Electromechanical band-pass filter with low passband ripple - uses flexural resonators in cascade coupled by longitudinal vibrating rods shorter than 0.25 of direct synthesis

The electro mechanical band pass filter consists of cascaded elements, each consisting of two resonators undergoing flexural vibrations and coupled by less than eighth wavelength resonator which undergoes longitudinal vibrations. A direct relationship is used between the frequency limits of the mechanical filter elements and the cut off frequency of the associated low pass prototype elements which leads to lower pass band ripple and better band edge definition. The flexural vibrating rods are parallel and consist of elinvar. The filter is coupled electrically by piezoelectric ceramic plates as input and output transducers. The resonators of each element are dimensioned such so that one of the relative frequency limits is related by a mathematical formula to the frequency cut off of the corresp. low pass filter and the coupling. The coupling of each stage is related by a mathematical formula to the upper or lower relative frequency of the stage. A 9 stage filter using the Chebyshev approximation with a 20% bandwidth at 50KHz and 0.4dB passband ripple has been produced with the technique. LA PRESENTE INVENTION CONCERNE UN FILTRE ELECTROMECANIQUE PASSE-BANDE A RESONATEURS VIBRANT EN FLEXION ET A COUPLEURS PLUS COURTS QUE L8 VIBRANT LONGITUDINALEMENT.CE FILTRE EST REALISE PAR MISE EN CASCADE DE CELLULES UNITAIRES COMPORTANT CHACUNE DEUX RESONATEURS 9, 10 VIBRANT EN FLEXION ET UN COUPLEUR 18 PLUS COURT QUE L8 VIBRANT LONGITUDINALEMENT; LA CELLULE DE RANG I EST DIMENSIONNEE DE TELLE SORTE QUE L'UNE DES FREQUENCES RELATIVES LIMITES (O) DE SA BANDE DE FREQUENCES (O A O) EST LIEE A LA FREQUENCE LIMITE (F) D'UNE CELLULE POUR UN FILTRE ELECTRIQUE PASSE-BAS CORRESPONDANT AU FILTRE ELECTROMECANIQUE A REALISER, PAR LA RELATION:(CF DESSIN DANS BOPI)L'INVENTION S'APPLIQUE NOTAMMENT AUX FILTRES ELECTROMECANIQUES PASSE-BANDE DE GRANDE PRECISION.