High-speed Signal Research Articles

A Study on Changes of Bead Shape and Metal Transfer Mode Affected by Molten Pool Behavior for Welding Position in GMAW Process

In gas metal arc welding, the molten pool is affected by gravity and this affects welding phenomena. This study investigated the changes in bead shape and metal transfer mode caused by the molten-pool behavior. We conducted gas metal arc welding with various welding positions. Images from high-speed camera and signals from current and voltage sensors were used to determine the differences with welding positions. Bead shapes were quantified through transverse cross-sectional bead images and image processing. Molten-pool images from the camera were analyzed through the molten-pool length and distance from the wire position. These were used to explain the differences between transverse and longitudinal cross-sectional bead images with welding positions. Changes in metal transfer based on current and voltage signals were investigated. To determine the exact change in metal transfer, the number of short-circuit transfers and spray transfers within the same time was captured by the welding position camera.

RESEARCH ON WIDE SPECTRUM FULL-COLOR NIGHT VISION ELDERLY FACIAL VIDEO HEART RATE AUTOMATIC MEASUREMENT AND WARNING SYSTEM

In recent years, the prevalence of cardiovascular diseases has been growing geometrically, especially among the elderly. Real-time heart rate monitoring becomes an effective measure for preventing cardiovascular diseases. Traditional contact-based real-time heart rate measurement methods require long-term wearing of contact electrodes, which can cause inconvenience to the elderly population. In this study, a wide spectrum full color night vision elderly face video heart rate automatic measurement and early warning system was designed and developed by combining imaging photoplethysmography (IPPG), video acquisition equipment based on starlight wide spectrum camera and high-speed face recognition signal processing algorithm based on deep learning. By constructing a software and hardware platform, a comprehensive evaluation of the system’s application in elderly facial video heart rate measurement experiments was conducted.

A kind of planar waveguides for cheating the high-speed digital signals into misidentifying the characteristic impedance

Since a planar periodic transmission line can suppress drastically the electromagnetic coupling, it would be advantageous to use such a kind of transmission lines in solving the problem of miniaturization of circuit area. By adjusting the lattice constants and geometric parameters of periodic microstrip lines, a time domain characteristic impedance that is the same as that of conventional microstrip lines (CMLs) can be achieved. Such periodic microstrip lines can therefore be used to trick high-speed digital signals, causing a digital signal to misjudge the time domain characteristic impedance of the transmission lines. The theoretical analysis has been verified by our experimental measurement results. Besides, a specific expression for the characteristic impedance of lossless periodic artificial materials is deduced by a circuit model and a standard of misidentification for the characteristic impedance of periodic microstrip lines is given for the digital signals.

An adaptive laser processing method of multilayer heterogeneous materials by monitoring dynamic spectrum at kHz-MHz level

Laser micro/nano processing exhibits significant advantages in manufacturing capability and performance. However, the properties of ablated materials cannot be sensed and identified during processing is an intractable challenge. In particular, multilayer heterogeneous materials often evolve into excessive residues and damages during laser selective removal. In this study, we developed an adaptive laser processing method that includes material interface adaptive and laser power adaptive for selective removal of multilayer heterogeneous materials by monitoring dynamic spectrum at kHz-MHz level. The mechanism of interface sensing and the threshold of laser selective removal of multilayer materials were investigated. Dual-channel parallel detection mode of the blazed grating with the ultrafast photodetector at the kHz-MHz pulse level has been designed and verified for monitoring adjacent layers synchronously. High-speed signals with a pulse width of 30 ns and a repetition frequency of 0–15 MHz were identified by the Field Programmable Logic Gate Array (FPGA), and pulse-level closed-loop feedback was finished. Patterned selective removal on an FR-4 copper clad laminate (CCL) and flexible printed circuit (FPC) was completed. The method exhibited sensitive signal characteristics, accurately sensed the material interface, and provided a clear criterion for identifying the removal process of multilayer materials by quantitative analysis of signal variation, which provides an innovative scheme for laser intelligent manufacturing of multilayer heterogeneous materials.

FPGA implementation for 44.2368-Gbit/s PAM8 signal transmission with pruned pre-equalization.

In this experiment, we demonstrated an intensity modulation and direct-detection (IM/DD) system based on a field-programmable gate array (FPGA). The PAM8 signals are successfully delivered at 44.2368 Gbit/s over a 45-km standard single-mode fiber (SSMF), satisfying the soft-decision forward error correction (SD-FEC) criterion of 2.4 × 10-2, and the net bit rate may reach 36.864 Gbit/s without the need of optical amplifiers. At the transmitter, we used a pruned pre-equalization algorithm to process the PAM8 signals, and the high-speed parallel PAM8 signals were processed at the receiver using 64 parallel constant modulus algorithm (CMA) and decision-directed least mean square (DD-LMS) equalizers. Additionally, we analyzed the bit error rate (BER) performance of the DD-LMS equalizer in FPGA simulation with various data lengths, both before and after equalization.

Photoacoustic Spectral Response using Ultrasound and Interferometric Sensors: A Correlation Study for a High Bandwidth Real-Time Blood Vasculature Monitoring Application in a Chick-Embryo Chorioallantoic Membrane (CAM) Model.

Photoacoustic (PA) spectral response technique has shown good promise in efficient preclinical tissue diagnosis by depicting mechano-biological properties due to high spatial resolution and penetration depth. The conventional PA-based system is a pump-probe technique that utilizes neodymium-doped yttrium aluminum garnet pulsed laser as a pump and an ultrasound sensor as a probe. For biomedical studies, high-speed PA signals need to be acquired, requiring higher bandwidth ultrasound sensors. While the bandwidth increases, they exhibit a very low signal-to-noise ratio that inhibits acquiring PA signals of biomedical samples. An interferometer-based probe has recently been investigated as a potential ultrasound probe for obtaining PA signals as an alternative. This optical PA detection technique offers high sensitivity by combining low acoustic impedance with high electromechanical coupling. However, there is a lack of exploration of the same for real-time biomedical studies. This work shows the development of a homodyne Mach-Zehnder interferometer-based PA spectral response (PASR) followed by a correlation study between the conventional ultrasound sensor and the interferometer-based sensor. Further, this study demonstrates the capability of continuous monitoring of vascular growth and the effect of an antidrug (Cisplatin) on the vasculature tested on a chick-embryo chorioallantoic membrane model. PASR was able to monitor growth changes within one day, which was not possible with conventional methods. This opens up potential possibilities for using this technique in biomedical applications.

Design of CSD based bi-orthogonal wavelet filter bank for medical image retrieval

Two-channel wavelet filter-banks (FBs) are universally used in many applications of signal processing. In this work, design of a bi-orthogonal wavelet FB with low complexity is suggested. The proposed design is based on canonical signed digit (CSD) implementation of the bi-orthogonal wavelet FB. CSD technique has been applied to the FB to eliminate the power consuming multipliers and to reduce the number of shifters and adders in the implementation of bi-orthogonal FB. The suggested FB design is suitable for the application of high speed signal processing applications. In addition, the proposed bi-orthogonal wavelet FB is implemented on hardware using Field Programmable Gate Array (FPGA) board Kintex-7 from Xilinx. It is found that the suggested bi-orthogonal wavelet FB attained low digital hardware requirement as compared to well-known rationalized existing bi-orthogonal wavelet FBs. The efficacy of the suggested wavelet FB is demonstrated on medical image retrieval application. NEMA, OASIS, and EXACT09, three publicly accessible medical image datasets, are utilized to measure the efficacy of image retrieval. It is shown that the suggested bi-orthogonal wavelet FB performs better than the bi-orthogonal wavelet FBs existing that are being used.

High-Speed and wideband multilevel Frequency-Hopping microwave signal generation based on a Sagnac loop

An approach for photonic generation of multilevel frequency-hopping (FH) microwave signal based on a Sagnac loop is proposed and investigated. In the Sagnac loop, several Mach-Zehnder Interferometers (MZI), driven by the coding signals, are connected in series to act as a tunable photonic filter. By carefully adjusting the coding signals, the photonic filter can select the specific frequency component from the input optical frequency comb (OFC), so as to generate multilevel FH microwave signal. Theoretical analysis and simulation works are performed to demonstrate a 7-level FH microwave signal generator, and the discussion about the impact of non-ideal factors is given. The approach features high FH speed, wideband and amenable to photonic integration. In addition, the Sagnac loop ensures the equal optical path for clockwise and counterclockwise lights, which can enhance signal performance due to the better phase stability.

High-speed real-time periodic weak pulse signal detection with simplified phase-weighted stacking.

Phase-weighted stacking (PWS) is an efficient noise reduction technique widely used in exploration seismology. It uses the coherence of the instantaneous phase to enhance signals by reducing incoherent noise. However, the high computational cost makes it difficult to apply PWS for the real-time detection of weak signals with high repetition frequency. This paper proposes a novel simplified PWS method with low computational complexity. The complex plane is divided into four quadrants, and the instantaneous phases in the same quadrant are simplified to the same phase. Based on the proposed method combined with a one-bit analog-to-digital converter, a novel field-programmable gate array-based high-speed real-time periodic weak pulse signal detection technique is presented. A prototype is implemented to verify the proposed technique. For weak pulse signals with an input signal-to-noise ratio (SNR) of -21 dB to -15 dB for 2500 cycles, the results obtained show that the simplified PWS algorithm can improve the SNR of the coherently integrated signals by about 10-15 dB with a latency of about 2 µs.

Segmented Silicon Modulator With a Bandwidth Beyond 67 GHz for High-Speed Signaling

We demonstrate an all-silicon segmented modulator with traveling-wave electrodes, achieving an electro-optic bandwidth beyond 67 GHz and a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$V_\pi$</tex-math></inline-formula> of 5V. We show that dividing a long optical modulator into shorter segments can help achieve a higher bandwidth without compromising modulation efficiency or optical loss. We analyze the bandwidth limitation due to the delay mismatch between the driving and optical signals. We show that the impact of misalignment of driving delays between segments on the overall bandwidth of the modulator can be described by a finite impulse response filter. Using this modulator, we achieve optical transmission of 120 Gbaud 8-level amplitude shift keying with coherent detection. Taking into account the forward error correction overhead, this yields 336.4 Gb/s net on a single polarization. Our design has the potential for achieving 1 Tb/s using dual-polarization IQ modulation.

Design of a Common-Mode Rejection Filter Using Dumbbell-Shaped Defected Ground Structures Based on Equivalent Circuit Models

An efficient design method is proposed for a compact common-mode rejection (CMR) filter utilizing dumbbell-shaped defected ground (DS-DG) structures and gap-coupled stub (GCS) resonators. A CMR filter for differential lines helps to improve the signal integrity of high-speed digital signals on printed circuit boards. The proposed CMR filter design is based on the equivalent circuit models, while the previous designs depended heavily on the DS-DG structure optimization using the EM simulations. The proposed CMR filter effectively rejects the common-mode components while minimally affecting the differential signals. To prove the simplified design approach, a fifth-order Chebyshev band-stop filter is designed with three DS-DG structures and two GCS resonators. From the simulated and measured results, it is found that the proposed CMR filter provides ~90% fractional frequency bandwidth with more than 20 dB of common-mode rejection ratio and less than 0.6 dB of insertion loss of the differential signal.

Mechanical model of back-drilling high-speed printed circuit boards with eccentricity effects

The rapid development of fifth-generation (5 G) communication technology is placing greater demands on the performance of high-speed printed circuit boards (PCBs). Back-drilling plays a crucial role in achieving high-frequency and high-speed signal transmission and is a key technology for improving the signal integrity of high-speed PCBs. The thrust force is considered the main factor affecting hole quality when drilling PCBs. Accurately predicting the thrust force is essential for optimizing the back-drilling process. However, back-drilling thrust force is strongly coupled with eccentricity, presenting a significant challenge in predicting its accuracy. In this paper, an ideal state mechanical model (without eccentricity effects) and an actual state mechanical model (with eccentricity effects) are proposed for the first time to predict the thrust force when back-drilling high-speed printed circuit boards. First, a length model for the effective cutting edge in back-drilling is established for the first time based on back-drilling characteristics. The contact conditions and back-drilling mechanism between the materials (glass fiber-reinforced plastic, resin and copper) and the microdrill (tungsten carbide) are further analyzed in terms of the effective cutting edge and contact mechanics. Then, by considering the eccentricity effects, mechanical models under ideal and actual states are proposed for predicting the thrust forces when back-drilling high-speed PCBs. In addition, by setting different feed rates and spindle speeds and using 4 types of microdrills with different structural parameters, a back-drilling experiment is performed on high-speed PCBs to determine eccentric distances, actual thrust forces, and stub lengths. Compared with the actual thrust force, the maximum error of the ideal model is 8.03%, while the actual model has a better applicability with a maximum error of 5.51% and a minimum error of 1.33%. The experimental results indicate that the thrust force first decreases and then increases as the eccentric distance increases when the chisel edge is involved in the cut during back-drilling. Moreover, the stub length increases with increasing eccentricity and decreasing point angle, while the back-drilling diameter has a negligible effect.

Application of Ferroelectric Capacitors for Equalization of High-Speed Digital Signaling

Application of Ferroelectric Capacitors for Equalization of High-Speed Digital Signaling

Satellite navigation method based on high-speed frequency hopping signal

Global navigation satellite system has been widely used, but it is vulnerable to jamming. In military satellite communications, frequency hopping (FH) signal is usually used for anti-jamming communications. If the FH signal can be used in satellite navigation, the anti-jamming ability of satellite navigation can be improved. Although a recently proposed time-frequency matrix ranging method (TFMR) can use FH signals to realize pseudorange measurement, it cannot transmit navigation messages using the ranging signal which is crucial for satellite navigation. In this article, we propose dual-tone binary frequency shift keying-based TFMR (DBFSK-TFMR). DBFSK-TFMR designs an extended time-frequency matrix (ETFM) and its generation algorithm, which can use the frequency differences in different dual-tone signals in ETFM to modulate data and eliminate the negative impact of data modulation on pseudorange measurement. Using ETFM, DBFSK-TFMR not only realizes the navigation message transmission but also ensures the precision and unambiguous measurement range of pseudorange measurement. DBFSK-TFMR can be used as an integrated solution for anti-jamming communication and navigation based on FH signals. Simulation results show that DBFSK-TFMR has almost the same ranging performance as TFMR.

An Experimental Study of Radar-Centric Transmission for Integrated Sensing and Communications

This study proposes a dual-function radar and communication (DFRC) system that utilizes radar transmission parameters as modulation indexes to transmit data to the users while performing radar sensing as its primary function. The proposed technique exploits index modulation (IM) using the center frequency of radar chirps, their bandwidths, and polarization states as indexes to modulate the communication data within each radar chirp. By utilizing the combination of these indexes, the proposed DFRC system can reach up to 17 Mb/s throughput, while observing a robust radar performance. Through our experimental study, we also reveal the trade-off between the radar sensing performance and communication data rate, depending on the radar waveform parameters selected in the DFRC system. This study also demonstrates the implementation of the proposed DFRC system and presents its real-time over-the-air experimental measurements. Consequently, the simulation results are verified by real-time over-the-air experiments, where ARESTOR, a high-speed signal processing and experimental radar platform, has been employed.

QTT Ultra-wideband Signal Acquisition and Baseband Data Recording System Design Based on the RFSoC Platform

Abstract The 110 m QiTai radio Telescope (QTT) will be equipped with multiple Ultra-WideBand (UWB) receivers in the primary and Gregory focus to achieve continuous frequency coverage from 270 MHz to 115 GHz, which poses great challenges to signal acquisition, transmission, and real-time processing. Aiming at 10 GHz and above full-bandwidth acquisition and multi-scientific processing for the QTT UWB signals, an experimental system with high-speed signal acquisition, 100 Gb network multi-path distribution, and fast recording is designed by using advanced direct RF-sampling technology and heterogeneous architecture. The system employs a ZCU111 board to digitize dual-polarization signals with a sampling rate of 4.096 GigaSamples-Per-Second and 12-bit quantization. The collected wideband signals are channelized into 2048 chunks, which are then assembled into 16 sets of digital narrow basebands with 128 MHz bandwidth and transmitted to the processing servers through two 100 Gb ports. A HASPIPE pipeline, UWB_HASHPIPE is designed to receive and store multiple subbands in parallel. Data distribution links can be flexibly configured based on IP addresses and port numbers. The system is verified by pulsar observation experiments on the Nanshan 26 m telescope. 512 MHz bandwidth is selected from the collected L-band receiver signals and recorded in VDIF file format with 8 parallel instances. The test results show that the data integrity is excellent, and the signal-to-noise ratio of the band-merged pulsar profile is stronger than single subband data. This paper provides a high-performance and flexible solution for the design of versatile UWB backends. Meanwhile, the developed platform can be integrated into QTT backends for baseband data collection and Very Long Baseline Interferometry observation.

All-optical matching structure for multi-order modulation formats

With the development and popularity of the Internet, network security has become a popular topic. The traditional solution for screening the security of network information is to convert the signal transmitted in the optical fiber into an electrical signal through an optical conversion. Then we perform symbol matching within the electronic firewall to determine whether the signal is a risk. However, due to the limitation of carrier recovery time in the semiconductor, the photoelectric converter cannot handle signals with too high rate, and it also causes a large power consumption. To improve the efficiency and scalability of signal matching, we propose an all-optical matching structure. This structure can identify the position of the target sequence in the input data sequence in the all-optical environment, and the structure is suitable for any amplitude and phase modulation format. The matching result of each bit of the target sequence and input data sequence is obtained by phase delay and interference. Then the matching result of each bit of the target sequence and input data sequence is integrated by logic AND gate, regenerator, and delay line. Finally, the matching result between the whole target sequence and the input data sequence is obtained. This structure can avoid photoelectric transformation and processes the signal directly at the optical domain, which greatly reduces the consumption of time and energy. We use VPItransmissionMaker software to simulate and verify the structure. The length of the input signal during the simulation is 8 bits, the length of the target signal is 4 bits, and the transmission rate of the signal is 100 GBaud. We simulated the binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), 8-phase shift keying (8PSK), and 16 quadrature amplitude modulation (16QAM) modulation formats and analyzed the noise performance of the system. The results show that the structure can achieve all-optical matching of high-speed optical signals in BPSK, QPSK, 8PSK, and 16QAM modulation formats and has good anti-noise performance.

AGATA phase 2 advancements in front-end electronics

The AGATA collaboration has a long-standing leadership in the development of front-end electronics for high resolution gamma -ray spectroscopy using large volume high purity germanium detectors. For two decades, the AGATA collaboration has been developing state-of-the-art digital electronics processing with high resolution sampling ADC, high-speed signal transfer and fast readout to a high throughput computing (HTC) farm for on-line pulse shape analysis. The collaboration is presently addressing the next challenge of equipping a 4pi array with more than 6000 channels in high resolution mode, generating approximately 10 MHz of total trigger requests, coupled to a large variety of complementary instruments. A next generation of front-end electronics, presently under design, is based on industrial products (System on Module FPGA’s), has higher integration and lower power consumption. In this contribution, the conceptual design of the new electronics is presented. The results of the very first tests of the pre-production electronics are presented as well as future perspectives.

Dual-anchor anti-corrosion coating of copper foil for high-speed interconnects

In this experiment, two similar molecules with bifunctional groups have been characterized to prove the advantages of dual-anchor molecular coating in the interfacial modification of the copper foil. The physicochemical properties of the modified copper foils have been studied. The obtained results indicate that the anti-corrosion performance and peeling strength were significantly improved for the copper foil treated with (2-(Methylthio)pyrimidin-4-yl)methanamine (MET), whose bonding information was analyzed via the density functional theory calculation. It was found that the S-Cu and N-Cu bonds were both formed on the Cu (1 1 1) surface for MET coating, and the adsorption of the double anchor points improves the stability of the interface. The peeling test exhibits the function of MET coating as the adhesion promotor between low-surface profile copper and resin for high-speed signal transmission.

Generation of high-speed PAM-4 signal with 3-bit DAC enabled by CRD-NS in optical interconnect.

In this paper, we experimentally demonstrated a 2-km high-speed optical interconnection with pulse-shaped pre-equalized four-level pulse amplitude modulation (PAM-4) signal generated by a 3-bit digital-to-analog converter (DAC) with the aid of in-band quantization noise suppression techniques under different oversampling ratios (OSRs) to reduce the influence of quantization noise. The simulation results show that the quantization noise suppression capability of high computational complexity digital resolution enhancer (DRE) is sensitive to taps number of the estimated channel and match filter (MF) response when OSR is sufficient, which will lead to further significant computational complexity increase. To better accommodate this issue, channel response-dependent noise shaping (CRD-NS) which also takes channel response into consideration when optimizing quantization noise distribution is proposed to suppress the in-band quantization noise instead of DRE. Experimental results show that about 2 dB receiver sensitivity improvement can be achieved at the hard-decision forward error correction (HD-FEC) threshold for 110 Gb/s pre-equalized PAM-4 signal generated by 3-bit DAC when the traditional NS technique is replaced by the CRD-NS technique. Compared to the high computational complexity DRE technique, in which channel response is also considered, negligible receiver sensitivity penalty is observed for 110 Gb/s PAM-4 signal, when the CRD-NS technique is utilized. Considering both the system cost and bit error ratio (BER) performance, the generation of high-speed PAM signal with 3-bit DAC enabled by the CRD-NS technique is regarded as a promising scheme for optical interconnection.