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Colour flow
Published in Peter R Hoskins, Kevin Martin, Abigail Thrush, Diagnostic Ultrasound, 2019
The pulse repetition frequency (PRF) is the total number of pulses which the transducer transmits per second. It is limited largely by the maximum depth of the field of view; the transmit-receive time is less for smaller depths and a higher PRF is then possible. The value of the PRF selected in the various system presets, such as arterial or venous, will depend on the expected velocities present in the region of interest, but PRF may need to be altered by the operator, e.g. to prevent aliasing or to enable the detection of low flow. On modern systems, there is not a single control labelled ‘PRF’. Instead, PRF is usually determined automatically from various controls, including the colour box size and the velocity scale.
Robust Time Resource Management in Cognitive Radar Using Adaptive Waveform Design
Published in IETE Journal of Research, 2023
M. Ghadian, R. Fatemi Mofrad, B. Abbasi Arand
In 2006, Cognitive radar concept was illustrated for the first time in [2]. The key point in any cognition-based system is the perception–action cycle [3]. In this concept, a cognitive radar “continuously learns about the environment through experience gained from interactions with the environment; the transmitter adjusts its illumination of the environment in an intelligent manner; and the whole radar system constitutes a dynamic closed feedback loop encompassing the transmitter, environment, and receiver”. The feature of a cognitive radar that differs from a classical radar is the active feedback between receiver to transmitter [4]. A classical adaptive radar is only able to extract information from the target and the disturbance signals through appropriate signal processing algorithms and to apply that information at the receive level to improve its performance [5]. Conversely, a cognitive radar is able to use all of the extracted information not only at the receive level but also at the transmit level by changing the transmit frequency channel, waveform shape, time on target, pulse repetition frequency, transmitted power, number of pulses, polarization, and so forth [6].
Hardware-in-the-Loop simulation algorithm for helicopter rotor time-varying echo signals
Published in Systems Science & Control Engineering, 2021
To verify whether the real-time simulation algorithm described above correctly generates echo signals similar to the actual echo signals, we conducted a simulation experiment. The parameters were set as follows: the wavelength λ was 0.3 m; the distance between the radar and rotor centre O’, R0, was 50,000 m; the length of the blade was 6 m; the interval between adjacent scattering points, d, was 0.04; the pulse repetition frequency (PRF) was 4000 Hz; the rotation frequency of the rotor, frot, was 5 Hz; and θ1 = β = 0. The amplitudes involved in this work were all normalized, and when not specified, they were unitless. We used the short-time Fourier transform (STFT) of a Gaussian window to analyse the time–frequency characteristics of the helicopter rotor blades.
A data classification method based on particle swarm optimisation and kernel function extreme learning machine
Published in Enterprise Information Systems, 2023
Ao Liu, Dongning Zhao, Tingjun Li
(1) Building radar cloud database. Cloud database was built according to enterprise cloud environment. The parameters were selected as radar operating frequency, pulse repetition frequency and pulse width. The working frequency obeys the uniform distribution, and the pulse repetition frequency and pulse width obey the normal distribution. The specific parameters are indicated in Table 1, where represents the type of radar, represents the operating frequency, represents the pulse repetition frequency, and represents the pulse width.