The distribution of the time-averaged electric and magnetic energy densities and of the energy flow (Poynting vector) in the focal plane is studied in detail, and the results are illustrated by diagrams and in a tabulated form based on data obtained by extensive calculations on an electronic computor. In particular the symmetry properties of the field with respect to the focal plane are noted and the state of polarization of the image region is investigated. Some general consequences of the formulae are then discussed. First the case of a linearly polarized incident field is examined and expressions are derived for the electric and magnetic vectors in the image space. Some miscellaneous investigations are also mentioned.Īn investigation is made of the structure of the electromagnetic field near the focus of an aplanatic system which images a point source. Certain applications in which tight focusing is desired are briefly discussed. Impact of the helical phase structure in the pupil function engineering and subsequently on the focused structure is discussed with special reference to the authors' investigations at IIT Delhi.
In the present paper, roles of the amplitude-, phase-, and polarization distribution on the tightly focused structure of the optical beams are reviewed. Tight focusing of an optical beam produces intensity distribution in the focal volume different from the well-known results based on scalar theory, and polarization distribution shows space variant characteristics. Helical phase structure arising due to phase singularity in the wave front plays an important role in shaping the focal spot. It is therefore possible to engineer the focal spot using the pupil function manipulation. The WHO/International Agency for Research on Cancer (IARC) has classified radiofrequency electromagnetic fields as possibly carcinogenic to humans (Group 2B), based on an increased risk for glioma, a malignant type of brain cancer, associated with wireless phone use.Complex amplitude and polarization distribution of an optical beam plays a dominant role in shaping the focused structure of the beam. These devices receive radio waves and convert them to mechanical vibrations in the speaker to create sound waves. Radio waves are a type of electromagnetic radiation best-known for their use in communication technologies, such as television, mobile phones and radios. (For a fuller treatment, see electromagnetic radiation: Radio waves.) Do radios use electromagnetic waves? They are used in standard broadcast radio and television, shortwave radio, navigation and air-traffic control, cellular telephony, and even remote-controlled toys. A conventional oven heats food using infrared radiation while a microwave oven uses microwaves to do the same job. Two regions of the EM spectrum that will be focused on in this unit are the infrared and microwave regions. Which electromagnetic wave can be used in baking and heating food? For instance, it can tenderize tough meat. The radiation does cause chemical changes in food, however. As such, it cannot leave any residue in food, unlike the chemical treatments it would replace. The gamma radiation used is much like the microwaves used for cooking: It is pure energy. Do microwaves cook with radio waves?Ī conventional oven heats food very slowly from the outside in, but a microwave oven uses tiny, high-powered radio waves to cook food more evenly (loosely speaking, we sometimes say it cooks from the "inside out"-although that isn't quite correct). Microwaves are widely used in microwave ovens as the resonant frequency of water molecules lies in the microwave region. The frequency of microwaves lies in the 300GHz to 300MHz.
It can be classified as a subclass of radio waves. Microwaves are a type of radio waves with short frequencies. High frequency microwaves have frequencies which are easily absorbed by molecules in food. Microwaves are used for cooking food and for satellite communications. They state that the energy waves are more precise and controlled, allowing for more variability in how each type of food cooks. Instead of using microwaves, it uses solid state radio frequencies (RF) to cook food. This means that they contain polar molecules that are positively and negatively charged, like water molecules.1 Can you cook food with radio waves? The method can be used on most foods, since they are what we call “dielectric”. Radio waves are electromagnetic, and can heat food by exposing it to an electric field.
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