Volume of a human skull
ivangrozny2009
Posts: 9
Hello! So I already phoned the tech dept. about this, but I thought I would post as well...
Here is my project:
I am looking for a way to measure the volume of an intact human skull via the foramen magnum (spinal hole), using IR, sonar or any other method out there. Right now, there is no good way to measure the endocranial volume of a skull, so I thought I would try something new.
- PIR sensor isnt accurate enough
- IR sensors could work, but may require multiple inputs
- PING sensor would probably be ideal, but is too BIG for the foramen magnum
Does anyone have ANY ideas/thoughts on gaining a volume measurement using a BS2 board and parallax sensor???
Thanks!
AB
Here is my project:
I am looking for a way to measure the volume of an intact human skull via the foramen magnum (spinal hole), using IR, sonar or any other method out there. Right now, there is no good way to measure the endocranial volume of a skull, so I thought I would try something new.
- PIR sensor isnt accurate enough
- IR sensors could work, but may require multiple inputs
- PING sensor would probably be ideal, but is too BIG for the foramen magnum
Does anyone have ANY ideas/thoughts on gaining a volume measurement using a BS2 board and parallax sensor???
Thanks!
AB
Comments
Anyway, I suppose that you can't submerse it in water, right? Also, by intact do you mean whole or still attached to living shoulders? An easy way would be to take two pictures from the front and from the side, and extrapolate a round object from that, and the volume from there. Something considerably less accurate could be done by rotating a distance sensor around a skull maybe...
Well, since the outside of the skull can vary greatly it is measured differently than the inside of the actual brain cavity. Measuring the outside CAN work, but it isn't something that I would be able to do unfortunately due to thickness of bone etc that could throw off the numbers. Currently the only way that we have to measure volume in the field is to fill it with rice, then pour the rice into a measuring cup to determine the cubic centimeters (in a lab, use a CT scan)
Im thinking that maybe its a bit too far fetched to work, which is sad [noparse]:([/noparse]
But thanks!
AB
John Abshier
I would go with acoustics as mentioned earlier.· My thinking would be something along the same lines as a Helmholtz resonator.· The brain cavity or area of interest would have a specific frequency based on the volume of that cavity.· Could be as simple as using·one of our Piezo Film Vibra Tab Mass sensors and slightly tapping the skull or acoustically exciting it in some way to see where a spectrum analyzer would peak.·(<- there is free software available on the web·that will turn your PC sound card into a spectrum analyzer.)
Of course this is just an idea and is open·for experimentation.· A spectrum analyzer may not even be necessary... I just measured a standard 20-oz plastic coke bottle using a Piezo Film Vibra Tab Mass·sensor attached to the side·of the bottle and my scope.· Seems to have a·definite resonant frequency of about 186Hz.
Edit:
Here is an interesting article that confirms my 186Hz measurement for a 20-oz plastic bottle.... http://www.vibrationdata.com/Newsletters/January2004_NL.pdf
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Post Edited (Beau Schwabe (Parallax)) : 1/23/2009 5:40:23 PM GMT
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Jessica Uelmen
Education Department
Parallax, Inc.
-Phil
THis is an awesome idea actually, thanks!
LOL now to parse what that means :P
Thanks John, but actually this is the way we do it now, I was searching for a less invasive and more high tech solution [noparse]:)[/noparse]
If the freq-vs-volume curve seems sufficiently consistent, then measure the res. freq. to determine the volume of any future skull.
To measure the res. freq., you might use a single acoustical transducer (speaker) and sweep it through a range of frequencies, monitoring continuously the voltage across the speaker and the current through it and computing the impedance therefrom.
The impedance of a speaker in an opening of a finite closed baffle (such as a skull) will vary with frequency. At resonance, the impedance will rise, often rather sharply. A Stamp ought to handle this nicely.
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· -- Carl, nn5i@arrl.net
Post Edited (Carl Hayes) : 1/24/2009 4:14:00 AM GMT
(1)· You must use sinusoids to feed the speaker, in order to avoid being fooled by resonances at harmonics present in nonsinusoidal waveform.
(2) There are many different VCOs (voltage-controlled oscillators)·on the market.· Use one of these, controlled by a voltage determined by the Stamp through a DAC, to create the swept-frequency signal.· You don't need to know the actual frequency -- knowing at what frequency-control voltage you supplied is sufficient, and naturally this will be known to the program in the Stamp.· In your preliminary testing you will have determined a curve, (frequency-control-voltage at resonance) vs (volume).· That's all you need.
(3) If the foramen is reasonably planar (for a passable seal), you can place the speaker in an opening in the plane top of a table.· Then just place the skull over the speaker and hit the "go" button.· If the program does all the rest automatically, including displaying on a numeric display the volume (from tables you place in the program), everyone will think you're a genius.
(4) In my prior post I said "finite closed baffle" but it actually needn't be closed.· The openings at the orbits needn't be closed off, for example.· As long as you always do it the same way the results should be consistent.
(5)· I see Beau made what amounts to a similar suggestion, with perhaps less specificity.· Beau has good ideas too.
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· -- Carl, nn5i@arrl.net
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· -- Carl, nn5i@arrl.net
I can't thank you guys enough, this has been a HUGE help! But I am not as intelligent as you guys however and the hardest part will be implementing all of this in my limited capacity. I am going to start I think with a another question:
If I use the Piezo Film Vibra Tab Mass to DETECT the resonance inside the skull, am I using a standard speaker to transmit a frequency or is there another accessory I can use with the STAMP to do it?
I am pretty new to not only robotics (building a PING bot sensor BOE-BOT is my most advanced project heh), and also the concepts of resonance/frequency and how to detect or use the data effectively, but I am looking forward to learning [noparse]:)[/noparse]
Thanks again!
"If I use the Piezo Film Vibra Tab Mass to DETECT the resonance inside the skull, am I using a standard speaker to transmit a frequency or is there another accessory I can use with the STAMP to do it?"
You can use a standard speaker, but as it was mentioned you should drive the speaker with a sine wave. The FREQOUT function for the BS2 provides a pseudo-sine wave that may be adequate for this application, but you will·need to increase the drive strength. i.e. feed the signal coming from the Stamp through an amplifier of some kind (LM386?) before you drive the speaker.
There are example programs that show how to interface the Piezo Film Vibra Tab Mass to a·Stamp that should be enough to get you started in the right direction.· The main thing that you are looking for though is a peak detector and not so much the resonant frequency although they will go hand in hand.· For a simple interface that the Stamp can understand, such a peak detector·can be formed with a·diode/capacitor arrangement feeding an ADC (Analog to Digital Converter) before going to the Stamp.· As you sweep the frequency from Low to High, you also monitor the output from the ADC keeping track of what·frequency created·the highest output level from the ADC.· Which in turn·will be the resonant frequency.··
If you don't have one, I would either invest, or see if you can borrow an oscilloscope.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Post Edited (Beau Schwabe (Parallax)) : 1/24/2009 6:31:22 AM GMT
It is a mistake to think that you have to measure the intensity of the sound waves inside the skull.· Not necessary, or even useful!· The speaker voice-coil· impedance (as it varies with frequency) is the only thing you need to measure; and one way to measure that is by measuring the voltage and current.· If you keep one of these constant, then you need measure only the other.· Voltage is easiest to keep consant, usually; but (unfortunately) current is the hardest to measure.· However, there are many ways to measure either or both; and there are other ways to measure impedance, too.· Research is in order, and many others here will have far better knowledge than I have, of how to measure them with a Stamp.
Experiment may show that you get two impedance peaks:· one at the speaker's own resonance, and another (typically higher) at the cavity's (skull's) resonance.· You want to assure that the speaker's own resonance is the lower of the two, because researchers (at RCA, mostly) determined in the 1920s that the impedance below the speaker's own self-resonance doesn't change much with the cavity dimensions; but above, it does.
Experiment may show that the idea works better with a vented-baffle arrangement (orbits not stopped up) or with a closed-baffle arrangement (orbits·stopped up).· In speaker systems whose purpose is to produce sounds rather than to measure volume, typically the impedance variation is greater with vented baffles.
What resonant frequency might you expect?· The lowest-frequency standing wave that can resonate inside the skull will be that at which the skull is about 1/2 wavelength tall on the inside.· Assume (I'm guessing -- you will have better info) that this dimension is typically 4 inches.· The wavelength at resonance, then, is 8 inches, or about 2/3 of a foot.· Take 1100 feet per second as the speed of sound in air, and then the frequency must be near 1650 Hz.· You ought to use a speaker whose own resonance is much less than that.· Perhaps the first experiment ought to be measuring the speaker's own self-resonant frequency in free air.· If you can't make that measurement, you can't make this project work anyway.· It ought to be easy to find a small speaker whose intrinsic res. freq. is less than 500 Hz, and start your frequecy sweep at, say, 700 Hz, sweeping upward.· But make your own calculations based on realistic (maximum) skull size.
All this is brainstorming.· I think I've suggested a scheme that can work, and shown how to calculate a reasonable place to start, but there's no assurance that it will actually work.· Experiment is in order.· First thing to do is gain an ability to measure that impedance as it varies by frequency.· For all I know, there may already exist cut-and-dried ways to do that with a Stamp.· When you can do that, you can test the concept to see if it'll work at all.· If it works, you'll be 99% done, with only another 99% to go.· That's the way these projects go.
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· -- Carl, nn5i@arrl.net
Good point.. Only a single speaker is necessary.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Thanks again!