Improved Permittivity Calibration Method for Wideband In Situ Permittivity Probe
This letter discusses about an improved permittivity probe calibration method for calculating the complex permittivity of soils from reflection data over a very wide bandwidth. The accuracy of this method is demonstrated using reflection data collected from a unique wideband (10-1000 MHz) permittivity probe specifically designed for quick in situ permittivity measurements of soils at different depths. The improved calibration method is based on the traditional capacitance model, which suffers from errors caused by the assumption that the capacitance is independent of the frequency and the permittivity of the ambient medium under test. The improved capacitance model is introduced here to account for the frequency- and permittivity-dependent effects. Thus, it produces more accurate permittivity estimation over a much wider frequency and permittivity ranges. This letter will discuss about the accuracy of this improved permittivity probe calibration method and a wideband in situ soil probe design.
Wideband in-situ soil permittivity coaxial probe
A novel probe design form measuring complex permittivity of soils in-situ from 10 to 1000 MHz and above without taking soil samples is presented. The dielectric constant and conudctivity of soil is derived from step-frequency reflection taken inside a small (1∼2 inches) freshly bored holes. As a result, permittivity at various depths from surface with in-situ moisture content and soil texture can be obtained in the fields. A novel calibration method was developed to account for the frequency-dependent geometrical factor which causes bias errors in conventional calibration methods. This paper will discuss about the novel probe design and calibration method based on numerical simulation data. We will present the fabricated instrument and measurement examples during the conference.
An analytical approach to the design of electrodes in high-power, fast-transverse-flow CO2 lasers
Abstract Usually, the design of the electrodes of fast-transverse-flow CO 2 lasers relies more on experimental data than on theoretical analysis. Traditional systems sustain a stable, high-power discharge but the current distribution generates a peaked, non-uniform small-signal-gain pattern. We present a theoretical model suitable for the design of electrodes that achieves a quasi uniform gain distribution. The analysis, based on a two-temperature model and the gas-transport equations, computes the electron density that supports a flat gain pattern. Combining the desired electron density with the electron-balance equations, the model determines the required electric field. The results were used to design a new set of electrodes for a home-made fast transverse flow CO 2 laser. A stable, large volume discharge ( 4 × 8 × 90 cm 3 ) with very good uniformity was obtained. The resulting gain distribution was registered in a bi-dimensional map. The peak gain rose from 1.2 m - 1 , attained with the old electrode set, to 1.6 m - 1 with the new one and the gain showed a homogeneous profile.