All The Answers

Buenos Dias! The last time I apologized for a short post, it didn't end up being a short post at all, but this time I honestly don't have too much to add. Even so, I feel like I accomplished a lot this week. Since practice presentations begin next week, this week I really had to bear down (ha) and finish up my powerpoint. It's one thing to do a ton of reading and research, but it's a totally different thing to sit down and try to figure out what is worth presenting to you guys, and most importantly, what the answers were to my original research questions. Just to recap for everyone, my primary research question was if the tracking system currently used to track sea otters in Monterey can be improved, and if so, how. After hours of reflection, making charts, and flipping coins (kidding), I can finally say that I have an answer to that question. If you want to know what my answer is... well, I won't spill the beans until my presentation, so you'll have to come and find out!

As for the secondary research question (that isn't really a research question), which was whether or not I like engineering, I can safely say that I do indeed enjoy engineering. Learning about and going through the engineering process was a lot of fun, but it also stretched me in a lot of ways that high school never had, which was really good for me. As a math guy, I thought that engineering was just a bunch of math, but I was actually totally wrong! The only calculations and equations I had to use in my entire research project were when I was making and analyzing antennas. There were a couple other equations that I would've had to use if I had the money, time and resources to actually build a tracking system, but my engineering project was mostly math-less. Some of you who know me well are wondering how I could possibly be okay with not using very much math, but the best parts of engineering (and my project) are when groups of people who know their subject get together and brainstorm ideas furiously. After months of research on tracking systems, I was able to join in these amazing discussions and get a lot of of them. I'm so glad even before I continue on to my undergraduate education I've had the opportunity to get a taste of what engineering is all about.

P.S. Engineers get free laser-pointer pens sometimes, and they are the best things in the world!

Dual Frequency PIFA

Well, judging from my fellow students' blogs, SRPs are finally slowing down and beginning to become more focused on presentations and final products. My project is no exception, as I've been rather busy this week trying to plan out my presentation. It's kind of funny, because when I began attending BASIS in 9th grade I was convinced that I was going to graduate early so that I could avoid the 20-minute presentation that was required for Senior Research Projects. Even though in this school year alone I've already given six or seven presentations that long, and presenting doesn't freak me out as much as it used to, it's still pretty surreal to actually be working on my SRP presentation.

Anyhow, this week I went back to the workshop (mostly for fun), and found a PIFA that had an L-shaped cut through the top plane. I was curious, so I decided to make one of my own to see what it does! Here's a picture of the one I made:

My dual frequency PIFA

As many of you are probably guessing because of what it probably my least creative blog-post title to date, this antenna resonates at two distinct frequencies! I painstakingly cut and measured the copper material exactly like I would to make a 1.575 GHz GPS PIFA, but I wasn't too careful with the L-cut that I made. That is to say, I didn't know that it would resonate at two frequencies, so I didn't place special care in the dimensions of the L-shaped cut I made. Take a look at the network analyzer readings I got from my antenna.

Remember that in order to get good transmission at a certain frequency, the network analyzer should have a reading of -10 dB or lower at that frequency, so this antenna resonates well at approximately 1.408 GHz (marker 1) and very well at approximately 2.131 GHz (marker 2). I put marker 3 at exactly 1.575 GHz, because I was curious about what it would look like since the dimensions of the PIFA without the cut would have led to a 1.575 GHz antenna, and interestingly enough there is a little blip at that frequency, but it's only about -4 dB. 

Something that I didn't know until Marcos taught me was that the 2-D area of each part of the dual antenna has a lot to do with the frequencies that they resonate at. I had thought that the piece with the longer perimeter would correspond to the longer wavelength (lower frequency), but it turns out that the piece with the larger area will correspond to the longer wavelength, even if it has a shorter perimeter. 

If PIFAs were to be used in tracking devices for larger animals, where they could be more easily integrated into the circuitry, and there were two frequencies that the device needed to transmit at, then a dual PIFA would be a great option. For instance, if the device had GPS capability, but it also needed to communicate with the receivers in a MURS frequency, one antenna would be able to facilitate both frequencies. That's pretty convenient!

As always, thanks for reading, and have a nice weekend!

Maybe We Can Have Nice Things!

Hello again readers! It's been a pretty crazy week, but that's not terribly uncommon these days, with both high school and the college choosing process coming down to the finish line, so it's always nice to just sit down and write a blog post where I can share with you guys and reflect on what I've learned so far. It's a little scary to think about it, but even this project is getting pretty close to finishing up, so I'm beginning to focus less and less on researching and learning new things and more on working towards writing my research paper and my final presentation. But that doesn't mean that I can't spend a little time messing around with antennas still!

Now that I've set my system requirements with a little table fairly similar to the example that I showed last week, my next important step is to solidify the possible systems that I will be proposing and analyzing in my final products. Soon, maybe even today, I'm going to email a man who is probably currently the premier California sea otter researcher to ask him if he thinks my idea for putting a collar-like device at the base of an otter's tail is viable. If so, then suddenly both GPS and multilateration systems become much more attractive options, but as I already mentioned, both systems require that we worry about battery-life significantly more because they use much more power than a triangulation system's device.

Fortunately, I have a couple of ideas to extend battery life! I know that I'm not reinventing the wheel here with my project, because I don't know enough about electrical engineering to create a brilliant new tracking system, but perhaps I can synthesize our current technology with the older technology still in use in animal tracking devices to make a system that is better overall. That's why it's not particularly novel for me to suggest that we use solar-rechargeable batteries in tracking devices, but as far as I can tell it hasn't been done much. Although solar-powered devices could be very useful in devices for tracking other animals, I'm not too optimistic about the prospect of using it on a sea otter transmitter. Putting a tiny solar panel on the ankle or the base of the tail of a sea otter may not capture very much of the sun's energy. On top of that, from the videos of sea otters swimming that I've seen, it appears that the most of the sea otter's body is underwater most of the time, including the base of the tail and the ankles.

What I am more excited about is the possibility of using kinetically-rechargeable batteries in the devices to prolong their lives. No external attachment would have to me made to accommodate these batteries; in fact, utilizing them would be as simple as purchasing the batteries and plugging them in. As a bonus, the batteries themselves aren't even that expensive, at less than $25 a pop. Certainly if a transmitting device was attached to an otter's ankle the battery would be constantly recharged by the sea otter swimming and foraging for food, and I believe that a device at the base of the tail would get a fair amount of kinetic energy.

Please forgive the following scientific digression... this is the stuff that I get excited about. If you've taken college physics in the area of electricity and magnetism, this explanation of how rechargeable batteries work will be almost trivially simple. If you have a solenoid (the helically shaped wire below), you can move a magnet back and forth inside it to create a changing magnetic field, which in turn "inducts" an electrical current in the solenoid wire. If the solenoid wire is hooked up to a capacitor, the energy can be stored and used to recharge the battery and supply current. This system seems to me a remarkably simple yet subtly elegant way to prolong the life of any battery to the point where the battery is so effective that it may last longer than the device itself!

Passing a magnet through this solenoid is an easy way to generate an electric current. 

Well, that's all I have for this week. As always, thanks for reading!

Pictures: http://www.wildnatureimages.com/images%203/080505-003..jpg
http://www.school-for-champions.com/science/images/electromagnetic_solenoid__wire.jpg

The Engineering Process

This past week I've gotten to look back at all the research I've done so far in order to outline my research paper, and it has made me think a lot about the engineering process in general. One of my projects this week was to create a timeline of ideas and achievements for the last three years of Senior Design Teams that have worked on a tracking system for the Golden Lion Tamarin (GLT). After hours of poring over their final papers and presentations, I did manage to consolidate their work into a single page of highlights, but rereading their work with the knowledge that I have now has only helped me get a better perspective on the sea otter problem.

Unfortunately, the time that I have to work on the sea otter problem is so short that I will not have time to build or buy any prototypes, and I don't have a budget anyways.  Therefore, all of my work and proposed solutions is theoretical, but that doesn't mean that I can't evaluate and analyze my own proposed systems to chose the option that is the most likely to succeed. This means that I will need to make some tables outlining the requirements for a successful sea otter tracking system, and another couple of tables that analyze the proposed systems and show which systems accomplish certain goals. These kinds of tables will look familiar to people who read Grant's blog and pretty much anyone who has done work as an engineer. Here's an example of a good table from this year's GLT group:

One of my goals for next week is to have a comprehensive list of all the requirements for a successful sea otter tracking system, which should be doable, but I doubt that I will be able to solidify the 2-4 proposed systems by next week, because it seems that the more I read and research, the more possibilities I find that I have to consider. For instance, just this week I realized that I should look into batteries that can be recharged by converting kinetic (moving) energy into chemical energy, because otters are constantly moving, and depending on where the transmitting device is on the otter, this could significantly increase the battery life of the transmitter. 

On a semi-unrelated note, another important aspect of engineering in general that I've come to learn is that engineering is extremely collaborative. Nearly every innovation nowadays is a result of somebody improving upon somebody else's work, so usually no one engineer really breaks away and invents something eons ahead of the standard technology. I know that if I were to sit in a room full of radio telemetry devices and a couple of books on the subject, I would not be able to come up with an innovative and new tracking device or system. However, since I am able to see the work of thousands of current engineers, biologists, and ecologists, I can see whose new work can best be implemented towards my possible solutions. This is a very exciting notion, that for any engineering project there are thousands of people out there whose work and research can be used to help you make your own contribution to solving a problem. 

Well, I get to go to an optical science lecture today, which I'm pretty excited about, so I'd better get going. Thanks for reading!

Circuits and Systems

Hello again! This has been a really slow week, due to almost everyone else being out on Spring Break, so this won't be too long of a blog post. Try not to celebrate too much about that!

Battery life is something that pretty much all of us think about. Laptops, phones, and iPods are just a few things that we constantly have to keep track of to make sure that their batteries aren't dead when we need them the most. The batteries that I just mentioned are relatively easy for us to recharge or change, but imagine if the batteries on an animal tracking device needed to be charged as often as a smart phone battery! The whole point of using tracking devices on wild animals is to be able to observe animals in their natural habitat without human interference, and a device with batteries that need to be changed more often than once every couple months necessitates too much interaction between researchers and the animals.

Sure, we could have all the battery power that we could possibly need if we use a giant car battery... but that's not very practical for any device on an otter. I read somewhere that a good goal for anybody designing a device to track animals is to have the device weigh less than 1% of the animal's body weight. Therefore, any device that would be attached to a sea otter would have to be extremely energy-efficient, because battery weight makes up a fairly high portion of any tracking device's total weight.

When using a triangulation system, energy-efficiency is easy to achieve. The device simply needs to put out a pulse at a certain radio-frequency about once every second (or more often). These devices can last for years, like the abdominally-implanted VHF devices currently in use for sea otters. However, when we try to use GPS or multilateration systems, the power required to have the system running constantly is unsustainable for periods longer than a couple days, and either a low-power sleep-mode or an on/off mechanism is necessary to achieve greater longevity. Here's a circuit diagram for a proposed device by last year's golden lion tamarin senior design team:

If you don't understand this diagram, don't worry. I don't fully understand it either, but arguably the most important piece to those of us trying to make devices power-efficient is the 32KHz clock that works with the MicroController. Ideally, when a location on the device is not needed, the only power-consumption by the entire device will be by that clock, which wakes up the device at specified times in order to determine a location. This specific circuit diagram is for a GPS-enabled device. 

Which is more battery-efficient, keeping the tracking device in a low-power sleep-mode when not in use, or turning the device on and off each time it needs to transmit? This is an important question because sometimes turning on the device can require a lot of power. Also, where, if at all, does solar-power technology fit into a sea otter tracking device? These are questions that I'm hoping to learn the answer to in the next week or so. Until then, I hope everyone else is enjoying their spring break (or not, sorry fellow seniors)!

Where Am I?

Well, to answer the question in the title, I am currently in a lab at the University of Arizona. But if I didn't tell you that, how would you know where I am without a search party? This week I am going to rant about the three different tracking systems that I've learned about. While the systems themselves are relatively easy to understand, I still have to take into account a whole bunch of considerations in order to figure out what system might be best for tracking sea otters.
I will warn you that I made some of the diagrams myself, so I apologize in advance if they only confuse you.

Triangulation is probably the simplest and the cheapest way to track via radio telemetry, and many of you are already familiar with how it works. The most commonly used antenna to receive the signals from the tracking device is a hand-held Yagi-Uda antenna, which is extremely directive, as some may remember from last week's post. Here's a picture of one, which may look familiar because it is commonly found on the roofs of houses. To start the triangulation a person will use their highly directive antenna to determine the direction where the signal from the transmitter is the strongest, creating a vector of possible places where the tracking device may be. Since the tracking device may be anywhere on that vector, at least one more person in a different position must go through the same process, and the transmitter will be located where the vectors from the different people meet. Only two different vectors are necessary, but having three or more vectors can make the estimated location more accurate. Here's a diagram!

Triangulation at its best

Another method for locating a tracking device is something that all of you are somewhat familiar with: the Global Positioning System. There are 24 GPS satellites orbiting the earth, each working constantly to give countless systems in the world updated information about their location. The GPS satellites do not use triangulation vectors. Instead, they measure how much time it takes for a signal to get to the satellite, which means that the satellite has a sphere of infinitely many location possibilities that are each the same distance from the given satellite. When a GPS transmitting device is able to lock on to a signal from three or more GPS satellites, then it is able to formulate a position. Interestingly enough, if a GPS device locks on to only three GPS satellites, then it is only able to calculate 2-dimensional coordinates on the earth, which is enough if you're using a car GPS. However, if you need to know the 3-dimensional coordinates of the tracking device, i.e. the coordinates and the depth, the device must lock on to four or more GPS satellites. Probably the most important consideration for GPS systems is that they can be much more expensive than triangulation systems. Here's another diagram!

Since he only has a lock on three satellites, he doesn't know how far above sea level he is.

The last system that I would like to consider is called multilateration, and is most commonly used with cell phones because this system requires cell towers. At least three different cell towers need to be involved in order to get a working location on a device, because the cell towers rely on communication with each other. Each pair of cell towers will calculate a TDOA (time-difference of arrival), which essentially is the difference in the distances of the device to both towers. Geometrically, this creates a hyperbola of possible locations for the transmitter (think y² – x² = C). Since this is incomplete, at least one more tower is needed to calculate two more hyperbolas so that the intersection of the three hyperbolas can be found, and a location on the device can be found. Multilateration can be cheap and effective if the infrastructure for the system is already there, but if you want to start building cell towers, the project gets really expensive. Again, here's another diagram!

Is he confused because he's lost, or because he can see an elephant? Who knows.

As always, thanks for reading, and please leave a comment if you feel compelled to ask me a question or tell me how much you like or hate this post!

Picture:
http://www.antenna-theory.com/antennas/travelling/yagi1.jpg

Whips, Zig-Zags, and More Weird Names for Antennas

Hello again! As promised, this post will be about what I've learned about antennas. I've been trudging my way through the first part of what I've heard is the essential book on antennas, eponymously named Antennas, by John Kraus. When I told Mr. Balanda that I wanted to do an engineering SRP, he warned me that engineers don't really learn things. He said that engineers learn how to learn and find information, and know I think I actually understand what he meant. The antenna book has hundreds of different equations relating to antennas, and I'm pretty sure I would cry (manly tears) if I had to learn everything in that book. That being said, going through the book is rather fun, because it involves a lot of step-by-step math and physics, and I even got to use some double integrals to solve some particularly cool problems.

From what I've gathered, the considerations for antennas most relevant to my project (and really almost any project involving antennas) is the size and the directivity of an antenna. Given a specific frequency, different types of antennas will be different sizes, so an appropriate antenna can be chosen based on specific considerations and conditions. For example, the proposed tracking devices will transmit in the MURS (multi-use radio system) band, which ranges from approximately 151-155 MHz. Let's consider the size of three different antennas that could be used for a small mammal tracking device: PIFAs, monopole antennas, and zig-zag antennas.

Hurray for computer programs!

Remember my 1.575 GHz PIFA? Well, I finally get to brag about it again. After I tried to make my HFSS model more accurate by giving it a stem, turning the planes into rectangular prisms, and adding dielectric where necessary, but the program claimed that its peak resonance is at 1.590 GHz. Close enough for government work, I suppose. Unfortunately, a PIFA in the MURS band, which is about one-tenth the frequency of my PIFA, would have to be ten times the size, meaning that the ground plate alone would be 30 cm wide! Even without the stem (which is a valid option), this is not a realistic antenna for a small mammal to have, especially with how fragile a PIFA can be.


Everybody recognizes a monopole antenna, which is essentially just a wire with a length equal to a quarter-wavelength of the frequency it is transmitting at. It can be as simple as a car radio antenna. Similar to a PIFA, a monopole antenna with its peak resonance in the MURS band will have a length of approximately 50 cm, but will be much lighter and more compact than a PIFA at the same frequency, and will fit on animals more easily. Known commonly as whips, monopole antennas are already commonly used on animal trackers, and usually interfere very little with an animal's regular activities.

A Golden Lion Tamarin with a Holohil RI-2D Transmitter

Unfortunately, the whip antenna does not work perfectly for every animal. Some animals, especially like the Golden Lion Tamarin pictured above, live in an environment where long and protruding antennas can easily get caught on things like branches, and a Senior Design Team of Dr. Melde's from 2013 came up with what I think is a brilliant new antenna to solve this problem. Pictured below is what they call the zig-zag antenna. It is very space-efficient because not only is it a mere 20 cm long, but it also can be easily integrated into a wearable collar, as suggested by the fact that the antenna in the picture below is sewn into a cloth.

A zig-zag antenna that does the same job as the other antennas, but it's smaller!

As I mentioned earlier, directivity is another important consideration when deciding on which type of antenna to use. What is directivity? It's one of those slightly annoying unit-less physical properties that doesn't mean anything by itself, but is useful when comparing them to those of other antennas. Basically, the more directive an antenna is, the more direct the beam of radiation the antenna puts out. Here's a wonderfully convenient picture that I'll use to explain:

These polar diagrams show how strong the radiation or the signal is from an antenna depending on what angle you are at around the antenna. The farther away the polar curve is from the origin at a particular angle, the stronger the signal from the antenna is at that angle. As the diagram shows, whip antennas are basically omnidirectional, and thus ideal for animal tracking because you want to use an antenna that will give you a signal no matter how the animal is oriented. Examples of more directive antennas are on the right, and the Yagi-Uda array is an antenna of particular interest to this project, but I'll talk more about that next week when I discuss tracking systems.

Speaking of tracking systems, my project is getting pretty interesting now that I know enough background information about antennas, devices, and otters to research tracking systems in a wider sense. After I read about existing systems that work and this sweet new book specifically about how electronic tracking devices work in water environments, hopefully in a few weeks I'll have a couple viable tracking systems for otters that I will be able to talk intelligently about. I'm excited about next week's blog post, because I'll get to blabber on about the difference between triangulation, GPS, and cell multilateration.

Hasta luego! As always, I'd love to hear any questions!

P.S. I've been listening to a ton of music (as usual) and I just found this awesome band called Ava Luna that reminds me of both Broken Social Scene and Dirty Projectors at the same time, and you can't go wrong with that. If you haven't heard of any of those bands, you're missing out!

Sources: 

Kraus, John, Antennas (McGraw-Hill Book Company, Inc., New York, 1950).

Pictures: 

http://www.holohil.com/GLTamarin.jpg

http://www.cdt21.com/parts/zu/zu_11.gif