Multiple Frequency Measurements Research Articles

Numerical computation of impedances of a human tooth for estimation of the root canal length.

Alternative current (ac) current conduction through a human tooth has been investigated through numerical simulation. Numerical calculation of impedance between the file (electrode) inserted in the root canal of the tooth and the outer electrode enables investigation of the impedance method used in dentistry for evaluation of the root canal length. Simulations confirm the improved sensitivity of the impedance method using the results of multiple frequency measurements.

Dielectric sleeve resonator techniques for microwave complex permittivity evaluation

Closed-form analytical solutions are derived for accurate microwave dielectric characterization of rod test specimens inserted into dielectric sleeve resonators placed centrally in a metal cavity. Low-loss sleeve resonators can be used advantageously for multiple frequency measurements of the same specimen and may be employed for accurate dielectric characterization of high-permittivity specimens having dielectric loss factors greater than 0.001. Uncertainty relations for permittivity and dielectric loss are also shown, which demonstrate that when sample electric energy filling factors are greater than 0.4, relative uncertainties in measured permittivity and dielectric loss tangent are less than 1% and 4%, even for relative permittivities greater than 600. Example measurements are given that illustrate how this dielectric resonator system can be employed for dielectric characterization of ferroelectric materials at temperatures both near or far from their Curie temperatures.

Gigahertz surface acoustic wave probe for chemical analysis

This paper considers the propagation of high frequency 0.1–2.6 GHz surface acoustic wave pulses in aqueous solutions of pure water, glycerol and protein. The GHz frequency components of the pulse are used to provide the highest operating frequencies so far reported and also to construct the first acoustic absorption spectrum associated with the evanescent field. Acoustic generation is sourced from a single non-linear SAW device that provides a series of harmonic frequencies, simultaneously. The received power level is determined from digital samples of the received pulse waveform. The power leaked into glycerol solutions at the fundamental frequency was found to be 50% smaller for pulses, than for continuous acoustic waves, an effect that could be related to the equilibration of the evanescent field. Increasing the concentration of the glycerol solutions or time exposed to the protein (IgG) solution, showed that the power losses from the surface acoustic wave pulse were broadly consistent with the behaviour of transverse shear mode sensors. Atomic force microscope measurements of the bare device revealed that the morphology of the silica overlayer was uniformly granular, whereas adsorbed protein films formed non-contiguous islands. Confirmation of the presence of the IgG film was obtained from quantitative X-ray photoelectron spectroscopy. An 8 gigasample per second digitising oscilloscope running a fast Fourier transform routine captured the acoustic absorption spectrum, and revealed a smooth characteristic for the glycerol and IgG, although for the latter, frequencies beyond 500 MHz were associated with an irregular spectrum. These multiple frequency measurements of the solid–liquid interface provide evidence that when the penetration depth and film thickness are similar, disruption of the predicted exponential form of the evanescent wave occurs, as indicated by the fluctuations seen in the absorption spectrum recorded. These preliminary results have shown that multiple frequency operation of single non-linear SH-SAW devices is possible, and an evanescent interfacial absorption spectrum can be obtained. By extending the measurement technique it may be possible to obtain additional information about the structure and composition of the solid–liquid interface.

Enhanced ELF wave generation efficiency using ‘O’ Mode HF heating of the ionosphere: An instrumental explanation

In [Barr et al. 1997] we presented ELF signals received near the Tromsø ionospheric heater facility when the heater radiated HF signals amplitude modulated by a 505Hz square wave. Square wave modulation enabled simultaneous multiple frequency measurements to be made of the signals radiated from the ionosphere as the heater was switched to radiate both ‘X’ and ‘O’ mode HF waves. We found that whereas the first 3 odd harmonics of the square wave (≥ 1515 Hz) all showed the accepted behaviour of reduced wave excitation on switching from ‘X’ to ‘O’ mode HF heating, the fundamental frequency showed enhanced excitation of more than 10dB with ‘O’ mode heating. These observations were given an ionospheric explanation in terms of a change from Hall to Pedersen current modulation with the change from ‘X’ to ‘O’ mode HF heating. We present here an alternative analysis, which has both instrumental and ionospheric components and is also able to explain the observations.

Bedside determination of fluid accumulation after cardiac surgery using segmental bioelectrical impedance.

Bioelectrical impedance analysis (BIA) is based on the physical property of tissues to conduct electrical currents, impedance being inversely related to tissue fluid content. At high frequency, the electrical current flows across both intracellular and extracellular pathways, making the assessment of fat-free mass possible while a low-frequency current flows through the extracellular space. Similarly, segmental BIA may be used to assess segmental body fluid repartition. The aim of this study was to assess fluid accumulation after cardiac surgery by multiple frequency segmental BIA. Observational, clinical study. A 17-bed, surgical intensive care unit in a university hospital. Twenty-six patients before and after open-heart surgery with cardiopulmonary bypass. None. After surgery, fluid accumulation resulted in a decrease in whole-body and segmental bioelectrical impedance in the arm and in the trunk. There was a good correlation between the fluid accumulation measured by fluid balance and by whole-body or segmental impedance changes. The major part (71%) of fluid accumulation occurred in the trunk. Multiple frequency measurements did not indicate a fluid shift between the intra- and extracellular compartments. Cardiac surgery produced a significant decrease in segmental trunk BIA, reflecting fluid accumulation at the trunk level.

D-region electron concentration profile produced by the July 9, 1962, nuclear detonation

Three possible D-region electron concentration profiles resulting from the July 9, 1962, ‘Starfish’ nuclear detonation are derived, using multiple frequency measurements of the absorption of cosmic radio noise. Two methods of profile determination are used. The first method uses both the classical magnetoionic theory of Appleton and the generalized magnetoionic theory of Sen and Wyler. The second method uses only the classical theory of Appleton. The electron cencentration height profiles obtained by the use of the two methods are then compared. The three profiles are found to differ by a maximum of 50% over the main absorbing region, which is centered about 60 km. A possible future application to the derivation of profiles produced by certain types of sudden ionospheric disturbances is discussed.