Wearable devices for transdermal product delivery

Abstract

The present invention relates to a wearable device for transdermal product delivery that includes a head (3) with an outer cavity (6) housing two resonating ultrasonic resonators (1, 2). The more distal first resonator (1) radiates toward the skin at a first frequency, while the more proximal second resonator (2) surrounds the cavity (6) and radiates parallel to the skin at a second frequency. One frequency is high-frequency sonophoresis (HFS) and the other is low-frequency sonophoresis (LFS). The second resonator (2) includes a hole (7) to allow the passage of waves from the first resonator (1). Waves from the second resonator (2) pass through the head (3), the hole (7), and the cavity (6) and bounce off the opposite area of ​​the head (3), interfering with the waves from the first resonator (1). The interference between the waves creates a static electric field, which increases the skin's permeability, allowing for miniaturized devices to be incorporated into wearable devices.

Description

[Technical Field]

[0001] The invention can be included more particularly in the health and personal care sector, for example for the delivery of active substance products such as drugs and cosmetics, and more particularly, the subject of the invention is a wearable device for the transdermal and non-invasive delivery of products. [Background technology]

[0002] A variety of techniques and devices exist for transdermally and non-invasively delivering drugs with molecules of considerable size, such as insulin.

[0003] To do so, the drug must pass through the stratum corneum of the patient's skin, which has a low absorption capacity, especially for high molecular weight molecules such as insulin.

[0004] The structure of human skin is a stratum corneum consisting of an outer layer of dead cells (corneocytes) embedded in a lipid matrix, which makes it difficult for substances such as insulin, especially those with molecular sizes larger than the hair follicles, to diffuse through the stratum corneum.

[0005] In this sense, some techniques were initially developed, such as electrophoresis (using voltages of up to 150 V) or iontophoresis, which use low voltages.

[0006] The benefits of sonophoresis, which involves applying ultrasound waves to a fluid containing a substance that is in contact with the skin and then applied to the interior of the skin, were first discovered in 1950. Initially, frequencies from 700 kHz to 10,000 kHz (high frequency sonophoresis, HFS) were used to deliver corticosteroids, disrupting the stratum corneum layers sufficiently to allow permeation of small molecules; a stable cavitation effect caused bubbles to vibrate within the stratum corneum in a lipid matrix, allowing up to 10 times more delivery than without ultrasound.

[0007] Beginning in the 1990s, research into sonoporation at low and mid-frequency waves began, based on the knowledge that cavitation improves the transmission of certain substances through the skin when ultrasound is applied, and that the effects associated with cavitation in liquids increase inversely with frequency. The effects of using low frequencies between 20 and 100 kHz (low-frequency sonophoresis, LFS) began to be studied, and it was discovered that the lower the frequency in LFS, the greater the permeability, demonstrating that transient cavitation is the most important mechanism for improving skin permeability using LFS.

[0008] Since 1996, several studies on multi-frequency sonophoresis (one frequency in the HFS range and another frequency in the LFS range) have been published with convincing results for the separate application of HFS and LFS. However, applying LFS frequencies has the drawback that the size of the transducer providing the LFS frequency increases with the lower the frequency and the higher the intensity. Therefore, devices providing sufficient intensity have proven too large for use as part of a wearable device. In other words, the low-frequency ultrasound transducers used to achieve the necessary intensity are too large to be added to a wearable device. Summary of the Invention

[0009] The present invention describes a wearable device for delivering transdermal products in a wearable, non-invasive manner, comprising the combination of two ultrasonic resonators, for example of the piezoelectric type, housed in one and the same head, one located at a distal position and the other located at a proximal position, each resonator defining a transducer in combination with the head configuration, one resonator resonating and operating at LFS frequencies and the other resonator resonating and operating at HFS frequencies, and similarly the resonator located at the proximal position has a through-hole inside through which radiation passes from the other resonator located at the distal side, so that the radiation from both resonators interact to form a static field, increasing the effect of transparency for a given resonator size and making it possible to reduce the size of the device for a given performance.

[0010] The device of the present invention allows the product to penetrate the stratum corneum by cavitation and opening of pores in a reversible manner and without damaging the skin.

[0011] The devices of the present invention optionally, but not exclusively, have medical applications, as explained below.

[0012] Usually, in the prior art, the thickness and size of the resonator are determined by the frequency and intensity at which they operate. However, the device of the present invention, by its design, radiates the wavefront in different ways throughout the entire head structure, so that in both the LFS and HFS cases, the generated wave provides the desired frequency and intensity, and as mentioned above, when forming a static field, due to the amplifying effect of transparency, it succeeds in amplifying the wave while obtaining a resonant peak at the desired frequency, especially in the LFS frequency range. This allows the device to be assembled in a size suitable for being part of a wearable device.

[0013] The configuration of the device allows it to be adapted to deliver a variety of products. The products can be liquids with high or low density or viscosity, as well as non-liquid in nature, such as gels, ointments, or creams. The device may also be a medical device, as both liquid and non-liquid products may contain drugs such as insulin. Alternatively, the device can be configured to deliver liquids or other types of cosmetic products with non-liquid properties, such as creams, gels, ointments, etc., as described above.

[0014] The present invention has preferred exemplary embodiments in which a proximally located resonator operates at a resonant frequency of the LFS frequency and a distally located resonator operates at a resonant frequency of the HFS frequency, and other preferred exemplary embodiments in which the reverse occurs, e.g., a proximally located resonator operates at a resonant frequency of the HFS frequency and a distally located resonator operates at a resonant frequency of the LFS frequency. [Brief explanation of the drawings]

[0015] For a better understanding of the foregoing and other advantages and features, they should be interpreted by way of example and not limitation based on the following detailed description of several embodiments with reference to the accompanying drawings. [Figure 1] 1 shows a schematic side view of the head of the device. [Figure 2A] 1 shows a schematic cross-sectional side view of the configuration of a first exemplary embodiment of a device of the present invention. [Figure 2B] 1 shows a schematic cross-sectional side view of a head. [Figure 3A] 1 shows a schematic cross-sectional side view of the configuration of a second exemplary embodiment of a device of the present invention. [Figure 3B] 1 shows a schematic cross-sectional side view of a head. DETAILED DESCRIPTION OF THE INVENTION

[0016] Next, with the aid of Figures 1 to 3B above, a detailed description of a preferred exemplary embodiment of a medical wearable device for transdermal delivery of a product in general is provided, which device is intended in particular, but not exclusively, to deliver a drug, more particularly insulin, which device allows the product to pass through the stratum corneum of the user's skin in a reversible manner and without causing damage to the skin, by cavitation and opening of pores.

[0017] As shown in Figure 1, the device of the invention comprises two ultrasonic resonators (1, 2), for example of the piezoelectric type, housed in one and the same head (3), which has a proximal region (4) intended to contact the user's skin and a distal region (5) opposite the proximal region (4) and therefore facing away from the user's skin.

[0018] In the proximal region (4), the head (3) has an outer cavity (6) intended to accommodate an ultrasound-conducting substance, which may be liquid or non-liquid, such as an ointment, cream, or gel, during use to prevent the presence of gas and thus allow ultrasound waves to be transmitted from the head (3) to the skin. Typically, the ultrasound-conducting substance corresponds to the product itself, but this is not necessarily the case. Specifically, the product may be deposited on the head (3) within the cavity (6), after which the head (3) is applied to the skin to bring the skin into contact with the product. Alternatively, the device may be applied to a product reservoir (not shown), such as a patch arranged to be fixed (e.g., by adhesive) or simply superimposed on the user's skin. Another possibility, for example, is that the device additionally includes a delivery element (not shown) attached, either detachably or non-detachably, to the head (3) near the cavity (6), particularly to allow delivery of the product according to a predetermined dose. The head (3) is preferably made of a biocompatible material or substance.

[0019] The resonators (1, 2) include a first resonator (1) located in the distal region (5) and therefore not affected by the cavity (6), and a second resonator (2) located in the proximal region (4) and surrounding at least a portion of the cavity (6) as described below. The resonators (1, 2) emit narrowband ultrasound waves, and each resonator (1, 2) is intended to resonate and operate at a predetermined frequency.

[0020] The first resonator (1) may be shaped, for example, like a disk, and in use emits ultrasonic radiation at a first frequency toward the user's skin, generally in a direction perpendicular to the skin, pointing toward the cavity (6). Furthermore, the second resonator (2), which emits waves at a second frequency in use, is hollow, i.e., includes an inner through-hole (7) so that waves at the first frequency can pass through the second resonator (2) without impinging on it. Preferably, the inner through-hole (7) is larger than the first resonator (1) so that all waves emitted by the first resonator (1) pass through the hole (7) of the second resonator (2). The second resonator (2) may have the shape of a torus, whether circular, rectangular, etc., with a generatrix, or a circular or other type of directrix. Preferably, it has the shape of a circular torus, i.e., a ring torus, or a torus with a rectangular cross section.

[0021] The first resonator (1) is positioned overlapping the second resonator (2), but not enclosed within it, i.e., at a different height. As previously shown, this overlapping allows waves emitted from the first resonator (1) to pass through the hole (7) without impinging on the second resonator (2).

[0022] The cavity (6) of the head (3) corresponding to the height of the second resonator (2) is surrounded by the second resonator (2). As a result, the waves radiated from the second resonator (2) are substantially parallel to the skin, which makes it possible to amplify the transmission effect due to the action of the first resonator (1).

[0023] The head (3) has three functions: supporting the resonators (1, 2), providing physical continuity for the wave path, and inducing resonance at the first and second frequencies, as described below. The head (3) is preferably made of a metal such as aluminum or a biocompatible polymer material such as polypropylene. Preferably, the head (3) is a monoblock. The resonators (1, 2) are assembled on the head (3), and the head is configured such that, when the resonators (1, 2) are assembled, the waves emitted from the resonators (1, 2) circulate through the head (3) without encountering any gaseous substances before exiting the head (3), preventing malfunction of the resonators (1, 2). For example, as shown in Figures 2A, 2B, 3A, and 3B, the head (3) includes a receiving portion (13) that is received in the hole (7) of the second resonator (2) and preferably occupies the periphery of the hole (7). Preferably, the housing (13) is integrally formed with the head (3).

[0024] As described above, the second resonator (2), for example having the ring shape described above, has a hole (7) and is accommodated inside the head (3) in correspondence with the cavity (6) such that the cavity (6) occupies the hole (7) as well as the accommodation portion (13) of the head (3). As a result, and primarily, radiation emitted from the first resonator (1) toward the user's skin passes through the hole (7) and the cavity (6) and reaches the skin. Secondly, the waves generated in the horizontal direction by the second resonator (2) do not leak "infinitely" from the head (3), but radiate from the holes (7), thereby passing through the head (3) and the cavity (6), and for that reason collide and bounce back to the opposite area of ​​the head (3) itself, generating in all horizontal directions, creating a static field in the cavity (6) for the waves from the second resonator (2), which interacts with the waves of the first resonator (1) and, under resonance conditions, increases the effect acting on the skin in the area surrounded by the head (3) and the second resonator (2), further increasing the permeability of the affected area of ​​the skin and therefore the delivery effect. Therefore, it is possible to obtain desired resonance and intensity conditions in a small device that can be incorporated into a wearable device.

[0025] The frequency emitted by one of the two resonators (1, 2), either the first resonator (1) or the second resonator (2), is significantly lower than the higher frequency emitted by the other resonator (1, 2). The low frequency is in the typical LFS zone, approximately 20 kHz to 100 kHz, i.e., the lowest zone of ultrasound. Values ​​close to 20 kHz, the upper threshold of human hearing, can cause auditory discomfort to the user, but still provide satisfactory results. A frequency in the 55 kHz range between 50 kHz and 60 kHz is selected as the preferred low frequency. Furthermore, the high frequency is in the typical HFS zone, e.g., around 1 MHz, between 800 kHz and 1200 kHz. The present invention also works well when the first frequency is high and the second frequency is low, or vice versa.

[0026] Another feature of the device of the invention, apart from the construction of the resonators (1, 2) shown above and their integration into the head (3), is the handling of the resonances, as will be explained below.

[0027] As previously indicated, one resonator (1, 2) is intended to emit ultrasound at the HSF frequency and be fed at the HSF frequency in order to resonate at the HSF frequency, and the other resonator (1, 2) is intended to emit ultrasound at the LSF frequency in order to resonate at the LSF frequency, each resonator (1, 2) having a fundamental frequency corresponding to a certain vibration mode, for example a thickness mode or a radial mode, due to its structure.

[0028] For example, cylindrical (disk)-shaped solid-state resonators (1, 2) have a thickness-mode fundamental frequency, and increasing the resonator size decreases the fundamental frequency, and vice versa. For example, a 4 MHz ceramic may be 0.5 mm thick and 6 mm in diameter, a 2 MHz ceramic may be 1 mm thick and 6 mm in diameter, and a 1 MHz ceramic may be 2 mm thick and 10 mm in diameter. That is, a disk-shaped resonator (1, 2) with a reduced size, like the first resonator (1), is suitable for achieving thickness-mode resonance at the HFS frequencies without requiring adaptation.

[0029] However, for example, a hollow resonator (1, 2) in the shape of a ring, such as the second resonator (2), would have to be large in size, which is unacceptable for a wearable device, in order to operate thickness mode resonance at the LFS frequency.

[0030] To solve the above-mentioned drawbacks, the present invention provides two solutions as shown below, which will be described in detail in the following examples.

[0031] The first solution, as described below, uses a first resonator (1), e.g., a solid disk-shaped resonator, with a fundamental thickness mode frequency in the HFS range to resonate and operate at LFS frequencies. The head (3) includes several components (8, 9, 10) intended to be in contact with the first resonator (1). As a result, the assembly of the first resonator (1) and the head (3) is formed with physical continuity, constituting a transducer that resonates in an extensional mode at an LFS frequency even though the LFS frequency is not the fundamental thickness mode frequency of the first resonator (1). The second resonator (2), which has a hollow shape such as a ring, can have a fundamental thickness mode frequency in the HFS range so that it resonates at an HFS frequency when an HFS frequency is applied. The first embodiment, described in detail below with reference to Figures 2A and 2B, shows dimensions and features that support the content described in the first solution.

[0032] Furthermore, the second solution utilizes the fact that the fundamental frequency of the ring-like hollow second resonator (2) is within the LFS range, not the thickness mode, due to its size and structure. Therefore, when an LFS frequency is supplied to the second resonator (2), it resonates and operates in the radial mode at the LFS frequency. Furthermore, the disk-shaped first resonator (1) has a fundamental frequency of the thickness mode within the HFS range due to its dimensions, and when an HFS frequency is supplied, it resonates at the HFS frequency. The second embodiment, which will be described in detail below with reference to Figures 3A and 3B, will show dimensions and features that support the content described in the second solution. [Example]

[0033] The device of the present invention has an operation that can be based on different types of operation of the resonators (1, 2), such as flexion-transmission (see FIGS. 2A and 2B) or transmission-transmission (see FIGS. 3A and 3B). In the case of resonators (1, 2) operating in flexion-transmission, according to FIGS. 2A and 2B, a membrane (8), preferably made of metal, is arranged as an integral part of the head (3) and vibrates by bending while in contact with the first resonator (1). Furthermore, the head (3) may further include two protrusions (9, 10), one proximal (9) and the other distal (10), which cooperate with the membrane (8) to operate in a resonant extension mode at a predetermined LFS frequency, integral with the first resonator (1). According to FIGS. 3A and 3B, in the case of transmission-transmission, the head (3) may also include a transmission disk (14) for transmitting vibrations, but the membrane (8) is not required.

[0034] The height of the cavity (6) is approximately 1-2 mm in a preferred exemplary embodiment and is related to the height of the second resonator (2), which is selected based on the desired product content that can be accommodated in the cavity (6). A small volume requires the user to frequently replace the product in the cavity (6), while a large volume increases the risk of administering a larger volume. The cavity (6) contains an ultrasound-conductive material to prevent the presence of gas during use, thereby enabling transmission of ultrasound from the head (3) to the skin. The ultrasound-conductive material may be liquid, or may have non-liquid properties, such as a cream, gel, or ointment, as long as it is ultrasound-conductive. Specifically, if it is ultrasound-conductive, it may be the product to be applied. The device of the present invention can also be used to dispense non-liquid products, such as the aforementioned creams, gels, and ointments. To this end, the device of the present invention is first used with a potentially harmless ultrasound-conducting substance to generate a cavitation effect and open the pores of the skin, and then, without the use of the device, this effect is used to apply and absorb an active product of a non-liquid nature, such as a cream, gel, ointment, etc.

[0035] As an illustrative, non-limiting example, the head (3) has a cylindrical shape with an inverted U-shaped cross section, a diameter of about 25 mm, a height of about 2 to 10 mm, preferably 5 to 10 mm, and a height of the cavity (6) of about 2 to 3.3 mm.

[0036] To achieve a sufficiently high acoustic pressure to generate a sufficient number of cavitation bubbles and to favor the aforementioned combined effect of opening skin pores by imploding the cavitation bubbles, a pressure of 0.5 W / cm 2 above 1 W / cm 2 In this sense, radiation waves that produce high ultrasonic intensities above 1 W / cm are more advantageous. 2 Intensities above 1 W / cm are considered to be adequate. To meet some legal restrictions, in particular to prevent the resulting risk of skin damage, an intensity value of 1 W / cm 2 ~2W / cm 2 It is desirable to maintain it between

[0037] Two illustrative examples of the characteristics of a head (3) with two resonators (1, 2) are given below, as illustrated in Figures 2A, 2B, 3A and 3B.

[0038] In both examples, the head (3) is an aluminium monoblock, alternatively it could be a polypropylene monoblock.

[0039] According to a first embodiment, called flexion-transmission (see FIGS. 2A and 2B), the following components are included: - A first resonator (1) configured as a ceramic disk for applying a force, the thickness of which varies between 0.5 mm and 1 mm, the diameter of which is 6 mm, and the fundamental frequency of vibration of the thickness of which is 2 MHz or 4 MHz. - a second resonator (2) in ceramic for applying force, configured as an annular body having a rectangular cross section and circular orthogonal axes, a thickness of 2 mm, an outer diameter of 20 mm, an inner diameter of 14 mm and a fundamental frequency of vibration of the thickness of 1 MHz; - a vibrating membrane (8) having a diameter of 11 mm and a variable thickness, inserted between the first resonator (1) and the second resonator (2), in contact with the first resonator (1), and vibrating integrally with the first resonator (1) in a stretching vibration mode supplied from the first resonator (1); - A cavity (6) of variable height, 11 mm in diameter, resting on a membrane (8). - two protrusions (9, 10), one proximal (9) and the other distal (10), between which the membrane (8) is supported, the distal protrusion (10) having an outer diameter of 14 mm and an inner diameter of 8 mm, and the proximal protrusion (9) having an outer diameter of 11 mm and an inner diameter of 8 mm, the protrusions (9, 10) working together with the membrane (8) in a first resonator (1) resonantly operating at a predetermined LFS frequency of 55 kHz; - a head (3) for fixing the resonators (1, 2), the head (3) being partly composed of a membrane (8) and protrusions (9, 10) and being supplied with vibrations transmitted by the first resonator (1); a receiving part (13) forming part of the head (3) and intended to be received in the area close to the periphery of the hole (7). an adhesive layer (12) of varying thickness between the second resonator (2) and the head (3);

[0040] In the first example, the coupled "thickness" mode of the second resonator (2) is used, with the resonant vibration transmitted by direct transmission to the head (3) to which the second resonator (2) is attached, the resonant frequency of the second resonator (2) essentially depending on the shape and material of the second resonator (2), with minor variations due to the wall thickness of the head (3). Similarly, the first resonator (1) is used as the source of the dominant frequency in a bending mode of 55 kHz, depending on the characteristics of the first resonator (1), in particular the overall bending of the first resonator (1) and the configuration of the vibrating membrane (8) and protrusions (9, 10).

[0041] Furthermore, according to a second embodiment called Transfer-Transfer (see FIGS. 3A and 3B), the following components are included: - a first resonator (1) configured as a ceramic disk for applying a force, the first resonator (1) having a thickness of 2 mm, a diameter of 10 mm and a main frequency of vibration in the thickness of 1 MHz; - a second resonator (2) made of ceramic for applying the force, configured as a ring with a rectangular cross section and circular orthogonal axes, a thickness of 2 mm, an outer diameter of 20 mm, an inner diameter of 14 mm, and a dominant frequency of radial vibration of 55 kHz; - a transmission disk (14) of 11 mm diameter and varying thickness, placed on the first resonator (1), for receiving the vibrations of the first resonator (1) by transmission and transmitting these vibrations from the first resonator (1) to the cavity (6). - A cavity (6) with a variable height of approximately 3.5 mm and a diameter of 11 mm, located above the transmission disc (14). - A head (3) for fixing the resonators (1, 2), the head (3) being partly constituted by a transmission disk (14) and receiving vibrations transmitted from the first resonator (1). - a receiving part (13) forming part of the head (3) and intended to be received in the hole (7).

[0042] In the second embodiment, the first radial mode of the second resonator (2) is used to excite bending modes of the head (3), specifically the housing (13), at low frequencies by radial transmission of the second resonator (2) to the wall of the head (3) to which the second resonator (2) is attached. The final frequency of the second resonator (2) is responsive to the overall bending of the second resonator (2) together with the head (3), in this case 55 kHz. Furthermore, the first resonator (1) operates by direct transmission of thickness modes at HFS frequencies.

[0043] Unlike the first embodiment, the second embodiment does not incorporate a vibrating membrane (8), and instead promotes direct wave transmission from the resonators (1, 2) to the cavity (6). The first embodiment incorporates a membrane (8) that vibrates in a bending manner so that the first resonator (1) and membrane (8) jointly resonate at an LFS frequency, such as 55 kHz, while the second resonator (2) radiates at an HFS frequency, such as 1 to 3 MHz. In contrast, in the second embodiment, the radiation frequency and the resonance frequency of the first resonator (1) are similar, close to 1 MHz, so that only transmission exists instead of bending. Therefore, since there is direct transmission between the two frequencies, this model is called transmission-transmission. In these two embodiments, the first and second frequencies are swapped. In the first embodiment, the first frequency is LFS and the second frequency is HFS, while in the second embodiment, the opposite is true.

[0044] For each of the two examples, and generally in any embodiment of the invention, it is envisaged that the head (3) may be made of a biocompatible material such as a metal, e.g., aluminium, or alternatively a polymer, e.g., polypropylene.

Claims

1. 1. A wearable device for transdermal product delivery, the wearable device comprising: A head (3) comprising: a proximal region (4) intended to be close to the user's skin in use; a distal region (5) further away from the user's skin; and a head including an outer cavity (6) defined in said proximal region (4) and intended to be oriented towards the skin of said user in use; a first resonator (1) housed in the distal region (5) of the head (3), operating in resonance at a first frequency and for emitting ultrasound waves at said first frequency towards the skin of a user; a second resonator (2) housed in the proximal region (4) of the head (3), operating in resonance at a second frequency and for emitting ultrasound waves at the second frequency in a direction parallel to the skin; wherein one of the first and second frequencies is a high frequency sonophoresis (HFS) frequency and the other frequency is a low frequency sonophoresis (LFS) frequency, and the head (3) is configured to allow waves emitted by the resonator (1, 2) to circulate through the head (3) without encountering gaseous matter before exiting the head (3); The second resonator (2) includes an inner through-hole (7) for allowing waves from the first resonator (1) to pass through without hitting the second resonator (2), and a portion of the cavity (6) of the head (3) corresponding to the height of the second resonator (2) is surrounded by the second resonator (2); wherein the waves from the second resonator (2) are directed through the head (3), the through-hole (7) and the cavity (6) to bounce back to the head (3) at an opposite position and interfere with the waves from the first resonator (1).

2. The wearable device of claim 1 , wherein the LFS frequency is in the range of 50 to 60 kHz.

3. The wearable device according to any one of claims 1 to 2, wherein the HFS frequency is in the range of 800 to 1200 kHz.

4. The wearable device according to any one of claims 1 to 3, wherein the first resonator (1) has a disk shape.

5. The wearable device according to any one of claims 1 to 4, wherein the second resonator (2) has an annular shape.

6. The wearable device according to any one of claims 1 to 5, wherein the first resonator (1), together with the head (3), is intended to resonate and operate at the LFS frequency, and the second resonator (2) is intended to operate at the HFS frequency.

7. 7. The wearable device of claim 6, wherein the second resonator (2) has a toroidal shape with a fundamental frequency of vibration in thickness mode within the HFS range to resonate in thickness mode at the HFS frequency when supplied with the HFS frequency, while the first resonator (1) has a disc shape with a fundamental frequency of vibration in thickness mode within the HFS range, wherein the head (3) further comprises at least one component (8, 9, 10) intended to be in contact with the first resonator (1), and wherein the assembly of the first resonator (1) + head (3) is formed with physical continuity to constitute a transducer with a fundamental frequency in extension mode within the LFS range to resonate at the LFS frequency when supplied with the LFS frequency.

8. 8. The wearable device of claim 7, wherein the components (8, 9, 10) include a membrane (8) that vibrates by bending and is inserted between the first resonator (1) and the second resonator (2) and in contact with the first resonator (1).

9. 9. The wearable device of claim 8, wherein the component (8, 9, 10) further comprises two protrusions (9, 10), one proximal (9) and one distal (10), between which the membrane (8) is supported.

10. A wearable device according to any of the preceding claims, wherein the first resonator (1) is intended to operate resonantly at HFS frequencies and the second resonator (2) at LFS frequencies.

11. 11. The wearable device of claim 10, wherein the first resonator (1) has a disk shape with a fundamental frequency of the thickness mode in the HFS range when powered at an HFS frequency, so as to resonate in a thickness mode at the HFS frequency, while the second resonator (2) has a toroid shape with a fundamental frequency of the radial mode in the LFS range when powered at an LFS frequency, so as to resonate in a radial mode at the LFS frequency.

12. The wearable device of claim 11, wherein the head (3) further includes a transmission disk (14) arranged on the first resonator (1) for transmitting vibrations from the first resonator (1) to the cavity (6) by a transmission means.

13. The wearable device according to any one of claims 1 to 12, wherein the head (3) is constructed from one single monoblock body.

14. The wearable device according to any of the preceding claims, wherein the head (3) is made of a metallic material or a biocompatible polymer material.

15. The wearable device according to any one of claims 1 to 14, wherein the head (3) includes a housing (13) that occupies at least a portion of the through hole (7) of the second resonator (2).

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