TECHNICAL FIELD

[0001] This specification relates generally to audio speakers.

BACKGROUND

[0002] This specification relates to actuators and to panel audio loudspeakers that feature the actuators.

[0003] Many conventional loudspeakers produce sound by inducing piston-like motion in a diaphragm. Panel audio loudspeakers, in contrast, operate by inducing distributed vibration modes in a panel through an electro-acoustic actuator. Typically, the actuators are electromagnetic or piezoelectric actuators.

SUMMARY

[0004] Disclosed are actuators for use in panel audio loudspeakers. The actuators can be attached to an acoustic radiator (e.g., a display panel). The actuators include springs that allow movement of a magnet assembly relative to a fixed, or rigid, frame. The springs can have a multi-layer structure including a damping layer, constraining layer, or both, that can improve the performance of the system.

[0005] Metal suspensions, or springs, in electromechanical transducers have many advantages as they are compact and stable with temperature compared to traditional suspension materials. Metal springs can be susceptible to high quality factor (Q factor) values at resonance frequencies, and can be susceptible to rocking. The high Q factor at resonance can lead to parasitic vibrations in devices using the transducer for actuating a panel to produce sound. The high Q factor can also lead to ringing that can result in high idle noise, and can reduce the effective usable audio bandwidth.

[0006] A damping layer and a constraining layer can be added to metal springs in order to improve the frequency response of an actuator. The constraining layer can be joined to a spring layer by a damping layer. The damping layer can be formed from a material such as a liquid adhesive or a foam material. The constraining layer can be made from a material with a greater stiffness than the damping layer such as a metal or plastic material.

[0007] The shape, size, and positioning of the layers of the spring structure, and the number of layers, can be changed based on the desired frequency response of the actuator. Alternatively, or additionally, the thickness and/or material properties of the constraining layer and the damping layer can be changed to affect the resonance frequency, Q factor, and rocking frequencies of the actuator. The actuator modules may be suitable for panel audio loudspeakers, especially those incorporated in mobile devices (e.g., mobile phones).

[0008] In general, one innovative aspect of the subject matter described in this specification can be embodied in an actuator module, including: a rigid frame defining a space; a magnet assembly positioned in the space such that the rigid frame extends around a perimeter of the magnet assembly; and a multi-layer spring structure suspending the magnet assembly within the space relative to the rigid frame. The spring structure is coupled to the rigid frame and to the magnet assembly and allows the magnet assembly to vibrate in an axial direction during operation of the actuator module. The multi-layer spring structure includes: a spring layer extending in a plane, the spring layer having a first surface and a second surface separated by a thickness in the axial direction; a constraining layer supported on the first surface of the spring layer; and a damping layer between the constraining layer and the spring layer.

[0009] The foregoing and other embodiments can each optionally include one or more of the following features, alone or in combination. In some implementations, the damping layer contacts the first surface and contacts a surface of the constraining layer.

[0010] In some implementations, the spring layer is formed from a hard metal alloy.

[0011] In some implementations, the constraining layer is formed from a material selected from the group consisting of a metal, plastic, foam, or elastomer.

[0012] In some implementations, the damping layer is formed from a material selected from the group consisting of a liquid adhesive material, a spray adhesive material, a squidgy adhesive material, a tape, or a pressure-sensitive material.

[0013] In some implementations, the spring layer and the constraining layer have different shapes in the plane.

[0014] In some implementations, the spring layer and the constraining layer have same shapes in the plane.

[0015] In some implementations, the spring structure further including a second constraining layer supported on the second surface of the spring layer.

[0016] In some implementations, a thickness of the spring structure in the axial direction is 0.4 millimeters or less.

[0017] In some implementations, a thickness of the constraining layer in the axial direction is 0.1 millimeters or less. [0018] In some implementations, a thickness of the damping layer in the axial direction is 0.075 millimeters or less.

[0019] In some implementations, a ratio of a thickness of the constraining layer in the axial direction and a thickness of the damping layer in the axial direction is in a range from 0.25 to 4.

[0020] In some implementations, the damping layer adheres the constraining layer to the spring layer.

[0021] In some implementations, the constraining layer includes one or more discontinuities.

[0022] In some implementations, the discontinuities are located between comer portions of the spring layer.

[0023] In some implementations, an outer perimeter of the spring structure defines a first quadrilateral shape with rounded comers, and an inner perimeter of the spring structure defines a second quadrilateral shape with rounded comers, the first and second quadrilateral shapes being concentric.

[0024] In some implementations, a distance between the outer perimeter and the inner perimeter defines a width of the spring structure, the width varying along a length of the spring structure.

[0025] In some implementations, the first quadrilateral shape and the second quadrilateral shape each include an approximately square shape.

[0026] In some implementations, a length of each side of the first quadrilateral shape is 14 millimeters or less.

[0027] In some implementations, the actuator module includes a second spring structure, the second spring structure including: a second spring layer having a third surface and a fourth surface separated by a second thickness in the axial direction; a third constraining layer supported on the third surface of the second spring layer; and a second damping layer between the third constraining layer and the second spring layer.

[0028] In some implementations, the second spring structure further includes a fourth constraining layer supported on the fourth surface of the second spring layer.

[0029] Another innovative aspect of the subject matter described in this specification can be embodied in a panel audio loudspeaker including a panel and the actuator attached to the panel.

[0030] Another innovative aspect of the subject matter described in this specification can be embodied in a mobile device including the panel audio loudspeaker. [0031] Another innovative aspect of the subject matter described in this specification can be embodied in a method of making an actuator including: providing a multi-layer spring structure including: a spring layer including a spring material and extending in a plane, the spring layer having a first surface and a second surface separated by a thickness in an axial direction perpendicular to the plane; a constraining layer including a constraining material and supported on the first surface of the spring layer; and a damping layer including an adhesive material between the constraining layer and the spring layer. An outer perimeter of the spring structure defines a first quadrilateral shape, and an inner perimeter of the spring structure defines a second quadrilateral shape, the first and second quadrilateral shapes being concentric. The method includes joining the multi-layer spring structure to a rigid frame and to a magnet assembly to suspend the magnet assembly within a space defined by the rigid frame, the spring structure allowing the magnet assembly to vibrate in the axial direction during operation of the actuator.

[0032] The foregoing and other embodiments can each optionally include one or more of the following features, alone or in combination. In some implementations, providing the multi-layer spring structure includes: laminating a layer of the constraining material, a layer of the adhesive material, and a layer of the spring material to form a multi-layer sheet; and cutting the spring structure from the multi-layer sheet.

[0033] In some implementations, providing the multi-layer spring structure includes: cutting the spring layer from a sheet of the spring material; cutting the constraining layer from a sheet of the constraining material; applying the adhesive material to at least one of the spring layer and the constraining layer; and joining the constraining layer to the spring layer with the adhesive material.

[0034] In some implementations, the constraining layer includes one or more handles. Providing the multi-layer spring structure includes joining the constraining layer to the spring layer with the adhesive material using the one or more handles; and upon curing of the adhesive material, removing the one or more handles.

[0035] Another innovative aspect of the subject matter described in this specification can be embodied in a spring structure including: a spring layer extending in a plane, the spring layer having a first surface and a second surface separated by a thickness of 0.2 millimeters or less in an axial direction perpendicular to the plane; a constraining layer supported on the first surface of the spring layer; and a damping layer between the constraining layer and the spring layer. An outer perimeter of the spring structure defines a first quadrilateral shape with rounded comers, and an inner perimeter of the spring structure defines a second quadrilateral shape with rounded comers, the first and second quadrilateral shapes being concentric. A length of each side of the first quadrilateral shape is 14 millimeters or less.

[0036] Among other advantages, embodiments feature lower Q factor at resonance frequencies and reduced rocking modes. Damping layers and constraining layer(s) can reduce rocking modes at roughly twice the resonant frequency of the actuator module. For example, for an actuator with a fundamental frequency of approximately 250 Hz, adding a damping layer and a constraining layer can reduce ringing at a rocking frequency around 500 Hz. Advantages also include reduced idle channel noise. Embodiments provide a stiffer suspension and greater suspension damping, while reducing an increase in fundamental frequency.

[0037] Other advantages will be evident from the description, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG. 1A is a perspective view of an example actuator module.

[0039] FIG. IB is a detailed view of the actuator module of FIG. 1A.

[0040] FIG. 1C is an exploded view of the actuator module of FIGS. 1A and IB.

[0041] FIG. 2A is an exploded view of an example multi-layer spring structure with three layers.

[0042] FIG. 2B is a cross-sectional view of an example multi-layer spring structure with three layers.

[0043] FIG. 2C is an exploded view of an example multi-layer spring structure with two layers.

[0044] FIG. 2D is a cross-sectional view of an example multi-layer spring structure with two layers.

[0045] FIGS. 3A to 3D show example shapes, sizes, and arrangements of the constraining layer of the multi-layer spring structure in relation to the spring layer.

[0046] FIG. 4A to 4D show cross-sectional views of example multi-layer spring structure arrangements.

[0047] FIG. 5 shows an example frequency response graph for an actuator with springs that do not have a multi-layer spring structure.

[0048] FIG. 6 shows an example frequency response graph for an actuator with at least one spring that has a multi-layer spring structure.

[0049] FIG. 7 is a perspective view of an embodiment of a mobile device.

[0050] FIG. 8 is a schematic cross-sectional view of the mobile device of FIG. 7. [0051] FIG. 9 is a schematic diagram of an embodiment of an electronic control module for a mobile device.

[0052] Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

[0053] Referring to FIG. 1 A, actuator module 100 includes a rigid frame 104, a magnet assembly 105, and a pair of springs 102a and 102b that suspends the magnet assembly 105 within a space defined by the frame 104. A Cartesian coordinate system is shown in FIG. 1A for reference.

[0054] The magnet assembly 105 is positioned in the space such that the frame 104 extends around a perimeter of the magnet assembly 105. The springs 102a and 102b can each have a multi-layer spring structure. In some embodiments, only one of the spring 102a or the spring 102b has a multi-layer spring structure. In some embodiments, both the spring 102a and the spring 102b have a multi-layer spring structure. The multi-layer spring structure of the spring 102a and the spring 102b can be the same or can be different. Varieties of multi layer spring structures are described with reference to FIGS. 3A-3D and FIGS. 4A-4D.

[0055] The springs 102a and 102b suspend the magnet assembly 105 within the space relative to the frame 104. The springs 102a and 102b each attach to the frame 104 and to the magnet assembly 105. The springs 102a and 102b allow the magnet assembly 105 to vibrate in an axial direction, e.g., the z-direction, during operation of the actuator module 100.

During operation of the actuator module 100, the frame 104 remains rigid, or substantially stationary, relative to the springs 102 and 102b and to the magnet assembly 105.

[0056] Referring to FIG. IB and 1C, the magnet assembly 105 includes a back plate 106 to which a center magnet 108 and a ring magnet 110 are joined. Back plate 106 and ring magnet 110 can make up a magnetic cup, having sidewalls defined by the inside edge of the ring magnet. Center magnet 108 and ring magnet 110 are sized and shaped so that the center magnet fits within a gap defined by the ring magnet, as shown by their relative placement in FIG. 1C. The gap between center magnet 108 and ring magnet 110 can be about 1.2 mm or less (e.g., 1.15 mm or less, 1.1 mm or less, 1.05 mm or less, 1 mm or less).

[0057] The actuator module 100 can be relatively compact. For example, the actuator module, which has a substantially square profile in the x-y plane, can have an edge length (i.e., in the x- or y-directions) of about 25 mm or less (e.g., 20 mm or less, 15 mm or less, such as 14 mm, 12 mm, 10 mm or less). The actuator module’s height (i.e., its dimension in the z-direction) can be about 10 mm or less (e.g., 8 mm or less, 6 mm or less, 4.2 mm or less). [0058] During operation, an electric current is applied to a voice coil located in an air gap between the center magnet 108 and the ring magnet 110. The resulting magnetic flux interacts with the suspended magnet assembly 105, and the resulting vibrations are transferred via a baseplate to a panel.

[0059] The magnet assembly 105 also includes a front center plate 112 and a front ring plate 114, which are j oined to bottom surfaces of center magnet 108 and ring magnet 110, respectively. The magnet assembly 105 further may include a bucking magnet 118, which is joined to front center plate 112. Front center plate 112 and front ring plate 114 are sized and shaped so that the front center plate fits with a gap defined by the front ring plate, as shown by their relative placement in FIG. 1C. Front center plate 112 and front ring plate 114 can be soft magnetic materials, e.g., ones having a high relative permeability. For example, the soft magnetic material may have a relative permeability of about 100 or more (e.g., about 1,000 or more, about 10,000 or more). Examples include low carbon steel and vanadium permendur.

In some embodiments, the soft magnetic material can be a corrosion resisting high permeability alloy such as a ferritic stainless steel.

[0060] While frame 104 has an approximately square shape when viewed in the x-y plane, each comer of the frame is curved so that the frame has rounded comers. Between each of the comers of frame 104 are portions of the frame that are substantially straight along their outside edges.

[0061] Spring 102a is coupled (e.g., welded) to frame 104 at connection points 116a and 116b. Spring 102b is coupled to frame 104 at a connection point 118c. While obscured in the view of FIG. 1C, spring 102b is coupled to frame 104 at an additional connection point that is symmetric to connection point 118c about an axis 120 that runs parallel to the y-axis.

[0062] Springs 102a and 102b share approximately the same shape when viewed in the x- y plane. The comers of springs 102a and 102b, as viewed in the x-y plane, are curved. Two sides of springs 102a and 102b, between the comers of the springs, are substantially straight. The remaining two sides of springs 102a and 102b are curved inward in a “c” shape. One example of the benefit provided by c-shaped notches 119a-d of springs 102a and 102b is that they allow stubs 104e-104h to extend in the z-direction.

[0063] Spring 102a is coupled to back plate 106 at connection points 106a and 106b.

Back plate 106 includes two slots at the locations of connection points 106a and 106b, so that spring 102a is significantly flush with the top surface of the back plate 106. The c-shaped notches 119a, 119b of spring 102a and the corresponding c-shaped slot of back plate 106 facilitate the connection between these components at connection points 106a and 106b. [0064] A width of each spring 102a and 102b varies along a length of the spring. For example, a first width of spring 102a at connection point 116a or 116b is greater than a second width of the spring at the comers of the spring. The first width can be about 0.8 mm or less (e.g., 0.75 mm or less, 0.7 mm or less, 0.65 mm or less), while the second width can be about 0.35 mm or less (e.g., 0.3 mm or less, 0.25 mm or less, 0.2 mm or less). Similarly, a third width of spring 102a at connection points 106a or 106b is greater than the second width of the spring. The third width can be about 0.55 mm or less (e.g., 0.5 mm or less, 0.45 mm or less, 0.4 mm or less). The width of the spring decreases as it extends along any midpoint that is on the spring and between two comers of the spring to any comer of the spring. That is, as spring 102a extends from connection point 106a or 106b to a closest comer of the spring, the width of the spring decreases. Similarly, as spring 102a extends from connection point 116a or 116b to a closest comer of the spring, the width of the spring decreases.

[0065] While spring 102a is coupled to back plate 106, spring 102b is coupled to a bottom surface of front ring plate 114. FIG. 1C shows where spring 102b is coupled to front ring plate 114 at a connection point 114a. While obscured in the view of FIG. IB, spring 102b is coupled to front ring plate 114 at a connection point 114b, which is symmetric about an axis 130 that runs parallel to the x-axis. Just as back plate 106 includes c-shaped slots at the locations of connection points 116a and 116b, front ring plate 114 also includes corresponding c-shaped slots at the locations where spring 102b connects to the front ring plate.

[0066] During operation of actuator module 100, the magnet assembly 105 moves in the z-direction in response to a Lorentz force resulting from interaction of the magnetic field of the magnetic assembly 105 with a changing magnetic field of the voice coil. The movement of the magnetic assembly 105 causes the springs 102a and 102b to bend in the z-direction. The springs 102a and 102b apply a restoring force to the magnet assembly 105.

[0067] The locations of the connections of springs 102a and 102b to actuator module 100 are chosen so that the actuator module has a desired resonant frequency. While the springs 102a and 102b, and components connected to the springs 102a and 102b, move in the z- direction, the frame 104 remains rigid relative to the springs 102a and 102b and to the connected components.

[0068] Spring 102b includes c-shaped notches 119c, 119d that correspond with connection point 114a and connection point 114b (not shown). The location of connection points 106a and 106b to a baseplate and connection points 114a and 114b to front ring plate 114 can be chosen to facilitate actuator module 100 to exhibit a desired resonant behavior. [0069] If actuator module 100 is dropped, springs 102a and 102b and their corresponding connection points can facilitate actuator module 100, e.g., the magnet assembly 105 of the actuator module, to exhibit a rocking mode. The frequency of the rocking mode can be at roughly twice a resonant frequency displayed by actuator module 100. Because the rocking mode is at roughly twice the resonant frequency of actuator module 100, it is not a favorable excitation for the actuator module during normal operation. However, because the rocking mode is the first normal mode above the resonant frequency, actuator module 100 can exhibit the rocking mode if actuator module 100 is dropped, and the force of the impact can be at least partially dissipated by the rocking mode.

[0070] The thickness to width ratio of the springs, favors displacement of actuator module 100 in the z-direction over displacement of the actuator module in the x or y- directions. However, during abnormal operation of actuator module 100, such as when the actuator is dropped, there may be some lateral displacement (e.g., displacement in the x or y- directions) of actuator module 100. The lateral displacement causes uneven forces in the z- direction, causing the rocking mode which dissipates the energy of the drop over time.

[0071] Not only can the placement of the connection points 116a, 116b, 114a, and 114b be chosen to facilitate a desired resonant behavior of actuator module 100, the shape of springs 102a and 102b can affect the resonant behavior of the actuator module. For example, the thickness of springs 102a and 102b, as measured in the z-direction, or the width of the springs, as measured in the x and y-directions, can be increased or decreased to promote a desired resonant behavior of actuator module 100, e.g., to promote a certain fundamental frequency. In addition, the thickness of frame 104 or the width of the frame can be increased or decreased to promote a desired resonant behavior of actuator module 100.

[0072] The dimensions of springs 102a and 102b, as measured in the x and y-dimensions, can be approximately equal. For example, springs 102a and 102b can fit within a square having side lengths of about 13.5 mm or less (e.g., 13.25 mm or less, 13 mm or less, 12.75 mm or less, 12.5 mm or less).

[0073] The spring 102a, the spring 102b, or both, can have multi-layer spring structures. The multi-layer spring structures can include a damping layer and a constraining layer to damp and constrain the main metal suspension, or spring layer. The constraining layer can be joined to the spring layer by the damping layer, which may include an adhesive material. [0074] The damping layer of the multi-layer spring structure can dampen movement of the springs 102a and 102b and can reduce unwanted vibration of the actuator module 100. The constraining layer of the multi-layer spring structure can further dampen and constrain movement of the springs 102a and 102b in order to balance stresses in the springs 102a and 102b. Balancing the stresses in the springs 102a and 102b can reduce long term fatigue failures in operation.

[0075] Combined effects of the constraining layer and the damping layer can include a reduction in the contributions of parasitic resonances in the actuator module 100. For example, the constraining layer and the damping layer can reduce the rocking modes and other higher order suspension bending modes, which can cause anomalies in the frequency response of the actuator module 100.

[0076] The constraining layer of the multi-layer spring structure can be formed from a material with a greater stiffness than the damping layer. For example, the damping layer can be formed from a material with a lower shear modulus, e.g., a shear modulus of less than 0.5 Gigapascals (GPa). The constraining layer can be formed from a material with a higher shear modulus, e.g., a shear modulus of greater than 1.0 GPa.

[0077] Because the constraining layer is formed from a material with a greater stiffness than the damping layer, a multi-layer spring structure having both the damping layer and the constraining layer can achieve the desired damping effects with a thinner overall profile, compared to a multi-layer spring structure having only the damping layer. A ratio of the thickness of the constraining layer to the thickness of the damping layer can be used to tune the fundamental resonance and Q factor of the actuator module 100, and to adjust the amount of damping in the actuator.

[0078] Referring to FIGS. 2A and 2B, the spring 102a has a multi-layer spring structure. FIG. 2A shows three layers of an example three-layer spring structure prior to fabrication. FIG. 2B shows an example three-layer spring structure after fabrication. A Cartesian coordinate system is shown in FIG. 2B for reference.

[0079] The multi-layer spring structure includes a spring layer 202, a constraining layer 206, and a damping layer 204. When assembled, as shown in FIG. 2B, the constraining layer 206 is supported on a first surface 232 of the spring layer 202, and the damping layer 204 is between the constraining layer 206 and the spring layer 202. The damping layer 204 contacts the first surface 232 and contacts a surface of the constraining layer 206. A thickness of the spring structure in the axial direction (z-direction) can be, for example, 0.4 mm or less.

[0080] Though FIGS. 2A and 2B each show a multi-layer spring structure that includes three layers, other numbers of layers are possible. For example, the multi-layer spring structure can include a second constraining layer supported on a second surface 234 of the spring layer 202. Other variations are described in greater detail with reference to FIGS. 4A- 4D.

[0081] The spring layer 202 extends in a plane, e.g., the x-y plane. The spring layer 202 includes an outer perimeter 214 defining a first quadrilateral shape with rounded comers. The spring layer 202 includes an inner perimeter 212 defining a second quadrilateral shape with rounded comers. The inner perimeter 212 and the outer perimeter 214 are concentric in a plane, e.g., the x-y plane. In some embodiments, the quadrilateral shapes defined by the inner perimeter 212 and the outer perimeter are each an approximately square shape. In some embodiments, a length of each side of the quadrilateral shape defined by the outer perimeter 214 is 14 millimeters or less. A distance between the outer perimeter 214 and the inner perimeter 212 defines a width of the spring layer 202. The width of the spring layer 202 can vary along a length of the spring layer 202.

[0082] The spring layer 202 can be made from a spring material such as a hard metal alloy. A hard metal alloy can be a combination of different metals that has a high yield strength, e.g., a yield strength of 1400 MPa or greater. For example, the spring layer 202 can be made from a stainless steel alloy such as 301 stainless steel. The first surface 232 and the second surface 234 are separated by a thickness in the axial direction. The thickness of the spring layer 202, as measured in the axial direction, can be, for example, between 0.15 mm and 0.20 mm. For example, the thickness of spring layer 202 can be 0.17 mm.

[0083] The multi-layer spring structure 102 includes the constraining layer 206 supported on the first surface 232 of the spring layer 202. The constraining layer 206 can have a similar size and shape as the spring layer 202. For example, the constraining layer 206 can be formed in a quadrilateral shape with rounded comers.

[0084] In the example of FIG. 2A, the constraining layer 206 includes two halves 222, 224. When assembled, each half 222, 224 of the constraining layer is supported on an aligning segment of the spring layer 202. The constraining layer 206 can be assembled onto the spring layer 202 using handles 208, 210. After assembly, the handles 208 can be removed by detaching the handles 208 at axes 216, 218.

[0085] In some embodiments, the constraining layer 206 can be shaped to have the same footprint (i.e., shape in the x-y plane) as the spring layer 202. In some cases, the constraining layer 206 can extend beyond the spring layer 202 in the x-y plane. Example shapes and arrangements of the constraining layer 206 in relation to the spring layer 202 are described in greater detail with reference to FIGS. 3 A to 3D. [0086] The constraining layer 206 can be made from a variety of constraining materials including metal, plastic, foam, or elastomer material. The material composition of the constraining layer can be selected based on strength, stiffness, hardness, flexibility, temperature resistance, water resistance, chemical resistance, flammability, resistance to wear, dynamic fatigue, and radiation resistance.

[0087] The material composition of the constraining layer 206 should be sufficiently resilient so that the constraining layer 206 does not deform or fatigue as a result of repetitive movement during operation of the actuator. The material should also be able to withstand forces that may occur due to dropping a device that contains the actuator module 100. The material composition of the constraining layer 206 can also be selected based on density and weight. For example, a material can be selected that does not increase the weight of the spring structure by more than a percentage of weight, e.g., twenty percent, thirty percent, forty percent, etc.

[0088] The material composition of the constraining layer 206 can be selected based on the desired damping effects on the actuator such as the desired fundamental frequency and quality factor (Q factor). For example, a material can be selected that changes the fundamental frequency by less than a maximum amount. The maximum amount can be, for example, ten percent, eight percent, five percent, etc.

[0089] In some embodiments, the constraining layer 206 can be made from a metal material such as a soft metal foil or a metal tape. For example, the constraining layer 206 can be made from stainless steel, copper, lead, tin, or aluminum.

[0090] In some embodiments, the constraining layer 206 can be made from a plastic, foam, or elastomer material. For example, the constraining layer 206 can be made from polyethylene terephthalate (PET) or other thermoplastic polymer. In some examples, the constraining layer 206 can be made from a Polyetheretherketone (PEEK) laminate material. [0091] A thickness of the constraining layer 206 in the z-direction can be between approximately 0.025 mm and 0.10 mm. The thickness of the constraining layer 206 can be selected based on the size profile of the actuator, the desired robustness of the actuator, and the damping effects on the actuator.

[0092] Some example materials and thicknesses of the constraining layer 206 are as follows. The constraining layer 206 can be made of, for example, 0.025 mm stainless steel foil, 0.10 mm soft metal foil, 0.075 mm PET material, or 0.05 mm PEEK laminate material. [0093] The multi-layer spring structure 102 includes the damping layer 204. When assembled, the damping layer 204 is between the constraining layer 206 and the spring layer 202. The damping layer 204 can have a similar size and shape as the spring layer 202. For example, the damping layer 204 can be formed in a quadrilateral shape with rounded comers. In some embodiments, the damping layer 204 includes a liquid adhesive applied to the constraining layer 206, the spring layer 202, or both. In these embodiments, the damping layer 204 forms the same approximate shape as the layer to which the liquid adhesive is applied.

[0094] In the example of FIG. 2A, the damping layer 204 includes two halves 226, 228. When assembled, each half 226, 228 of the damping layer 204 adheres a portion of the constraining layer 206 to an aligning portion of the spring layer 202.

[0095] In some embodiments, a width of the damping layer 204 in the x-y plane can be greater than the width of the spring layer 202, the constraining layer 206, or both. For example, as shown in FIG. 2B, the damping layer 204 can have an excess width 230 that extends a distance outward from between the spring layer 202 and the constraining layer 206 in the x-y plane.

[0096] The damping layer 204 can be made from a variety of damping materials. For example, the damping layer 204 can be made from a foam or elastomer material. In some examples, the damping layer 204 can be made from an adhesive material or can include an adhesive material. For example, the damping layer 204 can be made from or can include a tape (e.g., foam tape, elastomeric tape, very high bond (VHB) tape). In some examples, the damping layer 204 can be made from or can include an adhesive material (e.g., liquid adhesive, spray adhesive, squidgy adhesive). In some examples, the damping layer 204 can be made from a non-adhesive material and can include one or more adhesive surface to adhere to the spring layer 202 and to the constraining layer 206.

[0097] The material composition of the damping layer 204 can be selected based on size, density, reliability, humidity resistance, temperature resistance, and adhesiveness. For example, the material composition of the damping layer 204 can be a material that provides a desired amount of adhesiveness, flexibility, and durability while having a sufficiently small thickness.

[0098] The material composition of the damping layer 204 can also be selected based on the desired damping effects on the actuator. In some embodiments, a ratio of the thickness of the damping layer 204 to the thickness of the constraining layer 206 can be adjusted to tune the fundamental resonance and Q factor of the actuator module 100. [0099] In some embodiments, the damping layer 204 can be made from a pressure sensitive adhesive (PSA). The PSA can be, for example, a thin, flexible PSA tape. A PSA can form a rapid, cohesive bond with the spring layer 202 and the constraining layer 206.

[0100] In some embodiments, the damping layer 204 can be made from a liquid adhesive. For example, the damping layer 204 can be made from a glue, a squidgy adhesive, a spray acrylic adhesive, a urethane foam tape, or a spray urethane adhesive.

[0101] A thickness of the damping layer 204 in the z-direction can vary from approximately 0.025 mm to 0.075 mm. The thickness of the damping layer 204 can be selected based on the size profile of the actuator, the desired adhesiveness, and the desired damping effects on the actuator. In some cases, the thickness of the damping layer 204 may be approximate and may be variable, e.g., when the damping layer 204 includes a liquid adhesive material.

[0102] Some example materials and thicknesses of the damping layer 204 are as follows. The damping layer 204 can be made of, for example, 0.025 mm PSA, 0.030 TESA 4983 glue, or 0.040 mm 3M-77 spray adhesive.

[0103] A ratio of a thickness of the constraining layer 206 in the axial direction and a thickness of the damping layer 204 in the axial direction may be based on a damping effect of the multi-layer spring structure on the actuator. For example, the thickness ratio can be adjusted to tune the fundamental resonance and/or the Q factor of the actuator. The effects of various thickness ratios on the damping of the actuator can be determined experimentally, by simulation, or both.

[0104] The thickness ratio can be chosen to provide sufficient damping and resistance to impact, without increasing the overall thickness of the spring structure beyond approximately 0.4 mm. In some embodiments, the ratio of the thickness of constraining layer 206 to the thickness is damping layer 204 is approximately one. In certain embodiments, the thickness of constraining layer 206 is greater than the thickness of damping layer 204 (e.g., the ratio can be 1.05 or more, such as 1.1 or more, 1.2 or more, 1.5 or more, 2 or more, 3 or more, such as up to 4). Alternatively, the thickness of constraining layer 206 can be less than the thickness of damping layer 204 (e.g., the ratio can be 0.95 or less, 0.9 or less, 0.75 or less, 0.5 or less, 0.33 or less, such as low as 0.25).

[0105] An example process for making the actuator module 100 can include providing the multi-layer spring structure and attaching the multilayer spring structure to the frame 104 and to the magnet assembly 105 to suspend the magnet assembly within the space defined by the frame 104. [0106] In some examples, providing the multi-layer spring structure can include cutting a pre-laminated multi-layer spring structure from a multi-layer sheet. For example, a multi layer sheet can be constructed by laminating a layer of the constraining material, a layer of the adhesive material, and a layer of the spring material. The spring structure can then be cut, e.g., by laser cutting, from the multi-layer sheet.

[0107] In some examples, providing the multi-layer spring structure can include cutting each layer of the multi-layer spring structure separately. The layers can then be assembled to construct the spring structure from the pre-cut layers. For example, the spring layer 202 can be cut from a sheet of the spring material. The constraining layer 206 can be cut from a sheet of the constraining material. The adhesive material can then be applied to the spring layer 202, to the constraining layer 206, or to both. The constraining layer 206 can then be joined to the spring layer 202 with the adhesive material.

[0108] In some examples, as shown in FIG. 2A, the constraining layer 206 can be assembled onto the spring layer 202 using handles 208, 210. After attaching the constraining layer 206 the spring layer 202 with the adhesive material, and upon curing of the adhesive material, the handles 208, 210 can be removed by detaching the handles 208, 210 at axes 216, 218.

[0109] FIGS. 2C and 2D show an example multi-layer spring structure of the spring 102a with two layers. FIG. 2C shows two layers of an example two-layer spring structure prior to fabrication. FIG. 2D shows an example two-layer spring structure after fabrication. A Cartesian coordinate system is shown in FIG. 2D for reference.

[0110] The multi-layer spring structure includes a spring layer 242 and a damping layer 244. The spring layer 242 is similar in size, shape, and material to the spring layer 202. The damping layer 244 is similar in size, shape, and material to the damping layer 204.

[0111] When assembled, as shown in FIG. 2D, the damping layer 244 is supported on a first surface 272 of the spring layer 242 and contacts the first surface 272 of the constraining layer 246. In some implementations, the damping layer 244 can be made from an adhesive material. In some implementations, the damping layer 244 can be made from a non-adhesive material and can include an adhesive surface to adhere to the surface 272 of the spring layer 242.

[0112] Though FIGS. 2C and 2D each show a multi-layer spring structure that includes two layers, other numbers of layers are possible. For example, the multi-layer spring structure can include a second damping layer supported on a second surface 274 of the spring layer 242. [0113] FIGS. 3A to 3D show example shapes, sizes, and arrangements of the constraining layer in relation to the spring layer. The spring layer extends in a plane. The spring layer and the constraining layer can have the same shape in the plane, or can have different shapes in the plane. In some examples, the constraining layer can include one or more individual segments and can include one or more discontinuities. FIGS. 3A to 3D each illustrate the constraining layer in a darker shading. Portions of the spring layer that are visible between sections of the constraining layer are shown in a lighter shading.

[0114] In FIG. 3 A, the constraining layer and the spring layer 302a have different shapes in the plane. The constraining layer includes two sections 306a, 308a supported by the spring layer 302a. The sections 306a, 308a are each approximately a half quadrilateral shape. The sections 306a, 308 each cover slightly less than half of a surface of the spring layer 302a. The sections 306a, 308a each extend a distance 314a toward a center axis 318a of the spring layer 302a, the axis 318a passing through the c-shaped notches of the spring layer 302a. The distance 314a can be about 4.90 mm or.less (e.g., 4.80 mm or less, 4.83 mm or less, or 4.86 mm or less).

[0115] In FIG. 3B, the constraining layer and the spring layer 302b have different shapes in the plane. The constraining layer includes four sections 306b, 308b, 310b, 312b. The sections 306b, 308b, 310b, 312b are each joined to a comer area of the spring layer 302b. The sections 306b, 308b, 310b, 312b each extend a distance 314b from the comers toward a center axis 318b of the spring layer 302b, the axis 318b passing through the c-shaped notches of the spring layer 302b. The distance 314b can be about 4.90 mm or.less (e.g., 4.80 mm or less, 4.83 mm or less, or 4.86 mm or less). The sections 306b, 308b, 310b, 312b each extend a distance 316b from the comers toward a center axis 320b of the spring layer 302b, the axis 320b being perpendicular to the axis 318b. The distance 316b can be about 4.40 mm or.less (e.g., 4.20 mm or less, 4.25 mm or less, or 4.30 mm or less).

[0116] In FIG. 3C, the constraining layer 306c and the spring layer have the same shape in the plane. Both the constraining layer 306c and the spring layer have an approximately quadrilateral shape. The constraining layer 306c has approximately the same width as the spring layer around the perimeter of the spring layer.

[0117] In FIG. 3D, the constraining layer 306d and the spring layer have different shapes in the plane. The constraining layer 306d includes four discontinuities 308d, 310d, 312d,

314d. The discontinuities 308d, 310d, 312d, 314d are located between comer portions of the spring layer. Though four discontinuities are shown in FIG. 3D, the constraining layer 306d can include any appropriate number of discontinuities. The discontinuities can be located between comer portions of the spring layer, as shown, or at other positions with respect to the spring layer.

[0118] Referring to FIGS. 4A to 4D, a constraining layer can be applied to a first surface of the spring layer, a second surface of the spring layer, or both. Additionally, the constraining layer can be applied to a top spring, a bottom spring, or both. In some embodiments, the top spring and the bottom spring may have the same multi-layer spring structure. In some examples, the top spring and the bottom spring may have different multi layer spring structures.

[0119] FIG. 4A shows the actuator module 100 including the springs 102a and 102b. The spring 102a is a top spring, and the spring 102b is a bottom spring, with respect to the z-axis. A Cartesian coordinate system is shown in FIGS. 4A-4D for reference.

[0120] FIG. 4B shows an example three-layer spring structure 400b. The three-layer spring structure 400b can be the structure of the top spring 102a, the bottom spring 102b, or both. The three-layer structure includes a spring layer 402b on the bottom, with respect to the z-axis. A constraining layer 406b is supported on atop surface of the spring layer 402b. A damping layer 404b is between the spring layer 402b and the constraining layer 406b.

[0121] FIG. 4C shows another example three-layer spring structure 400c. The three-layer spring structure 400c can be the structure of the top spring 102a, the bottom spring 102b, or both. The three-layer structure includes a spring layer 402c on the top, with respect to the z- axis. A constraining layer 406c is supported on a bottom surface of the spring layer 402c. A damping layer 404c is between the spring layer 402c and the constraining layer 406c.

[0122] FIG. 4D shows an example five-layer spring structure 400d. The five-layer spring structure can be the structure of the top spring 102a, the bottom spring 102b, or both. The three-layer structure includes a spring layer 402d in the middle, with respect to the z-axis. Constraining layers 406d, 407d are supported on both a bottom surface of the spring layer 402d and a top surface of the spring layer 402d. Damping layers 404d are between the spring layer 402d and each constraining layer 406d, 407d.

[0123] In some embodiments, the constraining layer 406d can have a same size, shape, thickness, and/or material composition as the constraining layer 407d. In some embodiments, the constraining layer 406d can have a different size, shape, thickness, and/or material as the constraining layer 407d.

[0124] In some embodiments, the damping layer 404d can have a same size, shape, thickness, and/or material as the damping layer 405d. In some embodiments, the damping layer 404d can have a different size, shape, thickness, and/or material composition as the damping layer 405d.

[0125] FIG. 5 shows an example frequency response graph 500 for an actuator with springs that do not have a multi-layer spring structure. The graph 500 shows acceleration 510 in units of decibels relative to one volt (dB/lV) on the y-axis, and frequency 520 in units of Hertz (Hz) on the x-axis. The graph 500 shows the total acceleration level of the actuator graphed over a frequency range from approximately 100 Hz to 10.7 kHz.

[0126] The graph 500 shows a fundamental frequency peak 501 at approximately 240 Hz. The acceleration at the fundamental frequency peak 501 is approximately 62 dB/lV. The graph 500 also shows a first rocking mode 502 at approximately 500 Hz, and a second rocking mode 504 at approximately 7 kHz.

[0127] FIG. 6 shows an example frequency response graph 600 for an actuator with at least one spring that has a multi-layer spring structure. Similar to the graph 500, the graph 600 also shows acceleration 610 in units of dB/lV on the y-axis, and frequency 620 in units of Hz on the x-axis, and shows the total acceleration level of the actuator graphed over a frequency range from approximately 100 Hz to 10.7 kHz.

[0128] Differences between the graph 500 and the graph 600 illustrate some effects of the multi-layer spring structure on the frequency response of the actuator. The graph 600 shows a fundamental frequency peak 601 at approximately 250 Hz, which is slightly greater than the fundamental frequency peak 501. The increase in fundamental frequency can be caused by added stiffness in the spring due to the added constraining layer and damping layer.

[0129] Additionally, the graph 600 shows that the acceleration at the fundamental frequency peak 601 is approximately 57 dB/lV, which is slightly lower than the acceleration at the fundamental frequency peak 501. The decrease in the acceleration can be caused by a lower Q factor at resonance due to damping effects of the constraining layer.

[0130] The graph 600 shows rocking modes 602, 604 that are attenuated compared to the rocking modes 502, 504. The attenuation of the rocking modes is due to damping effects of the constraining layer. The multi-layer structure of the springs of the actuator causes increased damping of the system, which can reduce or even eliminate rocking modes. Eliminating rocking modes reduces ringing and idle channel noise.

[0131] While the foregoing figures cover a specific embodiment of an actuator module i.e., actuator module 100, more generally the principles embodied in this example can be applied in other designs too. For example, while actuator module 100 has a substantially square footprint (i.e., in the x-y plane), other shapes are possible, such as substantially rectangular, oval, or round.

[0132] The magnets of actuator module 100 can be an iron magnet, a neodymium magnet, or a ferrite magnet, such as one composed of iron and nickel. In some embodiments, one or more of the magnets of actuator module 100 can be replaced by an electromagnet. In some embodiments, actuator module 100 can include high permeability materials.

[0133] In general, the actuator modules described above can be used in a variety of applications. For example, in some embodiments, actuator module 100 can be used to drive a panel of a panel audio loudspeaker, such as a distributed mode loudspeaker (DML). Such loudspeakers can be integrated into a mobile device, such as a mobile phone. For example, referring to FIG. 7, a mobile device 700 includes a device chassis 702 and a touch panel display 704 including a flat panel display (e.g., an OLED or LCD display panel) that integrates a panel audio loudspeaker. Mobile device 700 interfaces with a user in a variety of ways, including by displaying images and receiving touch input via touch panel display 704. Typically, a mobile device has a depth (in the z-direction) of approximately 10 mm or less, a width (in the x-direction) of 60 mm to 80 mm (e.g., 68 mm to 72 mm), and a height (in the y- direction) of 100 mm to 160 mm (e.g., 138 mm to 144 mm).

[0134] Mobile device 700 also produces audio output. The audio output is generated using a panel audio loudspeaker that creates sound by causing the flat panel display to vibrate. The display panel is coupled to an actuator, such as a distributed mode actuator, or DMA. The actuator is a movable component arranged to provide a force to a panel, such as touch panel display 704, causing the panel to vibrate. The vibrating panel generates human- audible sound waves, e.g., in the range of 20 Hz to 20 kHz.

[0135] In addition to producing sound output, mobile device 700 can also produce haptic output using the actuator. For example, the haptic output can correspond to vibrations in the range of 180 Hz to 300 Hz.

[0136] FIG. 7 also shows a dashed line that corresponds to the cross-sectional direction shown in FIG. 8. Referring to FIG. 8, a cross-section of mobile device 700 illustrates device chassis 702 and touch panel display 704. Device chassis 702 has a depth measured along the z-direction and a width measured along the x-direction. Device chassis 702 also has a back panel, which is formed by the portion of device chassis 702 that extends primarily in the x-y plane. Mobile device 700 includes actuator module 100, which is housed behind display 704 in chassis 702 and attached to the back side of display 704. For example, a PSA can attach actuator module 100 to display 704. Generally, actuator module 100 is sized to fit within a volume constrained by other components housed in the chassis, including an electronic control module 820 and a battery 830.

[0137] In general, the disclosed actuators are controlled by an electronic control module, e.g., electronic control module 820. In general, electronic control modules are composed of one or more electronic components that receive input from one or more sensors and/or signal receivers of the mobile phone, process the input, and generate and deliver signal waveforms that cause actuator module 100 to provide a suitable haptic response.

[0138] Referring to FIG. 9, an exemplary electronic control module 820 of a mobile device, such as mobile device 700, includes a processor 910, memory 920, a display driver 930, a signal generator 940, an input/output (I/O) module 950, and a network/communications module 960. These components are in electrical communication with one another (e.g., via a signal bus 902) and with actuator module 100.

[0139] Processor 910 may be implemented as any electronic device capable of processing, receiving, or transmitting data or instructions. For example, processor 910 can be a microprocessor, a central processing unit (CPU), an application-specific integrated circuit (ASIC), a digital signal processor (DSP), or combinations of such devices.

[0140] Memory 920 has various instructions, computer programs or other data stored thereon. The instructions or computer programs may be configured to perform one or more of the operations or functions described with respect to the mobile device. For example, the instructions may be configured to control or coordinate the operation of the device’s display via display driver 930, signal generator 940, one or more components of I/O module 950, one or more communication channels accessible via network/communications module 960, one or more sensors (e.g., biometric sensors, temperature sensors, accelerometers, optical sensors, barometric sensors, moisture sensors and so on), and/or actuator module 100.

[0141] Signal generator 940 is configured to produce AC waveforms of varying amplitudes, frequency, and/or pulse profiles suitable for actuator module 100 and producing acoustic and/or haptic responses via the actuator. Although depicted as a separate component, in some embodiments, signal generator 940 can be part of processor 910. In some embodiments, signal generator 940 can include an amplifier, e.g., as an integral or separate component thereof.

[0142] Memory 920 can store electronic data that can be used by the mobile device. For example, memory 920 can store electrical data or content such as, for example, audio and video files, documents and applications, device sehings and user preferences, timing and control signals or data for the various modules, data structures or databases, and so on. Memory 920 may also store instructions for recreating the various types of waveforms that may be used by signal generator 940 to generate signals for actuator module 100. Memory 920 may be any type of memory such as, for example, random access memory, read-only memory, Flash memory, removable memory, or other types of storage elements, or combinations of such devices.

[0143] As briefly discussed above, electronic control module 820 may include various input and output components represented in FIG. 9 as I/O module 950. Although the components of I/O module 950 are represented as a single item in FIG. 9, the mobile device may include a number of different input components, including buttons, microphones, switches, and dials for accepting user input. In some embodiments, the components of I/O module 950 may include one or more touch sensor and/or force sensors. For example, the mobile device’s display may include one or more touch sensors and/or one or more force sensors that enable a user to provide input to the mobile device.

[0144] Each of the components of I/O module 950 may include specialized circuitry for generating signals or data. In some cases, the components may produce or provide feedback for application-specific input that corresponds to a prompt or user interface object presented on the display.

[0145] As noted above, network/communications module 960 includes one or more communication channels. These communication channels can include one or more wireless interfaces that provide communications between processor 910 and an external device or other electronic device. In general, the communication channels may be configured to transmit and receive data and/or signals that may be interpreted by instructions executed on processor 910. In some cases, the external device is part of an external communication network that is configured to exchange data with other devices. Generally, the wireless interface may include, without limitation, radio frequency, optical, acoustic, and/or magnetic signals and may be configured to operate over a wireless interface or protocol. Example wireless interfaces include radio frequency cellular interfaces, fiber optic interfaces, acoustic interfaces, Bluetooth interfaces, Near Field Communication interfaces, infrared interfaces, USB interfaces, Wi-Fi interfaces, TCP/IP interfaces, network communications interfaces, or any conventional communication interfaces.

[0146] In some implementations, one or more of the communication channels of network/communications module 960 may include a wireless communication channel between the mobile device and another device, such as another mobile phone, tablet, computer, or the like. In some cases, output, audio output, haptic output or visual display elements may be transmitted directly to the other device for output. For example, an audible alert or visual warning may be transmitted from the mobile device 700 to a mobile phone for output on that device and vice versa. Similarly, the network/communications module 960 may be configured to receive input provided on another device to control the mobile device. For example, an audible alert, visual notification, or haptic alert (or instructions therefor) may be transmitted from the external device to the mobile device for presentation.

[0147] The actuator technology disclosed herein can be used in panel audio systems, e.g., designed to provide acoustic and / or haptic feedback. The panel may be a display system, for example based on OLED or LCD technology. The panel may be part of a smartphone, tablet computer, or wearable devices (e.g., smartwatch or head-mounted device, such as smart glasses).

[0148] Other embodiments are in the following claims.

[0149] What is claimed is: