Resonance methods of dielectric measurement at centimetre wavelengths

Horner, F.; Taylor, T.A.; Dunsmuir, Robert; Lamb, James L.; Jackson, Willis

doi:10.1049/ji-3-2.1946.0010

Cited by 30 publications

(16 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…All measurements were carried out using hermetically sealed pans with a cell purge of 20 mL min -1 of dry oxygen-free nitrogen. The dielectric properties of silver iodide were measured during conventional heating using the cavity perturbation technique [9][10][11]. The apparatus consisted of a cylindrical brass cavity (245 mm diameter and 24.5 mm high) with two internal loops, constructed from semi-rigid coaxial cable, used probe the electromagnetic response of the system at its resonant frequencies.…”

Section: Methodsmentioning

confidence: 99%

Hysteresis in the β–α phase transition in silver iodide

Binner

Dimitrakis

Price

et al. 2006

J Therm Anal Calorim

View full text Add to dashboard Cite

IntroductionSilver iodide can exist in three crystal polymorphs at atmospheric pressure [1]. Below 147°C the b-phase is stable; this has a wurtzite structure with the iodide ions arranged in a hexagonal close packed structure and with the silver ions occupying a sublattice of interstitial tetrahedral sites. Above 147°C silver iodide undergoes a crystalline transition to the high temperature a-phase, which has a body centred cubic arrangement of iodine ions with the silver ions distributed over a sublattice of interstitial sites whose number exceeds the occupancy of silver ions. This phase is stable up to the melting temperature of 555°C. Also present below 147°C is the metastable g-phase which differs from the b-phase in that it has a zinc blende structure with the iodide ions occupying a cubic close packed lattice. This can be viewed as a defect b-phase structure in which the iodide ions are layered ABABAB rather than ABCABC. Migration of Ag + though the disordered cationic lattice gives rise to exceptionally high ionic conductivity of the a-AgI phase [2]. The ordering of Ag + has been studied using computer simulations and it is the tendency of the cations to condense into a locally monoclinic arrangement which is unstable relative to the hexagonal (wurtzite) structure which is proposed as the driving force for the a-b phase transition [3].Previous investigators have reported the heat capacity of silver iodide using conventional and AC calorimetry [4,5]. These measurements have been carried out in heating only whereas Hanaya et al. have reported DSC studies on heating and cooling of the stabilisation of a-AgI by incorporating AgI inside porous silica [6]. In this work the nucleation of the low temperature phase is claimed to be inhibited by the reduction in AgI particle size. For bulk AgI claims have been made that the b-a phase transition can be made to occur around 100°C when the specimen is heated by microwave radiation rather than be conventional heating [7]. In this particular case, multi-phonon coupling between the electromagnetic field and vibrational motions within the AgI crystal are conjectured to stabilise the high temperature form in the same way that mechanical stress by reduction in particle size might also achieve the same effect. An alternative mechanism is the so-called 'ponderomotive effect' whereby microwave-excited ionic currents become locally rectified at interfaces (such as grain boundaries) so as to promote mass transport [8]. In the case of AgI there is no bulk diffusion of material during its structural transformation but it is not unreasonable to propose that this process might promote the formation of a-AgI.This work reports studies on the silver iodide a-b phase transition by conventional and modulated-temperature calorimetry. We also report dielectric property measurements under conventional and microwave heating. ExperimentalThe silver iodide powder (99.999%, Acros Organics) used for these studies was made into pellets with a density of 4.9±0.3 g cm -3 , i.e. 83% of theoretical d...

show abstract

Section: Methodsmentioning

confidence: 99%

Hysteresis in the β–α phase transition in silver iodide

Binner

Dimitrakis

Price

et al. 2006

J Therm Anal Calorim

View full text Add to dashboard Cite

show abstract

“…This is realized by forming sample insertion holes in the cavity walls and allowing the sample to be heated in a hot zone before returning it to the resonant cavity for measurement. Despite the increased diculties associated with solving Maxwell's electromagnetic equations for a cavity with insertion holes and the increased uncertainties in the data obtained due to the necessity to make approximations concerning sample shape and the sample holder, this method is by far the most popular for measuring the high-temperature dielectric properties of materials in solid phase by a cavity resonator technique [18,19] and was employed in this study.…”

Section: Dielectric Property Measurement Techniquesmentioning

confidence: 99%

“…For the sample dimensions and magnitude of permittivity encountered in these experiments, simple perturbation theory may be used to calculate the permittivity of the sample by the following equations [18,19]:…”

Section: Dielectric Property Measurement Techniquesmentioning

confidence: 99%

Untitled

2002

View full text Add to dashboard Cite

The eects of temperature and microwave frequency on the dielectric properties of MoS 2 and Pt catalysts together with an aluminum oxide support were investigated. Dielectric constants and dielectric loss factors were measured in a temperature range of 200±800 8C by a cavity resonator technique with a cylindrical copper cavity resonating in TM 0n0 modes (n 1; 2; . . . ; 5), which corresponded to frequencies of 0.615, 1.413, 2.216, 3.020, and 3.825 GHz.

show abstract

“…For low-loss dielectrics measured by using LTM e' is determined by solving the resonance condition [1] = p 0 tan (0 t b) + & tan [j8 0 (i> -fc)] = 0 (1) for the phase coefficient /? E of the wave in the dielectric, applying the Newton-Raphson iterative method, where P e = 2nf^/e' -q 2 fc 0…”

Section: Real Part E'mentioning

confidence: 99%

“…For 40 years the closed cavity resonator operated in the low-attenuation TE 01 mode, which consists of a hollow metallic cylinder of circular cross-section terminated by two short-circuit plates, has been used to measure the real part e' of the complex relative permittivity e = e' -je" and the tangent of the dielectric loss angle ('loss tangent'), tan S = e"/e', of materials in the microwave range [1], in particular of low-loss solids. Reviews of literature on dielectric measuring methods including cavity resonator techniques have been given by Bussey [2], Lynch [3], Chamberlain and Chantry [4] and, more recently, by Birch and Clarke [5].…”

Section: Introductionmentioning

confidence: 99%

Permittivity measurements using a frequency-tuned microwave TE01 cavity resonator

Ni¹,

Stumper

1985

IEE Proc. H Microw. Antennas Propag. UK

View full text Add to dashboard Cite

A measuring system for determining the complex permittivity of low-loss solids using a frequencytuned TE 01 cavity resonator of fixed length is described. Its mechanical construction is simple, and measurements, in particular of the real part e' of the permittivity, can be performed within a relatively short measuring time with high precision (| Ae'/e' | < 7 x 10~4), for a large number of frequencies in a given frequency band. The method is compared with the standard method where a length-tuned resonator is involved. Theoretical error investigations and practical measurements at frequencies of about 10 GHz on polymers and fused silica are carried out showing that the uncertainties have comparable values in both methods. IntroductionFor 40 years the closed cavity resonator operated in the low-attenuation TE 01 mode, which consists of a hollow metallic cylinder of circular cross-section terminated by two short-circuit plates, has been used to measure the real part e' of the complex relative permittivity e = e' -je" and the tangent of the dielectric loss angle ('loss tangent'),of materials in the microwave range [1], in particular of low-loss solids. Reviews of literature on dielectric measuring methods including cavity resonator techniques have been given by Bussey [2], Lynch [3], Chamberlain and Chantry [4] and, more recently, by Birch and Clarke [5]. According to a widely known precision standard method, the lengthtuning method (LTM), e' and e" are obtained, at a fixed frequency /, from the measured changes of the length and of the (?-factor of t n e resonator at resonance which are caused by the disc-shaped dielectric sample which is inserted adjacent to one of the short-circuits [6]. To tune the resonator the short-circuit can be moved in the axial direction to vary the resonator length by a bearing and positioning device, which must be well designed and precisely constructed, to keep the measurement uncertainties small, especially that of e'.With a different principle of measurement already mentioned in Reference 1, the frequency-tuning method (FTM) which involves a very simple mechanical construction, no movable mechanical parts are used. Here the resonator is terminated only by two fixed short-circuits and, at constant resonator length, the frequency is altered to tune it to resonance. The permittivity s' and tan <5 are determined from the measured changes of resonance frequency and Qfactor which are due to the inserted sample. Both quantities and other geometrical parameters of the resonator necessary to calculate the complex permittivity are obtained by means of a frequency counter of good resolution {\Af/f\ ^ 10" 7 ) which, in any case, is required for both methods to determine the Q-factors. In spite of its simplicity the FTM has been used, hitherto, only in special cases for precision measurements [7,8].To test the applicability of the FTM as a precision standard method of measurement a theoretical and experimental error investigation has therefore been carried out the results of which are presented in ...

show abstract

Resonance methods of dielectric measurement at centimetre wavelengths

Cited by 30 publications

References 0 publications

Hysteresis in the β–α phase transition in silver iodide

Hysteresis in the β–α phase transition in silver iodide

Untitled

Permittivity measurements using a frequency-tuned microwave TE01 cavity resonator

Contact Info

Product

Resources

About