S.S. Stuchly

Permittivity measurements using open-ended sensors and reference liquid calibration-an uncertainty analysis

Results of the uncertainty analysis of the error-corrected permittivity measurements of materials using open-ended sensors are reported. Uncertainties in the permittivities of the reference liquids due to the uncertainties in the Cole-Cole parameters are discussed. The effect of the selection of these parameters of reference liquids, when used as calibration standards for error-corrected permittivity measurements, is highlighted. The results of measurements performed on 15 and 30 ppt saline test liquids are presented along with the measurement uncertainties resulting from uncertainties in the Cole-Cole parameters of the reference liquids. >

Propagation of transients in dispersive dielectric media

The propagation of transient electromagnetic fields in dispersive dielectric media is studied. The dielectric medium is assumed to be linear, isotropic, and homogeneous, and is described by the Debye model. Incident fields are assumed to be transverse electromagnetic plane wave pulses. The dielectric body can assume the form of infinite half space or an infinite circular cylinder, either of which may be homogeneous or stratified. The electric fields induced in the dielectric are calculated from time-domain Maxwells equations using the finite-difference time-domain method. >

Pulse-receiving characteristics of resistively loaded dipole antennas

The pulse-receiving characteristics of resistively loaded dipoles are analyzed using a time-domain numerical technique. The Wu-King nonreflecting dipole and several other dipoles with higher and lower distributed resistances are considered. The time-domain responses of these dipoles to Gaussian electromagnetic pulses (incident in boresite direction) are calculated. Frequency-domain receiving transfer functions are obtained using the fast Fourier transform (FFT) technique. Dipoles terminated with high resistance loads are also considered. The effect of the distributed resistance and terminal resistance on the pulse response and bandwidth is discussed. >

Capacitive sensors for in-vivo measurements of the dielectric properties of biological materials

Two open-ended coaxial sensors for in vivo measurements of the dielectric properties of biological tissues at low radio frequencies are described. The high fringing-field capacitance of these sensors allows accurate measurements of high-water-content tissues at frequencies as low as 10 kHz. Each sensor is represented by two capacitances, which are calculated using the method of moments. Theoretical and experimental results for experimental sensors terminating a standard 14-mm coaxial line with a GR900 connector are presented. >

Resistively loaded loop as a pulse-receiving antenna

The impedance-loaded loop antenna is theoretically analyzed in steady state using the Fourier series expansion technique. An expression is derived for the receiving transfer function or sensitivity. An equivalent circuit for the receiving antenna is presented. Numerical results are provided to illustrate the dependence of sensitivity on frequency, loop radius, distributed resistance, and incident wave direction. The time-domain receiving response of a resistively loaded loop antenna is calculated for Gaussian and differentiated-Gaussian incident wave pulses, and the numerical results are discussed. >

A broad-band resistively loaded V-antenna: experimental results

A broadband receiving antenna was realized using a resistively loaded thin-film V-monopole and a 500- Omega oscilloscope probe. The pulse-receiving performance of the antenna was evaluated in a time-domain antenna range, for various directions of the incident pulse. The antenna is capable of receiving a 520 ps electromagnetic pulse, incident within 45 degrees from the boresite direction, with good fidelity. The antenna was also tested in a transverse electromagnetic cell in the time and frequency domains. The frequency-domain receiving transfer function of the antenna was found to be within -57+or-3 dB in the 22 MHZ to 1.1 GHz frequency range. >

Uncertainties in radiofrequency dielectric measurements of biological substances

Capacitive sample holders and an automatic network analyzer are used to measure dielectric properties of biological tissues in vivo and in vitro at a controlled temperature in the frequency range of 10 kHz-100 MHz. An analysis of uncertainty is performed leading to the optimization of the sensor and the measurement system. Under optimized conditions, one sample holder can be used over the entire frequency range, and uncertainties below ±3% in the dielectric constant and ±1% in the loss factor are achieved for high water content tissues (blood, muscle, brain, liver, kidney, and spleen).

A new sensor for dielectric measurements

A new fringing-field capacitor for in-vivo studies of biological tissues at low radio frequencies is proposed. It consists of multiple coaxial rings fed with alternating polarity and allows an increase in the fringing-field capacitance by an order of magnitude, as compared with a standard open-ended coaxial line. The parameters of the equivalent circuit are found using the moment method. Theoretical and experimental results for test capacitors terminating a standard 14-mm coaxial line with a GR900 connector are presented.

A broadband E-field sensor

A broadband (10-kHz-350-MHz) E-field sensor based on an electrically small antenna for measurements of transient fields has been developed. The antenna is coupled to a receiver using a wideband buffer amplifier. The sensitivity of the sensor depends on the size of the antenna, while the broadband performance is determined by the size of the antenna, the input impedance of the amplifier, and the coupling between the two devices. The sensor is calibrated in a TEM (transverse electromagnetic) cell using CW (continuous-wave) and pulsed fields. Results of an analysis and calibration of the sensor are presented. For a sphere of 9.6-cm diameter coupled with a 1-M Omega microprobe, the sensor provides a flat response with sensitivity of 1 mV/(V/m) from 10 kHz to 350 MHz. The risetime of the output pulse is less than 500 ps. The dynamic range of the sensor is expected to be on the order of 80 dB.<<ETX>>

Uncertainties in the determination of dielectric properties in the infinite sample method

In the infinite-sample method, the sample permittivity is found from the measured input reflection coefficient. The reflection coefficient domain of a traveling-wave system is transformed into the complex permittivity domain by two subsequent mappings which include the inverse bilinear and Schwarz-Christoffel transformations. The error bounds in permittivity measurements are derived. The dielectric properties and respective uncertainties are presented for a water sample in the form of the Cole-Cole diagram. The case presented represents the first step leading to a more general presentation of uncertainties in dielectric measurements. >