US-12624986-B2 - Photo-acoustic conversion based sound emitter device

US12624986B2US 12624986 B2US12624986 B2US 12624986B2US-12624986-B2

Abstract

The photo-acoustic conversion based sound emitter device has a sound output surface for transmitting sound wave vibrations to a medium outside the device. An optical waveguide, is used to transmit light through an optical path within the device. First and second photo-acoustic conversion volumes, at different distances from the sound output surface, are used for transmitting sound generated in the first and second volume to the medium via the sound output surface, the optical path extending directly or indirectly successively through the first and second photo-acoustic conversion volume. The device comprises an intermediate volume separating the first and second photo-acoustic conversion volumes along the optical path, the intermediate volume having a lower light absorption coefficient than the first and second photo-acoustic conversion volumes; and/or the first and second photo-acoustic conversion volume have a different cross-section area size and/or shape with virtual planes perpendicular to the optical path; and/or the first and second photo-acoustic conversion volumes have different optical absorption coefficients, or a different optical wavelength dependence of these optical absorption coefficients.

Inventors

Maurits Sebastiaan van der Heiden
Paul Louis Maria Joseph van Neer
Peter Johan Harmsma
Robert Karl ALTMANN
Daniele Piras

Assignees

NEDERLANDSE ORGANISATIE VOOR TOEGEPAST-NATUURWETENSCHAPPELIJK ONDERZOEK TNO

Dates

Publication Date: 20260512
Application Date: 20210118
Priority Date: 20200116

Claims (11)

1 . A photo-acoustic conversion based sound emitter device, comprising: a sound output surface for transmitting sound wave vibrations to a medium outside the device; an optical waveguide, configured to transmit light through an optical path within the device, the optical waveguide being integrated on or in a substrate and extending in parallel with the sound output surface, and an optical coupling structure optically coupled to the optical waveguide and configured to redirect the light from the optical waveguide along said optical path in a direction having a component normal to the sound output surface; first and second photo-acoustic conversion volumes, at different distances from the sound output surface, for transmitting sound generated in the first and second volumes to the medium via the sound output surface, the first and second photo-acoustic conversion volumes being solid-state layers stacked one above the other between the optical waveguide and the sound output surface, the optical path being redirected by the optical coupling structure to extend successively through the first and second photo-acoustic conversion volume along said direction having a component normal to the sound output surface, wherein the device comprises an intermediate volume separating the first and second photo-acoustic conversion volumes along the optical path, the intermediate volume having a lower light absorption coefficient than the first and second photo-acoustic conversion volumes, the intermediate volume being an optically less absorbing layer; and/or the first and second photo-acoustic conversion volume have a different cross-section area size and/or shape with virtual planes perpendicular to the optical path; and/or the first and second photo-acoustic conversion volumes have different optical absorption coefficients, or a different optical wavelength dependence of these optical absorption coefficients.
2 . The device according to claim 1 , wherein the first and second photo-acoustic conversion volumes have different lengths along the optical path.
3 . The device according to claim 1 , wherein: the optical waveguide is integrated on a surface of the substrate; a first solid-state layer, or part of the first solid-state layer, of the first photo-acoustic conversion volume is formed on or in the substrate, wherein a surface of the first solid-state layer extends in parallel with the surface of the substrate, overlying or underlying the optical waveguide; a second solid-state layer, or part of the second solid-state layer, of the second photo-acoustic conversion volume is stacked over the first solid-state layer, wherein a surface of the second solid-state layer extends in parallel with the surface of the substrate, overlying or underlying the optical waveguide; and the optical coupling structure is located underneath or above said first and second solid-state layers, coupled to the optical waveguide, and is configured to redirect the light traveling in the optical waveguide through said first and second solid-state layers, and said direction being transverse to the surface of the substrate.
4 . The device according to claim 1 , wherein the first and second photo-acoustic conversion volumes are located in the optical waveguide or in a virtual extension of the optical waveguide along a direction of travel of light through the optical waveguide.
5 . The device according to claim 1 , comprising the intermediate volume.
6 . The device according to claim 1 , wherein the first and second photo-acoustic conversion volumes have different cross-section areas size and/or shape with virtual planes perpendicular to the optical path.
7 . The device according to claim 1 , wherein the first and second photo-acoustic conversion volumes have different optical absorption coefficients.
8 . The device according to claim 1 , wherein the first and second photo-acoustic conversion volumes have optical absorption coefficients with optical wavelength dependence, the optical absorption coefficient of the first photo-acoustic conversion volume providing for transmission of light from the optical waveguide to the first photo-acoustic conversion volume at an optical wavelength that causes the second photo-acoustic conversion volume to generate sound.
9 . The photo-acoustic converter device according to claim 1 , wherein the first and second photo-acoustic conversion volumes comprise a transparent solid material, with different doping to tailor absorption coefficients of the volumes.
10 . The photo-acoustic converter device according to claim 1 , wherein the first and second photo-acoustic conversion volume comprise polydimethylsiloxane.
11 . A system for measuring acoustic reflection, the system comprising: the device according to claim 1 with the intermediate layer, a sound receiver arranged to receive a reflection of sound transmitted via the sound output surface; a signal processing circuit configured to correlate the reflection with a reference signal comprising components delayed according to distances of the first and second photoacoustic conversion volume from the sound output surface.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a U.S. National Stage application under 35 U.S.C. § 371 of International Application PCT/NL2021/050024 (published as WO 2021/145767 A1), filed Jan. 18, 2021 which claims the benefit of priority to Application EP 20152263.8, filed Jan. 16, 2020. Benefit of the filing date of these prior applications is hereby claimed. Each of these prior applications is hereby incorporated by reference in its entirety. BACKGROUND In the field of ultrasound imaging, it is known to transmit ultrasound using an array of sound transmitters and to receive ultrasound using an array of sound receivers. In known devices, arrays of piezo-electric elements are used, wherein the piezo-electric elements at different locations in the array are used to generate sound in response to the application of electronic signals and/or to generate electronic signals in response incoming sound vibrations. In the field of photo-acoustics optical sound generators are known, which comprise an optical fiber that acts as a waveguide for light and light absorbing material at the tip of the fiber or along the fiber at a place where the fiber is made to couple light out of the fiber. When a light pulse is transmitted through such a fiber, it heats the light absorbing material, which causes sudden expansion of this material that results in the emission of sound waves. In the field of photo-acoustics optical sound detectors are known, which comprise a membrane that is exposed to incoming sound and an optical waveguide on the membrane. The membrane vibrates under the influence of incoming sound. This causes strain on the optical waveguide, which affects the transmission properties of light through optical waveguide, e.g. its delay. Measurements using the transmitted light can be used to detect the incoming waves. A photonic integrated device comprises a combination of different solid state optical components manufactured in a fixed arrangement on the same planar substrate such as a wafer, optionally including one or more components created by stacking volumes of different solid state materials on top of each other, without intermediate optical waveguides between these volumes. The photonic integrated device may be a device that contains only such components, or it may be a hybrid photonic integrated device that comprises one or more separately manufactured components that have been fixed on the integrated device coupled to one or more other components of the photonic integrated device. In the field of optical integration it is known to realize a device that transmits light in the direction nearly perpendicular to a surface of the device (e.g. at an angle of ten degree or more to the surface normal) using light that is supplied through one or more waveguides in the device that run parallel to the surface. This can be realized by using a grating on the waveguide, a mirror at the end of the waveguide or by means of evanescent coupling. See Vermeulen, ‘High-efficiency fiber-to-chip grating couplers realized using an advanced CMOS-compatible Silicon-On-Insulator platform’, OPTICS EXPRESS, 16 Aug. 2010/Vol. 18, No. 17/18278 For acoustic measurements it is desirable to shape the temporal, spectral and/or directional shape of the emitted sound. For example, it may be desirable to increase the energy content of an emitted sound pulse without increasing the peak amplitude in the sound signal as a function of time. As another example, it may be desirable to include components in different wavelength bands in a pulse, or to create a combination of a sharp direction dependent energy in one direction with a less pronounced direction dependent energy. In photo-acoustic sound emission sound is usually created by transmitting a light pulse to a photo-acoustic conversion volume, which responds by generating a pulse with a properties dependent on the size of the region where photo-acoustic conversion occurs and acoustic resonance effects. WO03057061 (published as EP1471848 by the European patent office) discloses a catheter with ultrasound capability at its tip. An optical fiber is used as a waveguide and absorbing regions are defined in or on the core of the fiber, or the absorbing regions are segments that are added to the fiber. In an embodiment, a guidewire for medical applications comprises such a wave-guide with wavelength-selective absorbing region at its end. When laser light of an absorbed wavelength is pulsed through the fiber, the absorbing region generates acoustic radiation. The shape, location and/or activation of the absorbing regions in one or more nearby fibers can be used to achieve various effects, especially, beam aiming, enhancement of a particular spectral component within the generated ultrasound and/or otherwise selecting a frequency spectrum. In an embodiment the position dependence of the absorption is graded to ensure a uniform energy distribution in spite of reduction of the wave amplitude as