BASIC PRINCIPLES of non-contact temperature measurement
By Optris 
1. Physical principles
2. Emissivity and temperature measurement
3. Optics, sighting techniques and electronics
4. Infrared thermometers and applications
5. Infrared cameras and applications
- Physical principles
With our eyes we see the world in visible light. Although visible light makes up only a small part of the radiation spectrum, the invisible light covers most of the remaining spectral range. The radiation of invisible light carries much more additional information.
Discovery of the infrared radiation
Searching for new optical material, William Herschel accidentally rediscovered the infrared radiation in 1800. He blackened the tip of a sensitive mercury thermometer and used it as measuring system to test the heating properties of different colors of the spectrum, which were directed to a tabletop by having beams of light shine through a glass prism. With this, he tested the heating of different colors of the Continue reading
A thermographic camera (infrared camera or thermal imaging camera) is a device that forms an image using infrared radiation, similar to a common camera that forms an image using visible light. Instead of the 400–700 nanometre range of the visible light camera, infrared cameras operate in wavelengths as long as 14,000 nm (14 µm). Their use is called thermography.
Theory of operation
Infrared energy is just one part of the electromagnetic spectrum, which encompasses radiation from gamma rays, x-rays, ultra violet, a thin region of visible light, infrared, terahertz waves, microwaves, and radio waves. These are all related and differentiated in the length of their wave (wavelength). All objects emit a certain amount of black body radiation as a function of their temperatures.
Generally speaking, the higher an object’s temperature, the more infrared radiation is emitted as black-body radiation. A special camera can detect this radiation in a way similar to the way an ordinary Continue reading
Waves – Lesson 1 – The Nature of a Wave
From Physics Classroom
Categories of Waves
Waves come in many shapes and forms. While all waves share some basic characteristic properties and behaviors, some waves can be distinguished from others based on some observable (and some non-observable) characteristics. It is common to categorize waves based on these distinguishing characteristics.
Longitudinal versus Transverse Waves versus Surface Waves
One way to categorize waves is on the basis of the direction of movement of the individual particles of the medium relative to the direction that the waves travel. Categorizing waves on this basis leads to three notable categories: transverse waves, longitudinal waves, and surface waves. Continue reading
Does Military Sonar Kill Marine Wildlife?
From Scientific American, June 10, 2009
Dear EarthTalk: Is it true that military sonar exercises actually kill marine wildlife? — John Slocum, Newport, RI
Unfortunately for many whales, dolphins and other marine life, the use of underwater sonar (short for sound navigation and ranging) can lead to injury and even death. Sonar systems—first developed by the U.S. Navy to detect enemy submarines—generate slow-rolling sound waves topping out at around 235 decibels; the world’s loudest rock bands top out at only 130. These sound waves can travel for hundreds of miles under water, and can retain an intensity of 140 decibels as far as 300 miles from their source.
These rolling walls of noise are no doubt too much for some marine wildlife. While little is known about any direct physiological effects of sonar waves on marine species, evidence shows that whales will swim hundreds of miles, rapidly change their depth (sometime leading to bleeding from the eyes and ears), and even beach themselves to get away from the sounds of sonar. Continue reading
How does sonar work?
From Science Wire
Sonar is simply making use of an echo. When an animal or machine makes a noise, it sends sound waves into the environment around it. Those waves bounce off nearby objects, and some of them reflect back to the object that made the noise. It’s those reflected sound waves that you hear when your voice echoes back to you from a canyon. Whales and specialized machines can use reflected waves to locate distant objects and sense their shape and movement.
The range of low-frequency sonar is remarkable. Dolphins and whales can tell the difference between objects as small as a BB pellet from 50 feet (15 meters) away, and they use sonar much more than sight to find their food, families, and direction. Continue reading
Quantum Dots: Applications for Artificial Atoms Expanding
By Lynn Savage, Feb 2011
Quantum dots, also known as semiconductor artificial atoms, have existed for several years now, and their use keeps on expanding. Primarily used as substitutes for dyes in fluorescence imaging, their propensity for being highly tunable emitters that resist photobleaching represents only a small fraction of their benefits.
Commonly but not always comprising cores of cadmium selenide with a coating of zinc sulfide, quantum dots are perhaps best known for the tunability of their emission wavelength, once excited by an external light source: Change the size of the particle, get a specific wavelength in return. Early research into the properties and potential uses for quantum dots kept them in solutions, and then later brought into proximity with a variety of other particles. This led to their nearly ubiquitous use as donors in Förster’s resonance energy transfer (FRET), a renowned method for near-diffraction-limit imaging of cells and other subjects. Continue reading