Evolution of fermented grain yeast communities in strong-flavored baijiu and functional validation of yeasts that produce superior-flavored substances.

BACKGROUND: Baijiu is a well-known alcoholic beverage in China and the quality is determined by various microorganisms during the fermentation process. Yeast is one of the most important microorganisms in the fermentation of baijiu. It has a strong esterification capacity and also affects the aroma. RESULTS: High-throughput sequencing results showed that the fermented grains (jiupei) during baijiu production were mainly composed of eight highly abundant yeast species. The species and abundance of yeasts changed significantly with the fermentation process. The flavor of 30 yeast strains in the jiupei was determined by a sniffing test and gas chromatography-mass spectrometry (GC-MS). The strain with the highest flavor substance content (2.34 mg L-1), named YX3205, was identified as Clavispora lusitaniae. Tolerance results showed that C. lusitaniae YX3205 can tolerate up to 15% (v v-1) ethanol. In a solid-state simulated fermentation experiment, the content of 24 flavor substances was significantly increased in the fortified group, and the total ester content reached 4240.73 µg kg-1, which was 2.8 times higher than that of the control group. CONCLUSION: The present study demonstrated the potential of C. lusitaniae YX3205 to enhance the flavor of baijiu, thereby serving as a valuable strain for the improvement of the flavor quality of baijiu. © 2024 Society of Chemical Industry.

Ka-band beam-scanning leaky-wave antenna fed by reconfigurable spoof surface plasmon polaritons.

A leaky-wave antenna (LWA) based on reconfigurable spoof surface plasmon polaritons (SSPP) is proposed for beam scanning in the Ka band, which consists of a reconfigurable SSPP waveguide and a periodic array of metal rectangular split rings. Both numerical simulations and experimental measurements show that the reconfigurable SSPP-fed LWA has good performance in the frequency range from 25 to 30 GHz. Specifically, as the bias voltage changes from 0 to 15 V, we can achieve the maximum sweep range of 24° at a single frequency and 59° at multiple frequency points, respectively. Owing to the wide-angle beam-steering feature, as well as the field confinement and wavelength compression properties derived from the SSPP architecture, the proposed SSPP-fed LWA possesses great potential applications in the compact and miniaturized devices and systems of the Ka band.

Dual-band chiral metasurface for independent controls of spin-selective reflections.

The development of chiral metasurfaces with spin-selective reflection or transmission provides a new way to control the circularly polarized (CP) waves. However, it is still a great challenge to independently manipulate the polarization, frequency, and phase of the spin-selective reflected waves in different operating bands, which may have potential applications in improving the data capacity of microwave and optical communication systems. Here, a dual-band chiral metasurface is proposed to generate gigantic intrinsic chirality with strong circular dichroism (CD) in two different frequency bands by piecing two typical mono-chiral units together. The polarization, frequency and phase of the spin-selective reflected waves can also be independently designed in the two operating bands by adjusting the configuration of the chiral unit structures. Based on the proposed chiral structures, a dual-band chiral metasurface with spin-selective anomalous reflections is designed and demonstrated by both simulations and experiments. The results show that the polarization of spin-selective reflected waves can be customized by selecting appreciate chiral structures, while the wavefront of the spin-selective reflected waves can be further controlled by designing their arrangement.

Near-infrared absorption-induced switching effect via guided mode resonances in a graphene-based metamaterial.

Optical switches based on dielectric nanostructures are highly desired at present. To enhance the wavelength-selective light absorption, and achieve an absorption-induced switching effect, here we propose a graphene-based metamaterial absorber that consists of a dielectric grating, a graphene monolayer, and a photonic crystal. Numerical results reveal that the dual-band absorption with an ultranarrow spectrum of the system is enhanced greatly due to the critical coupling, which is enabled by the combined effects of guided mode resonances and photonic band gap. The quality factor of the absorber can achieve a high value (>500), which is basically consistent with the coupled mode theory. Slow light emerges within the absorption window. In addition, electrostatic gating of graphene in the proposed structure provides dynamic control of the absorption due to the change of the chemical potential of the graphene, resulting in an optional multichannel switching effect. Unlike other one-dimensional devices, these effects can be applied to another polarization without changing the structure parameters, and the quality factor is significantly enhanced (>1000). The tunable light absorption offered by the simple structure with an all-dielectric configuration will provide potential applications for graphene-based optoelectronic devices in the near-infrared range, such as narrowband selective filters, detectors, optical switches, modulators, slow optical devices, etc.

Flexible control of light trapping and localization in a hybrid Tamm plasmonic system.

A hybrid Tamm plasmonic system is proposed to investigate light manipulation at near-infrared frequency. The numerical results reveal that two remarkable absorption peaks are generated due to the different types of resonant modes excited in the structure, which can be well explained theoretically by guided-mode resonance (GMR) and Tamm plasmon polaritons. It is found that the electromagnetic energy can be easily trapped in different parts of the structure. More importantly, strong interaction between the two modes can be achieved by adjusting the structure period or incident angle, resulting in obvious mode hybridization and exhibiting unique energy-transfer characteristics. In addition, the active modulation of GMR-based absorption can be controlled in a continuous type by tuning the polarization angle or in a jump type by adjusting the chemical potential of graphene. This work should be useful for developing many high-performance optoelectronic devices, including sensors, modulators, detectors, etc.

Angle-insensitive dual-functional resonators combining cavity mode resonance and magnetic resonance.

An angle-insensitive dual-functional resonator composed of a compound metallic grating is proposed and characterized numerically. The resonator exhibits different response characteristics for TE and TM polarization, thus enabling two functions, corresponding to a high-sensitivity sensor and a low Q-factor absorber. For TE polarization, the Q-factor, refractive index sensitivity, and figure of merit of the resonator can reach 283.4, 2577.6 nm/RIU, and 181.5 RIU-1, respectively, due to the excitation of cavity mode resonance. For TM polarization, the resonator can be regarded as an absorber with high absorptivity (>97%) based on magnetic resonance. Accordingly, these two mechanisms can be explained well by the waveguide theory and inductor-capacitor circuit model. The electromagnetic fields in the system can be selectively concentrated in the cavity or slit by simply adjusting the polarization angle, exhibiting unique energy localization characteristics. The resonator can also exhibit polarization-sensitive behavior due to the different bandwidths for the same wavelength. This simple structure provides a good paradigm for designing high-performance multi-functional devices.

Tailoring anisotropic perfect absorption in monolayer black phosphorus by critical coupling at terahertz frequencies.

A metamaterial perfect absorber composed of a black phosphorus (BP) monolayer, a photonic crystal, and a metallic mirror is designed and investigated to enhance light absorption at terahertz frequencies. Numerical results reveal that the absorption is enhanced greatly with narrow spectra due to critical coupling, which is enabled by guided resonances. Intriguingly, the structure manifests the unusual polarization-dependent feature attributable to the anisotropy of black phosphorus. The quality factor of the absorber can be as high as 95.1 for one polarization while 63.5 for another polarization, which is consistent with the coupled wave theory. The absorption is tunable by varying key parameters, such as period, radius, slab thickness, incident angle, and polarization angle. Furthermore, the state of the system (i.e., critical coupling, over coupling, and under coupling) can be tuned by changing the electron doping of BP, thus achieving various applications. This work offers a paradigm to enhance the light-matter interaction in monolayer BP without plasmonic response, and this easy-to-fabricate structure will provide potential applications in BP-based devices.

Strong coupling between magnetic plasmons and surface plasmons in a black phosphorus-spacer-metallic grating hybrid system.

We propose a black phosphorus-spacer-metallic grating hybrid system to investigate the strong coupling between black phosphorus surface plasmons (BPSP) and magnetic plasmons (MP) at far-infrared frequencies. We theoretically and numerically illustrate interactions between the BPSP mode and MP mode in the coupling regime, which leads to a prominent Rabi splitting and the formation of multiple hybrid modes. Since the mechanisms of the two resonance modes are completely different, the fields in the system can be selectively localized in the spacer layer or metallic slits by regulating the coupling between such modes. Due to the strong anisotropic in-plane properties of black phosphorus (BP), the coupling between BPSP and MP modes in both armchair and zigzag directions is quite different. This work offers a new paradigm to enhance the light-matter interaction through the coupling of multiple resonance modes, and the proposed device will provide potential applications in constructing easy-to-fabricate BP-based plasmonic devices.

Ultra-wideband surface plasmonic Y-splitter.

We present an ultra-wideband Y-splitter based on planar THz plasmonic metamaterials, which consists of a straight waveguide with composite H-shaped structure and two branch waveguides with H-shaped structure. The spoof surface plasmonic polaritons (SSPPs) supported by the straight waveguide occupy the similar dispersion relation and mode characteristic to the ones confined by the branch waveguides. Attributing to these features, the two branch waveguides can equally separate the SSPPs wave propagating along the straight plasmonic waveguide to form a 3dB power divider in an ultra-wideband frequency range. To verify the functionality and performance of the proposed Y-splitter, we scaled down the working frequency to microwave and implemented microwave experiments. The tested device performances have clearly validated the functionality of our designs. It is believed to be applicable for future plasmonic circuit in microwave and THz ranges.

Computer-Vision Based Gesture-Metasurface Interaction System for Beam Manipulation and Wireless Communication.

Hand gesture plays an important role in many circumstances, which is one of the most common interactive methods in daily life, especially for disabled people. Human-machine interaction is another popular research topic to realize direct and efficient control, making machines intelligent and maneuverable. Here, a special human-machine interaction system is proposed and namedas computer-vision (CV) based gesture-metasurface interaction (GMI) system, which can be used for both direct beam manipulations and real-time wireless communications. The GMI system first needs to select its working mode according to the gesture command to determine whether to perform beam manipulations or wireless communications, and then validate the permission for further operation by recognizing unlocking gesture to ensure security. Both beam manipulation and wireless communication functions are validated experimentally, which show that the GMI system can not only realize real-time switching and remote control of different beams through gesture command, but also communicate with a remote computer in real time by translating the gesture language to text message. The proposed non-contact GMI system has the advantages of good interactivity, high flexibility, and multiple functions, which can find potential applications in community security, gesture-command smart home, barrier-free communications, and so on.

Multichannel highly secure wireless communication system with information camouflage capability.

Information metasurface has shown great potential in wireless communications owing to its ability to flexibly control electromagnetic waves. However, it is still a big challenge to achieve high-security and large-channel capacity wireless communications by a simple system. Here, we propose a space-polarization-division multiplexing secure wireless communication system with information camouflage capability based on the information metasurface, which can realize multichannel encrypted wireless communications with different polarization coding strategies independently and simultaneously. A polarization mask key is introduced to encrypt the target message, and the cipher message is further concealed behind a cover image with steganography and sent to the user by using the polarization modulation strategy. Different polarization mask keys can be adopted in each individual communication by changing the polarization coding strategy to enhance the system security. The proposed scheme integrates computational algorithm encryption and physical layer security together and thus has the advantages of high security, large channel capacity, and strong camouflage ability.

Fully Breaking Entanglement of Multiple Harmonics for Space- and Frequency-Division Multiplexing Wireless Applications via Space-Time-Coding Metasurface.

Harmonic generation and utilization are significant topics in nonlinear science. Although the progress in the microwave region has been expedited by the development of time-modulated metasurfaces, one major issue of these devices is the strong entanglement of multiple harmonics, leading to criticism of their use in frequency-division multiplexing (FDM) applications. Previous studies have attempted to overcome this limitation, but they suffer from designing complexity or insufficient controlling capability. Here a new space-time-coding metasurface (STCM) is proposed to independently and precisely synthesize not only the phases but also the amplitudes of various harmonics. This promising feature is successfully demonstrated in wireless space- and frequency-division multiplexing experiments, where modulated and unmodulated signals are simultaneously transmitted via different harmonics using a shared STCM. To illustrate the advantages, binary frequency shift keying (BFSK) and quadrature phase shift keying (QPSK) modulation schemes are respectively implemented. Behind the intriguing functionality, the mechanism of the space-time coding strategy and the analytical designing method are elaborated, which are validated numerically and experimentally. It is believed that the achievements can potentially propel the time-vary metasurfaces in the next-generation wireless applications.

Experimental far-field imaging properties of a ~5-µm diameter spherical lens.

Microscale lenses are mostly used as near-sighted lenses. The far-field imaging properties of a microscale spherical lens, where the lens is spatially separated from the object, are experimentally studied. Our experimental results show that, for a blu-ray disc (an object) whose spacing is 300 nm, the lens can magnify the stripe patterns of the disc when the lens is spatially separated from the object. In the experimentally tested range (0-14 µm), all the magnified images are virtual images. When the distance is increased from 0 to 14 µm the magnification decreases from 1.47× to 1.20× and the field of view increases from 3.8 to 12.2 µm. The image magnification cannot be described by standard geometrical optics.

A Polarization-Modulated Information Metasurface for Encryption Wireless Communications.

Programmable and information metasurfaces have shown great potentials in wireless communications, but there are few reports on encrypted communications. In this paper, a programmable polarization-modulated (PoM) information metasurface is proposed, which can not only customize arbitrarily linearly polarized reflected waves, but also modulate their amplitudes in real time. Based on this feature, a physical-level wireless communication encryption scheme is presented and experimentally demonstrated by introducing a meta-key, which can be encrypted and sent by the programmable PoM information metasurface. To be specific, the key is encoded and concealed into different linear polarization channels, and then modulated and transmitted by the information metasurface at the transmitting end. At the receiving end, the modulated signal can be received and decoded by using a pair of polarization discrimination antennas. A wireless transceiver system is established to verify the feasibility of the scheme. It is shown that, once the meta-key is obtained, the corresponding encrypted target information that has been sent to the user in advance can be recovered.

Broadband and Programmable Amplitude-Phase-Joint-Coding Information Metasurface.

Information metasurfaces have attracted much attention in recent years due to the capability to link the physical world and information science. However, most of the current information metasurfaces are either phase-only coding or amplitude-only coding, limiting their functions and applications. Here, a broadband and programmable amplitude-phase-joint-coding (APJC) information metasurface is proposed and experimentally demonstrated, from which the phase and amplitude of reflected electromagnetic waves can be independently controlled by adjusting the bias voltage of PIN diode integrated in the meta-atom. In particular, the reflection amplitude can be continuously controlled from 0.1 to 0.9, and the reflection phase can be switched between two states with about 180° phase difference. Thus, the proposed metasurface is capable of realizing independent 1-bit or multibit amplitude coding and 1-bit phase coding, and both of them can be reprogrammed in real time in broad band from 8 to 13 GHz. The abilities of the programmable APJC information metasurface in manipulating the electromagnetic waves are demonstrated by both numerical simulations and experiments, including to suppress the sidelobes of scattering beam, generate the diffractive waves with arbitrary magnitudes, and so on. These results show unique advantages of APJC information metasurface in real-time independent controls of energy allocation and wavefront tailoring of the electromagnetic waves in a wide frequency band.

Spoof surface plasmonics: principle, design, and applications.

Surface plasmon polaritons (SPPs) are interactions between incident electromagnetic waves and free electrons on the metal-dielectric interface in the optical regime. To mimic SPPs in the microwave frequency, spoof SPPs (SSPPs) on ultrathin and flexible corrugated metallic strips were proposed and designed, which also inherit the advantages of lightweight, conformal, low profile, and easy integration with the traditional microwave circuits. In this paper, we review the recent development of SSPPs, including the basic concept, design principle, and applications along with the development from unwieldy waveguides to ultrathin transmission lines. The design schemes from passive and active devices to SSPP systems are presented respectively. For the passive SSPP devices, the related applications including filters, splitters, combiners, couplers, topological SSPPs, and radiations introduced. For the active SSPP devices, from the perspectives of transmission and radiation, we present a series of active SSPP devices with diversity and flexibility, including filtering, amplification, attenuation, nonlinearity, and leaky-wave radiations. Finally, several microwave systems based on SSPPs are reported, showing their unique advantages. The future directions and potential applications of the ultra-thin SSPP structures in the microwave and millimeter-wave regions are discussed.

Polarization-independent wide-angle triple-band metamaterial absorber.

We report the design, fabrication, and measurement of a microwave triple-band absorber. The compact single unit cell consists of three nested electric closed-ring resonators and a metallic ground plane separated by a dielectric layer. Simulation and experimental results show that the absorber has three distinctive absorption peaks at frequencies 4.06 GHz, 6.73 GHz, and 9.22 GHz with the absorption rates of 0.99, 0.93, and 0.95, respectively. The absorber is valid to a wide range of incident angles for both transverse electric (TE) and transverse magnetic (TM) polarizations. The triple-band absorber is a promising candidate as absorbing elements in scientific and technical applications because of its multiband absorption, polarization insensitivity, and wide-angle response.

Broadband Spin-Selective Wavefront Manipulations Based on Pancharatnam-Berry Coding Metasurfaces.

Spin-selective reflection metadevices are usually realized by using chiral metamirrors that can reflect one state of circularly polarized (CP) waves and restrain the other one. However, most of the chiral metamirrors only exhibit chirality in a narrow band, which may impede their potential applications. Here, we propose a Pancharatnam-Berry (PB) coding metasurface composed of the spin-decoupled elements to realize broadband spin-selective reflections with arbitrary wavefront manipulations. The spin-selective anomalous reflection is designed and measured to validate the performance of the proposed PB coding metasurface. Both simulation and experiment results show that the designated CP wave can be efficiently reflected without reversing the spin state, while at the same time, its orthogonally polarized wave is suppressed by random diffusion, in a broad band from 16 to 24 GHz. The results also reveal that the proposed PB coding metasurface has the chiral-like characteristics, even though it is composed of nonchiral meta-elements.

Virtual conversion from metal object to dielectric object using metamaterials.

We propose an illusion device which transforms a perfectly-electric-conducting (PEC) object into a virtual dielectric object with arbitrary material parameters. Such an illusion device has unconventional electromagnetic properties as verified by accurate numerical simulations. The presented illusion device is composed of inhomogeneous and anisotropic media with finite and positive permittivity and permeability components. Hence the designed device is possible to be realized using artificial metamaterials.

Diffuse reflections by randomly gradient index metamaterials.

We have demonstrated that a thin planar coating with randomly distributed index gradients can create diffuse reflections in front of a planar conducting sheet. This scheme is verified by two-dimensional near-field scanning measurement, in which the randomly gradient index coating is implemented by periodic crossed-I-shaped array whose unit cell's dimension varies spatially. Some qualitative principles of choosing the distribution mode of random index gradient are presented.