Complex propagation channels in indoor environments introduce considerable clutter and distortion... more Complex propagation channels in indoor environments introduce considerable clutter and distortions to frontal radar images. Autoencoders, when provided with corrupted and corresponding clean images during training, can learn how to mitigate clutter in these images during testing. The main advantage is that an analytical framework of the channel is not required. On the other hand, the algorithm relies on the availability of a large database of correctly labelled training data - the target scenarios in cluttered environments must be exactly replicated in free space. We propose to augment the conventional denoising autoencoder with sparsity based multiple layer representations to handle the labelling mismatch errors. We hypothesize that the deeper representations with sparsity constraints will enable extraction of more fundamental features of the images. Our radar data consists of measurements made with a wideband RF imaging sensor called the Walabot. Our algorithm improves upon the conventional autoencoder in terms of performance with respect to signal to clutter and signal to noise ratios, labelling mismatch errors and computational time during testing.
Directivity of an antenna is a figure of merit which shows how effective an antenna is at transmi... more Directivity of an antenna is a figure of merit which shows how effective an antenna is at transmitting / receiving in a desired direction. A highly directive antenna is useful for applications such as satellite communications and radar systems. Directivity is usually achieved using either large antenna apertures or array systems comprising lots of antenna elements. More recently, metamaterials have been investigated for improving the directivity of different types of antennas such as linear wire antennas, patch antennas and horn antennas. Electromagnetic metamaterials are manmade materials which have unusual fundamental properties not readily available in nature. In this thesis, we investigate the possibility of improving the directivity of a slot antenna with a metamaterial substrate. We consider a two-dimensional metal waveguide with a slot and a metamaterial substrate with a point source excitation inside the substrate. The metamaterial substrate is modeled as a Debye medium with...
2020 IEEE International Radar Conference (RADAR), 2020
Fabry Perot cavity (FPC) antennas have been extensively researched and developed for their reduce... more Fabry Perot cavity (FPC) antennas have been extensively researched and developed for their reduced fabrication complexity and cost as compared to other high gain planar antennas. Recently, the partially reflecting surfaces (PRS) of the FPC antennas have been engineered with metasurfaces with desirable electromagnetic properties in order to reduce their profile dimensions. These surfaces usually consist of an array of unit cells that are skillfully designed in order to obtain high bandwidth or desired polarization. In this paper, we have considered a unit cell design of a rectangular loop with a diagonal - with an objective of achieving circular polarization. Then we introduced a new design parameter in the form of peripheral roughness in the edge of each of the unit cells. We demonstrate that the incorporation of the new design feature in the unit cell results in an enhancement of the return loss bandwidth to 202.8 MHz (8.9%) and gain to 9.5 dBi along with a reduced axial ratio of 4...
We present a modified harmonic radar architecture for distinguishing between two dynamic targets ... more We present a modified harmonic radar architecture for distinguishing between two dynamic targets - a friend and a foe - in the radar propagation channel. The main application for our proposed radar is for search and rescue missions or surveillance. The radar consists of a narrowband sinusoidal transmitter and a dual channel receiver, wherein the primary and secondary channels are tuned to the fundamental transmitted frequency and its second order harmonic respectively. The radar scattered returns from both friend and foe are gathered at the primary receiver while the secondary receiver gathers the second order harmonics emanating from the harmonic radar tag on the friend. The secondary receiver data are used to train unique data driven dictionaries that characterize the motion of the friend. These dictionaries are used to disaggregate and reconstruct the returns from the friend and foe in the primary linear radar data. We validate our proposed radar concept on simulated radar data of a friend and foe and demonstrate that the radar signatures from the reconstructed radar data are qualitatively and quantitatively similar to the ground truth radar signatures from the friend and foe.
We present a framework for simulating realistic inverse synthetic aperture radar images of automo... more We present a framework for simulating realistic inverse synthetic aperture radar images of automotive targets at millimeter wave frequencies. The model incorporates radar scattering phenomenology of commonly found vehicles along with range-Doppler based clutter and receiver noise. These images provide insights into the physical dimensions of the target, the number of wheels and the trajectory undertaken by the target. The model is experimentally validated with measurement data gathered from an automotive radar. The images from the simulation database are subsequently classified using both traditional machine learning techniques as well as deep neural networks based on transfer learning. We show that the ISAR images offer a classification accuracy above 90% and are robust to both noise and clutter.
Narrowband and broadband indoor radar images significantly deteriorate in the presence of target ... more Narrowband and broadband indoor radar images significantly deteriorate in the presence of target dependent and independent static and dynamic clutter arising from walls. A stacked and sparse denoising autoencoder (StackedSDAE) is proposed for mitigating wall clutter in indoor radar images. The algorithm relies on the availability of clean images and corresponding noisy images during training and requires no additional information regarding the wall characteristics. The algorithm is evaluated on simulated Doppler-time spectrograms and high range resolution profiles generated for diverse radar frequencies and wall characteristics in around-the-corner radar (ACR) scenarios. Additional experiments are performed on range-enhanced frontal images generated from measurements gathered from a wideband RF imaging sensor. The results from the experiments show that the StackedSDAE successfully reconstructs images that closely resemble those that would be obtained in free space conditions. Furthe...
Doppler spectrogram analysis of the human gait is a useful tool for discriminating various microD... more Doppler spectrogram analysis of the human gait is a useful tool for discriminating various microDoppler tracks due to the movements of different body parts. A data-dependent algorithm, namely the short-time iterative adaptive approach, is used to obtain a more accurate spectrogram than the one provided by the conventional short-time Fourier transform-based approaches. The performance of the approaches is demonstrated and contrasted using both simulated and measured human gait data.
Highly directive antennas are useful in applications such as satellite communications, radar syst... more Highly directive antennas are useful in applications such as satellite communications, radar systems and biomedical applications. Directivity is usually achieved using either large antenna apertures or array systems comprising many antenna elements. In recent times, metamaterials have been investigated for improving the directivity of different types of antennas such as linear wire antennas, patch antennas, horn antennas, slot antennas etc. In this work, we investigate the possibility of improving the directivity of a slot antenna with a metamaterial substrate and a source excitation within the substrate. The metamaterial substrate is modelled as a Debye medium with dispersive permittivity and permeability. The refractive index of the substrate is (a) negative at frequencies below the plasma frequency, (b) zero at the plasma frequency, (c) positive at frequencies above the plasma frequency. We demonstrate a directive 3D (three-dimensional) two-slot antenna structure with a near zero...
Micro-Doppler signatures of dynamic indoor targets (such as humans and fans) serve as a useful to... more Micro-Doppler signatures of dynamic indoor targets (such as humans and fans) serve as a useful tool for classification. However, all the current classification methods are limited by the assumption that only a single target is present in the channel. In this work, we propose a method to classify multiple targets that are simultaneously present in the channel on the basis of a single channel source separation technique. We apply sparse coding based dictionary learning (DL) algorithms for disaggregating micro-Doppler returns from multiple targets into its constituent signals. The classification is subsequently carried out on the disaggregated signals. We have tested the performance of the proposed algorithm on simulated human and fan data.
Harmonic radar technology has been researched and developed for studying the foraging behaviour o... more Harmonic radar technology has been researched and developed for studying the foraging behaviour of honey bees. This work presents the development of a working prototype of a narrow-band harmonic radar system, at 2.5/5GHz, using off-the-shelf components to detect the presence of Indian honey bees. Based on empirical tests on the tag, we estimate the radar probability of detection and probability of false alarms as 88% and 0.3% respectively. The maximum detectable range for a monostatic configuration of the radar is 3.84 m.
Energy conservation is a key factor towards long term energy sustainability. Real-time end user e... more Energy conservation is a key factor towards long term energy sustainability. Real-time end user energy feedback, using disaggregated electric load composition, can play a pivotal role in motivating consumers towards energy conservation. Recent works have explored using high frequency conducted electromagnetic interference (EMI) on power lines as a single point sensing parameter for monitoring common home appliances. However, key questions regarding the reliability and feasibility of using EMI signatures for non-intrusive load monitoring over multiple appliances across different sensing paradigms remain unanswered. This work presents some of the key challenges towards using EMI as a unique and time invariant feature for load disaggregation. In-depth empirical evaluations of a large number of appliances in different sensing configurations are carried out, in both laboratory and real world settings. Insights into the effects of external parameters such as line impedance, background noi...
Complex propagation channels in indoor environments introduce considerable clutter and distortion... more Complex propagation channels in indoor environments introduce considerable clutter and distortions to frontal radar images. Autoencoders, when provided with corrupted and corresponding clean images during training, can learn how to mitigate clutter in these images during testing. The main advantage is that an analytical framework of the channel is not required. On the other hand, the algorithm relies on the availability of a large database of correctly labelled training data - the target scenarios in cluttered environments must be exactly replicated in free space. We propose to augment the conventional denoising autoencoder with sparsity based multiple layer representations to handle the labelling mismatch errors. We hypothesize that the deeper representations with sparsity constraints will enable extraction of more fundamental features of the images. Our radar data consists of measurements made with a wideband RF imaging sensor called the Walabot. Our algorithm improves upon the conventional autoencoder in terms of performance with respect to signal to clutter and signal to noise ratios, labelling mismatch errors and computational time during testing.
Directivity of an antenna is a figure of merit which shows how effective an antenna is at transmi... more Directivity of an antenna is a figure of merit which shows how effective an antenna is at transmitting / receiving in a desired direction. A highly directive antenna is useful for applications such as satellite communications and radar systems. Directivity is usually achieved using either large antenna apertures or array systems comprising lots of antenna elements. More recently, metamaterials have been investigated for improving the directivity of different types of antennas such as linear wire antennas, patch antennas and horn antennas. Electromagnetic metamaterials are manmade materials which have unusual fundamental properties not readily available in nature. In this thesis, we investigate the possibility of improving the directivity of a slot antenna with a metamaterial substrate. We consider a two-dimensional metal waveguide with a slot and a metamaterial substrate with a point source excitation inside the substrate. The metamaterial substrate is modeled as a Debye medium with...
2020 IEEE International Radar Conference (RADAR), 2020
Fabry Perot cavity (FPC) antennas have been extensively researched and developed for their reduce... more Fabry Perot cavity (FPC) antennas have been extensively researched and developed for their reduced fabrication complexity and cost as compared to other high gain planar antennas. Recently, the partially reflecting surfaces (PRS) of the FPC antennas have been engineered with metasurfaces with desirable electromagnetic properties in order to reduce their profile dimensions. These surfaces usually consist of an array of unit cells that are skillfully designed in order to obtain high bandwidth or desired polarization. In this paper, we have considered a unit cell design of a rectangular loop with a diagonal - with an objective of achieving circular polarization. Then we introduced a new design parameter in the form of peripheral roughness in the edge of each of the unit cells. We demonstrate that the incorporation of the new design feature in the unit cell results in an enhancement of the return loss bandwidth to 202.8 MHz (8.9%) and gain to 9.5 dBi along with a reduced axial ratio of 4...
We present a modified harmonic radar architecture for distinguishing between two dynamic targets ... more We present a modified harmonic radar architecture for distinguishing between two dynamic targets - a friend and a foe - in the radar propagation channel. The main application for our proposed radar is for search and rescue missions or surveillance. The radar consists of a narrowband sinusoidal transmitter and a dual channel receiver, wherein the primary and secondary channels are tuned to the fundamental transmitted frequency and its second order harmonic respectively. The radar scattered returns from both friend and foe are gathered at the primary receiver while the secondary receiver gathers the second order harmonics emanating from the harmonic radar tag on the friend. The secondary receiver data are used to train unique data driven dictionaries that characterize the motion of the friend. These dictionaries are used to disaggregate and reconstruct the returns from the friend and foe in the primary linear radar data. We validate our proposed radar concept on simulated radar data of a friend and foe and demonstrate that the radar signatures from the reconstructed radar data are qualitatively and quantitatively similar to the ground truth radar signatures from the friend and foe.
We present a framework for simulating realistic inverse synthetic aperture radar images of automo... more We present a framework for simulating realistic inverse synthetic aperture radar images of automotive targets at millimeter wave frequencies. The model incorporates radar scattering phenomenology of commonly found vehicles along with range-Doppler based clutter and receiver noise. These images provide insights into the physical dimensions of the target, the number of wheels and the trajectory undertaken by the target. The model is experimentally validated with measurement data gathered from an automotive radar. The images from the simulation database are subsequently classified using both traditional machine learning techniques as well as deep neural networks based on transfer learning. We show that the ISAR images offer a classification accuracy above 90% and are robust to both noise and clutter.
Narrowband and broadband indoor radar images significantly deteriorate in the presence of target ... more Narrowband and broadband indoor radar images significantly deteriorate in the presence of target dependent and independent static and dynamic clutter arising from walls. A stacked and sparse denoising autoencoder (StackedSDAE) is proposed for mitigating wall clutter in indoor radar images. The algorithm relies on the availability of clean images and corresponding noisy images during training and requires no additional information regarding the wall characteristics. The algorithm is evaluated on simulated Doppler-time spectrograms and high range resolution profiles generated for diverse radar frequencies and wall characteristics in around-the-corner radar (ACR) scenarios. Additional experiments are performed on range-enhanced frontal images generated from measurements gathered from a wideband RF imaging sensor. The results from the experiments show that the StackedSDAE successfully reconstructs images that closely resemble those that would be obtained in free space conditions. Furthe...
Doppler spectrogram analysis of the human gait is a useful tool for discriminating various microD... more Doppler spectrogram analysis of the human gait is a useful tool for discriminating various microDoppler tracks due to the movements of different body parts. A data-dependent algorithm, namely the short-time iterative adaptive approach, is used to obtain a more accurate spectrogram than the one provided by the conventional short-time Fourier transform-based approaches. The performance of the approaches is demonstrated and contrasted using both simulated and measured human gait data.
Highly directive antennas are useful in applications such as satellite communications, radar syst... more Highly directive antennas are useful in applications such as satellite communications, radar systems and biomedical applications. Directivity is usually achieved using either large antenna apertures or array systems comprising many antenna elements. In recent times, metamaterials have been investigated for improving the directivity of different types of antennas such as linear wire antennas, patch antennas, horn antennas, slot antennas etc. In this work, we investigate the possibility of improving the directivity of a slot antenna with a metamaterial substrate and a source excitation within the substrate. The metamaterial substrate is modelled as a Debye medium with dispersive permittivity and permeability. The refractive index of the substrate is (a) negative at frequencies below the plasma frequency, (b) zero at the plasma frequency, (c) positive at frequencies above the plasma frequency. We demonstrate a directive 3D (three-dimensional) two-slot antenna structure with a near zero...
Micro-Doppler signatures of dynamic indoor targets (such as humans and fans) serve as a useful to... more Micro-Doppler signatures of dynamic indoor targets (such as humans and fans) serve as a useful tool for classification. However, all the current classification methods are limited by the assumption that only a single target is present in the channel. In this work, we propose a method to classify multiple targets that are simultaneously present in the channel on the basis of a single channel source separation technique. We apply sparse coding based dictionary learning (DL) algorithms for disaggregating micro-Doppler returns from multiple targets into its constituent signals. The classification is subsequently carried out on the disaggregated signals. We have tested the performance of the proposed algorithm on simulated human and fan data.
Harmonic radar technology has been researched and developed for studying the foraging behaviour o... more Harmonic radar technology has been researched and developed for studying the foraging behaviour of honey bees. This work presents the development of a working prototype of a narrow-band harmonic radar system, at 2.5/5GHz, using off-the-shelf components to detect the presence of Indian honey bees. Based on empirical tests on the tag, we estimate the radar probability of detection and probability of false alarms as 88% and 0.3% respectively. The maximum detectable range for a monostatic configuration of the radar is 3.84 m.
Energy conservation is a key factor towards long term energy sustainability. Real-time end user e... more Energy conservation is a key factor towards long term energy sustainability. Real-time end user energy feedback, using disaggregated electric load composition, can play a pivotal role in motivating consumers towards energy conservation. Recent works have explored using high frequency conducted electromagnetic interference (EMI) on power lines as a single point sensing parameter for monitoring common home appliances. However, key questions regarding the reliability and feasibility of using EMI signatures for non-intrusive load monitoring over multiple appliances across different sensing paradigms remain unanswered. This work presents some of the key challenges towards using EMI as a unique and time invariant feature for load disaggregation. In-depth empirical evaluations of a large number of appliances in different sensing configurations are carried out, in both laboratory and real world settings. Insights into the effects of external parameters such as line impedance, background noi...
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