Band Radar Signals Research Articles

Respiratory motion-corrected T1 mapping of the abdomen.

The purpose of this study was to investigate an approach for motion-corrected T1 mapping of the abdomen that allows for free breathing data acquisition with 100% scan efficiency. Data were acquired using a continuous golden radial trajectory and multiple inversion pulses. For the correction of respiratory motion, motion estimation based on a surrogate was performed from the same data used for T1 mapping. Image-based self-navigation allowed for binning and reconstruction of respiratory-resolved images, which were used for the estimation of respiratory motion fields. Finally, motion-corrected T1 maps were calculated from the data applying the estimated motion fields. The method was evaluated in five healthy volunteers. For the assessment of the image-based navigator, we compared it to a simultaneously acquired ultrawide band radar signal. Motion-corrected T1 maps were evaluated qualitatively and quantitatively for different scan times. For all volunteers, the motion-corrected T1 maps showed fewer motion artifacts in the liver as well as sharper kidney structures and blood vessels compared to uncorrected T1 maps. Moreover, the relative error to the reference breathhold T1 maps could be reduced from up to 25% for the uncorrected T1 maps to below 10% for the motion-corrected maps for the average value of a region of interest, while the scan time could be reduced to 6-8s. The proposed approach allows for respiratory motion-corrected T1 mapping in the abdomen and ensures accurate T1 maps without the need for any breathholds.

An Excess Kurtosis People Counting System Based on 1DCNN-LSTM Using Impulse Radio Ultra-Wide Band Radar Signals

As the Artificial Intelligence of Things (AIOT) and ubiquitous sensing technologies have been leaping forward, numerous scholars have placed a greater focus on the use of Impulse Radio Ultra-Wide Band (IR-UWB) radar signals for Region of Interest (ROI) population estimation. To address the problem concerning the fact that existing algorithms or models cannot accurately detect the number of people counted in ROI from low signal-to-noise ratio (SNR) received signals, an effective 1DCNN-LSTM model was proposed in this study to accurately detect the number of targets even in low-SNR environments with considerable people. First, human-induced excess kurtosis was detected by setting a threshold using the optimized CLEAN algorithm. Next, the preprocessed IR-UWB radar signal pulses were bundled into frames, and the resulting peaks were grouped to develop feature vectors. Subsequently, the sample set was trained based on the 1DCNN-LSTM algorithm neural network structure. In this study, the IR-UWB radar signal data were acquired from different real environments with different numbers of subjects (0–10). As indicated by the experimental results, the average accuracy of the proposed 1DCNN-LSTM model for the recognition of people counting reached 86.66% at ROI. In general, a high-accuracy, low-complexity, and high-robustness solution in IR-UWB radar people counting was presented in this study.

Ultra-wide band radar for prospective respiratory motion correction in the liver

Objective. T1 mapping of the liver is time consuming and can be challenging due to respiratory motion. Here we present a prospective slice tracking approach, which utilizes an external ultra-wide band radar signal and allows for efficient T1 mapping during free-breathing. Approach. The fast radar signal is calibrated to an MR-based motion signal to create a motion model. This motion model provides motion estimates, which are used to carry out slice tracking for any subsequent clinical scan. This approach was evaluated in simulations, phantom experiments and in vivo scans. Main results. Radar-based slice tracking was implemented on an MR system with a total latency of 77 ms. Moving phantom experiments showed accurate motion prediction with an error of 0.12 mm in anterior-posterior and 0.81 mm in head-feet direction. The model error remained stable for up to two hours. In vivo experiments showed visible image improvement with a motion model error three times smaller than with a respiratory bellow. For T1 mapping during free-breathing the proposed approach provided similar results compared to reference T1 mapping during a breathhold. Significance. The proposed radar-based approach achieves accurate slice tracking and enables efficient T1 mapping of the liver during free-breathing. This motion correction approach is independent from scanning parameters and could also be used for applications like MR guided radiotherapy or MR Elastography.

A Near-Range Radar Target Simulator for Automotive Radar Generating Targets of Vulnerable Road Users

In this letter, a radar target simulator (RTS) for the generation of targets for frequency modulated continuous wave (FMCW) chirp sequence radar in the close range of a vehicles surroundings is presented. Key interest is the reproduction of micro-Doppler signatures of vulnerable road users, for example, pedestrians or cyclists. The received $E$ -band radar signal is first converted from the RF band to an IF band, in which the target is manipulated by modulating a range and velocity profile with an IQ modulator. To generate arbitrary signals forms, a PC controlled digital to analog converter (DAC) is used. The RTS has no delay lines to simulate the range, instead it is modulated directly. This allows the distance to be set individually for a large number of targets. In this contribution, the system itself and the underlying concept for the range generation are presented. Finally, measurements of generated static targets and micro-Doppler-signatures are shown.

Radar signals classification using energy‐time‐frequency distribution features

In this research, the authors extract features from intermediate frequency band radar signals in the time–frequency domain for classification. The extracted features are classified via support vector machine and K-nearest neighbour classifiers. They show the accuracy of classification is above 99% for different classes of radar signals except for frequency shift keying signal with accuracy 83% in negative signal-to-noise ratio (SNR). To identify the radars with the same class, the classification accuracy is 91% for SNR between 5 to 15 dB and 64% in the worst case for SNR between −1 to 10 dB. The proposed method is compared with some methods based on the empirical mode decomposition (EMD), cumulant and Zhao Atlas Mark Distribution (ZAMD). The results show that the classification error in the proposed method is less than that of EMD method 55% in the best case and 9% in the worst case. The performance of the cumulant-based method is weaker than that of the proposed method in common designed scenarios becoming almost similar only in one scenario. The ZAMD-based method could only distinguish the signals with different modulations in high SNR while it is unable to classify the signals with the same modulation but different parameters.

A feasibility study of C and X band radio frequency signals over fiber optic links for radar applications

Advancement in microwave photonics (MWP) along with optical fiber technology with its inherent advantages like low loss, immunity to electromagnetic interference (EMI), immense bandwidth and low cost, provides a very promising replacement for the conventional RF cabled distribution systems in radars. Normally conventional distribution systems are complex and bulky in nature. In this work, we intend to tap the advantages of fiber links for the distribution of C and X band radar signals. We analyse the performance of various commonly used radar signals like continuous RF, pulsed RF and linearly frequency modulated (LFM) signals over simple radio over fiber (RoF) links. Measurements are carried out to observe parameters like amplitude, delay, frequency and phase variations for different kinds of radar waveforms over these links. It is inferred from the analysis that the fiber optic links can be used effectively for transmission of higher order radar signals that are in C and X bands of frequencies without any significant degradation in performance.

Non‐uniform sampling and super‐resolution method to increase the accuracy of tank gauging radar

Different methods are proposed for fluid level measurement in storage tanks. Majority of these methods have some in-contact elements or are based on mechanical waves which are vulnerable to changes due to temperature change, pressure change or ageing. Electromagnetic based (i.e. radar) level measurement is a contactless method and it is less vulnerable to such changes. However, a wide band or ultra-wide band radar signal should be transmitted in order to achieve the required accuracy. Usually, linear frequency modulation or step frequency waveforms are used for this goal and matched filter (MF) processing or fast Fourier transform (FFT) are used to find the true level of the liquid inside the tank. In this study, the authors have shown that, those super-resolution methods used for array signal processing and direction finding can be also used in tank gauging problem. Through the simulations and also practical laboratory test, it is shown that, if the frequency steps are selected non-uniformly, the super-resolution methods produce more accurate result compared with MF or FFT processing.

New approach to target identification by use of a robust algorithm for optimal matching of wide band radar signal to target

Using an array of coupled oscillators, a novel broadband radar signalling scheme is introduced. It is shown that the collective output of the oscillator array is a flexible signal that can be matched to a target at a specific aspect. Also, a new robust algorithm based on eigenvectors of the correlation matrix is introduced, by which the generated signal can be matched to the target over a limited range of aspects. This capability is important, because radars are unable to estimate the aspect of a real target precisely. In this new approach to radar target identification, after estimation of the approximate aspect of an unknown target, a variety of waveforms matched to different potential targets are synthesised and transmitted to the target in turn. The maximum peak power of the backscattered signals will then specify the identity of the target. Computer simulations have shown that this technique is robust to both additive noise and aspect angle uncertainty.

Ultrawide band radar signal detection, estimation and experiment

With reference to the air target detection of ultra-wide band (UWB)/impulse radar(IR), the transient signal processing techniques was discussed. In weak UWB signal detection, the wavelet transforms and high order spectrum estimation techniques were preferred. In target characteristic analysis, a time domain bispectrum estimation algorithm was used to analyze the target impulse response, which could estimate accurately local scattering distribution of complex target. A free field IR experimental system installed in an anechoic chamber was used. With this system, experiments to several target models were made. The results of these experiments verified the signal processing method efficiency.

The modification of X and L band radar signals by monomolecular sea slicks

One methyl oleate and two oleyl alcohol surface films were produced on the surface of the North Sea under comparable oceanographic and meteorological conditions in order to investigate their influence on X and L band radar backscatter. Signals are backscattered in these bands primarily by surface waves with lengths of about 2 and 12 cm, respectively, and backscattered power levels in both bands were reduced by the slicks. The reduction was larger at X band than at L band, however, indicating that shorter waves are more intensely damped by the surface films. The oleyl alcohol film caused greater attenuation of short gravity waves than the film of methyl oleate, thus demonstrating the importance of the physicochemical properties of films on the damping of wind‐generated gravity capillary waves. Finally, these experiments indicate a distinct dependence of the degree of damping on the angle between wind and waves. Wind‐generated waves traveling in the wind direction are more intensely damped by surface films than are waves traveling at larger angles to the wind.