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16 pages, 3676 KiB

Open AccessArticle

Design and Structure of a Non-Coaxial Multi-Focal Composite Fresnel Acoustic Lens for Synergistic Ultrasound Stimulation of Multiple Brain Regions

by Ruiqi Wu, Fangfang Shi, Juan Tao, Jiajia Zhao, Jinying Zhang, Xianmei Wu and Jingjing Xu

Sensors 2025, 25(11), 3299; https://doi.org/10.3390/s25113299 - 24 May 2025

Viewed by 529

Abstract

Transcranial focused ultrasound (TcFUS) neuromodulation is hindered by skull-induced acoustic limitations. To enable synergistic multi-region brain stimulation, we designed non-coaxial multi-focal composite Fresnel acoustic lenses, including an overlapping Fresnel lens (OFL) and an alternating-segmented Fresnel lens (ASFL). These lenses convert planar ultrasound into [...] Read more.

Transcranial focused ultrasound (TcFUS) neuromodulation is hindered by skull-induced acoustic limitations. To enable synergistic multi-region brain stimulation, we designed non-coaxial multi-focal composite Fresnel acoustic lenses, including an overlapping Fresnel lens (OFL) and an alternating-segmented Fresnel lens (ASFL). These lenses convert planar ultrasound into multiple foci. Based on Fresnel theory, acoustic fields were analyzed via simulations and experiments, validating the generation of four non-coaxial foci (10/30 mm focal lengths) from a 1 MHz planar wave using both OFL and ASFL. The influence of lens parameters on focal pressure distribution was investigated, and morphology was quantified using a linear least-squares method. Significant differences in focal morphology and intensity between OFL and ASFL provide crucial guidance for optimizing multi-target TcFUS strategies. Full article

(This article belongs to the Section Biomedical Sensors)

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24 pages, 2793 KiB

Open AccessArticle

Dispersive Sweatt Model for Broadband Lens Design with Metasurfaces

by Weiyu Chen, Ko-Han Shih and C. Kyle Renshaw

Photonics 2025, 12(1), 43; https://doi.org/10.3390/photonics12010043 - 6 Jan 2025

Cited by 2 | Viewed by 1027

Abstract

The Sweatt model has been extensively used to design optical systems containing diffractive optical elements (DOEs) because it captures the dispersive characteristics of DOEs. We introduce a new dispersive Sweatt model (DSM) that can describe meta-atom (MA) dispersion, which has material and geometric [...] Read more.

The Sweatt model has been extensively used to design optical systems containing diffractive optical elements (DOEs) because it captures the dispersive characteristics of DOEs. We introduce a new dispersive Sweatt model (DSM) that can describe meta-atom (MA) dispersion, which has material and geometric contributions in addition to diffraction. It uses a wavelength-dependent scalar coefficient to modify the diffractive dispersion and describe the dispersion of a given MA basis. This provides a robust framework to design systems containing metasurface (MS) elements while including their unique dispersive properties in the design optimization. Importantly, the DSM is based on ray optics and enables the design of MS-containing systems using conventional optical design software such as Zemax and Code V. We use the DSM to demonstrate the design of a hybrid refractive/MS achromatic doublet for the midwave infrared (MWIR) band. The design example includes multiple wavelengths and field angles during optimization and demonstrates excellent agreement between the DSM and real hybrid lens performance modeled using wave optics. We discuss the limits of the DSM and present a simple model to predict performance limits due to phase mismatch at Fresnel zone boundaries. Full article

(This article belongs to the Special Issue Advancements in Optical Metamaterials)

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12 pages, 2404 KiB

Open AccessArticle

Investigation of an Active Focusing Planar Piezoelectric Ultrasonic Transducer

by Qiao Wu, Bin You, Xu Zhang and Jun Tu

Sensors 2024, 24(13), 4082; https://doi.org/10.3390/s24134082 - 23 Jun 2024

Cited by 1 | Viewed by 1957

Abstract

Ultrasonic focusing transducers have broad prospects in advanced ultrasonic non-destructive testing fields. However, conventional focusing methods that use acoustic concave lenses can disrupt the acoustic impedance matching condition, thereby adversely affecting the sensitivity of the transducers. In this paper, an active focusing planar [...] Read more.

Ultrasonic focusing transducers have broad prospects in advanced ultrasonic non-destructive testing fields. However, conventional focusing methods that use acoustic concave lenses can disrupt the acoustic impedance matching condition, thereby adversely affecting the sensitivity of the transducers. In this paper, an active focusing planar ultrasonic transducer is designed and presented to achieve a focusing effect with a higher sensitivity. An electrode pattern consisting of multiple concentric rings is designed, which is inspired by the structure of Fresnel Zone Plates (FZP). The structural parameters are optimized using finite element simulation methods. A prototype of the transducer is manufactured with electrode patterns made of conductive silver paste using silk screen-printing technology. Conventional focusing transducers using an acoustic lens and an FZP baffle are also manufactured, and their focusing performances are comparatively tested. The experimental results show that our novel transducer has a focal length of 16 mm and a center frequency of 1.16 MHz, and that the sensitivity is improved by 23.3% compared with the conventional focusing transducers. This research provides a new approach for the design of focusing transducers. Full article

(This article belongs to the Section Industrial Sensors)

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11 pages, 2614 KiB

Open AccessArticle

The Generation of Equal-Intensity and Multi-Focus Optical Vortices by a Composite Spiral Zone Plate

by Huaping Zang, Jingzhe Li, Chenglong Zheng, Yongzhi Tian, Lai Wei, Quanping Fan, Shaoyi Wang, Chuanke Wang, Juan Xie and Leifeng Cao

Photonics 2024, 11(5), 466; https://doi.org/10.3390/photonics11050466 - 15 May 2024

Cited by 1 | Viewed by 1727

Abstract

We propose a new vortex lens for producing multiple focused coaxial vortices with approximately equal intensities along the optical axis, termed equal-intensity multi-focus composite spiral zone plates (EMCSZPs). In this typical methodology, two concentric conventional spiral zone plates (SZPs) of different focal lengths [...] Read more.

We propose a new vortex lens for producing multiple focused coaxial vortices with approximately equal intensities along the optical axis, termed equal-intensity multi-focus composite spiral zone plates (EMCSZPs). In this typical methodology, two concentric conventional spiral zone plates (SZPs) of different focal lengths were composited together and the alternate transparent and opaque zones were arranged with specific m-bonacci sequence. Based on the Fresnel–Kirchhoff diffraction theory, the focusing properties of the EMCSZPs were calculated in detail and the corresponding demonstration experiment was been carried out to verify our proposal. The investigations indicate that the EMCSZPs indeed exhibit superior performance, which accords well with our physical design. In addition, the topological charges (TCs) of the multi-focus vortices can be flexibly selected and controlled by optimizing the parameters of the zone plates. These findings which were demonstrated by the performed experiment may open new avenues towards improving the performance of biomedical imaging, quantum computation and optical manipulation. Full article

(This article belongs to the Special Issue Space Division Multiplexing Techniques)

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9 pages, 5379 KiB

Open AccessCommunication

Generation of a Focused THz Vortex Beam from a Spintronic THz Emitter with a Helical Fresnel Zone Plate

by Xiaoqiang Zhang, Yong Xu, Bin Hong, Fan Zhang, Anting Wang and Weisheng Zhao

Nanomaterials 2023, 13(14), 2037; https://doi.org/10.3390/nano13142037 - 10 Jul 2023

Cited by 6 | Viewed by 1871

Abstract

Similar to optical vortex beams, terahertz (THz) vortex beams (TVBs) also carry orbital angular momentum (OAM). However, little research has been reported on the generation of TVBs. In this paper, based on the detour phase technique, we design a series of spintronic terahertz [...] Read more.

Similar to optical vortex beams, terahertz (THz) vortex beams (TVBs) also carry orbital angular momentum (OAM). However, little research has been reported on the generation of TVBs. In this paper, based on the detour phase technique, we design a series of spintronic terahertz emitters with a helical Fresnel zone plate (STE-HFZP) to directly generate focused TVBs with topological charges (TCs) of l = ±1, ±2 and ±3, respectively. The STE-HFZP is a hybrid THz device composed of a terahertz emitter and a THz lens, and it has a high numerical aperture (NA), achieving subwavelength focal spots. Its focus properties are surveyed systemically through accurate simulations. This STE-HFZP can also generate focused TVBs with higher order TCs. More importantly, the components of the focused electric field with OAM make up the majority of the intensity and have potential applications in the field of THz communications, THz imaging and atom trapping. Full article

(This article belongs to the Special Issue Laser-Matter Interaction for Nanostructuration and Characterization: From Fundamentals to Sensing and Energy Applications)

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16 pages, 30389 KiB

Open AccessArticle

Charging Mobile Devices in Indoor Environments

by Diogo Matos, Ricardo A. M. Pereira, Helena Ribeiro, Bernardo Mendes, Daniel Belo, Arnaldo Oliveira and Nuno Borges Carvalho

Energies 2022, 15(9), 3450; https://doi.org/10.3390/en15093450 - 9 May 2022

Cited by 7 | Viewed by 2783

Abstract

Wireless power transfer promises to revolutionize the way in which we use and power mobile devices. However, low transfer efficiencies prevent this technology from seeing wide scale real-world adoption. The aim of this work is to use quasioptics to develop a system composed [...] Read more.

Wireless power transfer promises to revolutionize the way in which we use and power mobile devices. However, low transfer efficiencies prevent this technology from seeing wide scale real-world adoption. The aim of this work is to use quasioptics to develop a system composed of a dielectric lens fed by a phased array to reduce spillover losses, increasing the beam efficiency, while working on the antenna system’s Fresnel zone. The DC-RF electronics, digital beamforming and beam-steering by an FPGA, and radiating 4 × 4 microstrip patch phased array have been developed and experimented upon, while the lens has been designed and simulated. This paper details these preliminary results, where the phased array radiation pattern was measured, showing that the beam is being generated and steered as expected, prompting the lens construction for the complete system experimentation. Full article

(This article belongs to the Special Issue Next Generation Wireless Charging System for Mobile Devices)

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12 pages, 2422 KiB

Open AccessArticle

A Setup for Measuring the Centering Error of a Dual-Element Pyroelectric Infrared Sensor Module

by Vu Toan Thang, Vu Van Quang and Ngoc-Tam Bui

Sensors 2021, 21(19), 6684; https://doi.org/10.3390/s21196684 - 8 Oct 2021

Cited by 3 | Viewed by 3462

Abstract

This paper presents an experimental setup to measure the horizontal centering error of a pre-built pyroelectric infrared (PIR) sensor module, in which a dual-element PIR sensor is aligned at the focal point of a single-zone Fresnel Lens. In the setup, the sensor module [...] Read more.

This paper presents an experimental setup to measure the horizontal centering error of a pre-built pyroelectric infrared (PIR) sensor module, in which a dual-element PIR sensor is aligned at the focal point of a single-zone Fresnel Lens. In the setup, the sensor module was placed facing a modulated infrared radiating source and turned over a range of horizontal angles. The position of the optical axis of the sensor module was determined based on the analysis of the output response of the sensor at turned angles. Thus, the horizontal centering error of the module is defined as the difference between the mechanical axis of the housing and the found optical axis. For the prebuilt sensor module, with the specific available equipment, the measurement of the centering error of the module achieved a resolution of 0.02 degrees. Full article

(This article belongs to the Section Optical Sensors)

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12 pages, 1785 KiB

Open AccessCommunication

Analysis of Predistortion Techniques on Fresnel Zone Plates in Ultrasound Applications

by José Miguel Fuster, Sergio Pérez-López, Francisco Belmar and Pilar Candelas

Sensors 2021, 21(15), 5066; https://doi.org/10.3390/s21155066 - 27 Jul 2021

Viewed by 2480

Abstract

In this work, we analyze the effect of predistortion techniques on the focusing profile of Fresnel Zone Plates (FZPs) in ultrasound applications. This novel predistortion method is based on either increasing or decreasing the width of some of the FZP Fresnel rings by [...] Read more.

In this work, we analyze the effect of predistortion techniques on the focusing profile of Fresnel Zone Plates (FZPs) in ultrasound applications. This novel predistortion method is based on either increasing or decreasing the width of some of the FZP Fresnel rings by a certain amount. We investigate how the magnitude of the predistortion, as well as the number and location of the predistorted rings, influences the lens focusing profile. This focusing profile can be affected in different ways depending on the area of the lens where the predistortion is applied. It is shown that when the inner area of the lens, closer to its center, is predistorted, this technique allows the control of the focal depth at the main focus. However, when the predistortion is applied to an area farther from the center of the lens, the acoustic intensity distribution among the main focus and the closest adjacent secondary foci can be tailored at a certain degree. This predistortion technique shows great potential and can be used to control, modify and shape the FZP focusing profile in both industrial and therapeutic applications. Full article

(This article belongs to the Section Physical Sensors)

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8 pages, 5676 KiB

Open AccessArticle

A Planar Fresnel Lens in Reflection Type Based on Azo-Dye-Doped Cholesteric Liquid Crystals Fabricated by Photo-Alignment

by Bing-Yau Huang, Ting-Hui Chen, Tzu-Yeh Chen, Jia-De Lin, Tsung-Hsien Lin and Chie-Tong Kuo

Polymers 2020, 12(12), 2972; https://doi.org/10.3390/polym12122972 - 12 Dec 2020

Cited by 4 | Viewed by 2548

Abstract

This paper presents a focusing efficiency and focal length tunable planar Fresnel lens in reflection type based on azo-dye-doped cholesterol liquid crystal film. The Fresnel-like pattern of a pumping beam can be formed by a Sagnac interferometer. When the azo-dye molecules are irradiated [...] Read more.

This paper presents a focusing efficiency and focal length tunable planar Fresnel lens in reflection type based on azo-dye-doped cholesterol liquid crystal film. The Fresnel-like pattern of a pumping beam can be formed by a Sagnac interferometer. When the azo-dye molecules are irradiated by the pumping beam, the photoalignment effect will be induced in the bright (odd) zones due to the trans–cis photoisomerization of azo-dye molecules. Thus, the structures of cholesteric liquid crystals in the odd zones will reorient from the imperfectly planar textures to the perfectly planar textures. The different structures of cholesteric liquid crystals in two adjacent zones will give rise to phase difference for the reflected light and thus function as a Fresnel lens. The focusing efficiency of the proposed Fresnel lens can be controlled by the applied voltages and affected by the polarization state of incident light. Moreover, various focal lengths of the Fresnel lens can be achieved by rewriting a different center radius of the Fresnel-like pattern. Full article

(This article belongs to the Special Issue Polymer-Based Materials in Liquid Crystals)

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Graphical abstract

9 pages, 1307 KiB

Open AccessLetter

Transient Analysis of Fresnel Zone Plates for Ultrasound Focusing Applications

by Sergio Pérez-López, Daniel Tarrazó-Serrano, Dimitry O. Dolmatov, Constanza Rubio and Pilar Candelas

Sensors 2020, 20(23), 6824; https://doi.org/10.3390/s20236824 - 29 Nov 2020

Cited by 3 | Viewed by 2693

Abstract

Fresnel Zone Plates are planar lenses that can be used to focus ultrasound beams. This kind of acoustic lenses can play a key role in the resolution of ultrasonic NDT systems. In this type of pulse-echo applications, the pulse duration is an important [...] Read more.

Fresnel Zone Plates are planar lenses that can be used to focus ultrasound beams. This kind of acoustic lenses can play a key role in the resolution of ultrasonic NDT systems. In this type of pulse-echo applications, the pulse duration is an important parameter that specifies the axial resolution, and thus, shorter ultrasound pulses provide higher resolutions. However, acoustic lenses exhibit a transient response that should be considered when setting the pulse duration, as pulses shorter than the transient state duration result in degradation in the response of acoustic lenses in terms of focal intensity, focal displacement, and lateral and axial resolutions. In this work, a thorough analysis of the transient response of Fresnel Zone Plates is discussed, demonstrating that the transient state should be considered in order to achieve optimal focusing performance. Theoretical and numerical results are presented, showing very good agreement. Full article

(This article belongs to the Section Physical Sensors)

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11 pages, 8171 KiB

Open AccessLetter

Simulation of Fresnel Zone Plate Imaging Performance with Number of Zones

by Ying Li, Ombeline de La Rochefoucauld and Philippe Zeitoun

Sensors 2020, 20(22), 6649; https://doi.org/10.3390/s20226649 - 20 Nov 2020

Cited by 8 | Viewed by 5469

Abstract

In recent years, integral imaging, a promising three-dimensional imaging technology, has attracted more and more attention for its broad applications in robotics, computational vision, and medical diagnostics. In the visible spectrum, an integral imaging system can be easily implemented by inserting a micro-lens [...] Read more.

In recent years, integral imaging, a promising three-dimensional imaging technology, has attracted more and more attention for its broad applications in robotics, computational vision, and medical diagnostics. In the visible spectrum, an integral imaging system can be easily implemented by inserting a micro-lens array between a image formation optic and a pixelated detector. By using a micro-Fresnel Zone Plate (FZP) array instead of the refractive lens array, the integral imaging system can be applied in X-ray. Due to micro-scale dimensions of FZP in the array and current manufacturing techniques, the number of zones of FZP is limited. This may have an important impact on the FZP imaging performance. The paper introduces a simulation method based on the scalar diffraction theory. With the aid of this method, the effect of the number of zones on the FZP imaging performance is numerically investigated, especially the case of very small number of zones. Results of several simulation of FZP imaging are presented and show the image can be formed by a FZP with a number of zones as low as 5. The paper aims at offering a numerical approach in order to facilitate the design of FZP for integral imaging. Full article

(This article belongs to the Special Issue EUV and X-ray Wavefront Sensing)

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9 pages, 2046 KiB

Open AccessArticle

Polarization-Independent Metasurface Lens Based on Binary Phase Fresnel Zone Plate

by Xing Li, Jing Tang and Jonathan Baine

Nanomaterials 2020, 10(8), 1467; https://doi.org/10.3390/nano10081467 - 27 Jul 2020

Cited by 20 | Viewed by 4346

Abstract

Based on the binary phase Fresnel zone plate (FZP), a polarization-independent metasurface lens that is able to focus incident light with any polarization state, including circular, linear, and elliptical polarizations, has been proposed and investigated. We demonstrate that the metasurface lens consisting of [...] Read more.

Based on the binary phase Fresnel zone plate (FZP), a polarization-independent metasurface lens that is able to focus incident light with any polarization state, including circular, linear, and elliptical polarizations, has been proposed and investigated. We demonstrate that the metasurface lens consisting of metal subwavelength slits can operate in a wide bandwidth in the visible range, and has a higher focusing efficiency than that of an amplitude FZP lens without phase modulation. A multi-focus FZP metasurface lens has also been designed and investigated. The proposed lens can provide potential applications in integrated nanophotonic devices without polarization limitations. Full article

(This article belongs to the Special Issue Planar Optical Components Based on the Prepatterned Surfaces, Metasurfaces, and Hybrid Nanomaterials)

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10 pages, 4245 KiB

Open AccessCommunication

Randomly Multiplexed Diffractive Lens and Axicon for Spatial and Spectral Imaging

by Vijayakumar Anand, Tomas Katkus and Saulius Juodkazis

Micromachines 2020, 11(4), 437; https://doi.org/10.3390/mi11040437 - 21 Apr 2020

Cited by 21 | Viewed by 4324

Abstract

A new hybrid diffractive optical element (HDOE) was designed by randomly multiplexing an axicon and a Fresnel zone lens. The HDOE generates two mutually coherent waves, namely a conical wave and a spherical wave, for every on-axis point object in the object space. [...] Read more.

A new hybrid diffractive optical element (HDOE) was designed by randomly multiplexing an axicon and a Fresnel zone lens. The HDOE generates two mutually coherent waves, namely a conical wave and a spherical wave, for every on-axis point object in the object space. The resulting self-interference intensity distribution is recorded as the point spread function. A library of point spread functions are recorded in terms of the different locations and wavelengths of the on-axis point objects in the object space. A complicated object illuminated by a spatially incoherent multi-wavelength source generated an intensity pattern that was the sum of the shifted and scaled point spread intensity distributions corresponding to every spatially incoherent point and wavelength in the complicated object. The four-dimensional image of the object was reconstructed using computer processing of the object intensity distribution and the point spread function library. Full article

(This article belongs to the Special Issue Micro/Nano-surfaces: Fabrication and Applications)

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9 pages, 4172 KiB

Open AccessArticle

Bifocal Ultrasound Focusing Using Bi-Fresnel Zone Plate Lenses

by Sergio Pérez-López, José Miguel Fuster, Pilar Candelas, Daniel Tarrazó-Serrano, Sergio Castiñeira-Ibáñez and Constanza Rubio

Sensors 2020, 20(3), 705; https://doi.org/10.3390/s20030705 - 28 Jan 2020

Cited by 10 | Viewed by 4356

Abstract

In this work, we present a bifocal Fresnel zone plate (BiFZP) capable of generating focusing profiles with two different foci. The performance of the BiFZP is demonstrated in the ultrasound domain, with a very good agreement between the experimental measurements and the finite [...] Read more.

In this work, we present a bifocal Fresnel zone plate (BiFZP) capable of generating focusing profiles with two different foci. The performance of the BiFZP is demonstrated in the ultrasound domain, with a very good agreement between the experimental measurements and the finite element method (FEM) simulations. This lens becomes an appealing alternative to other dual-focusing lenses, in which the foci location can only be set at a limited range of positions, such as M-bonacci zone plates. Moreover, the variation of the operating frequency has also been analyzed, providing an additional dynamic control parameter in this type of lenses. Full article

(This article belongs to the Section Physical Sensors)

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13 pages, 3045 KiB

Open AccessArticle

M-Bonacci Zone Plates for Ultrasound Focusing

by Sergio Pérez-López, José Miguel Fuster and Pilar Candelas

Sensors 2019, 19(19), 4313; https://doi.org/10.3390/s19194313 - 5 Oct 2019

Cited by 6 | Viewed by 3099

Abstract

In this work, we present a thorough analysis on M-bonacci zone plates for ultrasound focusing applications. These planar lenses are capable of providing bifocal focusing profiles with equal intensity in both foci and become very appealing for a wide range of scenarios including [...] Read more.

In this work, we present a thorough analysis on M-bonacci zone plates for ultrasound focusing applications. These planar lenses are capable of providing bifocal focusing profiles with equal intensity in both foci and become very appealing for a wide range of scenarios including medical and industrial applications. We show that in high-wavelength domains, such as acoustics or microwaves, the separation between both foci can be finely adjusted at the expense of slightly increasing the distortion of the focusing profile, and we introduce a design parameter to deal with this issue and simplify the design process of these lenses. Experimental measurements are in good agreement with numerical simulations and demonstrate the potential of M-bonacci lenses in ultrasound focusing applications. Full article

(This article belongs to the Section Physical Sensors)

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