Time Delay Devices Research Articles

Digital light processing 4D printing multilayer polymers with tunable mechanical properties and shape memory behavior

Four-dimensional (4D) printing has currently been renowned as a world-changing technology which has recently gained significant attention amongst researchers. It enables 3D printed objects to alter its shape, properties and functions through the application of external stimuli. However, the development of 4D printing has been impeded by the overexposure effect, which has made it difficult for photocuring to print gradient structures. In this paper, we propose a novel photocuring 4D printing strategy of gradient structures with tunable properties. Multi-walled carbon nanotubes (MWCNTs) are added to the intermediate layer (Fast Layer, FL) of multilayer shape memory polymers (SMPs) to reduce curing degree and absorb overexposure. The mechanical properties and shape memory behavior of multilayer SMPs can be tuned by adjusting the layer ratio of FL with low curing degree. Outcome of microscopic images, interlayer bonding force, and shore hardness originating from this study indicates that the printed multilayer SMPs possessed excellent interlayer bonding properties as well as obvious modulus differences between each layer. The average shape recovery speed (Sa) of multilayer SMPs was almost linearly related to the slice layer number of FL. The strategy was successfully demonstrated in the fabrication of multilayer SMPs with sequential recovery and multiple deformation behavior. An electrically responsive shape memory effect was also achieved by using embedded graphite electrothermal layer to exhibit its application in time-delay devices. The proposed strategy enables the application of multilayer SMPs gradient structures in soft robotics and flexible electronics.

Bio-Inspired Electro-Thermal-Hygro Responsive Rewritable Systems with Temporal/Spatial Control for Environment-Interactive Information Display.

Utilization of rewritable luminescent materials for secure information storage and delivery has long been envisaged to reduce the cost and environmental wastes. However, it remains challenging to realize a temporally/spatially controlled display of the written information, which is crucial for secure information encryption. Here, inspired by bioelectricity-triggered skin pattern switching in cephalopods, an ideal rewritable system consisting of conductive graphene film and carbon dots (CDs) gel with blue-to-red fluorescence-color changes via water-triggered CDs aggregation and re-dispersion is presented. Its rewritability is guaranteed by using water ink to write on the CDs-gel and employing Joule heat of graphene film to evaporate water. Due to the highly controlled electrical stimulus, temporally/spatially controlled display is achieved, enabling on-demand delivery and duration time regulation of the written information. Furthermore, new-concept environment-interactive rewritable system is obtained by integrating sensitive acoustic/optical sensors and multichannel electronic time-delay devices. This work opens unprecedented avenues of rewritable systems and expands potential uses for information encryption/delivery.

Coherence and stochastic resonance in the fractional-birhythmic self-sustained system subjected to fractional time-delay feedback and Lévy noise

This paper treats the nonlinear dynamics of an enzymatic-substrate modeled by the fractional multi-limit cycles Van der Pol oscillator with fractional time-delay feedback device subjected to Lévy noise perturbation and periodic excitation. The fractional electronic circuit has been used to model the system and the oscillations are described by a nonlinear fractional differential equation and show a new bifurcation parameter. The robustness of the stochastic resonance is examined by the use of standard measures within a continuous and a two-state description of the system. Firstly, the electronic circuit with the fractional-order operator and fractional delay feedback is used as a prototype of a fractional self-sustained system. Secondly, based on the minimum mean square error principle, the fractional derivative term is found to be equivalent to the linear combination of the damping force and restoring force, and the original system is further simplified to an equivalent integer order system. The stochastic bifurcation of a bistable Van der Pol system with fractional-order and time delay without and under Lévy noise excitation is studied where we show the considerable effect of these parameters on birhythmic region, escape time and energy barriers. Additionally, we study the multi-effects of fractional order and fractional time-delay feedback in the self-sustained system driven by Lévy noise. The effects of fractional-order parameter, time delay feedback parameter on the autocorrelation function, power spectral density and signal-to-noise-ratio used in this investigation are shown to be maximized for an appropriate choice of the Lévy noise intensity and for a convenient choice of fractional-order and time delay feedback parameters. For a choice of a control parameter in the birhythmic region, by varying the other parameters of the system like fractional and time delay parameters, it appears that, for a fixed value of skewness Lévy noise parameter, the initial selection of the attractor seems to have a large effect on the resonance and coherence.

Integratable electro-optic modulator based on a polymer-embedded silicon racetrack resonator with high electro-optic wavelength tuning.

Electro-optic (EO) modulators based on polymer-embedded silicon racetrack resonators (EOM-PSRR) are investigated. To obtain the single-mode propagation condition, the mode and transmission characteristics of the polymer-embedded silicon waveguide are simulated by the finite element method (FEM). By adding a static bias voltage, the EO modulation performances of EOM-PSRR embedded with lithium niobate (LiNbO3), EO polymer (AJ309), and hybrid EO polymer/TiO2 material (HEOT) are studied. The results show that the EOM-PSRR embedded with LiNbO3 achieves a high modulation depth (MD) of ∼27.6dB with a low EO wavelength tuning (λEO) of 10 pm/V. However, the EOM-PSRR embedded with HEOT has a high λEO of 100 pm/V but a low MD of ∼6.2dB with an extinction ratio of ∼5.2dB. The EOM-PSRR has potential application prospects in optical communication, optical signal processing, and optical network links. It can be produced as an optical frequency comb generator in a dense wavelength division multiplexing system, an EO frequency shifter for laser beams, an optical soliton former, and a photon time-delay device in a phased array radar.

Slow Light Mode at the Degenerate Band Edge for True Time Delay Applications

Tuneable true time delay device is designed at the degenerate band edge (DBE) by using two coupled periodic silicon ridge waveguides. The holes of the two ridge waveguides are well-tuned to let four modes couple and degenerate at the bandgap providing a slow light mode (the DBE mode). Transfer matrix method is utilized to trace and verify the slow light mode in the device. A 25-unit cell device ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10~ \boldsymbol {\mu m}$ </tex-math></inline-formula> length device) is constructed to realize the slow mode at the DBE with 70% transmission and 42.5 ps signal delay over 130 GHz dispersion free bandwidth. Liquid crystal cladding layer is incorporated to provide continuous control of the slow mode velocity around the DBE resonance for UWB antenna array beamforming applications.

Photonic Beamforming for 5G and Beyond: A Review of True Time Delay Devices Enabling Ultra-Wideband Beamforming for mmWave Communications

The next generations of wireless communications are promising high capacity, low latency, and high throughput, enabled by millimeter wave spectrum. Beamforming and beam steering are key requirements for millimeter wave systems due to the fundamental limitations of such high frequencies. Traditional phased array antennas are narrow band and conventional beamforming techniques are too bulky, energy hungry, and expensive to integrate into consumer electronics. Therefore, new approaches of beamforming and beamsteering are required for 5G and beyond due to shortcomings of existing technologies. Here we present a comprehensive review of the photonic true time delay units for application in beamforming of next generations of wireless communications. The prospects and progress of several photonic techniques are discussed here along with their challenges. The fundamental focus of this endeavor will be on the on-chip Silicon-on-Insulator based approaches which enable utilizing conventional CMOS fabrication process for integration with other optical components for compact photonic integrated circuit.

Stitching and Geometric Modeling Approach Based on Multi-Slice Satellite Images

Time delay and integration (TDI) charge-coupled device (CCD) is an image sensor for capturing images of moving objects at low light levels. This study examines the model construction of stitched TDI CCD original multi-slice images. The traditional approaches, for example, include the image-space-oriented algorithm and the object-space-oriented algorithm. The former indicates concise principles and high efficiency, whereas the panoramic stitching images lack the clear geometric relationships generated from the image-space-oriented algorithm. Similarly, even though the object-space-oriented algorithm generates an image with a clear geometric relationship, it is time-consuming due to the complicated and intensive computational demands. In this study, we developed a multi-slice satellite images stitching and geometric model construction method. The method consists of three major steps. First, the high-precision reference data assist in block adjustment and obtain the original slice image bias-corrected RFM to perform multi-slice image block adjustment. The second process generates the panoramic stitching image by establishing the image coordinate conversion relationship from the panoramic stitching image to the original multi-slice images. The final step is dividing the panoramic stitching image uniformly into image grids and employing the established image coordinate conversion relationship and the original multi-slice image bias-corrected RFM to generate a virtual control grid to construct the panoramic stitching image RFM. To evaluate the performance, we conducted experiments using the Tianhui-1(TH-1) high-resolution image and the Ziyuan-3(ZY-3) triple liner-array image data. The experimental results show that, compared with the object-space-oriented algorithm, the stitching accuracy loss of the generated panoramic stitching image was only 0.2 pixels and that the mean value was 0.799798 pixels, achieving the sub-pixel stitching requirements. Compared with the object-space-oriented algorithm, the RFM positioning difference of the panoramic stitching image was within 0.3 m, which achieves equal positioning accuracy.

Modeling Kelvin wake imaging mechanism of visible spectral remote sensing

Kelvin wake is an important detection target of ocean visible spectral remote sensing. In the case of slow ship speed and low atmospheric transmissivity, the wake signal is weak and the SNR (Signal-Noise Ratio) is low. Therefore, the image obtained by the visible spectral remote sensing imaging system is often “unclear”. In order to solve the problems above, this paper carries out the modeling of Kelvin wake imaging mechanism of visible spectral remote sensing. The Kelvin wake reflection distribution characteristics of rough sea surface are simulated based on the hydrodynamic model of Kelvin wake and the probability density distribution of rough sea surface, and a method to quantify the reflectance resolution for Kelvin wake imaging of rough sea surface is proposed. The changes in reflectance resolution caused by different wind speeds, ship parameters, source angle, receiver angle are also analyzed. Then the imaging link model of TDI-CCD (Time Delay and Integration Charge Coupled Devices) imaging system was established. The imaging results of a Kelvin wake reflected on the rough sea surface are simulated, and the impact of the changes of main imaging parameters (optical system F number, quantization bits, integration stages) on the imaging results of a Kelvin wake at different reflectance resolutions are analyzed. The research has clarified the mechanism of the visible spectral remote sensing system to clearly imaging the Kelvin wake, which can provide guidance on parameters design and attitude planning for the ocean visible spectral remote sensing system, and improve the ability of the imaging system to detect weak wake signals.

High Resolution Imaging Camera (HiRIC) on China’s First Mars Exploration Tianwen-1 Mission

The High-Resolution Imaging Camera (HiRIC) is one major payload of China’s first Mars exploration mission, and its main objective is to obtain the detailed observation images of the key areas on the Martian surface. In this paper, the leading group of HiRIC shows a full blueprint of the HiRIC. The HiRIC can achieve a high resolution (0.5 m at an altitude of 265 km) with a wide swath width of 9 km. The HiRIC adopts an Off-Axis Three-Mirror Astigmatic (TMA) optical system with a focal length of 4640 mm, an F-number of 12 and a Field of View (FOV) of 2° × 0.693°. In order to reduce the instrument weight, carbon-based material is widely used in the opto-mechanical structure which is in ultra-lightweight design, thus, a light-weight camera with a total mass of 42 kg is obtained. The Time Delay and Integration (TDI) Charge Coupled Devices (CCDs) and Complementary Metal-Oxide-Semiconductor Transistor (CMOS) detectors are all set on the imaging plane to achieve the push-broom imaging and frame imaging, respectively. And the high Signal-to-Noise Ratio (SNR) >100:1 can achieve in multi observation types for various scientific imaging tasks. After 4-year design and fabricate, the HiRIC has been assembly. The testing results show that the instrument is in good condition, and the Modulation Transfer Function (MTF) can achieve 0.18 at Nyquist frequency. The HiRIC can achieve a well image on China first Mars exploration mission.

Analysis of factors affecting delay accuracy of subfemtosecond liquid crystal variable retarders.

To obtain a wide range of high-precision time-delay controllable devices, a 100-µm-thick nematic liquid crystal (LC) cell was fabricated using the LC HTD028200-200. Factors influencing the delay calibration accuracy of LC variable retarders (LCVRs) were analyzed theoretically and experimentally. Subsequently, within the total voltage tuning range of 0-5 V, the LCVR had a delay of 4.977-97.404 fs, total delay range of 90 fs, tuning accuracy of ±0.216fs, and tuning resolution of 0.128 fs. This device will play an important role in spectral imaging.

Design of Very High Resolution Satellite Telescopes Part II: Comprehensive Performance Assessment

In Part I [1] , a Korsch-based optical telescope design of a very high resolution earth observation satellite with a ground sampling distance of 25 cm is presented. In this part II, a system performance evaluation of the Korsch optical design employing a time-delay and integration charge-coupled device is investigated. Several key performance metrics are assessed, including the system modulation transfer function (MTF), absolute signal-to-noise ratio (SNR), differential SNR, noise equivalent change of reflectance, and cutoff resolution. The level of the national imagery interpretability rating scales (NIIRS) for measuring the image quality is also predicted. The system MTF has been computed, involving optics, detector, platform, orbit, atmosphere, and target illumination conditions. The SNR has been analyzed at different target albedos, solar, and satellite zenith angles. A new strategy for expressing the system evaluation based on the low- and high-illumination conditions is adopted; providing the operational ranges of such metrics. The assessment shows that for the high- and low-illumination conditions, the predictable performance of the proposed telescope gives promising results and provides an acceptable image quality.

Time-Resolved Impulsive Stimulated Raman Spectroscopy with Synchronized Triple Mode-Locked Lasers.

A complete understanding of a photochemical reaction dynamics begins with real-time measurements of both electronic and vibrational structures of photoexcited molecules. Time-resolved impulsive stimulated Raman spectroscopy (TR-ISRS) with femtosecond actinic pump, Raman pump, and Raman probe pulses is one of the incisive techniques enabling one to investigate the structural changes of photoexcited molecules. Herein, we demonstrate that such femtosecond TR-ISRS is feasible with synchronized triple mode-locked lasers without using any time-delay devices. Taking advantage of precise control of the three repetition rates independently, we could achieve automatic scanning of two delay times between the three pulses, which makes both rapid data acquisition and wide dynamic range measurement of the fifth-order TR-ISRS signal achievable. We thus anticipate that the present triple mode-locked laser-based TR-ISRS technique will be of critical use for long-term monitoring of photochemical reaction dynamics in condensed phases and biological systems.

THzPrism: Frequency-Based Beam Spreading for Terahertz Communication Systems

With large available bandwidths, Terahertz (THz) band communication has been envisioned as a key technique to satisfy the increasing demand for ultra-high-speed wireless communications. To overcome severe path loss of THz signals, large antenna array based beamforming, i.e., directional communication, is required for THz communications. Beamforming increases distance coverage, but it significantly reduces angular coverage, which severely limits the efficiency and flexibility of THz systems. In this letter, a novel phased array architecture called THzPrism is designed to conduct beamforming for THz systems. The key idea of THzPrism is to insert several true time delay devices in a phased array so as to achieve frequency-based beam spreading. As a result, THzPrism can significantly enlarge angular coverage while maintaining the distance coverage for THz systems. Both theoretical analysis and numerical results are conducted to validate the effectiveness of THzPrism.

Design, Simulation and Fabrication of a Time-Delay Device Based on Micro-Channel

With the development of micro-machining technology, the application of microchannel is becoming more and more popular. In this paper, we design a set of time-delay device based on micro-channel and micro-fluidics technology. This paper describes the time-delay device’s working principle and analyses the micro-channel’s flow characteristics by simulation method based on Coventerware. From studies on the micro-channel’s cross section, geometry and dimension parameters, the micro-channel’s optimal form and dimension can be obtained. Finally, this paper chooses ultra-machining process to fabricate the time-delay device.

Cascaded Microbottle Resonator and Its Application in Add–Drop Filter

Whispering-gallery-mode (WGM) microresonators. reveal enormous potential applications in fields ranging from micro/nano-optics, integrated and quantum optics, to optical precision measurements. In this paper, we propose a novel cascaded WGM microresonator which is composed of two partially overlapped microbottle resonators. The distribution property of mode intensity and the variation characteristic of quality factors (Q factors) were analyzed theoretically, and demonstrated by evanescently exciting the microresonator with a tapered fiber at different axial positions. Based on the cascaded microbottle resonator, a stable add-drop filter was demonstrated, and the effective excitation properties of the modes in the microresonator were discussed for the first time. Due to the larger axial dimension, the proposed WGM microresonator could also find applications in strain sensors and time delay devices.

Low-Loss Continuously Tunable Optical True Time Delay Based on Si3N4 Ring Resonators

We design, fabricate, and characterize ultra-low loss continuously tunable optical true time delay devices based on Si3N4 ring resonators in a side-coupled integrated spaced sequence of resonators (SCISSOR) structure. A large tunable delay range up to 3.4 ns is demonstrated using the Balanced SCISSOR delay tuning scheme, for a record loss of only 0.89 dB/ns of delay. By optimizing the coupler design a device delay bandwidth of over 10 GHz is achieved with over 0.5 ns maximum time delay. This ultra-low loss delay line can enable distortion free operation for RF signals used in RF beamforming and other applications. Additionally, this device has the potential to be integrated with active photonic components to be part of a fully integrated photonic integrated circuit in an electronically scanned phased array system; utilizing a silicon photonics platform including heterogeneous integration.

Dual-Frequency Comb Transient Absorption: Broad Dynamic Range Measurement of Femtosecond to Nanosecond Relaxation Processes.

We experimentally demonstrate a dual-frequency comb-based transient absorption (DFC-TA) technique, which has a 12 fs time resolution and an ultrafast scan rate. Here, the fast scan rate is achieved by employing asynchronous optical sampling (ASOPS), which utilizes two independent mode-locked lasers with a slightly detuned repetition rates. The ASOPS approach is advantageous because photodegradation damage of optical sample during TA measurements can be minimized by a gated sampling. We show that the vibrational and electronic population relaxations of near-IR dye molecules in solution that occur in the time range from femtoseconds to nanoseconds can be resolved even with a single time scan measurement. The phase coherent nature of our dual-frequency comb lasers is shown to be the key for successful coherent averaging with femtosecond time resolution preserved over many data acquisitions. We anticipate that the present DFC-TA method without using any pump-probe time delay devices could be of use in developing ultrafast TA-based microscopy and time-resolved coherent multidimensional spectroscopy.

Radar wideband digital beamforming based on time delay and phase compensation

ABSTRACTIn conventional phased array radars, analogue time delay devices and phase shifters have been used for wideband beamforming. These methods suffer from insertion losses, gain mismatches and delay variations, and they occupy a large chip area. To solve these problems, a compact architecture of digital array antennas based on subarrays was considered. In this study, the receiving beam patterns of wideband linear frequency modulation (LFM) signals were constructed by applying analogue stretch processing via mixing with delayed reference signals at the subarray level. Subsequently, narrowband digital time delaying and phase compensation of the tone signals were implemented with reduced arithmetic complexity. Due to the differences in amplitudes, phases and time delays between channels, severe performance degradation of the beam patterns occurred without corrections. To achieve good beamforming performance, array calibration was performed in each channel to adjust the amplitude, frequency and phase of the tone signal. Using a field-programmable gate array, wideband LFM signals and finite impulse response filters with continuously adjustable time delays were implemented in a polyphase structure. Simulations and experiments verified the feasibility and effectiveness of the proposed digital beamformer.

Design of an Orthotropic Piezoelectric Composite Material Phased Array Transducer for Damage Detection in a Concrete Structure

ABSTRACTIn order to verify the feasibility and effectiveness of the sensor used in complex concrete materials, an innovative application of ultrasonic phased array detection for a concrete structure was investigated. Comparing with the traditional piezoelectric composites, orthotropic piezoelectric composite material (OPCM) can be used as transducers in damage detection show clear advantages because of their high sensitivity and directivity along the polarization direction. A low frequency ultrasonic phased array transducer consisting of 16 OPCM elements is studied. The optimal array parameters, such as the phased array element interval, the array element width, and number of elements, are obtained by studying the total displacement changes as various parameters change at the focus point in the concrete structure. This configuration allowed the variation and control of the wave field directivity in the concrete structure during the measurements. The measurements were taken on concrete specimens using a precise time-delay device. The experimental measurements were compared to theoretical calculations to investigate the influence of different array element parameters. The results show that an OPCM phased array transducer can be used to detect damage in a concrete block.

Ku대역 전파고도계 체계점검장비 개발

For performance improving of C-band radar altimeter used in a missile system, Ku-band radar altimeter is developed. To utilize the time delay devices which are used in testing C-band radar altimeter, we proposed C-band and Ku-band frequency conversion method and implemented it as a part of missile system test equipment. In this paper we present design contents, development results and test application results of radar altimeter test equipments.