Kitchen appliance

Abstract

A kitchen appliance comprising a metamaterials ventilation grille is described, the grille comprising grille elements having ventilation gaps defined therebetween. Metamaterial elements are included defining, co-operatively with the grille elements, first ventilation channels through the ventilation gaps between an interior side of the grille and an exterior side of the grille. The first ventilation channels have widenings and narrowings configured to dissipate sound-waves travelling along the first ventilation channels through harmonic dissipation at one or more predetermined frequencies.

Description

[0001] "KITCHEN APPLIANCE"

[0002] FIELD

[0003] The present invention relates to a kitchen appliance and to a method of manufacture of the same.

[0004] BACKGROUND

[0005] Noise is a long-standing problem in the field of kitchen appliances. This is particularly because they are typically located in one of the most regularly used rooms of the house in which space is restricted, and because kitchen appliances require the physical processing of food (including beverage) matter. They also require cooling of components within them, hindering the appliance of soundinsulation to them.

[0006] The fully-automatic coffee machine category of kitchen appliances in particular suffers from the noise problem. This is because they include heating elements, pumps, and coffee-grinders all within a single housing. This means that they represent a particularly acute problem as they require cooling of heating elements that generate heats of up to 105 degrees centigrade, but also generate high levels of noise at unpleasant frequencies in the auditory frequency band to which human hearing is typically receptive (-200 Hz to -10,000 Hz), and particularly in the frequency band at which human hearing is typically more sensitive (-2,500 Hz to -4,000 Hz).

[0007] Providing a baffle in a vent of the appliance is a known solution for reducing noise transmission from kitchen appliances whilst maintaining ventilation for cooling. However, the known baffles do not sufficiently reduce noise transmitted through the vent.

[0008] A solution to this problem is proposed in the applicant’s pat. pub. no. EP3937739A1. This places an elastomeric membrane within a void of the coffee machine in order to suppress noise transmission through this void. However, whilst effective in reducing noise, this impacts the ventilation and cooling of the appliance, and complicates manufacturing.

[0009] The present invention aims to at least partially ameliorate the above-described problems of the prior art.

[0010] SUMMARY OF THE INVENTION In an aspect of the invention, a kitchen appliance is disclosed comprising a metamaterials ventilation grille. The metamaterials grille comprises:

[0011] - grille elements having ventilation gaps defined therebetween,

[0012] - metamaterials elements defining, co-operatively with the grille elements, first ventilation channels through the ventilation gaps between an interior side of the grille and an exterior side of the grille, wherein the first ventilation channels have widenings and narrowings configured to dissipate sound-waves travelling along the first ventilation channels through harmonic dissipation at one or more predetermined frequencies. This is advantageous because both ventilation and sound-reduction are provided in the same grille using the same elements. This reduces the number of parts required, the complexity of the product, and improves the sound characteristics.

[0013] Preferably, the predetermined frequencies are in the range 200-10000 Hz, and preferably in the range 500-6000 Hz, and even more preferably in the range 3150- 4000Hz. These are hearing ranges at which human hearing is sensitive.

[0014] Optionally, the first ventilation channels are labyrinthine. The repeated turns involved in this can help to further attenuate / dissipate / disperse sound. Preferably the first ventilation channels have total turning angles of at least 360 degrees, this can further suppress noise. A direction of extension of the first ventilation channels may optionally be primarily along a direction of extension of the grille, for minimising thickness of the grille.

[0015] The metamaterials elements can be preferably provided on an interior side of the grille elements. This can help to protect the metamaterials elements. In an optional configuration, the first ventilation channels have a minimum width of approximately 1mm. This width can help ensure air-flow.

[0016] Optionally the grille-elements comprise baffle elements. These can further help noise reduction.

[0017] Preferably, the first ventilation channels are defined at least partially between the baffles and the metamaterials elements. This can help further simplify the construction.

[0018] In a preferable configuration, second ventilation channels connected to the first ventilation channels are co-operatively defined between neighbouring metamaterials elements. In this way longer ventilation channels overall can be provided without increasing the number of elements.

[0019] Optionally, the second ventilation channels are connected to the first ventilation channels by resonance chambers. Sound-reduction can thus be enhanced.

[0020] Preferably, the resonance chambers are at least 180 degree turns between the second ventilation channels and the first ventilation channels. Sound reduction can thus be enhanced.

[0021] Optionally, the metamaterials elements are substantially identical units repeating along the grille. Manufacturing can thus be simplified.

[0022] Preferably, the kitchen appliance is a coffee machine, preferably a fully- automatic coffee machine. These are machines in which the noise problem can be particularly acute.

[0023] Preferably, the metamaterials elements are any of:

[0024] - “T”-shaped,

[0025] - “r”-shaped,

[0026] - reverse “r”-shaped.

[0027] These shapes can tesselate well to create channels.

[0028] Preferably the metamaterials elements are “T” shaped, comprising at least one of:

[0029] - branches that extend at different points along the length of the stalk,

[0030] - branches that are of differing thickness, preferably in a ratio of 1 :2 of thickness of one branch to the thickness of the other.

[0031] Preferably the first ventilation channels and / or second ventilation channels have right-angle comers and / or gradually curved comers.

[0032] Preferably the metamaterials grille has a maximum thickness between an exterior-facing surface and an interior-facing surface of 1cm.

[0033] Preferably the harmonic dissipation is quarter- wav elength harmonic dissipation / dispersion.

[0034] Preferably the metamaterials ventilation grille comprises a first grille-section, and a second grille-section having a different vertical and / or horizontal extent from the first grille-section.

[0035] Preferably the first grille-section and the second grille-section comprise different repeated units. Preferably the first grille-section and the second grille-section are of different thickness and / or cooling efficiency.

[0036] In another embodiment of the invention, a method of manufacturing a kitchen appliance housing is disclosed, comprising steps of: a) providing a housing made of a material, b) forming a grille out of substantially the same material as the housing, c) forming a plurality of metamaterials elements made of substantially the same material as the housing on the grille so as to define first ventilation channels therebetween forming widenings and narrowings configured to dissipate sound- waves travelling along the first ventilation channels, d) providing the grille fixed within the housing so that the first ventilation channels interconnect an inside and an outside of the kitchen appliance.

[0037] Preferably step c) comprises forming the metamaterial elements integrally with the grille. Preferably step d) comprises forming the grille integrally with the housing.

[0038] Preferably the material is one of polycarbonate, nylon, and acrylonitrile butadiene styrene (ABS).

[0039] Preferably the forming steps comprise injection moulding.

[0040] In an aspect of the invention, an appliance is disclosed comprising a metamaterials ventilation grille. The metamaterials grille comprises:

[0041] - grille elements having ventilation gaps defined therebetween,

[0042] - metamaterials elements defining, co-operatively with the grille elements and / or respective neighbouring metamaterials elements, first ventilation channels through the ventilation gaps between an interior side of the grille and an exterior side of the grille, wherein the first ventilation channels have widenings and narrowings configured to dissipate sound-waves travelling along the first ventilation channels through harmonic dissipation at one or more predetermined frequencies.

[0043] The invention also encompasses a kit of parts for constructing any of the apparatuses or apparatus elements herein described.

[0044] Any apparatus feature as described herein may also be provided as a method feature, and vice versa. As used herein, means plus function features may be expressed alternatively in terms of their corresponding structure, such as a suitably programmed processor and associated memory.

[0045] Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus aspects, and vice versa. Furthermore, any, some and / or all features in one aspect can be applied to any, some and / or all features in any other aspect, in any appropriate combination.

[0046] The invention described here may be used in any kitchen appliance and / or as a stand-alone device. This includes any domestic food-processing and / or preparation machine, including both top-driven machines (e.g. stand-mixers) and bottom- driven machines (e.g. blenders). It may be implemented in heated and / or cooled machines. It may be used in a machine that is built-in to a work-top or work surface, or in a stand-alone device. The invention can also be provided as a stand-alone device.

[0047] BRIEF DESCRIPTION OF DRAWINGS One or more aspects will now be described, by way of example only and with reference to the accompanying drawings having like-reference numerals, in which:

[0048] Fig. la is a side-on drawing of a side of the kitchen appliance according to an embodiment of the invention;

[0049] Fig. lb is a side-on drawing of the kitchen appliance of Fig. la from the opposite side;

[0050] Fig. 1c is a side-one view of the rear of the kitchen appliance of Fig. la;

[0051] Fig. 2 is a highly schematic diagram of the interior of the kitchen appliance of Fig. la;

[0052] Figs. 3a-3d are horizontal sections through different variants of the grille of the kitchen appliance of Fig. la;

[0053] Fig. 4 is a perspective view from an exterior side of a further variant of a grille of the kitchen appliance of Fig. la;

[0054] Fig. 5 is a horizontal section through the grille of Fig. 4; and,

[0055] Fig. 6 is a graph showing the sound profile of a traditional kitchen appliance against that of the kitchen appliance of Fig. la.

[0056] SPECIFIC DESCRIPTION

[0057] Figs, la-lc and 2 show a kitchen appliance 100 (in this case a fully automatic coffee machine) according to an embodiment of the invention. The kitchen appliance 100 has a housing 110 that encapsulates and contains internal components that are used to carry out food / beverage processing activities in response to user instructions input into the user interface 111 provided on the housing. The user interface 111 may be a touch-screen interface, or knobs / buttons, or other suitable control means.

[0058] At the base of the housing 110 a drip-tray 112 is provided to catch any spilt water from the creation of beverages. The housing 110 may be a single-piece unitary construction, or, as shown in Figs, la to 1c, it may comprise discrete panels 110a, 110b held together by fasteners 113 (e.g., screws or bolts). A metamaterials grille 120 is provided through the housing 110 so that cooling air can enter and exit the appliance 100 to cool internal components of it, but so that noise from within can also be suppressed. Metamaterials are engineered constructions designed to exhibit properties rarely found in nature, typically through small, repeated units designed to have a particular shape or property. In this case the metamaterials grille 120 is engineered with repeated, shaped, interlocking / inter-relating metamaterials elements, to trap sound and reduce its transmission from within the housing 110 to the outside whilst still allowing cooling air to enter and exit the housing 110. Examples of suitable constructions of the metamaterials grille 120 for achieving this will be described later with reference to Figs. 3a-3d.

[0059] As can best be seen in Fig. 2, the interior of the appliance 100 contains a number of noise-generating internal components connected by water and / or coffeeconveying pipes shown in thick lines. When a user requests the preparation of a beverage via the user interface 111, water from the removably-attachable, dishwasher- washable, and food-safe water tank 130 is pumped by the pump 140

[0060] (which may be a vibration pump, a relatively noisy but convenient and effective type of pump) to the brewing module 150 (which may be moved by a noisegenerating motor), which is pressurised thereby. At the same time coffee beans from the coffee bean container 160 (which may also be removably-attachable, dish washer- washable, and food-safe) are ground into coffee powder by the grinder

[0061] 170, which may be a high-speed burr-grinder or similar grinder and hence also relatively noisy but also effective. The powder from the grinder 170 is then provided to the brewing module 150 via the interconnecting pipes. The brewing module 150 includes heating elements that raise the temperature of the watercoffee powder mix to a high temperature (e.g., 95 degrees centigrade or more) sufficient to brew a coffee beverage. The beverage is then dispensed from the brewing module 150 via the outlet 180 into a suitable container, and the exhausted coffee grounds are dispensed into a coffee grounds receptacle 190, which is accessible through a door in the housing 110 (not shown).

[0062] The pump 140, brewing module 150, grinder 170, and potentially other components within the housing produce noise. Even with traditional noisesuppression techniques, these can still transmit excessive and unpleasant levels of noise to the external environment. The loudness of a traditional appliance 100 without the metamaterials grille 120 at various frequencies in the range 200-10000 Hz in dB(A) with traditional noise suppression is shown in dotted line in the graph of Fig. 6. As can be seen from this graph, the noise peaks in three frequency bands - a lower frequency band peaking at roughly 500 Hz corresponding to noise emitted by the pump 140, a middle frequency band peaking around 1250 Hz corresponding to the motor moving the brewing module 150, and a higher frequency-band peaking around 3150 Hz corresponding to the grinder 170. For the brewing module 150 and grinder 170, noise level exceeds 55 dB(A). 55 dB is the EU Environmental Agency’s definition of noise pollution when averaged over a sustained period of time. Particularly the noise at 3150 Hz to 4000 Hz, a frequency range to which the human hearing system is particularly sensitive, is unpleasant, yet there is a peak in noise-emission from the grinder 170 in this frequency range that approaches 60 dB(A).

[0063] Therefore, in order to suppress noise-transmission, whilst still allowing cooling air to enter to cool the pump 140, brewing module 150, and grinder 170, the metamaterials grille 120 is used. Different potential constructions of the grille 120 are shown in Figs. 3a to 3d.

[0064] In Fig. 3a a first grille- variant 120a is shown. This comprises parallel grille-bars 121a that extend in parallel with, and as a continuation of, the external surface of the housing 110. Each grille-bar 121a is separated by a gap from its neighbouring grille-bars 121a through which air can flow. An “r”-shaped baffle-element 122a extends inwards, towards an interior of the housing 110, from a lateral side of each grille-bar 121a, partially across the gap separating each grille-bar 121a from its neighbours. The “r”-shaped baffle element 122a extends firstly (in a stalk-section of the “r” 122al) at an angle of more than 45 degrees relative to the plane in which the grille-bars 121a extend, and then (in a branch-section of the “r” 122a2) extends partially across the gap and inwards towards the interior of the housing 110, at an angle of less than 45 degrees relative to the plane in which the grille-bars 121a extend.

[0065] A reversed-“r”-shaped metamaterial element 123a extends inwards towards an interior of the housing 110 from an opposite lateral side of each grille-bar 121a to that from which the “r”-shaped baffle element 122a extends. The reversed- “r”- shaped metamaterial elements 123a extend inwardly towards an interior of the housing, and across the gap separating each grille-bar 121a from its neighbour. Similarly to the “r”-shaped baffle elements 122a, the reversed- “r”-shaped metamaterial elements 123a extend firstly (in a stalk-section of the reversed-“r” 123al, which connects to the grille-bar 121a) at an angle of more than 45 degrees relative to the plane in which the grille-bars 121a extend, and then (in a branchsection of the reversed- “r” 123a2) extend across the gap at an angle of less than 45 relative to the plane in which the grille-bars 121a extend, albeit in an opposite direction across the gap. However, the length of extension of both the stalk-section 123al and branch-section 123a2 of the reversed- “r”-shaped metamaterial elements 123a are greater than those of the “r”-shaped baffle elements 122a, and in the branch-section 123a2 of the reversed- “r”-shaped metamaterial elements 123a, they extend back towards the grille-bars 120a and the exterior of the housing 110, parallel to the corresponding branch-sections 122a2 of the “r”-shaped baffle elements 122a, so as to create a channel 124a therebetween. Extending laterally in opposite directions across the gaps separating the grillebars 121a, the “r”-shaped baffle elements 122a and reversed-“r”-shaped metamaterial elements 123a co-operatively cover the gaps. This ensures that sound cannot directly radiate through the grille-variant 120a to an exterior of the housing, and instead must travel along the channels 124a. However, the channels 124a allow air to flow through the gaps between the grille-bars 121a, “r”-shaped baffle elements 122a, and reversed-“r”-shaped metamaterial elements 123a, thus ensuring air-flow between an exterior and an interior of the housing 110 allowing cooling. As the channels 124a are long, they serve to lengthen the path of sound travelling through them, leading to it being attenuated. They also are labyrinthine / convoluted, leading to further attenuation. Preferably, they require sound-waves emanating from the interior of the appliance, perpendicular to the plane in which the grille-bars 121a, and travelling along the channels 124a, to turn through a total of at least 360 degrees. 360 degrees here refers to the sum of turning angles, with all turns counted as positive additions to that number regardless of direction. For example, as shown in Fig. 3a, sound-waves emanating from the interior of the appliance, perpendicular to the plane in which the grille-bars 121a extend, make one 90 degree (approx.) turn away from the perpendicular to enter the channel 124a at the interior side, one 90 degree (approx.) turn towards the perpendicular, then another turn away from it, and then another 90 degree (approx.) turn back towards the perpendicular on exit at the exterior side.

[0066] Additional effects noise-reduction effects come from the metamaterial nature of the first grille-variant 120a. The reversed- “r”-shaped metamaterial elements 123a act to reduce noise by creating, co-operatively with the “r”-shaped baffle elements 122a, channels 124a between them that vary in width to create wider sections 124al and narrower sections 124a2. A ratio of the width between the wider sections 124al and the narrower sections 124a2 in the channels 124a of the first grille-variant 120a can be between approximately 3:2 and 4:1. The narrow section 124a2 may have a width of approximately 1mm. The length of the channels 124a, and width of the wider sections 124al and narrower sections 124a2 are dimensioned such that they establish a quarter-wavelength-resonator-like and Helmholtz-resonator-like acoustic resonance in the frequencies that the human ear tends to be sensitive to and which the kitchen appliance 100 generates noise in. For example, the channel 124a, or a section of it between wider sections and narrower sections, may be 2cm in length to target a frequency of 4000 Hz with quarterwavelength resonance sound reduction. However, other lengths, other frequencies, and other fractional-wavelength-resonances may be selected. This resonance is established by wider sections 124al acting as the spring elements of a resonator and the narrower section 124a2 acting as the weight elements of a resonator, thus both attenuating and dissipating the noise at these frequencies. Narrow sections 124a2 also enhance thermo-viscous sound-reduction in targeted frequencies. An inner side 125a of each grille-bar 121a may be angled slightly (e.g., 5-10 degrees) relative to the plane of extension of the grille-bars 121a. This serves to aid de-moulding (i.e., extraction from the mould) during manufacturing.

[0067] The reversed- “r”-shaped metamaterial elements 123a have branch-sections 123a2 and stalk-sections 123al that extend roughly at right-angles to each other (e.g., 90 degrees + / - 10 degrees). In contrast the “r”-shaped baffle elements 122a have branch-sections 122a2 that extend at an obtuse angle (e.g., more than 90 degrees + / - 10 degrees) to their stalk-sections 122al . This means that sound radiating along the channels 124a from their inner opening, between the “r”-shaped baffle elements 122a and the reversed-“r”-shaped metamaterial elements 123a, and at a right-angle to the stalks 123al , hit the stalks 123al of the substantially at a right-angle, causing them to tend to be reflected back along the channels 124a towards the opening of the channels 124a into the interior of the housing 110. This backwards reflection also enhances the dissipating quarter-wavelength-resonator- like resonance discussed above.

[0068] Similar ledge-like reflection elements 126a are created by the stalks 123al of the reverse-“r”-shaped metamaterials elements extending from the inner side 125a of the grille-bars 121a slightly in-board (e.g., by l-2mm) of the lateral edge of grille-bars 121a, creating a ledge-like element. Thus, sound waves travelling along the channel 124a towards the exterior of the housing 110, parallel to the stalks 123al of the reverse-“r”-shaped metamaterials elements 123a, and at close to a right-angle to the ledges 126a, will encounter a second reflector in the ledges 126a causing further reflection and dissipation.

[0069] Forming the channels 124a co-operatively between the baffle elements 122a / grille-bars 121a and the reversed-“r”-shaped metamaterial elements 123a allows efficient utilization of space and material. As traditional ventilation grilles also typically comprise grille-bars with baffles, this can allow existing ventilation grilles to be upgraded by attaching metamaterials elements 123a to an interior side of them.

[0070] Fig. 3b shows a second grille-variant 120b. The second grille-variant 120b is similar to the first grille variant 120a except in three aspects. The first is that the metamaterial element 123b is “r”-shaped rather than reverse-“r”-shaped, whilst the baffle-element 122b is reverse-“r”-shaped rather than “r”-shaped (i.e., their lateral directions of extension from the grille-bars 121b are the opposite of the corresponding components of the first grille- variant 120a). The second way in which they differ is that the inner sides 125b of the grille-bars 121b are not angled but are essentially parallel to the external surface of the grille-bars 121b. The third way is that rather than the stalks and branches of the baffle-element 122b and metamaterials element 123b meeting at right-angles, they are instead joined by a curved element. This results in a channel 124b formed therebetween that also curves at the transition from stalk to branch. However, a near-right-angle reflector is still provided in the channel 124b by ledge 126b, and substantial attenuation and dissipation is still achieved, and this curved design is easier to manufacture and more robust. They may also allow longer wavelengths to be better targeted for sound-reduction by allowing resonating channels to extend more easily around comers.

[0071] Fig. 3c shows a third grille-variant 120c. The third grille-variant 120c is similar to the first grille-variant 120a except that the metamaterial element 123c is not reverse-“r”-shaped, but instead is “T” shaped, with the two branches, first branch 123c2 and second branch 123c3 of the “T”-shaped metamaterials element 123c extending in opposite directions, laterally relative to the grille-bars 121c, and orthogonally to the direction of extension of the stalk 123 cl . As the stalk 123 cl extends from the grille-bar 121c at an angle inclined slightly towards the gap separating the grille-bar 121c from its nearest neighbour on the lateral side at which the stalk 123cl joins the grille-bar 121c, this results in a first branch of the “T” 123c2 extending laterally across the gap and towards the plane of extension of the grille-bars 121c. As in the first grille- variant 120a, the first branch of the “T”- shaped metamaterials element 123c2 extends parallel to the branch of the “r”- shaped baffle 122c, creating a channel 124c therebetween. Meanwhile the second branch of the “T” 123c3 extends in the opposite direction laterally across the grillebar 121c to which its respective stalk 123cl is attached, and then laterally across the first branch 123c2 of its neighbouring “T” shaped metamaterials element 123 c, parallel to it on an inner side relative to the interior of the housing 110. Depending on length, the second branch of the “T” 123c3 may extend even laterally across, parallel to, but on an interior side of, part of the second branch 123c2 of its neighbouring “T” shaped metamaterials element 123c. In order to save on material, and also to allow a lower inclination of the stalksection 123cl of the “T”-shaped metamaterials element 123c relative to perpendicular to the plane of extension of the grille-bars 121c (allowing for greater structural strength), the second branch of the “T” 123c3 may be of lower thickness in a direction transverse to its direction of extension away from the stalk 123cl than the first branch 123c2. For example, the thickness of the second branch 123c3 may be approximately half that of the first branch 123c2.

[0072] As the second branch 123c2 of the “T”-shaped metamaterials element 123c extends parallel to, and on an interior side of, the branches of its neighbouring “T”- shaped metamaterials element 123c, a second channel 126c is created between each “T”-shaped metamaterials element 123c and its neighbour. This second channel 126c is connected to the first channel 124c by a widening chamber 127c. The widening chamber 127c is bounded by the branch-sections of neighbouring “T”-shaped metamaterials elements 123c on its interior side. On one of its lateral sides, facing towards the second channel 126c, it is bounded by the stalk section 123 cl of the “T”-shaped metamaterials element 123c attached to the grille-bar 121c which it is immediately located on an interior side of. On its exterior side it is bounded by the grille-bar 121c. On its other lateral side, towards the opening of the first channel 124c, it is bounded partly (towards the exterior of the housing 110) by the “r”-shaped baffle element 122c) and partly (towards the interior of the housing 110) by the first branch 123cl of the “T”-shaped metamaterials element 123c of the neighbouring grille-bar 121c. Providing more than one widening of the path through the grille- variant 120c allows more than one sound frequency-band to be targeted for noise-reduction through quarter-wavelength-resonator-like and Helmholtz-resonator-like acoustic resonance. It also lengthens the path further increasing attenuation.

[0073] Additionally, as sound waves must effectively turn through 180 degrees to travel from the second channel 126c to the first channel 124c to reach the exterior of the housing 110, opportunities for backward reflection and dissipation of the sound waves are increased. This is particularly as sound waves propagating along the second channel 126c are confronted firstly with the stalk 123cl, forming substantially a right-angle to their direction of propagation. Sound waves are then faced with the inside surface 125c of the grille-bar 121c which forms a near right- angle to their direction of propagation towards the exterior of the housing 110. Finally the stalk 122cl of the “r”-shaped baffle element forms another potential backwards-reflection surface, with the aperture of the first channel 124c forming a relatively small opening into the chamber 127c through which it can travel toward the exterior of the housing 110.

[0074] The first channel 124c and second channel 126c may be of similar width to provide a predetermined air-flow. A ratio between the minimum width of the second channel 126c and the maximum width of the chamber 127c may be between 1 :3 and 1 :6.

[0075] A fourth grille-variant 120d is shown in Fig. 3d. Similar to the second grillevariant 120b the stalk-sections and branch-section of the reverse-“r”-shaped baffle element 122d and the metamaterials element 123d are connected by curved sections. Similarly to the third grille-variant 120c the metamaterials element 123d is “T”-shaped, creating through its lateral over-lap with neighbouring “T”-shaped metamaterials elements 123d a second channel 126d as well as, through its lateral over-lap with the reverse-“r”-shaped baffle element 122d. Similarly, also the second channel 126d and the first channel 124d are connected by a chamber 127d requiring sound waves propagating between an interior and an exterior of the housing to turn through 180 degrees.

[0076] However, the fourth grille- variant 120d differs from the third grille variant 120c in that the first branch 123d2 and second branch 123d3 of the “T”-shaped metamaterials element 123d extend in opposite lateral directions from the stalk 123 d 1 at different points along the inward extent of the stalk 123dl . This inwardly- staggered configuration enables tighter fitting of the metamaterial elements 123 d with their neighbours and allows their stalks 123dl to meet the grille-bars 121 d at closer to a right-angle. This results in the enhancing of backwards-reflection of sound travelling parallel to the stalks 123 dl and strengthening of the structure of the grille-variant 120d.

[0077] A fifth grille-variant 120e is shown in Figs. 4 and 5. The fifth grille- variant 120e is a compound grille variant comprising two sections 120el and 120e2 extending across different parts of the lateral and vertical extent of the fifth grille-variant. The first section 120el comprises repeated units 121e essentially the same as that of the second grille- variant 120b. The second section 120e2 comprises grille-bars 122e having reverse-“r”-shaped baffle elements essentially the same as those of the second grille-variant 120b, but rather than metamaterials elements, have plates 123e separated by narrow gaps (0.8mm- 1.2mm). As the narrow gaps open into wider chambers, and sound-propagation directly through the gaps to the exterior of the housing 110 are blocked and instead meet a right-angle surface, sound is diminished in the targeted frequencies by a Helmholtz-like resonance. Thermo- viscous losses also occur in the narrow gaps. As the second section 120e2 is thinner than the first section 120el, the second section 120e2 may correspond to areas of the grille-variant 120e that closely abut with internal components of the appliance 100, or which require greater cooling. The first section 120el may, for example, have a thickness of 1cm or less, and preferably around 8.5mm, whilst the second section 120e2 may have a thickness of less than 8.5mm, and preferably around 4- 5mm.

[0078] The metamaterials of grille-variants 120a, 120b, 120c, 120d, and 120e are capable of excellent sound reduction through attenuation and dispersion created by resonance whilst not adding excessive thickness and weight, and whilst still allowing cooling of the interior. Additionally, they can all be formed using the same material as the housing 110 is made of, through, e.g., plastic injection moulding using e.g., polycarbonate, nylon, acrylonitrile butadiene styrene (ABS), or similar polymer. The grille- variants 120a, 120b, 120c, 120d, and 120e may be fixed in place in a corresponding through-hole provided in the housing 110 by glue, screws, sonic welding, or other suitable attachment means. Alternatively, they may be formed by similarly attaching metamaterials elements over grille-bars integrally formed with the housing 110. In a further alternative, the grille-variants 120a, 120b, 120c, 120d, and 120e may be entirely integrally formed with the housing together through, e.g., injection moulding.

[0079] Fig. 6 shows a graph of sound-pressure-level in dB(A) against sound frequency in l / 3rd octave bands from 200 Hz to 10000 Hz, measured at a distance of roughly 80cm (i.e., a typical distance of a user during operation of a coffee machine). As discussed above, the dotted line on the graph shows the profile of a traditional coffee machine without a metamaterial grille. In solid line is shown the sound profile of the kitchen appliance 100 with the fifth metamaterials grille-variant 120e installed. Whilst the graph still exhibits peaks at frequencies similar to those of the traditional coffee machine, the height of those peaks in terms of sound-level is lower by as much as 4 dB(A). As decibels are a logarithmic scale this is a significant reduction. Particularly, this reduces the noise-level to below 55 dB(A) across the frequencies sampled, reducing the noise-pollution risk.

[0080] As the second section 120e2 is thinner, it may correspond to sections of the housing 110 where space is more limited due to internal components, or a greater requirement for heating. As can be seen in Fig. 5, the fifth grille-variant 120e is also integrally formed with the housing 110.

[0081] Whilst the grille-variants 120a, 120b, 120c, 120d, and 120e have been described as parallel-barred grilles (i.e., grilles having bars extending in parallel along the surface of the housing 110, either horizontally or vertically or in another direction), other types of grilles may be used. This could include, for example, grilles having bars that cross over to form a mesh, or another suitable form of grille. The parallel bars grille is preferably, however, as it maximises ventilation whilst minimising complexity. The respective metamaterials elements of each of the grille-variants 120a, 120b, 120c, 120d, and 120e are preferably formed on an interior side of their respective grille-bars, so that they are protected from external harm. The metamaterials elements of each of the grille- variants 120a, 120b, 120c, 120d, and 120e are preferably elements varying substantially only in two dimensions for easier manufacture (i.e., in the horizontal plane only as represented in Figs 3a-3d, such that the sections shown in Figs. 3a-3d is true along substantially their entire vertical extent).

[0082] Whilst “T” and “r” / reverse-“r” shaped metamaterials elements have been described above, other shapes capable, when tessellated along the grille in repeating fashion, of forming channels either between them or with the grille (including its optionally “r” or reverse-“r” shaped baffles) interconnecting an interior side of the grille with an exterior side, may be used. This can include, for example, “L”-shaped metamaterials elements.

[0083] It will be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention.

[0084] Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination. Reference numerals appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims.

Claims

CLAIMS1. A kitchen appliance (100) comprising a metamaterials ventilation grille (120, 120a, 120b, 120c, 120d, 120e), the grille comprising:- grille elements (121a, 121b, 121c, 12 Id) having ventilation gaps defined therebetween,- metamaterials elements (123a, 123b, 123c, 123d) defining, co-operatively with the grille elements, first ventilation channels (124a, 124b, 124c, 124d) through the ventilation gaps between an interior side of the grille and an exterior side of the grille, wherein the first ventilation channels have widenings (124al) and narrowings (124a2) configured to dissipate sound-waves travelling along the first ventilation channels through harmonic dissipation at one or more predetermined frequencies.

2. The kitchen appliance of claim 1, wherein the predetermined frequencies are in the range 200-10000 Hz, and preferably the range 500-6000 Hz, and even more preferably in the range 3150-4000Hz.

3. The kitchen appliance of any preceding claim, wherein the first ventilation channels are labyrinthine, and preferably have total turning angles of at least 360 degrees.

4. The kitchen appliance of any preceding claim, wherein a direction of extension of the first ventilation channels is primarily along a direction of extension of the grille, for minimising thickness of the grille.

5. The kitchen appliance of any preceding claim, wherein the metamaterials elements are provided on an interior side of the grille elements, for protecting the metamaterials elements.

6. The kitchen appliance of any preceding claim, wherein the grille-elements comprise baffle elements (123a, 123b, 123c, 123d) and the first ventilation channels are defined at least partially between the baffles and the metamaterials elements.

7. The kitchen appliance of any preceding claim, wherein second ventilation channels (126c, 126d) connected to the first ventilation channels are co-operatively defined between neighbouring metamaterials elements and the second ventilation channels are connected to the first ventilation channels by resonance chambers (127c, 127d).

8. The kitchen appliance of claim 7, wherein the resonance chambers are at least 180 degree turns between the second ventilation channels and the first ventilation channels.

9. The kitchen appliance of any preceding claim, wherein the kitchen appliance is a coffee machine, preferably a fully-automatic coffee machine.

10. A method for manufacturing a kitchen appliance housing, comprising steps of: a) providing a housing made of a material, b) forming a grille out of substantially the same material as the housing, c) forming a plurality of metamaterials elements made of substantially the same material as the housing on the grille so as to define first ventilation channels therebetween forming widenings and narrowings configured to dissipate soundwaves travelling along the first ventilation channels, d) providing the grille fixed within the housing so that the first ventilation channels interconnect an inside and an outside of the kitchen appliance.

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