The use of ultrasonic sound to induce physiological effects

Abstract

A technique is disclosed for inducing physiological effects using a combination of two or more ultrasonic sounds to produce low-frequency fluctuations in sound pressure at one or more biologically specific frequencies. Combining ultrasonic sounds can produce a powerful consciousness-stimulating effect, which is distinct from traditional acoustic entrainment techniques such as binaural beats because audible sound frequencies are not employed. Alternative frequency pressure fluctuations induce other physiological effects, such as unclogging respiratory passages.

Description

[Technical Field]

[0001] The present invention relates to the use of ultrasonic sound combinations to induce physiological effects, and in particular to combining two or more ultrasonic sounds to produce low frequency fluctuations in sound pressure at one or more biologically specific frequencies. [Background technology]

[0002] Extensive research has shown that acoustic energy can produce stimulating effects on the human body when vibrating at certain frequencies. Numerous studies have focused on using audible sound waves with vibration patterns in the 3-40 Hz range to promote beneficial states such as concentration, learning, or relaxation through neural entrainment. Sensory stimulation using gamma frequencies (approximately 25-100 Hz) has emerged as a promising treatment for counteracting cognitive decline associated with Alzheimer's disease (Non-Patent Document 1). Other studies have found that acoustic vibrations in the 100-200 Hz range resonate with the sinuses and may be useful in treating nasal congestion.

[0003] Ultrasonic sounds, which generally have frequencies above 16 kHz, are much less perceptible to humans than sounds within the audible range. Furthermore, because the energy carried by an acoustic wave is proportional to the square of its frequency, ultrasonic sounds carry much more energy than lower frequency audible sound waves.

[0004] Medical applications of ultrasound typically use frequencies in the MHz range, but noninvasive neuromodulation has been described in the context of frequencies between 0.5 and 3 MHz (Non-Patent Document 2).Ultrasonic neuromodulation is typically based on pulsing a single frequency sound between binary states. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] "Gamma Oscillations in Alzheimer's Disease and Their Potential Therapeutic Role," Traikapi et al., Frontiers in Systems Neuroscience, December 2021 [Non-patent document 2] "A review on ultrasonic neuromodulation of the peripheral nervous system: enhanced or suppressed activities?" Feng et al., Applied Sciences, April 2019 Summary of the Invention

[0006] The inventors have discovered that it is possible to induce physiological effects consistent with neurostimulation, such as increased alertness, using ultrasound waves with longer wavelengths and lower power levels than those employed in medical neuromodulation. The longer wavelengths and lower power levels associated with the 16-48 kHz frequency range suggest a fundamentally different mechanism of action than medical ultrasound. This type of long wavelength, low power ultrasound is inaudible, even though it is within the output capabilities of smartphones.

[0007] Ultrasound propagates through a medium such as air by the transfer of motion energy between adjacent particles. When vibrating air particles come into contact with a denser object such as a human body, some of the energy is reflected back into the air and some is absorbed by the body. The reflected energy can be analyzed to detect motion using Doppler analysis and can be used for other imaging techniques. The absorbed energy, when transmitted by a low-power smartphone speaker, does not cause neural stimulation if it is constant over time. Therefore, low-power ultrasonic sounds with constant amplitude can be employed to detect body movement and breathing in applications such as sleep tracking without causing any neurological effects to the user.

[0008] The inventors have observed that when the amplitude of an ultrasound signal is varied over time, either by combining multiple frequency tones or using another amplitude modulation pattern, users can experience neurological effects such as increased alertness. This technique produces constantly fluctuating sound pressure, inducing a continuous stimulation that is fundamentally different from that achieved by binary pulsing of a single frequency tone. The neurological effects induced by these methods are substantially stronger than those induced by low-frequency audible tones with the same signal amplitude; therefore, one can infer that the stimulation effect is caused by the energy fluctuations induced by the ultrasound modulation, rather than by the maximum signal amplitude or by the overall signal energy, which does not induce neural stimulation when constant.

[0009] The inventors propose that one mode of stimulation effect occurs when neural receptors in the skin detect pressure changes in a manner similar to light, rhythmic touch patterns, which then transmit electrical impulses to the brain, causing effects such as increased alertness at beta and gamma frequencies. When biologically specific frequencies are matched, the effect is more consistent with mechanical rather than auditory stimulation.

[0010] Neural entrainment is a phenomenon in which neural oscillations naturally synchronize with the frequency of an external stimulus, and fluctuations in sound pressure using ultrasonic sounds induce sensations consistent with this phenomenon. The combination of ultrasonic sounds can produce a powerful consciousness-stimulating effect, and it is also distinguishable from other acoustic entrainment techniques, such as binaural beats, because it does not employ audible sound frequencies and does not require the user to wear headphones. The proposed mechanism of action, in which pressure fluctuations on nerve receptors in the skin trigger electrical impulses to the brain, makes this entrainment technique more similar to mechanical or electrical stimulation than to auditory techniques.

[0011] Because neural oscillations are not natural to have a fixed frequency over time, embodiments employ a duty cycle, e.g., 5 seconds of stimulation followed by 25 seconds of rest, to improve tolerance to the effects of neural stimulation.

[0012] High-amplitude sound pressure fluctuations above 20 dB can be perceived as a rhythmic breeze in the air and can induce a sensation of movement deep within the body. High-amplitude sound pressure fluctuations can induce physiological effects separate from and in addition to the neurological effects described above. For example, high-amplitude sound pressure fluctuations within the 100-200 Hz frequency range are particularly effective in clearing sinus congestion.

[0013] To achieve the desired effect, the overall pressure fluctuations and duration of stimulation may need to be controlled, with low amplitude pressure fluctuations causing nerve stimulation and high amplitude fluctuations being suitable for unblocking and deeper stimulation effects. Too much stimulation, either in terms of pressure fluctuations or exposure time, can lead to negative consequences such as headaches, so it is important to be able to control the level of stimulation using techniques such as duty cycles, time-limited or scheduled interventions, and triggered interventions based on feedback mechanisms such as analysis of the user's breathing.

[0014] The inventor's prior patent application, UK Patent Application No. 2302637.0, filed February 23, 2023, from which priority is claimed, entitled "Use of Amplitude Modulated Ultrasound for Motion Tracking and Inducing Awareness in a Target," presents a technique for using ultrasound for motion tracking based on measuring the Doppler shift of an ultrasound pilot tone. By modulating the ultrasound pilot tone at a rate according to the stimulation frequency, stimulation can be induced in the subject without impairing motion estimation. This can be particularly advantageous when used in sleep tracking applications, where the ultrasound pilot tone is inaudible but stimulation can be used to improve sleep quality.

[0015] Thus, the inventors have discovered that not only can ultrasound be used to create low frequency sound pressure fluctuations to induce a physiological effect, but that this effect can also be combined with another application of ultrasound, namely motion tracking using ultrasonic sound.

[0016] The embodiments described herein employ the same combination of ultrasonic stimulation triggering and motion tracking advantages by combining two or more ultrasonic tones of different frequencies, where one or more beat frequencies correspond to the respective one or more stimulation frequencies, while one of the ultrasonic tones also serves as a pilot tone for motion tracking.

[0017] More generally, the inventors recognize that motion tracking functionality is not a required feature of all of the described embodiments, and that combining ultrasonic sounds to induce physiological effects can be beneficially employed in a myriad of applications.

[0018] According to one aspect of the present invention, there is provided an apparatus for inducing one or more physiological effects in a subject, the apparatus comprising: a speaker configured to output two or more ultrasonic sounds, the two or more ultrasonic sounds combined to produce fluctuations in sound pressure at one or more frequencies corresponding to one or more biologically specific frequencies of the subject.

[0019] The two or more ultrasonic sounds may have frequencies in the range of 16 to 48 kHz. The speaker may be configured to activate one or more of the two or more ultrasonic tones according to a duty cycle of less than 100%, in which the output of one or more ultrasonic tones is periodically stopped.

[0020] In embodiments, the speaker is configured to transmit a first ultrasonic sound having a first frequency, a second ultrasonic sound having a second frequency higher than the first frequency, and a third ultrasonic sound having a third frequency higher than the second frequency, wherein the amplitude of the second ultrasonic sound is greater than the amplitudes of the first and third ultrasonic sounds. In such embodiments, the spacing between the first and second frequencies may be equal to the spacing between the second and third frequencies, the amplitudes of the first and third ultrasonic sounds may be equal, and the amplitude of the second ultrasonic sound may be at least twice the amplitude of the first ultrasonic sound, such that the combination of the first, second, and third ultrasonic sounds produces a sinusoidal variation in sound pressure at the frequency difference between the first and second ultrasonic sounds.

[0021] The apparatus may include a controller and a microphone configured to sample signals reflected by the object, and the controller is configured to estimate movement of the object based on a frequency analysis of the sampled signals and a determination of a Doppler shift in one or more of the ultrasonic sounds.

[0022] For two or more ultrasonic sounds, the sampling rate of the microphone is doubled. n It can have frequencies that are integer multiples of the value divided by (an integer n≧2). The device may further include a display for the application, and the controller may be configured to use the estimated movement of the subject to determine input to the application.

[0023] The speaker can be configured to combine two or more ultrasonic tones with music or a soundscape. The one or more biologically specific frequencies may be within a range associated with neural activity.

[0024] The one or more biologically specific frequencies may include one or more resonant frequencies of the subject's respiratory pathway. According to one aspect of the present invention, there is provided a sleep tracking device comprising the device described above, wherein the speaker: A predetermined time schedule, Rapid eye movement sleep was detected, Deep sleep is detected, Light sleep is detected, Body movements, the presence of breath sounds and / or snoring, or Breathing pattern a sleep tracking device configured to output two or more ultrasonic sounds in response to one or more of:

[0025] According to one aspect of the present invention, there is provided a method of inducing one or more physiological effects in a subject, the method comprising outputting two or more ultrasonic sounds that combine to produce fluctuations in sound pressure at one or more frequencies corresponding to one or more respective biologically specific frequencies of the subject.

[0026] The method may include modulating two or more ultrasonic tones according to a duty cycle of less than 100%, in which output of the two or more ultrasonic pure tones is periodically stopped. According to another aspect of the invention, there is provided a computer program configured to perform the above method when executed by an apparatus comprising a controller and a speaker.

[0027] In an embodiment, three ultrasonic tones are combined with specific relative weightings and frequency offsets to generate an interference signal having the same or similar frequency spectrum as a single ultrasonic tone modulated at a low frequency, as described in GB Patent Application No. 2302637.0. Furthermore, motion tracking can be performed based on observing the Doppler shift from the frequency of the ultrasonic tones.

[0028] More generally, two or more stimulation frequencies can be achieved by using different frequency intervals between pairs of ultrasonic tones. The nature and intensity of the stimulation can be controlled by varying the relative weighting of the ultrasonic tones (which affects the fluctuations in sound pressure in the combined signal) to regulate the subject's exposure to pressure fluctuations and allow sufficient recovery time, and by switching one or more ultrasonic tones on and off according to a duty cycle suitable for the particular application.

[0029] The ultrasonic sounds used can be generated by readily available devices such as smartphones. Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: [Brief explanation of the drawings]

[0030] [Figure 1] 3 shows an example of a signal obtained by combining two ultrasonic sounds in accordance with an embodiment of the present invention. [Figure 2] 1 shows an example of a signal obtained by combining three ultrasonic sounds in accordance with an embodiment of the present invention. [Figure 3] 10 shows an example of a signal obtained by combining three ultrasonic tones and applying a duty cycle in accordance with a further embodiment of the present invention. [Figure 4] 1 illustrates an example of the operation of a breathing improvement application, according to an embodiment of the present invention. [Figure 5] 1 illustrates an example of the operation of an application for facilitating lucid dreaming, according to an embodiment of the present invention. [Figure 6] 1 illustrates an example of the operation of a physical or mental wellness application according to an embodiment of the present invention. [Figure 7] 1 illustrates an example of the operation of a breathing exercise application, according to an embodiment of the present invention. [Figure 8] 1 illustrates the principle of motion tracking according to an embodiment of the present invention. [Figure 9] 1 shows an apparatus according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] When two sinusoidal signals of different frequencies are combined, the resulting signal contains a frequency component at a "beat" frequency, which is the difference between the frequencies of the two signals. Embodiments of the present invention are based on the principle of combining high-frequency ultrasound signals to create powerful acoustic pressure fluctuations at the beat frequency. The beat frequency is selected so that the acoustic pressure fluctuations induce a physiological effect in the subject, which occurs when the beat frequency is close to the subject's biological resonant frequency. The pressure difference relative to atmospheric pressure caused by this fluctuation is expressed as the product 2π × f × ρ × A, and is therefore proportional to the frequency f, where ρ is the air density and A is the signal amplitude.

[0032] While any beat interval can be employed to induce sound pressure changes and physiological effects, several precise frequencies are also used in embodiments of the present invention, described in more detail below, to provide compatibility with Doppler motion tracking systems, thereby enabling stimulation effects to be incorporated into versatile applications such as sleep tracking. Such compatibility is achieved by using frequencies that correspond to discrete bin frequencies in the FFT used in the Doppler motion tracking system. All of these precise frequencies have the property of completing an integer number of phase loops within a number of frames equal to the FFT size. These frequencies are calculated as integer multiples of the audio sampling rate divided by the FFT size (e.g., 2048). In embodiments, frequencies that are integer multiples of 23.4375 Hz are advantageous, which is the audio sampling rate of 48,000 Hz divided by 2048. This results in the generated beat frequency also being an integer multiple of 23.4375 Hz, which is chosen for demonstration purposes rather than a rounded frequency such as 25 Hz. 23.4375 Hz is within the range of neural oscillations known as beta waves (12-30 Hz), which are commonly associated with alertness, focus, and thought. For simplicity, this exact frequency will hereafter be referred to as approximately 23 Hz.

[0033] 1(a) shows an example of the signal amplitude resulting from combining two ultrasonic tones produced by a speaker on a device such as a smartphone, according to one embodiment of the present invention. The first ultrasonic tone has a frequency of 21,000 Hz (which is 896 x 23.4375), referred to herein as the "reference" frequency, and the second ultrasonic tone has a frequency offset from the reference frequency by approximately 23 Hz. The first and second ultrasonic tones have equal amplitude weighting.

[0034] The combined signal exhibits a roughly V-shaped amplitude drop, with periodic peaks and troughs at a rate of approximately 23 Hz, which is the beat frequency, the offset between the two ultrasonic tones. When the two ultrasonic tones are emitted from a speaker in the vicinity of a subject, the subject experiences fluctuations in sound pressure at a frequency of approximately 23 Hz. These fluctuations in sound pressure induce a stimulating effect in the subject.

[0035] Figure 1(b) shows the frequency spectrum of the combined signal, obtained using an FFT of size 2048, showing two peaks at adjacent frequency bins spaced approximately 23 Hz apart. The frequency bin with index 0 is the bin corresponding to the reference frequency.

[0036] In other embodiments, three or more ultrasonic tones are combined. In some embodiments, a "triad" of three equally spaced ultrasonic tones is particularly advantageous, in which the middle reference frequency ultrasonic tone has an amplitude weighting at least twice that of the higher and lower ambient ultrasonic tones. The signal obtained by combining three such ultrasonic tones is shown in Figure 2(a).

[0037] In contrast to Figure 1(a), the combined signal in Figure 2(a) shows sinusoidal fluctuations in sound pressure, rather than the V-shaped fluctuations associated with the combination of two ultrasonic tones. This combined signal is equivalent to a single 21,000 Hz ultrasonic tone amplitude-modulated with a Hann function 2048 frames long. The sinusoidal fluctuations represent a smoother fluctuation in sound pressure, with less abrupt transitions between drops and rises in sound pressure compared to the V-shaped signal in Figure 1(a), resulting in a greater overall variation in sound pressure and stimulation effect. The smooth transition at the lower end of the sound pressure fluctuations results in a softer, more pleasant experience for the subject, regardless of the stimulation frequency used. Furthermore, the FFT representation of the sound results in a symmetrical arrangement around the reference frequency, with offset tones of equal amplitude on either side of the reference frequency. This balanced and symmetrical arrangement is advantageous for applications in motion tracking systems that aim to identify Doppler shifts relative to the reference frequency.

[0038] Figure 2(b) shows the frequency spectrum of the combined signal based on an FFT size of 2048. Here, three peaks are shown in adjacent bins with indices −1, 0, and 1 relative to the reference frequency, where the central peak is twice as high as the two outer peaks.

[0039] When combining three ultrasonic tones of different frequencies, it is possible to use a different frequency offset between the lowest and reference frequency tones than between the reference and highest frequency tones. This allows for the generation of two different beat frequencies that can simultaneously induce multiple physiological effects. For example, it is possible to configure an embodiment that simultaneously provides beta stimulation and a sinus decongestant effect. In an embodiment, this is achieved by using offsets of approximately 140 Hz and approximately 117 Hz, thereby also introducing beat frequencies with an offset difference of approximately 23 Hz.

[0040] The use of more than two ultrasonic tones increases the scope in which the system can be configured for a particular application: in addition to the possibility of using asymmetric or irregular placement of frequency offsets, many more combinations of amplitude weighting can be used, which can improve the experience of receiving a particular stimulus.

[0041] The combination of ultrasonic sounds can be controlled in such a way that the amplitude of each ultrasonic sound and the duty cycle of their delivery are configured for a particular application, and the relative weighting of the ultrasonic sounds can be adapted to change the sound pressure fluctuations accordingly.

[0042] For example, Figure 3(a) shows a signal obtained by combining three ultrasonic tones spaced 46.875 Hz apart with a relative weighting of 1:6:1 when the ultrasonic tones are expressed in frequency order. The stimulation phase is followed by a rest phase of the same length as the stimulation phase, i.e., the duty cycle of the stimulation phase is 50%. During the rest phase of Figure 3(a), the three signals are weighted in a ratio of 0:6:0. To eliminate the stimulation effect, the offset frequency signal is zeroed, but to maintain motion tracking functionality, the reference frequency is maintained as described below. If motion tracking is not required, the reference frequency may also be zeroed during the rest phase.

[0043] Figure 3(b) shows the FFT of the stimulus phase, again using size 2048. A frequency spacing of 46.875 Hz results in frequency peaks at bins with indices −2, 0, and +2 relative to the reference tone, indicating an amplitude weighting of 1:6:1.

[0044] Increasing the weighting of the reference frequency ultrasonic sound is beneficial when combined with motion tracking because it allows for a weaker stimulating effect when combined with the stronger reference sound for motion tracking, which is due to the higher baseline sound pressure resulting from the reference sound, as opposed to the arrangements of Figures 1(a) and 2(a) where the minimum amplitude periodically becomes zero.

[0045] In a further embodiment, ultrasonic sounds are combined to generate sound pressure fluctuations in the range of approximately 100-300 Hz that resonate with one or more respiratory pathways of a subject. These frequencies are associated with human humming and meditative chanting and have been demonstrated to reduce nasal congestion and promote gas exchange during breathing. Stimulating respiratory pathways with sound pressure fluctuations in this manner can promote material movement in a manner that assists breathing, for example, by clearing congestion in the nasal passages.

[0046] In another embodiment, ultrasonic sounds are combined to produce sound pressure fluctuations at 140.625 Hz as part of a two-minute nasal decongestant application. An audible tone at the same frequency as the fluctuations may be played to help the user recognize that the decongestant effect is being acoustically generated. Additionally, by selecting the correct frequency to be compatible with the Doppler motion system described below, interactive motion-sensitive visualizations can be displayed to facilitate user breathing exercises. Analysis of reflected ultrasonic sounds can also estimate the user's breathing rate and dynamically display it in real time.

[0047] Unclogging the respiratory passages can be advantageously used to improve breathing, reduce snoring, and alleviate sleep apnea while a subject is sleeping. In the embodiment shown in FIG. 4, a device such as a smartphone detects that a subject is snoring based on audio captured by the smartphone's microphone. Detecting snoring initiates or controls a stimulation phase targeted to the respiratory passages. The microphone detects whether snoring is easing, and if so, stimulation is attenuated or stopped entirely. In an alternative embodiment, audio is captured by an external device and provided to the smartphone. In an alternative embodiment, disordered breathing is detected by an external device, such as a wrist-worn or mattress-based motion tracking system, and the smartphone is notified.

[0048] Employing these sleep improvement techniques using sound frequencies optimized for Doppler measurements allows for simultaneous measurement of a user's body movements and breathing, enabling detailed analysis of the user's sleep. By employing a primary reference tone that is maintained throughout the night for motion tracking capabilities, and then controlling the stimulation effect by controlling a weaker secondary sound at a frequency offset from the reference frequency to create sound pressure fluctuations through interference with the primary sound, the stimulation effect can be controlled without interrupting these sleep tracking functions.

[0049] In another embodiment, shown in FIG. 5, information derived from primary sound reflections for motion detection can be used to infer a user's sleep state. For example, breathing tends to be faster and more irregular during REM sleep compared to deep sleep. Once a user is estimated to have entered the REM sleep stage, which indicates dreaming, beta or gamma band sound pressure stimulation is employed by controlling ultrasonic sounds at a frequency offset from a reference frequency to promote lucid dreaming. Similar to the neural entrainment application presented above, the lucid dream stimulation has a duty cycle to allow the mind to wander freely between short stimulation bursts. This stimulation duty cycle can also be combined with a quiet soundscape to influence lucid dreaming. Lucid dreaming can provide insight into the user's unconscious mind and can be a powerful therapeutic aid. In an alternative embodiment, the user's sleep state is inferred from audio information or information from a system external to the device, instead of or in addition to information derived from primary sound reflections.

[0050] The biological natural frequency may vary from subject to subject and may be pre-derived, for example, using one or more imaging techniques to measure the dimensions of the sinuses. Alternatively, the frequency may be identified empirically by adjusting the beat frequency of the ultrasound sound and observing the resonant effect in the body, such as a tingling sensation in the sinuses.

[0051] Motion Estimation In each of the above-described embodiments, one or more of the ultrasonic sounds can be used as pilot tones for a Doppler motion tracking system. Figure 8 illustrates the motion tracking principle of an embodiment of the invention in relation to a device 1 comprising a speaker 3 and a microphone 4 that can be used to track the movement of a subject 2. In the illustrated configuration, the device is a smartphone and the subject 2 is a user moving in the vicinity of the smartphone. The device comprises processing means (not shown) configured to control the speaker 3 and the microphone.

[0052] In an embodiment of the present invention, motion is tracked based on analyzing the reflection of one or more ultrasonic sounds from an object. When an object is moving, the frequency of the signal reflected directly back to the microphone undergoes a Doppler shift, as known in the art. As the object moves closer to the microphone, the frequency of the reflected signal increases. As the object moves further away from the microphone, the frequency of the reflected signal decreases. In general, the change in frequency Δf is related to the relative velocity Δv between the object and the microphone in the direction toward the microphone according to Δf = f × Δv / c, where f is the frequency of the transmitted ultrasonic sound and c is the speed of sound in air. Therefore, the motion of an object can be estimated based on measuring the frequency shift of the received signal.

[0053] The frequency shift Δf can be estimated in a variety of ways based on spectral analysis of the received signal, and the present invention is not limited to any particular motion estimation technique. Spectral analysis is performed using the Discrete Fourier Transform (DFT) or the Fast Fourier Transform (FFT).

[0054] In embodiments, a smart alarm function is implemented in which the detection of a user's physical movement triggers the initiation of gamma frequency stimulation to wake the user. The stimulation may begin immediately upon detection of movement, after a predetermined delay, or may be gradually introduced to gently wake the user. The stimulation may be silent or may be combined with other sounds, such as music or natural soundscapes such as ocean waves.

[0055] 6, motion estimation is used as the basis for contactless input to the user interface of an application hosted by a device such as a smartphone that emits ultrasonic sounds. A user interacts with the application through a series of gestures toward and / or away from a microphone, which are detected and interpreted as specific input commands that the application processes.

[0056] While using such applications, neural stimulation can be simultaneously provided to the user without any modification to the pilot tone used for motion estimation. Such embodiments are suitable for physical and mental wellness applications. For example, pilot tones can be used to track a user's physical gestures while they are interacting with, for example, a puzzle or game application, while mental stimulation can be achieved by targeting beta or gamma (12-100 Hz) frequencies. In doing so, the user is stimulated through neural entrainment, application immersion, and physical movement, improving focus, awareness, and coordination. Such multifaceted applications are particularly effective in supporting patients with neurological disorders such as dementia. Ultrasound stimulation can be combined with music to further enhance mental stimulation.

[0057] During the rest phase of such a system, stimulation can be stopped by retaining the pilot tone used for motion tracking and stopping only the output of the offset ultrasonic sound, which generates a constant sound pressure without stimulation. In this way, the user's ability to interact with the application is uninterrupted.

[0058] In another embodiment shown in FIG. 7, the display of visualizations prompting the user to practice breathing, motion detection, and providing stimulation to clear sinuses may be combined, along with providing an audible signal indicating the presence of stimulation as described above.

[0059] Pilot Tone Frequency Selection In some embodiments, better motion estimates can be derived using techniques described in the inventor's earlier patent application, GB 2319856.7, filed December 21, 2023, from which priority is claimed, entitled "Pilot Signal Suppression for Acoustic Doppler Motion Tracking." In this technique, motion is determined by comparing successive phase-aligned sampling windows and taking an FFT or DFT of the comparison results to observe the effects caused by Doppler shifts. This approach allows the energy of the pilot tone to be suppressed relative to the Doppler component.

[0060] In particular, in such an embodiment of the present invention, each of the output ultrasonic tones is generated at a sampling rate of 2. n It is advantageous to have frequencies that are integer multiples of n divided by n (an integer n≧2), so that when the samples of the reflected signal are combined in the manner described above, 2 n The sampling window containing the frame always includes an integer number of complete phase periods of each of the ultrasonic sounds, thereby capturing the preceding two n Frame-by-frame comparison allows for the identification of differences caused by Doppler-shifted energy components.

[0061] Device 9 illustrates an apparatus 100 for inducing one or more physiological effects in a subject, according to an embodiment of the present invention. The components illustrated in FIG. 9 represent, in some embodiments, a stand-alone apparatus 100, with each component individually configured to implement a particular function. In other embodiments, the components are part of a device, such as a smartphone or tablet. For example, processor 400 may represent a portion of computer-readable instructions or code that is downloaded, installed, and executed by a processor or controller of the device.

[0062] The embodiment of FIG. 9 also includes components for performing motion estimation, namely, DFT module 500 and motion estimation module 600, although, as noted above, such functionality is not considered required. DFT module 500 and motion estimation module 600 may represent the execution of additional computer-readable instructions. Output module 700 may correspond to a display, audio output, or communication signal output component of the device, and microphone 200 and speaker 300 may be pre-installed on the device. In yet another embodiment, the microphone and speaker may be commercially available components connected to a personal computer. Additionally, the device includes a storage module 800 or memory for storing motion estimation results, which, in some implementations, may store the computer-readable instructions described above. To enable a user to interact with the device, a user interface module 900 is provided, which may implement a GUI or button-based interface for providing control or inputting configuration settings.

[0063] Although the DFT module 500 and the motion estimation module 600 are shown as separate components in Figure 9, in alternative embodiments they may be considered as a single component represented as part of the processor 400. In yet other embodiments, such a single component may be separate from or contained within the central processing unit of the apparatus 100 embodying Figure 9.

[0064] The specific configuration used will depend on the application of the motion estimation technique, examples of which are described below. It will also be appreciated that the components of Figure 9 may be embodied in hardware, software, or a combination of both.

[0065] 9, speaker 200 outputs two or more ultrasonic tones. Speaker 200 may also output music or soundscapes. Microphone 300 is employed for motion estimation by sampling reflections of the output ultrasonic tones and / or for breath sound detection, depending on the particular application in which it is used.

[0066] The motion analysis is performed by the DFT module 500 by generating a DFT of the signal received by the microphone 200 and identifying specific spikes in the spectrum that represent noise with predetermined frequency content. The motion estimation module 600 derives an estimate of the motion from the location of the spikes in the spectrum relative to the frequency of the pilot tones.

[0067] The nature of the output provided by output module 700 depends on the specific context in which the embodiment operates, and in some embodiments, output module 700 is not required at all. In some embodiments, output module 700 represents a display unit that visually indicates detected motion, allowing a user to take a specific action. In other embodiments, output module 700 generates and represents an audio and / or optical alarm or notification, or some other notification, such as an email or message, or an operating system notification.

[0068] It will be understood that various implementations are within the scope of the claims, and that the specific implementation will depend at least on the desired nature of the induced physiological effect and the motion estimation functionality added. Compatible features of the above-described embodiments can be combined as needed to form new embodiments, as needed for a particular application.

Claims

1. 1. A device for inducing one or more physiological effects in a subject, comprising: a speaker configured to output two or more ultrasonic sounds, the two or more ultrasonic sounds combining to produce fluctuations in sound pressure at one or more frequencies corresponding to one or more respective biologically specific frequencies of the subject; An apparatus comprising:

2. 10. The device of claim 1, wherein the two or more ultrasonic sounds have frequencies in the range of 16 to 48 kHz.

3. 3. The device of claim 1 or 2, wherein the speaker is configured to activate one or more of the two or more ultrasonic tones according to a duty cycle of less than 100%, wherein output of the one or more ultrasonic tones is periodically stopped.

4. 4. The device of claim 1, wherein the speaker is configured to transmit a first ultrasonic sound having a first frequency, a second ultrasonic sound having a second frequency higher than the first frequency, and a third ultrasonic sound having a third frequency higher than the second frequency, and wherein the amplitude of the second ultrasonic sound is greater than the amplitudes of the first ultrasonic sound and the third ultrasonic sound.

5. 5. The apparatus of claim 4, wherein the spacing between the first and second frequencies is equal to the spacing between the second and third frequencies, the amplitudes of the first and third ultrasonic sounds are equal, and the amplitude of the second ultrasonic sound is at least twice the amplitude of the first ultrasonic sound, such that the combination of the first, second, and third ultrasonic sounds produces a sinusoidal variation in sound pressure at the frequency difference between the first and second ultrasonic sounds.

6. a controller and a microphone configured to sample a signal reflected by the object; 6. The apparatus of claim 1, wherein the controller is configured to estimate the movement of the object based on a frequency analysis of the sampled signals and a determination of a Doppler shift in one or more of the ultrasonic sounds.

7. The two or more ultrasonic sounds are generated by multiplying the sampling rate of the microphone by 2. ｎ 7. The apparatus of claim 6, having a frequency that is an integer multiple of n divided by (an integer n≧2).

8. 8. The device of claim 6 or 7, further comprising a display for an application, the controller being configured to use the estimated movement of the subject to determine input to the application.

9. 9. The device of claim 1, wherein the speaker is configured to combine the two or more ultrasonic sounds with music or a soundscape.

10. 10. The apparatus of claim 1, wherein the one or more biologically specific frequencies are in a range associated with neural activity.

11. 10. The apparatus of claim 1, wherein the one or more biologically specific frequencies comprise one or more resonant frequencies of the subject's respiratory pathway.

12. A sleep tracking device comprising the device of any one of claims 1 to 11, wherein the speaker: A predetermined time schedule, Rapid eye movement sleep was detected, Deep sleep is detected, Light sleep is detected, Body movements, the presence of breath sounds and / or snoring, or Breathing patterns a sleep tracking device configured to output the two or more ultrasonic sounds in response to one or more of:

13. 1. A method for inducing one or more physiological effects in a subject, the method comprising outputting two or more ultrasonic sounds that combine to produce fluctuations in sound pressure at one or more frequencies corresponding to one or more respective biologically specific frequencies of the subject.

14. 14. The method of claim 13, comprising modulating the two or more ultrasonic tones according to a duty cycle of less than 100%, wherein output of the two or more ultrasonic pure tones is periodically stopped.

15. A computer program configured to perform the method of claim 13 or 14 when executed by a device comprising a controller and a speaker.

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