Microwave Resonance Measurements Research Articles

Dielectric Loss Spectrum of Ceramic MgTiO3 Investigated by AC Impedance and Microwave Resonator Measurements

MgTiO3 ceramic was selected as a model material of the microwave dielectric ceramics for the investigation of the dielectric loss spectrum. Conductivity spectra in the low‐frequency range 1–106 Hz at elevated temperatures and the dielectric loss spectrum in the microwave range 6–14 GHz at room temperature were characterized by AC impedance spectroscopy and the microwave resonator method, respectively. The experimental data were analyzed by using Jonscher's universal power law, the Arrhenius equation as well as the classic dispersion theory. Consequently, a dielectric loss spectrum (tg δ∼f plot) at room temperature in a wide frequency range was obtained. Based on the loss spectrum, the dielectric loss can be classified into three mechanisms in MgTiO3 ceramic (each dominates the loss in different frequency ranges): DC conductance (in DC field), AC conductance (<107 Hz), and anharmonicity of lattice vibration (in GHz range). The influence of defects on the microwave dielectric loss possibly is because of atom defects via damage of the perfection of lattice and modification of the anharmonic force in lattice, while the electronic defects trapped on the atomic defects affect the DC and AC losses.

Microwave spectroscopy of Al I atoms in Rydberg states: D and G terms

We present results of microwave and millimetre-wave resonance measurements in D, F and G Rydbergstates of neutral aluminium in the frequency range 4–423 GHz for principal quantum numbersn = 22–43. In all, 12, 27 and 19 resonances of or , or and or series, respectively, have been recorded. D-state fine-structure doublet splittings have been obtained withaccuracy ± 1.4 MHz. For D and G states, quantum defect Ritz-expansion parameters have been determined,from which the Rydberg series can be accurately reconstructed to an accuracy of order ± 1 MHz(3 × 10−5 cm−1) forall n.

Meissner-London state in superconductors of rectangular cross section in a perpendicular magnetic field

The distribution of magnetic induction in Meissner state with finite London penetration depth is analyzed for platelet samples of rectangular cross-section in a perpendicular magnetic field. The exact 2D numerical solution of the London equation is extended analytically to the realistic 3D case. Data obtained on Nb cylinders and foils as well as single crystals of YBCO and BSCCO are in a good agreement with the model. The results are particularly relevant for magnetic susceptibility, rf and microwave resonator measurements of the magnetic penetration depth in high-Tc superconductors.

Contactless Mass Determination of Arbitrarily Shaped Objects by Microwave Resonator Measurements

ABSTRACTThe basis is presented for using a microwave resonant cavity as an effective “contactless balance”, providing information about the mass of dielectric objects inserted into the cavity. An uncertainty analysis presented in the paper confirms that the mass of small dielectric objects can be determined by this technique with an accuracy better than 4%.

Moisture Content Determination in Single Peanut Kernels With a Microwave Resonator

Abstract Principles are discussed for determining moisture content of individual peanut, Arachis hypogaea L., kernels by microwave resonator measurements, and data illustrating the application of these principles are presented. By measuring the shift in the resonant frequency and the change in the cavity transmission characteristics when a peanut kernel is inserted into the cavity, and taking the ratio of these two parameters, it is possible to obtain the moisture content of the kernel independent of its mass (size) and apparently independent of peanut type, as far as runner and virginia market types are concerned. Moisture contents in the range from 4 to 14 percent, wet basis, were determined with an uncertainty of 0.9 percent moisture, at the 95-percent confidence level.

Nondestructive Microwave Measurement of Moisture Content and Mass of Single Peanut Kernels

Principles for determining moisture content and mass of individual peanut kernels by microwave resonator measurements are discussed, and data are presented showing the application of these principles. By measuring the shift in the resonant frequency and the change in the cavity transmission characteristics when a peanut is inserted into the cavity, it is possible to obtain the moisture content of the kernel independent of its mass and apparently independent of peanut type, as far as Runner and Virginia market types are concerned. It is also possible to determine the kernel mass independent of kernel shape simultaneously with the moisture determination. Moisture contents in the range from 4 to 14%, wet basis, were determined with an uncertainty of 0.9% moisture, and the uncertainty in the mass determination was less than 0.05 g.

SENSING MOISTURE CONTENT OF PECANS BY RF IMPEDANCE AND MICROWAVE RESONATOR MEASUREMENTS

The moisture content of in-shell pecans, Carya illinoensis (Wangenh.) K. Koch, was measured by radio-frequency (RF) impedance measurements of a parallel-plate capacitor with a pecan between the plates and by microwave resonant cavity measurements with a pecan in the resonant cavity. Impedance measurements were also taken on pecan kernel halves. Nuts of six pecan cultivars, four from the United States and two from Israel, with kernel moisture contents ranging from 3 to 11% (w.b.) were included in the study. Although equilibrium moisture contents (m.c.) of pecan kernels and shells differ greatly, and proportions of total nut weight represented by the kernel and shell vary significantly among cultivars, a high correlation was found between total nut m.c. and kernel m.c. Standard errors of calibration (SEC) of 0.6% m.c. and 1.5% m.c. were obtained for determination of entire nut moisture content with electrical measurements on the whole nuts for the RF impedance and microwave cavity measurements, respectively. RF impedance measurements on kernel halves and on the in-shell pecans predicted kernel moisture contents equally well with SEC values of 0.6% m.c for both measurements.

COMPARISON OF DC CONDUCTANCE, RF IMPEDANCE, MICROWAVE, AND NMR METHODS FOR SINGLE-KERNEL MOISTURE MEASUREMENT IN CORN

ABSTRACT Methods for rapidly measuring the moisture content of individual com, Zea mays L., kernels are discussed. Direct comparisons of kemel moisture content determinations by single-kernel oven drying, nuclear magnetic resonance (NMR) measurements, parallel-plate radio-frequency (RF) complex impedance measurements, and crushing-roller dc conductance measurements are presented. These single-kemel moisture content values are compared to standard oven drying and Karl Fischer moisture content determinations on bulk grain samples from the same com lots equilibrated at moisture contents between 10 and 40%, wet basis. Comparisons of the RF complex impedance and crushing-roller dc conductance determinations of single-kemel moisture measurements on com and similar data for microwave resonant cavity perturbation measurements for the same purpose are discussed. All four electrical methods can provide single kemel com moisture measurements with standard errors of performance of less than 1% moisture content, which should be suitable for practical use. Aspects of the development of suitable equipment to use these principles in practical applications are also discussed.

The magnetic anisotropy of holmium substituted into GdAl2

Microwave resonance measurements are reported of the contribution to the magnetocrystalline anisotropy fields arising arising from substitution of gadolinium by holmium in the ferromagnetic phase of GdAl2. The whole temperature range of interest, down to 2 K, is covered. The single-crystal specimen employed has 0.2% holmium replacing gadolinium. The results are compared with calculations based upon a single-ion molecular-field theory. Calculations correctly predict that (100) and (111) crystallographic directions are both hard directions of magnetisation and (110) are easy at low temperatures. Agreement between the measured and calculated magnitudes and temperature dependences of the anisotropy fields is not close if, in the calculations, crystal-field and exchange-field parameters based upon published values for HoAl2 and GdAl2 are employed. When values for these parameters are derived by fitting the theory to measurements they differ substantially from the published values. However, they are in good agreement with the parameters derived from measurements of NMR of holmium substituted for 1% of gadolinium in GdAl2. This shows that the interaction of a holmium ion with its neighbour differs in dilute substitution from that in HoAl2.

Influence of thermal ions on the n d3/2-n f5/2 and n d3/2-n g7/2 microwave transition of sodium

We have studied the dipole-allowed nd3/2-nf5/2 and the dipole-forbidden nd3/2-ng7/2 transitions of sodium in the presence of thermal ions for n=15–17. Although the cross sections for the relevant ion–Rydberg atom collisons are too small to influence the observed transitions, these microwave resonance measurements indicate that there is a remarkable influence of even very low densities, 105 cm−3, of ions on the atoms. For instance, the d-g transition can be easily driven with a single photon, and the d-f and d-g transitions are shifted and broadened. Furthermore, the thermal sodium ions destroy the interference fringes obtained with the Ramsey method of separated oscillatory fields. Although these results are incompatible with reasonable estimates of ion-atom collision cross sections, they may be explained quantitatively in terms of the time-averaged charge of the ions.

Two‐frequency microwave resonance measurements from an aircraft: A quantitative estimate of the directional ocean surface spectrum

Measurements of the relative strength of ocean surface wave spectral components have been made from an aircraft using the two‐frequency microwave resonance technique. A coherent Ku band radar was used to study the Bragg type resonance matching (at the difference frequency Δf) to the surface wave components. The spatial spectrum of the surface reflectivity modulation was then computed as the value of Δf was varied over a matching range of approximately 15 m to 150 m in surface wavelength. This paper contains experimental results from flights conducted during the 1979 MARSEN project and the 1980 ARSLOE project, plus a theoretical formuation of the relationship between the radar measurement and the directional surface elevation spectrum. The objective here is to evaluate the two‐frequency resonance technique in terms of the strength of the radar response and the effects of surface illumination geometry, and to demonstrate the inversion of the radar data to absolute directional surface elevation spectrum. An independent measurement from the aircraft of the modulation transfer function required in this inversion and the resulting estimate of the surface spectrum are presented. Finally, a comparison is drawn between the Langley two‐frequency results and an estimate of the spectrum produced by the Wallops Flight Center surface contour radar.

Spin–rotation and hyperfine parameters for the (001) excited vibrational state of NO2 from infrared–radiofrequency double resonance

Magnetic–dipole spin–rotation transitions within the ground and v3=1 excited vibrational states of 14N16O2 have been observed by the technique of infrared–radiofrequency double resonance, utilizing near coincidences between CO laser lines and NO2 ν3 band transitions around 6.2 μm. The ground state data contribute to the extensive body of microwave, EPR, and double resonance measurements now available for NO2. The excited state data are the first high resolution measurements within this state, and they are used here to determine a set of spin–rotation and hyperfine interaction parameters for NO2 in the v3=1 state.

Evidence for the stratification of epitaxial films of Y 2.85La 0.15Fe 3.75Ga 1.25O 12 from microwave resonance measurements

Ferromagnetic resonance experiments on thin epitaxial films of Y 2.85La 0.15Fe 3.75Ga 1.25O 12, grown by a vertical dipping technique, provide strong evidence for stratification of these films. Perpendicular resonance spectra recorded after etching off the magnetic film step by step show resonances due to six strata in 4 μm thick films. Of each stratum the thickness has been determined as well as the magnetic anisotropy. It is found that the layer next to the interface is 0.4 μm thick and has a strongly negative K u ( K u M = -400 Oe) . Strata remote from the substrate are 1 μm thick and have a positive K u ( K u M ≈ + 150 Oe) .

Measurements of dielectric anisotropy of films in the microwave region by resonator perturbation method

The complex permittivity of films may generally be derived from microwave resonator measurements. Especially for anisotropy measurements, the suitability of different resonator types depends on the degeneracy of their resonance mode. If it is degenerated, degeneracy is lifted by anisotropic materials, the frequency splitting and intensity of resonance depending on anisotropy and direction of principal axis, respectively. Frequency splitting is observed only with high resolution, as obtained by open resonators. Experiments with an open resonator (Q>105) and results on polyethyleneterephthalate (permittivities parallel to surface) at 19 GHz are reported. They are in agreement with results at 9 GHz.

A High Sensitivity Bridge Detector Circuit System for Microwave Resonance Measurement

A high sensitivity detector system for microwave resonance measurements utilizing a bridge balancing method is described. This system consists of a parametron preamplifier, a phase modulated pump circuit, and a phase discriminator. The preamplifier amplifies the measuring signal and the quadrature AFC error signal alternatively.

Radio-Frequency Determination of New Growth-Induced Anisotropy in Garnets for Bubble Devices

A new type of magnetocrystalline anisotropy has been observed under {110} faces in several fluxgrown mixed rare-earth iron garnets. This anisotropy is different in direction and magnitude from that previously reported in similar garnets under {211} faces. In Eu2ErGa0.6Fe4.4O12 with 4πM near 350 G at 300°K, microwave resonance measurements have shown that {110} face material has a large effective uniaxial anisotropy. The [100] in the growth plane is the easy axis, [011] normal to this plane is medium, and [011̄] parallel to this plane is hard. Using a resonance equation appropriate to the orthorhombic magnetic symmetry and neglecting the relatively small cubic terms, the effective uniaxial anisotropy field is ∼1300 Oe. This anisotropy leads to a new cutting procedure (type 3 cut) for bubble devices: {100} platelets are cut normal to the natural {110} faces. Using 15-μ-thick platelets of this type, bubbles ∼8μ in diameter were propagated. The domain wall mobility is ∼170 cm/sec/Oe. These properties are comparable to those of {111} platelets cut under {211} surfaces of the same crystals.

Microwave resonant cavity measurement of shock produced electron precursors.

Abstract : Microwave resonant cavities operated in the TM sub 010 mode and constituting a part of the driven section of a pressure driven shock tube are used in the investigation. With argon as the driven gas (at a density of approximately 0.001 to 0.02 atmospheres) and hydrogen as the driver gas, the shock Mach number is varied over a range between 10 and 13.5. With the cavities operated in the S-Band region, electron densities of the order of 5 x 10 to the 7th power to 1 x 10 to the 10th power el/cubic cm can be measured. Using two cavities in tandem, tuned for the same resonant frequency and separated by a known distance, a measure of the precursor velocity is obtained. Several experiments are performed to determine the nature of the electron precursor, i.e., whether the precursor is due to large scale diffusion of electrons from behind the incident shock, or to radiation effects. It was found that: electron precursor densities as high as 10 to the 8th power el/cubic cm were measured as far as 1/2 meters in front of the shock, the electron precursor velocity is equal to the shock velocity, and the electron precursor in front of the shock is generated by radiation emitted from the ionized gas behind the incident shock. (Author)

Microwave resonance observations in gadolinium solid solutions

Microwave resonance measurements have been made on a number of paramagnetic, ferromagnetic and antiferromagnetic Gd-Lu, Gd-Y, Gd-Sc and Gd-La alloys. A paramagnetic value for g = 1.998 ± 0.005 has been obtained for those Gd-Y alloys containing small concentrations of gadolinium and close to the free-ion value; g = 1 995 ± 0.010 for dilute alloys of gadolinium in scandium or lanthanum. These values compare with a value for g = 2.010 ± 0 010 reported by Harris et al. in 1965 for Gd-Lu alloys of similar gadolinium content. In all alloys examined the g factor increases as the gadolinium content of the alloy decreases. The resonance line intensity of the Gd-Y and Gd-Lu alloys falls rapidly on cooling below the Neel temperature and observations have been made well into the spiral-spin region. As with ferromagnetic observations there is some uncertainty as to the factors influencing the absorption and no interpretation of these lines is made.

Rare-Earth Ion Relaxation Time andGTensor in Rare-Earth-Doped Yttrium Iron Garnet. I. Ytterbium

Microwave-resonance measurements at 9.3 and 16.8 Gc/sec between 1.5 and 300\ifmmode^\circ\else\textdegree\fi{}K in the principal crystallographic directions of a single-crystal of yttrium iron garnet (YIG) doped with 5.1% Yb are compared with the predictions of the longitudinal (so-called slow relaxing ion) mechanism of relaxation, which is briefly reviewed. Except for the low-temperature anomaly in the [110] direction, excellent agreement is found. A quantitative analysis allows deduction of the tensor $G$ describing the anisotropic exchange splitting of the ground-state Kramers doublet of the Yb ion. We obtain ${G}_{1}=31.9$ ${\mathrm{cm}}^{\ensuremath{-}1}$; ${G}_{2}=22.4$ ${\mathrm{cm}}^{\ensuremath{-}1}$; ${G}_{3}=8.5$ ${\mathrm{cm}}^{\ensuremath{-}1}$, which is a similar result to that reported from spectroscopic measurements on ytterbium iron garnet. The small differences probably reflect the different lattice dimensions in the two cases. We also deduce $\ensuremath{\tau}$, the relaxation time of the Yb ion in the YIG environment. The results are most extensive and accurate in the [111] direction, where the temperature dependence for $Tl60$ \ifmmode^\circ\else\textdegree\fi{}K indicates the dominance of a direct process as described by ${(\frac{1}{\ensuremath{\tau}})}_{D}={(\frac{1}{{\ensuremath{\tau}}^{0}})}_{D}coth(\frac{\ensuremath{\delta}}{2kT})$ with ${(\frac{1}{{\ensuremath{\tau}}^{0}})}_{D}=2.1\ifmmode\times\else\texttimes\fi{}{10}^{9}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ for ${\ensuremath{\delta}}_{111}=21.0$ ${\mathrm{cm}}^{\ensuremath{-}1}$. Taking into account that the measured relaxation time in this direction is a weighted average of the two relaxation times associated with the two values of the doublet splitting, we find that the observed direct process is well described by spin-magnon relaxation, which also gives a more consistent evaluation of the $G$ tensor than does spin-lattice relaxation. At higher temperatures, the temperature dependence of the observed relaxation time follows that expected for the Raman process, viz., ${(\frac{1}{\ensuremath{\tau}})}_{R}=A{J}_{8}{T}^{9}$, with $A=4.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ ${(\mathrm{\ifmmode^\circ\else\textdegree\fi{}}\mathrm{K})}^{\ensuremath{-}9}$ for a Debye temperature of 550\ifmmode^\circ\else\textdegree\fi{}K. This is in excellent agreement with the Raman-process relaxation time reported for Yb in yttrium gallium garnet, though it is some 5 orders of magnitude shorter than the theoretical estimate. The Orbach process is found to be unimportant over the temperature range covered.

Variation with Temperature of the Magnetocrystalline Anisotropy of Several Nickel Iron Ferrites

An investigation of the magnetocrystalline anisotropy K1 by microwave resonance measurements is reported for a series of nickel iron ferrite crystals in the temperature range of 4.2° to 300°K. Values of K1/Ms, where Ms is the saturation magnetization, calculated from previous torque measurements of K1 on similar materials agree with the present measurements of K1/Ms over a temperature range from 300°K to some lower temperature that is dependent on the composition. At this temperature, which decreases with increasing Fe2+ content, the microwave values of K1/Ms decrease sharply, while those derived from torque measurements continue to increase with decreasing temperature. The linewidth ΔH is anisotropic and temperature dependent with ΔH in the [111] direction exhibiting a maximum as a function of temperature. The value of g-effective increases as the temperature is lowered. There is qualitative, although not quantitative agreement between our data and theoretical results due to Clogston. Large magnetic annealing effects occur for each sample below a certain temperature. This temperature also depends upon the Fe2+ content.