Ultrasonic spectroscopy of a layer between two materials has been developed mostly for nondestructive testing of adhesive joints. For a thin layer separating two substrates signals reflected from front and back surfaces of the layer are overlapped in the time domain and interfere. The velocity of the ultrasonic wave and the attenuation in the layer can be obtained from analysis of the interference signal. Chang [1] and Flynn [2] used ultrasonic velocity and attenuation extracted from the ultrasonic reflected signal for correlation with the joint cohesive strength. The influence of different attenuation functions on amplitude and phase spectra of the signal reflected from the joint bondline was studied in [3]. Through-thickness resonance measurements were used in [4] to calculate both thickness and modulus of adhesive layer. An ultrasonic technique for evaluation of thin layers [5] and adhesive joints [6] was proposed by Kinra et al. A review of the field is given in [7]. In all the studies joints of similar substrates, predominantly Al/ Al or steel/steel, were given the most consideration since these are widely used in industry. Emphasis was given to joint cohesive strength testing by normally incident ultrasonic waves. For adhesive/adherend interface evaluation ultrasonic spectroscopy at oblique incidence was developed [8, 9, 10]. Joints of similar substrates (Al/Al) were used for experiments; the data obtained was correlated with the joint adhesive strength. For general theory on elastic wave propagation in attenuating layered media the reader is referred to [11].