DM> What I am looking for is reading to check the feasability. I need the DM> freauencies that everything emits. We all enjoy discussing the design DM> strategy, but I haven't given out enough info to get much help on that. DM> Where I need the help is a treatment of what frequencies things emit DM> (Particularly people and the sun).
Hi Declan, in optics people rather talk about wavelengths than frequencies, because micrometers and nanometers are much easier to grasp than terrahertz. Many have already cited the black-body radiation and I don't have the time or energy to check the links you already have. Some values: -for a human body we talk about wavelengths of 5-10um for the peak of the emitted thermal radiation, that's in the far infrared -for the sun we talk about 0.5um, which is in the yellow part of the spectrum The problems with far infrared are mainly: - very few detector materials are able to "see" these wavelengths. There have recently been progresses with certain semiconductors, such as InAs, InP, PbTe which can be used in 2D imaging devices (e.g. FLIR cameras). Silicon, germanium, gallium arsenide are all blind in this part of the spectrum. - the refractive index of almost all common materials for lenses is too low to be useful - this means it is hard to make focusing optics for this wavelength range. Some materials used are certain plastics for Fresnel-type lenses, magnesium fluoride and germanium. - The fact that the thermal radiation of a 37 centigrade body does not differ too much from a 20 centigrade surrounding makes it necessary to cool the whole system - otherwise the thermal radiation of the electronics and optics itself will drown your signal! Of course if the surrounding on a summer's day is about as warm as the human body it will be impossible to detect the human body from its thermal signature! And the 37 centigrade only counts for the uncovered parts of the body! Even the thinnest layer of clothes is a very effective heat shield and the surface of clothes can be assumed to have ambient temperature! Alternatives to sensitive pn-junctions or PIR detectors are thermopiles which consist of several to several hundred of small thermocouple junctions connected in series. Combined with good thermal shielding and a focusing optical system these appear to give quite a good signal. The sun. Well the sun is a bright and hot spot in the sky, about half an angular degree in diameter. If it happens to be in the direction of the sensor, the only chances for you to detect a much cooler human being are: - the angular size of the human being might be significantly larger - the signal of a moving (living?) human being does change faster than the sun - but we are probably talking time constants in the order of a few seconds for the necessary filters here A great thermal source is the homepage of Omega. They offer a very thick "handbook" on temperature measurement technology on their web page which is an extraordinary resource - even though it is their own product catalog at the same time.... http://www.omega.com/ Uwe. DM> -- DM> With best Regards, DM> Declan Moriarty. -- Mit freundlichen Gr�ssen Uwe Zimmermann mailto:[EMAIL PROTECTED] -- Author: Uwe Zimmermann INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
