Claude Weil

Dielectric characterization of low-loss materials a comparison of techniques

Measurements on low-loss materials using closed and open cavity resonators, and dielectric resonator methods are presented. Results indicate that consistent measurement results can be obtained with a number of well-characterized fixtures. Uncertainties associated with each method are addressed. Measurements also were performed on materials used in previous intercomparisons.

Efficient and accurate testing of an EMC compliance chamber using an ultrawideband measurement system

This paper summarizes a joint NIST-Industry measurement effort. The purpose of this effort was to use a NIST-developed ultrawideband measurement system to assess the performance improvement of a ferrite tile anechoic chamber after a partial retrofit. Measurements were performed in the 30-1200 MHz frequency range before and after treatments were applied and excellent results were obtained. The system exhibited good sensitivity and the results highlight the effects of various retrofitting treatments. The effort also demonstrates that the NIST ultra wideband system is an efficient tool for the evaluation for both current and proposed anechoic EMC compliance test chambers.

Exposure of Rats to 425-MHz (CW) Radiofrequency Radiation: Effects on Lymphocytes

Four experiments were performed in which six pregnant rats were exposed from day 12 of pregnancy to parturition, for 4 hours a day in a temperature-controlled environment, to 425-MHz (CW) radiation, using a multimode rectangular strip transmission line. Four male pups born to each dam were subsequently irradiated under the same RF exposure condition for 20-21 days of age (2 pups) and 40-41 days of age (2 pups). Specific absorption rates (SARs) for rats of different ages were determined by twin-well calorimetry as well as from calculations of power measurements of incident, reflected, and transmitted energy. Values of SARs between 3.1 and 6.7 mW/g were obtained for rats so exposed at 425 MHz. At selected times, rats were weighed to determine if the irradiation affected growth. Two rats from each litter (4 pups) were euthanized at 20-21 and two at 40-41 days of age and blood was obtained for complete blood counts. The in vitro blastogenic response of blood and lymph-node lymphocytes was measured by 3H-thymidine incorporation into DNA following stimulation of cells with T- or B-lymphocyte mitogens. No difference was observed in the weights of irradiated compared with sham-irradiated rats. No consistent change in the peripheral blood picture was observed between irradiated and sham-irradiated rats. Significant increases in the response of lymph-node but not of blood lymphocytes from irradiated rats following stimulation with mitogens was observed in two of four experiments. These changes were observed for both T- and B-lymphocytes. In another experiment at the same frequency, six pregnant rats were irradiated for 16 hours daily from day 6 through day 19 of pregnancy. The pups born to these dams were not subsequently irradiated. These rats, born to irradiated dams, showed a similar increased response of node but not of blood lymphocytes to T-cell mitogens at 42 days of age. These results indicate that exposure to 425-MHz microwave radiation, under the conditions described, may lead to increased responsiveness of node lymphocytes to in vitro stimulation by mitogen.

Dielectric and Magnetic Measurements: A Survey of Nondestructive, Quasi-Nondestructive, and Process-Control Techniques" *

A review of the most common methods for nondestructive permittivity and permeability measurements is presented. Transmission-line techniques, coaxial apertures, open resonators, surface-waves, and dielectric resonator methods are examined. Measurements on bulk, thin materials, and thin films are addressed. Measurement fixtures that can be used as sensors are highlighted. The frequency range of applicability and typical uncertainties associated with each method are addressed.

On RF material characterization in the stripline cavity

We examine the accuracy of the air-filled stripline cavity in measuring the dielectric and magnetic properties of bulk materials in the frequency range of 150-2000 MHz. Measured data on complex permittivity and permeability for several different-sized specimens of dielectric and magnetic materials were compared with reference values obtained using other techniques of known uncertainties. Major differences were noted for both complex permittivity and permeability data, and we largely attribute these to less-than-optimal perturbation of the internal cavity fields by the material specimens under test. The technique is particularly unsuited to measuring the dielectric loss of the higher-permittivity low-loss materials due to energy scatter by the specimen under test. In order to improve measurement accuracy, we suggest guidelines on the range of specimen electric and magnetic volume needed for optimal cavity perturbation.

Chronic Exposure of Rats to 100-MHz (CW) Radiofrequency Radiation: Assessment of Biological Effects

A multidisciplinary approach was employed to assess the possible biological effects of chronic exposure of rats to 100-MHz continuous wave (CW) radiofrequency (RF) radiation. Pregnant dams and later their offspring were exposed daily for 4 hr for up to 97 days of age. Specific absorption rates (SARs) for rats of varying ages were determined by twin-well calorimetry. Between exposures, animals were evaluated using various developmental and biological indices. No difference was observed between 100-MHz-exposed and sham-exposed rats for complete blood counts, mitogen-stimulated response of lymphocytes, frequency of T- and B-lymphocytes, or antibody response to Streptococcus pneumoniae capsular polysaccharide. No mutagenic effect on the sperm cells of rats exposed for over 90 days to 100 MHz was observed using the Dominant Lethal Assay. The mean time to eye opening was significantly accelerated in exposed compared to sham-exposed rats. In rats exposed to 100 MHz, significant decreases in the activity of acetylcholinesterase were observed in the striatum and medulla oblongata of 22-day-old rats and in the midbrain of 40-day-old rats but not in 97-day-old animals.

Across-the-road photo traffic radars: new calibration techniques

We discuss simulator units for calibrating across-the-road Doppler traffic radar transceivers used in enforcement of highway speed limits. Two units of very similar design were developed, one operating at K-band (24 GHz) and the other at Ka-band (35 GHz). The signal received from the radar transmitter is frequency-modulated at rates that correspond to the expected Doppler shift for approaching and receding vehicles travelling at speeds of 25 to 200 km/h. The modulated signal is subsequently retransmitted back to the radar receiver, which demodulates it and then displays the simulated speed. The required calibration accuracy is 1.6 km/h at 90 km/h.

Fetal and Maternal Effects of Continual Exposure of Rats to 970-Mhz Circularly-Polarized Microwaves

Virtually continual exposure to 970-MHz microwaves in circularly-polarized waveguides was used to elicit fetal responses in Sprague-Dawley rats during gestation. A total of 250 rats were exposed to microwave radiation at whole-body averaged specific absorption rates (SAR) of 0.07, 2.4, or 4.8 W/kg or concurrently sham-irradiated for 22 h/day from the 1st through the 19th day of gestation. Prior to irradiation or sham irradiation, the rats were acclimated to cages in the waveguide system for 10 days and then bred. The rats were killed on the 20th day of gestation, and their fetuses counted and weighed, the fetal sternebrae ossifications counted, and the number of corpora lutea of the pregnancy determined. There were no alterations in pregnancy rates, fetal numbers (live, dead, resorbed, or total conceptuses), fetal weights, fetal skeletal maturation, or preimplantation losses after exposure at SARs of 0.07 or 2.4 W/kg. At SAR of 4.8 W/kg, only fetal body weight was significantly altered (- 12%, p = 0.012)....

Assessing the effects of an OATS shelter: is ANSI C63.7 enough?

This paper summarizes a previous measurement effort by NIST researchers at an open-area test site (OATS), operated by a large information technology equipment manufacturer. The purpose of this effort was to assess the effects on emissions measurements of a fiberglass dielectric shelter that is used to protect and temperature stabilize information technology equipment undergoing emissions tests. NIST researchers and industry are seeking to answer questions about the impact of OATS shelters using an ultra wideband time-domain measurement system. This paper summarizes the instrumentation used, the measurement methodologies, and the data obtained. The results indicate that the fiberglass shelter can have a significant impact at frequencies above 100 MHz, a result which should be of interest to the emissions testing community.

RF material characterization using a large-diameter (76.8 mm) coaxial air line

We report on the development of a 76.84 mm (3.025 in) diameter coaxial air line system whose purpose is to measure the dielectric and magnetic properties of bulk dielectric and ferrite materials over a frequency range of approximately 0.3 - 1500 MHz. We summarize the relative advantages and disadvantages of using large-diameter coaxial air lines for material characterization and we discuss the particular problems associated with calibrating vector network analyzers in this form of transmission line. We also present broadband measurement data on two lossy materials, including a ferrite-loaded polymer and carbon-loaded concrete.