Low Bit Research Articles

Side information-driven image coding for hybrid machine–human vision

With the development of machine learning, advanced photography and image transmission systems, images are being processed more and more by machines, so image coding for machines (ICM) came into being. After the image codec compresses and transmits the image, the image will be handed over to machine vision task networks. These vision tasks include image classification, semantic segmentation, and so on. We propose a side information-driven image coding for hybrid machine–human vision (SICMH) framework, not only for machine vision tasks, but also for human vision-oriented image reconstruction. The proposed SICMH framework can perform image classification, semantic segmentation, and coarse image reconstruction by using purely the side information. Moreover, SICMH can perform fine image reconstruction by using the residue information. In particular, we propose a multi-scale feature fusion block to enhance the usage of side information, and a novel semantic segmentation network named modified TrSeg to generate better semantic segmentation maps. The experimental results well demonstrated the effectiveness of our proposed framework. SICMH achieves the same image classification and semantic segmentation accuracy as the existing traditional or learning-based multi-task ICM frameworks using the lowest bitrate. For the image reconstruction task, the proposed SICMH achieved the same PSNR as existing learning-based multi-task hybrid ICM frameworks and the traditional image codec BPG again with the lowest bitrate.

Accounting the Ways of Weighing the Bits of the Data Vector when Constructing a Code with Summation in the Ring of Deductions Modulo M = 4 in the Synthesis of Self-Checking Discrete Devices Based on Boolean Signals Correction

The article shows that in the synthesis of concurrent error-detection circuit based on Boolean signals correction, weighted codes with summation in the ring of deductions modulo M = 4 (weight-based Bose — Lin codes) with various arrays of weighting coefficients can be effectively used. The codes with four data and two test symbols used in organizing the control of calculations in a group of six outputs of the diagnostic object are considered in more detail. Four arrays of weight coefficients are highlighted: [1, 1, 1, 2], [1, 1, 2, 3], [1, 2, 2, 3], [2, 2, 2, 3] — the use of which in the construction of a weight-based Bose — Lin code leads to the formation of for each the test vector has exactly one data vector of the following types: <00ab>, <01 ab>, <10ab>, <11 ab>, where a, b ' {0, 1}. This property allows the use of codes with the specified arrays of weighting coefficients in the synthesis of concurrent error-detection circuit with the conversion of only part of the signals from the diagnostic object — two signals involved in the formation of the lower bits of the data vector. The article presents the results of experimental studies of weight-based Bose — Lin codes in the synthesis of concurrent error-detection circuit based on the Boolean signals correction using two algorithms. The first algorithm is based on the use of converting only those signals from the diagnostic object that are involved in the formation of test symbols. The second algorithm is based on the conversion of only those signals from the diagnostic object that participate in the formation of the two lowest digits of the data vector. It has been experimentally established that self-checking devices synthesized using a code with an array of weighting coefficients have the highest efficiency in terms of structural redundancy [2, 2, 2, 3] (on average, the value of the structural redundancy index has been reached at 73 % of the duplication structure). Next, according to this indicator, there are devices synthesized using a code with an array of weighting coefficients [1, 2, 2, 3] (on average, 76—77 % of the duplication structure). The use of arrays of weighting coefficients [1, 1, 2, 3] and [1, 1, 1, 2] in the construction of the code gives a slightly lower effect (on average 79—81 % from the duplication structure). It is shown that in order to ensure complete self-checking of device structures, it will be necessary to use permutations of outputs within controlled groups of outputs of the initial diagnostic object and between groups. The results of the study can be taken into account when developing self-checking digital devices, as well as software tools for their computer-aided design.

Radiation‐Tolerant SRAM for Satellite Image Compression Systems: A Hybrid Memory Array Approach

ABSTRACTThis work is based on the design of an SRAM memory array for on board satellite image compression systems, including memory size, cost, power efficiency, and vulnerability to single event upsets (SEU). Initially, we designed a memory cell, RH_14T, specifically to mitigate the impact of SEUs. Subsequently, we incorporated RH_14T into the on‐board memory array in two variations: RH_14T with minimal area overhead (RH_14T_small) and RH_14T with substantial area overhead (RH_14T_large), which have critical charges of 30.10 and 38.77 fC, respectively. Given the higher sensitivity of higher order bits compared to lower order bits in image pixels, RH_14T_small was allocated for the least significant bit (LSB) positions. RH_14_large, on the other hand, was used for the most significant bit (MSB) positions within the memory array. This configuration enhanced the array's overall area, power, and space radiation tolerance. Furthermore, the RH_14T model was bench marked against other recently introduced radiation‐hardened SRAM cells and compared proposed RH_14T CC18T, RHC14T, RHMC12T, SARP12T, SRRD12T, DICE, and QUCCE12T across several critical design parameters. Notably, RH_14T's sensitive nodes can recover their original data even after radiation‐induced value flips. In addition to these benefits, RH_14T also demonstrates a high static voltage noise margin and reduced read and write delays compared to most of the cells it was compared with.

Transmission of High Data Rate Signals over Low-Frequency Passbands Using (DSSS-BPSK) Technique

This study presents an enhancement to the Direct Sequence Spread Spectrum (DSSS) algorithm aimed at transmitting high data rate signals over low-frequency passbands. By utilizing a random number to generate a new encryption key, the complexity of both encryption and decryption processes is significantly increased. The original signal undergoes multiplication with a spreading code, resulting in a random matrix that obscures the original data and enhances security. The research employs Binary Phase Shift Keying (BPSK) modulation to effectively transmit the spread signal, optimizing bandwidth utilization and mitigating channel impairments. Simulation results conducted using MATLAB demonstrate that the proposed DSSS method achieves low Bit Error Rates (BER) under various conditions, confirming its robustness against interference. Furthermore, the findings indicate that the combination of high data rate transmission and low-frequency passbands using DSSS has promising applications in diverse fields such as industrial automation, remote sensing, and military communications. Overall, this research contributes to advancing secure and efficient communication systems by leveraging DSSS techniques.

WS2/Graphene/MoS2 Sandwich van der Waals Heterojunction for Fast-Response Photodetectors.

Fast-response photodetectors have attracted considerable attention in the application of high-speed communication, real-time monitoring, and optical imaging systems. However, most reported photodetectors suffer from limitations of the inherent properties of materials, low carrier transport efficiency, and unmatched interfaces, which lead to a low response speed. Here, we report a WS2/graphene/MoS2 vertical van der Waals heterojunction fabricated by mechanical exfoliation and dry transfer methods for fast response. To improve the response speed of the previously reported WS2/MoS2 heterojunction with excellent photoelectric performances, the embedded graphene is employed to optimize the interface defects and improve the carrier transport efficiency due to its high mobility and smooth and flat surface. Under the illuminations of a 405 nm laser and a bias voltage of 0.5 V, our device can realize rise and fall times of 44 and 52 μs, respectively. For a bias voltage of 2.5 V, moreover, the device can also show outstanding performances including a high responsivity of 220 A/W, a considerable detectivity of 1.2 × 1013 Jones, a large external quantum efficiency of 6.7 × 104 %, and a low dark current of 1.05 × 10-13 A. Additionally, the device enables high-speed transmission with a low bit error rate in a closed-loop optical communication system. Therefore, the proposed scheme can provide an idea for the design of photodetectors with fast response and high performance.

Design of a Differential Chaotic Shift Keying Communication System Based on Noise Reduction with Orthogonal Double Bit Rate

In this paper, a differential chaotic shift keying communication system based on noise reduction with orthogonal double bit rate (NR-ODBR-DCSK) is proposed. The system incorporates Walsh orthogonalization at the transmitter side to orthogonalize the information signals so that two mutually orthogonal signals can be superimposed. At the receiving end, because the principle of orthogonal signals is used, it achieves the characteristic of double information transmission rate for information signal transmission while avoiding the problem of chaotic synchronization. In addition, the system employs a noise reduction transmission mechanism, which reduces the noise variance in the received signal, further reducing the BER of the system and thus improving the performance of the communication system. By analyzing the signal format of the system, the transmitter and receiver structures of the communication system are designed. Subsequently, theoretical analyses and simulations in an additive white Gaussian noise (AWGN) channel demonstrate the good performance of the system, including a low bit error rate (BER) and a good data-energy to bit-energy ratio (DBR). Finally, a simulation test of the NR-ODBR-DCSK system for a semi-physical communication system was carried out using two USRP devices to verify the experimental feasibility of the system. The simulation analysis results show that comparative analyses with conventional DCSK and SR-DCSK systems highlight the superior performance of the NR-ODBR-DCSK system.

5G NR sub-THz fiber-wireless integrated systems using polarization multiplexing-multiband technique and self-polarization diversity scheme

Fifth generation (5G) new radio (NR) fiber-wireless integrated systems using polarization multiplexing-multiband technique and self-polarization diversity scheme are successfully implemented. Polarization multiplexing-multiband technique is an effectual method to enhance the transmission capacity and spectral efficiency of systems. Self-polarization diversity scheme is an efficient scheme for polarization demultiplexing, in which an x-polarized (y-polarized) optical carrier with multiple x-polarized (y-polarized) optical signals can be detected using single-ended photodiodes. The transmission of 5G NR sub-terahertz (THz) signals through fiber-wireless integrated systems holds promise to afford high-speed and long-haul wired-wireless communications. It shows the robustness to achieve high aggregate data rates and lays the foundation to meet the evolving demands of future communication systems. Through an integrated medium of 20 km single-mode fiber, 1.6 km optical wireless, and 4/8/12 m 5G NR wireless, four 5G sub-THz 32-quadrature amplitude modulation-orthogonal frequency-division multiplexing signals at x- and y-polarizations are transmitted with good transmission performance in terms of low bit error rates and error vector magnitudes. The successful transmission of sub-THz signals at different carrier frequencies and polarizations over fiber-wireless integrated systems proves system’s ability to support cutting-edge 5G NR fiber-wireless integrated systems.

Analysis of the Dynamics of the Lower Drill String Assembly in a Deep Well Coring Operation

In order to carry out the geological characteristics, evolution law and other scientific research of the deep strata in the extra-deep well, it is necessary to carry out the coring operation in the extra-deep depth. However, with the increase of drilling depth, the force of drill string in the underground becomes more and more complicated, and there is contact collision between the core and the core after the core tool is bent, which makes the core broken. Clarifying the dynamic behavior of the BHA during the extra-deep well coring process is helpful to obtain a more complete core. Therefore, this paper adopts the simulation analysis method to simulate the coring process of the extra-deep well with a 163.5mm diamond bit and a 140mm corer under the real drilling hole trajectory. The stress, eddy motion and the contact between the inner barrel of the core tool and the core of the lower 1000m drill assembly are analyzed. The results show that the hole expansion rate of coring bit is 2.5% in the process of low bit weight and low rotational speed. When the core is 8m, the core barrel is under compression, bending and torsion, and under the restriction of the centralizer and the core hole, the middle and upper part of the core tool bend greatly, and the contact degree with the core is high, and the larger contact force is easy to cause the lower core to fracture.

Design and performance analysis of integrated sensing and communication scheme based on LoRa signals

LoRa (Long Range) has garnered widespread adoption in Internet of Things (IoT) communications due to its extensive transmission range and robust resistance to interference. Furthermore, its capability to linearly discern deviations across both frequency and time domains renders it an ideal signal for sensing applications. Consequently, this article proposes an Integrated Sensing and Communication (ISAC) scheme based on the LoRa signal. On the communication side, while the modulation and demodulation processes of the LoRa signal are currently kept confidential, this article has theoretically derived its principles and further implemented the communication functionality of LoRa through experimental simulations. On the sensing side, through theoretical derivation and experimental simulation, the influence of different modulation information on the peak amplitude and position of pulse compression was analyzed. Two signal processing schemes are proposed to overcome the impact of modulation information, thereby enabling the sensing function. The communication and sensing performance of the proposed ISAC scheme was evaluated. Experimental results demonstrated that, even in low signal-to-noise ratio (SNR) environments, the communication function maintained a low bit error rate (BER), while the sensing function achieved a high target detection rate, both of which exhibited excellent performance.

Bi-directional SMF-NDF-optical/5G NR wireless converged systems

This study presents the transmission of fifth-generation (5G) new radio (NR) signals over bi-directional single-mode fiber (SMF)-negative dispersion fiber (NDF)-optical/5G NR wireless converged systems, using two cascaded reflective semiconductor optical amplifiers (RSOAs). Downstream transmission of 5G NR 16-quadrature amplitude modulation (QAM) signals achieved an aggregate net bit rate of 228.037 Gb/s, comprising 59.813, 74.766, and 93.458 Gb/s at 150, 250, and 325 GHz, respectively. The system achieved a low bit error rate (BER) and clear constellation patterns. However, systems without NDF exceed the forward error correction 7% threshold, indicating the importance of NDF in compensating for fiber dispersion. Moreover, for upstream transmission, two cascaded RSOAs are used to transmit 5G 16-QAM-orthogonal frequency division multiplexing signals, achieving a total data rate of 40 Gb/s. The use of two cascaded RSOAs in the system significantly improved upstream performance, resulting in low BERs and clear constellation patterns. This system not only achieved high data rates but also extended transmission coverage to support the deployment of advanced 5G NR applications.

Development of Specialized PDC Drill Bits for the Interaction of Soft and Hard Strata in Igneous Rocks

In response to the technical challenges of low mechanical drilling speed and severe drill bit wear caused by the development of some igneous rocks in the Dongying and Shahejie formations of the Bozhong 34-9 oilfield, it is urgent to develop a specialized PDC drill bit suitable for the soft hard interaction formation of the BZ-34-9 oilfield. The PDC drill bit is required to have strong aggressiveness, as well as good impact resistance and abrasion resistance, in order to meet the drilling requirements of the soft hard interaction formation of the BZ34-9 oilfield. Through on-site use, the mechanical drilling speed has been significantly improved.

5 G new radio fiber-wireless converged systems by injection locking multi-optical carrier into directly-modulated lasers

The integration of fiber-optical wireless convergence with fifth generation new radio is crucial in building high-performance access networks. This approach not only provides high-transmission-rates but also ensures broad coverage, which is vital for future networks. Here we report fifth generation new radio fiber-wireless converged systems by injection locking multi-optical carrier into directly-modulated lasers. Data rates of 10 Gb/s, 20 Gb/s, and 40 Gb/s are achieved by direct modulation on directly-modulated lasers using 16-quadrature amplitude modulation-orthogonal frequency-division multiplexing signal. Through 25-km single-mode fiber, 1.5-km optical wireless, and 12-/22-/33-m millimeter-wave/sub-terahertz wireless integrated-media, 10-Gb/s/20-GHz, 20-Gb/s/60-GHz, and 40-Gb/s/100-GHz signals are transmitted with acceptably low bit error rates and error vector magnitudes, as well as distinct constellations. The successful transport of fifth generation new radio millimeter-wave and sub-terahertz signals at different carrier frequencies through fiber-wireless convergence demonstrates the potential of the system to meet the evolving requirement of next-generation communications.

Adaptive Measurement and Parameter Estimation for Low-SNR PRBC-PAM Signal Based on Adjusting Zero Value and Chaotic State Ratio

Accurately estimating the modulation parameters of pseudorandom binary code–pulse amplitude modulation (PRBC–PAM) signals damaged by strong noise poses a significant challenge in emitter identification and countermeasure. Traditionally, weak signal detection methods based on chaos theory can handle situations with low signal-to-noise ratio, but most of them are developed for simple sin/cos waveform and cannot face PRBC–PAM signals commonly used in ultra-low altitude performance equipment. To address the issue, this article proposes a novel adaptive detection and estimation method utilizing the in-depth analysis of the Duffing oscillator’s behaviour and output characteristics. Firstly, the short-time Fourier transform (STFT) is used for chaotic state identification and ternary processing. Then, two novel approaches are proposed, including the adjusting zero value (AZV) method and the chaotic state ratio (CSR) method. The proposed weak signal detection system exhibits unique capability to adaptively modify its internal periodic driving force frequency, thus altering the difference frequency to estimate the signal parameters effectively. Furthermore, the accuracy of the proposed method is substantiated in carrier frequency estimation under varying SNR conditions through extensive experiments, demonstrating that the method maintains high precision in carrier frequency estimation and a low bit error rate in both the pseudorandom sequence and carrier frequency, even at an SNR of −30 dB.

A color image encryption algorithm based on a novel 4D hyperchaotic system and bit-level diffusion

As digital images are widely used in social media, medical, military and other fields, ensuring the privacy and security of image data has become a critical concern. Firstly, we propose a novel four-dimensional hyperchaotic system and validate that it exhibits a broad chaotic range, as demonstrated by bifurcation diagrams and Lyapunov exponent experiments. Additionally, simulated circuit diagrams verify the hardware feasibility of the proposed system. Secondly, we design a dynamic iterative scrambling (DIS) scheme that dynamically divides the image into multiple matrices for spatially indexed scrambling. Excellent substitution performance can be ensured by multiple iterations. In the diffusion stage, a multidirectional bit-level L-shaped (MDBL) scheme is proposed. Diffusion is conducted on the bit plane using a designed cross-multiplanar selection algorithm, which fuses the high and low bit planes, thereby enhancing the diffusion performance of MDBL. Thirdly, Based on the above concepts, a novel four-dimensional hyperchaotic system and an encryption algorithm based on bit-level diffusion are proposed. Finally, experimental results and security analyses demonstrate the effectiveness of the novel 4D hyperchaotic system and image encryption scheme. The proposed encryption scheme exhibits robust anti-interference capabilities and effectively safeguards image security.

Signal processing for enhancing railway communication by integrating deep learning and adaptive equalization techniques.

With the increasing amount of data in railway communication system, the conventional wireless high-frequency communication technology cannot meet the requirements of modern communication and needs to be improved. In order to meet the requirements of high-speed signal processing, a high-speed communication signal processing method based on visible light is developed and studied. This method combines the adaptive equalization algorithm with deep learning and is applied to railway communication signal processing. In this research, the wavelength division multiplexing (WDM) and orthogonal frequency division multiplexing (OFDM) techniques are used, and fuzzy C equalization algorithm is used to softly divide the received signals, reduce signal distortion and interference suppression. The experimental results showed that increasing the step size could reduce the equalization effect, while increasing the modulation parameter will increase the bit error rate. Through deep learning to achieve channel equalization, visible light communication could effectively mitigate multi-path transmission and reflection interference, thereby reducing the bit error rate to the level of 0.0001. Under various signal-to-noise ratios, the system using the channel compensation method achieved the lowest bit error rate. This outcome was achieved by implementing hybrid modulation scheme, including Wavelength division multiplexing (WDM) and direct current-biased optical orthogonal frequency division multiplexing (DCO-OFDM) techniques. It has been proved that this method can effectively reduce the channel distortion when the receiver is moving. This study develops a dependable communication system, which enhances signal recovery, reduces interference, and improves the quality and transmission efficiency of railway communication. The system has practical application value in the field of railway communication signal processing.

Real-Time Reconfigurable Radio Frequency Arbitrary-Waveform Generation via Temporal Pulse Shaping with a DPMZM and Multi-Tone Inputs

Benefitting from a large bandwidth and compact configuration, a time-domain pulse-shaping (TPS) system provides possibilities for generating broadband radio frequency (RF) arbitrary waveforms based on the Fourier transform relationship between the input–output waveform pair. However, limited by the relatively low sampling rate and bit resolution of an electronic arbitrary-waveform generator (EAWG), the diversity and fidelity of the output waveform as well as its reconfiguration rate are constrained. To remove the EAWG’s limitation and realize dynamic real-time reconfiguration of RF waveforms, we propose and demonstrate a novel approach of RF arbitrary-waveform generation based on an improved TPS system with an integrated dual parallel Mach–Zehnder modulator (DPMZM) and multi-tone inputs. By appropriately adjusting the DC bias voltages of DPMZM and the power values, as well as the center frequencies of the multi-tone inputs, any desired RF arbitrary waveform can be generated and reconfigured in real time. Proof-of-concept experiments on the generation of different user-defined waveforms with a sampling rate up to 27 GSa/s have been successfully carried out. Furthermore, the impact of modulation modes and higher-order dispersion on waveform fidelity is also discussed in detail.

Two-way 5G NR FSO-HCF-UWOC converged systems with R/G/B 3-wavelength and SLM-based beam-tracking scheme.

A two-way fifth-generation (5G) new radio (NR) free-space optical (FSO)-hollow-core fibre (HCF)-underwater wireless optical communication (UWOC) converged systems with a red/green/blue (R/G/B) 3-wavelengths and spatial light modulator (SLM)-based beam-tracking scheme is practically built. It is the first to practically build a two-way FSO-HCF-UWOC converged system with high-speed and long-distance optical wireless-wired-underwater wireless communication characteristics. It shows a 5G NR FSO-HCF-UWOC convergence from drone or buildings to undersea, using R/G/B 3-wavelengths and an SLM as a demonstration. The R/G/B 3-wavelengths are used to enhance the downstream and upstream aggregate transmission rates. An SLM with electrical comparator is used to adjust the laser beam and mitigate laser beam misalignment caused by drone movement or ocean flow. Over a hybrid of 1-km FSO, 10-m HCF, and 10.44-m ocean water-air-ocean water medium, downstream/upstream 5G-millimeter-wave (MMW) 9.1-Gb/s/24-GHz signals are transmitted with satisfactorily low bit error rates and error vector magnitudes, as well as distinct constellations. This demonstrated that the 5G NR FSO-HCF-UWOC converged system exhibits promising potential as it advances the scenario implemented by the 5G-MMW signals over FSO, HCF, and UWOC convergence, paving the way for high-speed and long-distance communications across diverse media.

Solution-Processed CsPbBr3 Perovskite Photodetectors for Cost-Efficient Underwater Wireless Optical Communication System.

Underwater wireless optical communication (UWOC) has attracted increasing attention due to its advantages in bandwidth, latency, interference resistance, and security. Photodetectors, as a crucial part of receivers, have been continuously developed with the great progress that has been made in advanced materials. Metal halide perovskites emerging as promising optoelectronic materials in the past decade have been used to fabricate various high-performance photodetectors. In this work, high-performance CsPbBr3 perovskite PDs were realized via solution process, with low noise, a high responsivity, and a fast response. Based on these perovskite PDs, a cost-efficient UWOC system was successfully demonstrated on an FPGA platform, achieving a data rate of 6.25 Mbps with a low bit error rate of 0.36%. Due to lower background noise under environment illumination, perovskite PDs exhibit better communication stability before reaching a data rate threshold; however, the BER increases rapidly due to the long fall time, resulting in difficulty in distinguishing switching signals. Reducing the fall time of perovskite PDs and using advanced coding techniques can help to further improve the performance of the UWOC system based on perovskite PDs. This work not only demonstrates the potential of perovskite PDs in the application of UWOC, but also improves the development of a cost-effective UWOC system based on FPGAs.

Farm Monitoring System with Drones and Optical Camera Communication.

Drones have been attracting significant attention in the field of agriculture. They can be used for various tasks such as spraying pesticides, monitoring pests, and assessing crop growth. Sensors are also widely used in agriculture to monitor environmental parameters such as soil moisture and temperature. Due to the high cost of communication infrastructure and radio-wave modules, the adoption of high-density sensing systems in agriculture is limited. To address this issue, we propose an agricultural sensor network system using drones and Optical Camera Communication (OCC). The idea is to transmit sensor data from LED panels mounted on sensor nodes and receive the data using a drone-mounted camera. This enables high-density sensing at low cost and can be deployed in areas with underdeveloped infrastructure and radio silence. We propose a trajectory control algorithm for the receiving drone to efficiently collect the sensor data. From computer simulations, we confirmed that the proposed algorithm reduces total flight time by 30% compared to a shortest-path algorithm. We also conducted a preliminary experiment at a leaf mustard farm in Kamitonda-cho, Wakayama, Japan, to demonstrate the effectiveness of the proposed system. We collected 5178 images of LED panels with a drone-mounted camera to train YOLOv5 for object detection. With simple On-Off Keying (OOK) modulation, we achieved sufficiently low bit error rates (BERs) under 10-3 in the real-world environment. The experimental results show that the proposed system is applicable for drone-based sensor data collection in agriculture.

Side and front fast imaging of solid and liquid fed ablative pulsed plasma thruster’s discharge

Ultra-fast camera imaging is used to capture temporal evolution of the plasma discharge in an ablative Pulsed Plasma Thruster (PPT) fueled with solid polytetrafluoroethylene (PTFE) and liquid perfluoropolyether (PFPE), with the goal of comparing the mechanism of the expelled mass acceleration and getting insight into the physics of the processes involved in the discharge maintenance and impulse bit production. The fast photos are taken from two viewpoints (non-simultaneously), directing camera parallel (side view) and perpendicular (front view) to the ablative surface of the propellants, and are correlated with the relevant phases of the discharge current. Side view images reveal the presence of two distinct exhaust fractions, velocities of which differ by an order of magnitude. The speed of the faster fraction is comparable with the median of the ionized particles velocity expelled by the thruster. The vividness of the slow propagating component of the ablated mass, which mostly corresponds to neutral particles (based on velocity estimation) and lower mass bit of PFPE shots hint towards better propellant utilization by a liquid-fed PPT. Front view images confirm stable localization of PFPE discharge, forced by design of the propellant supplying plenum, whereas PTFE discharge is characterized by irregular path that covers an area of the propellant surface in random. The last half-period of the discharge is accompanied by vortices near the cathode spots. They are supposedly formed by evaporated electrode’s material and their trajectories imply further recombination in collisions with the electrodes, making this part of evaporated copper undetectable for charged particles diagnostics.