Amplitude Tuning Research Articles

A Tunable Long Duration Pulse Generation Circuit in Mammalian Cells.

Pulse generator circuits based on incoherent feed-forward logic have been developed in bacterial, yeast, and mammalian systems but are typically limited to production of short pulses lasting less than 1 day. To generate longer-lasting pulses, we introduce a feedback-based topology that induces multiday pulsatile gene expression with tunable duration and amplitude in mammalian cells. We constructed the circuit using the PERSIST platform, which consists of entirely post-transcriptional logic, because our experience suggests that this approach may attenuate long-term epigenetic silencing. To enable external regulation of PERSIST regulatory elements, we engineered inducer-stabilized CRISPR endoRNases that respond to FDA-approved drugs, generating small molecule responses with greater than 20-fold change. These inducer-responsive proteins were connected to a two-state cross-repression positive feedback topology to generate the pulse generator circuit architecture. We then optimized circuit design through chromosomal integration of circuit components at varying stoichiometries, resulting in a small library of circuits displaying tunable pulses lasting between two and 6 days in response to a single 24 h input of inducer. We expect that the small molecule-stabilized PERSIST proteins developed will serve as valuable components in the toolbox for post-transcriptional gene circuit development and that tunable post-transcriptional pulse generator circuits in mammalian cells will enable study of endogenous hysteretic gene networks and support advances in cell therapies and organoid engineering.

A terahertz broadband and narrowband switchable absorber based on joint modulation of vanadium dioxide and graphene surfaces

Abstract In this paper, a terahertz broadband and narrowband switchable absorber is proposed. The absorption performance tuning for both broadband and narrowband functions is realized based on the joint modulation of vanadium dioxide (VO2) and graphene surfaces. Concretely, while VO2 is in the metallic state, the absorber achieves broadband absorption function. The overall bandwidth of over 90% absorption is 4.04 THz corresponding to a relative bandwidth of 84%. Through regulating the conductivity of VO2, dynamic tuning of the absorption amplitude is obtained and the modulation depth is 96%. By manipulating the graphene Femi energy and VO2 conductivity simultaneously, dynamic tuning of the absorption bandwidth is realized. In particular, the spectral center frequency of broadband absorption remains stable without drifting during the tuning process. While VO2 is in the insulating state, the absorber achieves narrowband absorption function. Calculated results show that two separate perfect absorption peaks are formed, and the absorption amplitudes are 99.6% and 99.2% respectively. Through regulating the Fermi energy of graphene surface, the dynamic tuning of narrowband absorption frequency is realized. Compared with the ones reported in recent years, our absorber has the advantage on function realization, absorption characteristics and performance tuning.

Moth-wing-inspired metasurface for modulating sound amplitude and phase

Moth wings are multifunctional bio-composite structures serve varied purposes, including sound absorption and flight. Inspired by this, we propose a metasurface for reflective acoustic wave modulation. The metasurface features periodically arranged resonant elements, consisting of perforated plates and resonant cavities, mimicking moth wing scales. The hinged connection between the resonant elements and the background structure allows for precise and wide-range tuning of sound amplitude and phase, and enables deployment on irregular surfaces. We present three detailed metasurface designs, showcasing various structural parameters to demonstrate their quantitative manipulation of sound amplitude and phase, both individually and simultaneously. In addition to conventional energy absorption and path manipulation functions, the metasurface also highlights several striking features, including wavefront tailoring and reflection shunting, as demonstrated through numerical simulations. This study offers novel insights into the precise control of wave amplitude and phase over diverse scales and terrains, whilst also presenting a practical implementation in the field of acoustics.

Development and Standardization of Modified Simultaneous Multifrequency (SiMFy) Stimulus for Recording oVEMP And Its Interaction with the Alternate Electrode Montages.

Simultaneous Multifrequency (SiMFy) is a time-saving and reliable stimulus to determine the frequency tuning of ocular vestibular-evoked myogenic potential (oVEMP); however, the absence of 4000 Hz in SiMFy potentially makes it a less potent tool for the diagnosis of Superior semicircular canal dehiscence, a pathology with an ever-increasing prevalence. Further, SiMFy was validated using only the infra-orbital (IO) electrode montage. However, the recordings obtained using the IO montage might be susceptible to reference contamination introduced by a small separation between the recording electrodes, and also susceptible to reflex impurity due to the spatially displaced reference electrode from the inferior oblique muscle (IOM), rendering it vulnerable to picking up responses from other muscles. Nonetheless, little is known about the similarities/differences between the SiMFy-induced oVEMPs using alternate montages [belly-tendon (BT), chin-reference (CR), and sternum-reference (SR)] and the non-simultaneous multifrequency oVEMPs (NSM-oVEMPs) using the IO montage. To develop a modified SiMFy stimulus and investigate its effects on frequency tuning of oVEMP using various electrode montages. Within-subject experimental design. Thirty-three healthy adults aged 20-30 years. Tone bursts of octave and mid-octave frequencies from 250 Hz to 4000 Hz were generated and concatenated to create the modified SiMFy stimulus. All participants underwent non-simultaneous multifrequency oVEMPs and modified SiMFy oVEMPs using BT, CR, SR, and IO montages simultaneously. The response rate, peak-to-peak amplitude, and frequency tuning were compared between NSM-oVEMP and modified SiMFy oVEMP and also between the electrode montages. BT montage recorded the largest amplitude among the montages in non-simultaneous multifrequency stimulation and modified SiMFy stimulation. Although the response rates were comparable, the modified SiMFy produced significantly lower oVEMP amplitudes than the non-simultaneous multifrequency stimulation within each electrode montage (p < 0.05). A moderate-to-strong agreement on frequency tuning existed between the non-simultaneous multifrequency stimuli and modified SiMFy stimulus for all the montages, except for the SR montage. Although the modified SiMFy produces smaller amplitude oVEMPs than the non-simultaneous multifrequency stimulation for the respective montages, its use in combination with the BT montage yields higher response rates and larger peak-to-peak amplitudes than the non-simultaneous multifrequency recording using IO montage.

Seismic net-to-gross estimation for a geologic model update: A case study from a turbidite lobe reservoir in the deepwater of the Niger Delta

Geologic model updates are routinely performed in mature fields to obtain improved descriptions of facies distributions and reservoir properties such as volume of shale, net to gross (NTG), and porosity, for better understanding of the static and dynamic behaviors of reservoirs for effective well placement, improved production, and monitoring. A simple but integrated seismic NTG estimation approach, using detuned seismic amplitudes is used in guiding NTG modeling during the geologic model update of a thin turbidite lobe reservoir in a mature oil field in the deep offshore Niger Delta. The objective is to address NTG overestimation and gross rock volume (GRV) uncertainty in a previous model arising from seismic amplitude tuning effects. A seismic NTG approach is chosen relative to sophisticated deterministic or stochastic inversion techniques to avoid tuning effects, which usually bias NTG estimates in thin turbidite reservoirs. The primary data set is a 2019 reprocessed prestack depth-migrated (PSDM) seismic data vintage, which had better resolution, higher signal-to-noise ratio, and more appropriate angle-stack apertures for amplitude variation with angle fidelity, than the older 2011 PSDM seismic data that are used in the previous geologic model. The methodology involved rock-physics analysis, seismic data quality checks (QCs), tuned area determination, detuning of composite seismic amplitudes of the top and base reservoir, and their direct calibration to NTG at wells. Good correlations are obtained between the detuned composite seismic amplitudes and NTG at wells. The seismic NTG map shows good calibrations at wells and provides a robust trend for net sand modeling in the oil pool and aquifer. Static model QCs and dynamic simulations prove that the seismic NTG attribute addressed the GRV uncertainty in the earlier model, thus giving confidence for using the updated model for the planning and geosteering of infill wells, sand completions, reservoir monitoring, and production.

Wavelength continuously tunable and wavelength spacing variable comb filter based on a High-Birefringence fiber loop mirror

We demonstrated an all-fiber comb filter that can continuously tune the wavelength for four switchable wavelength spacings. The comb filter consists of a fiber loop mirror (FLM) that is inserted with three polarization maintaining fibers (PMFs) and three polarization controllers (PCs). The transmission characteristics of the comb filter was theoretically analyzed. The output characteristics of the comb filters shows a dependence of the orientation angles of the PCs. With the angles being optimally set, the comb filter with four different wavelength spacings can be achieved. The wavelength continuously tunable and wavelength spacing variable mechanisms are elaborated. The three PCs are employed to enable the tunable and switchable functions. The two PCs between the PMFs serve as a polarization rotator to align the birefringent axes of the PMFs for varying the wavelength spacing while the PC adjacent to the optical coupler can be used for wavelength tuning function. When the two quarter-waveplates (QWPs) of the PC are optimally set at π/4 and - π/4, the half-waveplate (HWP) acts as a wavelength tuning element, and when the QWPs are set at zero degrees, the HWP serves as an amplitude tuning element. The center wavelength of the comb filter could be linearly tuned with the rotation angle of the HWP, and a π/2 change in the rotation angle leads to a wavelength change in one free-spectral-range (FSR). A π/4 change in the rotation angle could bring the normalized peak transmission from its maximum at 1 to minimum at 0. The proposed tunable technique has been verified by our experimental results. We experimentally demonstrated the comb filters can switch among FSRs of 0.75 nm, 1.01 nm, 1.51 nm, and 3.1 nm with tunable functions.

Tunable Microwave Absorbing Devices Enabled by Reversible Metal Electrodeposition.

Tunable microwave absorbers have gained significant interest due to their capability to actively control microwaves. However, the existing architecture-change-based approach lacks flexibility, and the active-element-based approach is constrained by a narrowband operation or small dynamic modulation range. Here, a novel electrically tunable microwave absorbing device (TMAD) is demonstrated that can achieve dynamic tuning of the average reflection amplitude between -13.0 and -1.2 dB over a broadband range of 8-18 GHz enabled by reversible metal electrodeposition. This reversible tunability is achieved by electrodepositing silver (Ag) layers with controlled morphology on nanoscopic platinum (Pt) films in a device structure similar to a tunable Salisbury screen, employing Ag electrodeposited on Pt films as the modifiable resistive layer. Furthermore, this TMAD possesses a simple device architecture, excellent bistability, and multispectral compatibility. Our approach offers a new strategy for dynamically manipulating microwaves, which has potential utility in intelligent camouflage and communication systems.

Tunable VO2 cavity enables multispectral manipulation from visible to microwave frequencies

Optical materials capable of dynamically manipulating electromagnetic waves are an emerging field in memories, optical modulators, and thermal management. Recently, their multispectral design preliminarily attracts much attention, aiming to enhance their efficiency and integration of functionalities. However, the multispectral manipulation based on these materials is challenging due to their ubiquitous wavelength dependence restricting their capacity to narrow wavelengths. In this article, we cascade multiple tunable optical cavities with selective-transparent layers, enabling a universal approach to overcoming wavelength dependence and establishing a multispectral platform with highly integrated functions. Based on it, we demonstrate the multispectral (ranging from 400 nm to 3 cm), fast response speed (0.9 s), and reversible manipulation based on a typical phase change material, vanadium dioxide. Our platform involves tandem VO2-based Fabry–Pérot (F-P) cavities enabling the customization of optical responses at target bands independently. It can achieve broadband color-changing capacity in the visible region (a shift of ~60 nm in resonant wavelength) and is capable of freely switching between three typical optical models (transmittance, reflectance, and absorptance) in the infrared to microwave regions with drastic amplitude tunability exceeding 0.7. This work represents a state-of-art advance in multispectral optics and material science, providing a critical approach for expanding the multispectral manipulation ability of optical systems.

Greatly Improved the Tunable Amplitude of Ferromagnetism Based on Interface Effect of Flexible Pt/YIG Heterojunctions.

Flexible quantum spin electronic devices based on ferromagnetic insulators have attracted wide attention due to their outstanding advantages of low-power dissipation and noncontact sensing. However, ferromagnetic insulators, such as monocrystalline yttrium iron garnet (Y3Fe5O12, YIG), hve weak stress effects with a small magnetostrictive coefficient (λ110, 10 ppm), making it difficult to achieve a large magnetic tunable amplitude. In this paper, large-scale (with a diameter of 40 mm), flexible Pt/YIG heterojunctions were obtained by double-cavity magnetron sputtering technology, indicating typical soft magnetism and good bending fatigue characteristics. Here, the 3 nm thickness of the Pt layer triggers an obvious magnetic proximity effect, in which the in-plane ferromagnetic resonance field is decreased by 70 Oe compared to flexible Cu/YIG heterojunctions. Meanwhile, it shows a wide tunable amplitude of 110 Oe under the flexible bending stresses, which is induced by the sensitive interface effect of Pt (3 nm)/YIG heterojunctions. The saturation magnetization of Pt/YIG heterojunctions is negatively correlated with Pt thickness rather than the relative stability of Cu/YIG heterojunctions, depending on the magnetic proximity effect. It brings greater application possibilities for flexible stress-sensitive magnetic oxides in spin logic electronic devices.

Metamaterial-based vibration control for offshore wind turbines operating under multiple hazard excitation forces

Wind energy holds growing investment perspectives due to its renewable and sustainable energy production potential. The harvesting capability of wind turbines is directly related to their size. Therefore, those wind energy generators still encounter challenges related to excessive vibrations aggravated by environmental factors, compromising energy generation and resulting in fatigue damage and downtime. Various vibration control strategies have been explored to address these issues, with passive control emerging as a preferred choice due to its ease of manufacture, cost-effectiveness, and simple installation. Nevertheless, the limitations of these controls lie in their substantial size and weight associated with optimal installation positions for achieving a good performance. Recently, mechanical metamaterials have demonstrated tremendous advancements in efficiency regarding band isolation and vibration mitigation, coupled with enhanced manufacturing possibilities. Hence, this paper proposes a novel approach to control the vibration of wind turbines employing mechanical metamaterials in their design. A spectral approach is used to model the metamaterial turbine and its interaction with external excitations, such as wind, waves, and blade rotation. The numerical results show the efficiency of the metamaterial turbine by its tunable stopband features and vibration amplitude reduction under multiple hazard excitations, emphasising its superior suppressing vibrations compared to conventional tuned mass damper. Thus, the proposed wind turbine metastructures offer a compelling combination of effective vibration attenuation while reducing dynamic resonators’ overall stiffness, mass, and size. The outcome advances wind turbine design and energy technology for reliable wind energy production.

Ultra-high Q-factor and amplitude-tunable Fano resonance in vanadium dioxide-silicon hybrid metamaterials.

As the resonance response in magnetic systems usually occurs at low frequencies, previously known as terahertz high Q-factor resonances, are mainly excited by electrical resonances. In this paper, we present a metamaterial based on vanadium dioxide-silicon arrays capable of achieving a Q-factor of up to 165 198; the ultra-high Q-factor Fano resonance excited by the proposed metamaterial is mainly affected by strong magnetic resonance. The analysis of diffractive coupling theory, electric field, magnetic field and current distribution shows that strong magnetic resonance is mainly realized by coupling localized plasmon resonance with the lattice resonance. Due to the conductivity-tunable nature of vanadium dioxide, the proposed metamaterial features an amplitude tunable function with a modulation depth of 98.8%. The spectral response of the analyte demonstrates the capability of the proposed metamaterial for application as a sensor with a maximum sensitivity of 69.52 GHz per RIU and a figure of merit of 15 456. The ultra-high Q-factor performance and amplitude tunability of the proposed structure can be applied to terahertz devices, such as ultrasensitive sensors, filters and optical switches.

Similar Tuning of Distortion-Product Otoacoustic Emission Ratio Functions and Cochlear Vibrations in Mice.

When elicited by two stimulus tones (at frequencies f1 and f2, f2 > f1), the amplitudes of specific distortion-product otoacoustic emission (DPOAE) components exhibit a characteristic bandpass shape as the ratio between f2 and f1 is varied. This bandpass shape has been attributed to various mechanisms including intracochlear resonance, suppression, and wave interference, and has been proposed to be related to cochlear frequency tuning. While human studies suggest modest correlations between psychophysical tuning and the tuning of DPOAE amplitude vs. f2/f1 ratio functions, a relationship between the latter and the tuning of cochlear mechanical responses has yet to be established. This was addressed here through direct comparisons of DPOAEs and cochlear vibrations in wild-type CBA/CaJ mice. DPOAEs were elicited using a fixed-f2, swept-f1 paradigm, and optical coherence tomography was used to measure displacements from cochlear locations with characteristic frequencies near f2. The tuning sharpness of 2f1-f2 DPOAE ratio functions was found to be remarkably similar to that of basilar membrane and/or tectorial membrane responses to single tones, with the tuning sharpness of all responses increasing similarly with decreasing stimulus level. This relationship was observed for f2 frequencies ranging from ~8 to 22 kHz. Intracochlear distortion products did not exhibit a bandpass shape as the f2/f1 ratio was varied, indicating that interference between distortion products traveling to the stapes may be responsible for the tuning of the DPOAE ratio function. While these findings suggest that DPOAE ratio functions could be used to noninvasively infer cochlear tuning, it remains to be determined whether this relationship holds in other species and for lower frequency regions.

Coupling allows robust mammalian redox circadian rhythms despite heterogeneity and noise

Circadian clocks are endogenous oscillators present in almost all cells that drive daily rhythms in physiology and behavior. There are two mechanisms that have been proposed to explain how circadian rhythms are generated in mammalian cells: through a transcription-translation feedback loop (TTFL) and based on oxidation/reduction reactions, both of which are intrinsically stochastic and heterogeneous at the single cell level. In order to explore the emerging properties of stochastic and heterogeneous redox oscillators, we simplify a recently developed kinetic model of redox oscillations to an amplitude-phase oscillator with ‘twist’ (period-amplitude correlation) and subject to Gaussian noise. We show that noise and heterogeneity alone lead to fast desynchronization, and that coupling between noisy oscillators can establish robust and synchronized rhythms with amplitude expansions and tuning of the period due to twist. Coupling a network of redox oscillators to a simple model of the TTFL also contributes to synchronization, large amplitudes and fine-tuning of the period for appropriate interaction strengths. These results provide insights into how the circadian clock compensates randomness from intracellular sources and highlight the importance of noise, heterogeneity and coupling in the context of circadian oscillators.

DNA circuit-based immunoassay for ultrasensitive protein pattern classification.

Cytokines are important immune modulators, and pivotal biomarkers for the diagnostic of various diseases. In standard analytical procedure, each protein is detected individually, using for instance gold standard ELISA protocols or nucleic acid amplification-based immunoassays. In recent years, DNA nanotechnology has been employed for creating sophisticated biomolecular systems that perform neuromorphic computing on molecular inputs, opening the door to concentration pattern recognition for biomedical applications. This work introduces immuno-PUMA (i-PUMA), an isothermal amplification-based immunoassay for ultrasensitive protein detection. The assay couples the convenience of supported format of an ELISA protocol with the computing capabilities of a DNA/enzyme circuit. We demonstrate a limit of detection of 2.1 fM, 8.7 fM and 450 aM for IL12, IL4 and IFNγ cytokines, respectively, outperforming the traditional ELISA format. i-PUMA's versatility extends to molecular computation, allowing the creation of 2-input perceptron-like classifiers for IL12 and IL4, with tunable weight sign and amplitude. Overall, i-PUMA represents a sensitive, low-cost, and versatile immunoassay with potential applications in multimarker-based sample classification, complementing existing molecular profiling techniques.

A 10-20 GHz 6-Bit High-Accuracy Digital Step Attenuator with Low Insertion Loss in 0.15 µm GaAs p-HEMT Technology.

In a beamforming circuit for a modern broadband phased-array system, high accuracy and compactness have received sufficient attention as they are directly related to side lobe level and fabrication cost, respectively. In order to meet the low phase error required, this paper proposed an ultra-broadband 6-bit digital step switched-type attenuator (STA) with capacitive/inductive compensation networks. Compared to the conventional methods, the proposed technique employs an improved simplified T-structure with capacitive compensation networks, which simultaneously achieves low insertion loss and high-accuracy amplitude/phase control. In addition, on-chip level shifting circuit is integrated to avoid complex control schemes. The strategy of prioritizing return loss is adopted to alleviate the performance degradation caused by impedance mismatch after cascade. As a proof-of-principle demonstration, a wideband 6-bit STA with core area of only 0.5 mm × 1.8 mm was designed via 0.15-micrometer GaAs pHEMT technology. It exhibits ultra-broadband operation with a 31.5 dB amplitude tuning range and a 0.5 dB tuning step. The insertion loss of the reference state is 4-5.3 dB. The return loss is better than 15 dB for all the 64 states. The RMS amplitude and phase errors are less than 0.2 dB and 2° over the 10 to 20 GHz.

A tunable terahertz broadband absorber based on patterned vanadium dioxide

A patterning vanadium dioxide (VO2) tunable broadband terahertz absorber is designed, which consists of a resonant layer of VO2 and a metallic reflector layer separated by a dielectric layer of Topas. VO2 is a phase-changing material that behaves as a metallic phase at high temperatures and an insulating phase at low temperatures. Different from conventional metal-dielectric-metal three-layer structure, the innovation of this paper is that the resonant layer adopts vanadium dioxide, which is a phase change material, not only does it increase the operating bandwidth but it also allows active tuning of the absorption amplitude by varying the temperature and hence the vanadium dioxide conductivity. By optimizing the width of the vanadium dioxide resonant layer square ring and the thickness of the dielectric layer, broadband absorption is achieved in the frequency range of 0.72–1.92 THz. Numerical simulation results show that VO2 with low conductivity then behaves as an insulating phase, and its peak absorption in the corresponding broadband absorption band is only 3%, so it can be used for the reflector. When VO2 has a high conductivity, its absorption is greater than 90% in the absorption bandwidth up to 1.2 THz. In addition, the proposed absorber is polarization insensitive under vertical incidence conditions because of the symmetry of the structure. The absorber can also maintain good absorption performance by changing the angle of incidence and polarization state. In the terahertz wave sector, the tunable terahertz absorber developed in this article has several potential applications, including detectors, sensors, stealth technologies, etc.

Interactive Errors Analysis and Scale Factor Nonlinearity Reduction Methods for Lissajous Frequency Modulated MEMS Gyroscope.

Although the Lissajous frequency modulated (LFM) mode can improve the long-term and temperature stability of the scale factor (SF) for mode mismatch MEMS gyroscopes, its SF nonlinearity poses a significant limitation for full-scale accuracy maintenance. This paper examines the interaction effects among stiffness coupling, system phase delay, readout demodulation phase shift, and velocity amplitude mismatch within the control process. Based on the completion of frequency difference control and demodulation phase matching, we clarify that the remaining stiffness coupling and residual system phase error are the primary factors influencing SF nonlinearity. Furthermore, SF nonlinearity is reduced through error compensation. On one hand, this paper suppresses stiffness coupling through the observation of the instantaneous frequency difference and the application of the quadrature voltage. On the other hand, system phase error is compensated by observing the amplitude control force and tuning the reference in the Phase-Locked Loops (PLLs). Subsequent simulations of these methods demonstrated a remarkable 97% reduction in SF nonlinearity within the measurement range of ±500°/s. In addition, an observed rule dictates that maintaining a sufficiently large frequency split effectively constrains the SF nonlinearity.

Elliptically polarized, nanosecond dual-pulse Raman laser with tunable pulse interval and pulse amplitude ratio

Dual-pulse solid state lasers with pulse interval of tens nanoseconds have been applied in laser-induced breakdown spectroscopy, laser drilling, medical treatment, and atmospheric monitoring. Here, a Yb:YAG/Cr4+:YAG/YVO4 passively Q-switched Raman laser has been developed for generating dual-pulse lasers with tunable pulse interval and elliptical polarization. Pulse interval and pulse amplitude ratio between peaks of satellite pulse and main pulse are controlled by adjusting the incident pump power (Pin). As Pin increases from 1.3 to 5.9 W, the pulse interval decreases from 63.1 to 36.3 ns, and the pulse amplitude ratio between peaks of satellite pulse and main pulse increases from 0.1 to 1.1 for dual-pulse Raman lasers. At Pin = 4.9 W, dual-pulse Raman laser with equal peak power of 1.7 kW and pulse interval of 40.2 ns is obtained. The pulse widths are 2.7 and 3.6 ns, and the pulse energy are 4.6 and 6.2 μJ for the main pulse and satellite pulse, respectively. The elliptical polarization with ellipticity tunable from 0.08 to 0.54 is obtained for dual-pulse passively Q-switched Raman laser as Pin increases. Such a nanosecond dual-pulse laser source has the potential to expand simple, compact portable and economical laser applications in various fields.

A 40-50 GHz RF Front-End with Integrated Local Oscillator Leakage Calibration.

This article presents a transmitter (TX) front-end operating at frequencies covering 40-50 GHz, including a differential quadrature mixer with integrated amplitude and phase imbalance tuning, a power amplifier, and a detection mixer (DM) that supports local oscillator (LO) leakage signal or image signal calibration. Benefiting from the amplitude and phase imbalance tuning network of the in-phase quadrature (IQ) signal generator at the LO input, the TX exhibits more than 30 dBc image signal rejection over the full frequency band without any post-calibration. Based on the LO leakage signal fed back by the DM integrated at the RF output, the LO leakage of the TX has been improved by more than 10 dB through the LO leakage calibration module integrated in the quadrature mixer. When the intermediate frequency (IF) signal is fixed at 1 GHz, the TX's 1 dB compressed output power (OP1 dB) is higher than 13.5 dBm over the operating band. Thanks to the LO leakage signal calibration unit and the IQ signal generator, the TX is compliant with the error vector magnitude (EVM) requirement of the IEEE 802.11aj standard up to the 64-quadrature amplitude modulation (QAM) operating mode.

Terahertz characterization of combined pressure-shear shock loaded aromatic polyurea

Realistic shock loading scenarios imply combined, multiaxial stress states, where the mechanically induced energy competes for failing the material intrinsically due to cohesive failures. Under shock loading, failure encompasses various modes, including spallation, shear bands, microcracking, morphological alteration, phase transformation, and plastic deformation. However, elucidating failure in high strain loading conditions challenges the state-of-the-art characterization due to the disparity interfacing different loading and measurement techniques. This research used a novel spectro-mechanical characterization setup, integrating bulk terahertz spectroscopy synchronized in real-time with mixed-mode laser-induced shock waves. The latter was used to submit polyurea elastomers to concurrent pressure and shear waves by saddling a thin polymer sheet on the hypotenuse of a glass prism. Hence, the laser-induced pressure shock waves underwent simultaneous mode conversion at the glass-polyurea interface at the hypotenuse of the glass prism, effectively submitting the sample to tunable amplitude pressure-shear shock waves. The terahertz spectroscopy, operating in the right-angle reflection configuration, was modified to probe predetermined spots on the polyurea samples at different stress states (adjusted by changing the illumination energy) in a three-step sequence: before, during, and after shock loading. The shock-loaded polyurea samples were also characterized using the optical and scanning electron microscopes, revealing compression-shear and tensile-shear failure modes, including surface depression, nucleation of micro-voids and microcracks, and formation of small planes. The induced stress state based on the illumination energy was quantified using an accompanying finite element simulation, resulting in completing the quasi-isentropic behavior of polyurea elastomers, which was found to be in good agreement with previous experimental data from the plate impact experiments and the predictions based on the Lennard-Jones potential. Time domain analysis of terahertz data, using temporal shifting, hysteresis, and dynamic time warping based on the sum of the Euclidean distances between signal pairs, affirmed the microscopy observations while shedding insights on the elastic and plastic deformations and the reversible conformational changes. Irreversible changes to the macromolecule were also detected using the terahertz data spectral analysis. The current results establish a new experimental framework for fundamentally characterizing polymers and their composites at ultrahigh strain rate loading conditions.