Multi-resonant coupled system for flat panel actuation

A system includes a flat panel display having a panel resonant frequency response corresponding to a composition, shape, and structure of the flat panel display; and an actuator having an actuator resonant frequency response corresponding to a composition, size, and shape of the actuator; in which the actuator is mechanically-coupled to the flat panel display at a mechanical drive point, in which a coupled resonant frequency response of the system is lower than the panel resonant frequency response of the flat panel display.

BACKGROUND

Flat panel displays can be actuated to produce acoustic and/or haptic output through bending wave vibrations at frequencies near the natural resonant modal structure of the flat panel display. However, the lowest useful mode of many flat panel displays can often be too high in frequency for efficient delivery of desired low frequency feedback (e.g., low decibel levels and/or limited bandwidth), limiting low frequency response of devices that incorporate flat panel display for acoustic and/or haptic output.

SUMMARY

Technologies relating to extending the low frequency response of a flat panel display (or another bending-wave panel) are disclosed. The display can be coupled with one or more actuators (e.g., distributed mode actuators) to form a multi-resonant coupled system (e.g., a distributed mode loudspeaker (DML)) with improved performance at frequencies below the display's natural resonance. For example, a mobile device with a flat panel display having a limited range of natural frequency resonances below 500 Hz can be enhanced using a multi-resonant coupled system, whereby the low frequency bandwidth of the mobile device can be extended by the addition of one or more actuators such that the coupled system can produce resonant frequencies ranging between 300-500 Hz or 150 Hz to 300 Hz.

In general, in a first aspect, the invention features a system including a flat panel display having a panel resonant frequency response corresponding to a composition, shape, and structure of the flat panel display; and an actuator having an actuator resonant frequency response corresponding to a composition, size, and shape of the actuator; in which the actuator is mechanically-coupled to the flat panel display at a mechanical drive point, and in which a coupled resonant frequency response of the system is lower than the panel resonant frequency response of the flat panel display.

Embodiments of the system can include one or more of the following features.

The system can further include a controller programmed to provide electrical signal to drive the actuator such that the actuator produces the actuator resonant frequency response.

The mechanical drive point in the system can be selected based on a panel resonant mode of the flat panel display, the actuator having a mechanical impedance selected to match a mechanical impedance of the flat panel display at the mechanical drive point.

The actuator resonant frequency response of the actuator can be ⅔ to 1 octave below the panel resonant frequency response of the flat panel display. The actuator resonant frequency response can be at a lower frequency range with respect to a fundamental resonant frequency response of the flat panel display. The actuator can be a distributed mode actuator.

The coupled resonant frequency response can be within a range between 300-600 Hz.

The flat panel display can include a touch screen panel, a display panel, and an air gap coupled to the display panel. The system can be a component of a mobile device.

The system can include multiple actuators. For example, the actuator can be a first actuator and the mechanical drive point can be a first mechanical drive point and the system can further include a second actuator affixed to the flat panel display at a second, different mechanical drive point. The second, different mechanical drive point of the second actuator can be non-symmetrical with respect to the first mechanical drive point of the first actuator. The second actuator at the second mechanical drive point can have a second, different low frequency resonance. Each actuator affixed to the flat panel display at a respective mechanical drive point can provide a respective low frequency bandwidth and a respective level for the given low frequency bandwidth. The first respective low frequency bandwidth can correspond to a haptic response for the flat panel display and the second respective low frequency bandwidth can correspond to an acoustic response for the flat panel display.

In general, in a further aspect, the invention features a method (e.g., for extending a low frequency response of a system including a flat panel display), the method including determining, for the flat panel display, a resonant mode frequency of the flat panel display; determining, for the resonant mode frequency of the flat panel display, a mechanical drive point for the flat panel display at the resonant mode frequency; determining, for the mechanical drive point, a mechanical impedance of the flat panel display at the mechanical drive point; and selecting an actuator to mechanically couple to the flat panel display at the mechanical drive point, the selection of the actuator including: matching the mechanical impedance of the actuator to the mechanical impedance of the flat panel display at the mechanical drive point for the resonant mode frequency; tuning a frequency of the actuator such that the frequency of the actuator is at a second, different resonant frequency than the resonant mode frequency of the flat panel display.

Implementations of the method can include one or more of the following features.

The second, different resonant frequency of the actuator can be at a lower frequency with respect to the resonant mode frequency of the flat panel display. For example, the second different resonant frequency of actuator can be ⅔ to 1 octave below the resonant mode frequency of the flat panel display.

The flat panel display can include a touch screen panel, a display panel, and an air gap coupled to the display panel. The flat panel display can be a component of a mobile device.

The method can further include selecting an additional actuator to mechanically couple to the flat panel display at an additional, different mechanical drive point. The additional, different mechanical drive point of the additional actuator can be non-symmetrical with respect to the mechanical drive point of the actuator. The additional actuator at the additional mechanical drive point can have an additional, different low frequency resonance. Each actuator affixed to the flat panel display at respective mechanical drive points can provide a respective low frequency bandwidth and a respective level for the respective low frequency bandwidth. The first respective low frequency bandwidth can correspond to a haptic response for the flat panel display and the second respective low frequency bandwidth can correspond to an acoustic response for the flat panel display.

Among other advantages, coupling a first resonant system (e.g., a flat panel display with a coupled air gap) with a second resonant system (e.g., an actuator) can improve the force response and output fidelity at lower frequencies (e.g., for haptic response, audio output) of the combined multi-resonant coupled system (e.g., as a DML). Improved output can include increasing the low frequency bandwidth of the system to an acceptable (e.g., audible or perceptible) decibel level and/or increasing the efficiency of the system in its use of electrical power. The multi-resonant coupled system can be optimized in frequency bandwidth and decibel level for particular applications (e.g., acoustic, haptic applications) and use modes (e.g., receiver mode, loudspeaker mode).

DETAILED DESCRIPTION

Referring toFIGS. 1A-C, a mobile phone100includes a multi-resonant coupled system120that has a flat panel display102coupled to an actuator114. A cross section of phone100along the major axis (line A-A) shows a flat panel display102containing a touch screen panel103(e.g., a glass, plastic) and a display layer104(e.g., and LCD panel or an OLED panel). A suspension mechanism (e.g., mounting)106creates a gap108between display layer104and a back panel109of phone100. System120includes actuator (or transducer)114mounted to display panel104at a drive point118using a coupler116(e.g., a stub).

A controller122applies different electrical signals (e.g., through electrical connections in coupler116) to drive actuator114(e.g., a piezoelectric bimorph beam) to bend to different positions, e.g., positions112and112(1) by converting electrical voltages to mechanical energy. The bending motion of actuator114imparts force on display panel104, mechanically coupled to screen103, causing bending wave vibrations in the flat panel display102. These vibrations can couple to the air outside of flat panel display102to create sound (e.g., acoustics). Additionally, or alternatively, these vibrations can be used to create a haptic sensation for a user's finger in contact with flat panel display102.

Phone100includes electronics110in gap108. Electronics110can include a battery, input/output circuitry, and storage and processor electronics. Electronics110can include circuitry and power for controller122.

Flat panel display102can be sized appropriately for a mobile phone. For example, the display can have a diagonal dimension of about 4 inches to about 7 inches. More generally, larger displays (e.g., 8 inch diagonal or more) can be used in other applications (e.g., tablet computers). Flat panel display102can have a thickness between about 1 mm to about 5 mm.

In general, display panel104can be a transmissive display panel, a reflective display panel, or an emissive display panel. Example display panels include a liquid crystal display (LCD) display panel, an organic light emitting diode (OLED) display panel. Transmissive display panels will generally include an edge light or backlight and can include additional light management components to distribute light from a light source to the display panel.

Touch screen103can include glass, plastic, or any other transparent material. The touch screen can also include materials for sensing touch. For example, touch screen103can include a transparent conductor coating for capacitive sensing (e.g., indium tin oxide (ITO)).

Space in gap108between back panel109and flat panel display102is generally occupied, at least in part, by electronics110and other phone components (e.g., a battery). The remaining space in gap108forms an acoustic cavity, which acts like a spring when coupled to flat panel display102. The cavity may contain air and/or open-cell foam (e.g., a low-stiffness, open-celled elastomer). In some implementations, the acoustic cavity couples strongly with resonant modes of flat panel display102and can alter the way in which display102responds to the force from actuator114. Thus, in some embodiments, an air gap (or foam cavity) forms part of system120and/or part of flat panel display102. The coupled air gap (or foam cavity) in the display can have a thickness of 0.1 mm to 5 mm.

AlthoughFIGS. 1A-Cshows actuator114as a piezoelectric cantilever beam distributed mode actuator, various geometries of actuators and coupling schemes are contemplated, including centrally-coupled, simply-supported, multi-layered, and/or multi-tiered actuator geometries. Various active actuator materials are contemplated, such as piezoelectric, magnetostrictive or electret materials. The active material can be a bi-morph, a bi-morph with a central vane or substrate or a uni-morph. The active element can be fixed to a backing plate or shim which can be a thin metal sheet and can have a similar stiffness to that of the active element. Additionally, or alternatively, the actuator can be electromagnetic, such as a voice-coil motor system or a moving magnet motor system, with a dominant resonance in its force characteristic. Details about various actuator materials, geometries, and/or coupling designs are disclosed in the following applications, incorporated herein in their entirety by reference: U.S. Pat. No. 8,766,510, entitled Actuator; U.S. Pat. No. 7,916,880, entitled Transducer; U.S. Pat. No. 7,475,598, entitled Electromechanical Force Transducer; U.S. Pat. No. 7,635,941, entitled Transducer; U.S. Pat. No. 6,427,016, entitled Acoustic Devices; U.S. Pat. No. 7,684,576, entitled Resonant Element Transducer; U.S. Pat. No. 7,149,318, entitled Resonant Element Transducer; U.S. Pat. No. 6,618,487, entitled Electro-dynamic exciter.

In general, a multi-resonant coupled system may be incorporated as part of another device, for example, as part of a laptop, tablet, digital camera or video recorder, or other device that might incorporate a visual display (e.g., flat panel display102) with audible/vibrational feedback.

In general, the multi-resonant coupled system120including flat panel display102(e.g., with or without a coupled air gap) and actuator114is designed to have a resonance frequency response that is different (e.g., extends to a lower frequency bandwidth) than the individual natural (or native) resonance frequency responses of the components of the multi-resonant coupled system120. It is believed that physical objects have natural mechanical resonance modes at resonance frequencies. A resonant mode of an oscillating system is a pattern of motion in which all parts of the system move harmonically with the same frequency and with a fixed phase relation (e.g., forming a “standing wave”). A physical object, such as an actuator or a flat panel display, has a set of resonant modes, where the frequencies of these modes depend on the structure, materials, and boundary conditions of that object. When a mechanical system is driven at one of these natural resonance frequencies, the response of the mechanical system has a higher amplitude (e.g., acoustic output) than at other non-resonant frequencies. The mechanical impedance of the system (e.g., how much the system resists motion when subjected to a harmonic force) at resonance is also at a local minimum. In general, coupled resonators will have resonant frequencies that are related to, but different from, the resonant frequencies of the constituent components. Accordingly, judicious design of a coupled system can allow one to design a system having a resonance at a frequency lower than the resonant frequencies of the components.

Referring toFIG. 2A, a method200for designing a multi-resonant coupled system120that extends the low frequency response (e.g., location of resonance modes) of flat panel display102(e.g., with coupled air gap) is shown. Initially, the natural resonance modes of flat panel display102are determined in step202. These modes can result from display102being driven at force sensitivities between 10 mN per volt and 50 mN per volt. Alternatively, or additionally, these modes can result from display102being driven at forces between 500 mN and 1 N. Based on the shape of these resonance modes, drive point118, or location of attachment point of the actuator, is selected in step204. The mechanical impedance of flat panel display102at drive point118is determined in step206. Finally, an actuator design is selected for mechanical coupling to flat panel display102at drive point118in step208.

Referring toFIG. 2B, a method210of selecting an actuator design for step208id disclosed. Actuator114is designed in step212to have its mechanical impedance match the mechanical impedance of flat panel display102(e.g., with coupled air gap) at mechanical drive point118. Without wishing to be bound to a particular theory, if mechanical impedances of actuator114and display102are a poor match at the drive point, the two systems do not couple well and cannot extend the frequency response of the display effectively. In step215, actuator114is designed to have a second, different (e.g., lower) natural resonant frequency than the resonant frequency mode of flat panel display102. The selected actuator can extend the low frequency response (e.g., location of resonance modes) of flat panel display102.

Without wishing to be bound by any particular theory, the physics behind the selection and design methods inFIGS. 2A-2Bwill be explained in further detail below based on a specific finite element model of a smart phone100with a flat panel display102.

In general, in some implementations, finite element modeling (or hypothetical lumped parameter mathematical modeling) of a multi-resonant coupled system (e.g., flat panel display including an actuator) can be performed to determine one or more parameters of the multi-resonant coupled system. The one or more parameters may include mechanical drive point location, resonant frequency mode of a flat panel display included in the multi-resonant coupled system, actuator mechanical impedance, and actuator resonant frequency. In some implementations, the model may receive as input properties of the flat panel display (e.g., material, dimensions), mechanical ground connection, cavity (e.g., air or low-stiffness, open-celled foamed elastomer). The model may additionally receive as input information related to added mass and localized stiffening of the flat panel display due to the mechanical coupling of one or more actuators, which may change the resonance frequencies of the flat panel display. Additional inputs can include design constraints imposed by placement of other parts of the device (e.g., such as placement of other electronics110in phone100), desired output (e.g., acoustics, haptics), and use mode (e.g., loudspeaker, receiver).

In the model used forFIGS. 3-4, 6, and 8, the touchscreen panel103was made from aluminosilicate glass of 165×65×0.55 mm. An OLED display panel104of diagonal dimension 158.8 mm (6.25 in) was bonded onto the back of the touchscreen panel. The flat panel display was connected to a mechanical ground (e.g., back panel109) via a thin elastomeric adhesive tape106. A cavity108, including a small air gap of 0.5 mm behind the display and other internal air spaces, was included in the model.

FIG. 3shows a plot of the natural resonance modes of flat panel display102when driven by a force of 30 mN at two points along the major axis of display102(line A-A inFIG. 1A) at a range of frequencies. Specifically, the plot shows the response of display102in terms of sound pressure produced by the display for different applied frequencies, the response modeled as being measured 10 cm away from the source of the force. As shown on the plot, there are resonance modes at the following frequencies: 356 Hz, 500 Hz, 785 Hz, and 800 Hz.FIGS. 4A-4Dshow contour maps of flat panel display102in these various modes, where the contours indicate amplitude of the resonant frequency response over an area of the flat panel display102. Referring toFIG. 4A, an asymmetric mode 3,2 at 356 Hz has two poles (or antinodes)400and402of opposite polarity at the two ends of the panel. Referring toFIG. 4B, a symmetric mode 4,2 at 500 Hz has three poles404,406, and408. The two poles at the ends,404and408, have the same polarity and amplitude. The middle pole406has the opposite polarity and twice the amplitude of the side poles. Referring toFIG. 4C, an asymmetric mode 5,2 at 785 Hz has four poles410,412,414,416of alternating polarities. The amplitude of pole412is the biggest, followed by pole416,414, and410with the smallest amplitude. Referring toFIG. 4D, a tympanic mode 2,2 at 800 Hz is distorted due to coupling with acoustic cavity108. The mode has 3 poles of alternating polarity,418,420, and422. The two poles at the edges of the display,418and422, have significantly larger amplitudes than the pole420in the middle.

Certain shapes of resonant modes for flat panel display102can be more useful for different acoustic/haptics applications than others. For example, mode 4,2 inFIG. 4Bcan be more useful for acoustic radiation and for haptic feedback near the center of the panel than the other modes shown inFIGS. 4A, 4C, 4D, because of mode 4,2's central pole406. In other words, modes, such as 4,2, can be used in loudspeaker mode—e.g., when the display is being used to show visual content and is positioned in front of the user. Some of the modes, such as mode 3,2, can be more useful when phone100is being used as a receiver—e.g., when a user's ear is positioned near one of the two poles to receive a call.

Without wishing to be bound by any particular theory, attaching actuator114to flat panel display102at specific locations on the display (e.g., drive points118), can enhance the low frequency response of the phone (e.g., to 300 Hz or 350 Hz) below its lowest natural resonant frequency useful for acoustic and haptic output (e.g., 500 Hz). For example, with flat panel displays of smartphones, a shallow acoustic cavity (e.g., in gap108) or layer of open-cell foam couples strongly with the modes of flat panel display102, as modeled above. This coupling (as shown inFIGS. 4A-4B) can alter the sequence of natural mode shapes of the display, and increase the resonance frequency of the first symmetrical mode useful for audio output (e.g., mode 4,2 at 500 Hz for the modeled example inFIG. 4B). This effect can result in reduced acoustic/haptics response of panel102at lower audible/haptics frequencies.

Actuator114designed to have a specific impedance and resonance frequency can be coupled to flat panel display102at a selected drive point118to achieve an improved acoustic/haptic output at frequencies below 500 Hz (e.g., 300-350 Hz). As described above, finite element modeling was used to determine how the addition of actuator114to flat panel display102at a selected drive point118can be used to expand the frequency response of panel102to lower frequencies. For example, the addition of actuator114can increase the response of the multi-resonant coupled system120at the panel's native resonance (e.g., at 500 Hz for model 4,2) and possibly provide additional modes (e.g., from rotational forces on actuator114). The multi-resonant coupled system can increase the response of flat panel display102at a native resonance peak by 1 to 5 decibels. The increase in response may depend on the damping of the natural modes of display102, e.g., due to coupling with an air gap. Additionally, or alternatively, the multi-resonant coupled system can create an additional mode that provides 1 decibel to 5 decibels, or up to 10 dB, or up to 20 dB, of increased response at a new resonant frequency that is below the resonant frequencies of the natural modes of flat panel display102. Without wishing to be bound by any particular theory, creating additional modes slightly above the lower natural modes of display102can also increase the response of the system (e.g., make the output louder at those frequencies) and potentially smoothen it.

The choice of actuator114and drive point118depends on the desired frequency output of the multi-resonant coupled system120. For example, for acoustic output (e.g., in use in loudspeaker mode), the low frequency performance is preferably relatively continuous between 300 Hz to 600 Hz. In other words, there are no significant gaps in the frequency response at low frequencies (e.g., around 300 Hz). In such a case, the finite element model (with inputs as described above) showed that coupling an actuator114with resonance at about ⅔ to 1 octave below (63% to 50% of) the relevant panel120resonance frequency (e.g., symmetric 4,2 mode for acoustic output) produced improved, relatively continuous low frequency response around 300 Hz up to 600 Hz.

FIGS. 5A-5Cshow lumped parameter mathematical modeling results of how the difference between the native resonance frequency of a hypothetical actuator114and display panel102can change the response of multi-resonant coupled system120. Referring toFIG. 5A, the native response in decibels to a hypothetical driving force for a range of frequencies is plotted for: a flat panel display (plot502) with a symmetric 4,2 resonance peak502(1) at 500 Hz; an actuator (plot504; “⅔ octave actuator”) that has a resonance frequency504(1) at ⅔ of an octave below peak502(1); and a second actuator (plot506; “1 octave actuator”) that has a resonance frequency506(1) at 1 octave below peak502(1).

Referring toFIG. 5B, the response in decibels to the same hypothetical driving force as inFIG. 5Afor a range of frequencies is plotted for: a multi resonant coupled system (plot508) that combines flat panel display (in plot502) and the ⅔ octave actuator (in plot504); and a multi resonant coupled system (plot510) that combines flat panel display (in plot502) and the 1 octave actuator (in plot506). The system with the ⅔ octave actuator in plot508has an increased output508(1) at the 500 Hz natural resonance peak of the display panel, and an additional peak508(2) near 300 Hz. The system with the 1 octave actuator in plot510has an increased output510(1) at the 500 Hz natural resonance peak of the display panel, and an additional peak510(2) near 250 Hz.FIG. 5Bthus shows that an actuator with a natural resonance frequency of ⅔ to 1 octave below the natural resonance frequency of the flat panel display 4,2 mode peak can provide an increased system response when coupled to the display at frequencies around 250-500 Hz. Such a relatively continuous response can be beneficial for an acoustic loudspeaker use mode of phone100.

For haptics output (e.g., below 300 Hz), the response at low frequencies of multi-resonant system120can be discontinuous with the response at higher frequencies (e.g., at 500 Hz). Sufficient response at haptics frequencies can be achieved by coupling flat panel display102with actuators that have a resonance frequency difference from the 4,2 mode of the flat panel display of more than 3/2 or 2 octaves.

Referring toFIG. 5C, the response in decibels to the same a hypothetical driving force as inFIGS. 5A-5Bfor a range of frequencies is plotted for: a multi resonant coupled system (plot512) that combines flat panel display (in plot502) and an actuator (“3/2 octave actuator”) with a resonance peak 3/2 octaves below the panel's 4,2 mode; and a multi resonant coupled system (plot514) that combines flat panel display (in plot502) and an actuator (“2 octave actuator”) with a resonance peak 2 octaves below the panel's 4,2 mode. The system with the 3/2 octave actuator in plot512has an increased output512(1) at the 500 Hz natural resonance peak of the display panel, and an additional peak512(2) near 200 Hz. The system with the 2 octave actuator in plot514has an increased output514(1) at the 500 Hz natural resonance peak of the display panel, and an additional peak514(2) near 150 Hz.FIG. 5Cthus shows that an actuator with a natural resonance frequency of 3/2 to 2 octaves below the natural resonance frequency of the flat panel display 4,2 mode peak can provide an increased system response when coupled to the display at frequencies around 150-200 Hz. The improvement is low frequency response is less uniform or continuous, but the extra output at peaks512(2) and514(2) are useful for haptics output. These peaks can also be useful for close-coupled acoustics of “receiver mode” where the user puts their ear to one side of the display to receive a phone call. Without wishing to be bound by any particular theory, “receiver mode” can tolerate less continuity in response because receiver mode can be quieter e.g., than loudspeaker mode, therefore there can be more headroom available for equalisation of the frequency response.

The resonance frequency of actuator114can be selected to produce the desired output for the acoustic/haptics applications discussed above (as shown inFIGS. 5B-5C). The natural resonance of the actuator depends on the actuator geometry and attachment mechanism to flat panel display102. The material, length, shape, and mass of the actuator, for example, can be modified to achieve the resonance response required by the application. A variety of different actuator materials and geometries are contemplated, as discussed above. For example, for a piezoelectric beam actuator, an estimate of the resonance frequency may be made using well-known formulas for cantilever beam modes. Finite element modelling can be used to get a more accurate value. For simpler types of actuators, a simple mass-spring system may exist, from which the resonance frequency can be calculated.

Without wishing to be bound by any particular theory, aside from selecting the proper resonance frequency for actuator114, how the actuator is coupled to the flat panel display102can also be controlled to produce the application-dependent results shown inFIGS. 5B-5C. As detailed below, proper coupling includes attaching actuator114to flat panel display102at a specific driving point118and selecting a mechanical impedance for the actuator that matches that of flat panel display102at driving point118at the frequency range selected for enhancement (e.g., 300 to 600 Hz).

Mechanical drive point118can be selected to mechanically-couple actuator114to flat panel display102based on design constraints of phone100and the shape of the resonance modes (e.g., as shown inFIGS. 4A-4D) of display102. Design constraints of the phone that can limit the drive point118locations include the position of other elements in gap108of phone100, such as electronics110(e.g., battery, circuit boards, wiring etc.). For example, if electronics110are centrally located under flat panel display102, then drive point118has to be selected closer to the edges of the display.

Additionally, or alternatively, drive point118can be selected based on locations of one or more poles (e.g.,404,408) for a particular resonant mode (e.g., 4,2 resonant mode) of the flat panel display102. Without wishing to be bound by a particular theory, the drive point118determines which modes are achievable for multi-resonant coupled system120. For example, coupling the drive point to the location of a natural resonance mode pole of flat panel display102can result in enhancement of that mode in the combined actuator/display system (e.g., as shown at peak508(1) inFIG. 5Bor peak820(2) inFIG. 8).

In some embodiments, the drive point is located along the major axis of display102(e.g., along line A-A inFIG. 1A), away from the edge by 5% to 10% of the length of the display, or up to 30%, or up to 50%.

In some implementations, the intended output frequency range (e.g., low frequency acoustic radiation or haptic feedback) can also determine an appropriate mechanical drive point118for actuator114on the flat panel display102. For example, for acoustic radiation output in loudspeaker mode, a mechanical drive point118may be selected to be at a center pole of a panel resonant mode (e.g.,406,420) of flat panel display102. Without wishing to be bound by any particular theory, efficient loudspeaker mode acoustic output benefits from some net displacement of the panel, and driving display102near the center generally favours such output (e.g., modes shown inFIGS. 4B and 4D). For haptic feedback response (e.g., response at frequencies below 300 Hz) or receiver mode, a mechanical drive point118can be selected at a side pole (e.g., antinode400or402) near an edge of flat panel display102(e.g., mode shown inFIG. 4A). Without wishing to be bound by any particular theory, positioning the drive point at a side pole can provide favorable output at lower frequencies for haptics (e.g., mode 3,2 is the lowest frequency resonance mode for display102) and/or sufficient output for receiver mode (e.g., at near field acoustics).

Actuator114can be selected to have a mechanical impedance that approximately matches that of flat panel display102(coupled to gap108) at driving point118at the frequency range selected for enhancement (e.g., 300 to 600 Hz). Mechanical impedance determines how much a physical system resists motion when subjected to a harmonic force (e.g., at a specific frequency). For example, the impedance of display102depends on the material and dimensions of display102, the suspension mechanism106of phone100, and the air gap (part of gap108) coupled to the flat panel display102. Different displays and actuators produce different maximum velocities for a common specified force depending on their impedance. Without wishing to be bound to a particular theory, if mechanical impedances of actuator114and display102(or display102coupled to an air gap, as in the model described above) do not match at the drive point (at the driving frequency), the two systems do not couple (e.g., they oscillate independently) and cannot extend the frequency response of the display.

In addition, selecting actuator impedance is important for output efficiency. The velocity of display102(e.g., output) is determined jointly by the actuator force and by the actuator114and display102impedances. For example, with solid-state piezoelectric actuators, high actuator force can come with high source (actuator) impedance (e.g., force and impedance are proportional), so selecting the right actuator can be important. Too much force might not produce useful extra acoustic output due to high impedance, while costing more energy. Too little force could result in a reduction in performance.

FIG. 6shows a plot of the impedance (in Ns/m) of flat panel display102(coupled to an air gap and with properties described above) when driven by a force of 30 mN along the major axis of display102(line A-A inFIG. 1A) at a range of frequencies. The impedance reaches a minimum at the frequency of the tympanic (2, 2) mode at 800 Hz. Below this frequency, the impedance is essentially that of a spring, being roughly inversely proportional to frequency.FIG. 6shows that the response, along the major axis, of flat panel display120at frequencies around 300 Hz is low (as seen inFIG. 3) because the impedance of the display at those frequencies is high. In some embodiments, the target impedance of actuator114is designed to approximately match the low-frequency cut-off for the coupled system120(e.g., about 30 Ns/m at 300 Hz). The targeted cut-off frequency depends on the desired application to be enhanced (e.g., acoustics/haptics, loudspeaker/receiver) as described above. In some embodiments, the impedance of actuator114can range between 10 Ns/m and 50 Ns/m, or even 100 Ns/m. The actuator impedance can vary between 50% and 200% of the target impedance of display102at a selected frequency and drive point.

The mechanical impedance of actuator114may be tuned, for example, by changing one or more of the physical properties of the actuator. The impedance of actuator114depends on the actuator geometry. For example, the material, length, shape, and mass of the actuator can be modified to achieve impedance matching. A variety of different actuator materials and geometries are contemplated, as discussed above.

In some implementations, two or more actuators can be included in a multi-resonant coupled system. A multi-resonant coupled system including two or more actuators mechanically coupled to a flat panel display may further enhance a low frequency bandwidth response of the multi-resonant coupled system.FIGS. 7A-7Bare schematic views of such multi-actuator multi-resonant coupled systems.

Referring toFIG. 7A, a multi-resonant coupled system700includes two actuators114(1) and114(2) each mechanically coupled to flat panel display120at respective drive points118(1) and118(2) positioned at symmetric locations (e.g., approximately equidistant in opposite directions from the center of flat panel display120) along the major axis of flat panel display120(along line A-A inFIG. 1A). The addition of a second actuator at another symmetric resonant frequency response peak can further enhance an acoustic output (e.g., increase decibel level achievable) at lower frequencies for multi-resonant coupled system700. In some embodiments, the drive points are 5% to 10%, or up to 20%, or up to 30% of the length of the flat panel display102away from the respective edges of the display along the major axis.

FIG. 8shows, based on the finite element model described above, a curve810of the natural resonance modes of flat panel display102when driven by a force of 30 mN along the major axis of display102(line A-A inFIG. 1A) at a range of frequencies (as inFIG. 3) compared to a curve820of the resonance modes of coupled system700driven by the same force at drive points118(1) and118(2). Without wishing to be bound by any particular theory,FIG. 8shows that the added mass and localized stiffening of flat panel display102due to the attachment of actuators114(1) and114(2) changed the resonance frequencies of system700. The coupled system700changed the symmetry of the display panel102(plus coupled air gap) so that the asymmetric (3,2) mode started to give some acoustic output at 300 Hz, as shown at peak820(1). In addition, the moment (e.g., torque in addition to a normal force) generated by the swinging cantilever actuators114(1) and114(2) provided useful extra low-frequency force. An additional new coupled mode at 250 Hz, peak820(2), is also generated.

In some embodiments, additional actuators can be placed at asymmetrical positions along the flat panel display's major axis. Referring toFIG. 7Ba multi-resonant coupled system710includes two actuators114(1) and114(2) each mechanically coupled to flat panel display120at respective drive points118(1) and118(2) positioned at asymmetric locations (e.g., not equidistant from the center of flat panel display120) along the major axis of flat panel display120(along line A-A inFIG. 1A). In some embodiments, the drive point118(1) is 5% to 10%, or up to 20%, or up to 30% of the length of the flat panel display102away from one of the edges of the display along the major axis. In some embodiments, the drive point118(2) is 20% to 40%, or up to 50%, or up to 70% of the length of the flat panel display102away from same the edge of the display along the major axis.

Without wishing to be bound by any particular theory, asymmetric of placement of actuators allows the actuators to provide different mode enhancements, with one actuator potentially filling in the enhancement gap resulting from the other. For example, one actuator can enhance resonance modes for acoustic output (300-600 Hz) and the other actuator can enhance haptics output (below 300 Hz). Alternatively, or additionally, both actuators can enhance acoustic output, but for different use modes. For example, one of the actuators can enhance a broader range of low frequency bandwidths at a lower response level for receiver mode, while the other actuator can enhance a narrower low frequency bandwidth at a higher response level for loudspeaker mode.

FIG. 9is a schematic diagram of an example computer system900. The system900can be used to carry out the operations described in association the implementations described previously (e.g., those of controller92). In some implementations, computing systems and devices and the functional operations described above can be implemented in digital electronic circuitry, in tangibly-embodied computer software or firmware, in computer hardware, including the structures disclosed in this specification (e.g., system900) and their structural equivalents, or in combinations of one or more of them. The system900is intended to include various forms of digital computers, such as laptops, desktops, workstations, personal digital assistants, servers, blade servers, mainframes, and other appropriate computers, including vehicles installed on base units or pod units of modular vehicles. The system900can also include mobile devices, such as personal digital assistants, cellular telephones, smartphones, and other similar computing devices. Additionally, the system can include portable storage media, such as, Universal Serial Bus (USB) flash drives. For example, the USB flash drives may store operating systems and other applications. The USB flash drives can include input/output components, such as a wireless transmitter or USB connector that may be inserted into a USB port of another computing device.

The system900includes a processor910, a memory920, a storage device930, and an input/output device940. Each of the components910,920,930, and940are interconnected using a system bus950. The processor910is capable of processing instructions for execution within the system900. The processor may be designed using any of a number of architectures. For example, the processor910may be a CISC (Complex Instruction Set Computers) processor, a RISC (Reduced Instruction Set Computer) processor, or a MISC (Minimal Instruction Set Computer) processor.

In one implementation, the processor910is a single-threaded processor. In another implementation, the processor910is a multi-threaded processor. The processor910is capable of processing instructions stored in the memory920or on the storage device930to display graphical information for a user interface on the input/output device940.

The memory920stores information within the system900. In one implementation, the memory920is a computer-readable medium. In one implementation, the memory920is a volatile memory unit. In another implementation, the memory920is a non-volatile memory unit.

The storage device930is capable of providing mass storage for the system900. In one implementation, the storage device930is a computer-readable medium. In various different implementations, the storage device930may be a floppy disk device, a hard disk device, an optical disk device, or a tape device.

The input/output device940provides input/output operations for the system900. In one implementation, the input/output device940includes a keyboard and/or pointing device. In another implementation, the input/output device940includes a display unit for displaying graphical user interfaces.

To provide for interaction with a user, the features can be implemented on a computer having a display such as a CRT (cathode ray tube) or LCD (liquid crystal display) monitor for displaying information to the user and a keyboard and a pointing device such as a mouse or a trackball by which the user can provide input to the computer. Additionally, such activities can be implemented via touchscreen flat-panel displays and other appropriate mechanisms.