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• The passive structure of a fan-shaped holographic lens with different heights was developed to generate orbital angular momentum transferring acoustic vortices, resulting in acoustic trapping. • The helical acoustic vortices can be generated in the single-channel focused transducer by covering the lens. • Feasibility in acoustic trapping was investigated using several types of bioparticles (e.g., microbubbles, different sizes of polystyrene beads, and cancer cells). • The actuation mechanism of this approach is analyzed through understanding the relationship between drag and trapping forces. The utilization of acoustic vortices presents a promising technique for contactless particle manipulation. However, existing methods for generating acoustic vortices typically rely on complex active driving systems and array ultrasound transducers. Therefore, more simplified and robust approaches to inducing acoustic vortices should be considered. With inspiring the fact that acoustic vortices can be generated by the differences in the height of adjacent sectors in conventional four-panel transducers, we aim to develop a single-channel acoustic vortex tweezer with a simplified driving system by incorporating attachable fan-shaped polydimethylsiloxane (PDMS) holographic lens. This passive lens structure with different heights in adjacent sectors can generate phase-modulated ultrasonic waves. Therefore, the interaction of phase-modulated waves passing through the lens is expected to result in a vortex-like beam. The available materials of fan-shaped lens are not limited to the PDMS. This lens type can be appropriately fabricated with an understanding of the sound of speed within the desired material and predetermined thickness, inducing π/2 phase difference in the adjacent lobes. As a result, the excited acoustic waves propagated through the lens were under mutual interaction without any active electrical setup, forming a null pressure region enveloped by four distinct acoustic lobes. We systemically investigated the tweezing potential using vortex-like waves. Several types of bioparticles were utilized in these investigations: microbubbles, polystyrene (PS) beads, and cancer cells. Our findings demonstrate that the transducer with lens is sufficiently capable of spatial manipulation of bioparticles. Remarkably, the microbubbles traveling at a flow velocity of 32 cm/s in a blood vessel-mimicking phantom were feasibly trapped in the proposed transducer. Furthermore, the spatial control of PS and cells with higher acoustic impedance was also feasible in static conditions. Consequently, the proposed transducer offers an economically and practically viable solution for various biomedical applications, such as drug delivery and cell-based bioengineering. [Display omitted] [ABSTRACT FROM AUTHOR]

A multibeam radiator with each beam possessing independent polarization is developed by a single-feed holographic reflectarray (RA) antenna without using any optimization algorithms. Regardless of wave polarization, the relation between the electromagnetic properties of the antenna aperture (henceforth referred to as “hologram”) and impinging wave properties can be described by the holographic technique. For the practical implementation of such a hologram, we used a subwavelength metallic patch with anisotropic properties to satisfy the input admittance distribution of the hologram. In doing so, a fast numerical method, fundamentally inspired by the method of moments, is employed to calculate the input admittance of the element for all angles of incidence. This technique significantly speeds up the design process. Finally, as a typical case, a simple circularly polarized RA with four-beam radiation pattern was manufactured and tested at 13 GHz. The measured results showed that the aperture efficiency of 45.8%, cross-polarization discrimination of higher than 25 dB, 1 dB drop gain, 3 dB axial ratio bandwidths of 19.23% and 18.26%, sidelobe level of below −17 dB, and peak gain of around 19.43 dBi for each beam were obtained. [ABSTRACT FROM AUTHOR]

In this paper, a novel systematic method based on the holographic theory to design a reflectarray (RA) antenna is presented. According to the holographic technique, one can record features of electromagnetic waves impinging on a specific surface and then, whenever needed, reconstruct each of them. We exploit this property to design a single-feed RA with a multibeam linearly polarized pattern without using any iterative method such as optimization algorithms in the design process. At first, various kinds of interferograms along with related input admittance distributions are introduced according to the polarization and number of radiated beams. Afterward, a simple subwavelength metallic patch as a scalar admittance unit cell is employed to implement the input admittance distribution of the interferograms. Moreover, a fast analytical method, which is fundamentally inspired by the method of moments, has been employed to calculate the input admittance of the utilized element. Finally, as a typical case, an 18 cm $\times $ 18 cm linearly polarized RA with a two-beam radiation pattern has been manufactured and tested at 15 GHz. The sidelobe level, cross-pol, and efficiency of the antenna are found −26 dB, lower than −10 dB, and 47.2%, respectively, which meet the expectations. [ABSTRACT FROM AUTHOR]