Technique for measuring the parameters of polarization of an ultrasonic wave

Transcription

1 arxiv:physics/ v1 [physics.class-ph] 1 Apr 000 Technique for measuring the parameters of polarization of an ultrasonic wave A. M. Burkhanov, K. B. lasov,.. Gudkov, and B.. Tarasov February, 008 Among physical phenomena consisting in variation of the polarization of a shear ulrasonic wave the acoustic analogs of the Faraday and the Cotton- Mouton effects are investigated at present (see [1] and [] the first theorectical papers, [3] discovery of rotation of the polarization, and [4] [7] some experiments. They are observed when initially linearly polarized ultrasonic wave propagates inside a bulk specimen and are due to interaction between elastic and magnetic subsystems or conduction electrons. Quantitative characteristics of the effects are polarization parameters: ε the ellipticity which modulus is the ratio of the minor and major ellipse axes and φ the angle of rotation of the polarization plane or, more correctly, of the major ellipse axis if ε 0. Most of recent experiments on polarization phenomena were performed with the use of phase-amplitude methods. A review of them is given in Ref. [8]. Besides, a phenomenon is considered as the acoustic analog of magnetooptic Kerr effect if variation of the polarization occurs while reflection of the wave from an interface between magnetic medium and isotropic nonmagnetic one. It was predicted by lasov and Kuleev [9] in 1968, however, there was no papers yet about experiments in which both the parameters characterizing the polarization, ε and φ, were measured. We have completed such an experiment and the results will be published soon. While performing it we found that a very small variations of a high level signal took place and came to a conclusion that amplitude variant of a technique should be more suitable here. First amplitude technique for a precise measurement of φ was introduced by Boyd and Gavenda [10]. Its aplicability was limited to the case ε 0. Though, we developed an amplitude method free of this restriction for measuring φ as well as ε. A description of the technique is the subject of this paper. 1

2 The method consists of measuring the amplitude of the voltage, (H, on the receiving transducer at a certain B 1 relative to an initial B B 0 using three different angles for the receiving transducer ψ with futher processing of the data with the formulas (, (, and (3 presented below. It can be used for investigating the acoustic analogs of the Faraday and the Cotton-Mouton effects as well. A periodic motion of the volume element over an elliptic trajectory can be repersented with the help of amplitudes, u ±, and phases, ϕ ±, of circular elastic vibrations. Introducing a parameter expressions for ε and φ have the form: p (u /u + e i(ϕ ϕ +, (1 ε 1 p 1 + p, φ 1 Im [ln(p]. ( Projection of the elastic vibrations to polarization direction of the receiving transducer can be written as follows: u r (t u e r Re { u + exp [ i(ωt ϕ + ψ ] +u exp [ i(ωt ϕ + ψ ]}, (3 * designates the complex conjugate, e r is unit vector of the direction of the polarization of the receiving transducer, ψ is the angle between this direction and the plane of incidence, ω is frequency, and t is time. u r excite an ac voltage cos(ωtα ηu r ( η is the coefficient of transformation of elastic vibration energy into electric field energy, and α is a phase constant. Using Eq. (3 we have η [cos ωt cosα + sin ωt sin α] [ u + cos(ϕ + + ψ + u cos(ϕ ψ ] cos ωt + [ u + sin(ϕ + + ψ + u sin(ϕ ψ ] sin ωt. (4 Since Eq. (4 is valid for arbitrary t, it may be transformed into two equations: η cos α u+ cos(ϕ + + ψ + u cos(ϕ ψ, (5 η sin α u+ sin(ϕ + + ψ + u sin(ϕ ψ. (6

3 Multiplying Eq. (6 by i and adding the result to Eq. (5 we obtain η eiα u + e i(ϕ+ +ψ + u e i(ϕ ψ. (7 The method suggested here for determining the polarization of the reflected wave consists of measuring the amplitude of the signal at a certain B 1 relative to an initial B B 0 using three different angles for the receiving transducer: ψ 1, ψ, and ψ 3. We assume that ε(b 0 0 and φ(b 0 0. Relevant equations for the two different values of B and three of ψ may be obtained by making the appropriate substitutions into Eq. (7. Introducing indexes j 0, 1 for the two values of B and k 1,, 3 for the three values of ψ for kj, α kj, u ± j, and ϕ ± j we have: 10 + η eiα 10 u + 0 e i(ϕ 0 +ψ 1 + u 0 e i(ϕ 0 ψ 1, (8 11 Dividing Eq. (9 by (8, we obtain F ± 1 + η eiα 11 u + 1 ei(ϕ 1 +ψ 1 + u 1 e i(ϕ 1 ψ 1. ( e i(α 11α 10 F + 1 eiψ 1 + F 1 eiψ 1, (10 u ± 1 e iϕ ± 1 u + 0 exp[i(ϕ ψ 1 ] + u 0 exp[i(ϕ 0 ψ 1 ]. (11 Similar equations for ψ ψ have the form 1 10 e i(α 1α 10 δ e iλ F + 1 eiψ + F 1 eiψ, (1 λ and δ describe variations in phase and amplitude of the signal, respectively, caused by differences in transducer coupling to the sample while changing ψ from ψ 1 to ψ. One more change in ψ gives the following equations in addition to (10 and (1: e i(α 31α 10 δ 3 e iλ 3 F + 1 eiψ 3 + F 1 eiψ 3. (13 Here δ 3 and λ 3 have the same origin as δ and λ, but correspond to changing ψ from ψ 1 to ψ 3. 3

4 After multiplying the left and right sides of Eqs. (10, (1, and (13 by their complex conjugates we obtain ( ( 1 δ 10 ( 31 δ 3 10 F + 1 F + 1 F F 1 F 1 F F 1 + F1 F 1 + F1 F 1 + F1 cos ( ϕ 1 + ψ 1, (14 cos ( ϕ 1 + ψ, (15 cos ( ϕ 1 + ψ 3, (16 ϕ 1 ϕ + (B 1 ϕ (B 1, (17 and, due to the assumption of ε(b 0 0 and φ(b 0 0, δ i 10 cos (ψ i i0 cos (ψ 1. (18 These operations are necessary to remove the phase α kj from our equations since amplitude is the only parameter measured in this variant of a technique. We divide both sides of Eqs. (14 (16 by to obtain p p 1 + cos[(φ 1 ψ 1 ] ( 11/ 10, (19 p p 1 + cos[(φ 1 ψ ] ( 1 δ / 10, (0 p p 1 + cos[(φ 1 ψ 3 ] ( 31 δ 3 / 10, (1 p 1 p(b 1. Thus we have three equations with three unknowns, namely F 1 + F1, p 1, and φ 1. The latter two are the parameters we are interested in and corresponding solutions of the system have the form φ 1 1 tan1{ [ ( 1 δ 31 δ3 cos ψ1 + ( 31 δ3 11 [ ( 1 δ 31 δ 3 F + 1 F + 1 F + 1 F + 1 F 1 F 1 F 1 F 1 cos ψ + ( 11 1 δ cos ψ3 ] sin ψ1 + ( 31 δ 3 11 sin ψ + ( 11 1 δ sin ψ3 ] 1} ( 4

5 and p 1 a 1 c 1 ± [ (a1 c 1 1 ] 1/, (3 a 1 11 sin [(ψ ψ 3 ] + 1 δ sin [((ψ 3 ψ 1 ] + 31 δ3 sin [(ψ 1 ψ ]cos φ 1, c 1 ( 1 δ 31 δ 3 sin ψ1 + ( 31 δ 3 11 sin ψ + ( 11 1 δ sin ψ3. The ( sign should be taken before the square root in Eq.(3, since it alone allows p 1 0 and therefore ε 1. References [1] C. Kittel, Phys. Rev. 110, 836 (1958. [] K. B. lasov, Fizika Metallov i Metallovedenie 7, 447 (1959 [Phys. Met. Metallogr. (USSR 7, 11 (1959]. [3] R. W. Morse and J. D. Gavenda, Phys. Rev. Lett., 50 (1959. [4] H. Matthews and R. C. Le Craw, Phys. Rev. Lett. 8, 397 (196. [5] B. Luthi, Phys. Lett. 3, 85 (1963. [6] A. M. Burkhanov, K. B. lasov,.. Gudkov, and I.. Zhevstovskikh, Akusticheskii zhurnal 34, 991 (1988 [Sov. Phys.-Acoustics 34, 569 (1988] [7] B.. Tarasov A. M. Burkhanov, and K. B. lasov, Fiz. Tver. Tela 38, 135 (1996 [Sov. Phys.-Solid State 38, 1176 (1996]. [8].. Gudkov and B.. Tarasov, J. Acoust. Soc. Am. 104, 756 (1998. [9] K. B. lasov and. G. Kuleev, Fiz. Tver. Tela 10, 076 (1968 [Sov. Phys.-Solid State 10, 167 (1969]. [10] R. J. Boyd and J. D. Gavenda, Phys. Rev. 15, 645 (