TRANSDUCER WITH BULK WAVES SURFACE-GUIDED BY SYNCHRONOUS EXCITATION STRUCTURES

摘要

A surface-guided bulk wave transducer (102) comprises a stack of an acoustic substrate (6), an electric ground plane (8), and a network (110) of synchronous acoustic excitation sources with two combs (112, 114) of elementary piezoelectric transducers (122, 124, 126, 128, 130, 132) alternately interlaced two-by-two according to a periodic network step corresponding to a propagation mode of a surface-guided bulk wave of the acoustic substrate (6).;Each elementary piezoelectric transducer (122, 124, 126, 128, 130, 132) includes a single and different rod with a parallelepipedal shape for which the nature, the cut of the piezoelectric material, the height h, the width are selected for increasing the electromechanical coupling coefficient of the transducer assembly (102) to a high level.

主权项

1. A surface guided bulk wave transducer, intended to operate at an acoustic surface wavelength λ, and to convert an electric signal at an operating frequency ft corresponding to the acoustic wavelength λ into a surface-guided bulk wave and vice versa, comprising an acoustic substrate and an electric ground plane,
the acoustic substrate being made as a plate forming a first layer in a first single crystal or polycrystalline electrically insulating material cut along three planes of a first crystalline cut defined according to the nomenclature (YXwlt)/φ/θ/ψ of the IEEE Std-176 standard 1949 revision by a first angle φ, a second angle θ, and a third angle ψ, the substrate plate being extended along a first thickness t1, a first length l1 and a first width w1, the plate of the acoustic substrate having a first rest face and facing, in the direction of the first thickness t1, a second opposite supporting face having a roughness condition, the crystalline cut of the first material being selected and the roughness condition of the second face being sufficiently smooth for allowing propagation of elastic Rayleigh, Bleustein-Gulyaev elastic waves or pseudo-surface waves, PSAW, in the direction of the first length l1 of the acoustic substrate, the ground plane being made as a second layer in a second electrically conducting material, deposited on the acoustic substrate-on the side of its second face, the second layer being extended along a second uniform thickness t2, a second width w2, and a second length l2, the second layer having a third face, positioned facing the second face of the acoustic substrate, and having a fourth opposite face and facing the third face in the direction of the second thickness t2, the directions of the second thickness e2, the second width w2, the second length l2 respectively being the same as the directions of the first thickness e1, the first width w1, the second length l2; wherein the surface-guided bulk wave transducer comprises a network of synchronous acoustic excitation sources, configured so as to be mechanically and electrically connected to a synchronous excitation electric source, deposited on the ground plane, and including a first comb of one or several elementary piezoelectric transducers arranged along a first direction and a second comb of one or several elementary piezoelectric transducers in the same number as those of the first comb arranged along a second direction opposite to the first so that the elementary piezoelectric transducers of the first comb and of the second comb are alternately interlaced two-by-two according to a periodic network step p and along the propagation direction of the elastic surface waves along the second supporting face in the direction of the first length l1 of the acoustic substrate, double the network step 2p being substantially equal to the acoustic wavelength λ; each elementary transducer includes a single and different rod and a single and different electric excitation upper metal electrode, the rod being produced in a third single crystal or polycrystalline piezoelectric material, cut along three planes of a second crystalline cut defined according to the nomenclature (YXwlt)/φ/θ/ψ of the IEEE Std-176 standard-1949 revision-by a second angle φ2, a second angle θ2, and a third angle ψ2, having a same profiled shape with a rectangular or trapezoidal section, having a fifth face facing the face of the ground plane, a sixth face opposite to the fifth face on which is deposited the associated excitation electrode, and two side flanks connecting from both sides the fifth face and the sixth face, and defined by a third thickness h as being the height separating the fifth face and the sixth face, a third width d for covering the ground plane and a third length L; the third material and the second cut being selected so as to allow propagation of elastic bulk waves in the direction of the third thickness h with a high coupling coefficient at least greater than or equal to 0.1%, and the third thickness h is comprised between a quarter and three quarters of the wavelength λbulk of the elastic bulk mode propagating within the third material in the direction of the third thickness and corresponding to the operating frequency ft; the third width d being strictly less than half the acoustic wavelength and with a same orientation as the propagation direction of the surface-guided bulk waves of the acoustic substrate; two adjacent elementary transducers being separated from each other in the direction of their third width by a separation space of a non-zero separation length D, the sum of the third width d and of the separation length D being equal to the step p of the network, and the second material is acoustically pervious to elastic waves generated by piezoelectricity.