Failure of joints can lead to structural collapse. It is vital to monitor joint stiffness during operation to prevent such failures. This paper proposes a novel method for the quality assessment of structural joints using coaxial correlation in 6D space. Coaxially placed 6D sensors on either side of the joint implemented by 3D accelerometers and 3D gyroscopes with wide frequency range, automatic synchronisation between the input signal and receivers and response signal averaging are presented. The root mean square (RMS) value from the obtained signals convolution is proposed as a measure of the similarity between two signals for monitoring joint degradation. The method’s effectiveness was tested on steel beam splice connection, where it was found that the RMS of convolution signals in 6D space showed a direct correlation between the calculated RMS value in X, Y, GX, and GY axes directions and the stiffness grades of the joint. The paper concludes that the nature of the RMS during the degradation of the joint may change in different axes, and wrongly chosen axes may lead to wrong conclusions regarding the state of the investigated joint, especially in the case of complex joints, so that the measurements in 6D provide higher reliability of the result interpretation.

This paper presents a comparative evaluation of a wave union (WU) time-to-digital converter (TDC) implemented on two Microchip flash-based field-programmable gate arrays (FPGAs): the radiation-tolerant RTG4 (RT4G150-1CG) and the low-power SmartFusion2 (M2S150TS-1FCG1152). Both implementations use an identical VHDL architecture consisting of parallel tapped delay lines (TDLs) each with a WU pattern generator, edge-coded logic encoding, and real-time statistical bin width calibration. Single-shot precision (SSP), defined as the standard deviation of consecutive period measurements derived from calibrated timestamps, is evaluated across four independent input channels. Measurements are performed at five input frequencies (1, 2, 10, 20, and 40 MHz) and six ambient temperatures ranging from 20 °C to 60 °C. At a low input frequency, the RTG4 implementation achieves a mean SSP of 6.97 ps, while IGLOO2 yields 10.12 ps under identical conditions. As the input frequency increases, the SSP of both platforms decreases and converges to approximately 4.5 ps. However, at elevated temperatures, both devices experience observable degradation in SSP. To quantify thermal robustness, a thermal sensitivity coefficient (TSC) is introduced, defined as the rate of SSP variation with temperature. The results show that the same WU TDC core implemented on a space-graded FPGA exhibits improved thermal stability and reduced channel-to-channel variance compared to its equivalent on a commercial platform.

With the growing popularity of timber structures, the requirement for reliable and non-destructive methods to assess the quality and condition of structural joints becomes increasingly essential. A novel coaxial correlations method is investigated to assess the degradation of panel-to-panel moment joints in timber structures. The method involves analysing the response data obtained from accelerometers placed on both sides of the joint and comparing the readings to evaluate the joint’s condition. A specific joint solution to simulate the degradation of the moment joint in laboratory conditions is selected based on its simplicity and the ease with which its degradation can be simulated. The joint consists of angle brackets joined with timber screws and bolts to plywood panels. Gradually unscrewing the timber screws reduces the joint’s stiffness to simulate wear and tear over time. The experimental setup includes static loading and finite element modelling (FEM) to determine the rotational stiffness of the investigated joint at each degradation level. A dynamic experiment using vibration loading with sweep signal in the frequency range of 10 Hz to 2000 Hz is conducted to assess the quality of the joint. The conducted research provides valuable insights into the behaviour of timber panel-to-panel connections. The findings highlight the relationship between joint stiffness, vertical displacements, and the proposed dimensionless parameter, volume root mean square value (RMS_vol), which offers a more comprehensive assessment of the joint’s condition in three spatial directions. As a result of the research, it has been established that, in the case of linear-type connections, unlike point-type joints, there is a possibility of signal scattering, so it is recommended that power comparisons and evaluations of the response signals from both accelerometers at the initial stage of applying the coaxial correlations method are performed.

This work presents an experimental evaluation of a high-speed analog-to-digital conversion method based on passive reference waveform crossings combined with time-to-digital converter (TDC) time-tagging. Unlike conventional level-crossing event-driven analog-to-digital converters (ADCs) that require dynamically updated digital-to-analog converters (DACs), the proposed architecture compares the input waveform against a broadband periodic sampling function without active threshold control. Crossing instants are detected by a high-speed comparator and converted into rising and falling edge timestamps using a multi-channel TDC. A commercial ScioSense GPX2-based time-tagger with 30 ps single-shot precision was used for validation. A range of test signals—including 5 MHz sine, sawtooth, damped sine, and frequency-modulated chirp waveforms—were acquired using triangular, sinusoidal, and sawtooth sampling functions. Stroboscopic sampling was demonstrated using reference frequencies lower than the signal of interest, enabling effective undersampling of periodic radio frequency (RF) waveforms. The method achieved effective bandwidths approaching 100 MHz, with amplitude reconstruction errors of 0.05–0.30 RMS for sinusoidal signals and 0.15–0.40 RMS for sawtooth signals. Timing jitter showed strong dependence on the relative slope between the acquired waveform and sampling function: steep regions produced jitter near 5 ns, while shallow regions exhibited jitter up to 20 ns. The study has several limitations, including the bandwidth and dead-time constraints of the commercial TDC, the finite slew rate and noise of the comparator front-end, and the limited frequency range of the generated sampling functions. These factors influence the achievable timing precision and reconstruction accuracy, especially in low-gradient signal regions. Overall, the passive waveform-crossing method demonstrates strong potential for wideband, sparse, and rapidly varying signals, with natural scalability to multi-channel systems. Potential application domains include RF acquisition, ultra-wideband (UWB) radar, integrated sensing and communication (ISAC) systems, high-speed instrumentation, and wideband timed antenna arrays.

Integrated sensing and communications (ISAC) is a key enabling technology for 6G networks, as it unifies radar sensing and data transmission within a shared infrastructure. Analog radio-over-fiber (ARoF) has emerged as a crucial technology for extending radar coverage and enabling distributed radar sensing. By incorporating pulse position modulation (PPM), it is possible to simultaneously measure the target’s range and transmit data, thereby increasing the energy efficiency of such systems. In this research, we present a novel ARoF-based ISAC-capable pulse radar system that features a custom-built PPM modulator employing a digital-to-time converter, and a high-accuracy time tagger as the demodulator, allowing for pulse time of arrival measurements with an root mean square accuracy up to 1.5 ps. The experimental results show a 5 Mbit/s data transmission along with a bit error ratio less than 5.86 × 10⁻⁷ at a 95% confidence level, using a PPM slot duration of 750 ps in an optical system featuring more than 40 km of single-mode optical fiber and a simultaneous range measurement with error less than 0.86 cm. In addition to ISAC exploration, the impact of fiber-induced chromatic dispersion on the PPM signal is studied, and the system is validated in an outdoor environment with a moving target.

Promocijas darbā, kas sagatavots kā publikāciju kopa, izstrādāta un eksperimentāli validēta sinhronizēta daudzdimensionāla diagnostikas pieeja konstrukciju savienojumu integritātes novērtēšanai. Tā apvieno trīsdimensiju paātrinājuma mērījumu pārus savienojuma pretējās pusēs, kontrolētu daudzdimensionālu ierosmi, kas balstīta laika reversijas viļņu fokusēšanas principos, sinhronizētus ierosmes un mērīšanas kanālus, katras ass koherences novērtēšanu un virzienisko indikatoru apvienošanu vienā skalārā metrikā. Pieeja validēta, astoņos posmos samazinot skrūves pievilkšanas momentu.