Abstract: The invention describes a sensor comprising a substrate 1 and at least one resonator, said resonator is c mprised of an acoustic reflector 2, a piezoelectric layer 5, a first and a second elec ode 3, 4 placed on the same side of the piezoelectric layer 5, and a sensing layer 6. The sensing layer reacts with a chemical or biological agent by absorption, adsorption, desorption or chemical reaction. As a result the individual frequency of a resonator changes and conclusions about the agent can be drawn. Such sensor is very sensitive to an agent being sensed, especially when used in liquids.

Abstract: The invention relates to a resonator filter structure (10) for radio frequency (RF) filters, especially a bulk acoustic wave (BAW) filter structure. According to the invention, a resonator filter structure (10) is constructed with a BAW lattice filter section (20), in which all of the BAW resonator elements (20-1, 20-2, 20-3, 20-4) within the BAW lattice filter section (20) have substantially equal resonance frequencies. According to the invention, there are parallel capacitances (30-1, 30-2) connected in parallel to the BAW resonators (20-2, 20-3) of one branch type of the BAW lattice filter section (20). Thus, anti-resonance frequency of the respective BAW resonator (20-2, 20-3) is tuned. That results in a very narrow passband which corresponds approximately to the difference in anti-resonance frequencies between diagonal and horizontal branches of the lattice filter section (20). The parallel capacitances (30-1, 30-2) are used to tune the bandwidth: the smaller the capacitance, the smaller the bandwidth.

Abstract: The invention relates to a filter device equipped with at least one bulk acoustic wave resonator, which comprises a resonator unit and a reflection element (2) comprising several layers (6, 7, 8). The layers (6, 7, 8) each comprise a mixture of at least two materials. Within each layer (6, 7, 8), the composition of the mixture varies continuously and periodically relative to the layer thickness.