Method for operating a thermoacoustic sound generator, method for generating an acoustic signal

Abstract

The invention relates to a method for operating a thermoacoustic sound generator (4), comprising: providing an audio signal (16) having an oscillation S, an amplitude A and an oscillation duration T; converting the audio signal (16) into a frequency domain (18); halving the frequencies f in of the audio signal (16) to generate a modified audio signal (20) having halved frequencies f out ; converting the modified audio signal (20) into a time domain (22). The invention also relates to a method for generating an acoustic signal, in particular an otoacoustic stimulus signal (14), by means of a thermoacoustic sound generator (4), comprising receiving a modified audio signal (20) having frequencies f out and doubling the frequencies f out . The invention also relates to a microelectromechanical system (1) comprising a thermoacoustic sound generator (4) and an operating device (6), in particular a microelectromechanical biometric authentication device (2). It also relates to an in-ear device (200) comprising a microelectromechanical biometric authentication device (2). Furthermore, the invention also relates to the use of a microelectromechanical system (1) in a device for biometrically authenticating an authorized user.

Description

Technical Field

[0001] This invention relates to a method for controlling a thermoacoustic generator, wherein the method comprises: providing an audio signal having an oscillation S, an amplitude A, and an oscillation duration T; converting the audio signal to the frequency domain; and converting the frequency f of the audio signal... in Halve the frequency f to produce the modified audio signal. out ; and converting the modified audio signal to the time domain.

[0002] The present invention also relates to a method for generating acoustic signals, particularly otoacoustic stimulation signals, via a thermoacoustic generator, comprising: obtaining a signal having a frequency f out The modified audio signal and the frequency f out Frequency multiplication is performed.

[0003] The present invention also relates to a microelectromechanical system (MEMS) including a thermoacoustic generator and a control device, particularly a MEMS bio-authentication device, and to an in-ear device including a bio-authentication device according to the present invention.

[0004] Furthermore, the present invention also relates to the application of the microelectromechanical system according to the invention in devices for biometric authentication of authorized users. Background Technology

[0005] In the field of loudspeakers and microphones, various types of transduction principles are used to realize driving and sensing devices. Electromagnetic, electrostatic, and piezoelectric concepts can be applied to both driving and sensing devices. Optical or spintronic methods are mostly used only in microphones, while thermoacoustic transduction is used only in loudspeakers, especially miniature loudspeakers.

[0006] Electromagnetic, electrostatic, and piezoelectric principles cause the diaphragm of a loudspeaker to vibrate mechanically to generate pressure waves. In thermoacoustics, sound is generated by applying an alternating current to heat the diaphragm. During this process, heat energy is exchanged between the diaphragm and the surrounding medium, causing the medium around the diaphragm to contract or expand, and the pressure change produces sound. In short, thermal energy is converted into the acoustic vibration energy of the medium, which can be gaseous, liquid, or solid.

[0007] Thermoacoustic generators or transducers are made of materials such as carbon nanotubes or graphene films. For example, a typical thermoacoustic generator is described in US 8,019,099B2. Thermoacoustic generators are increasingly used in microelectromechanical systems (MEMS) due to their simple and lightweight design, especially given the relatively flat structure and minimal component movement required in current thermoacoustic generators.

[0008] However, a known problem with thermoacoustic generators is that the sound frequency will be harmonicized at a given excitation frequency. This harmonic phenomenon is based on the fact that when the electrical input signal presents a frequency like... Figure 1 During the harmonic oscillation I(t) of the excitation current shown, the thermoacoustic generator heats up during both the positive and negative half-cycles, resulting in a maximum pressure p(t) in both cases. The minimum pressure p(t) = 0 occurs at the zero-crossing point I(t) = 0 of the input signal.

[0009] Several solutions for avoiding frequency doubling are known from existing technologies.

[0010] For example, DE 10 2018 114 620 A1 discloses an audio signal processing apparatus for a thermoacoustic generator. This apparatus is configured to receive an audio signal and generate a control signal for the thermoacoustic generator based on the audio signal, wherein the control signal has an offset, which is a time-varying offset. The audio signal processing apparatus is configured to determine the time-varying offset at least segmentally based on the amplitude variation trend of the audio signal. DE 10 2018 114 620 A1 suggests, for example, determining and adjusting the offset only at the maximum or minimum amplitude of the audio signal, which may be more efficient than continuously adjusting the offset, but still requires significant computational overhead.

[0011] Another alternative to avoid frequency harmonics is based on so-called DC offset. Here, the offset of the excitation current used in the electromechanical generator is chosen such that the sum of the maximum negative amplitude and the offset is exactly zero. The problem is that DC offset causes crackling, distortion, and even volume loss in the thermoacoustic generator.

[0012] This can lead to biometric authentication failure, especially in systems that use thermoacoustic generators for user biometric authentication.

[0013] Biometric authentication can be based on the otoacoustic effect, which utilizes the sound produced by the user's inner ear in response to acoustic stimuli, also known as otoacoustic emissions (OAEs). In this process, the user's ear is stimulated with an otoacoustic stimulus signal, and the resulting otoacoustic response is captured. This response is then compared to a stored reference signal to identify the user.

[0014] The otoacoustic stimulation signal is generated by a thermoacoustic generator, particularly a miniature loudspeaker, which is controlled by a control device to produce the otoacoustic stimulation signal.

[0015] Therefore, existing systems cannot avoid frequency doubling without employing high-energy-consuming input signal offset. Summary of the Invention

[0016] According to the present invention, a method for controlling a thermoacoustic generator is provided, wherein the method includes the following steps: i) Provide an audio signal with oscillation S, amplitude A, and oscillation duration T; ii) Convert the audio signal to the frequency domain; iii) The frequency f of the audio signal in Halve the frequency f to produce the modified audio signal. out ;as well as iv) Convert the modified audio signal to the time domain.

[0017] According to the present invention, the thermoacoustic generator is controlled by a control device, particularly an ASIC (application-specific integrated circuit), which, together with the thermoacoustic generator, constitutes a component of a microelectromechanical system (MEMS), particularly a MEMS bio-authentication device. According to the present invention, the control device is designed and configured to control the thermoacoustic generator to generate otoacoustic stimulation signals, wherein, in a suitable embodiment, the thermoacoustic generator is designed to generate an average sound pressure level (SPL) in the range of 60 to 90 dB, and wherein, in a suitable embodiment, the frequency range for stimulating otoacoustic emissions is in the range of 500 Hz to 10 kHz.

[0018] According to the present invention, the audio signal is in the form of harmonic oscillation at a frequency f in Upon reaching the control device, the control device converts the audio signal to the frequency domain and halves it, resulting in a modified audio signal f. out , where f satisfies: out =0.5f in After being converted back to the time domain, the modified audio signal can be relayed to the thermoacoustic generator at half the frequency. The thermoacoustic generator produces an acoustic signal, specifically an otoacoustic stimulus signal. Due to the frequency f... in It has been halved to f out = 0.5f in Therefore, the frequency multiplication factor is 2f out Ultimately, it will not lead to an increase in frequency, but only to the initial frequency f. in This can be achieved according to the present invention without employing a high-energy-consuming input signal offset. In this way, the power consumption of the thermoacoustic generator can be significantly reduced.

[0019] In a suitable configuration of the manipulation method according to the invention, step ii) is performed by a modified discrete cosine transform (MDCT). Alternatively or additionally, to suit the purpose, step iv) is performed by an inverse modified discrete cosine transform (inverse MDCT).

[0020] In one embodiment of the control method according to the present invention, the method further includes the following steps: v) Transmit the modified audio signal to the amplifier; and vi) Amplify the converted and modified audio signal to obtain the amplified and modified audio signal.

[0021] According to the implementation using an amplifier, the modified audio signal, i.e., the audio signal with halved frequencies, is converted back to the time domain and amplified again before being forwarded to the thermoelectric generator. This results in an increase in the volume of the modified audio signal and also regulates the power consumption of the thermoelectric generator, preventing it from overloading or being damaged.

[0022] According to the present invention, the amplification in step vi) can be performed linearly or non-linearly. Since linear amplification is applied to all audio signals to the same degree, even if the modified audio signal exceeds the maximum input level of the thermoacoustic generator, it will not be amplified to exceed the maximum output level of the thermoacoustic generator. In the case of non-linear amplification, the amplification magnitude varies according to the input level. In this way, for example, the non-linear acoustic effects caused by thermoacoustic conversion can be compensated for by pre-distortion, thereby reducing the distortion coefficient.

[0023] According to the present invention, a method for generating acoustic signals, particularly otoacoustic stimulation signals, via a thermoacoustic generator is also provided, wherein the method comprises the following steps: a1) Obtain a frequency f out The modified audio signal, particularly according to the present invention's manipulation method without an amplifier; or a2) Obtain a frequency f out The amplified and modified audio signal, particularly according to the present invention's control method with amplifier; b) For frequency f out Frequency doubling is performed to obtain acoustic signals, especially otoacoustic stimulation signals.

[0024] As already discussed with respect to the control method of the present invention, due to the prior halving, the frequency f out The harmonics ultimately only result in the initial frequency f. in .

[0025] According to the present invention, a microelectromechanical system is also proposed, comprising a thermoacoustic generator and a control device, wherein the control device is designed and configured to control the thermoacoustic generator by means of the control method according to the present invention.

[0026] A particular advantage here is that the control device is constructed as an ASIC (Application-Specific Integrated Circuit), which, together with the thermoacoustic generator, forms part of the microelectromechanical system, especially integrated into the substrate.

[0027] In a particularly suitable embodiment of the microelectromechanical system according to the invention, the system includes a microphone in addition to the control device, wherein the control device is also designed to amplify and pick up the otoacoustic signal received by the microphone before controlling the thermoacoustic generator to generate an otoacoustic stimulus signal. It has proven advantageous that the microphone is integrated into the substrate along with the thermoacoustic generator and the control device. It has proven effective that the microphone is designed and configured to detect signals with a signal-to-noise ratio greater than or equal to 70 dB, thus being constructed as a high SNR (signal noise ratio) microphone.

[0028] In another suitable configuration of the microelectromechanical system according to the invention, the system further includes an amplifier. Here, the amplifier is designed and configured to power a modified microelectromechanical system with a frequency f. out The audio signal is amplified before reaching the thermoacoustic generator. Particularly suitable here is a control device that operates the thermoacoustic generator according to the control method of the invention.

[0029] In principle, the following configuration of the microelectromechanical system according to the invention is possible: in this configuration, the control device is integrated into the thermoacoustic generator. Such an implementation is particularly compact and space-saving, and therefore widely applicable. In an alternative configuration, the thermoacoustic generator and the control device can be arranged in a base plane. This offers the advantage that, depending on the application, a specific thermoacoustic generator can be individually connected to its corresponding control device, increasing design freedom. It has proven particularly suitable here that the control device is constructed as an ASIC.

[0030] In a preferred configuration, the microelectromechanical system according to the invention is configured as a microelectromechanical biometric authentication device for identifying a user based on otoacoustic effects. Particularly suitable here is the microelectromechanical biometric authentication device comprising a thermoacoustic generator in the form of a miniature loudspeaker and an ASIC, the thermoacoustic generator being designed and configured to generate an average sound pressure level in the range of 60 to 90 dB, and the ASIC being designed and configured to manipulate the miniature loudspeaker to generate an otoacoustic stimulation signal. Preferably, the microelectromechanical biometric authentication device further includes a microphone, wherein the ASIC is also designed to amplify and pick up the otoacoustic signal received by the microphone before manipulating the miniature loudspeaker to generate the otoacoustic stimulation signal. Also preferably, the microelectromechanical biometric authentication device further includes an amplifier designed and configured to amplify the modified otoacoustic signal having a frequency f out The audio signal is amplified before it reaches the miniature speaker.

[0031] According to the present invention, an in-ear device is also proposed, comprising a biometric authentication device and a main processor according to the present invention. In this configuration, either the ASIC of the biometric authentication device according to the present invention, or the main processor of the in-ear device, may also be designed and configured to compare the otoacoustic signal received by the microphone with a predefined reference signal of an authorized user, and assign the otoacoustic signal received by the microphone to a specific user based on the comparison.

[0032] Since the comparison and identification can be performed in either the ASIC or the main processor of the in-ear device of the present invention, the microelectromechanical bio-authentication device according to the present invention is extremely flexible in terms of processing and application.

[0033] In a particularly suitable configuration of the in-ear device according to the invention, the device may further include an external microphone. This external microphone is designed and configured to receive ambient signals in the frequency range of 20 Hz to 20 kHz, forward the ambient signals to the ASIC, and play a noise-canceling signal generated by the ASIC. Therefore, the external microphone is outward-facing, i.e., directed toward the user's environment, and is used for active noise cancellation (ANC). The active noise-canceling signal is played simultaneously with the otoacoustic stimulus signal played by the miniature speaker, thereby effectively eliminating ambient noise through destructive interference.

[0034] By integrating an external microphone into the in-ear device according to the invention, the in-ear device can be used even in noisy environments, maintaining clear audio quality for the user.

[0035] Furthermore, the application of the microelectromechanical system according to the present invention, particularly the biometric authentication device, is proposed for use in devices for biometric authentication of authorized users.

[0036] The method for controlling a thermoacoustic generator according to the present invention includes providing an audio signal having an oscillation S, an amplitude A, and an oscillation duration T, converting the audio signal to the frequency domain, and converting the frequency f of the audio signal to the frequency domain. in Halve to produce the frequency f of the modified audio signal out The method involves converting the modified audio signal to the time domain, which allows for the resolution of the harmonic problem without the need for energy-intensive offsets. Energy-intensive offsets either require enormous computational overhead or cause crackling, distortion, or even volume loss in thermal sound generators.

[0037] Therefore, the control method according to the present invention can also be effectively applied to microelectromechanical bio-authentication devices, because it can ensure that bio-authentication will not fail due to interference noise, distortion and volume loss.

[0038] The biometric authentication device according to the invention also provides a secure and tamper-proof authentication system that achieves a seamless authentication process without requiring active user interaction. Furthermore, the microelectromechanical biometric authentication system according to the invention has a very compact and robust structure, making it suitable for use in various in-ear devices. Integrating an external microphone into the in-ear device of the invention also enables the in-ear device to be used even in noisy environments, maintaining clear audio quality for the user. Attached Figure Description

[0039] The embodiments of the present invention will now be described in more detail with reference to the accompanying drawings and the specification.

[0040] The attached diagram shows: Figure 1 This is a schematic diagram showing the trend of the electrical input signal and the resulting pressure. Figure 2 This is a schematic diagram illustrating the principle of a thermoacoustic generator. Figure 3 A schematic overview diagram of the control method, and Figure 4 This is a schematic diagram of a microelectromechanical system. Detailed Implementation

[0041] In the following description of embodiments of the invention, the same or similar elements are denoted by the same reference numerals, and in some cases, repeated descriptions of these elements are omitted. The accompanying drawings are merely schematic illustrations of the subject matter of the invention.

[0042] Figure 1 The diagram shows an electrical input signal representing a harmonic oscillation I(t) without offset excitation current, exhibiting alternating positive and negative amplitudes. As can be seen in the corresponding T(t) or p(t) curves, both positive and negative amplitudes in the I(t) curve cause the thermoacoustic generator to heat up, resulting in either a maximum temperature or a maximum pressure.

[0043] Figure 2 The diagram illustrates the principle of a thermoacoustic generator, where the pressure frequency f(p) is approximately equivalent to the temperature frequency f(T), and the temperature frequency f(T) is approximately equivalent to the input signal frequency f. in twice the value of , therefore satisfying: f(p) ≈ f(T) ≈ 2f in Figure 3A schematic overview of the control method according to the invention is shown, wherein an audio signal 16 having an oscillation S, an amplitude A, and an oscillation duration T is first provided, illustrated here as an A(t) curve. In the next step, the audio signal 16 is transformed into the frequency domain 18 by a modified discrete cosine transform (MDCT) 24, as can be seen in the A(f) curve. The frequency f of the audio signal 16 is... in Then halved, resulting in a frequency f out The modified audio signal 20 is then transformed back into the time domain 22, as can be seen in the corresponding A(t) curve. The transformation back into the time domain 22 is performed via an inverse modified discrete cosine transform (inverse MDCT) 26. In the next step, the modified audio signal 20 is directed to amplifier 8, which amplifies it into an amplified modified audio signal 28. The amplified modified audio signal 28 is now fed to a thermoacoustic generator 4, which generates an otoacoustic stimulation signal 14.

[0044] Figure 4 A schematic diagram of a microelectromechanical system 1 is shown, wherein the system is configured as a microelectromechanical bio-authentication device 2, and includes a thermoacoustic generator 4 in the form of a miniature loudspeaker 10 and a control device 6 in the form of an ASIC 12. Here, the ASIC 12 receives an audio signal 16 having an oscillation S, an amplitude A, and an oscillation duration T, and is also designed and configured to control the miniature loudspeaker 10 to generate an otoacoustic stimulation signal 14, wherein a modified audio signal 20 is transmitted to the miniature loudspeaker 10, the modified audio signal 20 being based on... Figure 3 The present invention is generated by the control method.

[0045] This invention is not limited to the embodiments described herein and the aspects highlighted therein. Various modifications can be made within the scope of the claims, which are within the capabilities of those skilled in the art.

Claims

1. A method for controlling a thermoacoustic generator (4), wherein, The manipulation method includes the following steps: i) Provide an audio signal with oscillation S, amplitude A and oscillation duration T (16); ii) Convert the audio signal (16) into the frequency domain (18); iii) The frequency f of the audio signal (16) in Halve to produce the frequency f of the modified audio signal (20) out ;as well as iv) Convert the modified audio signal (20) into the time domain (22).

2. The control method according to claim 1, wherein, Step ii) is performed by the improved discrete cosine transform (MDCT) (24).

3. The control method according to claim 1 or 2, wherein, Step iv) is performed by inverse modified discrete cosine transform (inverse MDCT) (26).

4. The manipulation method according to at least one of the preceding claims, wherein, The manipulation method also includes the following steps: v) The modified audio signal (20) is transmitted to the amplifier (8); and vi) Amplify the converted and modified audio signal (20) to obtain the amplified and modified audio signal (28).

5. The control method according to claim 4, wherein, The amplification in step vi) can be performed linearly or nonlinearly.

6. A method for generating an acoustic signal, particularly an otoacoustic stimulation signal (14), via a thermoacoustic generator (4), comprising the following steps: a1) Obtain a frequency f out The modified audio signal (20), particularly the control method according to any one of claims 1 to 3; or a2) Obtain a frequency f out The amplified modified audio signal (28), in particular the manipulation method according to claim 4 or 5; b) For frequency f out Frequency doubling is performed to obtain acoustic signals, especially otoacoustic stimulation signals (14).

7. A microelectromechanical system (1) comprising a thermoacoustic generator (4) and a control device (6). Its features are, The control device (6) is designed and configured to control the thermoacoustic generator (4) by means of any one of claims 1 to 3.

8. The microelectromechanical system (1) according to claim 7 further includes an amplifier (8), said amplifier being designed and configured to supply power to a frequency f out The modified audio signal (20) is amplified before reaching the thermoacoustic generator (4), wherein, The control device (6) is also designed and configured to control the thermoacoustic generator (4) by means of any one of claims 4 to 5.

9. The microelectromechanical system (1) according to claim 7 or 8, wherein, The control device (6) is integrated into the thermoacoustic generator (4).

10. The microelectromechanical system (1) according to claim 7 or 8, wherein, The thermoacoustic generator (4) and the control device (6) are arranged in the base plane (30), wherein the control device (6) is constructed as an ASIC (12).

11. The microelectromechanical system (1) according to at least one of claims 7 to 10, wherein, The microelectromechanical system (1) is configured as a microelectromechanical bio-authentication device (2), comprising: a micro loudspeaker (10) designed and configured to generate an average sound pressure level in the range of 60 to 90 dB; a microphone (108) designed and configured to detect a signal-to-noise ratio greater than or equal to 70 dB; and an ASIC (12) designed and configured to manipulate the micro loudspeaker (10) to generate an otoacoustic stimulation signal (14) and amplify and pick up the otoacoustic signal (116) received by the microphone (108).

12. An in-ear device (200) comprising the microelectromechanical bio-authentication device (2) according to claim 11 and a main processor (300).

13. The in-ear device (200) according to claim 12, wherein, The ASIC (12) or the main processor (300) is designed and configured to compare the otoacoustic signal (116) received by the microphone (108) with a predefined reference signal (118) of an authorized user, and assign the otoacoustic signal (116) received by the microphone (108) to a determined user based on the comparison.

14. The application of the microelectromechanical system (1) according to at least one of claims 7 to 11, in a device for biometric authentication of authorized users.

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