This paper presents a disc-type stepper motor based on PCB technology. Aiming to provide a solution for the difficulty of torque enhancement in multi-pole PCB stepper motors under the limited wiring space of the PCB stator, a novel spiral winding configuration is proposed. Without increasing the number of PCB stator layers or the overall dimensions, an axially offset layout is employed to enlarge the coil flux-linkage area, thereby increasing the electromagnetic torque. Theoretical analysis and finite element simulation results show that the proposed winding achieves approximately 30% higher torque than conventional spiral windings. Meanwhile, to address the current fluctuation problem caused by the low-inductance characteristic resulting from the coreless PCB stator, the influence of current ripple on the microstepping drive of the stepper motor is analyzed. A series-inductor approach is adopted to suppress current fluctuation, and the optimal inductor value is selected through theoretical calculation and simulation, which effectively reduces the current ripple and significantly improves the microstepping performance. Finally, a prototype is fabricated and tested experimentally. The results indicate that the motor output torque reaches 46.4 mN & centerdot;m, and the step-angle error under 16-microstep drive is within 0.25 degrees, providing a feasible solution for the design and control of PCB stepper motors in compact spaces.

Two-dimensional (2D) Direction-of-Arrival (DOA) estimation is crucial in radar and wireless communications. However, traditional phased array antennas are complex and expensive, while existing digital coded metasurface schemes are limited to sensing in half-space. To overcome the limitation of existing digital metasurface schemes that can only perform DOA estimation within half-space, this paper proposes a transmission-reflection integrated time-domain coding metasurface architecture, enabling independent and dynamic manipulation of both transmitted and reflected waves within a single device, thereby constructing a 2D DOA estimation system capable of operating in full-space. The metasurface employs a double-layer cross metal structure, and its PIN diodes on the upper and lower layers are individually controlled by an FPGA to switch ON/OFF, forming four space-time coding modes: “00”, “11”, “01” and “10”, achieving 1-bit transmissive/reflective phase modulation at 12.5 GHz. By leveraging orthogonal time-domain coding sequences constructed using Hadamard matrices, the wavefront amplitude and phase distributions are reconstructed from the time-domain responses, and efficient 2D DOA estimation is then achieved by integrating this with the Capon algorithm. Experimental results demonstrate that the system achieved stable angular reconstruction with errors less than 3.5° within the ±60° range in both transmissive and reflective modes, validating its high accuracy, low complexity, and full-space sensing capabilities. This work breaks through the limitation of existing metasurface DOA estimation being limited to half-space, enabling full-space 2D DOA estimation based on a single time-domain coding metasurface structure. It provides an effective pathway for developing low-cost, integrable intelligent electromagnetic sensing systems.

Radio frequency (RF) energy harvesting offers a potential power source for low-power Internet of Things and wireless sensing nodes, but compact rectifiers must balance impedance matching, multiband response, and load-driving capability. This work presents a compact SMS7621 Schottky-diode RF rectifier for RF-powered wireless sensing applications. An 11-segment microstrip distributed-parameter collaborative optimization strategy is used to tune impedance transformation in a 3.48 cm & times; 1.98 cm single-layer layout while compensating for diode nonlinear impedance variation and package parasitics. Simulations show more than 40% RF-to-DC conversion efficiency from 1.90 to 2.35 GHz, with additional efficiency peaks of 40.55% at 4.45 GHz and 38.45% at 7.15 GHz. Measurements verify the 2.45 GHz output performance under controlled high-input-power excitation: with a 300 Omega load and 25 dBm input, the rectifier delivers a maximum DC voltage of 5.42 V. At 15 dBm input, the measured peak efficiency reaches 46.05% at 2 GHz and remains 35.69% at 4 GHz. These results indicate a compact rectifier front end with multiband harvesting potential and 5 V-class load-driving capability under dedicated RF powering conditions.

Previous studies on reconfigurable intelligent metasurface (RIS) design have primarily relied on full-wave electromagnetic simulation software, which often incurs high computational costs and lacks clear design direction. The design of multi-bit RIS remains challenging and there is currently no suitable systematic method for selecting the corresponding tuning devices. To overcome these limitations, this article proposes a novel equivalent circuit-based approach to RIS design. In contrast to the conventional approach, where the equivalent circuit model is derived from post-design evaluation of the scattering properties of RIS, our work is entirely driven by the equivalent circuit model from the outset to accomplish the unit cell design. A complete workflow as well as details of each constituent step are presented for the topology design of RIS based on equivalent circuit topology. Building on this circuit topology, a 3-bit reflective phase reconfigurable unit cell is developed based on a tunable band-stop filter circuit. We conducted adjustable phase verification experiments and beam deflection experiments. The consistency between the experimental results and circuit theory demonstrates the feasibility and practicality of the equivalent circuit method of RIS design. This circuit-to-structure methodology provides a physically interpretable and systematic framework for designing RIS with arbitrary electromagnetic responses, offering new insights into RIS design.

The computer-assisted inverse design of photonic computing, especially by leveraging artificial intelligence algorithms, offers great convenience to accelerate the speed of development and improve calculation accuracy. However, traditional thickness-based modulation methods are hindered by large volume and difficult fabrication process, making it hard to meet the data-driven requirements of flexible light modulation. Here, we propose a diffractive deep neural network (D2NN) framework based on a three-layer all-dielectric phased transmitarray as hidden layers, which can perform the classification of handwritten digits. By tailoring the radius of a silicon nanodisk of a meta-atom, the metasurface can realize the phase profile calculated by D2NN and maintain a relative high transmittance of 0.9 at a wavelength of 600 nm. The designed image classifier consists of three layers of phase-only metasurfaces, each of which contains 1024 units, mimicking a fully connected neural network through the diffraction of light fields. The classification task of handwriting digits from the ‘0’ to ‘5’ dataset is verified, with an accuracy of over 90% on the blind test dataset, as well as demonstrated by the full-wave simulation. Furthermore, the performance of the more complex animal image classification task is also validated by increasing the number of neurons to enhance the connectivity of the neural network. This study may provide a possible solution for practical applications such as biomedical detection, image processing, and machine vision based on all-optical computing.

Photonic Spin Hall Effect (PSHE) is a relativistic spin-orbit coupling phenomenon that can provide a wide range of spin-controlled nano-photon applications. However, most of the research results have been achieved only on 1D modulation of PSHE and the PSHE is very weak because of the extremely small spin-orbit interaction. Here, we propose a novel method to achieve a 2D manipulation of PSHE based on the broadband dielectric metasurface with refractive efficiency of above 80%. Using silicon nitride nanorods with perfect half-wave plates properties, a high-efficiency metasurface is designed, which demonstrated that directly realizes the high-performance PSHE in the ultraviolet region. Moreover, the metasurface can realize longitudinal focusing and transverse deflection of photons in different spin states by using the Pancharatnam-Berry (PB) phase and propagation phase, thus enabling 2D flexible manipulation of spin photons. The results show that the broadband dielectric metasurface offers a method to develop a high-efficiency PSHE for generating and manipulating spin-polarized photons, achieving important applications in optical communication, beam shaping, and optical sensors.

Vortex beam with inherent orbital angular momentum (OAM) is promising in high-capacity communication. On multimode vortex beam generation, metasurface has shown exceptional advantages of integration and miniaturization. For the current widely used phase-only methods on multimode vortex beam generation by metasurface, the purity of the OAM-mode spectrum is severely affected. A new method for generation of multimode vortex beam with high mode purity is proposed in this article by reconstructing the complete complex amplitude information on the meta-device aperture. A 20 dB suppression of the crosstalk modes is experimentally observed for the co-directional multimode vortex beam generation, which is much improved compared to the traditional phase-only scheme. In addition, the proposed scheme also provides the capability of generating high-purity multimode vortex beams with arbitrary preset propagation directions and power allocations. This study provides a platform for high-performance vortex beam communication by increasing the signal-to-noise ratio and enabling the multicasting scenarios with customized capacity requirements.

Elliptical airy vortex beams (EAVBs) can spontaneously form easily identifiable topological charge focal spots. They are used for topological charge detection of vortex beams because they have the abruptly autofocusing properties of circular airy vortex beams and exhibit unique propagation characteristics. We study the use of the dynamic phase and Pancharatnam–Berry phase principles for generation and modulation of EAVBs by designing complex-amplitude metasurface and phase-only metasurface, at an operating wavelength of 1500 nm. It is found that the focusing pattern of EAVBs in the autofocusing plane splits into |m|+1 tilted bright spots from the original ring, and the tilted direction is related to the sign of the topological charge number m. Due to the advantages of ultra-thin, ultra-light, and small size of the metasurface, our designed metasurface device has potential applications in improving the channel capacity based on orbital angular momentum communication, information coding, and particle capture compared to spatial light modulation systems that generate EAVBs.

This paper presents a novel metasurface design strategy to realize broadband radar cross section (RCS) reduction. The phase distribution across the metasurface aperture can be regarded as applying an additional parabolic phase upon periodically arranged parabolic subarrays. Such a design fully utilizes the diffusive scattering nature of the parabolic phase distribution. Since the proposed metasurface is governed by only two focal lengths, the optimization procedure is quite easy compared to metasurface with random coding sequence. Experimental results show that the proposed metasurface can achieve more than 10 dB RCS reduction from 7.52 GHz to 19.66 GHz with a fractional bandwidth of 89.3% under both linearly and circularly polarized normal incidences, and keeping a performance of more than 7 dB RCS reduction until the incident angle increases to 40° for both x -polarized and y -polarized incidences in the frequency range of 8–19.35 GHz. When the incident angle increases to 60°, 7 dB RCS reduction can still be obtained for x -polarized incidence from 7.9 GHz to 19.35 GHz with a fractional bandwidth of 84%.

This work proposes a method for surface wave (SW) coupling along with flexible complex amplitude modulation of its wavefront. The linearly polarized incident plane wave is coupled into the surface mode with complex wavefront by exploiting the spin-decouple nature of a reflective chiral meta-atom. As verification, two kinds of metasurface couplers are designed. The first kind contains two examples for SW airy beam generation with and without deflection under linearly polarized illumination, respectively. The second kind is a bi-functional device capable of SW focusing under left-handed circularly polarized illumination, and propagating wave deflection under right-handed circularly polarized illumination, respectively, to verify the fundamental spin-decoupled character. Simulated and experimental results are in good agreement. We believe that this method provides a flexible approach for complex SW applications in integrated optics, optical sensing, and other related fields.

Simultaneous and independent modulation of the amplitude and phase of surface waves (SWs) is critical in photonics and plasmonics. Here, we propose a method for flexible complex-amplitude modulation of SWs based on a metasurface coupler. Benefiting from the full range complex-amplitude modulation ability of the meta-atoms over the transmitted field, the coupler can convert the incident wave into a driven surface wave (DSW) with an arbitrary combination of amplitude and initial phase. By placing a dielectric waveguide that supports guided SWs below the coupler, the DSWs can resonantly couple to SWs while preserving complex-amplitude modulation. The proposed scheme provides a practical way for freely tailoring the phase and amplitude profiles of SWs wavefronts. As verification, meta-devices for normal and deflected SW Airy beam generation and SW dual focusing are designed and characterized in the microwave regime. Our findings may stimulate various advanced surface optical meta-devices.

Airy beams exhibit intriguing characteristics, such as diffraction-free propagation, self-acceleration, and self-healing, which have aroused great research interest. However, the spatial light modulator that generates Airy beams has problems such as narrow operational bandwidth, high cost, poor phase discretization, and single realization function. In the visible region (λ∼532 nm), we proposed a switchable all-dielectric metasurface for generating transmissive and reflective two-dimensional (2D) Airy beams. The metasurface was mainly composed of titanium dioxide nanopillars and vanadium dioxide substrate. Based on the Pancharatnam-Berry phase principle, a high-efficient Airy beam can be generated by controlling the phase transition of vanadium dioxide and changing the polarization state of the incident light. The optimized optical intensity conversion efficiencies of the transmissive and reflective metasurfaces were as high as 97% and 70%, respectively. In the field of biomedical and applied physics, our designed switchable metasurface is expected to offer the possibility of creating compact optical and photonic platforms for efficient generation and dynamic modulation of optical beams and open up a novel path for the application of high-resolution optical imaging systems.

A novel method for complex amplitude manipulation of spin light is proposed based on a double-layer compact anisotropic metasurface. A new degree of freedom (DOF) is introduced through independently rotating the two layers to achieve a full range control of the amplitude. Then additional full range phase shift is further imparted independently based on the traditional Pancharatnam-Berry (PB) phase mechanism by the global rotation of the meta-atom. As a result, the ability of full range and arbitrary complex amplitude manipulation is achieved on meta-atom level. Time consuming massive geometric parameter searching is avoided in the proposed method, which is beneficial to the complicated metadevice design. Based on this theory, two devices for multi-beam generation and Airy beam deflection are designed and experimentally verified, respectively. The good agreement between the calculated and measured results confirms the advantage of the proposed method. Our findings may trigger great interest in high-performance functional metaoptics devices with compact size in integrated systems.

Since the performance of electronic circuits is becoming rather limited in face of intensively increasing of amount of information and related operations, all-optical processing offers a promising strategy for future information system. It would benefit a great deal if the all-optical processing could be implemented within the developed electronic chips of nanoscale structures. In that it is highly desirable to break the diffraction limit of light for achieving effective light manipulations with deep subwavelength structures compatible with the state-of-the-art nanofabrication processes. It is of fundamental importance to get subwavelength optical localization, that is, squeeze light wave into subwavelength space for achieving freely manipulating of light fields. This review summarizes the development in realizing subwavelength optical localization by exciting toroidal mode in photonic metamaterials. The toroidal excitations in plasmonic metamaterials and Mie resonant metamaterials, in 3D structures and planar metamaterials, with single or few layers in spectral regime from microwave to optical frequencies are surveyed. Based on the discussion on the configurations of toroidal excitations, the recent development on toroidal-related optical scattering control actively manipulates the toroidal excitations, and promising applications are further investigated and highlighted.

Recently, the study of analog optical computing raised renewed interest due to its natural advantages of parallel, high speed and low energy consumption over conventional digital counterpart, particularly in applications of big data and high-throughput image processing. The emergence of metamaterials or metasurfaces in the last decades offered unprecedented opportunities to arbitrarily manipulate the light waves within subwavelength scale. Metamaterials and metasurfaces with freely controlled optical properties have accelerated the progress of wave-based analog computing and are emerging as a practical, easy-integration platform for optical analog computing. In this review, the recent progress of metamaterial-based spatial analog optical computing is briefly reviewed. We first survey the implementation of classical mathematical operations followed by two fundamental approaches (metasurface approach and Green's function approach). Then, we discuss recent developments based on different physical mechanisms and the classical optical simulating of quantum algorithms are investigated, which may lead to a new way for high-efficiency signal processing by exploiting quantum behaviors. The challenges and future opportunities in the booming research field are discussed.

The Pancharatnam–Berry geometric phase has attracted great interest due to the elegant phase control strategy via geometric transformation of optical elements. The commonly used geometric phase is associated with circular polarization states. Here, we show that by exploiting the geometric phase associated with the two elliptical eigen-polarization states in a racemic metallic helix array, exotic features including full range phase modulation for linear polarization states, diverse polarization conversion, and full complex amplitude modulation can be obtained with rotation of the helices. As a proof of concept, several devices for implementing polarization conversion, vortex beam generating, and lateral dual focusing are built with a racemic helix array in the microwave regime. The calculated and experimental results validate our proposals, which can stimulate various advanced metadevices.

Herein, a polarization‐pure Airy beam generation strategy based on twisted layer structures, which is broadband with efficiency approaching the theoretical limit, is proposed. As demonstration, an Airy beam generator operating in the microwave regime is built with stacked three‐layer identical complementary split ring resonators (CSRRs) as the unit cell. By spatially arranging the orientation angle of the middle layer in each unit cell, linearly polarized incident waves can be converted to an Airy beam in cross‐polarization, whereas the unmodulated copolarized component is strongly suppressed in the transmitted field. The proposed Airy beam generation strategy along with the transmission amplitude and phase modulation method can be implemented at terahertz and even infrared regimes using various other twisted multilayer structures.

We proposed a meta-atom design strategy that can achieve full complex-amplitude modulation based on analytical method for circularly polarized waves. The meta-atom can be regarded as two cascaded quarter wave plates, the orientation angles of which provide two degrees of freedom for obtaining arbitrary amplitude and phase modulation through accurate analytical method. As verification, a microwave meta-atom is designed and used to realize lateral and axial dual focusing. The proposed design strategy provides a straightforward route for full, continuous control of both amplitude and phase, and can stimulate various advanced meta-devices.

The active control of artificially structured metasurfaces is a promising route for solving the operation bandwidth limitation of metasurfaces due to their resonant nature. Herein, the active tunability of the toroidal response in a terahertz hybrid metasurface is proposed and experimentally demonstrated. The top metallic layer of the metasurface has a toroidal configuration and is coupled to an electrically biased phase‐change silicon layer, whose conductive thickness and conductivity can be changed significantly when applying increased external current. The electrically biased hybrid metasurface shows high efficiency and complete electrical switching on the toroidal response in a broadband manner. Also, the optoelectronic metasurfaces modulated by biased currents are much easier to integrate in on‐chip optical devices. The hybrid metasurface taking advantage of the silicon layer with insulating‐state to conductive‐state transition in optical conductivity may facilitate the development of high‐performance active photonic applications in, for example, smart sensing in the terahertz regime.