Topic
Fresnel zone
About: Fresnel zone is a research topic. Over the lifetime, 2337 publications have been published within this topic receiving 37650 citations.
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TL;DR: In this paper, a combination of a point source ion beam with a dwell-time algorithm has been proposed to ensure the etching depth uniformity of large-aperture Fresnel zone plates (FZPs) with controllable depths.
16 citations
TL;DR: In this article, a new Fresnel zone plate (FZP) and frequency selective screen (FSS) compound lens consisting of a binary FZP and FSS was designed for a paraxial plane-wave illumination at the frequency of 12 GHz, with a focal length of 15 cm.
Abstract: We describe a new Fresnel zone plate (FZP) and frequency selective screen (FSS) compound lens consisting of a binary FZP and FSS. The FZP has eight circular zones totally, four open and four closed, and the FSS is a square array of 40 × 40 four-leg loaded elements cut in a thin metal sheet. The FZP-FSS lens is designed for a paraxial plane-wave illumination at the frequency of 12 GHz, with a focal length of 15 cm. The compound lens is simulated and analyzed numerically by means of a specially developed hybrid PSTD-FDTD algorithm and software. The PSTD-FDTD results are contrasted with those obtained by lens prototype measurements. As a result, some attractive focusing and spectral properties of the FZP-FSS lens compared to the same-size FZP lens have been found: a frequency filtering property enhancement, about 2 dB increase in the peak focusing intensity, and more than 4 dB reduction of the first off-axis maximum. Both lenses have roughly the same transverse angular resolution.
16 citations
Patent•
TL;DR: In this article, an acoustic transducer is coupled with a phase fresnel zone in a section of the acoustic carrier to constructively interfere at the location in the prostate by moving the carrier along at least a portion of the urethra surrounded by the prostate.
Abstract: A system for treating a prostate includes an acoustic carrier, a phase fresnel zone in a section of the acoustic carrier, and an acoustic transducer. The phase fresnel zone is formed in the acoustic carrier adjacent a first end of the acoustic carrier and extends at least partially around the outer surface of the acoustic carrier. An acoustic transducer is coupled to a second end of the acoustic carrier. In treating the prostate, which surrounds a urethra, the acoustic carrier is inserted into the urethra and positioned so that the phase fresnel zone is situated in a region of the urethra surrounded by the prostate. Acoustic waves are transmitted into the second end of the acoustic carrier and the phase fresnel zone focuses the acoustic waves to constructively interfere at the location in the prostate. By moving the acoustic carrier, the phase fresnel zone may be moved along at least a portion of the region of the urethra surrounded by the prostate while the acoustic waves are being transmitted.
16 citations
TL;DR: The x-ray wavefront downstream of a Fresnel zone plate (FZP) was characterized using a two-dimensional grating interferometer to investigate the contribution of the incoming beam in contrast to the optical aberrations.
Abstract: The x-ray wavefront downstream of a Fresnel zone plate (FZP) was characterized using a two-dimensional grating interferometer. Transverse wavefront slope maps, measured using a raster phase-stepping scan, allowed accurate phase reconstruction of the x-ray beam. Wavefront measurements revealed that the wavefront error is very sensitive to the input beam entering the FZP. A small stack of one-dimensional compound refractive lenses was used to introduce astigmatism in the probing x-ray beam to investigate the contribution of the incoming beam in contrast to the optical aberrations. Experimental data were shown to be consistent with theoretical calculations.
16 citations
TL;DR: In this paper, an electrically and optically tunable Fresnel lens in a liquid crystal (LC) cell with an erasable and rewritable photoconductive layer was investigated.
Abstract: This work investigates an electrically and optically tunable Fresnel lens in a liquid crystal (LC) cell with an erasable and rewritable photoconductive layer. By using a Sagnac interferometer, a Fresnel-like pattern can be induced on the photoconductive polymer layer which results in conductive and nonconductive structures in bright and dark zones. This effect causes the mismatch of the LC refractive index between adjacent zones with external voltage, generating a LC Fresnel lens. The focal length of the proposed Fresnel lens can be easily tuned by varying the Fresnel pattern size, and the focusing efficiency can be optically and electrically controlled.
16 citations