SE545073C2

SE545073C2 - An acoustic system and method for controlling acoustic energy emitted from a parametric acoustic transducer array

Info

Publication number: SE545073C2
Application number: SE2151202A
Authority: SE
Inventors: Josef Hansson
Original assignee: Myvox Ab
Priority date: 2021-09-30
Filing date: 2021-09-30
Publication date: 2023-03-21
Also published as: WO2023055269A1; SE2151202A1

Abstract

An acoustic system contains a parametric acoustic transducer array (110, 210) emitting acoustic energy of periodically varying intensity in the form of a modulated acoustic signal (200) comprising a carrier wave (202) and an audible sound signal (204) modulated onto the carrier wave (202). The acoustic transducer array (110) includes a set of transducer elements (ei) arranged on a surface extending in at least two dimensions. The transducer elements (e,) are controllable in response to a control signal (C1, C2) so as to emit the acoustic energy at a wavelength and phase determined by the control signal (C1, C2). A controller (120) generates the control signal (C1, C2) such that the emitted acoustic energy forms a first directional beam of sound (B) having a first pressure maximum region (PMAX1) and a second directional beam of sound (B’) having a second pressure maximum region (PMAX2), wherein the relative strength between the first and second directional beams of sound (B, B’) is varied such that first pressure maximum region (PMAX1) has a first strength envelope signal, mg(t’), and the second pressure maximum region (PMAX2) has a second strength envelope signal, -mg(t’), that is in counter phase to the first envelope signal, mg(t’).

Description

AN ACOUSTIC SYSTEM AND METHOD FOR CONTROLLING ACOUSTIC ENERGY EMITTED FROM A PARAMETRIC ACOUSTIC TRANSDUCER ARRAY TECHNICAL FIELD The present invention relates generally to an acoustic system and method for controlling acoustic energy emitted from a parametric acoustic transducer array. Especially, the invention relates to a system and a corresponding computer- implemented method for controlling the acoustic energy from the parametric acoustic transducer array to be emitted as two beams of modulated acoustic energy. The invention also relates to a computer program and a non-volatile data carrier storing such a computer program.

BACKGROUND A parametric array, in the field of acoustics, is a nonlinear transduction mechanism that generates narrow, nearly side lobe-free beams of low frequency sound, through the mixing and interaction of high frequency sound waves, effectively overcoming the diffraction limit associated with linear acoustics. The main beam of low frequency sound is created as a result of nonlinear mixing of two high frequency sound beams at their difference frequency. Parametric arrays can be formed in water, air, and earth materials/rock. Using the principle of parametric arrays, an audible sound signal modulated onto an ultrasonic carrier wave will, during propagation in air, spontaneously demodulate, creating a virtual end-fire array of audible sources. ln effect, this creates a highly directional beam of sound. By modulating audio onto a carrier wave, for example an ultrasonics carrier wave, an end-fire virtual array of audible sources is created due to demodulation of the combined signal in the air due to nonlinear effects. lf the primary source consists of an array of transducers, it is possible to steer the beam by adjusting the phase delay of individual transducers. The audio envelope signal is typically amplitude modulated onto the carrier signal. This technology is for example described in the article "A review of parametric acoustic array in air", in Applied Acoustics, 73 (2012), by Gan, W-S., Yang, J., Kamakura, T.

The applications for parametric arrays, creating a highly directional beam of sound, arenumerous and include among others delivery of directional audible sound that is only audible to one person located in the correct position for receiving the directional beam of sound, but cannot be heard in the surroundings. A few non-limiting examples of when this is of interest are hands-free applications for vehicles, listening to music or talking over the phone in an open office environment or in public transport, information to museum visitors, presentation at fairs, etc.

There exist many solutions for how to apply directional, parametric, arrays to achieve audible sound in a specific location for applications such as the once mentioned herein. However, there are problems involved with the existing solutions. For ease of understanding, the problems are now described in connection with the specific application of controlling directional, parametric, arrays to achieve audible sound at the locations of two ears or a person. However, as described herein and as is apparent to a person skilled in the art, parametric arrays controlled in the manner of the present invention are useful in numerous other applications. ln prior art solutions wherein acoustic energy is emitted at frequencies around e.g. 40 kHz, a single beam from a parametric array is wide enough to reach both ears of the person. ln other words, this is a possible solution to the problem of how to achieve audible sound at the locations of two ears or a person. ln this case, there will be a one- to-one relationship between the parametric array and the person listening to the audio produced by the parametric array. lf higher frequencies are used, making the beam of the parametric array to narrow to reach both ears of a person at the same time, other solutions are needed. ln this case, in order to achieve audible sound at both ears, either two arrays may be used, and the beam of each array be controlled to reach a respective ear of the person, or a single array may be used, and beamforming applied to split one beam into two beams that are controlled to reach a respective ear of the person. ln the case of using two arrays the acoustic sound is delivered at each ear with the maximum, or close to the maximum, possible emitted output acoustic energy of each array. However, there is a problem in that driving the two arrays require double the input power of driving one corresponding array. Furthermore, using two arrays instead of one will double the cost for the units and increases the complexity of the system. ln the case of using one array and splitting the beam, the input power required to drive the array is half ofthat requiredto drive two corresponding arrays. However, the output acoustic energy delivered at each ear is only half, or less than half, of the maximum possible emitted output energy of the array. ln other words, the person listening will experience a much lower volume of the audio delivered at each ear in this scenario.

Clearly, there is a need for a solution that maximizes the amount of acoustic energy delivered to each of a listener's ears, while minimizing the amount of input power required to emit the acoustic energy. ln other applications, there is similarly a need for a solution that maximizes the amount of energy delivered to each of a two or more pressure maximum regions, while minimizing the amount of input power required to emit the energy.

SUMMARY The object of the present invention is to offer a solution that mitigates the above problem and renders it possible to maximize the amount of energy delivered to each of two or more pressure maximum regions, while minimizing the amount of input power required to emit the energy.

The inventor has realized that the problem can be solved by dividing or splitting a signal, e.g. an acoustic signal, emitted from a parametric array into two and control the relative strength of each beam in relation to the other. By varying the relative strength of the two beams, the strength of the first of the beams will obtain an envelope signal mg(t'), and the second beam will have the negative of the same envelope signal, - mg(t'), where g(t') contains the audio information and m is the modulation index. The envelope function g(t') can be the audio signal to be broadcasted, or a processed signal such that the reproduced audible sound has reduced distortion. The first and second beam will be emitted without losing much amplitude in either signal compared to a single beam, as the amplitude will vary such that one has a high amplitude as the other has a low amplitude. Rather than halving the signal strength compared with a single beam, each beam strength will have an amplitude of (2-m)/2*A_0, where A_0 is the amplitude of a single directional audio beam.

Thereby, the amount of energy delivered to each of the two pressure maximum regions is significantly higher than if the signal strength would be divided into two, or halved. ln fact amount of energy delivered to each of the two pressure maximum regions iscomparable to that received at each such region if two separate arrays are used. At the same time, the amount of input power required to emit the energy is significantly lower than that required to drive two arrays. lnstead, it will be substantially equal to, or close to, the input power required to driving the single array to emit a single beam at one pressure maximum region, depending on the system settings.

Aspects and embodiments of the invention, and advantages obtained, are described in further detail herein.

According to one aspect of the invention, the object is achieved by an acoustic system comprising a parametric acoustic transducer array and a controller. The parametric acoustic transducer array is configured to emit acoustic energy of periodically varying intensity in the form of a modulated acoustic signal comprising a carrier wave and an audible sound signal modulated onto the carrier wave. The parametric acoustic transducer array comprises a plurality of transducer elements which are controllable in response to a control signal so as to emit the acoustic energy at a wavelength and phase determined by the control signal. The controller is communicably connected to the acoustic transducer array and is configured to generate the control signal such that the emitted acoustic energy forms a first directional beam of sound having a first pressure maximum region and a second directional beam of sound having a second pressure maximum region. The controller is further configured to generate the control signal such that the relative strength between the first and second directional beams of sound is varied such that first pressure maximum region has a first strength envelope signal, mg(t'), and the second pressure maximum region has a second strength envelope signal, -mg(t'), that is in counter phase to the first envelope signal, mg(t'). ln other words, this will cause the first directional beam to be effectively amplitude modulated with the envelope signal mg(t') and the second directional beam to be effectively amplitude modulated with the inverse of the envelope signal -mg(t'). To the human ear these two modulated acoustic signals will sound identical. Thereby, if the first directional beam is directed to a first ear of a user and the second directional beam is directed to the second ear of the user, the user will perceive two equally strong signals, output without losing much amplitude compared to a single beam, providing the same audio information, using only the power needed to emit a single beam. This provides a great improvement in reduced power consumption without significant loss of output effect compared to previous solutions.

Another advantage is that in the invention, the acoustic system comprises a single acoustic transducer array. Thereby, a low complexity acoustic system is achieved.

According to one or more embodiment of this aspect of the invention, the parametric acoustic transducer array comprises micromachined ultrasonic transducer, MUT, elements configured to emit acoustic energy in the form of ultrasonic energy. Thereby, the acoustic system may advantageously be miniaturized. This enables application in for example handheld devices, such as mobile phones, and other applications which require small sized components.

According to one or more embodiment of this aspect of the invention, the parametric acoustic transducer array is a phased array. Suitably, a direct and simple generation and control of the acoustic-potential field is thereby enabled.

The controller may be configured to generate the control signal such that the first pressure maximum region and the second pressure maximum region are formed at a preset distance, d1, from each other. Thereby, the distance between the first pressure maximum region and the second pressure maximum region can be controlled to be generated at a preset distance selected according to the application to which they are intended. ln other words, the distance between the two modulated acoustic signals with human perceivable sound can be controlled. Advantageously, the preset distance, d1, may be set to any suitable value, depending on the application. ln some embodiments, the preset distance, d1, is set to 10 cm s d'| s 20 cm, and more preferably to 13 cm s d1 s 17 cm. ln a non-limiting example the distance d1 is preset to 15 cm. Advantageously, the exemplified distances and distance intervals correspond to the typical ear-to-ear distance of a human, thereby being suitable for the application of delivering acoustic sound to two ears of a user, by the first and second directional beams of sound. ln one or more embodiment of this aspect of the invention, the controller is configured to generate the control signal such that the acoustic energy is emitted at a frequency of 100-300 kHz, preferably 150-200 kHz. ln a non-limiting example, the controller is configured to generate the control signal such that the acoustic energy is emitted at a frequency of 160 kHz. Advantageously, the exemplified frequencies are suitable for the application of delivering acoustic sound to two ears of a user, by the first and second directional beams of sound. As an example, at or around the typical distance between the ears of a human two beams of acoustic energy at a lower frequency, for example around 40 kHz, the lobes would be so wide that there would be interference between the acoustic sound of the two beams. Since the beams are in counter phase, they would in this case be at risk of cancelling each other out, which means that the intended sound would not be perceived by the user.

According to one or more embodiment of this aspect of the invention, the transducer elements in the at least one acoustic transducer array are arranged in a first number of rows and a second number of columns. ln other words, the at least one acoustic transducer array has a general rectangular outline. Alternatively, the transducer elements in the parametric acoustic transducer array may be hexagonal in shape and be arranged in a hexagonal grid pattern. Thereby, an optimal packing/surface optimization of the acoustic transducer array elements in the acoustic transducer array is achieved.

The surface of the parametric acoustic transducer array may be flat. Thus, a simple and compact design is accomplished. Alternatively, the transducer elements may be arranged on a concave side of a spherical surface segment. This configuration facilitates concentrating high acoustic energies to each focal point.

According to another aspect of the invention, the object is achieved by a computer- implemented method for controlling the emission of audible sound from an acoustic system. The system comprises a parametric acoustic transducer array configured to emit acoustic energy of periodically varying intensity in the form of a modulated acoustic signal comprising a carrier wave and an audible sound signal modulated onto the carrier wave, wherein the parametric acoustic transducer array comprises a plurality of transducer elements. The transducer elements are controllable in response to a control signal, which is configured to cause the parametric acoustic transducer array to emit acoustic energy of periodically varying intensity at a wavelength and phase determined by the control signal. The system further comprises a controller communicably connected to the parametric acoustic transducer array. The method comprises generating the control signal, using the controller, such that the emitted acoustic energy forms a first directional beam of sound having a first pressure maximum region and a second directional beam of sound having a second pressure maximum region. Generating the control signal comprises generating it such that the relative strength between the first and second directional beams of sound is varied so as to cause the first pressure maximum region to have a first strength envelope signal, mg(t'), and the second pressure maximum region to have a second strength envelope signal, -mg(t'), that is in counter phase to the first envelope signal, mg(t').

The method involves generating a control signal which is configured to cause the parametric acoustic transducer array to emit acoustic energy of periodically varying intensity. lt is presumed that each of the at least one parametric acoustic transducer arrays contains a set of transducer elements arranged on a surface extending in two or three dimensions. l.e. transducer elements are located on a flat or a curved surface. lt is further presumed that the transducer elements are controllable in response to the control signal so as to emit the acoustic energy at a wavelength and a phase determi- ned by the control signal. The control signal is generated such that the emitted acoustic energy forms an acoustic-potential field of acoustic waves. ln some embodiments of this aspect of the invention the parametric acoustic transducer array is a micromachined ultrasonic transducer, MUT, and the method step of emitting acoustic energy by the parametric acoustic transducer array comprises emitting ultrasonic energy, wherein the modulated acoustic signal is a modulated ultrasonic signal and wherein the carrier wave is an ultrasonic carrier wave.

The method step of generating the control signal, by the controller, may comprise generating the control signal such that the first pressure maximum region and the second pressure maximum region are formed at a preset distance, d1 , from each other. The preset distance d1 is in some non-limiting embodiments set to 10 cm s d1 s 20 cm, preferably 13 cm s d'| s 17 cm, but any suitable distance value may be set depending on the application.

The method step of generating the control signal, by the controller, may comprise generating the control signal such that the acoustic energy is emitted at a frequency of 160 kHz.

According to a further aspect of the invention, the object is achieved by a computer program loadable into a non-volatile data carrier communicatively connected to a processor, or processing unit. The computer program includes software for executing the above method, according to any of the embodiments presented, when the program is run on the processing unit.

According to another aspect of the invention, the object is achieved by a non-volatile data carrier containing the above computer program.

Any advantages described herein for an embodiment of one aspects of the invention are equally applicable to the corresponding embodiments of the other aspects of the invenﬁon.

Further advantages, beneficial features and applications of the present invention will be apparent from the following description and the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is now to be explained more closely by means of preferred embodiments, which are disclosed as examples, and with reference to the attached drawings.

Figure 1A illustrates an example of controlling a parametric array to achieve audible sound in a specific location; Figure 1B illustrates an example of controlling a parametric array to achieve audible sound in a specific location; Figure 1C illustrates an example of controlling two parametric arrays to achieve audible sound in two specific locations; Figure 1D illustrates an example of controlling a parametric array to achieve audible sound in two specific locations; Figure 2 illustrates controlling a parametric array to achieve audible sound in two specific locations according to the invention; Figure 3 schematically shows an acoustic system according to a first embodiment of the invention; Figure4 schematically shows an acoustic system according to a second embodiment of the invention; and Figure 5 illustrates, by means of a flow diagram, a method according to one or more embodiment of the invention.

All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the respective embodiments, whereas other parts may be omitted or merely suggested. Any reference number appearing in multiple drawings refers to the same object or feature throughout the drawings, unless otherwise indicated. DETAILED DESCRIPTION Introduction Audio signals are herein defined as signals having frequencies in the audio frequency range of roughly 20 to 20,000 Hz, which corresponds to the lower and upper limits of human hearing.

All embodiments herein relating to audio signals refer to monaural or monophonic sound reproduction. Embodiments herein may be applied to stereophonic sound reproduction, but this would require further alterations of the presented solutions and a much higher energy consumption to provide a satisfactory result.

A distance is herein defined as a three-dimensional distance in space (x, y, z), unless otherwise specified.

Although the present disclosure is mainly focused on the division and control of relative strength of modulated audio signals, it is evident to a person skilled in the technical field of signal modulation that the division and control of relative strength may with slight modifications be applied to any amplitude modulated signal, for example radio signals, to achieve two separately directed beams conveying the same signal information, at the highest possible effect in the pressure maximum regions using the lowest possible energy consumption. The strength of the modulated signal herein typically refers to the amplitude of the modulated signal.

Turning first to Figs. 1A to 1D, there is shown examples of prior art solutions of controlling a parametric array to achieve audible sound in one or more specific location, having related problems as further described herein. All the illustrating examples are in the context of the application wherein acoustic sound is intended to be delivered to two ears of a user of an acoustic system. This example application is used because it is easy to illustrate, and a relevant application. However, as is evident to a person skilled in the art, the problems as well as the solutions presented herein are transferable to numerous other applications of controlling a parametric array to achieve two separately directed beams conveying the same signal information, at the highest possible effect in the pressure maximum regions using the lowest possible energy consumption. ln Fig. 1A, a single parametric acoustic transducer array 1 is configured to emit acoustic energy that forms a directional beam of sound B1 having a pressure maximum region P1. As is illustrated in the figure, the solution of directing one highly directional beam of sound B1 emitted from the single parametric acoustic transducer array 1 towards the center of the user's 10 head will lead to very little sound reaching either one of the user's 10 ears, since the beam B1 would be very narrow, especially at a higher frequency, e.g. in the interval of 100-300 kHz, or higher. ln this example, the energy consumption is low since only a single parametric acoustic transducer array is used. However, even though the acoustic energy in the pressure maximum region P1 is high since the parametric acoustic transducer array 1 is configured to emit the energy only at this region, little of the acoustic energy will reach the ears of the user 10 and the user 10 will therefore not be able to hear very much. ln likeness with Fig. 1A, Fig. 1B shows a single parametric acoustic transducer array 1 configured to emit acoustic energy that forms a directional beam of sound B2 having a pressure maximum region P2. ln this example the parametric acoustic transducer array 1 is controlled to emit the beam B2 such that the pressure maximum region P2 is formed at one of the user's 10 ears. Also in this example the energy consumption is low, since only a single parametric acoustic transducer array is used. The acoustic energy in the pressure maximum region P2 is also in this case high since the parametric acoustic transducer array 1 is configured to emit the energy only at the region P2, but only one ear is in focus of the sound beam. This means that the userwill be able to hear the audio well at one ear, but no sound will reach the other ear. ln Fig. 1C, two parametric acoustic transducer arrays 1, 2 are configured to each emit acoustic energy that forms a respective directional beam of sound B3, B4, which comprise the same signal information, having a respective pressure maximum region P3, P4 at a respective one of the user's 10 ears. ln this example, the acoustic energy in each of the pressure maximum regions P3 and P4 is high, since each parametric acoustic transducer array 1, 2 is configured to emit energy only at one respective region P3, P4. However, the energy consumption for driving the two arrays 1, 2 is double compared to driving the single array 1 in the examples of Figs. 1A and 1B. ln Fig. 1D, a single parametric acoustic transducer array 1 is configured to use beamforming to divide or split the emitted acoustic energy into two directional beams of sound B5, B6 having a respective pressure maximum region P5, P6 at a respective one of the user's 10 ears. ln this example, the same audio signal will reach, and can be heard at, each of the user's ears. However, the audio signal at each ear is emitted with only half the acoustic energy capacity of the parametric acoustic transducer array 1, whereby the volume/effect will be lower compared to e.g. the solution of Fig. 1C. Alternatively, the same volume of sound/effect may be conveyed from the single parametric acoustic transducer array 1 as from the two parametric acoustic transducer arrays 1, 2 of Fig. 1C in combination if the single array 1 is configured to emit the double amount of energy, but in that case the energy consumption for driving the single array 1 will also double.

As described herein, the object of the present invention is to offer a solution that renders it possible to maximize the amount of energy delivered to each of two (or more) pressure maximum regions, while minimizing the amount of input power required to emit the energy. System architecture Firstly, a system 100 according to embodiments of the invention will be described in connection with Figs. 2, 3 and ln Fig. 2, a solution according to embodiments of the present invention for controlling a single parametric array to achieve audible sound in two specific locations, which renders it possible to maximize the amount of energy delivered to each of the two pressure maximum regions generated, while minimizing the amount of input powerrequired to emit the energy. ln Iikeness with the prior art solution in Fig. 1D, Fig. 2 illustrates that a single parametric acoustic transducer array 110, 210 is controlled to use beamforming to divide or split the emitted acoustic energy into two directional beams of sound B, B' having a respective pressure maximum region Pil/m, PMAXZ at a respective one of the user's 10 ears. ln other words, the parametric acoustic transducer array 110, 210 is configured to emit acoustic energy of periodically varying intensity based on the control signal C1, C2 to form a first and second directional beam of sound B, B' having a first and second pressure maximum region PiviAx1, PMAXZ. ln contrast to in the solution of Fig. 1D, the parametric acoustic transducer 110, 210 according to embodiments of the invention is further configured to emit the acoustic energy, based on a control signal C1, C2, such that the relative strength between the first and second directional beams of sound B, B' is varied so that the first pressure maximum region PiviA><1 has a first strength envelope signal, mg(t'), and the second pressure maximum region PMA><2 has a second strength envelope signal, -mg(t'), that is in counter phase to the first strength envelope signal, mg(t').

The pressure maximum regions may also be referred to as first and second acoustic lobes, which are created around first and second focal points where the emitted acoustic energy is constructively combined.

By modulation of the amplitude of the respective first and second directional beams of sound B, B' according to the present invention, control of the relative amplitude between the first and second directional beams of sound B, B' is enabled. As described herein, the parametric acoustic transducer 110, 210 is controlled to emit acoustic energy at the same effect over time, typically full effect or possibly another selected effect level, and controlled to vary which amount of that energy that is emitted into the first and second directional beams of sound B, B', respectively such that the first pressure maximum region PiviA><1 has a first strength envelope signal, mg(t'), and the second pressure maximum region PMAXZ has a second strength envelope signal, - mg(t'), that is in counter phase to the first strength envelope signal, mg(t'). Thereby, the relative amplitude between the first and second directional beams of sound B, B' will be inverted, in counter phase. ln other words, one of the first and second directional beams of sound B, B' will convey the audible sound signal 204 (or other information signal) modulated onto the carrier wave 202 in its original form, and the other of the first and second directional beams of sound B, B' will convey the inversion/counterphase version of the audible sound signal 204 (or other information signal) modulated onto the carrier wave 202. To the human ear, sound and counter-sound is perceived as exactly the same, so this enables the user to hear the same audio information in both ears at the same time. Advantageously, the sound will also reach each ofthe ears of the user 10 at full, or close to full, effect, while the energy consumption for driving the single array 110, 210 is not increased compared to emitting only a single beam of sound, thereby solving the problems of the prior art solutions. ln the application of producing audible sound at the two ears of a user of the system, the envelope signal of the information signal/audible sound signal is typically amplitude modulated onto the carrier signal.

The splitting/dividing into two beams of sounds will result in bigger and stronger side lobes than if the beam was not split. However, in the application of delivering sound to the two ears of a user this will not interfere significantly with the user's sound experience because the relative amplitude will vary at a higher degree in the main lobes of the first and second directional beams of sound B, B' than in any of their side lobes, and it is the variation that renders audible sound. Therefore, the directionality and experienced sound quality of the directional beams of sound B, B' is not negatively affected, or at least not significantly negatively affected. At the intended distances and frequencies of the selected applications, which may be preset, selected and/or adjusted by the user in some embodiments, the audible sound of the first and second directional beams of sound B, B' will not interfere with each other in the first pressure maximum region PMA><1 and the second pressure maximum region PiviA><2. Between and outside of the first pressure maximum region PMA><1 and the second pressure maximum region PMA><2 the audible sound of the first and second directional beams of sound B, B' will instead interfere destructively, which is positive for the directionality as the sound can only be heard in the intended pressure maximum regions. lt is further noted that it is only the envelope function that is inverted between the two directional beams of sound B, B'. The carrier wave from the array is always in phase, or nearly in phase, so the carrier wave will not cause any destructive interference, or at least no significant destructive interference.

Fig. 3 shows an acoustic system 100 according to a first embodiment of the invention.The system 100 includes a parametric acoustic transducer array 110 and a controller 120. The parametric acoustic transducer array 110 is configured to emit acoustic energy of periodically varying intensity in the form of a modulated acoustic signal 200 comprising a carrier wave 202 and an audible sound signal 204 modulated onto the carrier wave 202. The parametric acoustic transducer array 110 comprises a plurality of transducer elements ei, the transducer elements e; being controllable in response to a control signal C1, C2 so as to emit the acoustic energy at a wavelength and phase determined by the control signal C1, C2. The controller 120 is communicably connected to the acoustic transducer array 110 and is configured to generate the control signal C1, C2 such that the emitted acoustic energy forms a first directional beam of sound B having a first pressure maximum region PMA><1 and a second directional beam of sound B' having a second pressure maximum region PiviA><2, wherein the relative strength between the first and second directional beams of sound B, B' is varied such that the first pressure maximum region PMA><1 has a first strength envelope signal, mg(t'), and the second pressure maximum region PMA><2 has a second strength envelope signal, -mg(t'), that is in counter phase to the first envelope signal, mg(t'). ln other words, audio reaching the different ears of a user of the system will have opposite phase. Thereby, if the first directional beam is directed to a first ear of a user and the second directional beam is directed to the second ear of the user, the user will perceive two equally strong signals, output without losing much amplitude compared to a single beam, providing the same audio information, using only the power needed to emit a single beam.

The acoustic transducer array 110 includes a set of transducer elements e; arranged on a surface. Here, the surface is flat and the transducer elements e; may be arranged in a first number of rows and a second number of columns. Alternatively, the transducer elements in the parametric acoustic transducer array may be hexagonal in shape and be arranged in a hexagonal grid pattern. Thereby, an optimal packing/surface optimization of the acoustic transducer array elements in the acoustic transducer array is achieved. Both alternatives render it comparatively straightfonNard to control the transducer elements e; to emit the acoustic energy. Namely, the transducer elements ei are controllable in response to a control signal C1, C2 so as to emit the acoustic energy at a wavelength and a phase determined by the control signal C.Fig. 4 shows an acoustic system 100 according to a second embodiment of the invention. Here, the transducer elements e; in the acoustic transducer array 210 are arranged on a concave side of a spherical surface segment, i.e. a surface extending in three dimensions. The transducer elements e; may be arranged in any suitable way on the spherical surface, for example but not limited to hexagonal transducer elements ei arranged in a hexagonal grid pattern The three-dimensional configuration on the concave side of a spherical surface segment is advantageous because it enables a higher concentration of acoustic energy towards first and second pressure maximum region PMA><2 than if the acoustic transducer array had extended along a flat, two- dimensional, surface.

The parametric acoustic transducer array 110, 210 in any embodiment of the system 100 may be a micromachined ultrasonic transducer, MUT, configured to emit acoustic energy in the form of ultrasonic energy, wherein the modulated acoustic signal 200 is a modulated ultrasonic signal and wherein the carrier wave 202 is an ultrasonic carrier wave. Thereby, the acoustic system may advantageously be miniaturized. This enables application in for example handheld devices, such as mobile phones, and other applications which require small sized components. ln some of these embodiments, the parametric acoustic transducer array may comprise piezoelectric micromachined ultrasonic transducer, pMUT, elements configured to emit acoustic energy in the form of ultrasonic energy. Thereby, the acoustic system may advantageously be miniaturized, and the power consumption may further be reduced, which even further enables use of the acoustic system in for example handheld devices, such as mobile phones, and other applications which require both low power consumption and small sized components.

The parametric acoustic transducer array 110, 210 may a phased array, enabling direct and simple generation and control of the generated acoustic-potential field. ln any embodiment of the system 100, the controller 120 may be configured to generate the control signal C1, C2 such that the first pressure maximum region PiviAx1 and the second pressure maximum region PMA><2 are formed at a preset distance, d1, from each other. Thereby, the distance between the first pressure maximum region and the second pressure maximum region can be controlled to be generated at a preset distance selected according to the application to which they are intended. ln a non-Iimiting embodiment, the preset distance, d1, is set to 10 cm s d1 s 20 cm, preferably 13 cm s d1 s 17 cm. ln a non-Iimiting example the distance d1 is preset to 15 cm. Advantageously, the exemplified distances and distance intervals correspond to the typical ear-to-ear distance of a human, thereby being suitable for the application of delivering acoustic sound to two ears of a user, by the first and second directional beams of sound.

The distance d1 may be defined as the distance between the center of the first pressure maximum region PiviA><1 and the second pressure maximum region PiviA><2, the distance between the focal points around which the first pressure maximum region PiviA><1 and the second pressure maximum region PiviA><2 are formed, or any other selected point on each of the first pressure maximum region PiviA><1 and the second pressure maximum region PiviA><2 are formed, e.g. the points on their periphery that provides the shortest or longest distance between the first pressure maximum region PiviA><1 and the second pressure maximum region PMAXZ. ln some embodiments, the distance d1 may be dependent on the distance between the center of the first pressure maximum region PiviA><1 and the second pressure maximum region PiviAx2 or the position of the focal points but be set to a value that is higher than the actual distance to further reduce the risk of interference between the first and second directional beam of sound B, B'. The controller 120 may apply any algorithm that allows for generating a control signal C1, C2 that is configured to cause the plurality of transducer elements ei of the parametric acoustic transducer array 110, 210 to emit acoustic energy of periodically varying intensity at a wavelength and phase determined by the control signal C1, C2 such that the emitted acoustic energy forms a first directional beam of sound B having a first pressure maximum region PiviA><1 and a second directional beam of sound B' having a second pressure maximum region PiviA><2, wherein the relative strength between the first and second directional beams of sound B, B' is varied such that first pressure maximum region PiviA><1 has a first strength envelope signal, mg(t'), and the second pressure maximum region PiviA><2 has a second strength envelope signal, -mg(t'), that is in counter phase to the first envelope signal, mg(t'). ln any embodiment of the system 100, the controller 120 may be configured to generate the control signal C1, C2 such that the acoustic energy is emitted at a frequency in the interval of 100-300 kHz, preferably in the interval of 150-200 kHz, including the end points of each interval. ln a non-Iimiting example, the controller isconfigured to generate the control signal such that the acoustic energy is emitted at a frequency of 160 kHz. Advantageously, the exemplified frequencies are suitable for the application of delivering acoustic sound to two ears of a user, by the first and second directional beams of sound. As an example, at or around the typical distance between the ears of a human two beams of acoustic energy at a lower frequency, for example around 40 kHz, the lobes would be so wide that there would be interference between the acoustic sound of the two beams. Since the beams are in counter phase, they would in this case be at risk of cancelling each other out, which means that the intended sound would not be perceived by the user. For other applications, wherein the distance d1 is more suitably set to a greater value, a lower frequency may be considered. ln any embodiment of the system 100, the controller 120 may be configured to generate the control signal C1, C2 such that the acoustic energy is emitted at a lower frequency than the ones exemplified above, for example but not limited to 40 kHz or thereabout, thereby generating wider first and second directional beams of sound B, B'. ln these embodiments, the locations of the first and second pressure maximum regions PiviAxt, PMAXZ to which the first and second directional beams of sound B, B', respectively, are directed at locations further apart than the two ears of a person, in order to avoid destructive interference between the first and second directional beams of sound B, B'. For example, the first and second directional beams of sound B, B' may be controlled to be directed at a first and second person standing a suitable distance apart from each other, such that the first person hears the acoustic signal having the first strength envelope signal, mg(t'), and the second person hears the acoustic signal having the second strength envelope signal, -mg(t'). Both persons will perceive that the same, in phase, sound is delivered to them and the advantages of maximizing the amount of energy delivered to each of the two or more pressure maximum regions, while minimizing the amount of input power required to emit the energy, is achieved also by these embodiments. To determine the location of the persons at which the first and second directional beams of sound B, B' should be directed, any suitable method for detection or tracking of a human face, feature recognition, motion tracking, or the like may be used, for example but not limited to those detection and tracking methods mentioned herein in connection with determining the location or position of one or more Gal".ln any embodiment, the system 100 may further comprise an input device 130 communicatively connected to the controller 120. The controller 120 may in these embodiments be configured to receive an input signal indicative of a distance value from the input device 130, and in response to receiving the input signal be configured to set or adjust the distance d1 based on the received distance value. Suitably, the preset distance, d1, may thereby be adjusted to optimize it to a changed position of one or both optimal positions for generation of the first and second pressure maximum regions PiviA><1, PMAXZ, respectively, such as e.g. a changed position of one or both ears of a user of the acoustic system. Furthermore, the distance d1 may, in the same application of the system, advantageously be adjusted based on differences in ear-to- ear distance, or a measurement from which this information can be derived, between different users of the system 100, thereby optimizing the acoustic experience for the current user of the system 100. ln some embodiments, the input device 130 may be configured to receive manual input whereby a user of the system 100 is enabled to interact with the input device 130 to manually input a selected value for the distance d1, or a distance change parameter indicating to the controller how the distance d1 should be adjusted. Alternatively, or additionally, the input device 130 may be configured to receive input from one or more distance measure device configured to identify in three dimensions one or both optimal positions for the first and second pressure maximum regions, Pil/m, PMAXZ, respectively, such as e.g. one or both ears of a user. Such a distance measure device may use ultrasound, laser, imaging and/or any other suitable technique known in the art. ln some embodiments, the three- dimensional position of the user's ears, e.g. the distance and angle at which each of the user's ear is located in relation to the parametric acoustic transducer array 110, 210, may be determined using any suitable technique known in the art, for example a head tracking technique. ln these embodiments, the controller 120 may be configured to generate the control signal C1, C2 such that the emitted acoustic energy forms a first directional beam of sound B having a first pressure maximum region PiviA><1 at the first determined location, i.e. at or close to the first ear of the user, and a second directional beam of sound B' having a second pressure maximum region PMAXZ, at the second determined location, i.e. at or close to the second ear of the user. The controller 120 may be configured to generate the control signal C1, C2 based on the determination of the three dimensional locations of the ears (or other points in space at which the audible sound is to be generated depending on the application), based onthe preset distance d1, based on a detected distance change, or any combination of these parameters. lt is generally advantageous if the controller 120 is configured to effect the above- described procedure in an automatic manner by executing a computer program 127. Therefore, the controller 120 may include a memory unit 125, i.e. non-volatile data carrier, storing the computer program 127, which, in turn, contains software for making processing circuitry in the form of at least one processor 123 in the controller 120 exe- cute the actions mentioned in this disclosure when the computer program 127 is run on the at least one processor 123. ln one or more embodiment, the invention may therefore comprise a computer program 127 loadable into a non-volatile data carrier 125 communicatively connected to a processor 123, the computer program 127 comprising software for executing the method according any of the method embodiments presented in connection with Fig. 5 when the computer program 127 is run on the processor 123. Furthermore, the invention may comprise a non-volatile data carrier 125 containing the computer program Method embodiments With reference to the flow diagram in Fig. 5, and also with reference to Figs. 2 to 4 as described above, we will now describe a computer-implemented method for controlling the emission of audible sound from an acoustic system 100 comprising a parametric acoustic transducer array 110, 210 and a controller 120 communicably connected to the parametric acoustic transducer array 110, 210, according to one or more embodiment of the invention. The method comprises: ln step 510: generating, by the controller 120, a control signal C1, C2 which is configured to cause the parametric acoustic array 110, 210 to emit acoustic energy of periodically varying intensity. lt is presumed that the parametric acoustic transducer array 110, 210 is configured to emit acoustic energy of periodically varying intensity in the form of a modulated acoustic signal 200 comprising a carrier wave 202 and an audible sound signal 204 modulated onto the carrier wavelt is also presumed that each of the at least one acoustic transducer arrays contains a set of transducer elements arranged on a surface extending in two or three dimensions. |.e. transducer elements are located on a flat or a curved surface. lt is further assumed that the parametric acoustic transducer array 110, 210 comprises a plurality of transducer elements ei, that are controllable in response to a control signal C1, C2 to emit acoustic energy of periodically varying intensity at a wavelength and phase determined by the control signal C1, C The control signal is generated such that the emitted acoustic energy forms a first directional beam of sound B having a first pressure maximum region PiviA><1 and a second directional beam of sound B' having a second pressure maximum region PiviA><2, wherein the relative strength between the first and second directional beams of sound B, B' is varied such that first pressure maximum region PiviA><1 has a first strength envelope signal, mg(t'), and the second pressure maximum region PiviA><2 has a second strength envelope signal, -mg(t'), that is in counter phase to the first envelope signal, mg(t').

Generating the control signal C1, C2, by the controller, may comprise generating the control signal C1, C2 such that the first pressure maximum region PiviA><1 and the second pressure maximum region PiviA><2 are formed at a preset distance, d1, from each other. The preset distance d1 is in some non-limiting embodiments set to 10 cm s d1 s 20 cm, preferably 13 cm s d1 s 17 cm, but any suitable distance value may be set depending on the application. Generating the control signal C1, C2 may in these embodiments comprise receiving, from an input device 130 communicatively connected to the controller 120, an input signal indicative of a distance value, and in response to receiving the input signal setting or adjusting the distance d1 based on the received distance value. Suitably, the preset distance, d1, may thereby be adjusted to optimize it to a changed position of one or both optimal positions for generation of the first and second pressure maximum regions PiviAx1, PiviA><2, respectively, such as e.g. a changed position of one or both ears of a user of the acoustic system. ln some embodiments, the method may comprise receiving, in the input device 130, manual input from a user or operator of the system 100 indicative of a selected value for the distance d1, or a distance change parameter indicating to the controller 120 how the distance d1 should be adjusted. Alternatively, or additionally, the method may comprise receiving, in the input device 130, input from one or more distance measure device configured to identify in three dimensions one or both optimal positions for the first and second pressure maximum regions, PMA><1, PMAXZ, respectively, such as e.g. detecting one or both ears of a user. Such a distance measure device may use uitrasound, laser, imaging and/or any other suitable technique known in the art. ln some embodiments, the three-dimensional position of the user's ears, e.g. the distance and angle at which each of the user's ear is located in relation to the parametric acoustic transducer array 110, 210, may be determined using any suitable technique, for example a head tracking technique, known in the art. ln these embodiments, generating the control signal C1, C2 in step 510, by the controller 120, may comprise generating the control signal C1, C2 such that the emitted acoustic energy forms a first directional beam of sound B having a first pressure maximum region PMA><1 at the first determined location, i.e. at or close to the first ear of the user, and a second directional beam of sound B' having a second pressure maximum region PMA><2, at the second determined location, i.e. at or close to the second ear of the user. Generating the control signal C1, C2, by the controller 120, may in these embodiments be based on the determination of the three dimensional locations of the ears (or other points in space at which the audible sound is to be generated depending on the application), based on the preset distance d1, based on a detected distance change, or any combination of these parameters.

The method may further comprise adjusting, by the controller 120, the distance d1 based on differences in ear-to-ear distance, or a measurement from which this information can be derived, between different users of the system 100, thereby optimizing the acoustic experience for the current user of the system ln one or more embodiments, generating the control signal, by the controller, may comprise generating the control signal such that the acoustic energy is emitted at a frequency of 160 kHz. Other suitable frequencies may be selected depending on the application. ln a subsequent step 520, the at least one acoustic transducer array emits acoustic energy, which acoustic energy has a wavelength and a phase delay determined by the control signal. ln embodiments wherein the parametric acoustic transducer array is a micromachined ultrasonic transducer, MUT, the modulated acoustic signal is a modulated ultrasonicsignal, and the carrier wave is an ultrasonic carrier wave. ln these embodiments, step 520 of emitting acoustic energy by the parametric acoustic transducer array 110, 210 comprises emitting ultrasonic energy.

Further embodiments All of the process steps, as well as any sub-sequence of steps, described with reference to Fig. 5 may be controlled by means of a programmed processor. Moreover, although the embodiments of the invention described above with reference to the drawings comprise processor and processes performed in at least one processor, the invention thus also extends to computer programs, particularly computer programs on or in a carrier, adapted for putting the invention into practice. The program may be in the form of source code, object code, a code intermediate source and object code such as in partially compiled form, or in any other form suitable for use in the implementation of the process according to the invention. The program may either be a part of an operating system or be a separate application. The carrier may be any entity or device capable of carrying the program. For example, the carrier may comprise a storage medium, such as a Flash memory, a ROM (Read Only Memory), for example a DVD (Digital VideoNersatile Disk), a CD (Compact Disc) or a semiconductor ROM, an EP- ROM (Erasable Programmable Read-Only Memory), an EEPROM (Electrically Erasable Programmable Read-Only Memory), or a magnetic recording medium, for example a floppy disc or hard disc. Further, the carrier may be a transmissible carrier such as an electrical or optical signal which may be conveyed via electrical or optical cable or by radio or by other means. When the program is embodied in a signal, which may be conveyed, directly by a cable or other device or means, the carrier may be constituted by such cable or device or means. Alternatively, the carrier may be an integrated circuit in which the program is embedded, the integrated circuit being adapted for performing, or for use in the performance of, the relevant processes.

Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

The term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps, or components. The term does not preclude the presence or addition of one or more additional elements, features, inte-gers, steps or components or groups thereof. The indefinite article "a" or "an" does not exclude a plurality. ln the claims, the word "or" is not to be interpreted as an exclusive or (sometimes referred to as "XOR"). On the contrary, expressions such as "A or B" covers all the cases "A and not B", "B and not A" and "A and B", unless otherwise indicated. The mere fact that certain measures are recited in mutually different dependent c|aims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the c|aims should not be construed as Iimiting the scope. lt is also to be noted that features from the various embodiments described herein may freely be combined, unless it is explicitly stated that such a combination would be unsuitable.

The invention is not restricted to the described embodiments in the figures but may be varied freely within the scope of the claims.

Claims

1. An acoustic system (100) comprising: a parametric acoustic transducer array (110, 210) configured to emit acoustic energy of periodically varying intensity in the form of a modulated acoustic signal (200) comprising a carrier wave (202) and an audible sound signal (204) modulated onto the carrier wave (202), wherein the parametric acoustic transducer array (110, 210) comprises a plurality of transducer elements (ei), the transducer elements (ei) being controllable in response to a control signal (G1, G2) so as to emit the acoustic energy at a wavelength and phase determined by the control signal (G1, G2); and a controller (120) communicably connected to the acoustic transducer array (110, 210), the controller (120) being configured to generate the control signal (G1, G2) such that the emitted acoustic energy forms a first directional beam of sound (B) having a first pressure maximum region (PiviAx1) in the form of a first acoustic lobe created around a first focal point where the emitted acoustic energy of the first directional beam of sound (B) is constructively combined and a second directional beam of sound (B') having a second pressure maximum region (PMAX2) in the form ofa second acoustic lobe created around a second focal point where the emitted acoustic energy of the second directional beam of sound (Bj) is constructively combined, and wherein the relative amplitude between the first and second directional beams of sound (B, B') is varied such that the first pressure maximum region (PiviAx1) has a first amplitude envelope signal, mg(t'), and the second pressure maximum region (PiviAx2) has a second amplitude envelope signal, -mg(t'), that is in counter phase to the first envelope signal, mg(t').

2. The acoustic system (100) of claim 1, wherein the parametric acoustic transducer array (1 10, 210) is a micromachined ultrasonic transducer, MUT, configured to emit acoustic energy in the form of ultrasonic energy, wherein the modulated acoustic signal (200) is a modulated ultrasonic signal and wherein the carrier wave (202) is an ultrasonic carrier wave. _ The acoustic system (100) of claim 1 or 2, wherein the parametric acoustic transducer array (110, 210) is a phased array. _ The acoustic system (100) according to any one of the preceding claims, wherein the controller (120) is configured to generate the control signal (C1, C2) such that the first pressure maximum region (PiviAx1) and the second pressure maximum region (PMAX2) are formed at a preset distance, d1, from each other. _ The acoustic system (100) of claim 4, wherein the preset distance, d1, is set tocm s d1 s 20 cm, preferably 13 cm s d1 s 17 cm. _ The acoustic system (100) according to any one of the preceding claims, further comprising an input device (130) communicatively connected to the controller (120), wherein the input device (130) is configured to receive information from one or more distance measurement devices on a first three dimensional position at which the first directional beam of sound (B) should be directed and a second three dimensional position at which the second directional beam of sound (B') should be directed, and wherein the controller (120) is configured to generate the control signal (C1, C2) based on the first three dimensional position at which the first directional beam of sound (B) should be directed and second three dimensional position at which the second directional beam of sound (B') should be directed such that the emitted acoustic energy forms the first directional beam of sound (B) to have the first pressure maximum region (PiviAx1) at the first determined position, and the second directional beam of sound (B') to have the second pressure maximum region (PiviAx2) at the second determined position. _ The acoustic system (100) according to any one of the preceding claims, wherein the controller (120) is configured to generate the control signal (C1, C2) such that the acoustic energy is emitted at a frequency of 100-300 kHz, preferably 150-200 kHz. The acoustic system (100) according to any one of the preceding claims, wherein the transducer elements (ei) in the parametric acoustic transducer array (110) are arranged in a first number of rows and a second number of columns. The acoustic system (100) according to any one of the claims 1 to 7, wherein the transducer elements (ei) in the parametric acoustic transducer array (110) are hexagonal in shape and are arranged in a hexagonal grid pattern. 10.The acoustic system (100) according to any one of the preceding claims, whereinthe transducer elements (ei) in the parametric acoustic transducer array (210) are arranged on a concave side of a spherical surface segment. .A computer-implemented method for controlling the emission ofaudible sound from an acoustic system (100), the system (100) comprising a parametric acoustic transducer array (110, 210) configured to emit acoustic energy of periodically varying intensity in the form of a modulated acoustic signal (200) comprising a carrier wave (202) and an audible sound signal (204) modulated onto the carrier wave (202), wherein the parametric acoustic transducer array (1 10, 210) comprises a plurality of transducer elements (ei), the transducer elements (ei) being controllable in response to a control signal (C1, C2), which is configured to cause the parametric acoustic transducer array (110, 210) to emit acoustic energy of periodically varying intensity at a wavelength and phase determined by the control signal (C1, C2), and a controller (120) communicably connected to the parametric acoustic transducer array (110, 210), the method comprising: generating, by the controller (120), the control signal (C1, C2) such that the emitted acoustic energy forms a first directional beam of sound (B) having a first pressure maximum region (PiviAx1) in the form of a first acoustic lobe created around a first focal point where the emitted acoustic energy of the first directional beam of sound (B) is constructively combined and a second directional beam of sound (B') having a second pressure maximum region (PiviAx2) in the form of a second acoustic lobe created around a second focal point where the emitted acoustic energy of the second directional beam of sound (Bj) is constructively combined, wherein the relative amplitude between the first and second directional beams of sound (B, B') is varied such that first pressure maximum region (PiviAx1) has a first amplitude envelope signal, mg(t'), and the second pressure maximum region (PMAX2) has a second amplitude envelope signal, -mg(t'), that is in counter phase to the first envelope signal, mg(t'). 12.The method of claim 11, wherein the parametric acoustic transducer array (110, 210) is a micromachined ultrasonic transducer, MUT, wherein emitting acoustic energy by the parametric acoustic transducer array (110, 210) comprises emitting ultrasonic energy, wherein the modulated acoustic signal (200) is a modulated ultrasonic signal and wherein the carrier wave (202) is an ultrasonic carrier wave. 13.The method of any of the claims 11 or 12, wherein generating the control signal (C1, C2), by the controller (120), comprises generating the control signal (C1, C2) such that the first pressure maximum region (PiviAx1) and the second pressure maximum region (PiviAx2) are formed at a preset distance, d1, from each other. 14.The method of claim 13, wherein the preset distance d1 is set to 10 cm s d1 scm, preferably 13 cm s d1 s 17 cm. 15.The method of any of the claims 11 to 14, further comprising receiving, via an input device (130) communicatively connected to the controller (120), information from one or more distance measurement devices on a first three dimensional position at which the first directional beam of sound (B) should be directed and a second three dimensional position at which the second directional beam of sound (B') should be directed, wherein generating the control signal (C1, C2), by the controller (120), comprises generating the control signal (C1, C2) based on the first three dimensional position at which the first directional beam of sound (B) should be directed and second three dimensional position at which the second directional beam of sound (B') should be directed such that the emitted acoustic energy forms the first directional beam of sound (B) to have the first pressure maximum region (PiviAx1) at the first determined position, and the second directional beam of sound (B') to have the second pressure maximum region (PMAX2) at the second determined position. 16.The method of any one of the ciaims 11 to 15, wherein generating the control signal (C1, C2), by the contro||er (120), comprises generating the control signal (C1, C2) such that the acoustic energy is emitted at a frequency of 160 kHz. 17.A computer program (127) Ioadable into a non-volatile data carrier (125) communicatively connected to a processor (123), the computer program (127) comprising software for executing the method according any of the ciaims 11 towhen the computer program (127) is run on the processor (123). 18.A non-volatile data carrier (125) containing the computer program (127) of the claim 17.