Patent Description:
It is imperative to advance the current state of the art such as Document D1 (<CIT>), which discloses an air-pulse generating device including a membrane structure, Document D2 (<CIT>), which discloses air pulse generating element including a membrane and valves, Document D3 (<CIT>), which discloses an ultrasonic chamber <NUM> including one vibrating membrane <NUM>, two shutters <NUM>, and <NUM>, and another ultrasonic chamber <NUM> including one vibrating membrane <NUM>, two shutters <NUM>, and <NUM>, Document D4 (<CIT>), which discloses a shutter device SH in a lateral movement direction B2 perpendicular to a vertical movement direction B1 of a diaphragm device M, Document D6 (<CIT>), which discloses an acoustic horn <NUM>, Document D7 (<CIT>), which discloses a conical top <NUM>, and Document D8 (<CIT>), which discloses a horn shaped tuning port <NUM>.

Speaker driver and back enclosure are two major design challenges in the speaker industry. It is difficult for a conventional speaker to cover an entire audio frequency band, e.g., from <NUM> to <NUM>. To produce high fidelity sound with high enough sound pressure level (SPL), both the radiating/moving surface and volume/size of back enclosure for the conventional speaker are required to be sufficiently large.

Therefore, how to design a small sound producing device while overcoming the design challenges faced by conventional speakers is a significant objective in the field.

It is therefore a primary objective of the present invention to provide an air-pulse generating device, to improve over disadvantages of the prior art.

This is achieved by an air-pulse generating device according to independent claim <NUM>. The dependent claims pertain to corresponding further developments and improvements.

A fundamental aspect of the present invention relates to an air-pulse generating device, and more particularly, to an air-pulse generating device comprising a modulating means and a demodulating means, where the said modulating means generates an ultrasonic air pressure wave/variation (UAW) having a frequency fUC, where the amplitude of UAW is modulated according to an input audio signal SIN, which is an electrical (analog or digital) representation of a sound signal SS. This amplitude modulated ultrasonic air pressure wave/variation (AMUAW) is then synchronously demodulated by the said demodulating means such that spectral components embedded in AMUAW are shifted by ±n·fUC, where n is a positive integer. As a result of this synchronous demodulation, spectral components of AMUAW, corresponding to sound signal SS, is partially transferred to the baseband and audible sound signal SS is reproduced as a result. Herein, the amplitude-modulated ultrasonic air pressure wave/variation AMUAW may be corresponding to a carrier component with the ultrasonic carrier frequency fUC and a modulation component corresponding to the input audio signal SIN.

<FIG> illustrates a schematic diagram of an air-pulse generating (APG) device <NUM> according to an embodiment of the present invention. The device <NUM> may be applied as a sound producing device which produces an acoustic sound according to an input (audio) signal SIN, but not limited thereto.

The device <NUM> comprises a device layer <NUM> and a chamber definition layer <NUM>. The device layer <NUM> comprises walls <NUM>, 124R and supporting structures 123R, <NUM> supporting a thin film layer which is etched to flaps <NUM>, <NUM>, <NUM>, and <NUM>. In an embodiment, the device layer <NUM> may be fabricated by MEMS (Micro Electro Mechanical Systems) fabrication process, for example, using a Si substrate of <NUM>~<NUM> in thickness, which will be etched to form <NUM>/R and 124R/L. In an embodiment, on top of this Si substrate, a thin layer, typically <NUM>~<NUM> in thickness, made of silicon on insulator SOI or POLY on insulator POI layer, will be etched to form flaps <NUM>, <NUM>, <NUM> and <NUM>.

The chamber definition layer (which may be also viewed/named as "cap" structure) <NUM> comprises a pair of chamber sidewalls 110R, <NUM> and a chamber ceiling <NUM>. In an embodiment, the chamber definition layer (or cap structure) <NUM> may be manufactured using MEMS fabrication technology. A resonance chamber <NUM> is defined between this chamber definition layer <NUM> and the device layer <NUM>.

In other words, the device <NUM> may be viewed as comprising a film structure <NUM> and the cap structure <NUM>, between which the chamber <NUM> is formed. The film structure <NUM> can be viewed as comprising a modulating portion <NUM> and a demodulating portion <NUM>. The modulating portion <NUM>, comprising the (modulating) flaps <NUM> and107, is configured to be actuated to form an ultrasonic air/acoustic wave within the chamber <NUM>, where air/acoustic wave can be viewed as a kind of air pressure variation, varying both temporally and spatially. In an embodiment, the ultrasonic air/acoustic wave or air pressure variation may be an amplitude DSB-SC (double-sideband suppress carrier) modulated air/acoustic wave with the ultrasonic carrier frequency fUC. The ultrasonic carrier frequency fUC may be, for example, in the range of <NUM> to <NUM>, which is significantly larger than the maximum frequency of human audible sound.

The terms air wave and acoustic wave will be used interchangeably below.

The demodulating portion <NUM>, comprising the (demodulating) flaps <NUM> and <NUM>, is configured to operate synchronously with the modulating portion <NUM>, shifting spectral components of DSB-SC modulated acoustic wave generated by the modulating portion <NUM> by ±n×fUC, where n is positive integer, producing a plurality air pulses toward an ambient according to the ultrasonic air wave within the chamber <NUM>, such that the baseband frequency component of the plurality air pulses (which is produced by the demodulating portion <NUM> according to the ultrasonic air wave within the chamber <NUM>) would be or be corresponding/related to the input (audio) signal SIN, where the low frequency component of the plurality air pulses refers to frequency component of the plurality air pulses which is within an audible spectrum (e.g., below <NUM> or <NUM>). Herein, baseband may usually be referred to audible spectrum, but not limited thereto.

In other words, in sound producing application, the modulating portion <NUM> may be actuated to form the modulated air wave according to the input audio signal SIN, and the demodulating portion <NUM>, operate in synchronous with modulation portion <NUM>, produces the plurality air pulses with low frequency component thereof as (or corresponding/related to) the input audio signal SIN. For sound producing applications, where fUC is typically much higher than the highest human audible frequency, such as fUC ≥<NUM> ≈ <NUM>×<NUM>, then through the natural/environmental low pass filtering effect (caused by physical environment such as walls, floors, ceilings, furniture, or the high propagation loss of ultrasound, etc., and human ear system such as ear canal, eardrum, malleus, incus, stapes, etc.) on the plurality air pulses, what the listener perceive will only be the audible sound or music represented by the input audio signal SIN.

Illustratively, <FIG> conceptually/schematically demonstrates the effect of (de)modulation operation by showing frequency spectrums of signals before and after the (de)modulation operation. In <FIG>, the modulation operation produces an amplitude modulated ultrasonic acoustic/air wave UAW with spectrum shown as W(f), according to the input audio signal SIN, which is an electrical (analog or digital) representation of a sound signal SS. The spectrum of SIN/SS is represented as S(f) in <FIG>. The synchronous demodulation operation, producing an ultrasonic pulse array UPA (comprising the plurality of pulses) with spectrum illustrated as Z(f), can be viewed as (comprising step of) shifting spectral components of the ultrasonic acoustic/air wave UAW by ±n×fUC (with integer n) and spectral component of the ultrasonic air wave UAW corresponding to the sound signal SS is partially transferred to the baseband. Hence, as can be seen from Z(f), baseband component of the ultrasonic pulse array UPA is significant, compared to the amplitude modulated UAW W(f). The ultrasonic pulse array UPA propagates toward ambient. Through the inherent low pass filtering effect of natural/physical environment and human hearing system, a resulting spectrum Y(f) corresponding to the sound signal SS can be reproduced.

Note that, different from conventional DSB-SC amplitude modulation using sinusoidal carrier, W(f) has component at ±<NUM>×fUC, ±<NUM>×fUC and higher order harmonic of fUC (not shown in <FIG>). It is because that the carrier of the modulation of the present invention is not purely sinusoidal.

Referring back to <FIG>, as an embodiment of the synchronous demodulation operation, the demodulating portion <NUM> may be actuated to form an opening <NUM> at the time and location which are corresponding/aligned to peak(s) of the modulated air wave. In other words, when the modulated air wave reaches its peak at the location of the opening <NUM>, the demodulating portion <NUM> may be actuated such that the opening <NUM> also reaches its peak.

In the embodiment shown in <FIG>, the demodulating portion <NUM> forms the opening <NUM> at a center location between the sidewalls <NUM> and 110R, which have a surface-to-surface, or <NUM> to 111R, spacing of (substantially) λUC between them, meaning that tips of the flaps <NUM> and <NUM> are (substantially) λUC/<NUM> away from the sidewalls <NUM> and 110R, or away from the sidewall surfaces <NUM> and 111R, where λUC represent a wavelength corresponding to the ultrasonic carrier frequency fUC, i.e., λUC = C / fUC with C being the speed of sound.

In an embodiment, the demodulating portion <NUM> may be actuated to form the opening <NUM> at a valve opening rate synchronous to/with the ultrasonic carrier frequency fUC. In the present invention, the valve opening rate being synchronous to/with the ultrasonic carrier frequency fUC generally refers that the valve opening rate is the ultrasonic carrier frequency fUC times a rational number, i.e., fUC×(N/M), where N and M represent integers. In an embodiment, the valve opening rate (of the opening <NUM>) may be the ultrasonic carrier frequency fUC. For example, the valve/opening <NUM> may open every operating cycle TCY, where the operating cycle TCY is a reciprocal of the ultrasonic carrier frequency fUC, i.e., TCY=<NUM>/fUC.

In the present invention, (de)modulating portion <NUM>/<NUM> is also used to denote the (de)modulating flap pair. Moreover, the demodulating portion (or flap pair) <NUM> forming the opening <NUM> may be considered as a virtual valve, which performs an open-and-close movement and forms the opening <NUM> (periodically) according to specific valve/demodulation driving signals.

In an embodiment, the modulating portion <NUM> may substantially produce a mode-<NUM> (or <NUM>nd order harmonic) resonance (or standing wave) within the resonance chamber <NUM>, as pressure profile P104 and airflow profile U104 illustrated in <FIG>. In this regard, the spacing between sidewall surfaces <NUM> and 111R substantially defines a full wavelength λUC corresponding to the ultrasonic carrier frequency fUC, i.e., W115 ≈ λUC = C / fUC. Furthermore, in the embodiment shown in <FIG>, a free end of the modulating flap <NUM>/<NUM> is disposed by the sidewall <NUM>/110R.

Please be aware that, inter-modulation (or cross-coupling) between the modulation of generating the modulated air wave and the demodulation of forming the opening <NUM> might occur, which would degrade resulting sound quality. In order to enhance sound quality, minimizing inter-modulation (or cross-coupling) is desirable. To achieve that (i.e., minimize the cross coupling between the modulation and the demodulation), the modulating flaps <NUM> and <NUM> are driven to have a common mode movement and the demodulating flaps <NUM> and <NUM> are driven to have a differential-mode movement. The modulating flaps <NUM> and <NUM> having the common mode movement means that the flaps <NUM> and <NUM> are simultaneously actuated/driven to move toward the same direction. The demodulating flaps <NUM> and <NUM> having the differential-mode movement means that the flaps <NUM> and <NUM> are simultaneously actuated to move toward opposite directions. Furthermore, in an embodiment, the flaps <NUM> and <NUM> may be actuated to move toward opposite directions with (substantially) the same displacement/magnitude.

The demodulating portion <NUM> may substantially produce a mode-<NUM> (or <NUM>st order harmonic) resonance (or standing wave) within the resonance chamber <NUM>, as pressure profile P102 and airflow profile U102 formed by the demodulating portion <NUM> illustrated in <FIG>. Hence, the demodulating portion <NUM> shall operate at a valve operating/driving frequency fD_V (corresponding to valve/demodulation-driving signal) such that W115 ≈ λD_V /<NUM>, where λD_V = C / fD_V, and the valve operating/driving frequency shall be half of the ultrasonic carrier frequency fUC, i.e., fD_v =fUC / <NUM>.

The common mode movement and the differential mode movement can be driven by (de)modulation-driving signals. <FIG> illustrates waveforms of demodulation-driving signals S101, S103 and a modulation-driving signal SM. The modulation-driving signal SM is used to drive the modulating flaps <NUM> and <NUM>. The demodulation-driving signals (or valve driving signals) S101 and S103 are used to drive the demodulating flaps <NUM> and <NUM>, respectively.

In an embodiment, the modulation-driving signal SM can be viewed as pulse amplitude modulation (PAM) signal which is modulated according to the input audio signal SIN. Furthermore, different from convention PAM signal, polarity (with respect to a constant voltage) of the signal SM toggles within one operating cycle TCY. Generally, the modulation-driving signal SM comprises pulses with alternating polarities (with respect to the constant voltage) and with an envelope/amplitude of the pulses is (substantially) the same as or proportional/corresponding to an AC (alternative current) component of the input audio signal SIN. In other words, the modulation-driving signal SM can be viewed as comprising a pulse amplitude modulation signal or comprising PAM-modulated pulses with alternating polarities with respect to the constant voltage. In the embodiment shown in <FIG>, a toggling rate of the modulation-driving signal SM is <NUM>×fUC, which means that the polarity of the pulses within the modulation-driving signal SM alternates/toggles twice in one operating cycle TCY.

The demodulation-driving signals S101 and S103 comprises two driving pulses of equal amplitude but with opposite polarities (with respect to a constant/average voltage). In other words, at a specific time, given S101 comprises a first pulse with a first polarity (with respect to the constant/average voltage) and S103 comprises a second pulse with a second polarity (with respect to the constant/average voltage), the first polarity is opposite to the second polarity. As shown in <FIG>, a toggling rate of the demodulation-driving signal S101/S103 is fUC, which means that the polarities of the pulses within the demodulation-driving signal S101/S103 alternates/toggles once in one operating cycle TCY. Hence, the toggling rate of the modulation-driving signal (SM) is twice of the toggling rate of the demodulation-driving signal S101/S103.

The slopes of S101/S103 (and the associated shaded area) are simplified drawing representing the energy recycling during the transitions between voltage levels. Note that, transition periods of the signals S101 and S103 overlap. Energy recycling may be realized by using characteristics of an LC oscillator, given the piezoelectric actuators of flap <NUM>/<NUM> are mostly capacitive loads. Details of the energy recycling concept may be referred to <CIT>. Note that, piezoelectric actuator serves as an embodiment, but not limited thereto.

To emphasize the flap pair <NUM> is driven differentially, the signals S101 and S103 may also be denoted as -SV and +SV, signifying that this pair of driving signals have the same waveform but differ in polarity. For illustration purpose, -SV is for S101 and +SV is for S103, as shown in <FIG>, but not limited thereto. In an embodiment, S101 may be +SV and S103 may be -SV.

In another embodiment, there may be a DC bias voltage VBIAS and VBIAS≠<NUM>, under such situation driving signal S101= VBIAS - SV, S103=VBIAS + SV. Variations such as this shall be considered as within the scope of this disclosure.

In addition, <FIG> demonstrates difference in toggling rate between the modulation-driving signal SM and the demodulation-driving signal ±SV. Relative phase delay, meaning timing alignment, between the modulation-driving signal SM and the demodulation-driving signal ±SV may be adjusted according to practical requirement.

In an embodiment, driving circuit for generating the signals SM and ±SV may comprise a sub-circuit, which is configured to produce a (relative) delay between the modulation-driving signal SM and the demodulation-driving signal ±SV. Details of the sub-circuit producing the delay are not limited. Known technology can be incorporated in the sub-circuit. As long as the sub-circuit can generate the delay to fulfill the timing alignment requirements (which will be detailed later), requirements of the present invention is satisfied, which will be within the scope of the present invention.

Note that, the tips of the flaps <NUM> and <NUM> are at substantially the same location (the center location between the sidewalls <NUM> and 111R) and experience substantially the same air pressure at that location. In addition, the flaps <NUM> and <NUM> move differentially. Hence, movements of the tips of the flaps <NUM> and <NUM> owns a common mode rejection behavior, similar to the common mode rejection known in the field of analog differential OP-amplifier circuit, which means that the displacement difference of the tips of the demodulating flaps <NUM> and <NUM>, or |d<NUM> - d<NUM>|, is barely impacted by air pressure formed by the modulating flaps <NUM> and <NUM>.

The common mode rejection, or modulator-to-demodulator isolation, can be evidenced by <FIG> illustrates simulated results generated from an equivalent circuit model of the device <NUM>. Curves d<NUM> and d<NUM> represents movements/displacements of the tips of the flaps <NUM> and <NUM>, respectively. As can be observed in <FIG>, even though d<NUM> and d<NUM> fluctuates quite significantly due to the acoustic pressure generated by the modulating flap <NUM>/<NUM> (P104), the differential movement, represented by the curve denoted by d<NUM> - d<NUM> in <FIG>, remains (substantially) consistent. That is, width/gap of the valve opening <NUM> would be consistent even when the modulation portion <NUM> operates. In other words, modulator movement produces negligible impact on the functionality and performance of the demodulator, which is what "modulator-to-demodulator isolation" means.

On the other hand, as for demodulator-to-modulator isolation, since the flaps <NUM>/<NUM> produce <NUM>st order harmonic resonance or standing wave within the chamber <NUM>, as can be seen from <FIG>, pressure exerted by P102 on the flap <NUM> and the flap <NUM> would have substantially the same magnitude but of opposite polarity, causing the movements of the flap <NUM> and the flap <NUM> to experience changes (due to P102) that are also of the same magnitude but of opposite polarity. This will produce two ultrasonic waves (one by <NUM>, the other by <NUM>) that also changes same magnitude but of opposite polarity. When these two ultrasonic waves propagate to the location above the valve opening <NUM> (indicated by the dotted area shown in <FIG>), they are merged into one pressure. Since the location of this "merge" occurs at the center of device <NUM>, along X-axis or X direction, with equal distance from the tips of <NUM> and <NUM>, the P102 induced changes would cancel/compensate each other and produce a net rest that is largely free from the interference of demodulator/virtual-valve operation.

Illustratively, <FIG> plots a simulated frequency response of an SPL (sound pressure level), measured at <NUM> meter away from the device <NUM>, under the condition that SIN is a <NUM>-tone equal amplitude test signal (within <NUM>~<NUM> Hz and with equal log scale spacing) and an equivalent circuit simulation model of the device <NUM> is used. In the current simulation, the ultrasonic carrier frequency is set as fUC = <NUM> and the valve operating frequency is set as fD_V= fUC/<NUM>=<NUM>.

The demodulator-to-modulator isolation can be evidenced by the absence of extraneous spectral component at and around <NUM> (pointed by block arrow in <FIG>), indicating a high degree of isolation.

As a result, the interference of the movements of these two flap-pairs (<NUM>/<NUM> versus <NUM>/<NUM>) is minimized through the common mode (on modulator) versus differential-mode (on demodulator) orthogonality/arrangement.

In addition, the percentage of time valve remains open, or duty factor, is a critical factor affecting the output of device <NUM>. Increasing amplitude of driving voltage S101 and S103 can increase the amplitude of the movements of the flaps <NUM> and <NUM>, which will increase the maximum open width of the valve opening <NUM>, and raising the driving voltage also raises the duty factor of valve opening. In other words, duty factor of the valve opening <NUM> and the maximum open width/gap of the valve opening <NUM> can be determined by the driving voltage S101 and S103.

When the opening duty factor of valve approaches <NUM>%, such as the example shown in <FIG>, which is generated from one of the equivalent circuit simulation models mentioned previously, the period of each valve opening, shown as curve labeled as V(opening) > <NUM>, overlaps with the same half-cycle of the amplitude modulated ultrasonic standing wave at the location atop the valve opening <NUM> (indicated by the dotted region in <FIG>). By synchronizing and timing-aligning the opening-closing of valve opening <NUM> to the in-chamber standing wave, illustrated as curve labeled as V(p_vlv) in <FIG>, a nicely shaped output pressure pulse, illustrated as curve labeled as V(ep_vlv), is produced.

In <FIG>, curve labeled as V(d2)-V(d3) represent difference in displacement of flaps <NUM> and <NUM>, i.e., d<NUM> - d<NUM>, curve labeled as V(opening) represent a degree of opening of the virtual valve <NUM>. V(opening) > <NUM> when | V(d2)-V(d3) | > TH, where TH is a threshold defined by parameters such as the thickness of the flaps <NUM> and <NUM>, width of slit between claps <NUM> and <NUM>, boundary layer thickness, etc. V(ep_vlv) being nicely shaped may refer that pulses illustrated by V(ep_vlv) are highly asymmetric, unlike V(p_vlv) which is highly symmetric. Asymmetricity of output pressure pulses would demonstrate low frequency component (i.e., frequency component in audible band) of air pulses generated by the air pulse generating device, or APG device for brief, which is a desirable feature for the APG device. The higher the asymmetric is, the stronger the baseband frequency component of the air pulses will be. A zoomed-out view of <FIG> is illustrated in <FIG>, showing the asymmetricity of V(ep_vlv) corresponding to the envelope of the baseband sound signal of <NUM>. In the present invention, the opening (<NUM>) is opened/formed or in an opened status when difference in displacement of flaps <NUM> and <NUM> is larger than a threshold, e.g., | V(d2)-V(d3) | > TH, and is closed or in a closed status otherwise.

Furthermore, it is observed that the maximum output will occur when the duty factor of valve opening, defined as | V(d2)-V(d3) | > TH, is equal to or slightly larger than <NUM>%, such as in the range of <NUM>~<NUM>%, but not limited thereto. However, when the duty factor of valve opening is significantly higher than <NUM>%, such as <NUM>~<NUM>%, more than half-cycle of the in-chamber ultrasonic standing wave will pass through the valve, leading portions of the standing wave with different polarities to cancel each other out, resulting in lower net SPL output from device <NUM>. It is therefore generally desirable to keep the duty factor of valve opening close to <NUM>%, typically in the range between <NUM>% and <NUM>% (where the duty factor in the range between <NUM>% and <NUM>% is within the scope of present invention).

In addition to duty factor, to ensure the modulator-to-demodulator isolation, resonance frequency fR_V of demodulating flaps <NUM>/<NUM> is suggested to be sufficiently deviated from the ultrasonic carrier frequency fUC, which is another design factor.

It can be observed (from equivalent circuit simulation model) that, under the constraint of valve open duty factor equals <NUM>%, for any given thickness of flaps <NUM>/<NUM>, the higher is the resonance-to-driving ratio (fR_V : fD_V or fR_V / fD_V), the wider the valve can open. Since the output of device <NUM> is positively related to the max width valve opens, it is therefore desirable to have the resonance-to-driving ratio higher than <NUM>.

However, when fR_V falls within the range of fUC ± max(fSOUND), flap <NUM>/<NUM> will start to resonate with the AM ultrasonic standing wave, converting portion of the ultrasound energy into common mode deformation of flap <NUM>/<NUM>, where max(fSOUND) may represent maximum frequency of the input audio signal SIN. Such common mode deformation of flaps <NUM>/<NUM> will cause the volume atop the flaps <NUM>/<NUM> to change, result in fluctuation of pressure inside chamber <NUM> at the vicinity of valve opening <NUM>, over the affected frequency range, leading to depressed SPL output.

In order to avoid valve resonance induced frequency response fluctuations, it is preferable to design the flap <NUM>/<NUM> with a resonance frequency outside of the range of (fUC ±max(fSOUND)) × M, where M is a safety margin for covering factors such as manufacturing tolerance, temperature, elevation, etc., but not limited thereto. As a rule of thumb, it is generally desirable to have fR_V either significantly lower than fUC as in fR_V ≤ (fUC - <NUM>) ×<NUM> or significantly high than fUC as in fR_V ≥ (fUC + <NUM>)×<NUM>. Note that <NUM> is used here because it is well accepted as highest human audible frequency. In applications such as HD-/Hi-Res Audio, <NUM> or even <NUM> may be adopted as max(fSOUND), and the formula above should be modified accordingly.

In addition, suppose w(t) and z(t) represent functions of time for the amplitude-modulated ultrasonic acoustic/air wave UAW and the ultrasonic pulse array UPA (comprising the plurality of pulses). Since the opening <NUM> is formed periodically in the opening rate of the ultrasonic carrier frequency fUC, a ratio function of z(t) to w(t), denoted as r(t) and can be expressed as r(t) = z(t)/w(t), is periodic with the opening rate of the ultrasonic carrier frequency fUC. In other words, z(t) may be viewed as a multiplication of w(t) and r(t) in time domain, i.e., z(t) = r(t) w(t), and the synchronous demodulation operation performed on UAW can be viewed as the multiplication on w(t) by r(t) in time domain. It implies that Z(f) may be viewed as a convolution of W(f) and R(f) in frequency domain, i.e., Z(f) = R(f)*W(f) where * denotes convolution operator, and the synchronous demodulation operation performed on UAW can be viewed as the convolution of W(f) with R(f) in frequency domain. Note that, when r(t) is periodic in time domain with the rate of the frequency fUC, R(f) is discrete in frequency domain where frequency/spectrum components of R(f) are equally spaced by fUC. Hence, the convolution of W(f) with R(f), or the synchronous demodulation operation, involves/comprises step of shifting W(f) (or the spectral components of UAW) by ±n×fUC (with integer n). Herein, r(t)/w(t)/z(t) and R(f)/W(f)/ Z(f) form Fourier transform pair.

<FIG> is a schematic diagram of an APG device <NUM> according to an embodiment of the present invention. The device <NUM> is similar to the device <NUM>, and thus same notations are used. Different from the device <NUM>, the device <NUM> further comprises an enclosing structure (enclosure) <NUM>. A chamber <NUM> is formed between the enclosing structure <NUM> and the cap structure <NUM>. Note that vents <NUM>/R are formed within the ceiling <NUM> located at λUC/<NUM> from the sidewalls <NUM>/R, respectively, on the nodes of the ultrasonic standing pressure wave P104, as indicated by lines <NUM>/<NUM>.

The purpose of vents <NUM>/R in <FIG> is to allow the airflow generated during the demodulation operation (as indicated by the two dashed <NUM>-way pointed-curves between <NUM> and <NUM>/R) to be vented from chamber <NUM>, such that the difference between the average pressure inside the chamber <NUM> and outside in the ambient is minimized and the function of chamber <NUM> is to disrupt the spectral components carried by the airflow into chamber <NUM>, preventing these airflow from forming additional audible sound signal. By locating vents <NUM>/R on the nodes of the standing pressure wave, the spectral components surrounding fUC are prevented from exiting chamber <NUM>, allowing demodulation to form UPA (ultrasonic pulse array) and produce the desired APPS (air pressure pulse speaker) effect.

In the present invention, APG device having APPS effect generally refers that, the baseband frequency component (especially frequency component in audible band) embedded within the air pulses output by the APG device at the ultrasonic carrier frequency is not only observable but also of significant intensity. For APG device producing APPS effect, the spectrum of the electrical input signal SIN will be reproduced acoustically within baseband of audible spectrum (low frequency compared to carrier frequency) via producing the plurality of air pulses by the APG device, which is suitable for being used in sound producing application. The intensity of baseband produced through APPS effect is related to the amount of, or degree of, asymmetricity of air pulses produced by the APG device, where asymmetricity will be discussed later.

Note the, the supporting structures <NUM> and 123R of the device <NUM> or <NUM> have parallel and straight walls (with respect to X-axis), where space/channel between <NUM> and 123R functions as an sound outlet. Simulation results using FEM (finite element method) show that, when the frequency rises above <NUM>, lateral standing waves, along the X direction, start to be formed between the walls of <NUM>/123R, and the output starts to self-nullify. Such lateral-resonance induced self-nullifying phenomenon cause the energy transfer ratio over the height of the walls of <NUM>-123R (in Z direction) to degrade.

To bypass this problem, a horn-shaped outlet is proposed. For example, <FIG> is a schematic diagram of a portion of an APG device <NUM> according to an embodiment of the present invention. Similar to the device <NUM>, the device <NUM> comprises the flaps <NUM> and <NUM>, anchored on the supporting structure <NUM>" and 123R", respectively, and configured to form the opening <NUM> to produces a plurality of air pulses via an outlet <NUM> toward an ambient. Different from the supporting structure <NUM> and 123R of the device <NUM> which have straight and parallel walls, walls of the supporting structure <NUM>" and 123R" of the device <NUM> are oblique and has a non-right angle θ with respect to X-Axis or X direction, such that the outlet <NUM> with horn-shape is formed. The non-right angle θ may be designed according to practical requirement. In an embodiment, the non-right angle θ may be <NUM>°, but not limited thereto. In the present invention, the horn-shaped outlet generally refers to an outlet with an outlet dimension or a tunnel dimension which is gradually widened from the film structure toward an ambient.

<FIG> and <FIG> illustrate frequency responses of energy transfer ratio of the device <NUM> and <NUM>, respectively, for <NUM> different displacements of flaps <NUM> and <NUM>, where Dvv=k means the displacement of the tips of each flap is kµM, which produces a differential movement of <NUM>kµM. <FIG> and <FIG> are simulated by using FEM. By comparing <FIG> and <FIG>, the device <NUM> produces energy transfer ratio that starts to roll-off above <NUM>, with a few jumps and dips as the frequency rises above <NUM>; while the device <NUM> produces energy transfer ratio that retains a rising trend roughly above120KHz, with a much smoother frequency response for frequency above <NUM>. It means, frequency response of energy transfer ratio (above <NUM>) of the device <NUM> is much smoother than which of the device <NUM>, which is benefit for the APG device operating at ultrasonic pulse rate (i.e., the ultrasonic carrier frequency fUC) and its high order harmonic (e.g., n×fUC). Furthermore, the device <NUM> produces a roughly <NUM> times energy transfer ratio higher than which produced by the device <NUM>. Hence, it can be validated from <FIG> and <FIG> that horn-shaped outlet brings better energy transfer ratio for APG device.

<FIG> shows an embodiment of a two-step etching/manufacturing method to etch walls at two different angles. First, the wall of 123R"/<NUM>" is etched with a tapered angle (as shown in <FIG>), and the tapered wall is then covered by photoresist or spin-on dielectric using a spray coating method (as shown in <FIG>). The photoresist or spin-on dielectric is then patterned by photolithography methods (as shown in <FIG>), followed by the etching of the wall of <NUM> and 124R at a straight angle (as shown in <FIG>). The fabrication method provided above is for illustration purpose only and the scope of the invention is not limited thereof.

<FIG> is a schematic diagram of an APG device <NUM> according to an embodiment of the present invention. The device <NUM> is modified from <FIG> of <CIT> and similar to the device <NUM> shown in <FIG> of the present invention. Different from the device <NUM>, the device <NUM> comprises only flap pair <NUM> (but no flap pair <NUM>). The flap pair <NUM> is configured to perform both the modulation operation (which is to form amplitude-modulated air pressure variation with the ultrasonic carrier frequency fUC) as well as the demodulation operation (which is to form the opening <NUM>, synchronous to the amplitude-modulated ultrasonic carrier at frequency fUC, to produce air pulses according to the envelope of the said amplitude-modulated ultrasonic air pressure variation).

In <FIG>, U104 and P104 represent pressure profile and airflow profile formed by the flap pair <NUM> in response to the modulation-driving signal SM, and U102 and P102 represent pressure profile and airflow profile formed by the flap pair <NUM> in response to the demodulation-driving signal ±SV. Herein the demodulation-driving signal is denoted by ±SV to emphasize the flap pair <NUM> is driven differentially (which implies the demodulation-driving signals +SV and -SV have the same magnitude but opposite polarity) to perform the demodulation operation. For example, S101 and/or S103 above may be represented by -SV and/or +SV.

In other words, modulator and demodulator are co-located at/as the flap pair <NUM>. Like the device <NUM>, the film structure <NUM> of the flap pair <NUM> of the device <NUM> is actuated to have not only a common mode movement to perform the modulation and a differential mode movement to perform the demodulation.

In other words, the "modulation operation" and the "demodulation operation" are performed by the same flap pair <NUM>, at the same time. This colocation of "modulation operation" together with "demodulation operation" is achieved by new driving signal wiring schemes such as those shown in <FIG>. Given that the device <NUM> may comprise an actuator 101A/103A disposed on the flap <NUM>/<NUM> and the actuator 101A/103A comprises a top electrode and a bottom electrode, both of the top and bottom electrodes may receive the modulation driving signal SM and the demodulation-driving signal ±SV.

In an embodiment, one electrode of the actuator 101A/103A may receive the common mode modulation-driving signal SM; while the other electrode may receive the differential mode demodulation-driving signal S101(-SV)/S103(+SV). For example, diagrams <NUM> to <NUM> shown in <FIG> illustrate details of a region <NUM> shown in <FIG>. As shown in the diagrams <NUM> and <NUM>, bottom electrodes of the actuator 101A/103A receive the common mode modulation-driving signal SM; while top electrodes of the actuator 101A/103A receive the differential mode demodulation-driving signal S101(-SV)/S103(+SV). A suitable bias voltage VBIAS may be applied to either the bottom electrode (like diagram <NUM> shows) or the top electrode (like diagram <NUM> shows), where the bias voltage VBIAS can be determined according to practical requirement.

In an embodiment (shown in diagram <NUM>), one electrode of the actuator 101A/103A may receive both the common mode modulation-driving signal SM and differential mode demodulation-driving signal S101(-SV)/S103(+SV); while the other electrode is properly biased. In the embodiment shown in diagram <NUM>, the bottom electrodes receive the common mode modulation-driving signal SM and differential mode demodulation-driving signal S101(-SV)/S103(+SV); while the top electrode are biased.

The driving signal wiring schemes shown in <FIG> achieve a goal that, (without considering VBIAS) an applied signal of one actuator (e.g., 101A) is or comprises -SM-SV while an applied signal of the other actuator (e.g., 103A) is or comprises -SM+SV. Note that, driving signal wiring schemes may be modified or altered according to practical situation/requirement. As long as a common-mode signal component between the two applied signals applied on the flap pair <NUM> comprises the modulation-driving signal SM (plus VBIAS) and a differential-mode signal component between the two applied signals applied on the flap pair <NUM> comprises the demodulation-driving signal SV, requirements of present invention is satisfied and is within the scope of the present invention. Herein (or generally), a common-mode signal component between two arbitrary signals a and b may be expressed as (a+b)/<NUM>; while a differential-mode signal component between two arbitrary signals a and b may be expressed as (a-b)/<NUM>.

Further note that, in order to minimize the cross coupling between the modulation operation (as a result of driving signal SM) and the demodulation operation (as a result of driving signal ± SV), in an embodiment, the flaps <NUM> and <NUM> are made into a mirrored/symmetric pair in both their mechanical construct, dimension and electrical characteristics. For instance, the cantilever length of flap <NUM> should equal that of <NUM>; the membrane structure of flap <NUM> should be the same as flap <NUM>; the location of virtual valve <NUM> should be centered between, or equally spaced from, the two supporting walls <NUM> of flap <NUM> and flap <NUM>; the actuator pattern deposited on flap <NUM> should mirror that of flap <NUM>; the metal wiring to actuators deposited atop flap <NUM> and <NUM> should be symmetrical. Herein, a few items are names for mirrored/symmetric pair (or the flaps <NUM> and <NUM> are mirrored/symmetric), but not limited thereto.

<FIG> illustrates a sets of frequency response measurement results of a physical embodiment of the device <NUM> in an IEC711 occluded ear emulator, where driving scheme shown in diagram <NUM> is used to drive the device <NUM>, Vrms for modulation-driving signal SM for bottom electrodes is <NUM> Vrms, Vpp (peak-to-peak voltage) for demodulation-driving signal ± SV for top electrodes is swept from 5Vpp to <NUM> Vpp, and a GRAS RA0401 ear simulator is used for measuring acoustic results. Operating frequency (i.e., ultrasonic carrier frequency fUC) of the device <NUM> is <NUM>, and the device dimension is designed accordingly (e.g., W115 ≈ λUC = C / fUC ≈ <NUM> for C = <NUM>/s). As can be seen from <FIG>, the device <NUM> is able to produce sound of high SPL at low frequency band (at least <NUM> dB for frequency less than <NUM>).

Furthermore, <FIG> illustrates and analysis of measurement results of the device <NUM> shown in <FIG>. In <FIG>, the SPL at <NUM> (bold dashed line) and <NUM> (bold solid line) of <FIG> is plotted versus Vvtop (Vpp), where Vvtop (Vpp) is the peak-to-peak voltage for the demodulation-driving signal applied on the top electrodes, as shown in connection diagram <NUM>. It can be seen from <FIG> and <FIG> that SPL increases as Vvtop increases. In addition, simulation results of equivalent lumped-circuit model of the device <NUM> also concurred that SPL increases as amplitude of (valve-driving or) demodulation-driving signal increases. Therefore, it can be obtained that a volume of a sound produced by the air-pulse generating device of the present invention may be controlled via an amplitude of the demodulation-driving signal.

Based on the results from <FIG> and <FIG>, it can be concluded that the concept of modulator-demodulator co-location is validated, meaning that modulation (forming amplitude-modulated ultrasonic air pressure variation) and demodulation (forming opening synchronously to produce asymmetric air pulses) performed by the device <NUM> successful produce APPS effect. Hence, it may be possible to shrink the chamber width (e.g., W115 of the device <NUM>).

For example, <FIG> is a schematic diagram of an APG device <NUM> according to an embodiment of the present invention. The device <NUM> is similar to the device <NUM>, where the flap pair <NUM> is also driven via one of the driving schemes shown in <FIG>, but not limited thereto. Compared to the device <NUM>, the chamber width W115' of the device <NUM> is reduced by half. In an embodiment, the chamber width W115' of the device <NUM> may be λUC/<NUM>.

Furthermore, standing wave within the chamber, such as <NUM> of <FIG> or <NUM>' of <FIG>, may not be required, which means, the chamber width (W115) does not have to be (related to) λUC or λUC/<NUM>, and there is no need to form/maintain/reflect planar wave between sidewalls 111R/111R' and <NUM>/<NUM>'. It is free/flexible to change the shape of chamber to optimize other factors, e.g., reducing the chamber length to enhance sound producing efficiency, which can be evaluated by SPL per area (mm<NUM>) of the device.

<FIG> is a schematic diagram of an APG device <NUM> according to an embodiment of the present invention. The device <NUM> may comprise subassemblies <NUM> and <NUM>. In an embodiment, the subassemblies <NUM> and <NUM> may be fabricated via known MEMS process, and be bounded together through layer <NUM> using bounding or adhesive material such as dry film or other suitable die attach material/methods. The subassembly <NUM> by itself may be viewed as an APG device (which will be detailed later in <FIG> and related paragraphs), which comprises the flap pair <NUM> or the film structure <NUM>. The subassembly <NUM> may be viewed as a cap structure.

Similar to the device <NUM>, the device <NUM> comprises the flap pair <NUM> with flaps <NUM> and <NUM> driven via one of the driving schemes shown in <FIG>, but not limited thereto, and the flap pair <NUM> of the device <NUM> is actuated to form amplitude-modulated ultrasonic air pressure variation with ultrasonic carrier frequency fUC and to form the opening <NUM> at the rate synchronous with the ultrasonic carrier frequency fUC and produce a plurality of air pulses via an outlet toward ambient according to the ultrasonic air pressure variation.

Different from the device <NUM>, a conduit <NUM> is formed within the device <NUM>. The conduit <NUM> connects air volume above the virtual valve <NUM> (the slit between flaps <NUM> and <NUM>) outward to the ambient. The conduit <NUM> comprises a chamber <NUM>, a passageway <NUM> and an outlet <NUM> (or zones <NUM>-<NUM>). The chamber <NUM> is formed between the film structure <NUM> and the cap structure (subassembly) <NUM>. The passageway <NUM> and the outlet <NUM> are formed within the cap structure (subassembly) <NUM>.

The chamber <NUM> may be viewed as a semi-occluded compression chamber, where an air pressure within the compression chamber <NUM> may be compressed or rarefied in response to the common-mode modulation-driving signal SM, and the ultrasonic air pressure variation/wave may be generated and directly fed into the passageway <NUM> via an orifice <NUM>. The passageway <NUM> serves as a waveguide, where the shape and dimension thereof should be optimized to allow the pressure variation/pulse generated in zone/chamber <NUM> to propagate outward efficiently. The outlet <NUM> is configured to minimize reflection/deflections and maximize the acoustic energy coupling to ambient. To achieve that, a tunnel dimension (e.g., a width in X direction) of the outlet <NUM> is gradually widened toward the ambient and the outlet <NUM> has a horn-shape.

In an embodiment, a length/distance L<NUM> of the conduit <NUM> between the opening <NUM> (equivalently, the flap pair <NUM> or the film structure <NUM>) and a surface <NUM> may be (substantially) a quarter wavelength λUC/<NUM> corresponding to fUC (with, for example, ±<NUM>% tolerance). For example, L<NUM> may be <NUM> µm for case of fUC = <NUM>, which is not limited thereto. Note that, (referring back to <FIG>) it is observed that air pressure wave (as a kind of air pressure variation) propagates within the chamber <NUM>' of the device <NUM> (or the chamber <NUM> within the device <NUM>) along X direction, and a distance between virtual valve (opening) <NUM> and sidewall surfaces <NUM>'/111R' is λUC/<NUM>. In <FIG>, the device <NUM> may be viewed as folding/rotating air wave propagation path by <NUM>°to align with Z-direction, such that air wave or air pressure pulse is emitted via the Z-direction toward ambient directly.

<FIG> illustrates a snapshot of FEM simulated pressure profile of a device similar to the device <NUM>, according to an embodiment of present invention. In <FIG>, auxiliary arrows are presented to indicate polarity/sign of the pressure values. Difference between the device <NUM> and the device shown in <FIG> is that, chamfer <NUM> is added on the subassembly <NUM> at an interface between the chamber <NUM> and the passageway <NUM> to minimize disturbance to the airflow. In <FIG>, pressure within zone <NUM> is about +<NUM> Pa, and pressure within zone <NUM> closed to <NUM> is about -<NUM> Pa. Brightest zone presents pressure nodal plane.

Note that, nodal plane within zone <NUM> indicates proper forming of wave propagation, and space/distance between nodal plane <NUM> and nodal plane outside the device is about <NUM>*λ/<NUM> (herein λ = <NUM>(m/s)/<NUM> (KHz)), which is close to (and slightly larger than) λ/<NUM>. It implies that, non-interrupted pressure wave propagation at the speed of sound exists. In other words, pressure pulses or air wave generated by the film structure of the device <NUM> radiate toward ambient, as shown in <FIG>.

<FIG> illustrates IEC711 occluded ear coupler SPL measurement results versus frequency of a physically implemented device <NUM>, where results corresponding to the demodulation-driving signal ±SV with <NUM> Vpp and <NUM> Vpp are plotted. Also, parameters of the devices <NUM> and <NUM> for producing maximum SPL are compared in TABLE I.

As can been seen from <FIG>, <FIG> and TABLE I, the device <NUM> can achieve slighter higher SPL than the device <NUM> with lower input amplitude while reducing the die size by <NUM>% at the same time. It means, the device <NUM> with conduit <NUM> is far more efficient both in terms of power consumed and in terms of silicon space/area occupied. In the invention, a width W631 of the chamber <NUM> is less than, e.g. significantly less than, λUC/<NUM>, for example, in the example of device <NUM> W631≈<NUM> while λUC/<NUM>≈ <NUM>. For zone <NUM> to perform chamber compression, the dimension of the chamber <NUM> should be much smaller than λUC. In the invention, a height H<NUM> of the chamber <NUM> is less than λUC/<NUM>, i.e., H<NUM> < λUC/<NUM>. Note that, the width of the chamber <NUM> (i.e., a dimension in X direction) may be getting narrower from the film structure <NUM> toward the passageway <NUM>, either in a staircase fashion or a tapered fashion, where both cases are within the scope of present invention.

<FIG> is a schematic diagram of an APG device <NUM> according to an embodiment of the present invention. Similar to the device <NUM>, the device <NUM> comprises subassemblies <NUM> and <NUM>, and has a conduit <NUM> formed therewithin. The subassembly <NUM> may be fabricated by MEMS process, and may be viewed as an APG device also. A chamber <NUM> is formed within the subassembly <NUM>. The subassembly <NUM> may itself be an APG device, which can be viewed as a combination of squeeze mode operation disclosed in <CIT>, virtual valve disclosed in No.<CIT>, and driving scheme illustrated in <FIG>.

The conduit <NUM> comprises a chamber <NUM>, a passageway/waveguide <NUM> and a horn-shaped outlet <NUM> (or zones <NUM>-<NUM>), and connects air volume below the virtual valve <NUM> outward to the ambient. Different from the device <NUM>, the subassembly <NUM> may be formed/fabricated via technologies such as 3D printing, precision injection molding, stamping, etc. The passageway/waveguide <NUM> comprises a first section which is the orifice <NUM> etched on the cap of the subassembly <NUM> and a second section which is formed within the subassembly <NUM>, where chamfer <NUM> may be added therebetween to minimize disturbance. The chamber <NUM> and <NUM> are overlapped. The pressure variation/wave generated by the flaps <NUM> and <NUM> would be fed into the passageway/waveguide <NUM> directly.

<FIG> is a schematic diagram of an APG device <NUM> according to an embodiment of the present invention. The device <NUM> comprises subassemblies <NUM> and <NUM>. The subassembly <NUM> may have the same or similar structure of the device <NUM>, which can be fabricated by MEMS process and be viewed as an APG device, comprises flaps <NUM> and <NUM> driven by one of the schemes shown in <FIG>, where the virtual valve (opening) <NUM> is formed. The subassembly <NUM> may be formed/fabricated via technologies such as 3D printing, precision injection molding, precision stamping, etc. Note that, via the (de)modulation operation, the subassembly <NUM> produces a plurality of airflow pulses.

A conduit <NUM>, connecting air volume below the virtual valve <NUM> outward to the ambient, is formed within the device <NUM>. The conduit <NUM> comprises a (compression) chamber <NUM>, a passageway/waveguide <NUM> and a horn-shaped outlet <NUM> (or zones <NUM>-<NUM>). The compression chamber <NUM> is configured to convert the plurality of airflow pulses into a plurality of air pressure pulses. Specifically, the chamber <NUM> would producing pressure pulses ΔPn ∝ P0_n. ΔMn/M0_n (Eq. <NUM>), where M0_n is the airmass inside chamber <NUM> before the start of pulse cycle n and ΔMn is the airmass associated with the airflow pulse of pulse cycle n. Eq. <NUM> represents converting airflow pulses into air pressure pulses, and the converted air pressure pulses propagate into the passageway/waveguide <NUM>. In an embodiment, the subassembly <NUM> in zone <NUM> may have a brass mouthpiece-like cross section profile.

The passageway/waveguide <NUM> may have an impedance that is close to, matched to, or within ±<NUM>% of, the compression chamber <NUM>, so as to maximize the propagation efficiency of the pressure pulse generated in zone <NUM> outward to the ambient. In an embodiment, the propagation efficiency may be optimized by properly choosing the cross section area of the passageway <NUM>.

In the embodiment shown in <FIG>, a tunnel dimension (e.g., width in X direction) of the outlet <NUM> is gradually widened toward the ambient with a piece-wise linear manner (where θ<NUM> < θ<NUM>), such that a horn-shape is formed. Note that, the horn-shape of the outlet may be designed according to practical requirements. The tunnel dimension of the outlet can be widen in polynomial manner, pure linear manner, piece-wise linear manner, parabolic manner, exponential manner, hyperbolic manner, etc., and not limited thereto. As long as the tunnel dimension of the outlet is gradually widened toward the ambient, requirement of the present invention is satisfied, which is within the scope of the present invention.

To perform chamber compression in zone <NUM>, dimension of chamber/zone <NUM> is suggested to be much smaller than wavelength λUC corresponding to operating frequency fUC. For instance, in an embodiment of fUC =<NUM> and λUC = (<NUM> / <NUM>) = <NUM>, a height H<NUM> may be in a range of λUC/<NUM> ~λUC/<NUM> (e.g., H<NUM> = λUC /<NUM> = <NUM> µm) and a width W<NUM> may be in a range of λUC/<NUM> ~λUC/<NUM> (e.g., W<NUM> in a range of <NUM>µm ~<NUM>µm), but not limited thereto.

Note that, the film structure <NUM> subdivide a volume of space into a resonance chamber <NUM> on one side and a compression chamber <NUM> on another (or the other) side, and by nature of this subdivision, the displacements due to common-mode movement of flaps <NUM> and <NUM>, as observed from the space of chamber <NUM> and chamber <NUM>, will have exactly the same magnitude but of opposite direction/polarity. In other words, along with the common mode movement of the flaps <NUM> and <NUM>, a push-pull operation will be formed, and such push-pull operation will increase (e.g., doubles) the pressure difference across flaps <NUM> and <NUM>, and thus the airflow will be increased when virtual valve <NUM> is opened.

Specifically, for the compression chamber <NUM> with volume V1and the resonance chamber <NUM> with volume V2, a membrane/flap movement, resulting in a volume difference DV (assuming DV << V1, V2), would cause a pressure change in V1 as Δ PV1 = <NUM> - V1/(V1-DV) = -DV/(V1-DV)≈ -DV/V1 and a pressure change in V2 as Δ PV2 = <NUM> - V2/(V2+DV) = DV/(V2+DV)≈ DV/V2. The pressure difference between two volume may be Δ PV2 -Δ PV1 = DV/(V2+DV) + DV/(V1-DV). When V1≈V2≈Va, Δ PV2 -Δ PV1 ≈ DV/(Va+DV) + DV/(Va-DV) = DV·2Va/(Va<NUM> - DV<NUM>) ≈ <NUM> DV/Va ≈<NUM>·Δ PV2, which means that the push-pull operating can doubles the pressure difference between the two subspaces separated by flaps <NUM> and <NUM>.

<FIG> is a schematic diagram of an APG device <NUM> according to an embodiment of the present invention. The device <NUM> comprises subassemblies <NUM> and <NUM>. The subassembly <NUM> may be fabricated by MEMS process and may be viewed as an APG device. The subassembly <NUM> may be fabricated by 3D printing. Similar to the device <NUM> or the subassembly <NUM>, the subassembly <NUM> may also be viewed as a combination of squeeze mode operation disclosed in No. <CIT>, virtual valve disclosed in No. <CIT>, and driving scheme illustrated in <FIG>. In the device <NUM>, squeeze mode operating chamber <NUM> and compression chamber <NUM> are separated; while in the device <NUM>, the squeeze mode operating chamber and the compression chamber are merged as chamber <NUM>.

The effect of the subassembly <NUM> and subassembly <NUM> are similar in terms of airflow pulse generation, but their operation principles are different. The subassembly <NUM> exploits resonance; while the assembly <NUM> exploits compression and rarefication of the squeeze mode operating chamber <NUM> caused by membrane (flaps <NUM>, <NUM>) movement. Hence, chamber width W<NUM> no longer needs not fulfill any relationship with λUC, and thus, the size of the chamber <NUM> may be shrunk as much as practical/desired.

<FIG> is a schematic diagram of an APG device A00 according to an embodiment of the present invention. Since resonance is not a requirement, restriction of rectangular cross-section of chamber, such as chamber <NUM>, can be removed, and it is more flexible in geometry to optimize the pressure wave generation or the propagation of wave out to the ambient. For example, chamber A05 or subassembly A40 may have brass mouthpiece-like cross-section.

Another aspect of device A00 of <FIG> is that of "direct pressure coupling". Instead of first going through an orifice <NUM> as in device <NUM>, the pressure wave generated in compression chamber A05 of device A00 is coupled directly to the conduit A32, and then goes out to the ambient via the outlet A33. Such direct coupling between compression chamber and the conduit/outlet eliminates the loss incurred by the orifice <NUM>, resulting in significant efficiency improvement over device <NUM>.

<FIG> is a schematic diagram of an APG device B00 according to an embodiment of the present invention. The device B00 is similar to the device A00. Different from the device A00, the device B00 further comprises a (cap) structure B11, and a chamber B05 is formed between the cap structure B11 and the film structure <NUM>. With the chamber A05 formed by one side of the film structure <NUM> and the chamber B05 formed by the other side of the film structure <NUM>, the push-pull operation may be performed, such that airflow pulse may be enhanced.

Note that, the air pulses produced by the subassemblies <NUM> and <NUM> may be viewed as airflow pulses, and the subassemblies <NUM> and <NUM> may be viewed as an airflow-to-air-pressure converter, which has a trumpet-like cross section profile. On the other hand, the air pulses produced by the subassemblies <NUM>, <NUM>, A10 and B10 may be viewed as air pressure pulses, which create demodulated/asymmetric air pressure pulses directly and may be more efficient than the devices <NUM> and <NUM>.

In addition, the subassembly with conduit formed therewithin or the subassembly having conduit with trumpet-like cross section profile may also be applied on the APG device disclosed in <CIT>, <CIT>, etc., filed by Applicant, or other device such as No. <CIT>, which is not limited thereto.

<FIG> demonstrates illustrations of timing alignment of virtual valve (VV) <NUM> opening for APG devices of present invention. In <FIG>, solid curves represent flaps common mode movement produced by modulation-driving signal SM and darkness in the background represents acoustic resistance corresponding to the virtual valve, where darker shade means higher resistance (VV closed, resulting in the volume within the chamber being disconnected from the ambient) and lighter means lower resistance (VV opened, resulting in the volume within chamber being connected to the ambient).

In <FIG>, the timing of the open status of virtual valve (VV) <NUM> is aligned to maximum (a first peak) of pressure within the chamber is achieved which typically lies slightly before the flaps reaching their most positive (a first peak) common-mode displacement; while the timing of the closed status of virtual valve <NUM> is aligned to minimum (a second peak) of pressure within the chamber is reached which typically lies slightly before the flaps reaching their most negative (a second peak) common-mode displacement. Timing alignment shown in <FIG>, where the maximum opening of VV <NUM> is aligned to a first peak of pressure within the chamber, is to maximize the pulse amplitude of the airflow pluses, which may be suitable for the devices <NUM>~<NUM> (with chamber but without conduit formed therein).

On the other hand, in <FIG>, inspired by valve timing of gas/piston engine in the automobile industry, the timing of the open status of virtual valve <NUM> is aligned to a maximum speed of the common mode movement of membrane (flaps) moving toward a first direction; while the timing of the closed status of virtual valve <NUM> is aligned to a maximum speed of the common mode movement of membrane (flaps) moving toward a second direction opposite to the first direction. The first direction is a direction from the film structure toward ambient. Timing alignment shown in <FIG> is to maximize the volume of the airflow pluses, which may be suitable for the device <NUM>, or the devices <NUM>~<NUM>, A00 and B00 (with chamber comprising conduit formed therein).

<FIG> is a schematic diagram of an APG device C00 according to an embodiment of the present invention. The deice C00 is similar to the APG devices previously introduced, which comprise the flaps <NUM> and <NUM>. The flaps <NUM> and <NUM> may also be driven by the driving scheme shown in <FIG>.

Different from those devices, the device C00 comprises no cap structure. Compared to the APG devices introduced above, the device C00 has much simple structure, requiring less photolithographic etching steps, done away complicated conduit fabrication steps, and avoid the need to bound two sub-components or subassemblies together. Production cost of the device C00 is reduced significantly.

Since there is no chamber formed under the cap structure to be compressed, the acoustic pressure generated by the device C00 arise mainly out of the acceleration of the flaps (<NUM> and <NUM>) movement. By aligning the timing of opening of the virtual valve <NUM> (in response to the demodulation-driving signal ±SV) to the timing of acceleration of common mode movement of the flaps <NUM> and <NUM> (in response to the modulation-driving signal SM), the device C00 would be able to produce asymmetric air (pressure) pulses.

Note that, the space surrounding flaps <NUM> and <NUM> is divided into two subspaces: one in Z><NUM>, or +Z subspace, and one in Z<<NUM>, or -Z subspace. For any common mode movements of flaps <NUM> and <NUM>, a pair of acoustic pressure waves will be produced, one in subspace +Z, and one in the subspace -Z. These two acoustic pressure waves will be of the same magnitude but of opposite polarities. As a result, when the virtual valve <NUM> is opened, the pressure difference between the two air volumes in the vicinity of the virtual valve <NUM> would neutralize each other. Therefore, when the timing of differential mode movement reaching its peak, i.e. the timing VV <NUM> reaches its maximum opening, is aligned to the timing of acceleration of common mode movement reaching its peak, the acoustic pressure supposed to be generated by the common mode movement shall be subdued/eliminated due to the opening of the virtual valve <NUM>, causing the auto-neutralization between two acoustic pressures on the two opposite sides of the flaps <NUM> and <NUM>, where the two acoustic pressures would have same magnitude but opposite polarities. It means, when the virtual valve <NUM> is opened, the device C00 would produce (near) net-zero air pressure. Therefore, when the opened period of the virtual valve <NUM> overlaps a time period of one of the (two) polarities of acceleration of common mode flaps movement, the device C00 shall produce single-ended (SE) or SE-liker air pressure waveform/pulses, which are highly asymmetrical.

In the present invention, SE(-like) waveform may refers that the waveform is (substantially) unipolar with respect to certain level. SE acoustic pressure wave may refer to the waveform which is (substantially) unipolar with respect to ambient pressure (e.g., <NUM> ATM).

<FIG> demonstrates illustrations of timing alignment of virtual valve (VV) opening according to an embodiment of the present invention. The timing alignment scheme shown in <FIG> may be applied to the device C00. In <FIG>, solid/dashed/dotted curve represents displacement/velocity/acceleration of common mode movement of membrane (flaps <NUM> and <NUM>) in response to the modulation-driving signal SM, and similar to <FIG>, background darkness represents acoustic resistance caused by open-close action of VV <NUM>. For illustration purpose, waveform of membrane/flaps movement in <FIG> is assumed to be (or approximately plotted as) sinusoidal with constant amplitude, where the velocity/acceleration waveform is the <NUM>st/<NUM>nd order derivative of the displacement waveform. As shown in <FIG>, the timing of peak VV opening is aligned to the timing of a first peak acceleration of common mode membrane/flaps movement toward a first direction, as discussed above, such timing alignment resulting in auto-neutralization between the two acoustic pressure waves generated in subspaces +Z and -Z, causing the net acoustic pressure to be suppressed, illustrated as the flattened portions of the SE air pressure waveform in <FIG>.

Also illustrated in <FIG>, the timing of VV being closed is aligned to the timing of a second peak acceleration of common mode membrane/flaps movement toward a second direction, the second direction is opposite to the first direction. Since the VV is closed during/around the second peak acceleration, the acoustic pressure generated by the second peak acceleration of flaps <NUM> and <NUM> is able to radiate away from flaps <NUM> and <NUM>, resulting in a highly asymmetrical acoustic pressure wave as illustrated by the half-sine portions of the SE air pressure waveform in <FIG>.

Note that, the opening of virtual valve <NUM> does not determine the strength/amplitude of the acoustic pressure pulse, but determines how strong is the "near net-zero pressure" (or the auto-neutralization) effect. When the virtual valve <NUM> opening is wide, the "net-zero pressure" effect is strong, the auto-neutralization is complete, the asymmetry will be strong/obvious, resulting in strong/significant baseband signal or APPS effect. Conversely, when the virtual valve <NUM> open is narrow, the "net-zero pressure" effect is weak, the auto-neutralization is incomplete, lowering the asymmetry, resulting in weak baseband signal or APPS effect.

In an FEM simulation, the device C00 can produce <NUM> dB SPL at <NUM>. From the FEM simulation, it is observed that, even though the SPL produced by the device C00 is about <NUM> dB lower than which produced by the device <NUM> (about <NUM> dB SPL at <NUM>), under the same driving condition, THD (total harmonic distortion) of the device C00 is <NUM>~<NUM> dB lower than which of the device <NUM>. Hence, the simulation validates the efficacy of the device C00, the APG device without cap structure or without chamber formed therewithin.

Please note that, the statement of the timing of VV opening being aligned to the timing of peak pressure within the chamber or peak velocity/acceleration of common mode membrane movement implicitly implies that a tolerance of ±e% is acceptable. That is, the case of the timing of VV opening being aligned to (<NUM>±e%) of peak pressure within the chamber or peak velocity/acceleration of common mode membrane movement is also within the scope of present invention, where e% may be <NUM>%, <NUM>% or <NUM>%, depending on practical requirement.

As for the pulse asymmetricity, <FIG> illustrates full-cycle pulses (within one operating cycle TCY) with different degrees of asymmetricity. In the present invention, degree of asymmetricity may be evaluated by a ratio of p<NUM> to p<NUM>, where p<NUM> > p<NUM>, p<NUM> represents a peak value of a first half-cycle pulse with a first polarity with respect to a level, and p<NUM> represents a peak value of a second half-cycle pulse with a second polarity with respect to the level. In acoustic area, the level may be corresponding to ambient condition, either ambient pressure (zero acoustic pressure) or zero acoustic airflow, where air pulses in the present invention may refer to either airflow pulses or air pressure pulses.

<FIG> illustrates a full-cycle pulse with r = p<NUM>/ p<NUM> > <NUM>%. The full-cycle pulse shown in <FIG> or with r = p<NUM>/ p<NUM> ≈ <NUM> has low degree of asymmetricity. <FIG> illustrates a full-cycle pulse with <NUM>% ≤ r = p<NUM>/ p<NUM> ≤ <NUM>%. The full-cycle pulse shown in <FIG> or with r = p<NUM>/ p<NUM> ≈ <NUM>% has median degree of asymmetricity. <FIG> illustrates a full-cycle pulse with r = p<NUM>/ p<NUM> < <NUM>%. The full-cycle pulse shown in <FIG> or with r = p<NUM>/ p<NUM> → <NUM> has high degree of asymmetricity.

As discussed in the above, the higher the degree of asymmetricity is, the stronger the APPS effect and baseband spectrum components of the ultrasonic air pulses will be. In the present invention, asymmetric air pulse refers to air pulse with at least median degree of asymmetricity, meaning r = p<NUM>/ p<NUM> ≤ <NUM>%.

Note that, the demodulation operation of the APG device of the present invention is to produce asymmetric air pulses according to the amplitude of ultrasonic air pressure variation, which is produced via the modulation operation. In one view, the demodulation operation of the present invention is similar to the rectifier in AM (amplitude modulation) envelope detector in radio communication systems.

In radio communication systems, as known in the art, an envelope detector, a kind of radio AM (noncoherent) demodulator, comprises a rectifier and a low pass filter. The envelope detector would produce envelope corresponding to input amplitude modulated signal thereof. The input amplitude modulated signal of the envelop detector is usually highly symmetric with r = p<NUM>/ p<NUM> → <NUM>. One goal of the rectifier is to convert the symmetric amplitude modulated signal such that rectified amplitude modulated signal is highly asymmetric with r = p<NUM>/ p<NUM> → <NUM>. After low pass filtering the highly asymmetric rectified AM signal, the envelope corresponding to the amplitude modulated signal is recovered.

The demodulation operation of the present invention, which turns symmetric ultrasonic air pressure variation (with r = p<NUM>/ p<NUM> → <NUM>) into to asymmetric air pulses (with r = p<NUM>/ p<NUM> → <NUM>), is similar to the rectifier of the envelope detector as AM demodulator, where the low pass filtering operation is left to natural environment and human hearing system (or sound sensing device such as microphone), such that sound/music corresponding to the input audio signal SIN can be recovered, perceived by listener or measured by sound sensing equipment.

It is crucial for the demodulation operation of the APG device to create asymmetricity. In the present invention, pulse asymmetric relies on proper timing of opening which is aligned to membrane (flaps) movement which generates the ultrasonic air pressure variation. Different APG constructs would have different methodology of timing alignment, as shown in <FIG> and <FIG>. In other words, a timing of forming the opening <NUM> is designated such that the plurality of air pulses produced by the APG device is asymmetric.

APG device producing asymmetric air pulses may also be applied to air pump/movement application, which may have cooling, drying or other functionality.

In addition, power consumption can be reduced by proper cell and signal route arrangement. For example, <FIG> illustrates a top view of an APG device D00 according to an embodiment of the present invention, and <FIG> illustrates a cross sectional view of the device D00 along an A-A' line shown in <FIG>. The device D00 comprises D01~D08 cells arranged in an array. Each cell (D0x) may be one of the APG devices (e.g., <NUM>~C00) stated in the above. In <FIG>, cap structures and subassemblies with conduit formed therein are omitted for brevity. Assume all the flaps in the device D00 are driven by the driving signal scheme <NUM>, where top electrodes receive either signal +SV or signal -SV and bottom electrodes receive SM-VBIAS.

In <FIG>, long rectangular elongating along Y direction represents flap or top electrode of the actuators disposed on the flap. Shaded in background may represent that bottom electrodes of the actuators are electrically connected.

In the device D00, flaps (e.g., <NUM>) receiving the signal -SV and flaps (e.g., <NUM>) receiving the signal +SV are spatially interleaved. For example, when the flap <NUM> of the cell D01 receives the signal +SV, the flap <NUM> of the cell D02 is suggested to receive the signal -SV. It is because when the signals +SV, -SV toggle polarity or during transition periods of the signals +SV, -SV, there will be capacitive load (dis)charging current flowing through the bottom electrode in X direction, and the effective resistance of the bottom electrode, RBT,P (where P refers to parallel current flow), will be low since L/W ≪ <NUM> and power consumption of the device D00 would be low, wherein L/W represents channel length/width in perspective of the (dis)charging current.

On the other hand, under a case that the driving signals -SV, +SV been wired in a pattern of {+SV, -SV}, {-SV, +SV}, {+SV, -SV}, {-SV, +SV}, {+SV, -SV}, {-SV, +SV}, {+SV, -SV}, {-SV, +SV} (not shown in <FIG>), where {. } designates a pair of differential driving signal for one cell D0x, the load (dis)charging current would be in Y direction, and the effective resistance of the bottom electrode, RBT,S (where s refers to series current flow), would be much higher (i.e., RBT,S ≫ RBTP, since L/W ≫ <NUM>) and power consumption of such scheme would be higher.

In other word, by utilizing the wiring scheme shown in <FIG>, (take cells D01 and D02 as an example,) given the flap <NUM> of the cell D01 receiving the signal +SV is spatially disposed next to the flap <NUM> of the cell D02 receiving the signal -SV and transition periods of the signals ±SV temporally overlap, the current from the bottom electrodes of one flap (e.g., <NUM> of D01) travels to a neighboring flap (e.g., <NUM> of D02) directly, without needing to leave the device D00 from a pad and reenter device D00 from another pad. Hence, effective resistance of the bottom electrode is reduced significantly, so is the power consumption.

In addition, operating frequency may be enhanced by incorporating multiple (e.g., <NUM>) cells. Specifically, the Air Pressure Pulse Speaker (APPS) sound producing scheme using APG devices of the present invention is a type of discrete time sampled system. On one hand, it is generally desirable to raise the sampling rate in such sampled system in order to achieve high fidelity. On the other hand, it is desirable to lower the operating frequency of the device in order to lower the required driving voltage and power consumption.

Instead of raising operating frequency as sampling rate for one APG device, it would be efficient to achieve high pulse/operating rate by interleaving (at least) two groups of (sub-systems) with low pulse/operating rate, temporally and spatially.

<FIG> (showing spatial arrangement) is a top view of an APG device E00 according to an embodiment of the present invention. The device E00 comprises two cells E11 and E12 disposed next/adjacent to each other. The cell E11/E12 may be one of the APG devices of the present invention.

<FIG> (showing temporal relationship) illustrates waveforms of two set of (de)modulation-driving signals, A and B, intended for the cells E11 and E12. The set A comprises demodulation-driving signal ±SV and modulation-driving signal SM; while the set B comprises demodulation-driving signal ±SV' and modulation-driving signal SM'. In the embodiment shown in <FIG>, the demodulation-driving signal +SV'/-SV' of the signal set B is a delayed version of the demodulation-driving signal +SV/-SV of the signal set A. Furthermore, the signal +SV'/-SV' of the signal set B is the signal +SV/-SV of the signal set A delayed by TCY/<NUM>, half of the operating cycle, where TCY = <NUM>/fUC and fUC represents operating frequency for cell E11/E12. The modulation-driving signal SM' of the set B may be viewed as an inverse of or a polarity inversion version of the modulation-driving signal SM of the set A. The signals SM and SM' may have a relationship of SM' = -SM or SM + SM' = C, where C is some constant or bias. For example, when the modulation-driving signal SM of the set A has a pulse with negative polarity with respect to a voltage level (shown as dashed line in <FIG>) within a time period T<NUM>, the modulation-driving signal SM' of the set B would have a pulse with positive polarity with respect to the voltage level (shown as dashed line in <FIG>) within the time period T<NUM>.

By providing one set of the sets A and B to the cell E11 and the other set of the sets A and B to the cell E12, the device E00 may produce pulse array with pulse/sampling rate as <NUM>×fUC and fUC is operating frequency for each cell.

<FIG> is a top view of an APG device F00 according to an embodiment of the present invention. The device F00 comprises cells F11, F12, F21 and F22, arranged in a <NUM>×<NUM> array. The cell in the device F00 may be one of the APG devices of the present invention. Two of the cells F11, F12, F21 and F22 may receive the signal set A, and the other two cells may receive the signal set B.

In an embodiment, the cells F11, F12 receive signal set A and the cells F21, F22 receive signal set B. In an embodiment, the cells F11, F22 receive signal set A and the cells F12, F21 receive signal set B. In an embodiment, the cells F11, F21 receive signal set A and the cells F12, F22 receive signal set B. Similar to the device E00, the device also produces pulse array with pulse/sampling rate as <NUM>×fUC.

Note that, conventional speaker (e.g., dynamic driver) using physical surface movement to generate acoustic wave faces problem of front-/back-radiating wave cancellation. When physical surface moves to cause airmass movement, a pair of soundwaves, i.e., front-radiating wave and back-radiating wave, are generated. The two soundwaves would cancel most of each other out, causing net SPL being much lower than the one that front-/back-radiating wave is measured alone.

Commonly adopted solution for front-/back-radiating wave canceling problem is to utilize either back enclosure or open baffle. Both solutions require physical size/dimension which is comparable to wavelength of lowest frequency of interest, e.g., wavelength as <NUM> meter of frequency as <NUM>.

Compared to conventional speaker, the APG device of the present invention occupies only tens of square millimeters (much smaller than conventional speaker), and produces tremendous SPL especially in low frequency.

It is achieved by producing asymmetric amplitude modulated air pulses, where the modulation portion produces symmetric amplitude modulated air pressure variation via membrane movement and the demodulation portion produces the asymmetric amplitude modulated air pulses via virtual valve. The modulation portion and the demodulation portion are realized by flap pair(s) fabricated in the same fabrication layer, which reduces fabrication/production complexity. The modulation operation is performed via common mode movement of flap pair and the demodulation operation is performed via differential mode movement of flap pair, wherein the modulation operation (via common mode movement) and the demodulation operation (via differential mode movement) may be performed by single flap pair. Proper timing alignment between differential mode movement and common mode movement enhances asymmetricity of the output air pulses. In addition, horn-shape outlet or trumpet-like conduit helps on improving propagation efficiency.

Claim 1:
An air-pulse generating device, comprising:
a film structure (<NUM>) and a subassembly;
wherein a conduit (<NUM>, <NUM>) is formed within the subassembly;
wherein the conduit comprises a first chamber (<NUM>, <NUM>), and a passageway (<NUM>, <NUM>);
wherein the film structure (<NUM>) is actuated such that the air-pulse generating device produces a plurality of air pulses;
characterised in that:
the conduit further comprises a horn-shaped outlet (<NUM>, <NUM>);
wherein the plurality of air pulses is propagated via the horn-shaped outlet;
wherein a dimension of the horn-shaped outlet is gradually widened from the film structure toward an ambient; and
wherein a height of the first chamber (H<NUM>) is less than a fifth of a wavelength corresponding to an operating frequency of the air-pulse generating device or a width of the first chamber (W<NUM>) is less than a half of the wavelength corresponding to the operating frequency of the air-pulse generating device.