Patent Description:
A modern aircraft propulsion system typically includes a gas turbine engine housed within a nacelle. The nacelle includes an inlet structure for directing incoming air to the gas turbine engine. This inlet structure includes an inlet lip, an inner barrel and an outer barrel. The inlet lip forms a leading edge of the inlet structure. The inner barrel is connected to a radial inner end of the inlet lip, and at least partially forms an outer peripheral boundary of an inlet duct into the aircraft propulsion system. The outer barrel is connected to a radial outer end of the inlet lip, and circumscribes the inner barrel.

Under certain environmental conditions, the inlet lip may be susceptible to ice accumulation. To melt ice that may accumulate on the inlet lip, the inlet structure may be configured with a thermal anti-icing system. A lip skin of the inlet lip, for example, may be configured with an electrical resistance heater. Such an electrical resistance heater may be attached to an interior surface of the lip skin to minimize a thermal conduction path length from the heater to an exterior surface of the lip skin / the inlet lip. While such electrical resistance heaters have various benefits, there is still room in the art for improvement. Damage to the lip skin and the electrical resistance heater arranged therewith following a foreign object impact, for example, may render a portion of or the entire electrical resistance heater inoperable where the damage severs one or more electrical resistance circuits within the electrical resistance heater.

It is known to configure the inlet structure with one or more acoustic panels for attenuating sound (e.g., noise) generated by the gas turbine engine. Some efforts have been made to integrate such acoustic panels into the inlet lip. Acoustic panels, however, are difficult to de-ice. A typical acoustic panel, for example, includes a perforated face skin, a back skin and a honeycomb core between the face and the back skins. The honeycomb core includes a plurality of cavities that extend between the face and the back skins. While the cavities facilitate sound attenuation, these cavities also thermally insulate the face skin from the back skin. It is therefore difficult to integrate an electrical resistance heater with an acoustic panel, particularly where the heater is designed to be attached to an interior-most surface of the acoustic panel.

Generally speaking, efficiency of the aircraft propulsion system may be increased by, inter alia, reducing weight and size of the aircraft propulsion system. Shortening the inlet structure is one known way to reduce the weight and the size of the aircraft propulsion system. However, certain thermal de-icing requirements and certain sound attenuation requirements currently provide obstacles to reducing the weight and the size of the inlet structure further. There is a need in the art therefore for improved systems and structures which can facilitate reducing weight and/or size of a nacelle inlet structure.

<CIT> discloses a composite material, uses thereof, and method for producing the same.

<CIT> Al discloses a thermal anti-icing system with microwave system.

<CIT> discloses an ice protection system and method.

According to an aspect of the present invention, an assembly is provided for an aircraft structure as claimed in claim <NUM>. The microwave system may include a microwave source and a waveguide. The microwave source may be configured to generate the microwaves. The waveguide may be arranged with the second skin. The waveguide may be configured to receive the microwaves from the microwave source and then direct the microwaves to the susceptor.

The susceptor is be configured with the first skin.

The susceptor may at least partially form the first skin.

The susceptor may be bonded to the first skin.

The susceptor may be arranged between the core and the exterior surface.

The microwave system may include a waveguide. The core may be arranged between the susceptor and the waveguide.

The microwave system may include a waveguide. The waveguide may be configured with the second skin.

The acoustic panel may include a perforated skin that forms the exterior surface. The perforated skin may include a plurality of perforated layers bonded together. One of the perforated layers may be configured as or otherwise include the susceptor.

The acoustic panel may include a perforated skin that forms the exterior surface. The perforated skin may include a first layer, a second layer and a third layer. The third layer may be disposed between and bonded by a microwave transparent adhesive to the first layer and the second layer. The third layer may be configured as or otherwise include the susceptor.

The first layer and/or the second layer may include fiberglass.

The susceptor may be configured from or otherwise include a layer of metal.

The microwave system may include a waveguide configured to direct the microwaves to the susceptor.

The waveguide may be configured as or otherwise include a hollow waveguide.

The waveguide may be configured as or otherwise include a microstrip waveguide.

The microwaves may be transmitted at a frequency between one gigahertz (<NUM>) and ten gigahertz (<NUM>).

The microwaves may be transmitted at a frequency between sixty gigahertz (<NUM>) and seventy-seven gigahertz (<NUM>).

The microwave system may include a microwave source configured as a magnetron, a klystron, a gyrotron or a solid state source.

The assembly may also include a nacelle structure. This nacelle structure may include the acoustic panel.

<FIG> illustrates an assembly <NUM> for an aircraft. This aircraft assembly <NUM> includes an aircraft structure <NUM> and a microwave thermal anti-icing system <NUM>.

The aircraft structure <NUM> includes at least one acoustic panel <NUM>. This acoustic panel <NUM> is configured to attenuate sound; e.g., noise. The acoustic panel <NUM> of <FIG>, for example, may be configured to attenuate sound generated by an aircraft propulsion system such as, for example, a turbofan propulsion system or a turbojet propulsion system. With such a configuration, the acoustic panel <NUM> may be configured with a nacelle of the propulsion system; e.g., the aircraft structure <NUM> may be a nacelle structure. The acoustic panel <NUM>, for example, may be configured as or otherwise included as part of a noselip, an inner barrel, and outer barrel, etc. Alternatively, the acoustic panel <NUM> may be configured with another component / structure of the aircraft such as its fuselage or a wing. Furthermore, the acoustic panel <NUM> may be configured to also or alternatively attenuate aircraft related sound other than sound generated by the propulsion system.

The acoustic panel <NUM> extends laterally in a first lateral direction (e.g., an x-axis direction) along an x-axis. The acoustic panel <NUM> extends laterally in a second lateral direction (e.g., a y-axis direction) along a y-axis. The acoustic panel <NUM> extends vertically in a vertical direction (e.g., a z-axis direction) along a z-axis. Note, the term "lateral" may be used herein to generally describe the first lateral direction, the second lateral direction and/or any other direction within the x-y plane. Also note, the term "vertical" may be used herein to describe a depthwise panel direction and is not limited to a gravitational up/down direction. Furthermore, for ease of illustration, the x-y plane is shown as a generally flat plane. However, in other embodiments, the x-y plane and, thus, the acoustic panel <NUM> may be curved and/or follow an undulating geometry. For example, the x-y plane and, thus, the acoustic panel <NUM> may be arcuate, cylindrical, conical, frustoconical, or tapered with or without radial undulations. In such embodiments, a solely vertical direction (e.g., z-axis direction) is defined relative to a position of interest on the x-y plane. For example, on a spherical x-y plane, the vertical direction (e.g., z-axis) direction is a radial direction.

The acoustic panel <NUM> of <FIG> includes a perforated first skin <NUM> and a solid, non-perforated second skin <NUM>. The acoustic panel <NUM> of <FIG> also includes a cellular core <NUM> arranged vertically between and connected to (e.g., bonded to, laid up integral with, etc.) the first skin <NUM> and the second skin <NUM>.

The first skin <NUM> may be configured as a face skin and/or an exterior skin of the acoustic panel <NUM>. This first skin <NUM> is configured as a relatively thin layer of material that extends laterally within the x-y plane. The first skin <NUM> has a vertical thickness <NUM>. This first skin vertical thickness <NUM> extends vertically between opposing side surfaces <NUM> and <NUM> of the first skin <NUM>. The first skin <NUM> includes a plurality of perforations <NUM>; e.g., apertures such as through-holes. Each of these first skin perforations <NUM> extends generally vertically through the first skin <NUM> between the first skin side surfaces <NUM> and <NUM>.

The second skin <NUM> may be configured as a back skin and/or an interior skin of the acoustic panel <NUM>. This second skin <NUM> is configured as a relatively thin layer of (e.g., continuous and uninterrupted) material that extends laterally within the x-y plane. The second skin <NUM> has a vertical thickness <NUM>. This second skin vertical thickness <NUM> extends vertically between opposing side surfaces <NUM> and <NUM> of the second skin <NUM>. The second skin vertical thickness <NUM> may be substantially equal to or different (e.g., greater or less) than the first skin vertical thickness <NUM>.

The cellular core <NUM> extends laterally within the x-y plane. The cellular core <NUM> has a vertical thickness <NUM>. This core vertical thickness <NUM> extends vertically between opposing sides <NUM> and <NUM> of the cellular core <NUM>, which core sides <NUM> and <NUM> are respectively abutted against the interior first skin side surface <NUM> and the interior second skin side surface <NUM>. The core vertical thickness <NUM> may be substantially greater than the first skin vertical thickness <NUM> and/or the second skin vertical thickness <NUM>. The core vertical thickness <NUM>, for example, may be at least ten to forty times (<NUM>-40x), or more, greater than the vertical thickness <NUM>, <NUM>; however, the acoustic panel <NUM> of the present disclosure is not limited to such an exemplary embodiment.

Referring to <FIG>, the cellular core <NUM> is configured to form one or more cavities <NUM> vertically between the first skin <NUM> and the second skin <NUM>. Referring to <FIG>, the cellular core <NUM> may be configured as a honeycomb core. The cellular core <NUM> of <FIG>, for example, includes a plurality of corrugated sidewalls <NUM>. These sidewalls <NUM> are arranged in a side-by-side array and connected to one another such that each adjacent (e.g., neighboring) pair of the sidewalls <NUM> forms an array of the cavities <NUM> laterally therebetween. Of course, in other embodiments, the sidewalls <NUM> may be formed integral with one other as a cellular grid structure <NUM> as shown, for example, in <FIG>.

Referring to <FIG>, each of the cavities <NUM> extends vertically through the cellular core <NUM> to and between the first skin <NUM> and its interior side surface <NUM> and the second skin <NUM> and its interior side surface <NUM>. Referring to <FIG>, one or more or all of the cavities <NUM> may each have a polygonal (e.g., hexagonal) cross-sectional geometry when viewed in a plane parallel to one or more of the elements <NUM>, <NUM> and/or <NUM> (see <FIG>); e.g., perpendicular to the z-axis. The present disclosure, however, is not limited to the foregoing exemplary cellular core configuration. In particular, various other types of honeycomb cores and, more generally, various other types of cellular cores for an acoustic panel are known in the art, and the present disclosure is not limited to any particular ones thereof.

Referring to <FIG>, one or more or all of the cavities <NUM> are each fluidly coupled with a respective set of one or more of the first skin perforations <NUM>. Each respective cavity <NUM> may thereby be configured as a resonance chamber. Sound waves, for example, may enter each respective cavity <NUM> through the respective first skin perforation(s) <NUM>. These sound waves may travel within the cavity <NUM> to the second skin <NUM>, where the second skin <NUM> may reflect the sound waves back through the respective cavity <NUM> to the respective first skin perforation(s) <NUM>. With such an arrangement, each respective cavity <NUM> (e.g., resonance chamber) may reverse phase of the sound waves using known acoustic reflection principles and subsequently direct the reverse phase sound waves out of the acoustic panel <NUM> through the respective first skin perforation(s) <NUM> to destructively interfere with other incoming sound waves. The acoustic panel <NUM> may thereby attenuate noise.

Referring to <FIG>, the thermal anti-icing system <NUM> is configured to melt and/or prevent ice accumulation on an exterior surface <NUM> of an exterior skin <NUM> of the aircraft structure <NUM>; e.g., the exterior first skin side surface <NUM> of the acoustic panel <NUM>. The thermal anti-icing system <NUM> of <FIG> includes at least one susceptor <NUM> and a microwave system <NUM>.

Referring to <FIG>, the susceptor <NUM> is configured to absorb electromagnetic energy (e.g., microwave radiation, also referred to as "microwaves") and convert that absorbed electromagnetic energy into heat. The susceptor <NUM>, for example, may be configured as a thin layer (or strip, or wire) of material. Examples of the susceptor material may include, but are not limited to: aluminum (Al) or an alloy thereof; ferrous metal such as stainless steel; titanium (Ti) or an alloy thereof; Inconel alloys; chromium (Cr) or an alloy thereof; graphite; composites of metal(s) and ceramic(s) (e.g., cermets); doped silicon carbide; and/or metal oxide(s). The present disclosure, however, is not limited to the foregoing exemplary susceptor materials.

The susceptor <NUM> is configured with the acoustic panel <NUM>, and thermally coupled with the aircraft structure exterior surface <NUM>; e.g., the exterior first skin side surface <NUM> of the acoustic panel <NUM>. The susceptor <NUM> of <FIG>, for example, is configured with the acoustic panel first skin <NUM>.

The susceptor <NUM> of <FIG> is formed as part of the first skin <NUM>. The first skin <NUM> of <FIG>, for example, includes one or more first skin layers 68A-D (generally referred to as "<NUM>"); e.g., intra-skin perforated layers. These first skin layers <NUM> are arranged together in a stack to form the first skin <NUM>, where each first skin perforation <NUM> extends vertically sequentially through each of the first skin layers <NUM>. The first skin layers <NUM> are bonded to one another by an adhesive <NUM>; e.g., a microwave transparent adhesive. Examples of the adhesive <NUM> may include, but are not limited to, thermoset epoxy resin or any other bonding material with low dielectric loss. The present disclosure, however, is not limited to the foregoing exemplary adhesive materials.

The interior first skin layer 68D may form the interior first skin side surface <NUM> that engages and is bonded to the cellular core <NUM>. The exterior first skin layer 68A may form the aircraft structure exterior skin <NUM>; e.g., the exterior first skin side surface <NUM> of the acoustic panel <NUM>. The intermediate first skin layers 68B and 68C are arranged vertically between the other first skin layers 68A and 68D.

At least one of the first skin layers <NUM> (e.g., 68C) may at least partially or completely form the susceptor <NUM>. The (e.g., interior) intermediate first skin layer 68C of <FIG>, for example, forms the susceptor <NUM>. More particularly, the intermediate first skin layer 68C of <FIG> is the thin layer of the susceptor material that forms the susceptor <NUM>. The susceptor <NUM> may thereby be located at (e.g., on, adjacent or proximate) the aircraft structure exterior surface <NUM> / the exterior first skin side surface <NUM>. For ease of description, this intermediate first skin layer 68C that forms the susceptor <NUM> may be referred to below as a susceptor layer <NUM>.

One or more of the remaining first skin layers 68A, 68B and 68D may be configured as structural layers, support layers and/or filler layers. Each of these remaining first skin layers 68A, 68B and 68D may be configured as a thin sheet of reinforcement material embedded within (or otherwise arranged with) a matrix. The reinforcement material may include fibrous and/or granular (e.g., powder) material that is transparent to the electromagnetic energy; e.g., the microwave radiation. Examples of the reinforcement material may include, but are not limited to, fiberglass or any other material with low dielectric loss. The matrix material is a bonding material that is also transparent to the electromagnetic energy; e.g., the microwave radiation. This matrix material may be the same type as (or may be) the adhesive <NUM> (e.g., a microwave transparent adhesive) bonding the first skin layers <NUM> together. In other embodiments, however, the matrix material may be different than, but complementary to for example, the adhesive <NUM> material. The present disclosure, however, is not limited to the foregoing exemplary reinforcement or matrix materials.

Each of the first skin layers <NUM> has a vertical thickness along the z-axis. The susceptor layer <NUM> vertical thickness may be equal to or different (e.g., less or greater) than the vertical thicknesses of the remaining first skin layers 68A, 68B and 68D. Generally speaking, the susceptor layer <NUM> vertical thickness is selected based on a frequency of interest of the electromagnetic radiation. The susceptor layer <NUM> vertical thickness may also or alternatively be selected to be one-quarter (<NUM>/<NUM>) of a wavelength of the electromagnetic radiation at the frequency of interest. The present disclosure, however, is not limited to such exemplary susceptor layer vertical thicknesses.

The intermediate first skin layer 68C is described above as forming the susceptor <NUM>. The present disclosure, however, is not limited to such an exemplary construction. For example, in some embodiments, referring to <FIG>, the susceptor <NUM> may alternatively (or also) be formed by another one of the intermediate first skin layers (e.g., 68B). In some embodiments, referring to <FIG>, the susceptor <NUM> may alternatively (or also) be formed by the interior first skin layer 68D. In some embodiments, referring to <FIG>, the susceptor <NUM> may alternatively (or also) be formed by the exterior first skin layer 68A. With each of the foregoing configurations, the susceptor <NUM> is arranged vertically between the cellular core <NUM> (see <FIG>) and the aircraft structure exterior surface <NUM> / the exterior first skin side surface <NUM>.

Referring to <FIG>, the susceptor <NUM> is configured to laterally overlap (along the x-axis and/or the y-axis) an entirety of the aircraft structure exterior surface <NUM> / the exterior first skin side surface <NUM>. The susceptor <NUM>, for example, may extend along an entire lateral extent of the aircraft structure exterior skin <NUM> / the acoustic panel first skin <NUM>. Alternatively, the susceptor <NUM> may laterally overlap (along the x-axis and/or the y-axis) a portion of the aircraft structure exterior surface <NUM> / the exterior first skin side surface <NUM>. For example, referring to <FIG>, the susceptor layer <NUM> may be configured as a strip of material with a lateral width (along the x-axis and/or the y-axis) that is less than a lateral width of the first skin <NUM> and its other first skin layers <NUM>. With such an arrangement, thermal anti-icing of the exterior surface <NUM>, <NUM> may be focused to a select region corresponding to the susceptor <NUM>. In other embodiments, referring to <FIG>, the susceptor <NUM> may include one or more (e.g., discrete or interconnected) susceptor segments <NUM>. Each of these susceptor segments <NUM> may focus thermal anti-icing to multiple corresponding regions, or provide effective coverage for the entire exterior surface <NUM>, <NUM>. Note, <FIG> illustrate the acoustic panel <NUM> without the first skin perforations <NUM> for ease of illustration.

Referring to <FIG>, the microwave system <NUM> includes a microwave source <NUM> and a microwave transmission system <NUM>. The microwave source <NUM> may be configured to generate microwaves at a frequency of, for example, between <NUM> gigahertz (GHz) and <NUM> gigahertz; e.g., at exactly or about (e.g., +/- <NUM> or <NUM>) <NUM> gigahertz (GHz). Of course, in other embodiments, the microwave source <NUM> may generate the microwaves at a frequency at or above <NUM> gigahertz. In still other embodiments, the microwave source <NUM> may generate the microwaves at a frequency at or below <NUM> gigahertz. For example, the microwave source <NUM> may be configured to generate microwaves at a frequency between one and ten gigahertz, or between one and three gigahertz, or between <NUM> and <NUM> gigahertz.

The microwave source <NUM> may be configured as or otherwise include a vacuum electron device (VED) such as, but not limited to, a magnetron, a klystron and a gyrotron. The microwave source <NUM> may alternatively be configured as or otherwise include a solid state device; e.g., a solid state microwave source. Such a solid state device may include one or more radio-frequency (RF) transistors configured to generate the microwaves. Generally speaking, a solid state device may have some advantages over a vacuum electron device. For example, a solid state device may require less (e.g., <NUM>-100x less) operational power than a vacuum electron device; e.g., <NUM>-<NUM> volts versus <NUM> volts. A solid state device may have a longer useful lifetime than a vacuum electron device; e.g., <NUM>-<NUM> plus years versus <NUM>-<NUM> hours. A solid state device may have a lower mass and, thus, weigh less than a vacuum electron device. A solid state device may have improved control over a vacuum electron device.

The microwave source <NUM> may be configured to generate a continuous output (e.g., stream) of the microwaves. The microwave source <NUM> may also or alternatively be configured to generate an intermittent (e.g., pulsed) output of the microwaves.

The microwave transmission system <NUM> is configured to transmit the microwaves generated by the microwave source <NUM> to a desired location or locations. The microwave transmission system <NUM> is further configured to selectively direct the microwaves at / to the susceptor <NUM> as described below in further detail.

The microwave transmission system <NUM> includes one or more waveguides 80A and 80B (generally referred to as "<NUM>"); e.g., electromagnetic feed lines. The upstream waveguide 80A is coupled with the microwave source <NUM>, and is configured to transmit the microwaves generated by the microwave source <NUM> to the downstream waveguide 80B. The downstream waveguide 80B is configured to direct the microwaves received from the upstream waveguide 80A at / to the susceptor <NUM>. These waveguides <NUM> may be configured as segments of a common waveguide. Alternatively, the waveguides <NUM> may be configured as discrete waveguide with common or different configurations.

The waveguides <NUM> may be configured as dielectric waveguides. Examples of a dielectric waveguide include, but are not limited to, an optical fiber, a microstrip, a coplanar waveguide, a stripline and a coaxial cable. Each dielectric waveguide may be constructed from or otherwise include a fluoropolymer such as, but not limited to, polytetrafluoroethylene (PTFE) (e.g., Teflon® material) or polyvinylidene fluoride (PVDF). The dielectric waveguide may also or alternatively include other polymeric materials and/or ceramics. The present disclosure, however, is not limited to the foregoing exemplary waveguide materials, nor to dielectric waveguides as discussed below in further detail.

Referring to <FIG>, the dielectric waveguide may be at least partially or completely covered by an insulating material <NUM>. This insulating material <NUM> is a microwave resistive material such as, but not limited to, metal or alumina (e.g., Al<NUM>O<NUM>) or silica (e.g., SiOs). The present disclosure, however, is not limited to the foregoing exemplary insulating materials. At least one side of the downstream waveguide 80B may be configured at least partially or completely without the insulting material to facilitate directing the microwaves from the dielectric waveguide towards / to the susceptor <NUM>. Of course, in other embodiments, the downstream waveguide 80B may be completely covered with the insulating material <NUM>, where one or more perforations pierce through the insulating material <NUM> to facilitate directing of the microwaves.

Referring to <FIG>, the downstream waveguide 80B is configured with the acoustic panel <NUM>. The downstream waveguide 80B of <FIG>, for example, is configured with the acoustic panel second skin <NUM>.

The downstream waveguide 80B of <FIG> is formed as part of the second skin <NUM>. The second skin <NUM> of <FIG>, for example, includes one or more second skin layers 84A and 84B (generally referred to as "<NUM>"); e.g., intra-skin layers. These second skin layers <NUM> are arranged together in a stack to form the second skin <NUM>. The second skin layers <NUM> are bonded to one another by an adhesive <NUM>; e.g., a microwave transparent adhesive. This adhesive <NUM> may be the same type as the adhesive <NUM> in the first skin <NUM>; however, the present disclosure is not limited thereto. Examples of the adhesive <NUM> may include, but are not limited to, thermoset epoxy resin or any other bonding material with low dielectric loss. The present disclosure, however, is not limited to the foregoing exemplary adhesive materials.

The interior second skin layer 84A may form the interior second skin side surface <NUM> that engages and is bonded to the cellular core <NUM>. The exterior second skin surface 84B may form the exterior second skin side surface <NUM>, which is vertically opposite the aircraft structure exterior surface <NUM> / the exterior first skin side surface <NUM>.

At least one of the second skin layers <NUM> (e.g., 84B) may at least partially or completely form the downstream waveguide 80B. The exterior second skin layer 84B of <FIG>, for example, forms the downstream waveguide 80B. More particularly, the exterior second skin layer 84B of <FIG> includes a thin layer of dielectric waveguide material that forms the downstream waveguide 80B. The downstream waveguide 80B may thereby be located at (e.g., on, adjacent or proximate) the exterior second skin side surface <NUM>. For ease of description, this second skin layer 84B that forms the second waveguide may be referred to below as a waveguide layer <NUM>.

The remaining second skin layer 84A may be configured as a structural layer, a support layer and/or a filler layer. The interior second skin layer 84A of <FIG>, for example, may be configured as a thin sheet of reinforcement material embedded within (or otherwise arranged with) a matrix. The reinforcement material may include fibrous and/or granular (e.g., powder) material that is transparent to the electromagnetic energy; e.g., the microwave radiation. Examples of the reinforcement material may include, but are not limited to, fiberglass or any other material with low dielectric loss. The matrix material is a bonding material that is also transparent to the electromagnetic energy; e.g., the microwave radiation. This matrix material may be the same type as (or may be) the adhesive <NUM> (e.g., a microwave transparent adhesive) bonding the second skin layers <NUM> together. In other embodiments, however, the matrix material may be different than, but complementary to for example, the adhesive <NUM> material. The present disclosure, however, is not limited to the foregoing exemplary reinforcement or matrix materials.

Each of the second skin layers <NUM> has a vertical thickness along the z-axis. The waveguide layer <NUM> vertical thickness may be equal to or different (e.g., less or greater) than the vertical thicknesses of the remaining second skin layer 84A.

The exterior second skin layer 84B is described above as forming the downstream waveguide 80B. The present disclosure, however, is not limited to such an exemplary construction. For example, in some embodiments, referring to <FIG>, the downstream waveguide 80B may alternatively (or also) be formed by the interior second skin layer 84A, or another (e.g., intermediate) second skin layer when included. With each of the foregoing configurations, the downstream waveguide 80B is arranged vertically between the cellular core <NUM> (see <FIG>) and the exterior second skin side surface <NUM>. Referring to <FIG>, at least the cellular core <NUM> is arranged vertically between and separates the downstream waveguide 80B and the susceptor <NUM>.

The downstream waveguide 80B is configured to laterally overlap (along the x-axis and/or y-axis) an entirety of the susceptor <NUM>. The downstream waveguide 80B, for example, may extend along the entire lateral extent of the acoustic panel second skin <NUM>. Alternatively, the downstream waveguide 80B may laterally overlap (along the x-axis and/or the y-axis) a portion of the second skin <NUM> as well as a portion of the exterior first skin side surface <NUM>, which corresponds to the susceptor <NUM>. For example, referring to <FIG>, the waveguide layer <NUM> may be configured as a strip of material with a lateral width (along the x-axis and/or the y-axis) that is less than the lateral width of the second skin <NUM>. In other embodiments, referring to <FIG>, the downstream waveguide 80B may include one or more (e.g., discrete or interconnected) waveguide segments <NUM>. Each of these waveguide segments <NUM> may focus the microwaves to a respective one of the susceptor segments <NUM>.

During operation of the thermal anti-icing system <NUM> of <FIG>, the microwave source <NUM> generates microwaves. These microwaves are received by the downstream waveguide 80B through the upstream waveguide 80A. Referring to <FIG>, the downstream waveguide 80B selectively directs the received microwaves <NUM> towards / to the susceptor <NUM> through the cellular core <NUM> as well as one or more other layers of the skin(s) <NUM> and/or <NUM>. These transmitted microwaves impinge against and are absorbed by the susceptor <NUM>, and are then transformed by the susceptor <NUM> into thermal energy <NUM>. This thermal energy <NUM> may be transferred via conduction from the susceptor <NUM> into a region of the aircraft structure exterior skin <NUM> adjacent and/or proximate the susceptor <NUM>. This transfer of the thermal energy <NUM> may heat the region of the aircraft structure exterior skin <NUM> and thereby melt and/or prevent ice accumulation over and/or about the aircraft structure exterior skin region.

To facilitate transmission of the microwaves through the cellular core <NUM>, the cellular core <NUM> may be constructed from dielectric material. This dielectric material may be or otherwise include a polymer (e.g., a fluoropolymer) such as, but not limited to, polytetrafluoroethylene (PTFE) (e.g., Teflon® material) or polyvinylidene fluoride (PVDF). The dielectric material may include fibrous material (e.g., glass fibers) within a polymer matrix. The dielectric material may also or alternatively include other polymeric materials and/or ceramics. For example, the dielectric material may include: ceramic matrix composite (CMC), alumina, silica, silicon carbide, silicon oxynitride, borosilicate glass, Pyrex, or other (e.g., "microwave safe") dielectrics used for conventional household microwave ovens. The present disclosure, however, is not limited to the foregoing exemplary dielectric materials.

In some embodiments, referring to <FIG> for example, the susceptor <NUM> may be an integral part of the first skin <NUM>. In other embodiments, referring to <FIG>, the susceptor <NUM> may be formed discrete from the first skin <NUM> and subsequently bonded to the first skin <NUM>.

In some embodiments, referring to <FIG> for example, the downstream waveguide 80B may be an integral part of the second skin <NUM>. In other embodiments, referring to <FIG>, the downstream waveguide 80B may be formed discrete from the second skin <NUM> and subsequently bonded to the second skin <NUM>, printed onto the second skin <NUM>, or otherwise attached to the second skin <NUM>. In still other embodiments, referring to <FIG>, the downstream waveguide 80B may be configured discrete from the acoustic panel <NUM> and its second skin <NUM>. The downstream waveguide 80B of <FIG>, for example, may be separated from the acoustic panel <NUM> and its second skin <NUM> by an air gap <NUM>.

In some embodiments, the waveguides <NUM> may be configured as dielectric waveguides as described above. In other embodiments, referring to <FIG>, one or each of the waveguides <NUM> may alternatively be configured as a hollow waveguide. At least the downstream waveguide 80B of <FIG>, for example, includes a tubular body <NUM> with an internal passage <NUM> (e.g., a bore) configured to communicate the microwaves. This tubular body <NUM> may include one or more apertures <NUM>; e.g., slots, slits and/or perforations. Each of these apertures <NUM> extends through / pierces a sidewall of the respective waveguide <NUM>. Each of the apertures <NUM> is thereby operable to direct some of the microwaves from within its internal passage <NUM> towards / or the susceptor <NUM> (see <FIG>). Of course, various other types of microwave waveguide are known in the art, and the present disclosure is not limited to any particular ones thereof.

In addition to facilitating heating of the aircraft structure exterior skin <NUM> through a thermally insulating structure such as the cellular core <NUM>, the thermal anti-icing system <NUM> of the present disclosure is also relatively resistant to foreign object damage (FOD). For example, during operation, the aircraft structure <NUM> of <FIG> may be subject to a foreign object impact. Under certain conditions, such an impact may crack and/or fracture, inter alia, the susceptor <NUM>; e.g., material within the susceptor layer <NUM> (e.g., see <FIG>). Even where cracked / fractured, however, the susceptor <NUM> may still be operable to transform the microwaves into heat energy since no electrical interconnection within the susceptor <NUM> is required. Furthermore, provision of the relatively light weight susceptor <NUM> and waveguides <NUM> may reduce aircraft weight by obviating the need for ducting and valve associated with a traditional forced hot air anti-icing system.

The thermal anti-icing system <NUM> of the present disclosure may also simplify manufacturing of the acoustic panel <NUM>. For example, where an acoustic panel is provided with an electrical resistance heater, electrical conduction paths for that heater must be carefully mapped to ensure that those paths are not severed during perforation of its exterior skin. However, as discussed above, perforation of the susceptor <NUM> does not adversely impact its operation. Therefore, the first skin perforations <NUM> may be formed without detailed, time intensive mappings.

In some embodiments, the microwave source <NUM> may be tuned to an absorption frequency of the susceptor <NUM>. This may facilitate provision of higher electromagnetic radiation frequencies, while reducing a footprint of the electromagnetic radiation. For example, the microwave source <NUM> may be tuned for a V-band frequency between forty gigahertz and eighty gigahertz; e.g., between <NUM> and <NUM>. Within such a frequency range, absorption by other aircraft structure materials is relatively low and the susceptor <NUM> may be made relatively small. The susceptor <NUM>, for example, may be about <NUM> thick for a microwave transmission frequency of about <NUM>. The present disclosure, however, is not limited to the forgoing exemplary frequencies or sizes.

<FIG> illustrates an inlet structure <NUM> of a nacelle for an aircraft propulsion system; e.g., a turbofan or a turbojet propulsion system. This inlet structure <NUM> includes an inlet lip <NUM>, an inner barrel <NUM> and an outer barrel <NUM>. The inlet lip <NUM> forms a leading edge <NUM> of the inlet structure <NUM>. The inner barrel <NUM> is connected to a radial inner end of the inlet lip <NUM>, and at least partially forms an outer peripheral boundary of an inlet duct <NUM> into the aircraft propulsion system. The outer barrel <NUM> is connected to a radial outer end of the inlet lip <NUM>, and circumscribes the inner barrel <NUM>.

The inlet structure <NUM> of <FIG> is configured with one or more of the acoustic panels <NUM>; one visible in <FIG>. These acoustic panels <NUM> may collectively form at least an inner portion of the inlet lip <NUM> and an entirety (or a portion) of the inner barrel <NUM>. Each acoustic panel <NUM> of <FIG>, for example, extends axially along an axial centerline <NUM> of the aircraft propulsion system from (or about) the leading edge <NUM> to (or towards) an aft end <NUM> of the inner barrel <NUM>. Each acoustic panel <NUM> may have an arcuate configuration, which extends partially circumferentially about the axial centerline <NUM>. With this arrangement, sound attenuation treatment may be carried past a typical forward end location <NUM> of the inner barrel <NUM> into the inlet lip <NUM>. An overall axial length of the inner barrel <NUM> and, thus, the entire inlet structure <NUM> may thereby be shorted while still providing a certain level of sound attenuation as well as thermal anti-icing for the inlet lip <NUM> as compared, for example, to a traditional inlet structure <NUM> as shown in <FIG>. Configuring the inlet structure <NUM> of <FIG> with the acoustic panel(s) <NUM> and the thermal anti-icing system <NUM> of the present disclosure may thereby facilitate a reduction in size and/or weight of the aircraft propulsion system and its nacelle.

While the acoustic panel(s) <NUM> and the thermal anti-icing system <NUM> is described above as being configured with the inlet structure <NUM>, the present disclosure is not limited to such an exemplary application. Rather, the acoustic panel(s) <NUM> and the thermal anti-icing system <NUM> of the present disclosure may be configured with any aircraft structure which would benefit from including sound attenuation as well as de-icing capability.

Claim 1:
An assembly (<NUM>) for an aircraft structure, comprising:
an acoustic panel (<NUM>) comprising an exterior surface (<NUM>); and
a thermal anti-icing system (<NUM>) comprising a susceptor (<NUM>) and a microwave system (<NUM>), the susceptor (<NUM>) configured with the acoustic panel (<NUM>), and the microwave system (<NUM>) configured to direct microwaves to the susceptor (<NUM>) for melting and/or preventing ice accumulation on the exterior surface (<NUM>),
characterised in that:
the acoustic panel (<NUM>) includes a first skin (<NUM>), a second skin (<NUM>) and a core (<NUM>); and
the core (<NUM>) is connected to the first skin (<NUM>) and the second skin (<NUM>), the core (<NUM>) forms a plurality of cavities between the first skin (<NUM>) and the second skin (<NUM>), and each of the plurality of cavities is fluidly coupled with one or more respective perforations through the first skin (<NUM>); and the susceptor (<NUM>) is configured with the first skin (<NUM>).