Radial Transit Time Research Articles

Design and Performance Analyses of a Ka-Band Radial Transit Time Oscillator With Low Magnetic Field and High Efficiency

Design and Performance Analyses of a <i>Ka</i>-Band Radial Transit Time Oscillator With Low Magnetic Field and High Efficiency

A Ku-band radial transit time oscillator with high-power capacity

In order to improve the power capacity of a high-power microwave (HPM) generator, a Ku-band radial transit time oscillator (RTTO) with a trapezoidal resonator is designed. Compared with the traditional RTTO, both the modulation cavity and the extraction cavity are trapezoidal, which can modulate the electron beam more effectively. At the same time, the conductor tips on both sides of the cavity are farther, which helps to avoid the enhancement of the local electric field at the conductor tip, so as to reduce the risk of radio frequency (RF) breakdown. In particle-in-cell (PIC) simulation, the proposed Ku-band RTTO can output HPMs with the power of 1.66 GW and the frequency of 14.33 GHz, and the working efficiency is 41%. The maximum radial electric field intensity in the extraction cavity is 0.76 MV cm−1, lower than the RF breakdown threshold of metallic materials, which can effectively improve the power capacity of the device.

Development of a high-precision and wide-range ultrasonic water meter

Ultrasonic water meters offer a number of advantages such as non-intrusiveness, low pressure loss, high accuracy, low power consumption and long service life, which make them a viable option for the next generation of smart water meters. However, the existing ultrasonic water meters have difficulties in balancing the range and accuracy. Therefore, in order to address this issue, this study proposes a novel ultrasonic water meter featured with high-precision and wide-range. First of all, the flow measurement principle of the ultrasonic time difference method is investigated, and a flow measurement model that includes the parameter of radial transit time (TD) is developed. The ultrasonic water meter is designed based on comprehensive consideration of the three aspects of hardware, software and algorithms, and a series of experiments are conducted to verify the performance of the water meter. Eighteen verification test points with the flow range of 0.015–4.509 m3/h are carried out, the results of which suggest that the accuracy level of the ultrasonic water meter reaches 0.5, with the repeatability of 0.09%, and the range ratio of 300:1, indicating the achievement of the design goal of high-precision and wide-range.

Design and simulation of a compact Ku-band RTTO with power divider extraction structure

The radial transit time oscillator (RTTO) has attracted much attention because of its high power capacity and pure mode of output microwave. To make the high power microwave (HPM) source devices more compact and to enable it to measure the output microwave mode quantitatively, this paper proposed a compact Ku-band RTTO with the power divider extraction structure (PDES). The radial decreasing magnetic field is applied to decreasing the mass of excitation system. Compared the conventional uniform solenoids, it can reduce the mass by about 30%. In the coaxial output waveguide, the PDES is used instead of the traditional support rods connecting the inner and outer conductors so as to convert TEM mode into TE10 mode efficiently. This structure can not only help shorten the axial dimension of the device, but also make it possible to measure the output microwave mode more accurately online. In particle-in-cell (PIC) simulation, the proposed Ku-band RTTO can output HPMs with the power of 3.05 GW and the frequency of 14.36 GHz, and the working efficiency is 40.3%. The maximum radial electric field intensity in the extraction cavity is 0.92 MV/cm, and the maximum electric field intensity in the PDES is 0.52 MV/cm, both of which are lower than the radio frequency (RF) breakdown threshold of metal materials.

A High-Power Ka-Band Radial Transit Time Oscillator With Over-Sized Extractor

Radial transit time oscillator (TTO) is a promising device to achieve a high-power Ka-band output. However, because the cavity number is limited, the power capacity of extractor and the radiation power are hard to improve. To solve this problem, a high-power Ka-band radial TTO with an over-sized extractor is proposed in this article. Taking the quasi-TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> mode as working mode, the electric field distribution, beam-loading conductance ratio, and external quality factor prove that the electric field in the extractor can interact with the radial intensity electron beam efficiently. Particle-in-cell (PIC) simulation results prove that a constant magnetic field or decreasing magnetic field can confine electron movement effectively. Setting the imposed diode voltage to be 400 kV, the corresponding current is 7.5 kA, and the microwaves with the power of 1.13 GW, the frequency of 32.15 GHz, and the efficiency of 38% can be generated. When the output power saturates, the maximum radial electric field on the surface of the extractor is only 980 kV/cm, which verified the high-power capacity of the over-sized extractor. Taking ohmic loss into consideration, the proposed radial TTO made of low-loss material (e.g., copper) is potential to output giga-watt level high-power microwaves (HPMs) at Ka-band.

Preliminary experimental research of a Ka-band radial transit time oscillator.

Radial transit time oscillator (RTTO) can be relied on to generate effective coherent electromagnetic radiation in the millimeter wave domain. In this paper, the preliminary experimental research on a Ka-band RTTO is reported for the first time. In experiments, the radial electron beam emitted from the knife edge of the disk cathode is guided by the radial magnetic field. The bombardment trace on the nylon target verifies the emission and transportation uniformity of the radial e-beam. When the diode voltage is 410 kV, the beam current is 7.8 kA, and the magnetic field is 0.6 T, the RTTO can output microwaves with the power of 320 MW and the frequency of 31.35 GHz. As the diode voltage increases from 350 kV to 430 kV, the output microwave power will grow accordingly. Taking the ohmic loss into consideration, the experimental results are in agreement with the simulation ones.

A high power capacity Ka-band radial transit time oscillator with one-gap extraction cavity

The radial transit time oscillator (RTTO) is promising to realize high power output of millimeter-waves. Although the radial structure can enhance the power capacity, less cavities and small radial dimension make it difficult to improve the power capacity in RTTOs, especially in the extraction cavity. A one-gap extraction cavity in the Ka-band RTTO is proposed in this paper to improve the power capacity. Without electrons, taking the TM011 cavity as an example, the radial reversal resonant electric field can intersect with radial electrons. By choosing the sizes of the cavity, the synchronization of the electrons and the electric field can be realized to achieve effective energy exchange. In particle-in-cell simulation, the RTTO with the TM011 extraction cavity can output 1.0 GW high power microwaves (HPMs) at 31.2 GHz, and the beam-wave conversion efficiency is 31.6%. The maximum electric field in the TM011 cavity is only 800 kV/cm, which is less than one third that in the TM010 extraction cavities. In addition, the TM012 extraction cavity is employed to improve the efficiency to 35.4%. At the same time, because of the increase in the output power, the maximum radial electric field in the TM012 cavity increases to 850 kV/cm. Therefore, the one-gap extraction cavity can realize multiple energy exchanges to get high beam-wave conversion efficiency and enhance the power capacity in the extraction cavity significantly.

A high power radial Ka-band transit time oscillator with nonuniform extractor

The radial transit time oscillator is promising to realize high power output of millimeter-waves. However, the enhancement of the electric field in extractor and the microwave extraction are two main problems to be overcome. A high power radial Ka-band transit time oscillator is proposed in the paper. Increasing the third gap by integer multiples of half the wavelength, the nonuniform extractor will be introduced. In the extractor, the radial mode of the electric field in the modified extractor is the same as that in the uniform extractor. Due to volume increase of the beam-wave interaction region, this structure can improve power capacity to a certain degree. In particle-in-cell simulation, the proposed radial Ka-band oscillator can output high power microwave with the power of 1.0 GW, the frequency of 31.3 GHz and the efficiency of 33%. Besides, the modified structure can decrease the maximum radial electric field in extractor to 0.9 MV cm−1. As the diode voltage ranges from 350 to 450 kV, efficiency of the oscillator is larger than 20% and the center frequency will not change, which proves the steady operation of this device. To realize high output power, the materials with high conductivity need to be employed, such as copper and aluminum. Besides, the microwave channel goes through the inner space of the high current coils, this design can decrease the number of the support posts to 50 and increase the bandwidth where the transmission efficiency is larger than 99% to be over 1.8 GHz.

Analysis and Simulation of a Gigawatt-ClassKa-Band Radial Transit Time Oscillator

Obtaining high power millimeter-wave output is a research hotspot of high power microwave (HPM) technology. Considering limited power capacity and mode competition in axial millimeter wave generators, the radial device is introduced to output high power millimeter waves. A gigawatt-class ${Ka}$ -band radial transit time oscillator (RTTO) is proposed in this paper. In guiding the magnetic field of 0.8 T, the radial TM01 mode is applied as the operation mode. Particle-in-cell (PIC) simulation demonstrates that when the diode voltage is 400 kV and the beam current is 7.5 kA, the HPMs at 31.2 GHz with an output power of 1.1 GW and a conversion efficiency of about 37% are generated. The maximum radial electric field is 1.2 MV/cm, proving that the radial structure is an effective way to enhance power capacity. 3-D PIC simulation proves there is no angular nonasymmetric mode intersection. Analysis of parameter sensitivity shows that, within a certain range, the thickness and axial position offset of the electron beam will not influence the performance of the RTTO. In addition, the oscillator can operate steadily as the radial guiding magnetic field changes from 0.6 to 6.0 T. With these characteristics, the RTTO is potential to output ${Ka}$ -band HPMs.

Detection of Internal Holes in Swietenia mahagoni Disks Using a Stress Wave Device

The objectives of this study were to evaluate the feasibility of detecting different sizes and positions of hidden defects in trees using a 2-sensor stress wave device. In addition, we attempted to evaluate the detection resolution of the stress wave method which was rarely discussed previously. Artificial holes were created in Swietenia mahagoni disks to imitate natural decay in a trunk and were then detected using stress waves. The results revealed that as the diameter of the artificial hole increased, the radial transit time of the disk increased. This increasing tendency was repeated in the relationship between the radial relative transit time (RT) and the relative hole diameter (RD) and was discordant in the tangential direction. The tangential RT was greatly influenced by the position of the hole: it was highly related to the RD when the hole was near the 2 sensors; while it is not related to the RD when the hole was far from the 2 sensors. We also found that detection resolutions of stress waves, defined as the diameter or area ratio when the radial velocity had decreased by 10%, were 0.29 and 8.4%, respectively. A tree was considered to be decayed when the relative velocity (RV) was ＜ 0.9 and was considered hazardous when the RV was ＜ 0.66 with a central hole. On the basis of the results obtained, it appears that a 2-sensor stress wave device allows the nondestructive inspection of the presence, size, and location of defects in trees and could be a cost-effective way to perform tree risk assessments.