Time domain response analysis with equivalent circuit models for dipole antennas under EMP

The normal mode helical antenna (NMHA) is widely used for RF communication applications and usually provides a potential front door path of coupling electromagnetic pulse (EMP). Many numerical methods are employed to analyze the transient response of antennas under EMP, such as time-domain finite difference (FDTD) and time domain integral equation (TDIF) methods. While the numerical methods give accurate results, they can be time-consuming and only provide snapshots of EMP response in very specific circumstances. In addition, the transient data obtained from numerical tools is often required to be handled for the subsequent EMP vulnerability assessment in the RF front end circuits of communication system. The analysis of transient response for communication systems in the presence of EMP was usually complicated in the traditional field-circuit method.

Objective To investigate the effects of electromagnetic pulse (EMP) on reproductive function of male adult mice. Methods A total of 48 healthy adult male BALB/c mice (8 weeks old) were randomly divided into sham group and EMP group with 24 animals in each group. The mice were whole-body exposed or sham exposed to EMP at 720 kV/m for 100 pulses with 1 Hz repetition rate and 40 ns pulse width. At 1, 7, 14 and 35 d after EMP exposure, the mice were anesthetized and the sperms were collected from the bilateral epididymal tail. After that, the sperm quality including the number of sperms, the ratio of abnormalities and the survival rate was evaluated. In addition, the morphology of testis was observed by HE staining and the diameter of seminiferous tubules was measured by Image J 1.43 u software. The protein level of stem cell factor (SCF) and glial-derived neurotrophic factor (GDNF) in testis tissue were detected by ELISA and Western blot. Results The sperm quality and the morphology of testis did not change obviously at different times after exposing mice to EMP at 720 kV/m for 100 pulses, compared with sham group (P>0.05). The diameters of seminiferous tubules at 1, 7, 14 and 35 d after exposure were (196.85±16.65), (196.79±14.33), (196.35±22.71) and (198.60±25.88) μm in exposed mice, respectively, while (204.31±27.13), (197.07±18.11), (194.37±21.45) and (200.59±19.36) μm in sham exposed mice, respectively. There was no significant difference between two groups (P>0.05). Additionally, the levels of SCF and GDNF in testis tissue between EMP group and sham group had no statistically significant difference (P>0.05). Conclusion Under this exposure condition, EMP couldn′t affect the reproductive function of male adult mice. Key words: Electromagnetic pulse; Mice; Testis; Sperm quality; Seminiferous tubules

Due to the increase in the threat of attacks with high-power electromagnetic (EM) pulses, there is great interest in metallic enclosures with high shielding effectiveness (SE). Necessary technological apertures in these enclosures reduce their effectiveness. Understanding the penetration and internal propagation of the high-power EM pulses into an apertured enclosure is fundamental to assessing the EM SE of the enclosure. In the present paper, results of the numerical simulations of development of the EM field in a shielding enclosure with aperture after the interference of a subnanosecond high-power EM plane wave pulse of the parallel polarization (having the duration of 0.3558 ns and the amplitudes of the electric and magnetic fields of 106 V/m and 2.6 × 103 A/m, respectively) are presented. The results obtained include 3D and 2D images , vector maps of the EM field developed inside the enclosure, and time-varying distributions of the electric charges formed on the inner walls of the enclosure. They revealed the mechanism of formation of the EM field inside the enclosure caused by the subnanosecond high-power parallelly polarized EM pulse. The EM field formed in the enclosure with aperture has the form of the electric and magnetic field interference structures. They are a superposition of the incident EM pulse field, which entered the enclosure through the aperture in the way described by the geometrical (ray) optics, the electric field generated by the electric charges formed on the aperture edges and inner sides of the walls of the enclosure, and the magnetic field generated by the surface current formed on the aperture edges and on the inner walls of the enclosure. The amplitudes of the electric and magnetic fields of the strongest EM interference structures decrease non-monotonically to about 0.7 × 105 V/m and 200 A/m at t = 5 ns. We found that the points in the enclosure are subjected to the disturbance of a long series of subnanosecond EM pulses, which we have called internal EM pulses. The amplitudes of these internal pulses are lower than those of the incident EM pulse. Nevertheless, they can pose a severe EM hazard inside the enclosure due to their large number (about 900 internal pulses in 30 ns). This means a fundamental change in the character of the EM disturbance caused by the subnanosecond pulse when the enclosure with aperture is used as a shield.

An equivalent circuit consisting of eight frequency independent lumped elements is derived for center-driven normal mode helical antennas. The equivalent circuit is composed of two parts; a five-element circuit representing the wire antenna and a three-element circuit for the helical turns. Comparison of the calculated input impedance of the equivalent circuit with full-wave simulations demonstrates reasonable agreement over a broad frequency range that includes the first resonant frequency, where the antenna usually operates. Application of the equivalent circuit does not require an EM solver and it is readily implemented in circuit simulators.

We detected electromagnetic (EM) pulses in the earth whose waveforms were quite different from those generated by lightning discharges. In order to confirm their propagation directions (up- or down-ward), we conducted comparative measurements of phase and amplitude between waveforms of horizontal magnetic fields of the EM pulses detected on the ground and at the depth of 95 m in a borehole. Clear differences in the phase and the amplitude seemed to suggest that some of them were up propagating modes and others were down propagations. We, however, found that the decision by this method was wrong, because EM pulses measured at the 95 m-depth in the borehole represented ellipsoidal polarizations whereas those simultaneously detected on the ground were linear polarizations. We concluded that EM pulses of this kind were artificial ones having propagated along the ground surface. For determining propagation directions of unknown EM pulses, we have to obtain their propagating directions from analysis of strict Poynting vector of EM pulses using field values detected by tri-axial electric dipole antennas and tri-axial magnetic search coils. In the present paper, we introduce the measuring method of Poynting vector of EM pulses in the earth.

The equivalent circuits modeling method is developed for the EMP(Electromagnetic pulse) generators of the equipment-level immunity test. On the double-exponential function of EMP waveform, the corresponding circuit structure is introduced, and the calculation method is given to obtain the circuit RLC parameters. For the generators of EFT(Electrical Fast Transient/Burst), surge combination wave, and ESD(Electro-Static Discharge), the equivalent circuits and components parameters are proposed. Finally, simulation results validate the proposed method and circuit models.

Transient thermal responses of GaAs field-effect transistors (FETs) in the presence of an electromagnetic pulse (EMP) are investigated in this paper. The numerical methodology employed is an efficient nonlinear finite-element method (FEM) that combines the element-by-element FEM and the preconditioned conjugate gradient technique. Parametric studies are carried out to show different pulse parameters on the transient thermal responses as well as maximum channel temperatures of some typical GaAs FETs, with silicon FETs also taken into account for comparison. It is numerically proven that the thermal impact caused by medium EMP will be the most serious compared with fast EMP or ultra-wideband pulse, and the captured maximum channel temperature is proportional to the input power density, approximately of the EMP injected. This research can serve as a base for taking further protection measures to prevent on-chip device from breakdown by the attack of an EMP.

Research on anti-interference capability of electromagnetic relay under electromagnetic pulse (EMP) is very important for assuring its reliable operation. In this paper, equivalent circuit of the relay was obtained, considering parasitic capacitance, inductance and resistance of electromagnetic system and contact system. The equivalent circuit is applied in a certain relay to analyze how the EMP interferes with inner structures, including coil, movable reeds and static reeds. The conclusion is valuable for improving the anti-interference capability of relay under EMP.

Since the diversification of the electromagnetic (EM) environment is spreading, it is essential to estimate the EM energy absorption rate [specific absorption rate (SAR)] of a pregnant woman's body and her fetus under various exposure situations. For example, if pregnant women work in jobs where they might wear business portable radios around their abdomens, they should also be concerned about this issue, because the fetuses are in their abdomens. In this paper, in order to evaluate the SAR in the pregnant woman and her fetus when wearing the wireless radio terminal on her abdomen, the SAR distribution in the fetus is calculated using the numerical model of the pregnant woman by exposed to near-field of a normal mode helical antenna (NHA) with a metallic case at 150 MHz. In addition, the SAR in the fetus will be evaluated under two fetal positions. It was found that the fetal SARs are greatly affected by the distance and penetration path from the antenna to the fetal surface. In addition, the fetal SARs are lower than the RF safety guidelines for occupational exposure.

The study here compares and evaluates the performance of different antennas such as the dipole, Yagi-Uda, and helical antennas in the context of FM broadcasting. The main goal here is to compare how these antennas perform in terms of signal strength and efficiency. The study carried out experiments in a controlled environment and tested the antennas in an outdoor environment by scanning the FM band from 88 to 108 MHz. The experiments were conducted in a similar environment to compare the performance of these antennas. The parameters taken for the study were gain in dBi, SNR, RSSI, bandwidth efficiency, and radiation pattern stability. The results obtained from the experiments show that the dipole antenna performed at an average gain of 2.1 dBi and an RSSI of -64 dBm at a distance of 1 km. The study also found that the SNR for the dipole was 18.4 dB. The results obtained from the experiments show that the dipole antenna performed well at a distance of 3 km. The performance of the dipole antenna was average. The study also found that the Yagi-Uda antenna performed very well in terms of directional efficiency. The results obtained from the experiments show that the Yagi-Uda antenna performed at an average gain of 9.6 dBi and an RSSI of -47 dBm at a distance of 1 km. The study also found that the SNR for the Yagi-Uda antenna was 27.8 dB. The results obtained from the experiments show that the Yagi-Uda antenna performed very well at a distance of 8.5 km. The study also found that the helical antenna performed at an average gain of 6.2 dBi and an RSSI of -55 dBm at a distance of 1 km. The study also found that the SNR for the helical antenna was 23.1 dB. The results obtained from the experiments show that the helical antenna performed very well at a distance of 6.2 km. The study found that the helical antenna performed better in an environment with buildings and foliage. The study concluded that the choice of the antenna depends upon the requirements. The study concluded that the Yagi-Uda antenna should be used for long-distance and high-gain requirements. The study concluded that the helical antennas should be used for difficult propagation environments. The study concluded that the dipole antennas should be used for economical requirements.

Stamping failures consist of, broadly speaking, either tearing (excessive local strain energy) or wrinkling (insufficient or inappropriate local strain energy). Good parts are produced when the strain energy or plastic work is effectively distributed during the forming process such that tears and wrinkles are eliminated. The process window framed by tearing and wrinkling limits can be rather small for some materials, notably aluminum alloys. At present, there are no established methods of directly controlling the forming energy distribution within the tool during a stamping operation. All current commercial methods attempt plastic strain control at the sheet boundary by various binder geometries and pressure profiles. While improvements by active control of draw beads and binder pressure have led to improved stamping performance, these methods still broadly rely on tool geometry to set the energy distribution. We have recently developed and demonstrated a method for more directly controlling the distribution of forming energy in a stamping operation based on an extension of electromagnetic (EM) impulse forming. We now have techniques for embedding and operating EM pulse actuator coils in stamping tools. These coils can be operated in a single high power pulse or as a series of lower energy pulses occurring several times during the forming stroke. A single high power pulse can provide the advantage of increased material forming limits of high velocity forming. However, applying a series of lower power pulses can increase forming limits without exposing the tooling and coil to large shock loads. Multiple pulses reduce the maximum strain levels by engaging more of the part material in the forming process which mimics (eliminates) the use of lubricants. Conventional production stamping rates are technically obtainable with proper integration of the EM impulse circuit with the forming press and tooling. This paper focuses on the basic design approach of our multiple pulse technique and integrated process forming results. Comparisons to other augmented stamping processes as well as conventional stamping are presented in terms of both simple metrics, such as draw depth and strain distributions.

Measurements of the modulation characteristics of semiconductor lasers under typical systems-operating conditions are discussed. Slow components in the transient response, which limit the speed of three different types of device, are found to be structure-dependent. On a device with a built-in lateral waveguide but no lateral current confinement, a slow tail is observed on the trailing edge of the light pulse. Calculations using a model which includes lateral diffusion suggest that charge storage coupled with diffusion are responsible for the tail. Devices with both a built-in lateral waveguide and lateral current confinement (through the use of reverse-biased blocking junctions) are found to contain significant parallel capacitance in their impedance. An equivalent electrical circuit, based on impedance measurements, is used in conjunction with the model to calculate the modulation response. It is found that the speed of these devices is limited by the parallel capacitive elements, which are attributed to reverse-bias blocking junctions used to give good DC laser characteristics.

As a small antenna of handsets for personal communication systems, a two-strip meander-line antenna and a normal mode helical antenna have been suggested. The values of quality factors of both antennas are from 20 to 30 when the size of the antennas are smaller than 0.1 wavelength. The quality factor Q is really important to evaluate the bandwidth of an antenna. The bandwidth is in inverse proportion to Q. Therefore, if the quality factor can be small, the bandwidth becomes broadband. A plate antenna whose quality factor is smaller than those of the meander line antenna and the normal mode helical antenna can be obtained with broadband characteristics. In order to realise the impedance matching, the antenna consists of two plates, and the currents of the two plates are produced in imbalance and balance modes. In this paper, the small plate antenna with slits is treated. The impedance characteristics of the antenna is made clear and increasing the bandwidth by using two plates is also discussed.

Evaluation of Local Loss Coefficients for Different Waveguide-Below-Cutoff (WBC) Arrays of Electromagnetic Pulse (EMP) Shied in Buildings

The resonant frequency of the normal mode helical antenna (NMHA) varies with its number of turns. Several experiments were conducted to investigate their relationship. This paper presents linear regression analysis on these experimental results and tries to find a simple equation relating the resonant frequency and number of turns of the NMHA. An empirical equation giving relationship between them is suggested.