## 3 Results and Discussion
The results of U\({}_{\text{OUT}}\)(H\({}_{\text{DC}}\)) measurements are shown in Figure 5. The gap in the characteristics is connected with the limited capabilities of the magnets used, as described previously. According to predictions, there is no influence of the DC magnetic field on the piezoelectric patch and the measured voltage values are very small (see the black point characteristic in Figure 5a and the scale on the right vertical axis). Changes in U\({}_{\text{OUT}}\) for the sample S1 should therefore be connected with the ME effect. Figure 5: Magnetoelectric voltage versus DC magnetic field characteristics: (**a**) for sample S1 and reference R at different frequencies; (**b**) for sample S1 at two different resonant frequencies. Measurement frequencies were selected from different regions of characteristics in Figure 4, i.e., 100 Hz, 1 and 10 kHz from the linear part and two resonant frequencies f\({}_{\text{res1}}\) = 32.21 kHz and f\({}_{\text{res2}}\) = 69.21 kHz. Figure 5 shows that all characteristics (excluding the one for f\({}_{\text{res1}}\)) have a similar trend. At low DC fields (up to 0.14 T) there is a linear increase of U\({}_{\text{OUT}}\) relative to H\({}_{\text{DC}}\). Next, the voltage reaches some maximum value and then gradually decreases between 0.34 and 0.45 T. The observed trend corresponds well to published data for PZT/Terfenol-D composites [13; 22; 23; 25; 29; 30]. The shape of characteristics is related to the dependence of the magnetostrictive coefficient of Terfenol-D on the DC magnetic field, as shown in [22; 29; 31]. Once the curve reaches saturation, U\({}_{\text{OUT}}\) starts to decrease with the increase in the magnetic field. Of particular note is the characteristic for f\({}_{\text{res1}}\) = 32.21 kHz (Figure 5b, red color). First, the magnetoelectric voltage drops between 0 and approximately 0.04 T, and then increases similarly to other characteristics. This behavior corresponds to observations in Figure 4, in which the resonant peak at about 32.2 kHz is inverted (directed downwards) up to 0.058 T. The downward orientation may suggest that the ME signal is 180\({}^{\circ}\) out of phase with the Faraday electromagnetic induction signal. Above the DC field value of 0.058 T, the peaks are directed upwards. It may be supposed that the origin of the resonant peak at 32.2 kHz is different because the direction of other peaks is not field-dependent. The characteristics of U\({}_{\text{OUT}}\)(f) for the sample S2 and reference sample R are presented in Figure 6. The measurements were taken under the same conditions as for the sample S1. Despite having additional piezoelectric and magnetostrictive layers, the composite exhibits qualitatively similar behavior to that shown in Figure 4. Each characteristic consists of a base ascribed to Faraday electromagnetic induction and a voltage signal due to the ME coupling. Several resonant peaks can also be observed. For the DC magnetic field of 0.133 T, resonance occurs at f\({}_{\text{res}}\) = 29.5, 61, 64.8, 69.8, and 82 kHz. For different DC field values, a resonance state in sample S2 is observed at approximately the same frequencies. Figure 6 also shows that the field response of the peaks regarding their direction is consistent with previous observations. The first peak at 29.3 kHz (Figure 6a) is inverted at 0.011 T of the DC field and directed upwards for fields above that value (Figure 6b). The key differences between the results shown in Figures 4 and 6 are the maximum voltage values recorded in the resonance states as well as their frequencies. For the sample S2, the highest observed value was 687 mV for 0.133 T at 64.65 kHz (Figure 6b). Since the composite S2 contains more layers, it is expected that the strain transfer between the components, as well as the Faraday voltage contribution, is greater; hence, the measured U\({}_{\text{OUT}}\) values should be larger. It also can be expected that the resonant frequencies are different for the composites S1 and S2.