Wave Modulation Research Articles

Tunable flexural waves by piezoelectric metasurface with shunt circuits

Elastic metasurfaces have been rapidly developed for effective modulation of elastic wave propagation. Among them, utilizing the electromechanical coupling effect of piezoelectric materials provides a promising way to design tunable and multifunctional elastic metasurfaces, but piezoelectric metasurfaces still face big challenges in theoretical guidance and experiments. In this paper, a tunable piezoelectric metasurface is proposed for achieving modulation of flexural wave in broad working frequency range. Based on the developed electromechanical coupling model, the piezoelectric patch with shunt resistor-inductor circuit is analyzed, and the functional unit of metasurface with only two piezoelectric patches is designed for modulating the flexural wave in thin plate. By using Antoniou’s circuit and considering the effect of impedance in circuit, the arbitral phase shift of functional unit is experimentally achieved by adjustable shunt circuits to verify the turnability in a full 2π range. Further, the piezoelectric metasurface by assembling functional units can realize multiple functions, like tunable anomalous refraction and wave focusing, by adjusting shunt circuits.

Mechanical modulation wave energy harvesting for self-powered marine environment monitoring

Small-scale wave energy harvesting can be used for self-powered marine environmental monitoring, with the advantages of sustainability, convenience, and environmental protection. The low-frequency and strong random fluctuations of ocean wave motion are not conducive to electromechanical conversion. In this paper, we propose a mechanically modulated wave energy harvester embedded with interference-free triboelectric nanogenerators. The mass pendulum oscillates under irregular low-frequency wave excitation, and then the oscillation is mechanically modulated into a unidirectional high-speed rotation of four permanent magnet disks. The elastic parts on both sides of the mass pendulum are functionalized into multi-layered folding triboelectric nanogenerators, which neither increase the volume of the wave energy harvesting system nor affect the operation of the electromagnetic generator. The prototype was manufactured and the experimental results show that the sum of the average power of the prototype is 4.8 W under excitation at a frequency of 3 Hz and a inclination angle of 40°. The 0.47 F capacitor can be charged to 5 V in 80 seconds by the prototype under the wave excitation generated by push plate, and then used for self-powered marine environmental monitoring (illumination, temperature and pH) and wireless information transmission.

High-efficiency wide-angle anomalous refraction with acoustic metagrating

Abstract The emergent metagrating, with its unique and flexible beam shaping capabilities, offers new paths to efficient modulation of acoustic waves. In this work, an acoustic metagrating is demonstrated for high-efficiency and wide-angle anomalous refraction. It is shown that the normal reflection and transmission can be totally suppressed by properly modulating the amplitude and phase characteristics of the metagrating supercells for high-efficiency anomalous refraction. The anomalous refraction behavior is achieved in the wide range of incident angles from 28° to 78°, and the efficiency of -1st order diffraction is higher than 90% by finely designing the metagrating structure. The anomalous refraction behaviors are verified experimentally at incidence angle of 28°, 45° and 78°, respectively. The demonstrated metagrating is anticipated to possess efficient wide-angle composite wavefront engineering applications in such fields as communications.

Influence of Ocean Currents on Wave Modeling and Satellite Observations: Insights From the One Ocean Expedition

AbstractThis study investigates the influence of ocean currents on wave modeling and satellite observations using in situ wave measurements from the One Ocean Expedition 2021–2023. In January 2023, six OpenMetBuoy drifters were deployed in the Agulhas Current region. Their high immersion ratio minimized wind effects, allowing them to follow the current and return to the Indian Ocean by the Agulhas retroflection, collecting data for about 2 months. Comparing surface current velocities from both the Mercator model and Globcurrent product with drifter data reveals underestimation for velocities over with Mercator showing greater variability. Significant wave height and Stokes drift parameters from MFWAM and ERA5 were also evaluated against drifters. Both models tend to overestimate Stokes drift more noticeable in ERA5, indicating sensitivity to wind seas. For significant wave height, both models agree well with drifter measurements with correlations of 0.90 for MFWAM and 0.83 for ERA5. However, ERA5's lack of surface current data combined with its coarse resolution (0.5) lead to underestimation of wave heights exceeding 2.5 m. MFWAM products including and excluding currents exhibit root mean square errors of 0.39 and 0.45 m, respectively, when compared to drifter measurements. This confirms that neglecting currents introduces additional errors particularly in areas with sharp current gradients. Analyzing MFWAM wave spectra, including and excluding currents, reveals wave energy transfer attributed to wave‐current interactions. The spatial extent of these interactions is captured by satellite altimeters, revealing wave modulations with considerable wave height variations when waves cross eddies and the current core.

Drain self-blocking ambipolar transistors for complementary circuit applications

The development of complementary metal-oxide-semiconductor field-effect transistor (CMOSFET) based on two-dimensional (2D) materials offers an important opportunity to reduce static power and increase the integration density of integrated circuits. One promising approach to realize these CMOSFETs is to employ ambipolar 2D materials as channel materials with designed device structure to control the carrier transport properties for CMOSFET characteristics. However, these devices always suffer from complex multi-gate electrode structure, and hence face challenges in complicated inter-connection design and excessive voltage source requirement for circuit implementation. Here, we develop a three-terminal CMOSFET using ambipolar 2D material based on the drain electric field-induced carrier injection self-blocking mechanism. The designed drain electrode can effectively suppress carrier injection from the drain to the channel material, while the gate voltage can only regulate carrier injection in the source region. As a result, we can configure the device as either N-field-effect transistors (FET) or P-FET with a high current on/off ratio of over 105 by adjusting the three voltages (gate, source, and drain). Furthermore, we utilize these devices to demonstrate multifunctional wave modulator, low-static-power logic inverter (<5 pW), and combinational logic computing in the form of a compact complementary circuit. Our work would explore an efficient approach for implementing complementary circuits using 2D materials.

Flexible printing paper-based reconfigurable smart metasurfaces

In the rapidly evolving wireless communication landscape, achieving full-dimensional coverage poses a gamut of challenges such as intricacy, high hardware costs and energy consumption. In addressing these issues, reconfigurable metasurfaces are being considered as a potential solution. However, traditional methods of producing reconfigurable metasurfaces via printed circuit board (PCB) technologies possess limitations such as high cost and extended production cycles. Particularly, in the context of large-scale communication scenarios, reconfigurable metasurfaces can also present high energy consumption issues. Therefore, this paper proposes a novel type of intelligent reflection surface (IRS) characterized by lower production costs, reduced energy consumption, enhanced flexibility, ease of manufacture, and superior electromagnetic wave modulation capabilities. The proposed reconfigurable smart metasurface is a paper-based metasurface printed with conductive ink, which uses conductive ink to draw base metal blocks on a flexible substrate, and uses silver-tin as a metal patch between the metal blocks, and the phase response is reconstructed with silver ink. By adjusting the distribution of these metallic patches, we tailor the phase and amplitude distributions to generate specific scattering effects. This paper presents designs of six patterns that yield single-beam and dual-beam, with experimental results aligning closely with simulated results, validating the feasibility of the proposed method. This low-power, low-cost, and efficient IRS is expected to pave a new path for advanced 5 G/6G wireless communication technologies.

Metasurface with high cross-polarization isolation using rectangular split rings for simultaneous amplitude and phase controls

Metasurfaces have demonstrated significant potential for versatile modulation of electromagnetic waves. To enhance the control of electromagnetic waves, simultaneous control of amplitudes and phases is often essential in certain applications. The C-shaped split ring (SR) with polarization conversion and its deformed structures can fulfill this requirement; however, such structures encounter the challenge of low polarization isolation, which is mainly reflected in its inherent characteristics of low polarization isolation and the deterioration of polarization isolation in amplitude control. In this paper, a reflective metasurface with improved polarization isolation is proposed. The designed metasurface consists of rectangular split ring (R-SR) elements, which can realize both amplitude and phase controls simultaneously and independently while exhibiting higher polarization isolation than the conventional SR element. Furthermore, an alternating mirror rotation method (AMRM) for the arrangement of amplitude-control elements is proposed to suppress the degradation of polarization isolation caused by amplitude control. Several metasurfaces are designed to verify the characteristics of the proposed R-SR structure and the effectiveness of the AMRM. Finally, two reflective metasurfaces composed of R-SR elements and SR elements with identical configurations are designed and manufactured. Both the simulation and measured results demonstrate the versatility of the proposed design and its advantages in terms of polarization isolation and transfer efficiency.

Modulation instability of whistler wave with electron loss cone distribution in magnetized plasma

Abstract The modulation instability of whistler mode waves caused by thermal electron anisotropy is studied. Based on MHD equations, the nonlinear schrödinger equation (NLSE) that describes the nonlinear modulation of whistler waves is derived by Using the Krylov-Bogoliubov-Mitropolsky (KBM) method. The condition for wave modulation instability is obtained from the loss cone distribution function of thermal electron anisotropy, revealing that the nonlinear growth of the waves tends towards electron perpendicular temperature anisotropy. By setting up continuous background waves and introducing small ion low frequency perturbations, we find that the change in the amplitude of the modulated wave is related with wave number. This finding has been validated through simulations that align with our analytical results. Additionally, we also calculate the maximum amplitude of the wave with loss cone angle and times, which revealed that the electron vertical temperature anisotropy will lead to the modulation instability of the whistler wave. This further confirms the occurrence of the modulation instability of the whistler wave in laboratory plasmas and strengthens their credibility.

Strain-Induced Tunable and Field-Free Spintronic THz Emitters Based on Flexible Substrate Heterostructures.

Spintronic THz emitters have been widely studied due to their advantages of broadband frequency, high efficiency, and easy fabrication. The spintronic THz signal is proportional to the magnetization of the ferromagnetic (FM) layer and requires an external magnetic field to maximize the THz signal intensity. Recently, a field-free emitter was designed based on a CoFeB/IrMn3 heterostructure via the exchange bias between two films. However, field-free spintronic THz emitters based on a common FM/nonmagnetic metal structure are rare. Here, we fabricate a tunable and field-free THz emitter with giant THz emission modulation ability based on a polyimide/CoFeB/Pt heterostructure. The THz emission can be modulated by changing the curvature radius of the polyimide substrate. After the emitter is forward bent, the THz radiation without an external magnetic field is stronger than in the flat state with a field, which we attribute to in-plane magnetic anisotropy on the FM layer induced by the tensile strain. When we curve the emitter backward, the THz intensity decreases sharply. Moreover, the modulation (ΔS/Smax) of the THz wave from the forward-curved and backward-curved emitter is over 95%, and the device shows good cyclic repeatability. We provide a novel way to design field-free spintronic THz sources, and flexible devices are promising for application in THz devices.

Generation of frequency-shift keying (FSK) and amplitude-shift keying (ASK) RF signals by diode-tuned Fourier domain mode-locked opto-electronic oscillator

An approach to the generation of frequency-shift keying (FSK) and amplitude-shift keying (ASK) RF signals with a diode-tuned Fourier domain mode-locked opto-electronic oscillator (FDML OEO) is proposed and demonstrated. We use a low-cost varactor diode tuned phase shifter to form a high speed tunable bandpass filter (TBF) to implement the FDML-OEO. When a square wave modulation signal is used to drive the TBF, FSK RF signals are generated, with the flexibility to easily change the center frequency and tuning bandwidth of the FSK signals. For the ASK RF signal generation, a band-pass filter (BPF) with a bandwidth less than the TBF tuning range is added to the FDML OEO RF feedback loop. When the TBF center frequency hops in and out of the BPF bandwidth within a mode locking period, the FDML OEO generates ASK RF signals. The phase noises of the FSK and ASK RF signals generated by our FDML-OEO are both measured to be −123dBc/Hz at 10 kHz offset frequency. The key significance of this approach is that no microwave source is required to generate the ASK signal and reconfigurable FSK and signals, which may find wide applications in future radar and communications systems.

Boundary excitation of nonlinearly modulated bending strain waves in a metamaterial

A non-linear modulation of bending waves in a metamaterial mass-in-mass lattice model is studied. Various kinds of non-linear wave modulation are obtained using a harmonic boundary excitation. It is shown, that these waves can be described by an asymptotic simplification of the equations of motion resulting in a non-linear modulation equation for the displacements. Exact periodic traveling wave solutions to the equation demonstrate a dependence on the sign of the equation coefficients or the elastic parameters of the original model. Dispersion relation for the carrier part of the solution is obtained as a function of wave number versus frequency, it is found how its solutions relate to the acoustic and optic branches and the band gap. This form of the dispersion relation is further used for a description of numerical results on the wave modulation by a harmonic boundary excitation.

Topological valley waveguide state transport based on the nesting difference

Acoustic topological waveguide states are characterized by topologically protected transport. Existing acoustic topological valley-locked waveguide state transport structures can only realize single-scene acoustic field modulation due to the limitation of structural tunability, and it is difficult to realize width degree of freedom and reconfigurable transport paths of acoustic waves by adjusting the transport structure for complex acoustic field. Therefore, the transport structures become a conceptualized idea in terms of tunability. Our study introduces a nesting method in the design of the sonic crystal scatterer, which splits the scatterer structure into a removable outer shell and a core, and three topological phase transitions can be realized by only changing the nesting method of the sonic crystal shell, this approach constructs a fully reconfigurable topological waveguide. The results demonstrate that changing the nesting of the sonic crystals induces effective spatial inversion symmetry breaking, which leads to the valley topological phase transitionSimulations and experiments demonstrate that this transport structure has excellent robust transport properties with large inflection corners, and it is capable of realizing acoustic focusing, acoustic channeling, and acoustic logic gates. This fully reconfigurable sonic crystal design method can provide implications for the modulation of other classical waves.

Emergence of extreme events from randomly chirped condensate

We explore rogue wave emergence in generic wave systems governed by the nonlinear Schrödinger equation. We highlight the interplay between the stochastic focusing induced by a random chirp of a continuous wave condensate and modulation instability of the condensate to periodic and/or random perturbations. We show that regardless of its statistical properties, the random chirp of the condensate leads to a non-Gaussian, heavy-tailed probability density distribution of peak powers of the waves excited atop of the condensate, which is a statistical signature of rogue waves, or more broadly, extreme events in physics.

Research on the generation and modulation of active pressure wave for pipelines leak diagnosis

In this paper, a novel device that uses compressed air to generate pressure waves in the liquid pipeline is proposed. Experimental investigations are carried out to explore the modulation method of the pressure wave generated and the application potential of the device in leak diagnosis. The consequences show that the device can generate safe, stable and controllable pressure waves. The characteristics of produced pressure wave under different excitation frequencies and inflation pressure are investigated with the combination of experiments and theory analysis. The parameters that affect the excitation behaviors of the device are pointed out theoretically. Finally, the performance of the device under continuous excitation and single excitation is tested in the leaking pipe. Through the extraction and analysis of the signal features in the frequency domain, the leakage can be diagnosed and distinguished under both excitation methods.

Longitudinal combustion instability in a hypergolic liquid bipropellant combustor with single dual-swirl coaxial injector

Self-excited longitudinal combustion instabilities were investigated in a hypergolic liquid bipropellant combustor, which applied single dual-swirl coaxial injector. Hot-fire tests were conducted for four different injector geometries, while extensive tests on injection conditions were carried out for each injector geometry. The synchronous measurement of the pressure and heat release rate was applied, successfully capturing the process of the pressure and heat release rate enhanced coupling and developing into in-phase oscillation. By calculating Rayleigh index at the head and middle section of the chamber, it is shown that Rayleigh index of the middle section is even higher than that of the head, indicating a long heat release zone. When the combustion instability occurs, the pressure in propellant manifolds also oscillates with the same frequency and lags behind the oscillation in the combustor. Compared to the oscillation in the outer injector manifold, the oscillation in the inner injector manifold shows a higher correlation with that in the chamber in amplitude and phase. Based on numerical simulations of the multiphase cold flow inside the injector and combustion process in the chamber, it is found that injector geometries affect longitudinal combustion instability by changing spray cone angle. The spray with small cone angle is more sensitive to the modulation of longitudinal pressure wave in combustion simulations, which is more likely to excite the longitudinal combustion instability. Meanwhile, the combustion instability may be related to the pulsating coherent structure generated by the spray fluctuation, which is determined by injection conditions. Besides, a positive feedback closed-loop system associated with the active fluctuation and passive oscillation of the spray is believed to excite and sustain the longitudinal combustion instability.

Modulation of Internal Solitary Waves by One Mesoscale Eddy Pair West of the Luzon Strait

Abstract The characteristics of modulated internal solitary waves (ISWs) under the influence of one mesoscale eddy pair in the Luzon Strait, involving one anticyclonic eddy (AE) and one cyclonic eddy (CE) induced by the Kuroshio intrusion, were investigated using a nested high-resolution numerical model in the northeastern South China Sea (SCS). The presence of mesoscale eddies greatly impacts the nonlinear evolution of type-a and type-b ISWs. The eddy pair contributes to distinct wave properties and energy evolutions. Compared to type-b waves, type-a waves display more pronounced modulatory characteristics with a larger spatial scale. CE currents and horizontal inhomogeneous stratification are crucial in modulating the wave behaviors, which induce extremely large-amplitude depression ISWs. The AE thereafter yields retardation effects on the wave energy evolution. The average depth-integrated available potential and kinetic energy showed relative growth rates of −66.12% and −46.07%, respectively, for type-a waves, and −24.26% and −20.15%, respectively, for type-b waves along the propagation path up to the AE core. The deformed and distorted ISW crest lines propagating further northward exhibit a more dramatic shoaling evolution. The maximum total energies of type-a and type-b waves at the north station are approximately 13.5 and 3.5 times, respectively, greater than those at the south station on the continental shelf of the Dongsha Atoll. This work provides essential insights into modulated ISW dynamics under the mesoscale eddy pair within the northeastern SCS deep basin.

All-fiber coherent supercontinuum generation in a cascade of silica, fluoride, and chalcogenide fibers

Abstract We present an all-fiber coherent supercontinuum spanning the spectral range of 1.7–5.0 µm from a cascade of silica, ZBLAN, and chalcogenide (ChG) nonlinear fibers (NLFs). Coherence is maintained by the combined use of femtosecond pump pulses as well as by allowing deterministic spectral broadening mechanism at every stage of the cascade. The use of femtosecond pump pulses enables avoiding modulation instability (MI) at the onset of the supercontinuum generation process and thus prevent subsequent MI-seeded random noise. Once in the NLF cascade, the pump pulse is instead converted into a soliton of order maintained at N < 6 in the silica and ZBLAN NLFs, ensuring soliton fission followed by self-frequency shift of a few solitons. Finally, in the ChG NLF, spectral broadening is facilitated through self-phase modulation and dispersive wave generation. The deterministic nature of these nonlinear phenomena results in the generation of a coherent supercontinuum. The supercontinuum delivers an average power of 54 mW from an average pump power of 300 mW, yielding a power conversion efficiency of 18%. The experimental results closely align with numerical simulations, from which coherence is estimated. Such a coherent supercontinuum with a megahertz repetition rate is essential for spectroscopic systems based on optical frequency combs and applications in high-precision optical coherence tomography.

Broadband reconfigurable instantaneous microwave multifrequency measurement system based on a nonuniform optical frequency comb

A broadband reconfigurable instantaneous microwave multifrequency measurement system based on a nonuniform optical frequency comb has been proposed and investigated. An amplitude nonuniform optical frequency comb (OFC) with 2l+1 lines is generated using periodic sawtooth wave modulation. One path of the OFC is passed through an optical frequency selector (OFS) to output one of the lines as the optical carrier, which, along with the unknown signal, are input into a dual-parallel Mach–Zehnder modulator (DPMZM) for carrier-suppressed single-sideband (CS-SSB) modulation and then channelized by using demultiplexer (DEMUX1). The other path is input into DEMUX2 for comb line separation. A 90° optical hybrid coupler (OHC) is used to merge the signals output from the two demultiplexers, and a pair of balanced photodetectors (BPD) is employed to convert the optical signals into electrical signals. Finally, the frequency of the unknown microwave signal can be determined by detecting the channel position i in which the signal falls, and the frequency fPD detected within channel i. Simulation experiments show that when the OFC consists of 35 lines, the measurement range is 0.01–70 GHz, with an error within ±3.24MHz. By adjusting the number of OFC to 51, the measurement range can be expanded to 0.01–102 GHz, while the measurement error of the system remains nearly unchanged. All these results demonstrate that the proposed approach possesses broadband reconfigurability.

Perovskite polycrystal for optically tuning terahertz interference fringes

We optically tuned the terahertz interference fringe using a perovskite polycrystal. Specifically, we used CH3NH3PbI3 polycrystals with different morphologies that were annealed at different temperatures. The largest modulations depth (23 %) was obtained for the CH3NH3PbI3 polycrystal drop-coated at 130 °C; this was also greater than that of a spin-coated CH3NH3PbI3 thin film. We demonstrated that the combination of a drop-coated CH3NH3PbI3 polycrystal with a metasurface allows modulation of terahertz waves. Using the interference formed by partial-through measurement and the shift of the periodic peak in the terahertz time-domain spectroscopy system, we experimentally verified that the perovskite polycrystal can redshift the terahertz-band interference fringes by 50 GHz by changing the optical power density of the external excitation light source. This provides a new idea and possibility for the development of novel terahertz modulation devices.

Fluid-Infiltrated Metalens-Driven Reconfigurable Intelligent Surfaces for Optical Wireless Communications.

A reconfigurable intelligent surface (RIS), a leading-edge technology, represents a new paradigm for adaptive control of electromagnetic waves between a source and a user. While RIS technology has proven effective in manipulating radio frequency waves using passive elements such as diodes and MEMS, its application in the optical domain is challenging. The main difficulty lies in meeting key performance indicators, with the most critical being accurate and self-adjusting positioning. This work presents an alternative RIS design methodology driven by an all-silicon structure and fluid infiltration, to achieve real-time control of focal length toward a designated user, thereby enabling secure data transmission. To validate the concept, both numerical simulations and experimental investigations of the RIS design methodology are conducted to demonstrate the performance of fluid-infiltrated metalens-driven RIS for this application. When combined with different fluids, the resulting ultra-compact RIS exhibits exceptional varifocal abilities, ranging from 0.4 to 0.5 mm, thereby confirming the adaptive tuning capabilities of the design. This may significantly enhance the modulation of optical waves and promote the development of RIS-based applications in wireless communications and secure data-transmission integrated photonic devices.