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Item type:Publication, Access status: with files , Mikrometer-präzise Entfernungsbestimmung mit mehrkanaligen FMCW-Radaren basierend auf kommerziellen Sendeempfängern(2026); The present dissertation „Mikrometer-präzise Entfernungsbestimmung mit mehrkanaligen FMCW-Radaren basierend auf kommerziellen Sendeempfängern“ highlights the mathematical and technical foundations of high-precision FMCW-radars and in particular addresses limiting factors of the hardware, algorithms and environment. The designed demonstrator shows that accuracies better than 50 µm in range estimation and smaller than 0,5 degree in angle estimation can be achieved even with low-cost commercial hardware.Publicationtype: Doctoral Thesis41 23 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Near-field scattering phenomena in monostatic radar applications derived from physical opticsIn the context of radar, this article examines phenomena that occur in conditions where the physical extent of the target cannot be considered negligible compared to the range and, thus, far-field assumptions are violated. Based on physical optics principles, a transfer function of the radar channel between the antenna input and output power wave is derived for a monostatic configuration. The effects are studied using a circular metallic disk as an exemplary target. Exact and approximative expressions for the transfer function are derived incorporating the influence of the antenna radiation characteristic in addition. Measurements with targets of different sizes performed with horn as well as open-ended waveguide antennas at 24 and 61 GHz validate the phenomena of receive power level fading and nonlinear phase distortion.Publicationtype: Journal Article81 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Print! Place! Perform! : additively manufactured surface-mounted bandpass filter in X band(IEEE, 2024-06-01); ; ; ; The advance of 3D-printing technology over the last decade makes additive manufacturing not only attractive for rapid prototyping, but also provides it as a trendsetting approach to realize conventional as well as sophisticated functional microwave and millimeter-wave passive components. It has proven its ability to replicate conventional waveguides with a comparable electrical performance [1]. In this way, low-cost, lightweight waveguides with customized dimensions and shapes are realizable. Moreover, 3D printing enables the implementation of unconventional complex-shaped waveguide components, such as filters [2], [3], interconnects, or antennas [4], whose design is restricted by the engineer's creativity rather than by limitations of conventional fabrication techniques.Publicationtype: Journal Article59 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A modular 61 GHz vital sign sensing radar system for long-term clinical studiesThis paper presents a continuous wave (CW) radar system operating at the 61 GHz ISM (industrial, scientific and medical) band for contactless heart sound monitoring optimized for use in the clinical environment. Due to the high temporal resolution, this radar system allows an exact acquisition of the heart rate variability (HRV). It can be mounted under the bed for long-term monitoring without disturbing the patient. This measurement system is beneficial for e.g. seizure disorders that can be detected based on HRV changes. This paper presents the basic principle of the radar system and the optimizations necessary for clinical application. The measurement data extracted from a clinical study shows excellent agreement with an electrocardiography (ECG), thus validating the systems performance.Publicationtype: Conference Paper59 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Characterization of the influence of clothing and other materials on human vital sign sensing using mmWave radar(IEEE, 2023-09); ; ; ; In this work the effects of clothing and other fabric materials such as blankets on radar vital sign measurements are analyzed. The signal loss for six different materials at 61 GHz, 122 GHz and 175 GHz was measured using a modulated reflector on a test bench. In addition the effect of sweat in the fabrics at different concentrations was researched. It is shown, that thin fabrics show very little loss when they are dry but cause significant damping once they get wet. These results conclude, that the dampening effect of fabrics is not negligible for high frequency radar systems.Publicationtype: Conference Paper211 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Contactless in-bed movement in various scales classification with CW radarContinuous wave (CW) radar has been used to detect motions in various scenarios. In this paper, we first present a data-driven method to classify in-bed movement from various scales with CW radar. Data augmentation techniques are used to address the small sample size problem, resulting in a significant improvement of over 10% in accuracy. Three machine learning classifiers, namely random forest, k-nearest neighbor (k-NN), and multilayer perceptron (MLP), are evaluated, with random forest demonstrating the highest accuracy of 81.94% and relative improvement of 22.5% compared to k-NN. The movement sitting up from the bed can be classified with 97.5% accuracy. Additionally, the method can classify two types of movements involving only arm and leg movements, which are not visible to the radar, by detecting small-scale joint movements from the back with an accuracy of 74.8%.Publicationtype: Conference Paper24 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , The Design Process for Monolithically Manufactured Millimeter-Wave Antenna Arrays Using Stereolithography 3D PrintingThis paper presents a design flow enabling monolithic structures for milimeter-wave (mmW) applications utilizing cost-effective stereolithography (SLA). Particular emphasis is given to the design of complex shaped, phase-adjusted 3D waveguide interconnects that allow array elements to be arranged on any three-dimensional or two-dimensional grid. A horn antenna array at 61 GHz with 19 elements fed by a radial power divider is designed, manufactured, and validated. Simulations and measurements show excellent agreement.Publicationtype: Conference Paper84 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Antenna Phase Center Determination Using a Six-Port-Based Direction-of-Arrival Detector(2023-05-01); ; This article presents a novel technique to determine the antenna phase center. It relies on measuring the direction of arrival of the radiated field. Therefore, no access of the measurement equipment to the antenna under test is required. A direction-of-arrival detector is implemented that performs phase difference measurements in two orthogonal planes. Six-port interferometers are used for this purpose. By considering phase differences, the proposed method is robust against phase disturbances, which may occur at the feed of the antenna under test, e.g., due to flexible cables or rotary joints. Besides, impairments stemming from reflections in the measurement environment are addressed. Measurements of a K-band horn and a patch antenna in an anechoic chamber validate the approach. A single phase center is determined for each principle plane as well as for the three-dimensional main beam. In addition, the phase center locus is retrieved.Publicationtype: Journal Article116 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Catch Your Breath! Vital Sign Sensing With Radar(2023-02-02); ; ; ; Vital signs are most essential in medical care to evaluate a patient’s health situation. Today, electronic devices reliably measure the most important vital signs: heartbeat and respiration. Electrocardiography (ECG) measures the electrophysiological heart activity, while breathing can be detected with impedance pneumography (IP), which evaluates the periodic change of thorax impedance as we breathe in and out. While continuous monitoring of vital signs provides valuable medical information that can improve diagnostics, enable adaptive therapy, and generate new medical knowledge, there are also disadvantages. Medical procedures like ECG or IP require cables and electrodes, thus considerably reducing a patient’s mobility. Furthermore, electrodes cause skin irritation if applied too long, which often limits the continuous monitoring of vital signs to situations of absolute medical necessity.Publicationtype: Journal Article171 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Long-distance heart sound detection using 122 GHz CW radar with 3D printed high-gain antennasThis contribution presents a 122 GHz continuous wave (CW) radar system capable of detecting human heart sounds over a distance of at least five meters. A bidirectional long short-term memory (LSTM) neural network is used to extract precise inter-beat-intervals (IBIs) from the radar data. A small-scale human trial with two persons is carried out, and the resulting accuracy of the system is compared to a gold-standard electrocardiogram (ECG). The proposed system shows a mean absolute error of 5 ms and a standard deviation (SD) of 63 ms compared to the ECG IBIs.Publicationtype: Conference Paper268