Ultrasonic PA Beacon

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Ultrasound is annoying and long-term exposure mey b harmful.

Use infrared with multiple transmitters.  Email me if you\'d like tech
help for $$$.

Thanks Joerg.

The concept is "inaudible", so low freq is fine (and probably more benign). In any event, the actual sound levels would be very weak.

This particular study is in New York City, and was begun before 9/11 but gained additional attention due to the pulverised building material.

Tom

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You misunderstood.  "Low frequency" radio refers to the carrier
frequency which would be used to contact the samplers, not to any low
frequency audio.

There are many options, all depending on your budget. The radio is probably your best bet. Since you're in New York, I imagine that your school has a high-concentration of always-on computers. You can stick a Wi-Fi dongle on each computer, and do the same for the collection device (is it custom or off-the-shelf?). The same could be done at home.

Then write a program (Visual Basic or C/C++ or whatever) on the portable unit to detect which node it is close to. Note that it is not necessary to have customized software on the field nodes - all you need to do is induce the stationary nodes to emit an Ethernet frame containing their MAC addresses. This means that Wi-Fi access points (Linksys/Netgear) will act as field nodes too. Depending on the resolution required, you may need to process the RSSI, but probably not.

There is another benefit - you get "free" fixed-points, throughout the world. You can build (or find on the web) a database in the lab mapping 6-byte MAC address to latitude/longitude coordinates.

When it comes time to render, you get a much richer visualization from your dataset, and get to see dynamic movements over time for the samples.

You can find USB Wi-Fi dongles anywhere, as you know, and if you need help structuring the program, drop me a note.

-Chaud Lapin-

Hello Tom,

20kHz isn't a great idea. It can be heard by some people and would drive them crazy. It would certainly drive most animals crazy. I would never do that.

A low frequency radio system can work. For ideas you could study instrument landing systems, especially older versions. For example, how an airplane could stay on the glide path in pre-GPS times during a low visibility approach.

There may be a market for this stuff. In our area of El Dorado County in California a big natural asbestos scare has started. People in space suits milling about and all that. I guess pretty soon they'll start long term sampling studies on a larger scale.

Regards, Joerg

Hello Tom,

That can become a challenge in terms of foreign noise. A lot of machinery such as air conditioners, fans, pumps, motors and so on generate a noise spectrum well into the tens of kHz. Even if you had a really clever matched filter algorithm there comes a point when the signal is so far down in the noise that positioning would become impossible.

Also, don't underestimate the ingenuity of students who object to wearing one of these. Or studentr who want to foil it just for bragging rights. Maybe they bring dog whistles or what not.

Out here it is tremolite that is found in rock formations. Unfortunately people have placed crushed rock onto driveways and roads. In other areas smog particles or soot have to be measured.

Regards, Joerg

Thanks for the reply. I will look into whether WiFi is available in the schools (probably is).

Tom

Sure.

Find trainable monkeys to carry the sniffers around, and train them to press the "Library", "Home", "Room 101" and so on, buttons when they go into the specific environment. Geez, they can train human larvae to do text messaging on a video telephone; what should be so hard about training your subjects to push a button or three?

Good Luck! Rich

Then it's imperative - train your sniffer carriers.

If you were installing these devices on, for example, sewer rats, then there might be some justification for automatic localization, but for heaven's sakes, how cheap are you hiring your help? Are they _completely_ illiterate?

Feh, Rich

I don't what they will pay them, if anything.

Even the best > >