Waveguide Chamber Research Articles

Computational Modeling and Measurement of a Waveguide Chamber for Two Photoconductive Semiconductor Switches

Computational Modeling and Measurement of a Waveguide Chamber for Two Photoconductive Semiconductor Switches

Estimation of S-parameters and dielectric permittivity of quartz ceramics samples in millimeter waveband

A modified Nicholson – Ross – Weir method was used to determine complex parameters and dielectric permittivity of ceramic materials in the range 78.33–118.1 GHz. The measuring equipment is a meter of complex reflection and transmission coefficients, a waveguide measuring canal with a special measuring cell, consisting of two irregular waveguides and a waveguide chamber between them, which provides insignificant influence of higher-order modes. The dependences of the amplitude and phase of the reflection and transmission coefficients on frequency were obtained experimentally for fluoroplastic and three ceramic samples in the frequency range 78.33–118.1 GHz. The obtained S-parameters are processed according to an algorithm that includes their averaging based on the Fourier transform in order to obtain the values of the dielectric permittivity. Fluoroplastic was used as a reference material with a known dielectric constant. The dielectric constant of fluoroplastic has a stable value of 2.1 in the above mentioned frequency range. The dielectric constant of sample No. 1 varies from 3.6 to 2.5 at the boundaries of the range, sample No. 2 – from 3.7 to 2.1, sample No. 3 – from 2.9 to 1.5. The experimental data are in satisfactory agreement with the literature data for other frequencies taking into account the limits set by the measurement uncertainty.

A New Hybrid Chamber for Generating a Spectrum of Oblique Incident Plane Waves at the DUT

A novel type of hybrid measurement facility comprising a chamber antenna array (CAA) inside an overmoded waveguide (WG) is proposed and analyzed numerically. The reflecting walls of the metal rectangular WG are used in conjunction with a CAA to synthesize obliquely incident plane-wave (PW) fields at the device under test (DUT). This enables increased flexibility in emulating almost any PW multipath testing conditions in the WG chamber without the high cost and complexity of classical anechoic measurement systems employing relatively large phase-steered PW generators (PWGs). A modeling framework is proposed that has been used to devise first-order design rules (e.g., the number of independent propagating modes, dimensions of the WG, CAA, and DUT). Afterward, an optimally beamformed CAA example is presented to numerically validate the quality of the on- and off-axis PW fields in the test zone (TZ). This study shows design tradeoffs between the amplitude ripple in the DUT region, the total power focused in this region, the DUT size, and the angle of incidence.

Waveguide Planar E-plane Filter with Ultra-Wide Stopband

A waveguide planar bandpass filter for 2-cm wavelength range (13.5–14.5 GHz) with an ultra-wide stopband (up to the 6th harmonic of the central frequency of the bandwidth) is proposed, developed and experimentally investigated in this article. The filter with a bandwidth is designed on the basis of the antipodal fin-line (AFL) with an extremely high overlap of ridges, which has an overlap size to a waveguide height ratio is equal to 0.773. It allows to significantly reduce the cross-section of the filter waveguide chamber. The compact waveguide planar transformers located on the same substrate are used as the input and output transformers of the filter. It excludes the influence of inaccuracy in the filter structure adjustment relative to the joints with the supply waveguides. Despite the smallness of the resonators longitudinal dimensions in comparison with the half-wavelength in a AFL, the filter synthesis with an acceptable for practice accuracy can be carried out according to Cohn method, modified for its specified feature. At the same time, the decrease in the filter resonators’ intrinsic Q-factor, associated with a strong overlap of the AFL ridges, leads to dimension correction. However, this correction is performed in one of the common program packages of electrodynamic analysis based on the measuring results of the filter resonators’ intrinsic Q-factor.

Simulation of electromagnetic field distribution in the measuring cell for determining the dielectric permittivity of materials at microwave frequencies

To determine the dielectric permittivity of materials in a wide frequency range with the automation of measurements and the necessary accuracy, measuring cells have been created to ensure the simplicity of the design of the waveguide path. In order to obtain information about the suitability of measuring cells based on irregular SHF waveguides for estimation of dielectric parameters of materials, we simulated the structure of electromagnetic field in the system consisting of two irregular waveguides and waveguide chamber placed between them using a three-dimensional electrodynamic simulation in Ansoft HFSS package environment. The distribution of the electric field was simulated when an empty polyethylene tube, a rod of fluoroplastic and a rod of textolite are placed in the measuring cell. It was demonstrated that high order modes fade out in irregular waveguide and do not affect the precision of obtained results, and significant edge effects were not detected. It allows one to utilize measuring cells based on irregular waveguides together with a scalar or vector network analyzer and using the partial filling of the waveguide method or the modified Nicholson – Ross – Weir method for measurements of dielectric permittivity  of materials. The results of modeling the dependence of the amplitude and phase of the reflection coefficient of the textolite and fluoroplastic on the frequency in Ansoft HFSS environment are given. The simulation results are compared with the results obtained experimentally. The frequency dependencies of  were obtained experimentally for test materials – textolite and fluoroplastic – in the frequency range of 25,95–37,50 GHz. The experimental data are in satisfactory agreement with the results of theoretical calculations and do not go beyond the boundaries specified by the measurement uncertainty.

Reflection phase of electromagnetic bandgap structure measurement based on parallel‐plate waveguide system

A carefully designed parallel-plate waveguide measurement system is constructed to measure the reflection phase of a compact electromagnetic bandgap (EBG) structure. A quasi-plane wave is created in the parallel-plate waveguide chamber, which is the basic condition of phase measurement. Two EBG samples with different parameters are measured in this system. The data of the two samples agree well with those of infinite array EBG mode simulations, which proves that this measurement method has good accuracy and reliability. This system reduces the cost of EBG reflection phase measurement and the samples used in the experiment have a much smaller size.

Cylindrical Waveguide Electromagnetic Exposure System for Biological Studies with Unrestrained Mice at 1.9 GHz

This paper presents the development of an in vivo exposure system for exposing small rodents. The system consists of four identical cylindrical waveguide chambers, each with a plastic cage for housing the animal. The chamber is fed by circularly polarized radiofrequency power in the 1.9 GHz cellular frequency band and is vertically mounted so that the long axis of the animal is co-planar with the rotating incident electric field. Power sensors were used along with directional or hybrid couplers and a digital voltmeter for data acquisition for real-time dose rate monitoring. The system was tested to evaluate its dose rate performance when a mouse phantom or a mouse cadaver was inside the cage. The dose rate was quantified in terms of whole-body-average (WBA) specific absorption rate (SAR) per input power using both measurement and computational methods. The exposures of the mouse phantom and cadaver were evaluated for various possible postures and positions. The measurement results showed that the highest WBA-SAR was 16.9 W kg per 1 W incident power when the cadaver was lying prone against the cage wall and the lowest WBA-SAR was 10.4 W kg per 1 W incident power when the cadaver was standing upright in the cage center. These results were found to be in good agreement with those obtained from the computational method.

Dosimetry evaluation of a cylindrical waveguide chamber for unrestrained small rodents at 1.9 GHz

An exposure system, consisting of four identical cylindrical waveguide chambers, was developed for studying the effects of radiofrequency (RF) energy on laboratory mice at a frequency of 1.9 GHz. The chamber was characterized for RF dose rate as a function of animal body mass and dose rate variations due to animal movement in the cage. Dose rates were quantified in terms of whole-body average (WBA) specific absorption rate (SAR), brain average (BA) SAR and peak spatial-average (PSA) SAR using measurement and computational methods. Measurements were conducted on mouse cadavers in a multitude of possible postures and positions to evaluate the variations of WBA-SAR and its upper and lower bounds, while computations utilizing the finite-difference time-domain method together with a heterogeneous mouse model were performed to determine variations in BA-SAR and the ratio of PSA-SAR to WBA-SAR. Measured WBA-SAR variations were found to be within the ranges of 9-23.5 W/kg and 5.2-13.8 W/kg per 1 W incident power for 20 and 40 g mice, respectively. Computed BA-SAR variations were within the ranges of 3.2-10.1 W/kg and 3.3-9.2 W/kg per 1 W incident power for 25 and 30 g mouse models, respectively. Ratios of PSA-SAR to WBA-SAR, averaged over 0.5 mg and 5 mg tissue volumes, were observed to be within the ranges of 6-15 and 4-10, respectively.

SAR and efficiency evaluation of a 900 MHz waveguide chamber for cell exposure

In this work we present the results of numerical and experimental dosimetry carried out for an in vitro exposure device to irradiate sample groups at 900 MHz. The cells are kept in 8 and 15 ml cell cultures, contained, respectively in T25 and T75 rectangular flasks. The dosimetric assessment of the distribution of the specific absorption rate (SAR) is performed for both the bottom of the flask and the whole volume of the sample to provide results for experiments on either the cell layer or the cell suspension. The irradiating chamber is a rectangular waveguide (WG). Different configurations are considered to assess the optimum orientation and positioning of the cell cultures inside the WG. The system performance is optimal when the electric field is parallel to the sample and the WG is terminated by a matched load. In this condition two 15 or four 8 ml cells cultures can be exposed. The efficiency (ratio between the power absorbed by the sample and the incident power) and the non-uniformity degree (ratio between the standard deviation of SAR values and the average SAR over the sample) are calculated and successfully verified through measurements of the scattering parameters and local temperature increases. In the chosen exposure configuration, the efficiency is 0.40 and the non-uniformity degree is 39% for the 15 ml samples. For the 8 ml samples, the efficiency is 0.19 and a low non-uniformity degree (15%) is found.

Design of an Exposure Chamber for Biological Experiments

The main aim of this work is to design and to simulate an exposure chamber which can simulate mobile phone emission patterns in order to analyze the influence of electromagnetic field on small animals. During our previous research we found the most suitable type of an exposure chamber for this purpose. The basic properties such as electromagnetic field distribution and impedance matching of our designed chamber were optimized and verified by the aid of a 3D electromagnetic field simulator. As a result of our effort a cylinder waveguide chamber with a working frequency 900MHz has been designed. In the cylindrical structure a circular polarization is excited in order to even the exposure. The chamber is terminated by matched loads on both lateral sides which serve for preventing a possible resonance between sides and the animal.

Ornithine decarboxylase activity of L929 cells after exposure to continuous wave or 50 Hz modulated radiofrequency radiation—a replication study

A replication study with some extensions was made to confirm enhancement of ornithine decarboxylase (ODC) activity in murine L929 fibroblasts after radiofrequency (RF) field exposure reported in earlier studies. L929 cells purchased from two cell banks were exposed for 2, 8, or 24 h to continuous wave or DAMPS (burst modulated at 50 Hz, with 33% duty cycle) signals at specific absorption rate (SAR) levels of 2.5 or 6.0 W/kg. Exposures were carried out in Crawford and waveguide chambers, at frequencies 835 and 872 MHz, respectively. The results did not confirm findings of previous studies reporting increased ODC activity in RF-exposed cells. When Crawford cell exposure system was used, ODC activity was either not affected (in the case of 8 or 24 h exposures) or decreased after 2 h exposure at the highest SAR level (6 W/kg). The decrease was most pronounced when cooling with air flow was not used, and is most likely related to increased temperature. The minor methodological differences (use of antibiotics, increased sensitivity of ODC assay) are not likely to explain the inconsistency of the findings of the present and previous studies. Different results were obtained in experiments with the waveguide system that involves more efficient temperature control. In this exposure system, ODC activity was increased after 8 h exposure at 6 W/kg. Further studies are warranted to explore whether this finding reflects a true non-thermal effect. The present study did not provide evidence for modulation-specific effects reported in earlier studies.

A high-efficiency waveguide applicator for in vitro exposure of mammalian cells at 1.95 GHz

A standardized exposure device for a set of in vitro bioelectromagnetic experiments, to be carried out in different laboratories under strictly standardized exposure conditions, was designed and tested on the basis of efficiency and field uniformity criteria. In particular, a WR-430 waveguide was chosen in order to expose mammalian cells cultures at 1.95 GHz. The cells could be exposed in either one, two, or four 35-mm Petri dishes filled with 3-mL samples. Numerical and experimental dosimetry was carried out in order to assess the optimum orientation and positioning of the circular Petri dishes inside the simple waveguide chamber, obtaining very satisfactory performances of the system when the electric field is parallel to the sample. The efficiency and the nonuniformity degree simulated were successfully verified through measurements of the scattering parameters and local temperature increases.

A Waveguide Chamber for Measurements of Temperature Distributions in Raw Materials under Microwave Heating

A demountable waveguide chamber designed for the measurement of temperature distributions in raw materials under microwave heating is described. The thermovision oscillograms of temperature fields in nonferrous ore samples are presented.

Instrumentation for faint microwave line emission measurement

It is difficult to detect faint microwave line emission from a low-temperature source. In this paper, cost-effective methods of detecting these emissions are presented. A Dicke-type receiver (DTR) with an analog lock-in amplifier has been constructed to detect 22 GHz spontaneous emission from water vapor. The receiver compares the brightness temperatures of two waveguide chambers, one containing water vapor and the other empty. The system is capable of detecting a brightness temperature difference as small as 0.2 K. The experimental results prove that the emission from water vapor is detected for the first time with water vapor at 18 mm Hg and room temperature. The observed brightness temperature difference is 0.41 K. A "sampling digital" integration technique (SDIT) is also used to detect the emission from water vapor. The experimental results agree with the results obtained with the analog lock-in amplifier. The main advantage of SDIT over the DTR is the flexibility on the integration time and the range. In both methods, cost-effective brass plates are used for the low-temperature backgrounds for the first time.

Development and use of a nonrestraining waveguide chamber for rapid microwave radiation killing of the mouse and neonate rat

The use of microwave energy for rapid killing of small rodents such as the mouse or rat has become a standard pharmacologic technique since approximately 1975. This method allows investigation of rapidly modulated neurochemical indices, neuromodulatory substances, and some neurotransmitters to be determined at basal concentrations in brain regions and microregions. Previously described devices for use with microwave generators have relied on total body restraining holders in order to properly position rodents and neonates within a closed waveguide during microwave energy exposures. The present information describes two alternate chamber designs which do not require restraint of the rodent. A positioning device is described which must be used with the waveguide chambers. The animal chambers are designed to be used with 2450 MHz energy.

Effects of microwave radiation on erythrocyte membranes

Suspensions of rabbit, human, and dog erythrocytes were irradiated by S‐band microwaves in a WR‐284 waveguide chamber for a period of 20 minutes or three hours. The release of K+ and hemoglobin, and the osmotic fragility of the cells, were assayed to determine the effects of microwave and conventional heating on erythrocyte membranes. Conventional heating and microwave radiation resulted in sample temperatures that ranged from 25 to 44°C. There were no statistically significant differences between freshly prepared cells that were irradiated and those heated in a temperature‐controlled water bath at energy absorption rates near 200 mW g−1 for three‐hour exposures at a frequency of 3.0 GHz, and near 80 and 100 mW g−1, respectively, for frequencies of 2.45 and 3.95 GHz. Freshly prepared suspensions of rabbit erythrocytes and ouabain‐treated suspensions were also exposed to 3.0‐GHz microwaves at an absorption rate of 170 mW g−1 for 20 minutes or for three hours. No statistically signficant differences were detected between irradiated and water‐bath‐heated samples. In addition, effects of 3.0‐GHz microwaves on rabbit erythrocytes that had been held for seven days at 4°C prior to three hours of exposure were studied at a range of absorption rates to 170 mW g−1; no statistically significant effects of microwave irradiation were observed compared with the water‐bath‐heated controls although both modes of heating induced permeability changes relative to room‐temperature controls.