Bessel beam

About: Bessel beam is a research topic. Over the lifetime, 1946 publications have been published within this topic receiving 42264 citations.

Low‐Cost 2D Collimation of Real‐Time Pulsed Ultrasonic Beams by X‐Wave‐Based High‐Voltage Driving of Annular Arrays

Abstract: Experimental limited-diffraction waves, based on proposals in the electromagnetic field for ideal infinite apertures (where the Bessel beam concept was already implicit), were reported for finite transverse apertures, firstly in the optic field and soon extended to an acoustic context, as the so-called X-waves. The first verification of the X-waves in acoustics was based on the sequential driving of the elements in an annular array and posterior synthesis of a limited-diffraction beam by using software composition of all the radiated patterns. This would need a complex and rather expensive multi-channel electronic instrumentation, to be extended for ultrasonic generation applicable in a strict real-time regime, as it is required for effective beam collimation in practical ultrasonic applications like non-invasive medical diagnosis by imaging or industrial inspection. In this chapter, principles and implementation details are shown for an author s proposal, by means of which an efficient and simple real-time generation of limiteddiffraction ultrasonic waves can be achieved in an impulsive regime. This is based on approaching X-wave non-diffracting solutions, by converting the complex morphology of the classical X-wave excitation signals in two-level simpler pulses (equivalent, -only for driving & vibration effects-). The pulses are optimized in amplitude & width using, as target functions, time-pulsed responses in emitting faces of all the array annuli. This approach would permit to attain efficient electronic X-beam collimation in Megahertz range, having both cost and size very reduced in the multi-channel hardware involved. A real-time ultrasonic emitting and beamforming configuration, based on the new proposal for the array electric excitations, is described in detail showing: the array elements characterization, HV driving pulses and related electronic procedure. Transient acoustic field results with good focusing pattern and large field depth are demonstrated. Our optimized results for the array excitations and the acoustic beam patterns, related to an ad-hoc designed 8-annuli array (with similar dimensions and working frequency as that proposed in the classical approach), are compared with those calculated using the exact 0-order X-wave solution. The comparison shows the viability of our proposal with only small deviations from the ideal case, which can be very acceptable for imaging.

Bessel beam forming method based on optical fiber end face pyramid

Abstract: The embodiment of the invention provides a Bessel beam forming method based on an optical fiber end face pyramid. The method comprises the following steps that: one end of an optical fiber is immersedinto corrosive liquid to carry out at least two times of corrosion operation so as to obtain the optical fiber with an optical fiber end face pyramid; one end of the optical fiber is a bare fiber with a coating layer removed; and a light beam is input from the other end of the optical fiber and output through the optical fiber end face pyramid to form a Bessel light beam. The temperature of the corrosive liquid in each corrosion operation is kept unchanged, the temperatures of the corrosive liquid in different corrosion operations are different, and the temperature of the corrosive liquid is25-100 DEG C; after each corrosion operation, one end of the optical fiber is cleaned with deionized water; and one end of the cleaned optical fiber is dried in inert gas. By adopting the embodiment of the invention, the processing efficiency of the optical fiber end face pyramid can be improved.

Topological Transformation OAM Based on Metasurface Generated Bessel Beam

Abstract: Metasurfaces have provided new opportunities to control electromagnetic waves, which may find applications in areas such as wireless communications, imaging, energy harvesting, and invisible cloaks. Among all of the applications, Bessel beams and orbital angular momentum (OAM) beams have been investigated extensively. The combination of Bessel beam and OAM can engender some interesting phenomenon. In this work, we report a topological transformation of mode in the transmission of OAM using millimeter wave metasurface. Unit cell of the metasurface is designed to adjust phase of the transmitted wave. Two kinds of Bessel beams carrying OAM are encoded simultaneously with a crossed arrangement. Simulation results show that with the propagation of the beam, the mode number of OAM transformed from one to four and the energy delivered to all four modes. This work may be helpful in the transportation exploring of OAM and can be used in multifunction wireless communication.

On the “tunneling” of full-vector X-Waves through a slab under frustrated total reflection condition

Abstract: “Tunneling” of full-vector X-Waves through a dielectric slab under frustrated total reflection condition is investigated. Full-vector X-Waves are obtained by superimposing transverse electric and magnetic polarization components, which are derived from the scalar X-Wave solution. The analysis of reflection and transmission at the dielectric interfaces is carried out analytically in a straightforward fashion using vector Bessel beam expansion. Investigation of the fields propagating away from the farther end of the slab (transmitted fields) shows an advanced (superluminal) transmission of the X-Wave peak. Additionally, a similar advanced reflection is also observed. The apparent tunneling of the peak is shown to be due to the phase shift in the fields' spectra and not to be causally related to the incident peak.

Integrated Coding Metasurface in a Single-Layered Printed Circuit Board

Abstract: Coding metasurface is a good candidate to achieve flexible electromagnetic wave beam manipulations, but with challenges of integration and alignment issues, especially at millimeter-wave band. To alleviate the above problems, an integrated coding metasurface is designed, to inherently integrate a planar feeding with coding metasurface in a single-layered printed circuit board. In addition, by pre-designing the coding sequence, multiple beam functions can be achieved. As a validation, this paper demonstrates a single coding metasurface to generate boresight pencil beam in the far-field and tilted zero-order Bessel beam in the near-field simultaneously.