it can be done in a fish tank!

   

OK, now for the advanced section. The principle works using the parasitic capacitance of the diode. During half the AC cycle, the diode will be forward biased, and nothing happens. During the reverse biased half-cycle, a parasitic capacitance will cause a charge to be built up across the diode terminals. The electric field from the capacitor causes fluid to flow via electroosmosis (basically, charged ions in the fluid move in response to an electric field). The motion of the fluid around the diode causes an "equal and opposite" force on the diode, propelling it forward. Of course, there are many factors that affect the rate (such as fluid pH). The whole process is described (along with the applications previously mentioned) in the article.

This all begs the question, "What sort of propulsion can you get, and what other devices can be used?" Can we cause rotation using one diode? Can we inhibit or enhance the effect for better control? Can it be controlled by a microcontroller? Can it be done over large distances using RF coupling instead? What if a bipolar transistor (NPN or PNP) is used? What sort of motions are produced by them? Obviously, a parallel-plate capacitor would have a zero net electroosmotic flow, but can the geometry be altered so that even a capacitor can exhibit this effect? All very good questions, and I intend to build a fish tank to test them out!

Anyway, the article also includes a "supplementary material" section that has a whole bunch of movies, which are described below.

All movies are real time except Movie M7 (double-speed) and in WMV format. The semiconductor devices on Movies M1-M6 float in a large Petri dish full of 1e-6 M NaCl solution. Two AC-powered electrodes from thin wire are placed above and below (or left and right) of the scale. E(ext) was 120 V/cm and the frequency was 1 kHz. The scale on the back is spaced at 1 cm in movies M1 to M3, M6 and at 0.5 cm in movies M4 to M5.

• Supplementary Movie M1: A 1-mm long semiconductor diode propels to the right when the field is turned on. Field direction is horizontal.

• Supplementary Movie M2: A low magnification view of a miniature diode propelling. The diode (small speck near the bottom of the first frame) covers a distance of almost 5 cm in about 43 s. Field direction is vertical.

• Supplementary Movie M3: Two LEDs orient vertically when the field is turned on, light up and begin propelling. Note that the diodes move in opposite directions because they are oriented oppositely with respect to their electrode polarity.

• Supplementary Movie M4: "Diode-powered gear" begins rotating when the field is applied due to the directional propellant force of the diodes attached around the O-ring.

• Supplementary Movie M5: LED-powered gear without external illumination. The diodes rotate the gear and light up - note that the lit diodes are always to the left and right of the gear as they are the ones receiving most power from the surrounding vertical field.

• Supplementary Movie M6: Motility of photodiodes controlled by exposure to light (from laser pointer). The photodiode velocity drops sharply when they are illuminated and is restored when the light is turned off.

• Supplementary Movie M7: Separation of two types of particles within the channel of the microfluidic device in Figure 1. At first, only an AC field is applied and both types of particles rapidly move to the right by diode pump driven flow. However, under the simultaneous action of balanced AC + DC external fields, the small particle (1 µm amidine-stabilized latex) very slowly moves to the right, while the large particle (2 µm sulfate-stabilized latex) begins moving to the left. Compare with Figure 5.

I've also saved local copies of the movies (M1, M2, M3, M4, M5, M6, and M7). I originally found out about this article from New Scientist.

For a class of mine (specifically, a class on Micro-ElectroMechanical Systems, or MEMS), I'm doing a semester project on a "Thermo-Electric Generator (TEG) for Energy Scavenging." I'm most interested in Ubiquitous Computing applications for such a device, but I'm certain that there are many other possible application spaces. Anyway, this first article will address how they work and a sample application (expect a second follow-up to discuss some technical specifics such as manufacturing and capabilities).

The physical effect being realized is the Seebeck/Peltier effect, in which a temperature difference is converted into a voltage difference, and vice versa. In one operating mode, a voltage is converted into a temperature difference -- this is referred to as the Peltier effect. There are a number of devices that use these for heating and cooling (even for microprocessor cooling). In the other operating mode, a temperature difference is converted into a voltage (referred to as the Seebeck effect), thus generating electrical power. It is the 2nd operating mode that a TEG uses to generate power (see image).

So, wherever there is a temperature difference, there is a chance to use a TEG. On-body applications are a real possibility; this fits nicely in Ubiquitous Computing. A good paper on the subject was written by one of my professors/friends, Dr. Thad Starner (here also for posterity). Not only is it possible to use them on-body, a MEMS TEG was created by Seiko to power their Thermic series of wristwatch!

Let's look at the Seiko Thermic (pictured). According to this website, only 500 of these were made (back in 1998), at a cost of 300,000 Yen (or over $2500 USD at the current exchange rate). Seiko also has an informative page about the Thermic. If you take a look at a Scanning Electron Microscope (SEM) picture of the TEG inside the Thermic wristwatch, you can see the P-N junctions stacked vertically (pictured below). I'll explain how these are made, and their capabilities in the next post on the subject.

As a side-note, I'd be interested in acquiring one of these watches. If you're feeling philanthropic, you could buy me one as a gift. Otherwise, I'd be almost as happy if you just notified me when one came up for sale.