Invisible light electromagne<c radia<on

Transcription

1 Invisible light electromagne<c radia<on Name Comments Typical wavelength Frequency AM radio Ordinary old radio 300 m 1 MHz TV, FM radio Microwaves Heat infrared (IR) Near infrared (NIR) Visible light Ultraviolet (UV) X-rays Gamma rays Higher frequency for more bits/s Radar, microwave oven, cell phones EmiKed by warm bodies (e.g., humans) A strong color from the sun that we can't see Detectable by human eyes Responsible for sunburn and can cause skin cancer Passes through water, not bone EmiKed by nuclei, can cause cancer and are detectable from distant galaxies 3 m 100 MHz 10 cm 3 GHz.002 cm = 20 μm 15,000 GHz 1 μm Hz 0.5 μm Hz 0.3 μm Hz 10-9 m = 1 nm Hz m Hz

2 All objects are glowing due to their Temperature PTFFP

3 All objects are glowing due to their Temperature Total power emiked is propor`onal to T 4. This is very important! PTFFP

4 All objects are glowing due to their Temperature Total power emiked is propor`onal to T 4. This is very important! Peak wavelength increases in propor`on to frequency, or to 1/wavelength L = 3000/T T in Kelvin and L in micro-meters PTFFP

5 Incandescent light bulbs are inefficient! PTFFP

6 Infrared imaging L = 3000/T Body temperature is about 300 degrees, so what is the peak wavelength emiked? Answer = 10 μm This is 20 `mes the wavelength of green light. If we build a camera to see this wavelength, we can see in the dark.

7 Infrared imaging PTFFP

8 Wikipedia

9 Wikipedia

10 In spite of its detec`on of infrared light, the infrared detec`on mechanism is not similar to photoreceptors - while photoreceptors detect light via photochemical reac`ons, the protein in the pits of snakes is a type of transient receptor poten`al channel, TRPA1 which is a temperature sensi`ve ion channel. It senses infrared signals through a mechanism involving warming of the pit organ, rather than chemical reac`on to light. In structure and func`on it resembles a biological version of warmthsensing instrument called a bolometer. This is consistent with the thin pit membrane, which would allow incoming infrared radia`on to quickly and precisely warm a given ion channel and trigger a nerve impulse, as well as the vasculariza`on of the pit membrane in order to rapidly cool the ion channel back to its original temperature state. While the molecular precursors of this mechanism are found in other snakes, the protein is both expressed to a much lower degree and is much less sensi`ve to heat. Wikipedia

11 Ultra-violet light Wikipedia

12 Radar and Microwave Ovens Wikipedia

13 The cavity magnetron Wikipedia

14 Magnetrons helped the allies win WW2. Read about the Tizard Mission. Wikipeddia: The Tizard Mission, officially the Bri`sh Technical and Scien`fic Mission, was a Bri`sh delega`on that visited the United States during the Second World War in order to obtain the industrial resources to exploit the military poten`al of the research and development (R&D) work completed by the UK up to the beginning of World War II, but that Britain itself could not exploit due to the immediate requirements of warrelated produc`on. It received its popular name from the program's ins`gator, Henry Tizard. On September 6, 1940, a delega`on of poli`cians, generals, and scien`sts arrived in Halifax, Nova Sco`a on the Bri`sh liner Duchess of Richmond. One of the scien`sts, Dr. George 'Taffy' Bowen carried in his coat pocket a small device which proved to be the most potent weapon of the war. It was not nuclear material, or secrets for the atomic bomb. It was a prototype cavity magnetron. This device directly led to the MIT radar laboratory, and by the end of the war the US had prodeced over a million magnetrons.

15 Cell phones and Wifi From your book: Cell phones also use microwaves to carry their signals. Do you dare put a cell phone up to your ear? There are many urban legends about that. Low levels of microwaves cause only low levels of hea`ng, and your eyes can handle that with no trouble. Microwaves do not have the ability to damage DNA in the same way as x-rays and gamma rays. Most of the fear that microwaves can cause cancer is simply a reac`on to the fact that microwaves are some`mes called microwave radia`on, and the use of the term radia`on frightens some people.

16 X-rays TransmiKed by water, but blocked by bone. X-rays can damage `ssue they pass through. In large amounts, they cause hea`ng and destruc`on of cellular organelles. They can cause DNA to mutate and result in cancer. In small doses, this effect can be offset by medical benefits.

17 X-ray backscaler imaging BackscaKer X-ray is an advanced X-ray imaging technology. Tradi`onal X- ray machines detect hard and sop materials by the varia`on in x-ray intensity transmiked through the target. In contrast, backscaker X-ray detects the radia`on that reflects from the target. It has poten`al applica`ons where less-destruc`ve examina`on is required, and can operate even if only one side of the target is available for examina`on. Wikipedia

18 X-ray backscaler imaging BackscaKer X-ray is an advanced X-ray imaging technology. Tradi`onal X- ray machines detect hard and sop materials by the varia`on in x-ray intensity transmiked through the target. In contrast, backscaker X-ray detects the radia`on that reflects from the target. It has poten`al applica`ons where less-destruc`ve examina`on is required, and can operate even if only one side of the target is available for examina`on. Wikipedia

19 X-ray backscaler imaging Yahoo.com

20 X-ray backscaler imaging Wikipedia: Unlike cell phone signals, or millimeterwave scanners, the energy being emiked by a backscaker X-ray is a type of ionizing radia`on that breaks chemical bonds. Ionizing radia`on is considered carcinogenic even in very small doses but at the doses used in airport scanners this effect is believed to be negligible for an individual. If 1 million people were exposed to 520 scans in one year, one study es`mated that roughly four addi`onal cancers would occur due to the scanner, in contrast to the 600 addi`onal cancers that would occur from the higher levels of radia`on during flight. Yahoo.com

21 Magne<c resonance imaging Protons are likle magnets. They spin in a magne`c field. You can drive that spin just like pushing a child in a swing, usually with radio waves or microwaves. By looking at the scakered radio waves, you see where the protons (meaning water) are. This can be applied to other nuclei than protons. Fun fact: MRI used to be called NMR for nuclear magne`c resonance but the name was changed because the public was afraid of the term nuclear.

22 Ultrasound imaging Uses sound waves, not invisible light.