We propose a method to generate microwave holograms using impedance metasurfaces for multiple simultaneous wavelengths. For recent impedance hologram designs in the microwave band, radiation from leaky waves can be controlled in the far field by creating holograms based on the interference of reference and object waves at a specific frequency. In our design, we vary only one physical dimension in the unit cell to simultaneously satisfy the requirement of impedance distribution for two frequencies in the same aperture. Two excitation ports are used to simultaneously generate the beams at 17 and 20 GHz. The simulation and measurement results show a very good agreement, confirming the validity of the proposed design method. The new low-profile holographic leaky-wave antenna has potential applications in designing multifrequency communication and radar systems.

A design method of programmable transmitarray antenna with independent controls of transmission amplitude and phase is proposed in C-band. The unit cell with cascaded structures mainly consists of four parts, including the receiving antenna, reconfigurable attenuator with p-i-n diodes, reconfigurable phase shifter with varactors, and transmitting antenna. Correspondingly, various manipulations of spatial electromagnetic (EM) fields are achieved by varying the bias voltages of p-i-n diodes and varactors in the transmitarray antenna. The fabricated unit cell is measured in a standard waveguide, and the whole array with $8\times 8$ unit cells is measured with two horns for calibration of the programmable EM features. The experimental results show that the transmission amplitude can range from −16 to −3.6 dB, and the transmission phase achieves 270° coverage independently at the operating frequency of 5.67 GHz under 16 bit programmable control. To further exhibit the capability and functionality of the proposed transmitarray antenna, the waveform engineering of adaptive beamforming and power-allocation beamforming is separately realized in the experiment. The measured results have good agreements with our theoretical calculations, verifying the validity of our design method.

Recent years have witnessed a rapidly growing interest in exploring the use of spiral sound carrying artificial orbital angular momentum (OAM), toward establishing a spiral-wave-based technology that is significantly more efficient in energy or information delivering than the ordinary plane wave technology. A major bottleneck of advancing this technology is the efficient excitation of far-field spiral waves in free space, which is a must in exploring the use of spiral waves for long-distance information transmission and particle manipulation. Here, we report a low-profile planar acoustic antenna to modulate wavefronts emitted from a near-field point source and achieve far-field spiral airborne sound carrying OAM. Using the holographic interferogram as a 2D modulated artificial acoustic impedance metasurface, we show the efficient conversion from the surface wave into the propagating spiral shape beam both numerically and experimentally. The vortex fields with spiral phases originate from the complex inter-modal interactions between cylindrical surface waves and a spatially-modulated impedance boundary condition. This antenna can open new routes to highly integrated spiral sound emitters that are critical for practical acoustic functional devices.

Due to the strong ability of recognizing electromagnetic (EM) environment and adaptively control of EM waves, the intelligent metasurfaces have received great attention recently. However, the intelligent metasurface with frequency recognition for adaptive manipulation of the EM waves has not been studied. Here, we propose a frequency‐recognition intelligent metasurface to precisely control the spatial EM waves under the agile frequencies with the help of a real‐time radio‐frequency sensor and an adaptive feedback control system. An active meta‐atom is presented to reach 2 bit phase coding and 1 bit amplitude coding capacities to control the amplitude and phase independently. Experimental results demonstrate that the metasurface can recognize different frequency of the incoming wave with very high resolution, and can adaptively realize the self‐defined multiple frequency agilities to manipulate the reflected EM waves without any human participation. As example, the intelligent metasurface with frequency recognition can adaptively operate wave absorption at 5.36 GHz, reflection to normal direction at 5.38 GHz, deflection to −30° at 5.40 GHz, random diffusion at 5.42 GHz, and deflection to +33° at 5.44 GHz by detecting the incoming frequency at the resolution of 0.02 GHz.

Metasurfaces have been developed as a promising approach for manipulating electromagnetic waves. Recently, deep learning algorithms have been introduced to design metasurfaces, but the network can only output one solution for each desired input and suffers from nonunique issue. To overcome the aforementioned challenges, a deep neural network model for inverse designs of anisotropic metasurfaces with full phase properties in ultrawideband is proposed. Given the target reflection spectra as inputs, the candidate metasurface patterns are generated through a generative adversarial network (GAN), and the corresponding predictions are simply achieved by the accurate forward neural network model to match the target spectra in the whole band with high fidelity. By training the generator and discriminator in GAN in an alternating order combined with setting a threshold of discriminator loss to trigger the phase prediction, the proposed method is much more efficient and consumes less time in the training process. Numerical simulations and experimental results demonstrate that the reflection phases of the generated meta‐atoms have excellent agreements with the given targets, providing an efficient way in automatically designing metasurfaces. The most important advantage of this approach over the previous schemes is to improve the design speed significantly with very good accuracy.