Metal-free super-wideband THz absorber for electromagnetic shielding

Abstract A technique is implemented for obtaining the high absorption over super-wideband (SWB) in a metal-free THz absorber. The multiple resonant modes with wide spectra are generated in a graphite-based resonator placed on a dielectric cavity merging of which provides the SWB response. The low permittivity dielectric slab sandwiched between the graphite sheet at its bottom and graphite resonator at its top acts as the Fabry–Perot cavity where absorption takes place. The high absorption rate of graphite in the THz regime can make it a suitable candidate for its utilization in implementing the broadband absorber. Thus, the molecular transition due to interaction of energy in graphite also provides the high absorption. The absorption bandwidth can further be enhanced by stacking of multiple layers in two different configurations of the proposed unit cell. The absorber maintains the polarization insensitivity due to symmetry and allows the high absorption for the electromagnetic wave incident up to the angle of more than 75 ° . The proposed absorber can be utilized in the THz electromagnetic shielding applications due to its SWB response.

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Small-Sized Interferometer with Fabry–Perot Resonators for Gravitational Wave Detection

Sensors ◽

10.3390/s21051877 ◽

2021 ◽

Vol 21 (5) ◽

pp. 1877

Author(s):

Nikolai Petrov ◽

Vladislav Pustovoit

Keyword(s):

Correlation Function ◽

Gravitational Waves ◽

Laser Interferometer ◽

Zero Order ◽

Wave Detection ◽

Resonant Modes ◽

Fabry Perot ◽

Spatially Distributed ◽

Wave Laser ◽

Higher Sensitivity

It is highly desirable to have a compact laser interferometer for detecting gravitational waves. Here, a small-sized tabletop laser interferometer with Fabry–Perot resonators consisting of two spatially distributed “mirrors” for detecting gravitational waves is proposed. It is shown that the spectral resolution of 10−23 cm−1 can be achieved at a distance between mirrors of only 1–3 m. The influence of light absorption in crystals on the limiting resolution of such resonators is also studied. A higher sensitivity of the interferometer to shorter-wave laser radiation is shown. A method for detecting gravitational waves is proposed based on the measurement of the correlation function of the radiation intensities of non-zero-order resonant modes from the two arms of the Mach–Zehnder interferometer.

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Analysis of Embedded Optical Interferometry in Transparent Elastic Grating for Optical Detection of Ultrasonic Waves

Sensors ◽

10.3390/s21082787 ◽

2021 ◽

Vol 21 (8) ◽

pp. 2787

Author(s):

Chayanisa Sukkasem ◽

Suvicha Sasivimolkul ◽

Phitsini Suvarnaphaet ◽

Suejit Pechprasarn

Keyword(s):

Thin Film ◽

Grating Period ◽

Ultrasonic Waves ◽

Optical Interferometer ◽

Ultrasonic Detection ◽

Grating Pattern ◽

Flexible Material ◽

Resonant Modes ◽

Elastic Film ◽

Fabry Perot

In this paper, we propose a theoretical framework to explain how the transparent elastic grating structure can be employed to enhance the mechanical and optical properties for ultrasonic detection. Incident ultrasonic waves can compress the flexible material, where the change in thickness of the elastic film can be measured through an optical interferometer. Herein, the polydimethylsiloxane (PDMS) was employed in the design of a thin film grating pattern. The PDMS grating with the grating period shorter than the ultrasound wavelength allowed the ultrasound to be coupled into surface acoustic wave (SAW) mode. The grating gaps provided spaces for the PDMS grating to be compressed when the ultrasound illuminated on it. This grating pattern can provide an embedded thin film based optical interferometer through Fabry–Perot resonant modes. Several optical thin film-based technologies for ultrasonic detection were compared. The proposed elastic grating gave rise to higher sensitivity to ultrasonic detection than a surface plasmon resonance-based sensor, a uniform PDMS thin film, a PDMS sensor with shearing interference, and a conventional Fabry–Perot-based sensor. The PDMS grating achieved the enhancement of sensitivity up to 1.3 × 10−5 Pa−1 and figure of merit of 1.4 × 10−5 Pa−1 which were higher than those of conventional Fabry–Perot structure by 7 times and 4 times, respectively.

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