Ultrasonic transducers comprising an ultrasonic transducer element, a pair of electrodes provided on opposite sides of the element, and an acoustic impedance-matching layer formed on an ultrasonic wave-radiating surface of the element through one electrode. The acoustic impedance-matching layer is made of a porous polymer film or a composite material comprising thermally expanded resin microspheres dispersed in a cured product of thermosetting resin and has an acoustic impedance not larger than 0.6×10 6 Ns/m 3 . Two-layer constructions may also be used as the acoustic impedance-matching layer.

Piezoelectric ultrasonic transducers having acoustic impedance-matching layers

An ultrasonic transducer assembly for making measurements within a fluid, the assembly including a transducer, a backing member and a matching member all supported within a cylindrical metal housing with the transmitting face of the housing being sealed with a thin sealing element formed of a non-resilient relatively high impedance material encasing a matching layer having an acoustic impedance intermediate between that of the transducer element and the fluid. The thickness of the sealing element is between 1/10 and 1/1000th of a wavelength at the center frequency of the wave emitted by the transducer.

Sealed, matched piezoelectric transducer

The acoustical coupler has a closed-bottom containment with compliant diaphragm attached to the containment periphery to form an acoustic chamber. A length of tubing is connected through the side or bottom or the containment of the chamber for conveying sound pressure between the chamber and an electroacoustic transducer connected at the other end of the tubing. The transducer may be either a microphone or a hearing aid receiver. The electroacoustic transducer, being too large for direct placement within the middle ear cavity may be located elsewhere in the skull, such as behind the ear adjacent to the surface of the skin. When connected to a microphone, the coupler may be placed within the middle ear cavity behind the tympanic membrane and may be attached to the malleus with a wire hook secured to the coupler diaphragm. When attached to a vibration sending unit the coupler may transfer the generated vibration directly to the incus end of the stapes. In one embodiment, this transfer is effected by means of a hollow tube having a generally hollow member therein and containing a quantity of low loss material. The member defines one end connected to the vibration sending unit and a second end connected directly to the stapes.

Implantable hearing aid coupler device

An acoustic transducer has an electrically energized crystal in contact with a flexible plate. The crystal drives the plate in a flexural mode. Particularly, the plate is oscillated so that different circular areas of the plate, referred to as nodes, do not vibrate. The nodes separate adjacent annular anti-node areas referred to as positive anti-nodes and negative anti-nodes which oscillate oppositely. An impedance matching material of uniform thickness is disposed between the plate and the surrounding medium to improve efficiency. To avoid cancellation of waves, concentric plastic layer rings are disposed between the impedance matching layer and the oscillating disk. The plastic rings act as a barrier to negative anti-nodes, thus eliminating cancellation between waves from the positive and negative anti-nodes.

Midrange ultrasonic transducer

A transit time ultrasound sensor is employed for the measurement of liquid flow in a conduit, the sensor having an acoustic path formed of materials matched in ultrasound properties to the flow under test, and designed to conform to the shape of the conduit. The sensor can be configured as a clamp on device, wherein the conduit walls are constructed from such an ultrasonically-matched material. Alternately, in a perivascular configuration, the ultrasonically-matched material is operably intermediate the blood vessel and the sensor.

Acoustically coupled ultrasonic transit time flow sensors

A transducer assembly incorporating a stratified medium for conducting acoustic waves from an acoustic source of relatively high impedance, such as a piezoelectric crystal, to a gaseous environment of relatively low impedance, the stratified medium including typically at least one layer of a foam structured low density plastic material, whereby uniform variations in impedance are provided progressively from the source through the layers of the stratified medium into the gaseous environment to effect an impedance match.

Edward Hands

Papers

Acoustic impedance matching system