A Novel Hybrid-Channel Attenuation Measurement System at 50–110 GHz
A novel hybrid-channel attenuation measurement system has been built for the measurement of Vand W-band waveguide attenuators from 50 to 110 GHz. The measurement system combines two single channels of the V and W bands together into one system. The V-band channel is used as the measurement channel and the W-band channel is used as the synchronization channel when the V-band attenuator is measured and vice versa. The measurement system is free of cross talk between the two channels and removes the need for isolators between the local oscillator and the mixer since the RF signal frequencies in the two channels are different. In addition, a compensation module was designed to cancel the self-mixing produced by the W-band mixer at frequencies above 102 GHz. The expanded uncertainty of the system is evaluated to be 0.004-0.08 dB at frequencies ≤102 GHz and 0.005-0.11 dB at frequencies 102 GHz for an attenuation range from 0 to 80 dB.
A New Dual-Channel Measurement Method for Accurate Characterization of Low-Permittivity and Low-Loss Materials
A dual-channel attenuation measurement system has been developed to measure the dielectric properties of low-permittivity and low-loss homogenous materials. The scattering parameters are derived from a series of transmission measurements, which were performed under different reflection coefficients of the source and load ports set by a pair of automatic tuners. The reflection coefficients of the automatic tuners were calibrated with the vector network analyzer (VNA) before the measurements. The mismatch error is effectively eliminated with the measurement and calculation process. The measurement scattering parameters are of much smaller uncertainties than those with the VNA. A polyimide aerogel sample is measured at X-band frequencies, its permittivity is about 1.075, and the loss tangent is about 0.001. The corresponding standard uncertainties are 0.0014 and 0.00048, respectively. The uncertainty of the loss tangent is reduced by one order compared to the results based on VNA. For validation of the proposed method, measurements of two polytetrafluoroethylene (PTFE) samples with different thicknesses were also conducted. This paper provides a broadband method for dielectric characterization with improved accuracy for low-permittivity and low-loss materials and can easily be extended to other waveguide bands.
Within and Inter-Institutional Differences Between Death Certifiers on Autopsy Conclusions
This study seeks to establish whether medico-legal practitioners differ in their autopsy conclusions within and across medico-legal institutions. Data include 459 violent deaths (homicides, suicides, and accidents) autopsy reports written by more than 20 death certifiers from four medico-legal institutions in two countries (France and the United States). Multinomial models show that compared with accidental deaths, weapon use and decedents’ characteristics both influence a homicide verdict, but not a suicide one. In addition, French practitioners are more likely than Americans to reach a conclusion of homicide or suicide compared with accident, and homicides are more likely to be certified by male practitioners.