A dual-coupled monolithic crystal element is connected to a crystal filter to bypass signals of a predetermined frequency which are applied through the filter. The shunt connected crystal element can be used with a bandpass filter to bypass frequencies at which the crystal filter produces a spurious response so that such frequencies will not appear in the filter output. Alternatively, the monolithic element can be selected to bypass frequencies adjacent the edges of a band which is selected, to provide sharp attenuation at the edges of the band thereby providing a very steep filter characteristic. The monolithic element includes a flat quartz wafer with electrodes provided on both sides at two separate portions of the wafer to form two resonant portions coupled through the wafer. The electrodes of one portion are connected across the input or the output of the crystal filter, and both electrodes of the other resonating portions are grounded.

In a multiresonator modified monolithic crystal filter employing a combination of mass loading and acoustic coupling, a direct nongrounded conductor, external to the piezoelectric body between two of the resonators, establishes a second transmission path through the filter. Attenuation peaks with control over their position are established thereby which enhances filter selectivity.

A multi-element ultrasonic transducer in which elements are arrayed and in which a plate-shaped piezoelectric material has its one face formed with a uniform electrode and its other face formed alternately with electrodes corresponding to the respective elements and electrodes for separating the elements. These electrodes for the element separation are connected the uniform electrode opposed thereto and is fed with a ground potential. On the other hand, the electrodes corresponding to the respective elements are fed individually with transmitting and receiving signals independently of the elements so that the electronic scanning or focusing operations can be achieved.

A multi-resonator crystal body is physically supported by electrical lead wires extending from a support substrate having individual shaped electrical conductors thereon which are thus connected to each resonator on the crystal body such that the individual resonator electrodes can be selectively short-circuited, or open-circuited, or displayed to an external electrical network to facilitate final finishing of the resonator electrodes. Predetermined electrical circuits (e.g. a short-circuit effected by conductive cement or paint) are thereafter connected across some of the resonator electrodes via the shaped conductive areas on the support substrate before the entire assembly is encapsulated in a standard pin connector housing arrangement. Besides greatly facilitating the tuning of individual crystal resonators to desired frequencies during the finishing operation, this mounting arrangement is also believed to provide improved temperature characteristics and/or shock mounting of the crystal body.

A bulk acoustic wave device has a number of resonator elements (14) which are laterally spaced such that a signal (26) applied between to one resonator element (14.sub.1) at a resonant frequency of the device is coupled to the other resonator elements (14.sub.2, 14.sub.3, 14.sub.4) by acoustic coupling between piezoelectric layers of the resonator elements (14). There are two outer resonator elements (14.sub.1, 14.sub.5) and at least one inner resonator element (14.sub.2, 14.sub.3, 14.sub.4). The terminals of the inner resonator elements are electrically connected together. This connection provides an AC short which eliminates the effect of the parasitic capacitances of the inner resonator elements, and provides electromagnetic shielding between the input and output of the device, by reducing the parasitic capacitance between the input and output upper electrodes.