Double-frequency transcranial ultrasonic stimulation system

Abstract

The invention relates to the technical field of medical ultrasonic instruments, and discloses a dual-frequency transcranial ultrasonic stimulation system, which comprises a dual-frequency ultrasonic transducer and a control circuit, and is characterized in that the dual-frequency ultrasonic transducer is used for carrying out resonance at a first frequency and a second frequency and outputting ultrasound; the double-frequency ultrasonic transducer is composed of a backing layer, a piezoelectric element layer and an acoustic matching layer which are connected in sequence; and the control circuit is used for outputting continuous or pulse type sine electric signals at the first frequency and the second frequency respectively, and is matched with the double-frequency ultrasonic transducer so as to output the electric signals at the maximum transmission efficiency. Ultrasonic waves can be efficiently output at resonance points of two different frequency bands of the first frequency and the second frequency, and a user can flexibly select and use the most appropriate frequency according to the positions, sizes and ranges of different target spots, so that the optimal balance between the penetration depth and the stimulation precision is realized.

Description

Technical Field

[0001] This invention relates to the field of medical ultrasound equipment technology, and more specifically, to a dual-frequency transcranial ultrasound stimulation system. Background Technology

[0002] Transcranial ultrasound stimulation (TUS) is a non-invasive neuromodulation technique that uses low-frequency pulsed ultrasound to stimulate neural or functional areas of the brain to achieve neuromodulation. It is characterized by being non-invasive, having high resolution (down to the millimeter level), controllable penetration depth, and good electromagnetic compatibility. Focused ultrasound waves penetrate the skull to act on specific areas of the brain, modulating neuronal activity or promoting neuroplasticity. It is widely used in the treatment of neurodegenerative diseases (such as Alzheimer's disease), depression, epilepsy, and other brain diseases, as well as in basic neuroscience research. Secondly, compared to traditional drug treatments (such as oral or intravenous medications), which are limited by the blood-brain barrier (resulting in 95% of drugs not reaching the brain lesion), TUS can directly dilate cerebral blood vessels, improve cerebral blood circulation, and enhance cellular metabolism through the mechanical effects (such as cavitation) and physicochemical effects of ultrasound waves, demonstrating unique potential in the treatment of cerebrovascular diseases such as cerebral infarction and cerebral arteriosclerosis. Furthermore, TUS can be combined with magnetic resonance imaging (MRI) to construct a three-dimensional model of the brain and guide ultrasound focusing in real time, providing technical support for targeted therapy of neurological diseases.

[0003] Recent studies have shown that by adjusting combinations of ultrasound frequency, stimulation intensity, and pulse parameters (such as duty cycle and pulse repetition frequency), neuronal activity can be selectively enhanced or inhibited, providing possibilities for the modulation of complex neural circuits. However, existing TUS technologies and systems have certain limitations. For example, existing TUS systems generally use transducers with a single operating frequency, mainly concentrated in the 0.2-1MHz range. Low-frequency ultrasound (0.2-0.5MHz) has strong skull penetration and relatively small energy attenuation, which is beneficial for stimulating deep brain regions. However, its disadvantage is that its acoustic focal spot size (focal spot) is large, resulting in low spatial resolution, which is not conducive to precise stimulation of small targets in deep brain regions. It is more suitable for unfocused or slightly focused stimulation of superficial or large target areas. High-frequency ultrasound (0.5-1MHz), although the attenuation effect increases when penetrating the skull, and the effective acoustic energy reaching the target depth decreases, has significantly improved spatial resolution, forming a smaller focal spot, which is suitable for precise stimulation of small targets in deep brain regions. A single-frequency transducer cannot simultaneously achieve good skull penetration and high spatial resolution. In clinical applications, when faced with treatment targets of different depths and sizes (such as deep nuclei or cortical functional areas), single-frequency transducers and corresponding systems lack flexibility and cannot switch or combine the most suitable frequency range for stimulation according to specific scenarios and treatment needs.

[0004] Currently, control circuits used in single-frequency ultrasonic stimulation typically consist of a power supply, a main control circuit, an ultrasonic drive circuit, and a matching circuit. Their core function is to drive the transducer to operate efficiently at a single designed resonant frequency, generating an ultrasonic signal of a specific intensity. These circuits rely on matching near a single resonant point; energy transfer efficiency is highest and output power is greatest when the circuit operates at the transducer's designed resonant frequency. However, when driving the transducer at other frequencies, the frequency generation section of the circuit and its impedance matching section with the transducer may no longer be compatible. This can result in either the inability to generate the required drive frequency or low efficiency and excessive heat generation at the required drive frequency, failing to provide stable and efficient driving capability at other frequencies.

[0005] In summary, existing transcranial ultrasound stimulation technology is mainly limited by the inability of a single-frequency transducer to balance the contradiction between penetration depth and spatial resolution, and the control circuit architecture with a single resonant point design, which does not have the ability to achieve efficient matching and stable driving at two or more resonant frequencies.

[0006] No effective solutions have yet been proposed to address the problems in the relevant technologies. Summary of the Invention

[0007] To address the problems in related technologies, this invention proposes a dual-frequency transcranial ultrasound stimulation system to overcome the aforementioned technical issues in existing technologies. This system, through a specifically designed dual-frequency transducer (two resonant frequencies) and a matching dual-frequency drive and matching control circuit, effectively overcomes the limitations of existing single-frequency systems, improves the accuracy of transcranial ultrasound stimulation, the effectiveness of deep stimulation, and its adaptability to clinical scenarios, thereby promoting the wider application of this technology in cutting-edge research on brain diseases and neuroscience.

[0008] Therefore, the specific technical solution adopted by the present invention is as follows:

[0009] A dual-frequency transcranial ultrasound stimulation system includes a dual-frequency ultrasound transducer and a control circuit. The dual-frequency ultrasound transducer is used to resonate with a first frequency and a second frequency and output ultrasound. The dual-frequency ultrasound transducer is composed of a backing layer, a piezoelectric element layer and an acoustic matching layer connected in sequence.

[0010] The first frequency band ranges from 0.2 to 0.5 MHz, and the second frequency band ranges from 0.5 to 1.0 MHz.

[0011] The control circuit is used to output continuous or pulsed sinusoidal electrical signals at a first frequency and a second frequency, respectively, and to match the dual-frequency ultrasonic transducer to output at maximum transmission efficiency.

[0012] Furthermore, the expression for the first frequency is:

[0013] F1≈c p / (2t p );

[0014] t p =λ p / 2;

[0015] The expression for the second frequency is:

[0016] F2≈c m / (4t m );

[0017] t m =λ m / 4;

[0018] In the formula, F1 represents the first frequency, and c p The longitudinal wave velocity, t, represents the vibration mode of the piezoelectric element material thickness. p λ represents the thickness of the piezoelectric element layer. p F1 represents the ultrasonic wave length in the piezoelectric element layer at the first frequency, F2 represents the second frequency, and c represents the second frequency. m The sound velocity t represents the acoustic matching layer material. m λ represents the thickness of the acoustic matching layer. m This indicates the length of the ultrasonic wave in the acoustic matching layer at the second frequency.

[0019] Furthermore, at the first frequency F1, the overall thickness of the piezoelectric element and the acoustic matching layer is 1 / 2 wavelength, and the resonant node is located inside the piezoelectric element; at the second frequency F2, the interface between the piezoelectric element and the acoustic matching layer is the resonant node, the thickness of the acoustic matching layer is 1 / 4 wavelength, the thickness of the piezoelectric element is 3 / 4 wavelength, there is a node inside the piezoelectric element, and the overall coupling between the piezoelectric element and the acoustic matching layer is one wavelength.

[0020] Furthermore, the thickness, sound velocity, and material properties of the acoustic matching layer are configured such that the second frequency F2 is higher than the first frequency F1, and both are within the effective operating frequency band of the transducer.

[0021] Furthermore, the first frequency is dominated by the vibration of the piezoelectric element layer. When it is necessary to reduce the first frequency, the thickness of the piezoelectric element is increased or a soft piezoelectric material is used to reduce the longitudinal wave velocity in the vibration mode. When it is necessary to increase the first frequency, the thickness of the piezoelectric element is decreased or a hard piezoelectric material is used to increase the longitudinal wave velocity in the vibration mode.

[0022] The second frequency is dominated by the coupling between the acoustic matching layer and the piezoelectric element layer. When it is necessary to adjust the resonant point of the second frequency separately, the thickness of the acoustic matching layer or the density and material sound velocity of the acoustic matching layer are adjusted within the preset range so that the acoustic impedance of the acoustic matching layer and the piezoelectric element layer meets the preset ratio, so as to ensure that the two resonant peaks are clearly separated and in the target frequency band, and finally achieve efficient dual-frequency output.

[0023] Furthermore, the material of the piezoelectric element layer is piezoelectric ceramic, piezoelectric composite material or single crystal material, and the polarization direction is consistent with the thickness direction;

[0024] The acoustic matching layer is made of epoxy resin substrate and metal or metal oxide powder filler, polymer and ceramic particles, glass or microporous ceramic.

[0025] Furthermore, the dual-frequency ultrasonic transducer can be a focused transducer or a non-focused transducer.

[0026] Furthermore, the ratio of acoustic impedance of the backing layer to that of the piezoelectric element layer is 0.8-1.2, and the ratio of acoustic impedance of the acoustic matching layer to that of the piezoelectric element layer is 0.1-0.6.

[0027] Furthermore, the control circuit consists of a power supply, a main control circuit, an ultrasonic drive circuit, and a matching circuit;

[0028] The main control circuit is used to generate baseband signals at the first and second frequencies.

[0029] The ultrasonic drive circuit is used to amplify the power of the first and second frequency fundamental frequency signals generated by the main control circuit in order to drive the dual-frequency ultrasonic transducer to work.

[0030] The matching circuit is used to ensure that the first and second frequencies operate at maximum transmission efficiency when matched with the dual-frequency ultrasonic transducer.

[0031] Furthermore, the control of the dual-frequency ultrasonic transducer includes:

[0032] Impedance curve scanning of the dual-frequency ultrasonic transducer was performed using an impedance analyzer to determine the resonant frequencies of the low and high frequencies, obtain the first and second frequencies, and acquire the first and second static capacitances of the dual-frequency ultrasonic transducer at the first and second frequencies.

[0033] Based on the first static capacitor and the second static capacitor, the optimal first matching inductor and the second matching inductor are determined by adjusting the matching network, and the first frequency, the second frequency, the optimal first matching inductor and the second matching inductor are written into the memory chip of the main control circuit or recorded in the control software.

[0034] The first or second frequency is selected based on clinical needs. When the first frequency is selected, the main control circuit calls the optimal first matching inductor corresponding to the first frequency and adjusts the equivalent inductance of the matching circuit to the optimal first matching inductor by controlling the relay switch. At the same time, the main control circuit outputs a PWM signal of the first frequency to ensure that the dual-frequency ultrasonic transducer works efficiently at the first frequency and outputs the preset ultrasonic energy. When the second frequency is selected, the main control circuit calls the optimal second matching inductor corresponding to the second frequency and adjusts the impedance matching network. At the same time, the main control circuit outputs a PWM signal of the second frequency to ensure that the dual-frequency ultrasonic transducer works efficiently at the second frequency and outputs the preset ultrasonic energy.

[0035] The beneficial effects of this invention are as follows: By designing a dual-frequency transducer (whose structure includes a backing layer, a piezoelectric element layer, and an acoustic matching layer, the thickness of the piezoelectric element layer and the acoustic properties of the material are precisely correlated with the first frequency F1 and the second frequency F2) and a dedicated dual-frequency control circuit, signals can be output at frequencies F1 and F2 respectively, and power amplification and impedance matching can be performed. This allows for efficient ultrasound output at two different frequency band resonant points: the first frequency (0.2-0.5MHz) and the second frequency (0.5-1MHz). Furthermore, users can flexibly select the most suitable frequency F1 or F2 according to the location, size, and range of different target points, thereby achieving an optimal balance between penetration depth and stimulation accuracy. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a schematic diagram of a traditional transcranial single-frequency ultrasound transducer.

[0038] Figure 2 This is a frequency impedance curve of a traditional single-frequency ultrasonic transducer.

[0039] Figure 3 This is a schematic diagram of the structure of a dual-frequency ultrasound transducer in a dual-frequency transcranial ultrasound stimulation system according to an embodiment of the present invention;

[0040] Figure 4 This is an axial amplitude curve of a dual-frequency ultrasound transducer at two frequencies in a dual-frequency transcranial ultrasound stimulation system according to an embodiment of the present invention.

[0041] Figure 5This is a diagram showing the relationship between the geometric dimensions and focusing parameters of a dual-frequency ultrasound transducer in a dual-frequency transcranial ultrasound stimulation system according to an embodiment of the present invention.

[0042] Figure 6 This is a frequency impedance curve obtained from the simulation of a dual-frequency ultrasound transducer in a dual-frequency transcranial ultrasound stimulation system according to an embodiment of the present invention.

[0043] Figure 7 This is a measured frequency impedance curve of a dual-frequency ultrasound transducer impedance analyzer in a dual-frequency transcranial ultrasound stimulation system according to an embodiment of the present invention.

[0044] Figure 8 This is a measured axial focal length diagram of a dual-frequency ultrasound transducer at 330kHz with a hydrophone in a dual-frequency transcranial ultrasound stimulation system according to an embodiment of the present invention.

[0045] Figure 9 This is a diagram showing the transverse beam diameter of a dual-frequency ultrasound transducer at -3dB sound pressure in a dual-frequency transcranial ultrasound stimulation system according to an embodiment of the present invention.

[0046] Figure 10 This is a measured axial focal length diagram of a dual-frequency transcranial ultrasound transducer at 590 kHz with a hydrophone in a dual-frequency transcranial ultrasound stimulation system according to an embodiment of the present invention.

[0047] Figure 11 This is a diagram showing the transverse beam diameter of a dual-frequency ultrasound transcranial ultrasound transducer at -3dB sound pressure at 590kHz in a dual-frequency transcranial ultrasound stimulation system according to an embodiment of the present invention.

[0048] Figure 12 This is a schematic diagram of the principle structure of a dual-frequency ultrasound transducer control circuit in a dual-frequency transcranial ultrasound stimulation system according to an embodiment of the present invention.

[0049] Figure 13 This is a flowchart of a control method for a dual-frequency ultrasound transducer in a dual-frequency transcranial ultrasound stimulation system according to an embodiment of the present invention. Detailed Implementation

[0050] To further illustrate the various embodiments, the present invention provides accompanying drawings, which are part of the disclosure of the present invention. These drawings are mainly used to illustrate the embodiments and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these drawings, those skilled in the art should be able to understand other possible implementation methods and the advantages of the present invention. The components in the drawings are not drawn to scale, and similar component symbols are generally used to represent similar components.

[0051] According to an embodiment of the present invention, a dual-frequency transcranial ultrasound stimulation system is provided.

[0052] According to an embodiment of the present invention, a dual-frequency transcranial ultrasound stimulation system includes a dual-frequency ultrasound transducer and a control circuit. The dual-frequency ultrasound transducer is used to resonate with a first frequency and a second frequency and output ultrasound. The dual-frequency ultrasound transducer is composed of a backing layer 1, a piezoelectric element layer 2 and an acoustic matching layer 3 connected in sequence.

[0053] The first frequency has a frequency band range of 0.2-0.5MHz, and the second frequency has a frequency band range of 0.5-1.0MHz;

[0054] The control circuit is used to output continuous or pulsed sinusoidal electrical signals at a first frequency and a second frequency, respectively, and to match the dual-frequency ultrasonic transducer to output at maximum transmission efficiency.

[0055] In one embodiment, the thickness of the piezoelectric element layer and the first frequency satisfy the following formula:

[0056] F1≈c p / (2t p );

[0057] t p =λ p / 2;

[0058] The matching layer thickness and the second frequency satisfy the following formula:

[0059] F2≈c m / (4t m );

[0060] t m =λ m / 4;

[0061] In the formula, F1 represents the first frequency, and c p The longitudinal wave velocity, t, represents the vibration mode of the piezoelectric element material thickness. p λ represents the thickness of the piezoelectric element layer. p F1 represents the ultrasonic wave length in the piezoelectric element layer at the first frequency, F2 represents the second frequency, and c represents the second frequency. m The sound velocity t represents the acoustic matching layer material. m λ represents the thickness of the acoustic matching layer. m This indicates the length of the ultrasonic wave in the acoustic matching layer at the second frequency.

[0062] In one embodiment, when the piezoelectric element layer vibrates, at the first frequency F1, the overall thickness of the piezoelectric element and the acoustic matching layer is 1 / 2 wavelength, and the resonant node is located inside the piezoelectric element; at the second frequency F2, the interface between the piezoelectric element and the acoustic matching layer is the resonant node, the thickness of the acoustic matching layer is 1 / 4 wavelength, the thickness of the piezoelectric element is 3 / 4 wavelength, there is a node inside the piezoelectric element, and the overall coupling of the piezoelectric element and the acoustic matching layer is one wavelength.

[0063] In one embodiment, the thickness, sound velocity, and material properties of the acoustic matching layer are configured such that the second frequency F2 is higher than the first frequency F1, and both are within the effective operating frequency band of the transducer.

[0064] In one embodiment, the first frequency is dominated by the vibration of the piezoelectric element layer. When it is necessary to reduce the first frequency, the thickness of the piezoelectric element is increased or a soft piezoelectric material is used to reduce the longitudinal wave velocity in the vibration mode. When it is necessary to increase the first frequency, the thickness of the piezoelectric element is decreased or a hard piezoelectric material is used to increase the longitudinal wave velocity in the vibration mode.

[0065] The second frequency is dominated by the coupling between the acoustic matching layer and the piezoelectric element layer. When it is necessary to adjust the resonant point of the second frequency separately, the thickness of the acoustic matching layer or the density and material sound velocity of the acoustic matching layer are adjusted within the preset range so that the acoustic impedance of the acoustic matching layer and the piezoelectric element layer meets the preset ratio, so as to ensure that the two resonant peaks are clearly separated and in the target frequency band, and finally achieve efficient dual-frequency output.

[0066] In one embodiment, the material of the piezoelectric element layer is piezoelectric ceramic, piezoelectric composite material or single crystal material, and its polarization direction is consistent with the thickness direction; the material of the acoustic matching layer is usually epoxy resin substrate + metal or metal oxide powder filler, polymer (polyimide, polyurethane) + ceramic particles (alumina, silicon dioxide particles), glass or microporous ceramic.

[0067] In one embodiment, the dual-frequency ultrasonic transducer is either a focused transducer or a non-focused transducer.

[0068] In one embodiment, the ratio Z of the acoustic impedance of the backing layer to the piezoelectric element layer (Z = ρc, where ρ is density and c is the speed of sound) is... b / Z p The ratio Z of the acoustic impedance of the acoustic matching layer to the piezoelectric element layer is 0.8-1.2. m / Z p It ranges from 0.1 to 0.6.

[0069] In one embodiment, the control circuit consists of a power supply, a main control circuit, an ultrasonic drive circuit, and a matching circuit.

[0070] The power supply provides power to each module in the circuit.

[0071] The main control circuit is used to generate baseband signals at the first and second frequencies;

[0072] The ultrasonic drive circuit is used to amplify the power of the first and second frequency fundamental frequency signals generated by the main control circuit in order to drive the dual-frequency ultrasonic transducer to work.

[0073] The matching circuit is used to ensure that the first and second frequencies operate at maximum transmission efficiency when matched with the dual-frequency ultrasonic transducer.

[0074] In one embodiment, the control of the dual-frequency ultrasonic transducer includes:

[0075] Impedance curve scanning of the dual-frequency ultrasonic transducer was performed using an impedance analyzer to determine the resonant frequencies of the low and high frequencies, obtain the first and second frequencies, and acquire the first and second static capacitances of the dual-frequency ultrasonic transducer at the first and second frequencies.

[0076] Based on the first static capacitor and the second static capacitor, the optimal first matching inductor and the second matching inductor are determined by adjusting the matching network, and the first frequency, the second frequency, the optimal first matching inductor and the second matching inductor are written into the memory chip of the main control circuit or recorded in the control software.

[0077] The first or second frequency is selected based on clinical needs. When the first frequency is selected, the main control circuit calls the optimal first matching inductor corresponding to the first frequency and adjusts the equivalent inductance of the matching circuit to the optimal first matching inductor by controlling the relay switch. At the same time, the main control circuit outputs a PWM signal of the first frequency to ensure that the dual-frequency ultrasonic transducer works efficiently at the first frequency and outputs the preset ultrasonic energy. When the second frequency is selected, the main control circuit calls the optimal second matching inductor corresponding to the second frequency and adjusts the impedance matching network. At the same time, the main control circuit outputs a PWM signal of the second frequency to ensure that the dual-frequency ultrasonic transducer works efficiently at the second frequency and outputs the preset ultrasonic energy.

[0078] To facilitate understanding of the above technical solutions of the present invention, the following description, in conjunction with the accompanying drawings, further illustrates the above technical solutions of the present invention from the perspectives of architecture and principle, as follows:

[0079] Figure 1This diagram illustrates the structure of a traditional transcranial single-frequency ultrasound transducer (a represents the backing layer, b represents the piezoelectric element, and f represents the emitted wave). As shown, the transducer consists of two parts: a backing layer and a piezoelectric element. When the transducer operates, the piezoelectric element vibrates under electrical signal excitation, emitting ultrasonic waves. The backing layer, located behind the piezoelectric element, primarily absorbs the backward-propagating sound waves, preventing reflections within the transducer that could cause interference signals, such as ringing effects. It ensures the sound waves propagate unidirectionally forward and also aids in heat dissipation, protecting the piezoelectric element. The backing layer must meet the requirements of high attenuation, acoustic impedance matching with the piezoelectric element layer, and ease of processing. Commonly used materials for the backing layer include epoxy resin-based composites, rubber / polymer-based composites, and special sound-absorbing ceramic materials. Furthermore, traditional single-frequency transducers, in order to reduce the significant difference in acoustic impedance between the piezoelectric element and the transmission medium (such as the human body) that leads to excessive ultrasonic energy reflection, also add a matching layer (but the matching layer thickness, sound velocity, and acoustic impedance parameters do not couple with the piezoelectric element to bring about a high resonant frequency peak). This only improves the transmission coefficient at the interface, allowing ultrasonic waves to be effectively transmitted to human tissue. However, this type of single-frequency transducer can only transmit ultrasonic waves at a fixed resonant frequency (such as...). Figure 2 While operating efficiently at 550 kHz (as shown), it cannot simultaneously achieve the good skull penetration required for superficial stimulation and the high resolution required for deep small target stimulation. Furthermore, when the operating frequency deviates from its single resonant point, it will lead to severe impedance mismatch (e.g., Figure 2 As shown in the curve, the impedance rises sharply, causing a sharp drop in electroacoustic conversion efficiency, resulting in energy loss and heat damage.

[0080] Figure 2 This is a frequency-impedance curve of a traditional single-frequency ultrasonic transducer. The graph, presented through simulation, illustrates the frequency-impedance characteristics of a single-frequency transducer. The horizontal axis represents frequency (Hz), and the vertical axis represents impedance (Ω). The curve shows a clear impedance minimum (resonance point) at 550kHz, indicating that this frequency is the optimal operating point for the transducer. When the operating frequency deviates from 550kHz or when a frequency doubling input is used, the impedance rises sharply. This impedance mismatch directly leads to two serious consequences: firstly, the electroacoustic conversion efficiency decreases sharply, resulting in insufficient effective output acoustic power; secondly, most of the input electrical energy is ineffectively lost and converted into heat, causing overheating of the transducer and circuit components, reducing system reliability and lifespan.

[0081] Figure 3 This is a schematic diagram of the transcranial dual-frequency ultrasound transducer structure of the present invention (in the figure, 1 is the backing layer, 2 is the piezoelectric element layer, 3 is the acoustic matching layer, f is the transmitted wave, and g is the first reflected wave). As shown in the figure, the transducer consists of three layers: a backing layer, a piezoelectric element layer, and an acoustic matching layer. The acoustic impedance ratio Z between the backing layer and the piezoelectric element layer is... b / Z pThe thickness t needs to be controlled between 0.8 and 1.2 to ensure that the backing layer has high attenuation performance in both low-frequency F1 and high-frequency F2, avoiding reflection interference in either frequency band. The core design principle of the dual-frequency ultrasonic transducer lies in designing the piezoelectric element layer thickness t... p and the speed of longitudinal wave c p Acoustic matching layer thickness t m Acoustic matching layer material sound velocity c m Acoustic impedance Z m Physical parameters, etc. When the piezoelectric element layer is bonded with an acoustic matching layer and vibrates, when the piezoelectric element emits the fundamental frequency F1, the matching layer does not completely transmit this sound wave; its front surface (the interface in contact with the transmission medium) reflects a portion of the sound wave (the first reflected wave). This reflected wave returns and superimposes with the fundamental frequency of the piezoelectric element, changing the boundary vibration conditions of the piezoelectric element. From a mechanical vibration perspective, bonding the matching layer is equivalent to adding a load mass to the piezoelectric element, increasing the equivalent mass of the entire vibration system. This increase in mass leads to a slight decrease in the fundamental frequency of the transducer. Secondly, when the piezoelectric element is bonded with an acoustic matching layer, the piezoelectric element is equivalent to introducing an acoustic resonator. The thickness of the matching layer is designed to be 1 / 4 wavelength (t). m =λ m / 4,F2≈c m / (4t m Under these conditions, the matching layer will resonate at a frequency of 1 / 4 wavelength at F2. After the piezoelectric element and the matching layer are coupled, the resonance of the matching layer acts on the piezoelectric element, causing the piezoelectric element and the matching layer to resonate synchronously in their higher-order vibration modes, thus generating a second resonance peak F2. Figure 4 The axial amplitude curves of the transcranial dual-frequency transducer at two frequencies show that when the resonant frequency is F1, the resonant node is located within the piezoelectric element, and the overall thickness of the piezoelectric element and matching layer is approximately 1 / 2 wavelength. When the resonant frequency is F2, since the matching layer thickness is designed to be 1 / 4 wavelength, the interface between the piezoelectric element and the matching layer is the resonant node. The resonance of the matching layer acts on the piezoelectric element, causing the piezoelectric element to become 3 / 4 wavelength, and a node is also generated inside the piezoelectric element. Therefore, the overall coupling between the piezoelectric element and the matching layer is approximately one wavelength. Based on the above theory and vibration modes, the dual-frequency transducer forms two resonant peaks in the 0-1MHz operating frequency band. By rationally designing the two specific resonant points of low frequency F1 and high frequency F2, the dual-frequency ultrasonic transducer can generate a resonant frequency at 0.2-0.5MHz low frequency and 0.5-1MHz high frequency, thus achieving dual resonant frequencies. Figure 5The diagram shows the relationship between the geometric dimensions and focusing parameters of a dual-frequency ultrasonic transducer (where d is the aperture width of the piezoelectric element, r is the radius of curvature of the piezoelectric element, A is the aperture plane of the dual-frequency ultrasonic transducer, J is the geometric focus, B1 is the plane focal length, B2 is the geometric focal length, C1 is the near Fresnel region, C2 is the focusing Franhofer region, and C3 is the far Fresnel region). The aperture width d and radius of curvature r of the piezoelectric element are key geometric parameters that determine the focusing capability and geometric focus. When the aperture width d of the piezoelectric element is significantly larger than the wavelength λ of the sound wave at the excitation frequency, the position of the geometric focus is mainly determined by the radius of curvature r of the piezoelectric element. The aperture width mainly affects the beam diameter and focal length of the focus. The larger the aperture, the sharper the focusing (smaller focal spot and shorter focal column), but it does not change the focus position. The operating frequency also affects the beam diameter and focal length of the focus. The higher the operating frequency, the shorter the wavelength λ of the sound wave, the weaker the diffraction effect, and the more concentrated the energy in the axis, i.e., the smaller the focal spot and the shorter the focal column. In summary, the specific design of the dual-frequency transducer is as follows:

[0082] 1) Piezoelectric element layer thickness t p According to the formula F1≈c p / (2t p ),t p =λ p / 2 design, where c p The longitudinal wave velocity, t, represents the vibration mode of the piezoelectric element material thickness. p λ represents the thickness of the piezoelectric element layer. p This indicates the length of the ultrasonic wave in the piezoelectric element layer at the first frequency F1, causing it to generate a fundamental frequency resonance at the first frequency F1 (0.2-0.5MHz);

[0083] 2) Acoustic matching layer thickness t m According to the formula F2≈c m / (4t m ),t m =λ m / 4 wavelength design, where c m The sound velocity t represents the acoustic matching layer material. m λ represents the thickness of the acoustic matching layer. m This indicates the length of the ultrasonic wave in the acoustic matching layer at the second frequency F2, causing the second frequency F2 to resonate within the range of (0.5-1MHz);

[0084] 3) Determine the aperture width d and radius of curvature of the piezoelectric element based on the required geometric focal length, focal column and focal ring diameter, and import the designed piezoelectric element and acoustic matching layer thickness and material parameters to obtain two frequency points in the range of F1 (0.2-0.5MHz) and F2 (0.5-1MHz) for the dual-frequency ultrasonic transducer;

[0085] 4) The low frequency F1 is dominated by the vibration of the piezoelectric element. To reduce the low frequency F1, the thickness t of the piezoelectric element layer can be increased. p Alternatively, when the thickness is too large and the structural design is limited, soft piezoelectric materials can be used to reduce the sound velocity c of the piezoelectric element. p To improve the low-frequency F1, the piezoelectric element layer thickness t can be reduced. p Alternatively, when the thickness is too thin and vibration is limited, a rigid piezoelectric material can be used to increase the sound velocity c of the piezoelectric element. p ;

[0086] 5) The high-frequency F2 is dominated by the coupling of the matching layer and the piezoelectric element. If you want to adjust the high-frequency resonant point separately, you can adjust the thickness t of the acoustic matching layer. m =λ m / 4 is adjusted within ±10%, or by adjusting ρ m (Acoustic matching layer density) and c m (Sound velocity of the acoustic matching layer material) makes Z m = (10% - 60%)Z p (where Z) m Acoustic impedance of acoustic matching layer, Z p To ensure that the two resonant peaks (F1 and F2) are clearly separated and located in the target frequency band (around 0.2-0.5MHz and 0.5-1MHz), the dual-frequency high-efficiency output is ultimately achieved.

[0087] Figure 6 The simulation results of the dual-frequency ultrasonic transducer yielded a frequency-impedance curve, which was then used to derive its theoretical frequency-impedance curve. The simulation results show two significant impedance minima (double resonant peaks): the first at 300kHz (low frequency) and the second at 600kHz (high frequency). These two resonant points correspond to the design target frequencies F1 (0.2-0.5MHz) and F2 (0.5-1MHz), respectively. Furthermore, when the operating frequency deviates from 300kHz (low frequency) and 600kHz (high frequency), respectively, the impedance increases sharply, and the electroacoustic conversion efficiency decreases. The simulation results demonstrate that precisely controlling the structure and key material parameters of the piezoelectric element and matching layer can effectively regulate the position of the double resonant frequency points (F1-300kHz, F2-600kHz) and the impedance, ensuring that the dual-frequency transducer operates efficiently in both the target low-frequency range (0.2-0.5MHz) and the high-frequency range (0.5-1MHz). The low-frequency resonant point of 300kHz corresponds to a larger focal range and better penetration, making it suitable for stimulating superficial or large brain regions (such as the cortex); the high-frequency resonant point of 600kHz corresponds to a smaller focal range and higher resolution, making it suitable for precisely stimulating deep, small targets (such as the hippocampus).

[0088] Figure 7This is a measured frequency impedance curve of a dual-frequency ultrasonic transducer, obtained using an impedance analyzer. The curve shows two resonance peaks at 330 kHz and 590 kHz, which corresponds to... Figure 5 The simulation predictions are highly consistent, with low-frequency and high-frequency errors of <5%, verifying the t p Relationship with F1 and t m The accuracy and effectiveness of the relationship with F2 and the acoustic impedance Z-matching principle were verified. Experimental results of the dual-resonance peaks indicate that this dual-frequency transducer can dynamically switch its operating frequency according to the treatment target, allowing for the selection of 330kHz to stimulate superficial brain regions (such as the motor cortex) or 590kHz to precisely target deep targets (such as the hippocampus), overcoming the clinical limitations of single-frequency transducers.

[0089] Figure 8 and Figure 9 The acoustic field characteristics of the hydrophone in 330kHz low-frequency F1 mode were demonstrated. When the dual-frequency transducer excited a 330kHz vibration, the sound wave diffraction effect was significant. Figure 6 It can be seen that the axial focal length in the -3dB range is 48mm, and the ultrasonic energy can maintain a high intensity over a relatively long axial range, such as... Figure 7 As shown, its -3dB transverse beam diameter is 6mm, which means that at this frequency, the ultrasound beam has a wide transverse coverage range. The wide beam is suitable for superficial large-area stimulation such as the motor cortex mapping area. After adjusting the focus by coupling pads or water bags, it can be flexibly adapted to larger target areas at different depths.

[0090] Figure 10 and Figure 11 The sound field characteristics of the hydrophone in the measured 590kHz high-frequency mode were demonstrated. Figure 8 It can be seen that the axial focal length in the -3dB range is 30mm, such as Figure 9 The -3dB transverse acoustic beam diameter is 3.3mm. When the dual-frequency transducer excites 590kHz high-frequency vibrations, its total sound pressure level increases compared to low frequencies, diffraction weakens, and a pencil-shaped focused acoustic beam is formed, resulting in more concentrated sound energy. When used for deep brain region stimulation, it can precisely inhibit target points without damaging surrounding tissues. This confirms the enhanced focusing effect of acoustic wave interference under high-frequency stimulation. The smaller wavelength (λ) and diffraction angle at high frequencies reduce acoustic wave diffraction and increase spatial resolution, making it more suitable for precise treatment of small lesions at specific depths.

[0091] Figure 12This diagram illustrates the schematic of a dual-frequency ultrasonic transducer control circuit. The overall ultrasonic circuit consists of a power supply module, a main control module (MCU), an ultrasonic drive circuit, a matching network, and a memory chip integrated into the transducer. The power supply module converts 220V / 50Hz AC mains power to 48V or 36V DC power via a switching power supply. This DC / DC power supply is then precisely adjusted by the PWM0 signal output from the MCU to the voltage required by the ultrasonic drive circuit. The main control module, based on the STM32 platform, generates two complementary PWM signals (PWM1 and PWM2), whose frequencies are locked to the transducer's dual resonant points (F1 = 330kHz, F2 = 590kHz) to achieve precise frequency control. The ultrasonic drive circuit consists of a MOSFET driver chip and two MOSFETs Q1 and Q2, amplifying the PWM signal output from the MCU into a high-voltage AC excitation signal within the range of 0.2–1MHz. The matching module includes a 1:1:N turns ratio transformer T0 and a matching capacitor C. p And the adjustable inductor array consists of M inductance values ​​(L1 to L...) m The inductors are connected in series, and each inductor is connected to a magnetic latching relay (K1-K). m ) by MCU's RL1-RL m Signal control switches the inductance between L1 and L2, allowing the inductance value to be controlled between L1 and L2. m Dynamic switching within the range. The matching module is mainly used to compensate for the influence of changes in the transducer's static capacitance C0 on the resonance condition, making the entire transducer equivalent circuit tend to be purely resistive, so as to ensure that the ultrasonic circuit and the dual-frequency transducer work at maximum transmission efficiency. In this example, a storage module SC can be integrated inside the transducer to pre-store dual-frequency parameters, resonant frequencies F1 / F2 and optimal matching inductors LDS-1 / LDS-2. In another embodiment, parameters F1 / F2 and LDS-1 / LDS-2 can be recorded in the control software, so that the MCU can automatically call the corresponding parameters according to the selected operating frequency to ensure that the circuit always works in the optimal resonance state.

[0092] Figure 13 This is a flowchart of a control method for a transcranial dual-frequency ultrasound transducer, which includes the following steps:

[0093] Step 1: Use an impedance analyzer to scan the impedance curve of the dual-frequency ultrasonic transducer to determine its two resonant frequencies F1 and F2. It is also necessary to obtain the static capacitances C0-1 and C0-2 of the transducer at frequencies F1 and F2.

[0094] Step 2: Based on the static capacitors C0-1 and C0-2 corresponding to the resonant frequencies of F1 and F2, adjust the matching network to find the optimal matching inductors LDS-1 and LDS-2.

[0095] Step 3: Write the resonant frequencies F1 and F2 and the optimal matching inductors LDS-1 and LDS-2 into the internal memory chip SC or record them in the control software.

[0096] Step 4: During transcranial ultrasound, select the required frequency (F1 or F2) according to clinical needs. If frequency F1 is selected, the MCU will activate the optimal matching inductor LDS-1 corresponding to F1, and control the relay switch (e.g., Figure 11 As shown in ki), the equivalent inductance of the matching circuit is adjusted to LDS-1. Simultaneously, the MCU outputs a PWM signal of F1, ensuring the transducer operates efficiently at frequency F1 and outputs the preset ultrasonic energy. If frequency F2 is selected, the MCU will activate the optimal matching inductance LDS-2 corresponding to F2 and adjust the impedance matching network to ensure the transducer operates efficiently at frequency F2 and outputs the preset ultrasonic energy.

[0097] The dual-frequency transcranial ultrasound stimulation system proposed in this invention overcomes the technical bottlenecks of traditional single-frequency ultrasound stimulation. The system employs a coupling of a backing layer, a piezoelectric element layer, and an acoustic matching layer. By controlling the thickness of each layer and the matching of acoustic impedance, it successfully achieves dual-frequency resonant output in the low-frequency F1 range (0.2-0.5MHz) and the high-frequency F2 range (0.5-1MHz). The accompanying control circuit uses an adjustable inductor array and stores resonant parameters (F1 / F2, LDS-1 / LDS-2) to dynamically match the dual-frequency impedance, ensuring maximum energy transmission efficiency at both 330kHz and 590kHz. Experimental data shows that the system can generate a 48mm long focal range and a 6mm wide acoustic beam in the F1 low-frequency mode, suitable for superficial, large-area stimulation; and in the F2 high-frequency mode, it can form a 31mm short focal range and a 3.3mm narrow acoustic beam, meeting the needs of deep, precise stimulation.

[0098] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A dual-frequency transcranial ultrasound stimulation system, comprising a dual-frequency ultrasound transducer and a control circuit, characterized in that, The dual-frequency ultrasonic transducer is used to resonate at a first frequency and a second frequency and output ultrasound, and the dual-frequency ultrasonic transducer is composed of a backing layer, a piezoelectric element layer and an acoustic matching layer connected in sequence. The first frequency has a frequency band range of 0.2-0.5MHz, and the second frequency has a frequency band range of 0.5-1.0MHz; The control circuit is used to output continuous or pulsed sinusoidal electrical signals at a first frequency and a second frequency, respectively, and to match the dual-frequency ultrasonic transducer to output at maximum transmission efficiency.

2. The dual-frequency transcranial ultrasound stimulation system according to claim 1, characterized in that, The expression for the first frequency is: F1≈c p / (2t p ); t p =λ p / 2; The expression for the second frequency is: F2≈c m / (4t m ); t m =λ m / 4; In the formula, F1 represents the first frequency, and c p The longitudinal wave velocity, t, represents the vibration mode of the piezoelectric element material thickness. p λ represents the thickness of the piezoelectric element layer. p F1 represents the ultrasonic wave length in the piezoelectric element layer at the first frequency, F2 represents the second frequency, and c represents the second frequency. m The sound velocity t represents the acoustic matching layer material. m λ represents the thickness of the acoustic matching layer. m This indicates the length of the ultrasonic wave in the acoustic matching layer at the second frequency.

3. The dual-frequency transcranial ultrasound stimulation system according to claim 1, characterized in that, At the first frequency F1, the overall thickness of the piezoelectric element and the acoustic matching layer is 1 / 2 wavelength, and the resonant node is located inside the piezoelectric element. At the second frequency F2, the interface between the piezoelectric element and the acoustic matching layer is the resonant node, the thickness of the acoustic matching layer is 1 / 4 wavelength, the thickness of the piezoelectric element is 3 / 4 wavelength, there is a node inside the piezoelectric element, and the overall coupling between the piezoelectric element and the acoustic matching layer is one wavelength.

4. The dual-frequency transcranial ultrasound stimulation system according to claim 1, characterized in that, The thickness, sound velocity, and material properties of the acoustic matching layer are configured such that the second frequency F2 is higher than the first frequency F1, and both are within the effective operating frequency band of the transducer.

5. A dual-frequency transcranial ultrasound stimulation system according to claim 1, characterized in that, The first frequency is dominated by the vibration of the piezoelectric element layer. When it is necessary to reduce the first frequency, the thickness of the piezoelectric element is increased or a soft piezoelectric material is used to reduce the longitudinal wave velocity in the vibration mode. When it is necessary to increase the first frequency, the thickness of the piezoelectric element is decreased or a hard piezoelectric material is used to increase the longitudinal wave velocity in the vibration mode. The second frequency is dominated by the coupling between the acoustic matching layer and the piezoelectric element layer. When it is necessary to adjust the resonant point of the second frequency independently, the thickness of the acoustic matching layer or the density and material sound velocity of the acoustic matching layer are adjusted within a preset range so that the acoustic impedance of the acoustic matching layer and the piezoelectric element layer meets the preset ratio, so as to ensure that the two resonant peaks are clearly separated and in the target frequency band, and finally achieve efficient dual-frequency output.

6. A dual-frequency transcranial ultrasound stimulation system according to claim 1, characterized in that, The material of the piezoelectric element layer is piezoelectric ceramic, piezoelectric composite material or single crystal material, and the polarization direction is consistent with the thickness direction; The acoustic matching layer is made of epoxy resin substrate and metal or metal oxide powder filler, polymer and ceramic particles, glass or microporous ceramic.

7. A dual-frequency transcranial ultrasound stimulation system according to claim 1, characterized in that, The dual-frequency ultrasonic transducer is either a focused transducer or a non-focused transducer.

8. A dual-frequency transcranial ultrasound stimulation system according to claim 1, characterized in that, The acoustic impedance ratio of the backing layer to the piezoelectric element layer is 0.8-1.2, and the acoustic impedance ratio of the acoustic matching layer to the piezoelectric element layer is 0.1-0.

6.

9. A dual-frequency transcranial ultrasound stimulation system according to claim 1, characterized in that, The control circuit consists of a power supply, a main control circuit, an ultrasonic drive circuit, and a matching circuit. The main control circuit is used to generate a baseband signal at a first frequency and a second frequency. The ultrasonic drive circuit is used to amplify the power of the first and second frequency fundamental frequency signals generated by the main control circuit to drive the dual-frequency ultrasonic transducer to work. The matching circuit is used to ensure that the first and second frequencies operate at maximum transmission efficiency when matched with the dual-frequency ultrasonic transducer.

10. A dual-frequency transcranial ultrasound stimulation system according to claim 9, characterized in that, The control of the dual-frequency ultrasonic transducer includes: Impedance curve scanning of the dual-frequency ultrasonic transducer was performed using an impedance analyzer to determine the resonant frequencies of the low and high frequencies, obtain the first and second frequencies, and acquire the first and second static capacitances of the dual-frequency ultrasonic transducer at the first and second frequencies. Based on the first static capacitor and the second static capacitor, the optimal first matching inductor and the second matching inductor are determined by adjusting the matching network, and the first frequency, the second frequency, the optimal first matching inductor and the second matching inductor are written into the memory chip of the main control circuit or recorded in the control software. The first or second frequency is selected based on clinical needs. When the first frequency is selected, the main control circuit calls the optimal first matching inductor corresponding to the first frequency and adjusts the equivalent inductance of the matching circuit to the optimal first matching inductor by controlling the relay switch. At the same time, the main control circuit outputs a PWM signal of the first frequency to ensure that the dual-frequency ultrasonic transducer works efficiently at the first frequency and outputs the preset ultrasonic energy. When the second frequency is selected, the main control circuit calls the optimal second matching inductor corresponding to the second frequency and adjusts the impedance matching network. At the same time, the main control circuit outputs a PWM signal of the second frequency to ensure that the dual-frequency ultrasonic transducer works efficiently at the second frequency and outputs the preset ultrasonic energy.

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