A pass-band electromechanical filter, comprising a mechanical unit vibrating in the longitudinal mode mounted between two electromechanical transducers, said unit comprising a plurality of half wave resonators mounted in series and coupling rods connecting the consecutive resonators, the resonators being distributed into two groups of which one comprises the resonators of odd rank and the other the resonators of even rank, the filter comprising moreover at least a bridging coupling rod connecting a resonator of rank k to a resonator of rank k+(2p+1) (p being a positive integer different from zero), said bridging coupling rod having its ends fixed at a certain distance from the end faces of the resonators, at least the bridging coupling rod on the one hand, or the coupling rod placed between the resonator of rank k and that of rank k+(2p+1) on the other hand, having a length which is respectively different from a three quarter wave or different from a quarter wave.

A method of manufacturing an ultrasonic probe which comprises the steps of forming a first metal electrode layer fully covering one surface of a plate-shaped piezoelectric or ultrasonic vibrator and further extending over part of the opposite surface for a prescribed length; providing a second metal electrode layer electrically insulated from the first metal electrode layer and stretched over substantially the remaining portion of said opposite surface of the plate-shaped piezoelectric vibrator; brazing one of both edge portions of a first metal plate bored with many internal slits to which both ends of a plurality of leads are jointly connected, to that part of the first metal electrode layer which is disposed flush with one end face of the aforesaid plate-shaped piezoelectric vibrator, and similarly brazing one of both edge portions of a second metal plate of the same construction to that part of the second metal electrode layer which is positioned flush with the opposite end face of said piezoelectric vibrator; bonding an ultrasonic absorber to the aforesaid opposite surface of the piezoelectric vibrator by proper adhesive so as to cause that part of the first metal electrode layer which extends over part of the opposite surface of the plate-shaped piezoelectric vibrator, the almost entire surface of the second metal electrode layer and one of both edge portions of each slitted metal plate to which a plurality of leads are jointly connected all to be interposed between said ultrasonic absorber and opposite surface of the piezoelectric vibrator; cutting the first and second metal electrode layers, the piezoelectric vibrator, and the brazed common connection sections of the first and second slitted metal plates at a prescribed interval to separate the leads in the opposite common connection sections thereof from each other, such that each cut element of the piezoelectric vibrator contains one pair of leads, thereby providing on the ultrasonic absorber an array of a plurality of independently operative piezoelectric vibrator elements positioned substantially flush with each other.

In a mechanical filter, a pair of transducer elements of truncated circular cross-section are disposed at the input and output sides respectively, and they are mechanically connected in cascade to each other by means of a coupler member. The areas of the truncated cross-section of the transducer elements are made different from each other. Between said pair of transducer elements may be provided one or more resonator elements each provided with a recess and connected to each other and to said transducer elements by said coupler member. Each of the transducers and resonators are mounted on a mount base plate by means of a bent wire-like support member having a pair of legs. The foregoing mechanical filter is accommodated in a container which is pressure-reduced and hermetically sealed.