![]() ![]() ![]() “Unfortunately these signals are very weak. A second light pulse can diffract off the acoustic-wave copy of the grating, when the wave reaches the surface”, PhD student Thomas van den Hooven explains. “The sound waves coming from the surface, reflect off the hidden grating and copy their shape in the process. ![]() In 2020 group leader Paul Planken and his colleagues showed that they could detect a hidden nanostructure using very high frequency sound waves induced by light. The Light Matter Interaction group at ARCNL develops techniques to overcome this problem. Detecting these alignment gratings is not always straightforward, because they get buried under many layers of material, some of which can be opaque to light. To make sure consecutive layers are aligned accurately, wafers contain grating lines that act as markers. Nanolithography machines print several layers of nano-sized structures on a wafer to produce state-of-the art computer chips and components. The researchers have published their findings in Photoacoustics on May 9th 2023. The relative enhancement of the diffraction signal is even two to three times larger than the enhancement of the reflection signal. This amplifies reflection and diffraction changes caused by laser-induced acoustic waves in the sample. With a gold-covered segmented grating they can induce a so-called plasmonic resonance. Yes, phenomena of diffraction can occur in sound waves.ARCNL researchers Thomas van den Hooven and Paul Planken have found a way to enhance acoustic-wave-induced diffraction changes from a sample similar to those used for wafer alignment in nanolithography. When a sound wave encounters an obstacle or passes through a small aperture, it bends around the edges and spreads out into the region behind the obstacle. This bending of sound waves around the corners or edges of an obstacle is called diffraction. When sound waves travel through a medium, they move in a straight line, but when they encounter an obstacle or a small aperture, they bend or diffract around the edges of the obstacle. The larger the wavelength, the more significant the diffraction.ĭiffraction can be observed in several scenarios, such as: The amount of diffraction depends on the size of the obstacle or aperture and the wavelength of the sound wave. When sound waves pass through a narrow slit or aperture, they diffract and create a series of interference patterns on a screen placed behind the slit. When sound waves encounter a sharp edge of an obstacle, they diffract and spread out into the region behind the obstacle, creating a shadow zone where the sound intensity is lower. When sound waves encounter an obstacle with a curved surface, they diffract around the curved surface and create a sound shadow zone behind the obstacle. Thus, diffraction is a fundamental property of sound waves that plays a crucial role in several applications, such as soundproofing, acoustic design, and music production. Understanding the principles of diffraction in sound waves can help us design better sound systems and optimize their performance. Read the following text and answer the following questions on the basis of the same:Diffraction in a hall:A and B went to purchase a ticket of a music programme. But unfortunately only one ticket was left. They purchased the single ticket and decided that A would be in the hall during the 1st half and B during the 2nd half.Both of them reached the hall together. A entered the hall and found that the seat was behind a pillar which creates an obstacle. He thought that he would not be able to hear the programme properly.B was waiting outside the closed door. There was a little opening.But surprisingly, A could hear the music programme.This happened due to diffraction of sound.The fact we hear sounds around corners and around barriers involves both diffraction and reflection of sound.Diffraction in such cases helps the sound to "bend around" the obstacles.In fact, diffraction is more pronounced with longer wavelengths implies that we can hear low frequencies around obstacles better than high frequencies.B was outside the door. But he noticed that when the door opening is comparatively less he could hear the programme even being little away from the door. This is because when the width of the opening is larger than the wavelength of the wave passing through the gap then it does not spread out much on the other side. But when the opening is smaller than the wavelength more diffraction occurs and the waves spread out greatly – with semicircular wavefront. A and B could hear the music programme due to phenomenon named The opening in this case functions as a localized source of sound.Q. ![]()
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