Millimeter-wave solid-state cloud and precipitation radars and signal processing

In this paper proposed is a cost-efficient signal processing algorithm of a frequency modulation continuous wave (FMCW) radar for the close range under indoor environments. Recently, the use of an FMCW radar has been expanded to short distance from long distance due to easy production and inexpensive designing costs. In order to obtain satisfying resolution of the close range radar, it still requires a wide modulation bandwidth, which results in high costing wideband RF devices. This paper proposes a cost-efficient signal processing method using correlations between a reflected signal in frequency-domain and a lookup table which holds the frequency information depending on distances. The proposed algorithm shows the similar performance to a wideband system just by updating a firmware of low costing narrowband RF FMCW radar devices without additional hardware modification.

In this paper, we compare the performances of impulse radio ultra-wideband (IR-UWB) and frequency modulation continuous wave (FMCW) radars in measuring noncontact vital signs such as respiration rate and heart rate. These two type radars have been widely used in various fields and have shown their applicability to extract vital signs in noncontact ways. IR-UWB radar can extract vital signs using distance information. On the other hand, FMCW radar requires phase information to estimate vital signs, and the result can be enhanced with Multi-input Multi-output (MIMO) antenna topologies. By using commercial radar chipsets, the operation of radars under different conditions and frequency bands will also affect the performance of vital sign detection capabilities. We compared the accuracy and signal-to-noise (SNR) ratios of IR-UWB and FMCW radars in various scenarios, such as distance, orientation, carotid pulse, harmonics, and obstacle penetration. In general, the IR-UWB radars offer a slightly better accuracy and higher SNR in comparison to FMCW radar. However, each radar system has its own unique advantages, with IR-UWB exhibiting fewer harmonics and a higher SNR, while FMCW can combine the results from each channel.

As an improvement of regular frequency-modulated continuous-wave (FMCW) radar in transmitter-receiver isolation, frequency-modulated interrupted continuous-wave (FMICW) radar has many advantages such as high range resolution, low peak power and high duty cycle. However, the false targets introduced by range aliasing may interfere with radar performance when it comes to long-range detection. In this paper, a range aliasing elimination method for FMICW radar is proposed based on batch Poisson disk sampling (BPDS) and sparse reconstruction. The received echoes are sampled by the newly developed BPDS pattern, which consists of uniform sampling bursts and Poisson disk inter-burst delays, so that the echoes from the maximum unambiguous range can be collected. Taking advantages of the excellent spectrum anti-aliasing performance of BPDS, the range aliasing phenomenon can be effectively eliminated and the range-Doppler spectrum containing multiple targets can be accurately reconstructed by the Iterative Soft Thresholding like (IST-like) algorithm. Compared with the existing signal processing methods for FMICW radar, the proposed method can obtain a larger maximum detection range without range aliasing. The effectiveness of the proposed method is verified by simulations and experiments on real FMICW radar data.

Gliding discharges driven by microsecond-pulse power supply can generate non-thermal plasmas with high energy and high power density at atmospheric pressure. However, the flowing air significantly influences the characteristics of the microsecond-pulse gliding discharges in a repetitive mode. In this paper, in order to obtain the characteristics of the microsecond-pulse gliding discharges in a needle-to-needle gap, a microsecond-pulse power supply with an output voltage up to 30 kV, a pulse width 8 s, and a pulse repetition frequencies 1 Hz 3000 Hz is used to investigate the electrical characteristics of gliding discharges by analyzing the voltage-current waveforms and obtaining the discharge images. Experimental results show that there are three typical discharge modes in the microsecond-pulse gliding discharges as the applied voltage increases, i.e. corona discharge, diffuse discharge, and gliding-like discharge. Both voltage-current waveforms and the discharge images at different discharge modes have significantly different behaviors. Corona discharge only exists near the positive electrode with a small radius of curvature. Diffuse discharges behave as the overlapped plasma channels bridge the entire gap. The channel of diffuse discharge is full of gap, which starts from the positive electrode, spreads in all directions, and ends at the negative electrode. Gliding-like discharge behaves as a continuous spark channeling, showing a continuous spark, which is discharging strongly and influenced by flow rates. Furthermore, both pulse repetition frequency (PRF) and flow rate remarkably affects the characteristics of microsecond-pulse gliding discharges. When the flow rate is small (2 L/min), the spark channels of gliding-like discharge gradually concentrate with the increase of the PRF. However, when the flow rate is larger (16 L/min), the spark channels of gliding-like discharge behave dispersively when the PRF increases. In our opinion, different characteristics of microsecond-pulse gliding discharge at different flow rates are closely related to the memory effect of the residual particles in the discharges and the state of the air flow. When the flow rate is small (2 L/min), the air flow is stable, and the discharge is generated in a laminar flow state. In this case, the memory effect of particles in repetitive microsecond-pulse gliding discharges dominates the formation of the discharges. These particles could enhance the electric field strength for the next pulse. Because the time interval between two pulses at high PRF is shorter than that at low PRF, there are fewer particles leaving the air gap at high PRF. Thus, memory effect is more significant at high PRF. As a result, the channel of spark discharge concentrates with the increase of the PRF. When the flow rate increases to 16 L/min, the calculated Reynolds number increases to 2864, indicating the transition from laminar state to turbulence state. The residual particles are more likely to escape from the gap. Thus, memory effect slightly affects the characteristics of the microsecond-pulse gliding discharges. In this case, the state of the air flow dominates the formation of the discharge. The spark channels spread towards the top in the direction of the gas flow, making the region of the spark channels gradually disperse as the PRF increases.

Frequency-modulated continuous wave (FMCW) radar has seen a significant increase in use due to its ability to operate in low-power and mobile environments suited for low peak power solid state transmitters. Though there are many current applications for the FMCW technique, the majority are focused on measuring “hard” targets (e.g., cars, humans, etc.) and it is not heavily used in the measurement of volume targets such as precipitation. Moreover, current FMCW radars used for volumetric measurements are generally focused on very specific use cases such as vertical profiling. This work presents DARMA, a low-power, dual-polarized, FMCW radar with a phased array antenna capable of being deployed on unmanned aircraft systems (UAS). It will be used to test the feasibility of measuring and classifying complex weather events on a mobile platform which will provide different perspectives at the lowest kilometer of precipitation volumes.

Phase noise can severely degrade the radar performances by producing strong sidelobes which may mask small targets. Reducing those sidelobes by improving the radar analog front-end severely increases the system complexity. Another approach consists in developing waveforms more robust to phase noise. Even if the phase noise phenomenon is well known, it has been intensively investigated only in Frequency Modulated Continuous Wave (FMCW) radars, not so much in Phase Modulated Con-tinuous Wave (PMCW) radars. In this paper, we will provide a detailed analysis of the impact of phase noise on FMCW radars and on different code sequences for PMCW radars. This analysis will be used to compare the impact of phase noise on different waveforms. Both range profile and Doppler profile will be investigated. We will show that radar waveforms can be designed to provide low sidelobes in presence of phase noise. Our model will be validated by simulation.

Copper vapour lasers (CVL) are high power, pulsed, visible lasers capable of diffraction limited beam quality and kilohertz pulse repetition frequencies. Kinetic enhancement of elemental CVLs has been reported to significantly increase the output power and pulse repetition frequency range of a given laser architecture.This paper reports the performance of medium scale CVLs when kinetically enhanced using small partial pressures of hydrogen halides to the Ne:H2 buffer gas. Kinetic enhancement increased the output power by factors of up to 2.5. Using a 1 x 0.025m discharge tube, an output power of 60W was achieved at 15 – 20kHz and over 50W at frequencies in excess of 30kHz. Using a high magnification unstable cavity, over 35W was achieved at close to the diffraction limit. Sealed-off operation of the laser with excellent power stability was also demonstrated.The combination of high power, visible, diffraction-limited beam with short pulse widths, high pulse repetition frequency from a compact industrial package is of great interest for a number of micromachining and advanced manufacturing applications. In addition it is an excellent source for generating high power, narrow linewidth UV (255nm) by frequency doubling.Copper vapour lasers (CVL) are high power, pulsed, visible lasers capable of diffraction limited beam quality and kilohertz pulse repetition frequencies. Kinetic enhancement of elemental CVLs has been reported to significantly increase the output power and pulse repetition frequency range of a given laser architecture.This paper reports the performance of medium scale CVLs when kinetically enhanced using small partial pressures of hydrogen halides to the Ne:H2 buffer gas. Kinetic enhancement increased the output power by factors of up to 2.5. Using a 1 x 0.025m discharge tube, an output power of 60W was achieved at 15 – 20kHz and over 50W at frequencies in excess of 30kHz. Using a high magnification unstable cavity, over 35W was achieved at close to the diffraction limit. Sealed-off operation of the laser with excellent power stability was also demonstrated.The combination of high power, visible, diffraction-limited beam with short pulse widths, high pulse repetition frequency from a compact industrial pa...

The continuous operation of frequency modulated continuous wave (FMCW) radar transceivers leads to permanent leakage from the transmit into the receive path. Besides leakage within FMCW radar systems itself, unwanted reflections from a close object in front of the radar antennas results in so-called short-range (SR) leakage. Specifically the phase noise (PN) contained in the SR leakage causes a severe sensitivity degradation of the radar. In this work, we propose a mixed-signal approach to mitigate the SR leakage, including its contained PN. It makes use of an artificial on-chip target (OCT), whose output signal is modulated on a sinusoidal generated in the digital domain. The concept is based on cross-correlation properties of the residual PN between the OCT and the SR leakage in the intermediate frequency (IF) domain of the transceiver. We prove our analytical investigations with an FMCW radar simulation, wherein almost perfect SR leakage cancelation is achieved.

Nanosecond surface dielectric barrier discharge (ns-SDBD) actuators have broad applications in flow control, where the discharge characteristics are significantly influenced by the pulse repetition frequency (PRF) through its modulation of surface ionization wave (SIW) dynamics. This study investigates the effects of PRFs and nanosecond-pulse number on energy accumulation mechanisms, discharge mode transitions, and SIW propagation in SDBDs. Experimental results show distinct discharge characteristics in the case of two dielectric barriers, epoxy glass cloth (FR-4) and polytetrafluoroethylene (PTFE), respectively. In the case of FR-4, the single-pulse energy initially increases with higher PRFs and pulse numbers, but subsequently decreases after reaching its peak. In the case of PTFE, the results demonstrate pronounced energy accumulation, with energy continuously increasing under the same conditions. Furthermore, SDBD actuators with PTFE require significantly higher PRF thresholds and greater pulse quantities to induce transitions in discharge mode compared to those with FR-4. At elevated PRFs, both materials exhibit accelerated propagation of SIW and streamers as the PRF and pulse number increase. However, while SIW propagation tends to saturate at high PRFs, streamer velocity shows a slightly saturated trend under similar conditions. These findings provide critical insights for optimizing ns-SDBD performance through proper material selection and PRF control in practical applications.

Ground Penetrating Radar (GPR) application in road surface detection has been greatly developed in the past few decades, which enables rapid and economical estimation of pavement thickness and other physical properties in non-destructive testing (NDT) and non-contact testing (NCT). In recent years, with the rapid development of microwave and millimeter-wave solid-state devices and digital signal processors, the cost of Frequency-Modulated Continuous-Wave (FMCW) radar has dropped significantly, with smaller size and lighter weight. Thereafter, FMCW GPR is considered to be applied during pavement inspection. To improve the precision of FMCW GPR for NDT and NCT of pavement thickness, a Chirp Z-transform (CZT) algorithm is introduced to FMCW GPR and investigated in this paper. A FMCW + CZT GPR at 2.5 GHz with a bandwidth of 1 GHz was built, and laboratory and field experiments were carried out. The experimental results demonstrate that the FMCW + CZT GPR radar can obtain the sample thickness with low error and recognize subtle thickness variations. This method realizes the high precision thickness measurement of shallow asphalt pavement by FMCW radar with a narrow bandwidth pulse signal and would provide a promising low-cost measurement solution for GPR.

In order to reduce the probability of automobile safety incidents, the in-vehicle occupant monitoring is indispensable. However, occupant monitoring using frequency-modulated continuous wave (FMCW) radar can be challenging due to the interference from passengers’ posture, movement, and the presence of multiple people. This paper proposes an improved method for generating point clouds using FMCW radar. The approach involves point cloud clustering, post-processing operations such as segmentation, merging, and filtering of the clustered point cloud to match the actual in-vehicle environment, and a state machine combination step. Experimental results show that the proposed method can achieve high recognition accuracy in scenarios with multiple passengers who are moving and sitting in a relaxed manner.

Human body detection is very important in the research of automotive safety technology. The extraction and analysis of human micro-motion based on frequency-modulated continuous wave (FMCW) radar is gradually receiving attention. Aimed at the modulation effect of human micro-motion on FMCW radar, a human running model is proposed to study human radar characteristics. According to the scattering characteristics of rigid bodies, the analytical expression of human running radar echoes is established. By using time–frequency analysis, the micro-Doppler features in the radar echoes are extracted during the running period. Under running conditions, the micro-Doppler characteristics of key components are studied. This model is applied to the real FMCW radar verification platform, and the runners are measured at a distance of 10 m. The fit rate of all parts of the human body can reach above 90%. The overall fit rate of the human model can reach up to 90.6%. The model proposed is a realistic and simple human kinematic model. This model, which can realize the real simulation of a running human body and provide strong support for human target radar echo analysis, can fill the deficiency of FMCW radar technology in the complex motion model.

Conventionally, a pulse radar is used for middle-sized or large-sized ships to detect other ships or obstacles located at a long distance. However, it is hardly equipped for most of the small-sized ships due to mounting and maintenance costs. Therefore, FMCW(frequency modulated continuous wave) radar is suggested as an alternative for the small-sized ships. Since it operates with low power and has good range resolution for relatively close objects, it is eligible for the small-sized ships. In previously proposed FMCW radar system, it only estimates distance and velocity of a target ship placed in the direction of main beam and is hard to detect several ships simultaneously. Thus, we suggest the method for detecting several ships at the same time by applying MUSIC(multiple signal classification) algorithm to FMCW radar signal received by a phased array antenna. In addition, by combining digital beam forming with the MUSIC algorithm, better angle resolution is achievable. 논문 15-40-06-19 The Journal of Korean Institute of Communications and Information Sciences '15-06 Vol.40 No.06 http://dx.doi.org/10.7840/kics.2015.40.6.113

Effect of pulse repetition frequency of high-intensity focused ultrasound on in vitro thrombolysis

This letter presents a novel method to reduce measurement time for remote heart rate measurement using millimeter-wave frequency-modulated continuous wave (FMCW) radar. The proposed method is based on the sampling theory and the frame structure of recent FMCW radar systems. The range displacement from heartbeat is measured by 60 GHz FMCW radar with a fixed frame interval, 50 ms. With additional chirp repetition in each frame, the heartbeat signal can be sampled with increased or decreased interval. By adopting three different sampling rates from a single radar measurement, the resolution of heart rate measurement is improved in a short time, 2.5 s. The proposed method is evaluated with a commercial off-the-shelf FMCW radar system and three different human subjects, for no respiration and natural status. To evaluate the performance of the proposed method, the heart rate result is compared with electrocardiogram (ECG) sensor and conventional signal processing method. The results show that the proposed method estimates the heart rate with lower error and shorter measurement time.