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Item type:Publication, Access status: with files , Simulation framework for the evaluation of the radar channel transfer function in the near field of electrically large targets(Cambridge University Press, 2026-10-05); ; ; ; A simulation framework to evaluate the radar channel transfer function in the near field of electrically large targets is presented in this article. The framework is based on the concepts known from physical optics adapted to the near-field conditions. The impact of the radar antenna characteristics on the scattering, which is non-negligible in the target near field, is incorporated by means of the antenna’s far-field radiation patterns. The inputs of the simulation framework are an STL-file-based model of the target and the gain and phase patterns of the antenna. The required sampling density of the target surface is examined in the context of convergence. The framework accounts for absorption effects due to dielectric or ohmic losses. Because the framework relies on direct evaluations without the need to solve equations, it exhibits a low computational effort, leading to fast computations. The applicability of the simulation framework is validated by measurements with different antennas at 24 and 61 GHz.Publicationtype: Journal Article37 185 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A novel concept for a wake-up receiver for LoRa communication with improved selectivityThis work presents a novel approach for the implementation of a wake-up receiver for LoRa communication. It is designed to exploit the LoRa modulation based on chirp spread spectrum and is inherently less susceptible to false wakeups caused by interfering signals. The theory of the concept is presented indicating key parameters. For validation, a proof-ofconcept implementation is developed with exemplary measurement results.Publicationtype: Conference Paper35 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Determination of the radar channel transfer matrix in the near field of electrically large targets based on physical optics principlesThis contribution deals with the determination of the radar channel transfer matrix in short-range radar applications. In these, the radar antennas are often located in the near field of an electrically large target, in which the scattering properties, in contrast to far-field relationships, depend on distance as well as the antenna. Based on physical optics and the antenna radiation pattern, a bistatic complex-valued transfer function between the feed of a transmit antenna and the output port of a receive antenna is derived. For multiple antennas, it extends to a channel matrix, which allows to predict the radar response of multiple-input multiple-output (MIMO) systems as well as antenna arrays. Measurements of the channel matrix in the case of a disk target conducted with horn and open-ended waveguide antennas at 24 GHz prove the validity of the proposed approach. It accurately predicts near-field effects such as power level fading and nonlinear phase distortion for MIMO radar configurations.Publicationtype: Conference Paper30 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Open sync board – an open-source tool for hardware synchronization of multimodal physiological sensor setups(University of Western Ontario, Western Libraries, 2026-05-01); ; ; The fusion of multimodal sensor data gains increasing importance in medical and psychological research. In particular, the analysis of multi-modal data contributes to a broader understanding of human well-being. When experimenting with different sensing modalities, precise synchronization of recorded data is a crucial problem that needs to be addressed. We have developed a hardware-based solution capable of synchronizing up to seven arbitrary measurement modalities. These modalities can be mounted to a PCB with various connectors to be either triggered synchronously or receive simultaneous synchronization signals. In the latter case, data can be aligned after the measurement. All PCB outputs are galvanically decoupled to avoid interference and ensure safe usage in human-centered research. In this project, we put particular emphasis on flexibility, high usability, and accuracy. Thus, different synchronization signal options are provided to suit short- as well as long-term measurements. Settings can be configured easily with an accompanying graphical user interface. Additionally, we ensured a high precision of the output signals is ensured with an estimated maximum delay of 125 μs between the output ports. This enables sub-sample synchronization accuracy for sensors with up to 8 kHz sampling rate.Publicationtype: Journal Article12 6 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , A novel differential incoherent heterodyne continuous-wave radar receiver architecture with increased phase sensitivity(IEEE, 2026-02); ; ; ; This work presents a novel heterodyne radar transceiver architecture based on two separate, incoherent radio frequency (RF) sources. Unlike conventional continuous-wave (CW) radar systems, the proposed approach measures the square of the channel transfer function, resulting in doubled phase sensitivity. This enhancement arises from a di erential evaluation of the downconverted intermediate-frequency (IF) signals, which enables precise tracking of phase changes without requiring phase-locked local oscillators. The associated signal-processing and calibration methods are derived, allowing for accurate reconstruction of the dynamic target response, even in the presence of static reflections and without needing knowledge of the calibration target’s absolute position. Additionally, the e ect of oscillator phase noise is evaluated. Experimental validation using high-precision linear motion confirms that the system accurately tracks target displacement and delivers results comparable to those obtained with a commercial vector network analyzer (VNA). By eliminating the need for RF phase synchronization between transceivers, the architecture significantly reduces hardware complexity and is well-suited for integration and miniaturization. Although demonstrated with a single transceiver pair, the method scales naturally to multichannel configurations, enabling low-complexity multiple-input–multiple-output (MIMO) radar systems with enhanced sensitivity.Publicationtype: Journal Article53 40 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Contactless sleep staging with Radar: a transfer learning approach(IEEE, 2026); ; ; ; Krebber, Carlos HerreraAccurate sleep monitoring is essential to assess sleep quality and diagnose sleep disorders. Although sleep laboratories provide precise assessments, they are expensive, labor-intensive, and unsuitable for long-term or large-scale monitoring. Radar-based sensing offers a fully contactless alternative, enabling unobtrusive real-world sleep monitoring. However, the lack of large, labeled datasets has limited the development of robust sleep stage classification models. We address this with transfer learning to improve classification accuracy and generalization to unseen participants within the radar cohort. An LSTM model was pretrained on movement, HRV, and respiratory features from the MESA Sleep dataset (>1,100 participants) and fine-tuned using radar data from 44 synchronized polysomnography recordings. Transfer learning increased the Matthews Correlation Coefficient from 0.25 to 0.47 (five-class staging), particularly for Wake, N3, and REM sleep. Future work should explore domain-adaptation across modalities and cohorts. Our results highlight the potential of radar-based sleep analysis for scalable, contactless long-term sleep monitoring.Publicationtype: Journal Article32 48 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Analysis of the radar channel and its variability in vital-sign sensing applicationsIn millimeter-wave (mmWave) radar-based vital-sign sensing, the radar sensor usually operates in the radiative near field of the target, which is the human body. Therefore, in contrast to far-field conditions, scattering cannot be quantified by a target-inherent radar cross section (RCS) as it strongly depends on the relative position and directivity of the radar antenna. To investigate the resulting consequences for the application, this article examines the radar channel transfer function, i.e., the ratio between the power waves feeding and being received by the antenna, with particular focus on its variability due to changes of the relative antenna position. The analysis is supported by a physical-optics-based simulation model tailored to practical circumstances. Measurements at 24 GHz and 61 GHz using antennas with different directivities and a human-like mannequin as a target confirm the simulative predictions. The radar channel suffers from significant variations, e.g., displacing the antenna by less than 1mm can cause a 30-dB receive power drop. A statistical analysis comprehensively evaluates the radar channel variability and clarifies the challenges for the application that stem from target near-field effects.Publicationtype: Journal Article150 36 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , PEPbench - Open, reproducible, and systematic benchmarking of automated pre-ejection period extraction algorithmsThe pre-ejection period (PEP) is a widely used cardiac parameter in psychophysiology that reflects the duration between the onset of ventricular depolarization and the opening of the aortic valve. PEP is often used as a marker of cardiac sympathetic nervous system (SNS) activity, particularly in within-subject comparisons under similar hemodynamic conditions. While many algorithms for automated PEP extraction from electrocardiography (ECG) and impedance cardiography (ICG) signals (more precisely, its first derivative, dZ/dt) have been proposed in literature, they have not been systematically benchmarked. This lack of standardized algorithm comparisons originates from the absence of open-source algorithms and annotated datasets for evaluating PEP extraction algorithms. To address this issue, we introduce PEPbench, an open-source Python package with different Q-peak and B-point detection algorithms from literature that can be combined to create comprehensive PEP extraction pipelines, and a standardized framework for evaluating PEP extraction algorithms. We use PEPbench to systematically compare 108 different algorithm combinations. All combinations are evaluated on two datasets with manually annotated Q-peaks and B-points, which we make publicly available as the first datasets with reference PEP annotations. Our results show that the algorithms can differ vastly in their performance and that B-point detection algorithms introduce a considerable amount of error. Thus, we suggest that automated PEP extraction algorithms should be used with caution on a beat-to-beat level as their error rates are relatively high. This highlights the need for open and reproducible benchmarking frameworks for PEP extraction algorithms to improve the quality of research findings in the field of psychophysiology. With PEPbench, we aim to take a first step toward this goal and encourage other researchers to engage in the evaluation of PEP extraction algorithms by contributing algorithms, data, and annotations. We hope to establish a community-driven platform, fostering innovation and collaboration in the field of psychophysiology and beyond.Publicationtype: Journal Article45 23 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Fast determination of the monostatic radar channel in the near-field of electrically large targetsThis contribution addresses the determination of the radar channel when operating in the near field of electrically large targets, which is a common scenario in modern short-range radar applications such as vital-sign sensing. With the focus on computational simplicity and the inclusion of near-field scattering phenomena, the proposed approach combines physical optics (PO) concepts and the far-field radiation pattern of the radar antenna to determine both amplitude and phase of the receive signal. The numerical implementation relies on basic scalar evaluations. The agreement between the simulated and measured radar channel of a metallized human-body-shaped object at 24 GHz and 61 GHz proves the effectiveness of the approach.Publicationtype: Conference Paper19 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Fast determination of the monostatic radar channel in the near-field of electrically large targetsThis contribution addresses the determination of the radar channel when operating in the near field of electrically large targets, which is a common scenario in modern short-range radar applications such as vital-sign sensing. With the focus on computational simplicity and the inclusion of near-field scattering phenomena, the proposed approach combines physical optics (PO) concepts and the far-field radiation pattern of the radar antenna to determine both amplitude and phase of the receive signal. The numerical implementation relies on basic scalar evaluations. The agreement between the simulated and measured radar channel of a metallized human-body-shaped object at 24 GHz and 61 GHz proves the effectiveness of the approach.Publicationtype: Conference Paper74