A solidly mounted resonator structure comprising: a substrate; an acoustic reflector structure arranged over the substrate and comprising a plurality of sequentially arranged differential acoustic impedance layer units, wherein each differential acoustic impedance layer unit of the plurality of sequentially arranged differential acoustic impedance layer units comprises a low acoustic impedance material layer in contact with a high acoustic impedance material layer; at least one first electrode structure arranged over at least a portion of the acoustic reflector structure; a piezoelectric material layer arranged over the at least one first electrode structure; and at least one second electrode structure arranged over at least a portion of the piezoelectric material layer; wherein: at least one portion of the piezoelectric material layer is arranged between the at least one first electrode structure and the at least one second electrode structure to form at least one active region; and the solidly mounted resonator structure is configured for transduction of an acoustic wave including a longitudinal component and a shear component in the at least one active region, whereby the piezoelectric material layer exhibits first and second harmonic resonances of a longitudinal response and exhibits first, second, and third harmonic resonances of a shear response; characterized in that the differential acoustic impedance layer units have thicknesses configured such that a frequency corresponding to a minimum transmissivity of the second harmonic resonance of the longitudinal response is within 5% of a frequency corresponding to a minimum transmissivity of the third harmonic resonance of the shear response. a substrate; an acoustic reflector structure arranged over the substrate and comprising a plurality of sequentially arranged differential acoustic impedance layer units, wherein each differential acoustic impedance layer unit of the plurality of sequentially arranged differential acoustic impedance layer units comprises a low acoustic impedance material layer in contact with a high acoustic impedance material layer; at least one first electrode structure arranged over at least a portion of the acoustic reflector structure; a piezoelectric material layer arranged over the at least one first electrode structure; and at least one second electrode structure arranged over at least a portion of the piezoelectric material layer; wherein: at least one portion of the piezoelectric material layer is arranged between the at least one first electrode structure and the at least one second electrode structure to form at least one active region; and the solidly mounted resonator structure is configured for transduction of an acoustic wave including a longitudinal component and a shear component in the at least one active region, whereby the piezoelectric material layer exhibits first and second harmonic resonances of a longitudinal response and exhibits first, second, and third harmonic resonances of a shear response; characterized in that the differential acoustic impedance layer units have thicknesses configured such that a frequency corresponding to a minimum transmissivity of the second harmonic resonance of the longitudinal response is within 5% of a frequency corresponding to a minimum transmissivity of the third harmonic resonance of the shear response. at least one portion of the piezoelectric material layer is arranged between the at least one first electrode structure and the at least one second electrode structure to form at least one active region; and the solidly mounted resonator structure is configured for transduction of an acoustic wave including a longitudinal component and a shear component in the at least one active region, whereby the piezoelectric material layer exhibits first and second harmonic resonances of a longitudinal response and exhibits first, second, and third harmonic resonances of a shear response; characterized in that the differential acoustic impedance layer units have thicknesses configured such that a frequency corresponding to a minimum transmissivity of the second harmonic resonance of the longitudinal response is within 5% of a frequency corresponding to a minimum transmissivity of the third harmonic resonance of the shear response.