Impedance-matching acoustic transducer

Abstract

The acoustic transducer includes a first layer including an elastomer. The acoustic impedance of the first layer substantially matches the acoustic impedance of a medium the transducer is configured to monitor. The transducer also includes a second layer including an electrode. The transducer also includes a third layer including a polymer. The second layer is at least partially positioned between the first and third layers.

Description

Technical Field

[0001] (Cross - Reference to Related Applications) This application claims priority to U.S. Provisional Patent Application No. 63 / 089,702, filed on October 9, 2020, the entire disclosure of which is incorporated herein by reference.

[0002] (Government Support) This application was made with government support under grants HL133043 and MD014104 awarded by the National Institutes of Health. The government has certain rights in the invention.

[0003] The present invention generally relates to transducers. More particularly, the present invention relates to impedance - matched acoustic transducers.

Background Art

[0004] We are constantly surrounded by large amounts of acoustic energy, whether from conversation, music, or environmental noise. When these sound waves are captured, they can provide rich information about humans and their surroundings, and this information can be utilized for a number of applications. In a first example, body sounds can provide details of health and diagnosis. In a second example, sounds in water can be used for guidance and tracking. In a third example, vibrations from physical objects can provide details regarding structural monitoring and energy harvesting to power small devices.

[0005] Currently, there are various acoustic transducers (e.g., electrodynamic, electromagnetic, electrostatic, and piezoelectric transducers) available for the above - mentioned applications, depending on the frequency range of interest, the required sensitivity, and the medium being monitored. Despite this wide range of options, the problem these transducers face is acoustic impedance mismatch between the device and the medium being monitored, which results in a decrease in energy density in the transducer element and interference from other sound sources.

Summary of the Invention

[0006] An acoustic transducer is disclosed. The transducer includes a first layer including an elastomer. The acoustic impedance of the first layer substantially matches the acoustic impedance of a medium configured to be monitored by the transducer. The transducer also includes a second layer including an electrode. The transducer also includes a third layer including a polymer. The second layer is at least partially positioned between the first layer and the third layer.

[0007] An acoustic transducer is further disclosed. The acoustic transducer includes a first layer including an elastomer. The first layer has a monomer to curing agent ratio of about 5:1 to about 20:1. The first layer includes a plurality of microstructures having a height of about 50 μm to about 1 mm. The first layer is doped with about 1% to about 60% silicon dioxide so that the acoustic impedance of the first layer substantially matches the acoustic impedance of a medium configured to be monitored by the transducer. The first layer is the only layer used to match the acoustic impedance of a medium configured to be monitored by the transducer. The acoustic transducer also includes a second layer including an electrode. The second layer substantially conforms to the microstructures such that the second layer includes peaks and valleys. The acoustic transducer also includes a third layer including a polymer. The polymer includes spin or spray coated cyclic olefin copolymer (COC) with or without corona charged fluorinated ethylene propylene (FEP), corona charged polytetrafluoroethylene (PTFE), polystyrene (PS) nanoparticles, or combinations thereof. The second layer is at least partially positioned between the first layer and the third layer. The third layer is substantially flat. There is a gap between the valleys of the second layer and the third layer.

[0008] A method is also disclosed. The method includes constructing a transducer configured to measure mechanical vibrations of a medium. The step of constructing the transducer includes doping a first layer of the transducer with a dopant based at least in part on the medium. The acoustic impedance of the first layer substantially matches the acoustic impedance of the medium by virtue of the material of the first layer, the dopant, or both. The step of constructing the transducer also includes disposing a second layer at least in part on the first layer. The step of constructing the transducer also includes disposing a third layer at least in part on the second layer. The method also includes disposing the first layer in contact with the medium. The method also includes measuring mechanical vibrations of the medium using the transducer.

[0009] The accompanying drawings provide visual representations that are used to more fully describe representative embodiments disclosed herein and that can be used by one skilled in the art to understand them and their inherent advantageous effects. In these drawings, like reference numerals identify corresponding elements.

Brief Description of the Drawings

[0010]

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DETAILED DESCRIPTION OF THE INVENTION

[0011] The subject matter of the present disclosure will be described more fully herein with reference to the accompanying drawings, in which embodiments of the invention, but not all embodiments, are shown. Like reference numerals refer to like elements throughout. The subject matter of the present disclosure can be realized in many different forms and should not be construed as limited to the embodiments described herein. Rather, these embodiments are defined so as to meet the legal requirements applicable to the present disclosure. Indeed, many variations and other embodiments of the subject matter of the present disclosure described herein will be apparent to those of ordinary skill in the art in the field related to the present disclosure, who will benefit from the teachings presented in the foregoing description and the related drawings. Accordingly, it is to be understood that the subject matter of the present disclosure is not limited to the specific embodiments disclosed, and that variations and other embodiments are intended to be included within the scope of the following claims.

[0012] The acoustic impedance (Z) is a function of the density of the material and the speed of sound within / through that material. When sound propagates between multiple media, due to the difference in acoustic impedance, at least a portion of the acoustic energy (e.g., sound waves) is reflected at the boundary. For example, when sound propagates between the body (Z = 1.54 MRayl) and air (Z = 0.0004 MRayl) or between water (Z = 1.50 MRayl) and a ceramic transducer (Z > 6 MRayl), most of the incident energy may not be captured by the transducer. Since only a very small amount of incident energy is transmitted to the transducer, both amplification techniques and very high-sensitivity transducers are used to capture the functional signal, and environmental power generation (energy harvesting) becomes inefficient. Transducers with impedance mismatched to the medium are also more vulnerable to being impaired by external noise. To increase the amount of incident energy that can be captured by the transducer and / or to reduce the adverse effects of noise, a matching layer can be used, but the matching layer creates a new set of limitations such as limited bandwidth, sensitivity dependent on thickness, and problems with the bonding between and within the matching layers.

[0013] To address these problems, the systems and methods described herein are directed to a wide-bandwidth self-powered impedance-matching transducer for improved sound monitoring. The transducer can be adjusted to match the acoustic impedance of the medium being monitored in the range of about 0.5 MRayl to about 5 MRayl or about 1 MRayl to about 2.5 MRayl. This maximizes signal transmission and eliminates the need for additional (e.g., matching) layers. This range of acoustic impedance includes materials such as living bodies (e.g., skin), fresh water, salt water, and most plastics.

[0014] In one application, the transducer can be specifically adapted to monitor surviving patients with respiratory and / or cardiovascular diseases, which are two of the leading causes of death worldwide. When placed on a patient's body (e.g., chest) together with an on-board electrical circuit, the transducer can record lung sounds and / or heart sounds over a long period of time, which can be used to remotely monitor and diagnose the patient for abnormalities without interference from conversation or ambient noise. The transducer can be flexible, thereby allowing it to be comfortably worn and deformed to fit the patient's movements. Low power consumption and the ability to generate environmental power enable continuous and sustainable use. The transducer can be used further or alternatively on low-density wood and / or underwater.

[0015] The transducer can include one or more polymer layers that are adjusted to substantially match the acoustic impedance of the medium being monitored without a matching layer. This minimizes the energy reflected from the transducer while maximizing its signal-to-noise ratio (SNR). Additionally, airborne noise sources can be passively eliminated as their energy is reflected at the air-transducer interface, preventing noise from contaminating the observed signal. This passive noise suppression mechanism effectively performs noise cancellation without computationally intensive and / or expensive signal processing and noise cancellation algorithms.

[0016] The transducer can capture the sound of the monitored medium (e.g., a human chest) with minimal processing (e.g., without processing) while still removing most of the background noise at a sound level of about 80 dB or more. For example, the transducer can remove about 97% to about 99.5% (e.g., 98.89%) of the background noise at a sound level of 71 dB to 90 dB (e.g., 85 dB), which can improve the function of a stethoscope. By comparison, conventional stethoscopes achieve equivalent performance only at about 70 dB due to costly electrical circuits for noise suppression. In other words, the transducer can be adjusted to the impedance of the human body to maximize the transmission of acoustic energy achieved with minimal interference and / or attenuation. For example, the transducer can be specifically adjusted to the human voice, internal sounds of the human body (e.g., heartbeat, lung sounds, etc.) or a combination thereof.

[0017] The acoustic impedance matching of the transducer can be customizable. As will be described in more detail below, one or more elastomers can be used as an adjusted acoustic impedance polymer layer, which is similar to the skin, breathable and safe. Furthermore, the transducer can be fabricated in various shapes and sizes, further facilitating mounting and integration. The simplicity and simple fabrication of the transducer are advantageous effects over current transducers, making the transducer adaptable to various applications.

[0018] In contrast to conventional transducers, the transducers described herein can generate an electrical response (e.g., voltage output) using the principle of electrostatic conversion. This is advantageous over methods based on piezoelectric and triboelectric conversion that have been prototyped in wearable transducers. Electrostatic conversion is less susceptible to mechanical wear and environmental conditions compared to triboelectric conversion. Electrostatic conversion is very low cost with simple (e.g., low temperature, without chemicals) processing, biocompatible, and reduces the coupling between acoustic impedance and electrical output without the use of lead-based materials compared to piezoelectric conversion. The voltage output is based on position and charge movement / recombination, and thus, low-frequency sounds can be observed / isolated.

[0019] The transducer is flexible, conformable to various surfaces, and complements its customizable acoustic impedance matching. The emergence of flexible electronic components and electrical circuits can facilitate the application of the transducer to curved surfaces. The conformal nature of the sensor enables a new paradigm in monitoring sounds from the body, thereby allowing the use of adhesives to place the transducer on the skin to capture sounds from the voice, heart, and lungs.

[0020] FIG. 1 shows a schematic cross-sectional view of a transducer 100 on a medium 102 according to one embodiment. The transducer 100 can be or include an electrostatic transducer. The medium 102 can be or include a human body (e.g., chest, neck, nose, etc.). In other embodiments, the medium 102 can be or include musical instruments, wood, water, infrastructure structural members (e.g., buildings, bridges), aerospace materials (e.g., aluminum, titanium), etc. In one embodiment, the transducer 100 can include a housing 104 having one or more components (e.g., layers) located at least partially herein. In other embodiments, the housing 104 can be omitted.

[0021] The transducer 100 can include a first (e.g., lower) layer 110 configured to be in direct contact with the monitored medium 102. The first layer 110 can be or include one or more elastomers. More particularly, the first layer 110 can be or include a tailored elastomeric matrix. For example, the first layer 110 can be or include polydimethylsiloxane (PDMS), ECOFLEX®, or polyurethane. The first layer 110 can be a single layer fabricated and / or doped to have specific parameters that control (e.g., adjust) the acoustic impedance to substantially match the impedance of the medium 102. As used herein, the impedance of the transducer 100 (e.g., the first layer 110) substantially matches the impedance of the medium 102 when the difference between the impedances is less than about 10%, about 5%, or about 1%. In one embodiment, the acoustic impedance of the transducer 100 can be controlled by varying the weight ratio of the elastomer and / or nanoparticle additives (also referred to as dopants) added to the elastomer. The nanoparticle additives can be or include ceramics, silicon dioxide, titanium dioxide, barium titanate, or combinations thereof. The concentration of the additive can be from about 1% to about 60%. For example, the concentration of the additive can be from about 1% to about 5%, from about 5% to about 10%, from about 10% to about 20%, from about 20% to about 40%, or from about 40% to about 60%.

[0022] In one embodiment, the first layer 110 can be the only layer that is used / adjusted to match the impedance of the medium 102. On the other hand, a conventional transducer can include a plurality of layers disposed between the medium 102 and the surface of the sensing element. These plurality of layers have different acoustic impedances and are laminated to provide a gradient and / or a stepwise transition from the impedance of the medium 102 to the impedance of the sensing element. On the other hand, the first layer 110 in the transducer 100 described herein provides impedance matching, also acts as a sensing element, minimizes reflections, and maximizes energy transfer. This can minimize reflections. In other words, the transducer described herein has only a single layer between the monitored medium and the impedance-matched sensing element as compared to a conventional transducer having a plurality of matching layers where reflections occur at each matching layer boundary, thereby minimizing reflections and maximizing energy transfer.

[0023] In one embodiment, the first layer 110 can include one or more arrayed microstructures 112. The microstructure 112 can be or include protrusions extending from the medium 102. The electrical and / or frequency response of the transducer 100 can be controlled (e.g., adjusted) by maintaining or changing the shape (e.g., hemispherical, conical, cylindrical) and / or dimensions of the microstructure 112. For example, the height 114 of the microstructure 112 can be from about 50 μm to about 1 mm, and the spacing 116 between two adjacent microstructures 112 can be from about 50 μm to about 1 mm.

[0024] The transducer 100 can also include a second layer 120 configured to be in direct contact (e.g., on top) of the first layer 110. As shown, the second layer 120 can conform to the outer surface of the first layer 110 that includes the microstructures 112. The second layer 120 can be or include a thin-film deposited electrode.

[0025] The transducer 100 may also include a third layer 130 configured to be in direct contact (e.g., on top) with the second layer 120. In the illustrated embodiment, the third layer 130 may be configured to contact the peaks of the second layer 120 but not the valleys of the second layer 120. The third layer 130 may be or include an electret polymer layer. An electret is a dielectric material having a semi-permanent charge or dipole polarization. An electret generates an internal electric field and an external electric field and is the electrostatic equivalent of a permanent magnet. For example, the third layer 130 may be or include fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE), cyclic olefin copolymer (COC), carbon nanotubes, other polarizing materials, or combinations thereof. In one embodiment, the COC may be spin-coated or spray-coated and corona charged, electron sprayed, or electrospun. In one embodiment, the FEP film may be corona charged, which may capture a charge that can be retained over a long period of time. For example, room temperature FEP is estimated to retain charge for about 200 years. The electrical and / or frequency response of the transducer 100 may be controlled (e.g., adjusted) by changing or maintaining the design of the third layer 130. For example, the surface area of the third layer 130 may be changed to vary the electrical response of the transducer 100.

[0026] The transducer 100 may also include a fourth (e.g., upper) layer 140 configured to be in direct contact (e.g., on top) with the third layer 130. The fourth layer 140 may be or include a conductive (e.g., metal) backing plate. The fourth layer 140 may be separated from the third layer 130 to vary the behavior of the transducer 100. This may help the transducer 100 collect energy. For example, this may increase the external electric field on both sides of the third layer 130. By physical deformation (e.g., patterning, porosification, etc.), by changing the material of the third layer 130, or by changing parameters, more charges may become available at the surface of the third layer 130.

[0027] In at least one embodiment, the transducer 100 may also include an intermediate layer 125. The intermediate layer 125 is at least partially positioned between the second layer 120 and the third layer 130 and may maintain the distance and / or deflection between the second layer 120 and the third layer 130 at high pressure. The intermediate layer 125 may be or include a gas such as air, nitrogen, helium, or a combination thereof. The gas may be at least partially fixed / captured between the second layer 120 and the third layer 130. In other embodiments, the intermediate layer 125 may be or include a porous polymer that is less rigid than the first layer 110. The porous polymer may prevent the microstructure 112 from collapsing, but the microstructure 112 may still deform due to the density of the porous material. The intermediate layer 125 may be used for underwater applications.

[0028] In still other embodiments, the transducer 100 may also include another / different intermediate layer (not shown) that is at least partially positioned between the third layer 130 and the fourth layer 140. This intermediate layer may be or include a piezoelectric material, which may promote ambient power generation.

[0029] In one embodiment, the transducer 100 may be connected to a field effect transistor (FET) conditioning circuit 160. The conditioning circuit 160 may be connected to the second layer 120 and / or the fourth layer 140 (e.g., the one that is not grounded). The conditioning circuit 160 may be configured to receive an electrical signal from the transducer 100 and reduce the impedance of that signal. In other words, the conditioning circuit 160 may act as a preamplifier to strengthen the signal, which may be transmitted to an amplifier 170.

[0030] FIG. 2 shows a graph 200 showing the range of impedance values that can be obtained by a first layer 110 (e.g., an elastomer) according to an embodiment. More specifically, graph 200 shows the acoustic impedance of two different elastomer substrates (e.g., PDMS and ECOFLEX®) doped with various levels of additive (e.g., silicon dioxide) nanoparticles. PDMS has a monomer to curing agent ratio of 10 to 1. PDMS is doped with 0% SiO 2 , 10% SiO 2 , 20% SiO 2 , 30% SiO 2 , 40% SiO 2 , 50% SiO 2 and 60% SiO 2 . ECOFLEX® is doped with 0% SiO 2 , 33% SiO 2 and 50% SiO 2 . Further, three reference materials of skin, soft wood and water are also shown. As can be seen from the graph, by selecting different materials and varying the dopant values, any impedance value can be achieved. Although not shown, in addition to PDMS and ECOFLEX®, polyurethane can also be used as an elastomer substrate.

[0031] To measure the acoustic impedance, the sample is experimentally characterized in a setup that includes an ultrasonic transducer immersed in water. The insertion technique is a relative measurement method that examines the transmission of longitudinal wave ultrasound through a solid medium immersed in water, using water as a reference.

[0032] FIG. 2 includes only a sampling of possible combinations of elastomer matrix and dopant. By exploring the use of elastomers at different densities, the user may be able to further expand the range of acoustic impedance values that can be obtained. In one embodiment, ECOFLEX® may be selected for its biocompatibility, flexibility and ease of cleaning.

[0033] FIG. 3A shows a graph 300A showing the acoustic output of the transducer 100 without noise (e.g., at ambient noise of 45 dB SPL), FIG. 3B shows a graph 300B showing the acoustic output of the transducer 100 with noise (e.g., at 80 dB SPL), FIG. 3C shows a graph 300C showing the acoustic output of the ambient microphone without noise (e.g., at ambient noise of 45 dB SPL), and FIG. 3D shows a graph 300D showing the acoustic output of the ambient microphone with noise (e.g., at 80 dB SPL), all of which relate to embodiments. Graphs 300A - 300D are spectrograms when counting from 6 to 10. As can be seen from the graphs, the quality of the acoustic recording is maintained even in a very noisy environment due to impedance matching of the transducer 100. The transducer 100 also preserved most of the spectral power in the conversation. The frequency response of the transducer 100 can be further optimized by changing the structure of the first layer (e.g., the elastomer 110).

[0034] Stability and stored charge can vary based on parameters including the duration, temperature, and grid voltage used to charge the sample medium. The upper surface of the third layer 130 can be in contact with the fourth layer 140. When the surface of the transducer 100 is subjected to mechanical vibrations caused by acoustic waves, the first layer 110 vibrates as well. This deforms the microstructures 112 on the surface of the first layer 110, causing a change in the size of the gap between the first layer 110 and the third layer 130 (e.g., the electret film layer). The deformation of the gap results in a corresponding voltage output proportional to the original mechanical vibration.

[0035] Figures 4A - 4C show graphs 400A - 400C indicating the stability of the third layer 130 of the transducer 100 according to this embodiment. More specifically, graphs 400A - 400C show the surface potential of the third layer (e.g., FEP film) 130 monitored over a period of 20 - 30 days. The third layer 130 in the first graph 400A is charged at room temperature for 1 hour with various grid voltages. The third layer 130 in the second graph 400B is charged at various temperatures for 1 hour with a grid voltage of 2000V. The third layer 130 in the third graph 400C is charged at room temperature for various durations with a grid voltage of 2000V.

[0036] The surface potential indicates the amount of charge stored in the third layer 130. Corona charging can be used to trap charge in the third layer 130. Corona charging applies a high voltage to a point electrode, which ionizes the air around it. The ions are accelerated towards the grounded sample, and charge is deposited. The corona charging conditions are selected to enhance both the amount and stability of the charge trapped in the third layer 130. In other embodiments, the third layer 130 can be charged using an electron beam or an electron spray. The charge stability of FEP can be stable at room temperature for over 100 years.

[0037] Figure 5 shows a graph 500 illustrating an example of the voltage response of the transducer to a force applied at 1 Hz according to an embodiment. More specifically, graph 500 shows the voltage response of the transducer 100 over time due to a force of 0.3 N and a preload of 1.3 N applied at 1 Hz. The average voltage output over a duration (e.g., 4 seconds) is 0.57 V. The size, shape, and / or spacing of the microstructure 112 can be changed to optimize the electrical response of the transducer 100.

[0038] FIG. 6 shows a graph 600 depicting the voltage response of the transducer 100 as a function of frequency, according to one embodiment. The average voltage generated by the transducer 100 under a mechanical load can be measured using a long-stroke oscillator, a loudspeaker, etc. Stress can be applied to one side of the transducer 100 (e.g., the first layer 110) by the oscillator at a specific frequency and force. The opposite side of the transducer 100 (e.g., the fourth layer 140) can be attached to a load cell that measures the applied force. The oscillator can be adjusted to apply various preloading forces to the sample medium. Data can be collected by a data acquisition system (DAQ). In the data shown in FIG. 6, the voltage response is normalized by the applied force. The average preloading force applied to the transducer is 1.3 N.

[0039] As can be seen from the figure, the transducer 100 is very sensitive to low frequencies. On the other hand, conventional transducers for airborne noise are not as sensitive. This increased sensitivity generates a high energy density in response to ocean wave undulations, chest wall sounds and movements, material vibrations, or combinations thereof. The transducer 100 can be optimized by changing the geometry and layout of the microstructure 112 (including, but not limited to, spacing and orientation). The measurement can also be optimized by removing the preloading that compresses the microstructure 112, which can be more sensitive to higher frequencies, in the setting.

[0040] FIG. 7 shows a schematic cross-sectional view of another transducer 700 on a medium 102 according to an embodiment. The transducer 700 may be similar to the transducer 100. For example, the transducer 700 may include a first layer 110 (e.g., including a microstructure 112), a second layer 120, and a third layer 130. However, the transducer 700 may include a fourth layer 740 located on (e.g., on top of) the third layer 130 instead of the fourth layer 140 (e.g., a conductive backing plate). The fourth layer 740 may be or include a thin-film electrode. For example, both the second layer 120 and the fourth layer 740 may be or include thin-film electrodes. In one embodiment, the fourth layer 740 may be a rigid upper electrode. In other embodiments (not shown), the fourth layer 740 may include a plurality of flexible upper electrodes. Using a plurality of flexible upper electrodes coupled to thin-film electronic components, the transducer 700 may be deformed into a fully conformal device.

[0041] The transducer 700 may also include a fifth layer 750 located on (e.g., on top of) the fourth layer 740. The fifth layer 750 may be or include an insulating layer (e.g., polyimide). The transducer 700 may also include a sixth layer 760 located on (e.g., on top of) the fifth layer 750. The sixth layer 760 may be or include one or more circuits coupled to a flexible interconnect that may provide energy, amplification, and transmission electrical circuitry.

[0042] Transducers 100, 700 can be flexible, biocompatible transducers that are envisioned to be worn by a user to improve long-term monitoring of sounds from the body and electrical communications. Continuous acoustic monitoring can be used to alert patients of abnormalities associated with diseases such as heart failure (HF), pneumonia, coronavirus, COPD, or asthma. Specifically for heart failure, which is the leading cause of death worldwide, long-term monitoring is essential to observe acute events with a high risk of readmission for patients. Approximately 22% of heart failure patients are readmitted within one month of discharge. The prevalence of heart failure is predicted to increase by approximately 46% from 2012 to 2030, and the associated medical costs are expected to increase from $21 billion to $53 billion. Readmission is the main cause of these costs, accounting for over 75% of the annual cost of heart failure. With the transducers 100, 700 described herein, patients can be monitored for signs of congestion and the acoustic signature of pulmonary hypertension while at home without the need to worry about noise or wasted data, thereby enabling standard treatment to shift from reactive hospitalizations to preventive interventions. For both heart and respiratory diseases, transducers 100, 700 can rationalize patient treatment, save millions of dollars in readmission costs, and provide home monitoring during times of social distancing.

[0043] Regarding electrical communications, transducers 100, 700 can be used to improve communication in online meetings or in high-noise environments for personnel such as construction workers, engine workers, military aviators, and firefighters. Transducers 100, 700 can also facilitate communication in environments where high sound levels are undesirable and visual communication is restricted, intermittent, or impossible, such as in law enforcement activities and covert military operations.

[0044] Underwater acoustic waves are a form of communication, and one or more transducers 100, 700 can be used to facilitate this communication. Conventional underwater transducers are composed of lead-based piezoelectric ceramic material lead zirconate titanate (PZT) and require processing at high voltages and high temperatures to obtain an electrical response. These transducers are expensive, with an average cost of $2000 to $3000, and can typically weigh more than 50,000 lb, forming a large group of more than 1000. In contrast to these conventional transducers, the transducers 100, 700 described herein are a more environmentally friendly option that does not use lead-based materials, requires little preparation to obtain an electrical response, and is low-cost. The transducers 100, 700 may be well-suited for shipboard sonar arrays due to their flexibility, lightweight, scalability, and acoustic impedance matched to water.

[0045] FIG. 8 shows a flowchart of a method 800 for monitoring a medium according to one embodiment. Although an exemplary order of method 800 is given, one or more steps of method 800 may be executed in a different order, simultaneously, iteratively, or omitted.

[0046] Method 800 may include, at 802, the step of identifying medium 102. As described above, in one example, medium 102 may be or include a living body. For example, the medium may be or include the chest of a living person such that transducers 100, 700 can monitor the heart. The identified medium 102 has a specific acoustic impedance.

[0047] Method 800 may also include, at 804, the step of selecting a first layer 110 based at least in part on medium 102. More specifically, this may include the step of selecting a material to use as the first layer 110 based at least in part on the impedance of medium 102. Exemplary materials are those described above (e.g., PDMS, ECOFLEX® or polyurethane).

[0048] Method 800 may also include, at 806, forming one or more microstructures 112 on the first layer 110 based at least in part on the medium 102. The shape and / or dimensions of the microstructures 112 may be selected based at least in part on the impedance of the medium 102 and the desired frequency response.

[0049] Method 800 may also include, at 808, doping the first layer 110 based at least in part on the medium 102. More particularly, this may include selecting a material to use as a dopant for the first layer 110 based at least in part on the impedance of the medium 102. Exemplary materials (e.g., additives and / or dopants) are described above (e.g., silicon dioxide nanoparticles). Doping the first layer 110 may also include selecting the amount and / or concentration of dopant to apply to the first layer 110 based at least in part on the impedance of the first layer 110. An example is provided in FIG. 2 above.

[0050] The material of the first layer 110, the material of the dopant, the amount of dopant, the concentration of dopant, the size of the dopant, or combinations thereof may be selected to substantially match the impedance of the transducer 100, 700 (e.g., the impedance of the first layer 110) to the impedance of the medium 102.

[0051] Method 800 may also include, at 810, disposing a second layer 120 on the first layer 110. The second layer 120 may conform to the microstructures 112. Thus, the upper surface of the first layer 110 and / or the second layer 120 may have peaks and valleys.

[0052] Method 800 may also include, at 812, the step of disposing a third layer 130 on the second layer 120. In at least one embodiment, the third layer 130 may not conform to the microstructure 112 and / or the second layer 120. In other words, the third layer 130 may not have ridges and valleys. Thus, gas (e.g., air) may be trapped in the gap between the second layer 120 and the third layer 130.

[0053] Method 800 may also include, at 814, the step of disposing a fourth layer 140, 740 on the third layer 130. Method 800 may optionally include, at 816, the step of disposing a fifth layer 750 on the fourth layer 140, 740. Method 800 may optionally include, at 818, the step of disposing a sixth layer 760 on the fifth layer 750.

[0054] One or more of the above steps may be performed to construct / configure the transducer 100, 700. Once constructed / configured, method 800 may include, at 820, the step of disposing the transducer 100, 700 in contact with the medium 102. More specifically, this may include the step of contacting the first (e.g., lower) surface of the first layer 110 with the medium 102. In one example, this may include the step of coupling (e.g., attaching) the lower surface of the first layer 110 to the chest of a living body. The microstructure 112 may be located on the second (e.g., upper) surface of the first layer 110.

[0055] Method 800 may also include, at 822, the step of measuring the properties of the medium 102 using the transducer 100, 700. This may include the step of converting an acoustic signal (e.g., wave) from the medium 102 into an electrical signal using the transducer 100, 700.

[0056] Differences between the transducer 100, 700 and a conventional transducer (1) Electrostatic induction for high electrical output and stability in detection applications Conventional acoustic impedance matching transducers use piezoelectric materials. The output of a piezoelectric material is proportional to its hardness, and generally, the higher the hardness, the higher the acoustic impedance, but the acoustic response is limited. The electrical response of a flexible and biocompatible piezoelectric material is also greatly limited. To increase the sensitivity of the transducer using a piezoelectric material, rigid lead-based ceramics are often used. Piezoelectrets overcome the low sensitivity of piezoelectric bodies, but also have limitations such as breakdown during charging, charge neutralization when the opposite sides of voids come into contact, and limited temperature stability. Triboelectric materials require separation or fragmentation of materials, which is difficult in thin and wearable applications. Similarly, triboelectric nanogenerators have mechanical limitations and are unreliable in practical applications due to electrical output instability such as changes due to humidity. The transducers 100, 700 are based on electrostatic conversion, which is less affected by mechanical wear and environmental conditions. Compared with piezoelectric conversion, electrostatic conversion does not involve the use of lead-based materials, is very low-cost through simple (e.g., low-temperature, without chemicals) processing, is biocompatible, and reduces the coupling between acoustic impedance and electrical output.

[0057] (2) Acoustic impedance matching by elastomer doping with ceramic nanoparticles Conventional transducers rely on the use of conventional air-based microphones or piezoelectric materials embedded in or coupled to the matching layer. These systems are limited by a series of limitations due to the matching layer, such as their design (further impedance mismatch between the conversion material and the bonding material), or sensitivity depending on the limited bandwidth, thickness, and problems with the bonding to the matching layer. Thus, these conventional systems do not provide noise removal / suppression. Transducers 100, 700 utilize the acoustic matching layer 110 as a conversion membrane and integrate the bonding layer and the sensing layer into a single layer for increased transmission. It may be shaped into any 3D solid by the use of silicone, be stable for months or even years, and be unaffected by rough handling. It is also non-toxic during preparation and application. However, transducers 100, 700 may further or alternatively use ceramic nanoparticle doping to produce materials with the exact acoustic parameters of the intended medium. Transducers 100, 700 may also include acoustic wave conversion in the range of 1 Hz to 20 kHz.

[0058] (3) Microstructured elastomer surface for adjusting mechanical and frequency responses The microstructures 112 included in the transducers 100, 700 provide a restoring force. The magnitude of the force can be modeled as a spring having a spring constant proportional to the dimensions and hardness of the microstructure 112. Thus, the size, shape, aspect ratio, and / or distribution of the microstructure 112 can be adjusted to capture higher or lower frequencies. Accordingly, the transducers 100, 700 can be adjusted for a specific frequency range to enhance sensitivity and improve the original noise cancellation ability of the transducer. Furthermore, microstructures 112 of multiple sizes, shapes, aspect ratios, and / or distributions can be implemented for the same transducers 100, 700 or in an arrayed manner, increasing the bandwidth of the transducers 100, 700. The composition of the first layer 110 can also be further adjusted to tune the frequency response and control the acoustic impedance and mechanical properties of the observation interface of the transducer. The acoustic impedance of the first layer 110 can be made to match a specific medium and can also be fabricated to remove interference from external noise sources, such as removing airborne noise when observing sounds from the human body. The degree of flexibility with respect to the structure and mechanical properties of this elastomer facilitates the wide application of the transducers 100, 700 to a number of environments.

[0059] (4) Flexibility of the system for application to curved surfaces The flexibility and conformability of the transducers 100, 700 are useful for use in fluid media and on curved surfaces. Conventional transducers are limited by a rigid body design following the bonding layer.

[0060] (5) Integratable electronic components The transducers 100, 700 can have electronic components directly integrated on their upper surfaces. As described above, amplification, energy harvesting, and transmission electrical circuits can be integrated into the transducers 100, 700 using stretchable interconnects.

[0061] One or more of the above steps can be implemented using a non-transitory computer-readable medium loaded into a computing device such as a personal computer, tablet, phablet, smartphone, computer server, or any other arbitrary computing device well-known or conceivable to those skilled in the art. In fact, any appropriate hardware and software well-known or conceivable to those skilled in the art can be used. The non-transitory computer-readable medium may be incorporated into a device for evaluating a patient (PAT).

[0062] The non-transitory computer-readable medium is understood to mean any product readable by a computer. Such non-transitory computer-readable media include, but are not limited to, magnetic media such as floppy disks, flexible disks, hard disks, open reel tapes, cartridge tapes, cassette tapes, or cards; optical media such as CD-ROMs, writeable compact disks; magneto-optical media in the form of disks, tapes, or cards; and paper media such as punch cards and paper tapes. The computing device may be a special computer specifically designed for this purpose. The computing device may be specific to the present invention and specifically designed to implement the method of the present invention.

[0063] Many features and advantageous effects of the present invention are apparent from the detailed description, and accordingly, it is intended that the appended claims encompass all such features and advantageous effects of the present invention that fall within the spirit and scope of the present invention. Also, since numerous modifications and variations can be readily conceived by those skilled in the art, it is not desirable to limit the present invention to the exact construction and operation described and illustrated. Accordingly, all appropriate modifications and equivalents rely on the present invention and fall within the scope of the present invention.

Claims

**Claim 1** An acoustic transducer comprising: A first layer comprising an elastomer, the acoustic impedance of the first layer being substantially matched to the acoustic impedance of a medium configured such that the transducer monitors it; A second layer provided with electrodes; A third layer comprising a polymer, the second layer being at least partially located between the first layer and the third layer; Comprising; The elastomer comprises polydimethylsiloxane, the acoustic transducer. **Claim 2** The acoustic transducer according to claim 1, wherein the first layer has a monomer-to-curing agent ratio of about 2:1 to about 20:

1. **Claim 3** The acoustic transducer according to claim 1, wherein the first layer is doped with a ceramic material so that the acoustic impedance of the first layer substantially matches the acoustic impedance of the medium configured such that the transducer monitors it, and the first layer is the only layer doped so that the acoustic impedance substantially matches the acoustic impedance of the medium configured such that the transducer monitors it. **Claim 4** The acoustic transducer according to claim 1, wherein the first layer is doped with a ceramic, silicon dioxide, titanium dioxide, barium titanate or a combination thereof so that the acoustic impedance of the first layer substantially matches the acoustic impedance of the medium configured such that the transducer monitors it, and the first layer is the only layer doped so that the acoustic impedance substantially matches the acoustic impedance of the medium configured such that the transducer monitors it. **Claim 5** The acoustic transducer according to claim 4, wherein the first layer is doped with about 1% to about 60% silicon dioxide. **Claim 6** The acoustic transducer according to claim 1, wherein the first layer is provided with a plurality of microstructures on a first surface of the first layer, a second surface of the first layer is on the opposite side of the first surface, and is configured to be disposed in contact with the medium configured such that the transducer monitors it. **Claim 7** The height of the microstructure is from about 50 μm to about 1 mm, and the distance between two adjacent microstructures is from about 50 μm to about 1 mm, the acoustic transducer according to claim 6.

8. The second layer substantially conforms to the microstructure such that the second layer includes ridges and valleys, the third layer is substantially flat, and there is a gap between the valleys of the second layer and the third layer, the acoustic transducer according to claim 1.

9. The polymer includes ethylene tetrafluoride propylene (FEP), polytetrafluoroethylene (PTFE), or a combination thereof, the acoustic transducer according to claim 1.

10. The polymer includes a charged electret polymer, the acoustic transducer according to claim 1.

11. The acoustic transducer further includes a fourth layer including a conductive metal, and the third layer is at least partially located between the second layer and the fourth layer, the acoustic transducer according to claim 1.

12. The acoustic transducer further includes a fourth layer including another electrode, and the third layer is at least partially located between the second layer and the fourth layer, the acoustic transducer according to claim 1.

13. The acoustic transducer according to claim 12 further includes a fifth layer including polyimide, and the fourth layer is at least partially located between the third layer and the fifth layer.

14. The acoustic transducer according to claim 13 further includes a sixth layer including a circuit configured to provide energy, signal amplification, signal transmission, or a combination thereof, and the fifth layer is at least partially located between the fourth layer and the sixth layer.

15. The acoustic transducer is configured to be connected to a field effect transistor (FET) adjustment circuit, and the FET adjustment circuit is configured to receive an electrical signal from the acoustic transducer and amplify the electrical signal, the acoustic transducer according to claim 1.

16. The acoustic transducer according to claim 1 further includes a field effect transistor (FET) adjustment circuit connected to the second layer, and the FET adjustment circuit is configured to receive an electrical signal from the second layer and amplify the electrical signal.

17. The acoustic transducer is part of a stethoscope configured to acquire sounds of a human body, the medium includes the human body, and the acoustic transducer reduces interference from noise generated in a surrounding environment around the human body that degrades a signal output by the stethoscope. The acoustic transducer according to claim 1.

18. An acoustic transducer, A first layer including an elastomer, the first layer having a monomer-to-curing agent ratio of about 5:1 to about 20:1, the first layer including a plurality of microstructures having a height of about 50 μm to about 1 mm, the first layer being doped with about 1% to about 60% silicon dioxide to substantially match the acoustic impedance of the first layer to the acoustic impedance of a medium configured to be monitored by the transducer, the first layer being the only layer used to match the acoustic impedance of the medium configured to be monitored by the transducer; a first layer, A second layer including electrodes, the second layer substantially conforming to the microstructures such that the second layer includes peaks and valleys; a second layer, A third layer including a polymer, the polymer including corona-charged fluorinated ethylene propylene (FEP), corona-charged polytetrafluoroethylene (PTFE), or a combination thereof, the second layer being at least partially positioned between the first layer and the third layer, the third layer being substantially flat, and a gap existing between the valleys of the second layer and the third layer; a third layer, Comprising, The elastomer includes polydimethylsiloxane. The acoustic transducer.

19. The acoustic transducer according to claim 18, further comprising a fourth layer including a conductive metal, the third layer being at least partially positioned between the second layer and the fourth layer.

20. The acoustic transducer according to claim 18, further comprising a fourth layer including another electrode, the third layer being at least partially positioned between the second layer and the fourth layer.

21. A fifth layer including polyimide, the fourth layer being at least partially positioned between the third layer and the fifth layer; a fifth layer, A sixth layer comprising a circuit configured to provide energy, signal amplification, signal transmission, or a combination thereof, wherein the fifth layer is at least partially positioned between the fourth layer and the sixth layer, the sixth layer, The acoustic transducer according to claim 20, further comprising.

22. A step of constructing the acoustic transducer according to claim 1 configured to measure mechanical vibrations of a medium, the step of constructing the transducer comprising: Doping a first layer of the transducer with a dopant at least partially based on the medium, wherein the material of the first layer, the dopant, or both substantially match the acoustic impedance of the first layer to the acoustic impedance of the medium, the step of, Placing a second layer comprising electrodes at least partially on the first layer; Placing a third layer comprising a polymer at least partially on the second layer; Placing the first layer in contact with the medium; Measuring the mechanical vibrations of the medium using the transducer; Comprising, The method, wherein the material of the first layer comprises polydimethylsiloxane.

23. The step of applying the dopant comprises applying from about 1% to about 60% ceramic, silicon dioxide, titanium dioxide, barium titanate, or a combination thereof to the first layer to substantially match the acoustic impedance of the first layer to the acoustic impedance of the medium, the method according to claim 22.

24. The method according to claim 22, wherein the first layer comprises an elastomer, the dopant comprises a ceramic material, the second layer comprises electrodes, and the third layer comprises a charged electret polymer.

25. The step of constructing the transducer further comprises forming a plurality of microstructures on the surface of the first layer, the microstructures having a height of about 50 μm to about 1 mm, the second layer substantially conforming to the microstructures such that the second layer comprises peaks and valleys, and the third layer being substantially flat such that there is a gap between the valleys of the second layer and the third layer, the method according to claim 22.

26. The method according to claim 22, wherein the transducer uses electrostatic conversion to convert the measured property from an acoustic signal to an electrical signal.

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