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[en] The coupling constants appearing in the two-band model are derived from recent microscopic calculations. The resulting order parameters are close to the BCS value. The model allows the effects of interband impurity scattering to be discussed. (author)
Source
Lee, M.J.G.; Perz, J.M.; Fawcett, E. (eds.); Institute of Physics Conference Series; no. 39; p. 670-674; ISBN 0 85498 130 6; 
; 1978; p. 670-674; Institute of Physics; Bristol; International conference on transition metals; Toronto, Canada; 15 - 19 Aug 1977
; 1978; p. 670-674; Institute of Physics; Bristol; International conference on transition metals; Toronto, Canada; 15 - 19 Aug 1977
[en] For the first time experimental observations are made of the oscillation in the intensity of the unshifted line and in the intensities of the US satellites when the γ-resonance radiation is modulated by the coherent US excitation. It is stated that the coherent US can be excited in the investigated sample if the US amplitude is transmitted homogeneously from the generator to the sample. A special sample-unit is described which provides a homogeneous transmission, and it is shown that the lifetime of the US phonons is not substantial and does not affect the oscillation of the absorption line intensities. (author)
Journal
Physica Status Solidi. B, Basic Research; ISSN 0370-1972; ; v. 92(1); p. 23-29
; v. 92(1); p. 23-29
[en] J. D. Aindow and R. C. Chivers [J. Acoust. Soc. Am. 73, 1833 (1983)] compared the precision of the direct ''time-of-flight'' technique with the ''sing-around'' method for sound velocity measurement. Their conclusion is changed by the newer, faster, commercial clocks (2 ns HP5345<0.1 ns HP5370), giving the advantage to the time of flight method. The analysis is herewith augmented by calculating the time jitter in terms of signal to noise ratio, which was correctly shown to be negligible with 100-ns clocks, but becomes increasingly more significant with faster clocks
Journal
Journal of the Acoustical Society of America; ISSN 0001-4966; ; v. 75(6); p. 1909-1909
; v. 75(6); p. 1909-1909
[en] A new method to obtain one-dimensional map of ultrasonic wave speed is proposed. The method consists of insonifying a medium with an ultrasonic pulse and receiving the reflected echo on the same transducer used as transmitter and in another one placed adjacent. Each interface iluminated by the irradiated wave returns an echo to both transducers. Then by measuring the time-of-flight for each echo arrived on both transducers, the position of each interface, related to the transmitting transducer, and the wave speed existent between consecutive interfaces can be obtained. In the present work a phantom was made. Consisting of 3 layers: epoxi(9,9mm), acrilic (9.7mm) and pvc (10.2mm). The phantom was imersed in a tank filled with water, together with a holder with the 2 transducer in it. Using a digital osciloscope and microcomputer can implement the method proposed. The values calculated for the distancers interface-transducers have shown errors from 0.1% to and can be acceptable to a certain extent. On the other hand, all the obtained for the width of layers and for the of the US wave inside them are acceptable. The width of the of the echo from interface acrilic-pvc and it is necesary an exciting pulse with greater amplitude to enhance it. Results can be accepted as first approximation and encourage us to proceed exploring this method. (author)
[pt]
Propoe-se um novo metodo para se obter o mapeamento unidimensional da velocidade de ondas ultra-sonicas. O metodo consiste em se irradiar um meio com um puslo de ultra-som (US) e receber o eco no transdutor transmissor e em outro colocado ao lado deste. Tomando-se medidas do tempo de chegada de cada eco em ambos os transdutores, a posicao de cada interface que refletiu o pulso incidente e a velocidade da onda no meio entre duas interfaces consecutivas pode ser obtida. Construiu-se um corpo de prova consistindo de 3 camadas: epoxi, acrilico e pvc (espessuras: 9,9mm; 9,7mm e 10,2mm, respect.) O corpo de prova foi imerso em um tanque com agua, juntamente com o suporte com os 2 transdutores em pararelo. Utilizando-se um osciloscopio digital e um microcomputador pode-se fazer as medidas dos tempos de chegada e implementar o metodo. Os valores calculados para as distancias interface - transdutores apresentaram erros de 0,19% a 7,94% e sao considerados satisfatorios. Ja os valores obtidos para a espessura de cada camada e velocidade do US nas mesmas nao sao, de todo, satisfatorios. A espessura da camada de acrilico apresentou um erro grande. Isto e devido a baixa amplitude do eco proveniente da interface acrilico-pvc, sendo necessario, um puslo de excitacao de maior amplitude. Os resultados iniciais sao considerados satisfatorios em uma primeira aproximacao e encorajam a prosseguir explorando as potencialidades do metodo. (autor)Journal
RBE, Caderno de Engenharia Biomedica; ISSN 0102-2644; ; v. 6(2); p. 58-63
; v. 6(2); p. 58-63
[en] Highlights: • Dynamic range improvement of electrostatically actuated circular microplates. • Pull-in instability tuning based on geometric nonlinearity and imperfections. • Predictive computational model for the nonlinear behavior of circular microplates. - Abstract: Dynamic range improvement based on geometric nonlinearity and initial deflection is demonstrated with imperfect circular microplates under electrostatic actuation. Depending on design parameters, we prove how the von Kármán nonlinearity and the plate imperfections lead to a significant delay in pull-in occurrence. These promising results open the way towards an accurate identification of static parameters of circular microplates and the development of a predictive model for the nonlinear dynamics of imperfect capacitive micromachined ultrasonic transducers.
Journal
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