So all of this would be great if I were using these to locate objects in air at simply the speed of sound but that has no real allure. Instead I want to go below beneath the surface. I am interested in SONAR (SOund Navigation And Ranging), though this term wasn't adopted until the end of the WWII. Before that it was often referred to as Submarine signaling. What is interesting is that reports vary on it's discovery. One of the earliest references to the fact that sound exists beneath the surface of the sea, as well as in the air above, occurs in writings by Leonardo da Vinci in 1490. He wrote: "If you cause your ship to stop, and place the head of a long tube in the water and place the other side of the tube to your ear, you will hear ships at a great distance from you." Although this is an extremely simple example of passive (listen only) sonar. However Wikipedia gives the credit to Lewis Nixon who, in 1906, invented the very first passive sonar-type listening device, as a way of detecting icebergs. Then came the first example of active (transmit and listen) sonar when, in 1827, Daniel Colladon and Charles Sturm measured the speed of sound in water. They accomplished this by measuring the time it took for the sound of an underwater bell to travel between two boats separated by many miles. Their primitive measurements were surprisingly accurate. Another innovation team, and the pair more closely responsible to modern SONAR was The French physicist Paul Langevin, working with a Russian emigré electrical engineer, Constantin Chilowski, invented the first active sonar-type device for detecting submarines in 1915. By 1918 Allied forces utilized SONAR in all Navy ships.
Essentially the SONAR set-up is the same as the air transducers; a transmitter, receiver, transducer, and a feedback device, which in this case is a display. An electrical impulse from a transmitter is converted into a sound wave by the transducer and sent into the water. When this wave strikes an object (i.e. fish, structure or bottom) a certain amount of the wave is reflected back depending on the composition, size and shape of the object. This reflected signal, echo, returns to the transducer, which converts it back into an electric signal, and is amplified by the receiver, processed and sent to the display. Since the speed of sound in water is about 4855.46 ft./sec (depending on water temperature, salinity and depth), the time lapse between the transmitted signal and the received echo can be measured and the distance to the object determined. This process repeats itself up to 40 times per second, which results in a continuous line being drawn across the display, showing the bottom signal.
During my search I came across International Transducer Corporation. This site has a wealth of knowledge concerning the actual function of each specific transducer. Through researching the various types I determined I needed an Omni Directional High Frequency Transducer. Such as the ITC-1042. This seemed like my best option until
Two weeks after I had first inquired I called ITC and found that this device was about $1000US. So I then started over.
Through my research I discovered numerous design opportunities. If funding were not an issue this project could achieve a much higher and more readily attributed technological advancement. However necessity has led me in the direction of using an already established through water transducer. This being a FishFinder which are available at any sporting goods store.
The key issues I have faced other than cost, is that air transducers do not have the capability to transmit a signal through water. There is also the problem of having in water in contact with the piezoelectric transducer.
Which brings to mind a question, why are the FishFinders so cheap? My first forray into the market is with the Smartcast RF20, made by Humminbird,which is a pole mounted wireless, castable transducer and screen. This unit was reccomended to me by Engineers at Humminbird who immediately were compelled by the project.
For my first tests I am interested in utilizing a limited field, i.e. a fish tank. This in itself greatly complicates the process as all of the transducers avialable function up to 100ft. and usually shut off in less than 8 feet.
What is also interesting here is that the engineers at Eagle, another FishFinder Manufacturer felt that their finder could be adjusted to the tank, but it would achieve varying results. The reason why I am intersted in this technology is because if each fish knew the location of the other fish then their behaviors could be adjusted and programmed accordingly. As I move forth the best news to report is that these Smartcast transducers cost about $20. Which is far better than the others I looked into .
Here is a copy of a letter I sent out to various schools and industry leaders whom I thought might take an interest in my research. Response to this letter was limited though I will continue to move forward. My perception is that my development will not be taken seriously without significant innovation.
The most interesting feedback I got was from William O'Halleran a former ITP graduate currently working in the field.
"Here are some casual observations that I have made, or have been privy to over the last few years. • Never put anything in the ocean you want back. • The ocean eats everything that comes from the land. What it can't eat, it covers in biomatter until it is useless. • Marine mammals are not fond of sonar. • Environmentalists are not fond of sonar. • You need sonar to navigate underwater. • Figure out what ever you think it ought to cost, then start adding exponents. The same is true for time. • Get used to thinking in meters, KM, and radians. Northings and eastings will become necessary as well. • There aren't a lot of companies making subses gear, becasue, it is really hard, and really easy to go bankrupt doing it. "
With that in mind I set the boat adrift.
For these tests I found a small RC Submarine made by Newqida. For the first tests I will be using three. These devices are much smaller than I anticipated though they certainly will function. As it turns out these units are a copy of the Megatech Ocean Explorer-1, which apparently has a patent ( US Patent D503,754 S) Though as far as I can tell mine are exactly thhe same, though I question the circuitry.
They are all operating on the same frequency so I am able to control all three simultaniously.
This was quite interesting in itself because they seemed to be autonimous as they do not react identically, almost as though they were part of a small school. I scheduled use the diving pool at NYU for these tests. My time there was extrememly limited so my first round of testing had only a vague amount or precision.
The SmartCast unit did immediately and affectively locate the bottom of the pool within a few inches. The total depth was 12'6' with a 10? slope at the edges. As this unit does not have decimal precision it is possible the sonar transducer inside the unit has a more accurate reading. In the first test I was able to locate all three submarines simultaineously in the sensor field. The first problem was that the RC transmitter did not penitrate the water at a distance greater than five feet. Do realize that these submarines were very inexpensive costing, in fact, only $12 a piece. Due largely to this, I think, two of the submarines failed in the first tests and sank to the bottom. This turned out to be good for the sonar tests as I was able to monitor, though loosly, their decent.
The following morning I returned to the pool for an additional test. This test was to answer some of the questions I had. At the conclusion of the first round, I felt as though i hadn't been able to focus on many of the details since I was filming, testing, and controlling the subs.
The second day I had a camera man so my role as tester was more complete. Through the second test I could watch more closely and compare the actual depth with the recorded depth. In water the speed of sound travels 1480 m/s this is more than three times as fast as sound travels in air.This also means that it takes about a second for sound to travel a mile (0.92). To bring this into the pool the transducer took about 6 miliseconds to send and recieve the bottom depth.The sonar data readings are reported in the hand unit about three times per second. The speed of sound is determined by the density (?) and compressibility (?) of the medium. Density is the amount of material in a given volume, and compressibility is a meaasure of how much a substance could be compacted for a given pressure. The denser and the more compressible, the faster the sound waves would travel. Therefore, the speed of sound is about four times faster in water than in air. The speed of sound in a medium can be determined by the equation ... v = (??)-1/2 Where... v is the speed of sound, ? is the bulk modulus of elasticity, and ? (rho) is the density.
The best news that has come of this is that the manufacturer of the Smartcast device has agreed to send me not only additional transducers, but transducers not in their shell which means I may be able to create my own device housing. Unfortunately the minature subs I have now are too small to work with which means I need to find another.
As an additional NOTE. I heard that marine mammals really do not like any SONAR device. In the Bahamas in 2000, a trial by the United States Navy of a 230 decibel transmitter in the frequency range 3 – 7 kHz resulted in the beaching of sixteen whales, seven of which were found dead. The Navy accepted blame in a report published in the Boston Globe on 1, January 2002. This reality has casued me to one, definately stay inside a tank, two maybe find something else. For further information on the potential damage active sonar may cause go HERE