Amplitude Modulation Mode Research Articles

MEMS reservoir computing system with stiffness modulation for multi-scene data processing at the edge

Reservoir computing (RC) is a bio-inspired neural network structure which can be implemented in hardware with ease. It has been applied across various fields such as memristors, and electrochemical reactions, among which the micro-electro-mechanical systems (MEMS) is supposed to be the closest to sensing and computing integration. While previous MEMS RCs have demonstrated their potential as reservoirs, the amplitude modulation mode was found to be inadequate for computing directly upon sensing. To achieve this objective, this paper introduces a novel MEMS reservoir computing system based on stiffness modulation, where natural signals directly influence the system stiffness as input. Under this innovative concept, information can be processed locally without the need for advanced data collection and pre-processing. We present an integrated RC system characterized by small volume and low power consumption, eliminating complicated setups in traditional MEMS RC for data discretization and transduction. Both simulation and experiment were conducted on our accelerometer. We performed nonlinearity tuning for the resonator and optimized the post-processing algorithm by introducing a digital mask operator. Consequently, our MEMS RC is capable of both classification and forecasting, surpassing the capabilities of our previous non-delay-based architecture. Our method successfully processed word classification, with a 99.8% accuracy, and chaos forecasting, with a 0.0305 normalized mean square error (NMSE), demonstrating its adaptability for multi-scene data processing. This work is essential as it presents a novel MEMS RC with stiffness modulation, offering a simplified, efficient approach to integrate sensing and computing. Our approach has initiated edge computing, enabling emergent applications in MEMS for local computations.

A 1-bit DACs precoding for MU-MIMO based on binary equilibrium constraint: An alternating direction method

High power consumption is one of the main problems in the practical application of massive multi-user multi-input-multi-output (MU-MIMO) systems, and using 1-bit digital-to-analog converters (DACs) instead of high-resolution DACs is an effective way to reduce the power consumption of massive MU-MIMO systems. How to design efficient precoding schemes to improve the performance of 1-bit MU-MIMO systems has become a hot research field. This paper mainly studies the precoding problem of 1-bit DACs based on minimum mean squared error (MMSE). We first transform the non-convex constraints of the traditional optimization problem using binary equilibrium constraints. Then, to solve the transformed objective problem, we establish a framework based on the alternating direction method (ADM), use the fast projection gradient (FPG) method, and propose an alternating maximum minimum (AMM) algorithm to solve the optimization variables alternately. We have verified the convergence of the proposed algorithm and analyzed the accuracy of the proposed ADM framework and the computational complexity of the proposed algorithm in detail. In the simulation section, we analyze the uncoded bit error rate (BER) performance of the proposed algorithm in phase-shift keying (PSK) modulation and quadrature amplitude modulation (QAM) modes. The simulation results show that compared with existing advanced algorithms, the proposed algorithm can achieve performance advantages of about 1 dB and 2 dB in QPSK modulation mode and 16QAM modulation mode, respectively.

Pulse‐Modulation Controllable Monolithic Full‐Color Semipolar GaN‐based Light Emitting Diodes

AbstractMonolithic multi‐color light‐emitting diodes (LEDs) offer numerous advantages as multi‐functional lighting sources. However, the achievement of full‐color monolithic LEDs spanning from red to blue wavelengths is limited by the InN‐GaN material system. To overcome this limitation, this work demonstrates a new approach using hexagonal epitaxial lateral overgrowth to reduce the density of crystal defects and form micro‐surface structures. By utilizing arrowhead‐like surfaces in semipolar GaN films, indium incorporation can be controlled, leading to larger band‐filling effects and enabling full‐color red, green, and blue emissions from a single LED. Nonetheless, the red emission in monolithic full‐color LEDs is weaker than the blue emission due to the band‐filling induced blueshift that occurs with increasing current injection. To address this issue, pulse amplitude modulation and pulse width modulation modes are introduced to control the emission intensity from red to blue wavelengths. As a result, the study achieves a monolithic trichromatic white LED with color coordinates of (0.2985, 0.3948) and a color temperature of ≈6700 K by simultaneously emitting red, green, and blue LEDs with the same emission intensities. This achievement holds great promise for the development of high‐performance full‐color LEDs for multifunctional lighting sources that can span red, green, and blue wavelengths.

Compound relaxation oscillations in Duffing oscillator driven by a low frequency amplitude-modulated excitation

Low frequency amplitude-modulated excitation is a recently reported excitation that can induce relaxation oscillations and prolongs the system’s slow processes. This investigation aims to research the effects of different modulation modes of low frequency amplitude-modulated excitation on relaxation oscillations. Generally, intriguing dynamical characteristics can be observed in compound relaxation oscillations when amplitude-modulated modulation is introduced. Specifically, the quasi-static processes of the system exhibit different relaxation oscillations while the active phase of the relaxation oscillations remains relatively constant. We investigate the dynamical behaviors of the entire excitation through the fast-slow analysis method. For this purpose, a three-dimensional visualization is proposed to explore the relaxation oscillations induced by different modulation modes, providing insights into the system’s dynamical behaviors from multiple perspectives. The results show that the oscillations depend on the modulation mode of the amplitude-modulated excitation. Modulation frequency changes extend the quasi-static processes and increase the number of oscillations. Besides, variations in the modulation index can trigger amplitude variations that lead to an increased number of bifurcation points during overmodulation. Based on these findings, we reveal the dynamic mechanism of composite relaxation oscillations. Our study demonstrates that the introduction of amplitude-modulated excitation can induce compound relaxation oscillations in the system, and different modulation modes significantly influence the fast-slow dynamics. Moreover, our results provide a valuable reference for investigating other dynamic systems that incorporate amplitude-modulated excitation.

Unveiling the Layered Structure of Sulfobetaine Polymer Brushes through Bimodal Atomic Force Microscopy

Many zwitterionic polymer brushes exhibit highly stimuli-responsive properties stemming from the strong dipole and electrostatic interaction of their building blocks. Here, we showed how a combination of two atomic force microscopy (AFM) modes can reveal the layered structure of poly(sulfobetaine methacrylate) brushes synthesized by surface-initiated atom-transfer radical polymerization. Due to polydispersity and anti-polyelectrolyte effect, a diffused layer emerges on top of a condensed layer of the brush as a function of salt concentration. The amplitude-modulation mode of the AFM, owing to the tip’s dynamic motion, can only probe the more stable condensed layer near the substrate, whereas the force-spectroscopic mode with its high sensitivity can accurately detect the diffused layer and hence determine the total brush thickness. Infrared spectroscopy and quartz crystal microbalance monitoring revealed the strong ion-screening effect and higher brush hydration propensity of multivalent ions. Different cation valencies also showed subtle effects on the dimensionality of the layered structure. Our results highlight the usefulness of AFM in revealing various contextual phenomena that arise from the unique properties of zwitterionic polymers.

Long-Range Electrification of an Air/Electrolyte Interface and Probing Potential of Zero Charge by Conductive Amplitude-Modulated Atomic Force Microscopy.

The structure of an electrical double layer (EDL) at the interface of electrode/electrolyte or air/electrode/electrolyte is a fundamental aspect, however not fully understood. The potential of zero charge (PZC) is one of the clues to dictate the EDL, where the excess charge on the electrode surface is zero. Here, a nanoscale configuration of immersion method was proposed by integrating an electrochemical system into conductive atomic force spectroscopy under the amplitude modulation (AM) mode and agarose gel as the solid-liquid electrolyte. The PZC of boron-doped diamond was determined to be at 0.2 V (vs Ag/AgCl). By AM spectroscopy, the capacitive force shows remote electrification without direct electrode/electrolyte contact, which is dependent on the population of ions at the air/electrolyte interface. The surface potential by alignment of water is also evaluated. Prospectively, our study could benefit applications such as PZC measurement and non-electrode electrochemical processes at the air/electrolyte interface.

Opto-electric flash Raman method for in situ measuring temperature variation of power device with a high temporal resolution

This paper develops an in-situ high temporal resolution opto-electric flash Raman method to accurately measure the temperature fluctuation of power devices caused by modulated driving voltage. By synchronous modulation, the pulsed laser can maintain the same frequency as the driving voltage of the power device, and the working temperature of the device during the laser pulse can be obtained from the excited Raman spectrum. By adjusting the time delay between the pulsed laser and the electric signal with 100 ps resolution, the temperature variation in a cycle can be accurately determined. This method measures the temperature changes of GaN high electron mobility transistors device versus a square wave driving signal with different frequencies. The experimental results show that, in amplitude modulation mode with 100 Hz, the maximum temperature change through a driving cycle can be more than 20 K. This illustrates that high temporal resolution measurement is significant in determining the peak temperature of hot spots in the power devices. Two samples fixed using different methods had considerably different transient temperature fluctuations under the same driving frequency, indicating that the transient temperature variation is a promising way to gauge how well the devices dissipate heat. The temperature variations caused by a complex driving signal were also determined in this work. As a transient method, the opto-electric flash Raman method is promising to be used in multi-type power devices to in situ detect temperature fluctuation and provide a reference for the evaluation and optimization of the device.

Direct measurement of surface photovoltage by AC bias Kelvin probe force microscopy.

Surface photovoltage (SPV) measurements are a crucial way of investigating optoelectronic and photocatalytic semiconductors. The local SPV is generally measured consecutively by Kelvin probe force microscopy (KPFM) in darkness and under illumination, in which thermal drift degrades spatial and energy resolutions. In this study, we propose the method of AC bias Kelvin probe force microscopy (AC-KPFM), which controls the AC bias to nullify the modulated signal. We succeeded in directly measuring the local SPV by AC-KPFM with higher resolution, thanks to the exclusion of the thermal drift. We found that AC-KPFM can achieve a SPV response faster by about one to eight orders of magnitude than classical KPFM. Moreover, AC-KPFM is applicable in both amplitude modulation and frequency modulation mode. Thus, it contributes to advancing SPV measurements in various environments, such as vacuum, air, and liquids. This method can be utilized for direct measurements of changes in surface potential induced by modulated external disturbances.

Decision Model of Wireless Communication Scheme Evaluation via Interval Number

This study aims to evaluate the communication schemes of wireless communication systems to make reasonable decisions. Firstly, the wireless communication scheme is assessed based on the interval number technology, and the primary evaluation process and evaluation index system are described. Secondly, the analytic hierarchy process of interval numbers is studied. Besides, a decision model has been established for wireless communication scheme evaluation. Thirdly, the evaluation index of the wireless communication scheme is determined through the simulation analysis of the model. Finally, experiments verify the decision model for evaluating wireless communication schemes based on interval numbers. Channel encoding can be adjusted automatically and can effectively track electrical signals. The results demonstrate that under the same high signal-to-noise ratio (SNR), the error rate in the 16 quadrature amplitude modulation (QAM) mode decreases faster than that in the 2 frequency shift keying (FSK) mode, so the 16QAM mode is better than the 2FSK mode. Under a low SNR, the binary phase shift keying mode is superior to the 2FSK mode, and the 2FSK mode is superior to the 16QAM mode. The bit error rate of the communication signal in the additive white Gaussian noise channel is the lowest. These findings provide a solid foundation for a universal and scalable wireless communication system. This research has practical application value for scheme evaluation and model decision-making in the wireless communication field. Models need to be tested and evaluated based on large amounts of statistical data in future studies.

Digital high-speed data modulation techniques

Most radio stations use frequency modulation (FM) to broadcast yet amplitude modulation (AM) ensures long distance modulation. The limitations of FM reception are the line of sight and the area of reception. These two parameters are much smaller in FM compared to AM which makes AM modulation have an added advantage over FM modulation. The results presented in this paper include; direct modulation at different bias currents and different transmission fiber lengths and the amplitude modulation using the Mach-Zehnder. The results show the possibility to transmit huge data at high speeds to over 100Gbps.

Investigation on turbulent characteristic of crossflow under suction in a T-junction using Holo-Hilbert spectral analysis

To investigate the crossflow of ventilation in high-speed train, a T-junction experimental setup is built and velocity data of crossflow under different conditions and positions are measured. Specifically, the conditions include the different velocities of crossflow and different intensities of suction, and the positions include upstream, mid-centre, and downstream. To give full information of the crossflow characteristics, the Holo-Hilbert spectral analysis (HHSA) method is used to analyse these velocity data. The results show that the components of frequency modulation (FM) and amplitude modulation (AM) can be found in the crossflow suffered from the suction. Furthermore, there exists an obvious difference between the crossflow with and without vanes. The crossflow without vanes has more components of FM modulation and AM modulation with high frequency. The increase of the velocity and velocity ratio both can influence the turbulent characteristics of crossflow, which presents high energy with a higher frequency of AM and FM. The crossflow at the upstream and the downstream has similar components presented in the AM–FM spectrum, while the crossflow at the mid-centre has more high-frequency components. In addition, the turbulent intensity at the mid-centre is inversely proportional to the distance from the suction.

High speed, complex wavefront shaping using the digital micro-mirror device

Digital micro-mirror devices (DMDs) have been deployed in many optical applications. As compared to spatial light modulators (SLMs), they are characterized by their much faster refresh rates (full-frame refresh rates up to 32 kHz for binary patterns) compared to 120 Hz for most liquid crystal SLMs. DMDs however can only display binary, unipolar patterns and utilize temporal modulation to represent with excellent accuracy multiple gray-levels in display applications. We used the built-in time domain dynamic range representation of the DMD to project 8-bit complex-fields. With this method, we demonstrated 8-bit complex field modulation with a frame time of 38.4 ms (around 0.15 s for the entire complex-field). We performed phase conjugation by compensating the distortions incurred due to propagation through free-space and a scattering medium. For faster modulation speed, an electro-optic modulator was used in synchronization with the DMD in an amplitude modulation mode to create grayscale patterns with frame rate ~ 833 Hz with display time of only 1.2 ms instead of 38.4 ms for time multiplexing gaining a speed up by a factor of 32.

Linear Signal Cancellation of Nonlinear Pulsing Schemes in a Verasonics Research Scanner.

Contrast-enhanced ultrasound (CEUS) is a real-time imaging technique that allows the visualization of organ and tumor microcirculation by utilizing the nonlinear response of microbubbles. Nonlinear pulsing schemes are used exclusively in CEUS imaging modes in modern scanners. One important aspect of nonlinear pulsing schemes is the near-complete elimination of the linear signals that originate from tissue. Up until now, no study has investigated the performance of Verasonics scanners in eliminating the linear signals during CEUS and, by extension, the optimal pulsing sequences for performing CEUS. The aim of this article was to investigate linear signal cancellation of the Verasonics scanner performing nonlinear pulsing schemes with two different probes (L7-4 linear array and C5-2 convex array). We have considered two pulsing schemes: pulse inversion (PI) and amplitude modulation (AM). We have also compared our results from the Verasonics scanner with a clinical scanner (Philips iU22). We found that the linear signal cancellation of the transmitted pulse by Verasonics scanner was ~40 dB in AM mode and ~30 dB in PI mode when operated at 0.06 MI. The linear signal cancellation performance of Verasonics scanner was comparable with Philips iU22 scanner in focused AM mode and on average 3 dB better than Philips iU22 scanner in focused PI mode.

High-speed photoacoustic-guided wavefront shaping for focusing light in scattering media.

Wavefront shaping is becoming increasingly attractive as it promises to enable various biomedical applications by breaking through the optical diffusion limit that prevents light focusing at depths larger than in biological tissue. However, despite recent advancements in wavefront shaping technology, such as those exploiting non-invasive photoacoustic-guidance, in vivo demonstrations remain challenging mainly due to rapid tissue speckle decorrelation. In this work, we report a high-speed photoacoustic-guided wavefront shaping method with a relatively simple experimental setup, based on the characterization of a scattering medium with a real-valued intensity transmission matrix. We demonstrated light focusing through an optical diffuser by optimizing 4096 binary amplitude modulation modes of a digital micromirror device within , leading to a system runtime of 75 µs per input mode, which is 3 orders of magnitude smaller than the smallest runtime reported in literature so far using photoacoustic-guided wavefront shaping. Thus, our method is a solid step forward toward in vivo applications of wavefront shaping.

Torsional Harmonic Kelvin Probe Force Microscopy for High-Sensitivity Mapping of Surface Potential

This article presents a torsional harmonic Kelvin probe force microscopy (TH-KPFM) working in amplitude modulation (AM) mode for high-sensitivity mapping of surface potential (SP). Compared with frequency modulation KPFM with higher spatial resolution, AM-KPFM has higher potential sensitivity and scanning speed. However, the traditional AM-KPFM is usually limited in the crosstalk from topography measurement and cantilever homogenization effect which causes the measured SP to be seriously affected by the substrate. TH-KPFM can effectively suppress the artifacts induced by the cantilever homogenization effect, and the coupling crosstalk caused by the topography measurement. The torsional harmonic cantilever suitable for TH-KPFM is fabricated and calibrated using the nanorobotic system first. Then, this technique is applied to determine the SP of the tobacco mosaic virus (TMV), and detect surface contaminants of a silicon wafer. Experimental results show that TH-KPFM has a 3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 4 mV energy resolution and sub-20 nm spatial resolution. Compared with the proposed TH-KPFM, the energy level of TMV obtained by the traditional AM-KPFM is pulled down by 80 meV. TH-KPFM is a powerful and useful technique to study the SP on the nanoscale, and greatly simplifies the difficulty of high-sensitivity measurement of the actual SP of many important nanoscale systems.

Sinusoidal FM patterns of fault-related vibration signals for planetary gearbox fault detection under non-stationary conditions

Vibration signals related to planetary gearbox faults under non-stationary conditions will be equipped with sinusoidal modulation laws in their amplitude modulation (AM) and frequency modulation (FM) modes. Extracting fault features implied in the AM and FM modes is the key issue to detect inner gear faults occurring in planetary gearboxes. However, there exist few signal analysis approaches that are able to track the fast oscillating nature implied in the fault-induced sinusoidal FM patterns. To address such a challenging issue, this paper conducts a detailed study on sinusoidal FM patterns of the fault-related vibration signal model and proposes a novel method to extract them successfully. To be specific, the proposed method firstly separates the AM and FM modes via Hilbert transform to avoid their mutual interference. The intrinsic modulation features implied in the AM and FM modes can then be separately extracted by a developed signal decomposition method named iterative-joint chirp mode decomposition (I-JCMD) with a composite mode optimization scheme. Compared with the existing fault detection techniques, the proposed method is not only able to avoid the complicated sideband analysis but also identify the fast and time-varying oscillating nature of the FM mode with a high accuracy. The performance of our method is finally verified by three simulated cases and four groups of real vibration signals related to four types of sun gear faults occurring in a planetary gearbox test-rig, which also reveals a potential scaling relation between load strength and the oscillating coefficient of the FM mode.

Modulation Spectra Capture EEG Responses to Speech Signals and Drive Distinct Temporal Response Functions.

Speech signals have a unique shape of long-term modulation spectrum that is distinct from environmental noise, music, and non-speech vocalizations. Does the human auditory system adapt to the speech long-term modulation spectrum and efficiently extract critical information from speech signals? To answer this question, we tested whether neural responses to speech signals can be captured by specific modulation spectra of non-speech acoustic stimuli. We generated amplitude modulated (AM) noise with the speech modulation spectrum and 1/f modulation spectra of different exponents to imitate temporal dynamics of different natural sounds. We presented these AM stimuli and a 10-min piece of natural speech to 19 human participants undergoing electroencephalography (EEG) recording. We derived temporal response functions (TRFs) to the AM stimuli of different spectrum shapes and found distinct neural dynamics for each type of TRFs. We then used the TRFs of AM stimuli to predict neural responses to the speech signals, and found that (1) the TRFs of AM modulation spectra of exponents 1, 1.5, and 2 preferably captured EEG responses to speech signals in the δ band and (2) the θ neural band of speech neural responses can be captured by the AM stimuli of an exponent of 0.75. Our results suggest that the human auditory system shows specificity to the long-term modulation spectrum and is equipped with characteristic neural algorithms tailored to extract critical acoustic information from speech signals.

CSES observations of ELF wave radiation excited by the EISCAT heater

Modulation heating of the ionosphere using high-power high-frequency (HF) radio waves can generate an extremely low frequency (ELF) radiation source in the ionosphere, such as amplitude-modulation (AM) heating of the auroral electrojet or using two HF radio waves to illuminate the same region of the ionosphere to form beat-wave (BW) modulation. We first present observations of ELF waves received on the China seismo-electromagnetic satellite (CSES) and on the ground simultaneously, which were excited in the European Incoherent Scatter Scientific Association (EISCAT) modulation heating experiment carried out alternately in the AM and BW modes. When the CSES passed over the EISCAT heater, ELF waves excited in the AM and BW modes were received successfully by an electric field detector on board. The comparison of the received results between the satellite and the ground demonstrates that although the intensity of the ELF signals excited in the BW mode is far lower than that in the AM mode on the ground, the ratio of ELF wave intensities between the satellite and the ground in the BW mode is significantly larger than that in the AM mode. According to the experimental results, the propagation characteristics are simulated using the full-wave method when the ELF radiation sources are located in the D and F regions in the ionosphere.

Stable and Highly Flexible Perovskite Solar Cells with Power Conversion Efficiency Approaching 20% by Elastic Grain Boundary Encapsulation

Here, we show that flexible perovskite solar cells (PSCs) with high operational stability and power conversion efficiency (PCE) approaching 20% were achieved by elastic grain boundary (GB) encapsul...

Bond-level imaging of organic molecules using Q-controlled amplitude modulation atomic force microscopy

The bond imaging atomic force microscopy (AFM) technique has become an invaluable tool for studying organic molecules on surfaces. The key feature of this technique is the functionalization of the AFM-tip with a single CO molecule, which improves the lateral resolution and allows us to visualize the chemical structure of adsorbed organic molecules. Such experiments are usually performed at low temperatures in an ultrahigh vacuum environment in the frequency modulation (FM) mode. Here, we use the Q-controlled amplitude modulation (AM) mode for imaging organic molecules with CO-functionalized tips in constant-height mode. By reducing the effective quality factor (Qeff) of the sensor from about 20 000–30 000 to 1500–4000, we are able to image molecules with atomic resolution. Detailed instructions for determining the optimum Qeff and oscillation amplitude are given. To compare the phase and frequency shift images of the Q-controlled AM and the FM mode, we define an effective signal-to-noise ratio (SNR) that relates the observed contrast between the bonds and centers of imaged carbon rings to the noise in the respective image regions. This effective SNR is systematically analyzed in different regions of the imaged molecule for different oscillation amplitudes and average tip-substrate distances. By using appropriate imaging parameters, an increased effective SNR is achieved in the Q-controlled AM mode (on the order of 30–60%). This advantage over the conventional FM mode might, e.g., be used for increasing the experimental throughput.