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지식나눔

지식나눔

left-handed materials에 대해 알려주세요.

2005-06-24 org.kosen.entty.User@1197bcb3 허광학(kwanghak)
  • 2
이 뭔가요? 어떠한 재료이며, 어떠한 특성을 가지는지 궁금합니다.
  • left-handed materials
  • metamaterials
지식의 출발은 질문, 모든 지식의 완성은 답변! 
각 분야 한인연구자와 현업 전문가분들의 답변을 기다립니다.
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  • 답변

    신정규님의 답변

    2005-06-24
    • 0

    첨부파일

    >이 뭔가요? >어떠한 재료이며, 어떠한 특성을 가지는지 궁금합니다. 참고하세요.. 관련 논문도 10여개 첨부해 드립니다. Left-Handed Materials NOTE: More information on Left-handed materials, including publications and job opportunities, can be found at the site http://physics.ucsd.edu/~drs. What is a Left-Handed Material? In general, materials have two parameters, permeability and permittivity, that determine how the material will interact with electromagnetic radiation, which includes light, microwaves, radio waves, even x-rays. A Left-Handed material is a material whose permeability and permittivity are simultaneously negative. Our material is a structure composed of copper elements, some in the shape of rings, some ordinary wires, that causes microwaves to behave in a manner that is unusual. Physics allows us to predict how electromagnetic radiation will interact with a material. By combining different materials, or materials structured in different patterns, engineers can create structures to control light (or EM radiation). This is, for example, the basis of 'photonic band gap' materials. In our case, we have created a material that, in a certain band of frequencies, behaves in a manner that can be simply described as Left-Handed. Why are Left-Handed Materials Interesting? A Left-Handed material reverses a basic feature of light: that is, in a left-handed medium, light propagates (or appears to move) in the opposite direction as energy flows! One could visualize this as a one dimensional wave packet propagating in a Right-Handed (MPEG:1.6MB) medium or a Left-Handed (normal) (MPEG:1.6MB) medium. This leads to some very interesting consequences, such as the reversal of the Doppler shift for radiation, and the reversal of Cherenkov radiation. Cherenkov radiation is the light emitted when a charged particle passes through a medium, under certain conditions. In a normal material, the emitted light is in the forward direction, while in the Left-Handed medium, light is emitted in the reverse direction. In addition, one of the most basic principles of optics, Snell's law, is reversed at the interface of a left-handed medium to a normal material. So, for example, light that enters a left-handed material from a right-handed medium will undergo refraction, but opposite to that usually observed. What is really happening is that a Left-Handed material has a negative index of refraction, so Snell's Law is still valid. If one puts a negative index of refraction into Snell's Law, the refraction angle predicted will be exactly what was observed in our experiments. As a further consequence, lenses and optics made from left-handed materials will produce unusual optics. As an example, a lens made from LHM that would be converging if made from conventional material, will be diverging, and vice-versa. Also, a thick flat plate (window) of LHM can focus radiation from a point source back to a point. Here are simulated ray tracings of electromagnetic radiation emanating from a point source in air (RH) then incident upon a slab of Right-Handed (JPEG:200KB) media or Left-Handed (JPEG:200KB) media. Can these effects be found in other materials? This is technical. Yes, but not without complication. Microwave and optics have been around for a long time, and people have created very clever and useful devices. In a photonic band gap structure, for example, or any device which is spatially periodically modulated on the scale of the wavelength of light, it generally occurs that the direction of propagation can be opposite to energy flow. What is different about our LHM is that we are able to discuss phenomena in terms of simple plain waves. In these other structures, one cannot call the observed modes “plane waves.“ Furthermore, surface waves inevitably occur that complicate the analysis of the material. In our LHM, all structure is much smaller than the wavelength of interest, so those complications do not occur. We can discuss the effects with reference to plane waves, and analyze the effect on radiation using very simple ray tracing and basic formulas. Why do these effects seem so counter intuitive? Because we are talking about plane waves. Plane waves are a mathematical construction used by physicists and engineers to help us think about how light behaves. In free space, they work quite satisfactorily; however, when a medium is involved, it becomes more complicated. In our case, the predictions for plane waves are entirely correct, even though they appear to violate our intuition. But, if we were to be more careful, and solve practical problems (such as pulses, current sources, etc.), we would find that our intuition is again satisfied. An analogy is the phase waves in a waveguide which travel faster than the speed of light. These waves exist, but are not useful by themselves, as any realistic problem always requires a sum over such waves to produce a pulse that travels more slowly than the speed of light. What are some applications for this material? We can't anticipate specific examples, yet. We believe that when one creates a new material that scatters electromagnetic radiation in a unique manner, some useful purpose will be found. We can envision, for example, uses in the cellular communications industry, where novel filters, antennas, and other electromagnetic devices are of great importance. Even slight improvements to these devices can make a significant financial impact. As our research progresses, we will look for areas suited to this technology and develop appropriate structures. What was the basis for this work? Recent developments by Professor John Pendry, who has reexamined metal structures, led us to the current discovery. Pendry has shown that certain configurations of metal can have a unique response to electric fields, while other configurations of metal can have a unique response to magnetic fields. The latter discovery is rather surprising, since no magnetic elements are needed only conductors. This effective magnetic material has the further property that it can have a negative permeability, something not observed in ordinary materials, especially at microwave and higher frequencies. As this is the first time a clean negative permeability substance has been found, this is naturally the first chance that a left-handed medium, simultaneously negative permeability and permittivity, could be created.
    답변수정
    >이 뭔가요? >어떠한 재료이며, 어떠한 특성을 가지는지 궁금합니다. 참고하세요.. 관련 논문도 10여개 첨부해 드립니다. Left-Handed Materials NOTE: More information on Left-handed materials, including publications and job opportunities, can be found at the site http://physics.ucsd.edu/~drs. What is a Left-Handed Material? In general, materials have two parameters, permeability and permittivity, that determine how the material will interact with electromagnetic radiation, which includes light, microwaves, radio waves, even x-rays. A Left-Handed material is a material whose permeability and permittivity are simultaneously negative. Our material is a structure composed of copper elements, some in the shape of rings, some ordinary wires, that causes microwaves to behave in a manner that is unusual. Physics allows us to predict how electromagnetic radiation will interact with a material. By combining different materials, or materials structured in different patterns, engineers can create structures to control light (or EM radiation). This is, for example, the basis of 'photonic band gap' materials. In our case, we have created a material that, in a certain band of frequencies, behaves in a manner that can be simply described as Left-Handed. Why are Left-Handed Materials Interesting? A Left-Handed material reverses a basic feature of light: that is, in a left-handed medium, light propagates (or appears to move) in the opposite direction as energy flows! One could visualize this as a one dimensional wave packet propagating in a Right-Handed (MPEG:1.6MB) medium or a Left-Handed (normal) (MPEG:1.6MB) medium. This leads to some very interesting consequences, such as the reversal of the Doppler shift for radiation, and the reversal of Cherenkov radiation. Cherenkov radiation is the light emitted when a charged particle passes through a medium, under certain conditions. In a normal material, the emitted light is in the forward direction, while in the Left-Handed medium, light is emitted in the reverse direction. In addition, one of the most basic principles of optics, Snell's law, is reversed at the interface of a left-handed medium to a normal material. So, for example, light that enters a left-handed material from a right-handed medium will undergo refraction, but opposite to that usually observed. What is really happening is that a Left-Handed material has a negative index of refraction, so Snell's Law is still valid. If one puts a negative index of refraction into Snell's Law, the refraction angle predicted will be exactly what was observed in our experiments. As a further consequence, lenses and optics made from left-handed materials will produce unusual optics. As an example, a lens made from LHM that would be converging if made from conventional material, will be diverging, and vice-versa. Also, a thick flat plate (window) of LHM can focus radiation from a point source back to a point. Here are simulated ray tracings of electromagnetic radiation emanating from a point source in air (RH) then incident upon a slab of Right-Handed (JPEG:200KB) media or Left-Handed (JPEG:200KB) media. Can these effects be found in other materials? This is technical. Yes, but not without complication. Microwave and optics have been around for a long time, and people have created very clever and useful devices. In a photonic band gap structure, for example, or any device which is spatially periodically modulated on the scale of the wavelength of light, it generally occurs that the direction of propagation can be opposite to energy flow. What is different about our LHM is that we are able to discuss phenomena in terms of simple plain waves. In these other structures, one cannot call the observed modes “plane waves.“ Furthermore, surface waves inevitably occur that complicate the analysis of the material. In our LHM, all structure is much smaller than the wavelength of interest, so those complications do not occur. We can discuss the effects with reference to plane waves, and analyze the effect on radiation using very simple ray tracing and basic formulas. Why do these effects seem so counter intuitive? Because we are talking about plane waves. Plane waves are a mathematical construction used by physicists and engineers to help us think about how light behaves. In free space, they work quite satisfactorily; however, when a medium is involved, it becomes more complicated. In our case, the predictions for plane waves are entirely correct, even though they appear to violate our intuition. But, if we were to be more careful, and solve practical problems (such as pulses, current sources, etc.), we would find that our intuition is again satisfied. An analogy is the phase waves in a waveguide which travel faster than the speed of light. These waves exist, but are not useful by themselves, as any realistic problem always requires a sum over such waves to produce a pulse that travels more slowly than the speed of light. What are some applications for this material? We can't anticipate specific examples, yet. We believe that when one creates a new material that scatters electromagnetic radiation in a unique manner, some useful purpose will be found. We can envision, for example, uses in the cellular communications industry, where novel filters, antennas, and other electromagnetic devices are of great importance. Even slight improvements to these devices can make a significant financial impact. As our research progresses, we will look for areas suited to this technology and develop appropriate structures. What was the basis for this work? Recent developments by Professor John Pendry, who has reexamined metal structures, led us to the current discovery. Pendry has shown that certain configurations of metal can have a unique response to electric fields, while other configurations of metal can have a unique response to magnetic fields. The latter discovery is rather surprising, since no magnetic elements are needed only conductors. This effective magnetic material has the further property that it can have a negative permeability, something not observed in ordinary materials, especially at microwave and higher frequencies. As this is the first time a clean negative permeability substance has been found, this is naturally the first chance that a left-handed medium, simultaneously negative permeability and permittivity, could be created.
    등록된 댓글이 없습니다.
  • 답변

    송준희님의 답변

    2005-06-27
    • 0
    Left-handed라는 의미는 전자기적 방사의 응답으로 인하여 일반재료에서 관찰되는 많은 물리적 특성들에 비해 반대의 특성을 가지는 성질때문에 명명된 이름입니다. 오른손잡이가 일반적인 경우고 왼손잡이는 반대인 이치와 같습니다. 다른 표현으로는 double-negative metamaterials라고도 합니다.
    답변수정
    Left-handed라는 의미는 전자기적 방사의 응답으로 인하여 일반재료에서 관찰되는 많은 물리적 특성들에 비해 반대의 특성을 가지는 성질때문에 명명된 이름입니다. 오른손잡이가 일반적인 경우고 왼손잡이는 반대인 이치와 같습니다. 다른 표현으로는 double-negative metamaterials라고도 합니다.
    등록된 댓글이 없습니다.
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