| 1. |
- Fhager, Lars Ohlsson, et al.
(författare)
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Pulsed Millimeter Wave Radar for Hand Gesture Sensing and Classification
- 2019
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Ingår i: IEEE Sensors Letters. - 2475-1472. ; 3:12
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Tidskriftsartikel (refereegranskat)abstract
- A pulsed millimeter wave radar operating at a frame rate of 144 Hz is utilized to record 2160 scattering signatures of 12 generic hand gestures. Gesture recognition is achieved by machine learning, utilizing transfer learning on a pretrained convolutional neural network. This yields excellent classification results with a validation accuracy of 99.5%, based on a 60% training versus 40% validation split. The corresponding confusion matrix is also presented, showing a high level of classification orthogonality between the tested gestures. This is the first demonstration where data from a pulsed millimeter wave radar is used for gesture recognition by machine learning. It proves that the range-time envelope representation of high frame-rate data from a pulsed radar is suitable for hand gesture recognition. Further improvements are expected for more complex detection schemes and tailored neural networks.
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| 2. |
- Heunisch, Sebastian, et al.
(författare)
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A phase-correlated duo-binary waveform generation technique for millimeter-wave radar pulses
- 2020
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Ingår i: International Journal of Circuit Theory and Applications. - : Wiley. - 0098-9886 .- 1097-007X. ; 48:1, s. 103-114
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Tidskriftsartikel (refereegranskat)abstract
- We propose a technique for generating millimeter-wave radar waveforms using edge-triggered pulse generator circuits. By synchronizing the chip rate to the oscillation frequency of a binary control signal, a phase shift is introduced in the generated pulses. This way, the millimeter-wave signal can be phase-modulated without the need of additional circuit elements. We show that high-resolution radar waveforms with low range side lobes can be generated with this technique. Using brute-force optimization, we evaluate all possible sequences up to a sequence length of 25 chips and identify optimal waveforms for each length. Optimal sequences with the energy centered at zero delay and side lobes not exceeding unity are presented. The optimized waveforms are measured and verified using an in-house resonant tunneling diode (RTD) metal-oxide-semiconductor field-effect transistor (MOSFET) pulse generator. The matched filter response of the optimal waveforms is reproduced closely in the measurements. The results enable increased sensitivity in radar systems using coherent millimeter-wave pulse generators for low power applications, as for instance, radar gesture recognition in handheld devices. Using pulsed millimeter-wave radar systems with low duty cycles, continuously running oscillators can be avoided and systems with ultra-low power consumption are possible.
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| 3. |
- Heunisch, Sebastian, et al.
(författare)
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Clutter analysis in a time-domain millimeter-wave reflectometry setup
- 2018
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Ingår i: 12th European Conference on Antennas and Propagation (EuCAP 2018). - : Institution of Engineering and Technology. - 9781785618161
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Konferensbidrag (refereegranskat)abstract
- In this work, we study the clutter and multi-path propagation in a time-domain millimeter-wave reflectometry setup, used for material characterization or short-range imaging. The signal energy and fidelity factor of the different reflection components is analyzed in dependence of the distance from the target. Due to the change in pulse distortion in the multi-path components, the system impulse response is dependent on the target position. The principal reflection from the target on the other hand is only influenced by the path loss. By coherent superposition we are able to separate the target reflection from the static system clutter and multi-path reflections in the setup.
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| 4. |
- Heunisch, Sebastian, et al.
(författare)
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Millimeter-Wave Pulse Radar Scattering Measurements on the Human Hand
- 2019
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Ingår i: IEEE Antennas and Wireless Propagation Letters. - 1536-1225. ; 18:7, s. 1377-1380
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the backscattering of low-power millimeter-wave pulses (wavelets) on the human hand in order to determine the detection limit of scattering features. Using an in-house wavelet radar setup with a nominal spatial resolution of 2.29 cm, we measure a hand in three different postures: a flat hand, a fist, and a hand with raised index finger. For the latter, we are able to resolve backscattering from at least two different scattering centers, attributed to the heel of the hand and the finger. The effective radar cross section in the measurements was in the range from -29.5 to -35.1 dBsm. We demonstrate that detecting scattering features from the hand with an equivalent isotropically radiated power spectral density of -68.5 dBm/MHz is possible. This shows that, compared to most conventional radar systems operating close to the regulatory emission limits (13 dBm/MHz), the energy of the transmitted waveform can be significantly reduced. The result shows that low-power radar systems for gesture recognition are feasible using pulsed systems with ultrashort pulses and low duty cycles. This is key for integration in battery-powered devices.
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| 5. |
- Heunisch, Sebastian, et al.
(författare)
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Pulse-Distortion Analysis for Millimeter-Wave Time-Domain Material Identification
- 2018
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Ingår i: 2018 48th European Microwave Conference, EuMC 2018. - 9782874870514 ; , s. 572-575
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Konferensbidrag (refereegranskat)abstract
- Analyzing the frequency dependent dielectric properties can be used to identify and distinguish materials in biomedical instruments. In the millimeter-wave range, the dielectric properties of biological tissues are mainly determined by their water content. For instance, it has been shown, that cancer cells have a lower water content than healthy skin cells, resulting in a significant dielectric contrast between them. In this work, we analyze the pulse distortion observed in measurements of the millimeter-wave reflection of water and porcine skin. We propose to use the distortion caused by the frequency dependent reflection coefficient at the interface of a material as a feature for identification. Using a simplified model for the reflection coefficient of the material under test, we simulate the distortion caused by the frequency dispersion. In simulation as well as in measurement, we observe different startup transients depending on the dispersion properties of a material under test. The startup behavior can therefore be used as feature, to directly identify dispersive materials in the time domain.
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| 6. |
- Heunisch, Sebastian, et al.
(författare)
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Reflection of Coherent Millimeter-Wave Wavelets on Dispersive Materials : A Study on Porcine Skin
- 2018
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Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480. ; 66:4, s. 2047-2054
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Tidskriftsartikel (refereegranskat)abstract
- Differences in the material reflection are required for any contrast in microwave- and millimeter-wave (mm-wave) imaging systems. Therefore, the dielectric properties, which determine the reflection of materials, need to be characterized. The characterization of skin and other biological tissue is, therefore, necessary, to apply imaging systems for instance in cancer diagnosis. In this paper, short, coherent mm-wave pulses (wavelets) are generated and their reflection on dispersive materials is studied. The reflections of wavelets on porcine skin and water are examined in time and frequency domain. A first-order Debye model is fitted to the reflection coefficient in frequency domain to quantify material dispersion. The frequency-dependent reflection on dispersive materials causes a distortion of the wavelets in the time domain. The startup behavior of the pulses is examined by simulation and measurements. The rise time of the pulses is identified as a feature in time domain for wavelets reflected on dispersive media. Together with other features characteristic for a pulse, for instance the wavelet amplitude, this enables identification of dispersive materials by reflectometry measurements, making it suitable for applications in mm-wave imaging systems.
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