Acoustic mechanisms to improve separation of airborne contaminants with fiber filters

Abstract

A filtration system includes a fluid movement system configured to displace fluid along a flow direction, an acoustic wave generator comprising an acoustic transducer and an acoustic reflector spaced apart from one-another according to a predetermined distance, together configured to generate a standing acoustic wave, and a filter medium disposed adjacent the acoustic wave generator having a thickness defined by a first side and a second side, the filter medium configured to trap particles in fluid being displaced by the fluid movement system, wherein the filter medium and the standing acoustic wave each has a corresponding orientation relative to the flow direction.

Description

ACOUSTIC MECHANISMS TO IMPROVE SEPARATION OF AIRBORNE CONTAMINANTS WITH FIBER FILTERSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present non-provisional patent application is related to and claims the priority benefit of U.S. Provisional Patent Application Serial 63 / 548,709, filed February 01, 2024, the contents of which are hereby incorporated by reference in its entirety into the present disclosure.STATEMENT REGARDING GOVERNMENT FUNDING

[0002] None.TECHNICAL FIELD

[0003] The present disclosure generally relates to a system and method filtering particles in a fluid and in particular to a system and method of filtration utilizing acoustic standing waves.BACKGROUND

[0004] This section introduces aspects that may help facilitate a better understanding of the disclosure. Accordingly, these statements are to be read in this light and are not to be understood as admissions about what is or is not prior art.

[0005] Air and water pollution is a pervasive global concern that has detrimental effects on human health, ecosystems, and the climate. The particulate matter below 2. pm (PM2.5) and gaseous pollutants generated from anthropogenic sources, such as industrial processes, transportation, and energy production and use, significantly contribute to air pollution. Additionally, particulates in water supply or in the oceans present a clear and present danger to human health. Inhaling polluted air or ingesting harmful particulates in water has been linked toan increased risk of diseases, in particular to respiratory and cardiovascular diseases, resulting in a substantial burden on public health systems. Given people can spend 80-90% of their life inside buildings indoor air quality is especially important. Conventional indoor air purification methods, such as filtration and adsorption, often face challenges related to energy consumption, maintenance requirements, and disposal of waste materials. Filters can become clogged with particulates, necessitating frequent replacement or cleaning, and adsorbent materials can become saturated, requiring regeneration or disposal. Innovative indoor air purification techniques that overcome these limitations would significantly improve human health and wellness.

[0006] Acoustically enhanced filtration leverages sound pressure waves at audible or ultrasonic frequencies to increase performance. These sound pressure waves can be generated by piezoelectric or electrostatic actuators. Particles in the resulting acoustic field are subjected to steady time-averaged hydrodynamic forces. These forces, known as acoustic radiation forces, provide a mechanism to manipulate particle motion. Applications of acoustic radiation forces include cell sorting, cell trapping, spectroscopy signal enhancement, separation of nanoparticles from suspensions, nanoparticle self-assembly, and porous media filtration enhancement. When used in combination with porous filtration media acoustics have been shown to result in higher capture efficiencies and reduced fouling. Acoustic effects can modify the capture efficiency of a filter through acoustic agglomeration generated by orthokinetic interactions and acoustic wakes, turbulence, interaction forces, and acoustic streaming. Acoustic pre-treatment in air has demonstrated increases in capture efficiency of 8 % using a bag filter and 10 % using a MERV 11 filter. These prior studies attributed the increase in capture efficiency due to increased effective particle size resulting from agglomeration.

[0007] Acoustic filtration studies have predominantly focused on agglomeration pre-treatment; however, this can be difficult to achieve with nano-scale, dilute, and monodisperse suspensions, as the probability of collision is reduced. This issue is particularly relevant for fine and ultrafine pollutants, which can have serious health effects even at low concentrations. Similar mechanisms affecting inter-particle collisions can be applied to increase particle-filter interactions, improving capture efficiency. In liquids, acoustically suspended stationary particle clusters has been used to effectively trap low abundance bacteria, with 95% efficiency, and nanoparticles down to 110 nm,both examples of suspensions notoriously difficult to capture. With other filter media, acoustics have been shown to trap particles two orders of magnitude smaller than the pore size with capture efficiencies of up to 80 %. Many of these improvements can be attributed to the acoustic scattering from the filter surfaces, and how these can interact with the particles to induce an attractive force. In practice, most fiber filters consist of many closely spaced fibers whose relative position affects the pressure distribution within the acoustic field. Currently, little is known about how the geometrical arrangement of the porous domain influences both the acoustic field and the effect of the acoustic field on capture efficiency. Gupta & Feke demonstrated that the filter medium impacts the acoustic enhancement, showing upwards of -20% retention improvement for an aluminum mesh when compared to packed glass beads. Other works have investigated fiber arrangements with oscillating fibers, or lower frequency acoustics, however, none have studied this dependence with high frequency standing acoustic waves, particularly in the context of non-agglomerative particle interactions. This lack of knowledge limits our ability to design acoustically enhanced filters with optimally high capture efficiencies for harmful pollutants that are difficult to separate with other techniques.

[0008] Therefore, there is an unmet need for a novel system and method that can improve filtration efficiency of particles in a fluid.SUMMARY

[0009] A filtration system is disclosed. The system includes a fluid movement system configured to dispiace fluid along a flow direction, an acoustic wave generator comprising an acoustic transducer and an acoustic reflector spaced apart from one-another according to a predetermined distance, together configured to generate a standing acoustic wave, and a filter medium disposed adjacent the acoustic wave generator having a thickness defined by a first side and a second side, the filter medium configured to trap particles in fluid being displaced by the fluid movement system. The fitter medium and the standing acoustic wave each has a corresponding orientation relative to the flow direction.

[0010] In the above system, the acoustic transducer includes a first piezoelectric element or a first electrostatic clement configured to generate a first acoustic excitation.

[0011] In the above system, the acoustic reflector includes a passive acoustic reflector plate configured to reflect the first acoustic excitation thus generate the standing acoustic wave.

[0012] In the above system, the acoustic reflector includes an active acoustic plate including a second piezoelectric element or a second electrostatic element configured to generate a second acoustic excitation which together with the first acoustic excitation generate the standing acoustic wave.

[0013] In the above system, the fluid movement system is disposed on the first side of the filter medium, thus configured to push fluid across the filter medium.

[0014] In the above system, the fluid movement system is disposed on the second side of the filter medium, thus configured to pull fluid across the filter medium.

[0015] In the above system, the filter medium includes continuous strands across the filter medium, discontinuous strands, one or more porous solids each including a plurality of holes, or a combination thereof, made of glass fiber, polypropylene, Polyvinylidene fluoride (PVDF), cellulose acetate, polytetrafluoroethylene (PTFE), or any combinations thereof.

[0016] In the above system, the continuous strands, the discontinuous strands, or the plurality of holes are aligned along a uniform direction.

[0017] In the above system, the continuous strands, the discontinuous strands, or the plurality of holes are randomly aligned.

[0018] In the above system, the filter medium includes acoustically reactive strands or reactive porous solid.

[0019] In the above system, the reactive strands or reactive porous solid scatter and generate supplemental acoustic waves that when combined with the standing acoustic wave generated by the acoustic wave generator enhance the filter medium’s trapping of the particles.

[0020] In the above system, the reactive strands or reactive porous solids include piezoelectric elements.

[0021] In the above system, the filter medium is defined by a porosity defined as ratio of void volume to total volume of between about 0.5 and about 0.99.

[0022] The above system further includes a first pressure sensor disposed adjacent the first side of the filter medium and a second pressure sensor disposed adjacent the second side of the filter medium.

[0023] In the above system, first pressure sensor and the second pressure sensor each generates a corresponding pressure signal which together generate a pressure differential value across the filter medium.

[0024] In the above system, the pressure differential value is used as an automatic pressure differential feedback signal to operate the fluid movement system and the acoustic wave generator to thereby modify the standing acoustic wave.

[0025] In the above system, the pressure differential feedback signal is used as a harmonic feedback signal configured to modify the standing acoustic wave based on acoustic harmonics.

[0026] In the above system, the pressure differential feedback signal is used as a resonance feedback signal configured to modify the standing acoustic wave based on acoustic resonance.

[0027] In the above system, the fluid movement system is configured to displace gases.

[0028] In the above system, the fluid movement system is configured to displace liquids.

[0029] In the above system, the acoustic wave generator is shut down to clean the filter medium.

[0030] In the above system, the filter medium presents an acoustic reflectance between about 0.1 and about 1.

[0031] In the above system, the filter medium is oriented with respect to the flow direction based on an angle of between about 0 and about 180 degrees.

[0032] In the above system, the filter medium is oriented substantially perpendicular to the flow direction.

[0033] In the above system, the acoustic wave generator is oriented such that the standing acoustic wave has an angle with respect to the flow direction of between about 0 and about 180 degrees.

[0034] A method of filtering particles in a fluid is also disclosed. The method includes displacing a fluid by a fluid movement system along a flow direction, generating a standing acoustic wave by an acoustic wave generator comprising an acoustic transducer and an acoustic reflector spaced apart from one-another according to a predetermined distance, and trapping particles inthe fluid by a filter medium disposed adjacent the acoustic wave generator having a thickness defined by a first side and a second side. The filter medium and the standing acoustic wave each has a corresponding orientation relative to the flow direction.

[0035] In the above method, the acoustic transducer includes a first piezoelectric element or a first electrostatic element configured to generate a first acoustic excitation.

[0036] In the above method, the acoustic reflector includes a passive acoustic reflector plate configured to reflect the first acoustic excitation thus generate the standing acoustic wave.

[0037] In the above method, the acoustic reflector includes an active acoustic plate including a second piezoelectric element or a second electrostatic element configured to generate a second acoustic excitation which together with the first acoustic excitation generate the standing acoustic wave.

[0038] In the above method, the fluid movement system is disposed on the first side of the filter medium, thus configured to push fluid across the filter medium.

[0039] In the above method, the fluid movement system is disposed on the second side of the filter medium, thus configured to pull fluid across the filter medium.

[0040] In the above method, the filter medium includes continuous strands across the filter medium, discontinuous strands, one or more porous solids each including a plurality of holes, or a combination thereof, made of glass fiber, polypropylene, Polyvinylidene fluoride (PVDF), cellulose acetate, polytetrafluoroethylene (PTFE), or any combinations thereof.

[0041] In the above method, the continuous strands, the discontinuous strands, or the plurality of holes are aligned along a uniform direction.

[0042] In the above method, the continuous strands, the discontinuous strands, or the plurality of holes are randomly aligned.

[0043] In the above method, the filter medium includes acoustically reactive strands or reactive porous solid.

[0044] In the above method, the reactive strands or reactive porous solid scatter and generate supplemental acoustic waves that when combined with the standing acoustic wave generated by the acoustic wave generator enhance the filter medium’s trapping of the particles.

[0045] In the above method, the reactive strands or reactive porous solids include piezoelectric elements.

[0046] In the above method, the filter medium is defined by a porosity defined as ratio of void volume to total volume of between about 0.5 and about 0.99.

[0047] The above method further includes a first pressure sensor disposed adjacent the first side of the filter medium and a second pressure sensor disposed adjacent the second side of the filter medium.

[0048] In the above method, first pressure sensor and the second pressure sensor each generates a corresponding pressure signal which together generate a pressure differential value across the filter medium.

[0049] In the above method, the pressure differential value is used as an automatic pressure differential feedback signal to operate the fluid movement system and the acoustic wave generator to thereby modify the standing acoustic wave.

[0050] In the above method, the pressure differential feedback signal is used as a harmonic feedback signal configured to modify the standing acoustic wave based on acoustic harmonics.

[0051] In the above method, the pressure differential feedback signal is used as a resonance feedback signal configured to modify the standing acoustic wave based on acoustic resonance.

[0052] In the above method, the fluid movement system is configured to displace gases.

[0053] In the above method, the fluid movement system is configured to displace liquids.

[0054] In the above method, the acoustic wave generator is shut down to clean the filter medium.

[0055] In the above method, the filter medium presents an acoustic reflectance between about 0.1 and about 1.

[0056] In the above method, the filter medium is oriented with respect to the flow direction based on an angle of between about 0 and about 180 degrees.

[0057] In the above method, the filter medium is oriented substantially perpendicular to the flow direction.

[0058] In the above method, the acoustic wave generator is oriented such that the standing acoustic wave has an angle with respect to the flow direction of between about 0 and about 180 degrees.

[0059] BRIEF DESCRIPTION OF DRAWINGS

[0060] FIG. 1 is a basic schematic of a filtration system, according to the present disclosure, having a fluid movement system, an acoustic wave generator, and a filter medium having a first side and a second side, wherein the fluid movement system is positioned on the first side of the filter medium.

[0061] FIG. 2 is a corollary schematic to the schematic shown in FIG. 1 wherein the fluid movement system is position on the second side of the filter medium.

[0062] FIGs. 3A, 3B, 3C, 3F and 3G are scanning electron microscopy (SEM) imaging of different configurations of the filter medium.

[0063] FIGs. 3D and 3E are photographs of the filter medium according to various configurations.

[0064] FIG. 4 is a schematic of filter medium strands formed in a uniformly aligned manner.

[0065] FIG. 5 is a schematic of forces applied to particles in a fluid based on implementation of the filtration system of the present disclosure.

[0066] FIG. 6 A are aligned fibers with a capture efficiency in % defined as the ratio of the number of particles trapped in the filter medium to that of number of particles that enter the first side of the filter medium vs. particle size in pm.

[0067] FIG. 6B are staggered continuous fibers with a capture efficiency in % vs. particle size in pm.

[0068] FIG. 7A provides graphs of capture efficiency in % vs. particle size in pm for both aligned and staggered fibers.

[0069] FIG. 7B provides graphs of capture efficiency ratio vs. particle size in pm for both aligned and staggered fibers.

[0070] FIGs. 8 A and 8B a e schematics of particle trapping with and without acoustic wave generation is shown for aerosol particles, according to the present disclosure.

[0071] FIG. 8C is a graph of capture efficiency in % vs. particle diameter in pm for both cases of acoustic wave generation on and off.

[0072] FIG. 9A represents a multiphysics model used in evaluating the capture efficiency of a filter medium with and without acoustics.

[0073] FIG. 9B is a representation of porosity vs. disorder vs. acoustic scattered pressure in a filter medium for different porosity values.

[0074] FIG. 10 is a schematic of a bench-scale experimental setup which led to the physical realization of this technology.DETAILED DESCRIPTION

[0075] For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of this disclosure is thereby intended.

[0076] In the present disclosure, the term “about” can allow for a degree of variability in a value or range, for example, within 15%, within 10%, within 5%, or within 1% of a stated value or of a stated limit of a range.

[0077] In the present disclosure, the term “substantially” can allow for a degree of variability in a value or range, for example, within 85%, within 90%, within 95%, or within 99% of a stated value or of a stated limit of a range.

[0078] A novel system and method is disclosed herein that can improve filtration efficiency of particles in a fluid. Towards this end, the present disclosure describes how standing acoustic waves can act on porous filter media to enhance capture efficiency. By considering particles as point-forces, and neglecting the mutual inter-particle forces, thus isolating particle-fiber interactions, we find that particles become attracted to fiber surfaces of the filter medium due to acoustic radiation forces caused by pressure wave scattering. Different fiber arrangements lead to varied levels of scattering, indicating that there’s an optimal arrangement of fibers to harness acoustic radiation interactions. As a result, upwards of 123 times capture efficiency enhancementfrom non-acoustic counterparts is observed. The present disclosure reveals that standing acoustic waves can be used to enhance capture efficiencies of filter media through acoustically induced particle boundary interactions, which could be applied to various micro / nano particle separation processes.

[0079] Referring to FIG. 1, a basic schematic of a filtration system 100 is shown. The filtration system 100 includes a fluid movement system 102 configured to displace fluid 104 along a flow direction 106 from an inlet side 101. The fluid 104 includes particles 108 to be filtered by the filtration system 100. The filtration system 100 further includes an acoustic wave generator 110 that includes an acoustic transducer 112 and an acoustic reflector 114 spaced apart from one- another according to a predetermined distance 113. The acoustic transducer 112 and the acoustic reflector 114 together are configured to generate a standing acoustic wave 115. The filtration system 100 further includes a filter medium 116 disposed adjacent the acoustic wave generator 110. The filter medium 116 has a thickness 117 and is defined by a first side 118 and a second side 120. The filter medium 116 is configured to trap particles 108 in fluid 104 being displaced by the fluid movement system 102. The filter medium 116 and the standing acoustic wave 115 each has a corresponding orientation 122 and 124, respectively, relative to the flow direction 106. The filter medium 116 presents an acoustic reflectance between about 0.1 and about 1.

[0080] Referring to FIG. 2, a corollary schematic to the schematic shown in FIG. 1. In FIG. 2, the fluid movement system 102 of FIG. 1 is shown on the opposite side (second side 120 of FIG. 1 of the filter medium 116 of FIG. 1, thus causing fluid movement to be pulled through the filter medium 116 of FIG. 1 rather than being pushed through the filter medium 116 of FIG. 1. This change results in the same flow direction 106 shown in FIG. 1. Additionally, shown in FIG. 2 is a fluid channel configured to direct flow of fluid within the fluid channel. This fluid channel is not shown in FIG. 1, but it is within the ambit of the present disclosure.

[0081] The acoustic transducer (shown as 112 in FIG. 1) includes a first acoustic device 126 which can be a first piezoelectric element or a first electrostatic element or any other acoustic devices known to a person having ordinary skill in the art that is configured to generate a first acoustic excitation. Additionally, the acoustic reflector (shown as 114 in FIG. 1) includes a passive acoustic reflector plate that is configured to reflect the first acoustic excitation thusgenerate the standing acoustic wave shown as 1 15 in FIG. 1 . According to one embodiment, the acoustic reflector 114 includes an active acoustic plate including a second acoustic device (not shown) which can be a second piezoelectric element or a second electrostatic element or other acoustic devices known to a person having ordinary skill in the art (not shown) configured to generate a second acoustic excitation, which together with the first acoustic excitation generate the standing acoustic wave shown as 115 in FIG. 1.

[0082] Referring to FIGs. 3 A, 3B, 3C , 3F, and 3G are five figures showing the scanning electron microscopy (SEM) imaging of different configurations of the filter medium (116 in FIG. 1), while FIGs. 3D and 3E are photographs of the filter medium 116 (FIG. 1) according to various configurations. FIG. 3A shows the filter medium shown as 116 in FIG. 1 which includes continuous strands across the filter medium (i.e., from top to bottom or left to right) that randomly aligned. These continuous strands can be formed in a uniformly aligned manner as shown in the schematic of FIG. 4. Alternatively, the fibers can be formed as discontinuous strands that can be randomly aligned (not shown) or can be uniformly aligned (not shown) similar to the uniformly aligned continuous strands of FIG. 4. The fibers may be made of glass fiber, polypropylene, Polyvinylidene fluoride (PVDF), cellulose acetate, polytetrafluoroethylene (PTFE), or any combinations thereof. Alternatively, the filter medium shown as 116 in FIG. 1 can be formed of one or more porous solids each including a plurality of holes with such holes formed according to a uniform pattern or according to a random pattern as shown in the scanning electron microscope photograph of FIG. 3C. Alternatively, the filter medium shown as 116 in FIG. 1 can be formed of a spongy material (e.g., fluorinated graphite nanofiber) shown in FIG. 3B. Alternatively the filter medium shown as 116 in FIG. 1 can be formed from any combinations of the above forms including the continuous strands (randomly aligned as shown in FIG. 3A and FIG. 3F or uniformly aligned as shown in FIG. 3D, FIG. 3E and FIG. 4), the discontinuous strands (e.g., randomly aligned (FIG. 3F) or uniformly aligned (FIG. 3D and FIG. 3E)), spongy material (shown in FIG. 3B) or porous solids with plurality of holes (shown in FIG. 3C). Generally, the filter medium 116 (FIG. 1) is defined by a porosity which is defined as a ratio of void volume to total volume of between about 0.5 and about 0.99. Furthermore, the filter medium shown as 116 in FIG. 1 is oriented with respect to the flow direction shown as 106 basedon an angle of between about 0 and about 180 degrees. Additionally, the acoustic wave generator shown as 110 in FIG. 1 is oriented such that the standing acoustic wave shown as 115 in FIG. 1 has an angle with respect to the flow direction shown as 106 in FIG. 1 of between about 0 and about 180 degrees. The acoustic wave generator shown as 110 in FIG. 1 may be configured to be driven by a harmonic sinusoidal wave with a variable fundamental frequency between about 20 kHz and about 1000 MHz with an adjustable amplitude, phase, and DC offset. The harmonic sinusoidal wave may be configured to be a pure tone not containing significant higher harmonic or non-DC offset sub-harmonic components to avoid energy leakage to frequencies other than the drive frequency. The amplitude, phase, frequency, DC offset will be set by the properties of the acoustic wave generator, the properties of the filter, and the geometry of the channel. Furthermore, a pressure range inside the channel (see FIG. 2) of between about 20 Pa and about 8000 Pa (i.e. between about 120 dB to about 172 dB)are withing the ambit of the present disclosure.

[0083] While not shown, the filter medium shown as 116 in FIG. 1 may also include acoustically reactive strands or reactive porous solids. These reactive strands or reactive porous solids scatter and generate supplemental acoustic waves that when combined with the standing acoustic wave generated by the acoustic wave generator shown as 110 in FIG. 1 enhance the filter medium’s trapping of the particles in the fluid. These reactive strands or reactive porous solids may include piezoelectric elements, electrostatic elements, or other acoustic generating elements known to a person having ordinary skill in the art.

[0084] The filtration system 100 of FIG. 1 may further include a first pressure sensor (not shown) that is disposed adjacent the first side 118 of the filter medium 116 and a second pressure sensor (not shown) that is disposed adjacent the second side 120 of the filter medium 116. The first pressure sensor (not shown) and the second pressure sensor (not shown) each generates a corresponding pressure signal which together generate a pressure differential value across the filter medium 116. The pressure differential value can be used as an automatic pressure differential feedback signal to operate the fluid movement system 102 and the acoustic wave generator 110 to thereby modify the standing acoustic wave 115. The pressure differential feedback signal can be used as a harmonic feedback signal configured to modify the standingacoustic wave based on acoustic harmonics. The pressure differential feedback signal can also be used as a resonance feedback signal configured to modify the standing acoustic wave based on acoustic resonance.

[0085] The fluid movement system 102 (see FIG. 1) may be configured to displace gases such as air, oxygen, nitrogen, and inert gases. Alternatively, the fluid movement system 102 may be configured to displace liquids such as water. In any such cases, the fluid 104 may include particles 108 that are to be filtered by filter medium 116. As shown in FIG. 1, when the acoustic wave generator 110 is shut down, the filter medium 116 can be cleaned.

[0086] It should be understood that the filter medium shown as 116 in FIG. 1 may be oriented such that a main axis (not shown) of the filter medium 116 is substantially perpendicular to the flow direction 106. Alternatively, the filter medium shown as 116 in FIG. 1 may be oriented such that the main axis (not shown) of the filter medium 116 is substantially parallel (not shown) with the flow direction 106. Still yet alternatively, the filter medium shown as 116 in FIG. 1 may be oriented such that the main axis (not shown) of the filter medium 116 has an angle (not shown) with respect to the flow direction 106, wherein the angle is between 0° and 90°.

[0087] It should further be understood that the acoustic wave generator shown as 110 in FIG. 1 may be oriented such the standing acoustic wave 115 is substantially perpendicular to the flow direction 106. Alternatively, the acoustic wave generator shown as 110 in FIG. 1 may be oriented such that the standing acoustic wave 115 is substantially parallel (not shown) with the flow direction 106. Still yet alternatively, the acoustic wave generator shown as 110 in FIG. 1 may be oriented such that the standing acoustic wave 115 has an angle (not shown) with respect to the flow direction 106, wherein the angle is between 0° and 90°.

[0088] With reference to FIG. 5, a schematic of forces applied to particles 108 (see FIG. 1) in the fluid 104. When a particle is exposed to an acoustic field near a porous medium, several phenomena work together to influence its motion and interaction with the medium. The key effects include acoustic radiation force, acoustic streaming, and acoustic interaction forces, all of which are shaped by the structure of the porous medium and the nature of the acoustic waves.

[0089] The acoustic radiation force arises from the interaction between the standing acoustic waves and the particle. These waves create pressure gradients, which exert steady forces on theparticle, either pulling it toward regions of lower acoustic potential (if the particle has positive acoustic contrast) or repelling it (if it has negative contrast). Near the porous medium, scattered acoustic waves from the fibers enhance these forces, drawing particles toward the fiber surfaces where they are more likely to be captured.

[0090] Acoustic streaming is a secondary effect of the acoustic field, caused by the nonlinear interactions of the sound waves with the fluid. This streaming generates steady flows within the medium, creating a circulation that directs particles toward the porous structure. These streaming flows can extend beyond the immediate vicinity of the fibers, increasing particle residence time within the acoustic field and further enhancing the probability of interception.

[0091] The acoustic interaction force originates from re-scattering events and other particleboundary interactions within the medium. As the scattered acoustic waves interact with particles and boundaries, they create complex local pressure gradients that lead to additional forces acting on the particles. These forces can either attract particles toward fiber surfaces or push them into regions of higher particle concentration, facilitating interactions with the porous medium. In many cases, the attractive component of these interaction forces dominates, further improving the particle capture efficiency.

[0092] Together, these effects lead to significant enhancements in particle capture compared to conventional filtration systems. The specific arrangement of the porous medium, such as aligned or staggered fiber configurations, influences the scattered acoustic pressure and streaming patterns, with some designs showing dramatic improvements in filtration performance. By carefully tuning the acoustic field and optimizing the medium's geometry, particles are guided more efficiently to the fiber surfaces, allowing for improved separation of micro- and nanoparticles from the surrounding fluid.

[0093] In order to demonstrate effectiveness of the acoustic wave generation on enhancing particle trapping in the filter medium, two configurations of the continuous fibers were tested with acoustic wave generator on and off. The results are shown in FIG. 6A where aligned fibers are shown with a capture efficiency in % defined as the ratio of the number of paticles trapped in the filter medium to that of number of particles that enter the first side of the filter medium vs. particle size in pm, and in FIG. 6B where staggered continuous fibers (staggered fibers andrandomly aligned fibers are different. Staggered fibers are a sub-category of uniformly arranged fibers) arc shown with a capture efficiency in % vs. particle size in pm. As seen in these two figures acoustic wave generation improves particle trapping as seen in both figures comparing the capture efficiency between acoustic on and acoustic off configurations.

[0094] Referring to FIG. 7A graphs of capture efficiency in % vs. particle size in pm for both aligned and staggered fibers are provided. FIG 7A. presents the capture efficiency for aligned and staggered configurations of the filter medium. FIG. 7 A shows the capture efficiency improvements with acoustic ON condition for various air velocities of the fluid flowing through the filter medium.

[0095] Referring to FIG. 7B graphs of capture efficiency ratio defined as the ratio between the acoustic capture efficiency and the non-acoustic (standard) efficiency, therefore representing the enhancement from acoustic actuation vs. particle size in pm for both aligned and staggered fibers are provided. The improvements in capture efficiency due to acoustics ON are shows as 12x to 122x improvements for flow velocities of 0.1 m / for aligned and staggered configurations.

[0096] Referring to FIGs. 8 A and 8B schematics of particle trapping with and without acoustic wave generation is shown for aerosol particles. FIG. 8C is a graph of capture efficiency in % vs. particle diameter in pm for both cases of acoustic wave generation on and off. FIG. 8C shows the experimental demonstration of the capture efficiency increase of a continuous random fiber filter medium when operated under an acoustic ON condition. The flow velocity in the channel was 0.25 m / s and the size of the synthetic particles (made of polystyrene latex) used to mimic the real-world particle size distributions were of 100 nm diameter

[0097] Fig 9A represents a multiphysics model used in evaluating the capture efficiency of a filter medium with and without acoustics. Furthermore, it also presents the modeling inputs that were used in the simulation. FIG. 9B conveys the importance of porosity for harnessing the effects of acoustic filtration. FIG. 9B shows the acoustic scattered pressure in a filter medium for different porosity values. The increase in scattered pressure in a system consequently increases the acoustic interaction forces between the particles and the filter fiber medium leading to increase particle trapping

[0098] FIG. 10 is a schematic of a bench-scale experimental setup which led to the physical realization of this technology. Furthermore it also highlights how the active components of the system such as pressure feedback signal can be measured. The setup includes a clean air supply that is treated to remove humidity and any particulates through a desiccant drier and HEPA filter, respectively. The air flow then splits into two mass flow controllers (MFC), regulating the degree of particulate seeding from a vibrating mesh nebulizer and the concentration through mass flow ratios. A mixing chamber ensures a homogenous particle distribution prior to entering the acoustic system. The acoustic system consists of an acoustic generating device next to the acoustically enhanced filter medium. Also shown in FIG. 10 is a particle counter a particle counter which is used to measure the number of particles entering the first side and leaving the second side of the filter medium to measure the number of particles trapped in the filter medium.

[0099] Those having ordinary skill in the art will recognize that numerous modifications can be made to the specific implementations described above. The implementations should not be limited to the particular limitations described. Other implementations may be possible.

Claims

Claims:

1. A filtration system, comprising: a fluid movement system configured to displace fluid along a flow direction; an acoustic wave generator comprising an acoustic transducer and an acoustic reflector spaced apart from one-another according to a predetermined distance, together configured to generate a standing acoustic wave; and a filter medium disposed adjacent the acoustic wave generator having a thickness defined by a first side and a second side, the filter medium configured to trap particles in fluid being displaced by the fluid movement system, wherein the filter medium and the standing acoustic wave each has a corresponding orientation relative to the flow direction.

2. The filtration system of claim 1, wherein the acoustic transducer includes a first piezoelectric element or a first electrostatic element configured to generate a first acoustic excitation.

3. The filtration system of claim 2, wherein the acoustic reflector includes a passive acoustic reflector plate configured to reflect the first acoustic excitation thus generate the standing acoustic wave.

4. The filtration system of claim 2, wherein the acoustic reflector includes an active acoustic plate including a second piezoelectric element or a second electrostatic element configured to generate a second acoustic excitation which together with the first acoustic excitation generate the standing acoustic wave.

5. The filtration system of claim 1, wherein the fluid movement system is disposed on the first side of the filter medium, thus configured to push fluid across the filter medium.

6. The filtration system of claim 1, wherein the fluid movement system is disposed on the second side of the filter medium, thus configured to pull fluid across the filter medium.

7. The filtration system of claim 1, wherein the filter medium includes continuous strands across the filter medium, discontinuous strands, one or more porous solids each including a plurality of holes, or a combination thereof, made of glass fiber, polypropylene,Polyvinylidene fluoride (PVDF), cellulose acetate, polytetrafluoroethylene (PTFE), or any combinations thereof.

8. The filtration system of claim 7, wherein the continuous strands, the discontinuous strands, or the plurality of holes are aligned along a uniform direction.

9. The filtration system of claim 7, wherein the continuous strands, the discontinuous strands, or the plurality of holes are randomly aligned.

10. The filtration system of claim 7, wherein the filter medium includes acoustically reactive strands or reactive porous solid.

11. The filtration system of claim 10, wherein the reactive strands or reactive porous solid scatter and generate supplemental acoustic waves that when combined with the standing acoustic wave generated by the acoustic wave generator enhance the filter medium’s trapping of the particles.

12. The filtration system of claim 10, wherein the reactive strands or reactive porous solids include piezoelectric elements.

13. The filtration system of claim 1, wherein the filter medium is defined by a porosity defined as ratio of void volume to total volume of between about 0.5 and about 0.99.

14. The filtration system of claim 1, further comprising a first pressure sensor disposed adjacent the first side of the filter medium and a second pressure sensor disposed adjacent the second side of the filter medium.

15. The filtration system of claim 14, wherein first pressure sensor and the second pressure sensor each generates a corresponding pressure signal which together generate a pressure differential value across the filter medium.

16. The filtration system of claim 15, wherein the pressure differential value is used as an automatic pressure differential feedback signal to operate the fluid movement system and the acoustic wave generator to thereby modify the standing acoustic wave.

17. The filtration system of claim 16, wherein the pressure differential feedback signal is used as a harmonic feedback signal configured to modify the standing acoustic wave based on acoustic harmonics.

18. The filtration system of claim 16, wherein the pressure differential feedback signal is used as a resonance feedback signal configured to modify the standing acoustic wave based on acoustic resonance.

19. The filtration system of claim 1, wherein the fluid movement system is configured to displace gases.

20. The filtration system of claim 1, wherein the fluid movement system is configured to displace liquids.

21. The filtration system of claim 1, wherein the acoustic wave generator is shut down to clean the filter medium.

22. The filtration system of claim 1, wherein the filter medium presents an acoustic reflectance between about 0.1 and about 1.

23. The filtration system of claim 1, wherein the filter medium is oriented with respect to the flow direction based on an angle of between about 0 and about 180 degrees24. The filtration system of claim 23, wherein the filter medium is oriented substantially perpendicular to the flow direction.

25. The filtration system of claim 1, wherein the acoustic wave generator is oriented such that the standing acoustic wave has an angle with respect to the flow direction of between about 0 and about 180 degrees26. A method of filtering particles in a fluid, comprising: displacing a fluid by a fluid movement system along a flow direction; generating a standing acoustic wave by an acoustic wave generator comprising an acoustic transducer and an acoustic reflector spaced apart from one-another according to a predetermined distance; and trapping particles in the fluid by a filter medium disposed adjacent the acoustic wave generator having a thickness defined by a first side and a second side, wherein the filter medium and the standing acoustic wave each has a corresponding orientation relative to the flow direction.

27. The method of claim 26, wherein the acoustic transducer includes a first piezoelectric element or a first electrostatic element configured to generate a first acoustic excitation.

28. The method of claim 27, wherein the acoustic reflector includes a passive acoustic reflector plate configured to reflect the first acoustic excitation thus generate the standing acoustic wave.

29. The method of claim 27, wherein the acoustic reflector includes an active acoustic plate including a second piezoelectric element or a second electrostatic element configured to generate a second acoustic excitation which together with the first acoustic excitation generate the standing acoustic wave.

30. The method of claim 26, wherein the fluid movement system is disposed on the first side of the filter medium, thus configured to push fluid across the filter medium.

31. The method of claim 26, wherein the fluid movement system is disposed on the second side of the filter medium, thus configured to pull fluid across the filter medium.

32. The method of claim 26, wherein the filter medium includes continuous strands across the filter medium, discontinuous strands, one or more porous solids each including a plurality of holes, or a combination thereof, made of glass fiber, polypropylene,Poly vinylidene fluoride (PVDF), cellulose acetate, polytetrafluoroethylene (PTFE), or any combinations thereof.

33. The method of claim 32, wherein the continuous strands, the discontinuous strands, or the plurality of holes are aligned along a uniform direction.

34. The method of claim 32, wherein the continuous strands, the discontinuous strands, or the plurality of holes are randomly aligned.

35. The method of claim 32, wherein the filter medium includes acoustically reactive strands or reactive porous solid.

36. The method of claim 35, wherein the reactive strands or reactive porous solid scatter and generate supplemental acoustic waves that when combined with the standing acoustic wave generated by the acoustic wave generator enhance the filter medium’s trapping of the particles.

37. The method of claim 35, wherein the reactive strands or reactive porous solids include piezoelectric elements.

38. The method of claim 26, wherein the filter medium is defined by a porosity defined as ratio of void volume to total volume of between about 0.5 and about 0.99.

39. The method of claim 26, further comprising a first pressure sensor disposed adjacent the first side of the filter medium and a second pressure sensor disposed adjacent the second side of the filter medium.

40. The method of claim 39, wherein first pressure sensor and the second pressure sensor each generates a corresponding pressure signal which together generate a pressure differential value across the filter medium.

41. The method of claim 40, wherein the pressure differential value is used as an automatic pressure differential feedback signal to operate the fluid movement system and the acoustic wave generator to thereby modify the standing acoustic wave.

42. The method of claim 41, wherein the pressure differential feedback signal is used as a harmonic feedback signal configured to modify the standing acoustic wave based on acoustic harmonics.

43. The method of claim 41, wherein the pressure differential feedback signal is used as a resonance feedback signal configured to modify the standing acoustic wave based on acoustic resonance.

44. The method of claim 26, wherein the fluid movement system is configured to displace gases.

45. The method of claim 26, wherein the fluid movement system is configured to displace liquids.

46. The method of claim 26, wherein the acoustic wave generator is shut down to clean the filter medium.

47. The method of claim 26, wherein the filter medium presents an acoustic reflectance between about 0.1 and about 1.

48. The method of claim 26, wherein the filter medium is oriented with respect to the flow direction based on an angle of between about 0 and about 180 degrees.

49. The method of claim 48, wherein the filter medium is oriented substantially perpendicular to the flow direction.

0. The method of claim 26, wherein the acoustic wave generator is oriented such that the standing acoustic wave has an angle with respect to the flow direction of between about 0 and about 180 degrees.

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