acoustics Archives - Perfect 3D Printing Filament

Acoustically Assembled Multidimensional Filler Networks 3D Printed Polymer Composites for Thermal Management

In ‘3D-printed polymer composites with acoustically assembled multidimensional filler networks for accelerated heat dissipation,’ authors Lu Lu, Zhifeng Zhang, Jie Xu, and Yayue Pa explore a new technique for printing composites with filler that could eliminate overheating in electronics. Part of the challenge for the researchers in this project was in thermal management and finding a balance in filler loading.

With acoustic field-assisted projection stereolithography, the research team focused on using just a small amount of filler to create a network of heat-diverting paths. This work could be critical to a variety of different applications, as many electronics are overloaded due to heating and may fail completely; in fact, the researchers include data from a U.S. Air Force survey reporting that over half of their issues with electronics are due to overheating. These problems need to be solved, in military applications especially, but also in other fields centered around chipsets, wearables, and flexible electronics.

Acoustic Field Assisted Projection Stereolithography (A-PSL) setup

Polymer composites are ‘promising’ due to their conductive qualities, along with being insulating and flexible. The traditional method involves mixing fillers in the matrix, with some success in adding ‘heavy filler loading.’ Historically, however, this has led to problems such as:

Clogging
Difficulty in mixing
Agglomeration
Trouble in filler embedding
Limited manipulation of filler distribution
Orientation issues

“Additionally, the manufactured composites with heavy filler loading usually suffer from insufficient binding, mechanical deterioration, and thermal expansion coefficient mismatch,” state the researchers. “The disordered distribution of fillers limits thermal performance enhancement due to the phonon scattering between isolated fillers.”

a. Photograph of parallel filler line pattern in liquid resin; SEM images of b.The uniform composite, c. The patterned composite, d. Acoustically assembled filler microstructure in cross-sectional view. (Filler: aluminum powder).

3D printing offers better results in alignment and orientation, but also allows for multi-material fabrication. Here, the researchers see the potential for superior performance with their acoustic-field-based filler manipulation technique, including the following features:

Filler distribution controls
Lack of manufacturing restrictions
No filler shape or property requirements

The module is made up of electro-piezo elements, a function generator, and an amplifier.

“A function generator provides the sinusoidal signal with adjustable frequency and voltage. This signal is applied to the electro-piezo element after amplified. The piezo element actuation leads to structural deformation of the PET film, which subsequently induces an acoustic field in the filler-resin suspension. The acoustic radiation force drives fillers to the pressure nodes of the acoustic field to form a pattern,” state the researchers.

The team created five different composites, P1-P5, with the three patterned composites (P2, P3, P4) exhibiting better performance due to their 3D particle assembly networks—causing the researchers to state that the samples ‘proved the effects’ of filler assembly in regard to the new composite and technique.

a. Schematics of unit layers. b. Photograph of a printed sample P-1 and its microscopic images. c. Schematics of different filler distribution patterns and the microscopic images of fabricated samples in side views.

“By controlling the manufacturing parameters, such as the layer thickness and the projection mask, multidimensional filler networks formed,” concluded the researchers. “Multidirectional heat transfer paths provided by multidimensional filler networks accelerate the cooling process in the isolated polymer matrix. With the same feedstock or even the same number of particles filled in the polymer matrix, the patterned composites are superior to the uniform composite with significantly higher heat dissipation efficiencies.

“Future work will be to quantify the relationship of composite functionality with particle pattern design parameters.”

Composites are accentuating the realm of 3D printing materials as users in research, development, engineering, and industrial settings around the world seek better ways to make prototypes and products, including bioprinting structures—from graphene reinforced nanocomposites to wood composites and chitosan-gelatin hydrogels.

Find out more about 3D printing polymer composites for electronics here. What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

[Source / Images: ‘3D-printed polymer composites with acoustically assembled multidimensional filler networks for accelerated heat dissipation’]

Illustration of the cooling experiment.

Nanyang Technological University: Experimenting with Acoustic Nozzles to Disrupt Clogging in 3D Printing

Thesis student, Yannapol Sriphutkiat, of the School of Mechanical and Aerospace Engineering at Nanyang Technological University recently published, ‘Development of acoustic nozzle for 3D printing,’ exploring the use of acoustic vibrations to solve one of the most common problems: clogging.

As with so many innovations and improvements allowed through 3D printing, it all makes perfect sense—using acoustics to manipulate microparticles and prevent clogging. For this study, Sriphutkiat researched the use of standing surface acoustic waves (SSAWs) in microchannels to reduce the issue.

Proper alignment of printing materials in the nozzle and elimination of clogging leads to a better outcome not only for 3D printing overall, but especially in bioprinting practices as it limits cell density in the material. While there are numerous challenges in bioprinting, clogging is one that still confounds and thwarts researchers:

“Suspensions are likely to sediment and aggregate in the cell reservoir, tube and nozzle of the printing system, the sedimentation reduces the width of the flow path which may also lead to clogging within the narrow geometry of the inkjet nozzle. The clogging could significantly increase the normal stress and shear stress applied to the cells, which may decrease the cell viability and proliferation rate, and decrease formation of nonuniform droplet sizes of bioink,” stated the researchers.

The schematic of clogging mechanism

Although clogging continues to be a mystery in many ways, in this study, researchers are optimistic about the use of vibration as a solution for both stability in production and reduction of clogging too. The overall idea of such a technique is to ‘disturb the clogging behavior,’ which often seems to occur around the entrance of the pore throats, and then completely blocking or bridging the area.

“SSAWs move microparticles away from the wall, towards the center of the microchannel, and therefore, reduce the chance of microparticle accumulation/clogging,” stated the researchers, who employed dual-frequency excitation for the SSAWs, for better control.

The acoustic nozzle caused cells to accumulate toward the center of a cylindrical tube in the lab, allowing for success in 3D printing, with tuning of SSAWs decreasing the width of accumulated microparticles.

Schematic diagram of SSAW consisting of (a) PDMS-LiNbO3 and (b) superstrateLiNbO3

“In comparison to the conventional printing strategy, acoustic excitation could significantly reduce the width of accumulated microparticles in the printed structure (p < 0.05). In addition, the microparticle motion excited at higher harmonics (385 kHz and 657 kHz) was also studied,” stated the researchers.

The study continued successfully with bioprinting as the researchers observed C2C12 cells being controlled by the acoustics. Once printed, they were studied for a week. The cells exposed to acoustic excitation accumulated near the center of the nozzle, while cells from the control group were scattered. Acoustically manipulated cells also showed more ‘significant dense cell structure,’ while the control group cells were still more chaotic.

“Overall, the acoustic approach is able to accumulate microparticles/cells in the printed construct at a low cost, simple configuration, and low power, but high biocompatibility,” concluded the researchers. “In the future, acoustic patterning of various biological cell types in printed construct could be investigated. As acoustic method has a capability to manipulate the microparticle/biological cells depending on their physical properties (compressibility, density and size).

Sound has played a role in numerous 3D printing techniques, from the development of acoustic metamaterials to implanting items with sound data, or even 3D printed symphonies. Find out more about how innovations such as acoustic nozzles can improve the 3D printing process here. What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

Schematic diagram of experimental setup.

[Source / Images: Development of acoustic nozzle for 3D printing]

Acoustic Nozzles Improve the Performance of 3D Printed Parts

Usually when we’re talking about 3D printing in terms of acoustics, it has to do with making a good set of speakers. But, recent research has determined that acoustic signal processing could be used to monitor the build quality of a 3D printed part while in progress. There are 3D printable sound-shaping super-materials, and 3D printed objects have even been implanted with sound data for tagging purposes. New research out of Nanyang Technological University (NTU) in Singapore looks at using acoustics to manipulate microparticles inside the actual 3D printing ink itself to improve the final object’s performance and functionality.

Properly orienting and aligning the fibers in a polymer matrix could help transfer loads from critical areas for better performance, and creating 3D scaffolds with a controlled hierarchical structure at the nano- and micro-scale levels could increase their mechanical strength, which is good for cell and tissue regeneration and load-bearing bone defect repair. In addition, using surface acoustic waves to focus microparticles inside the microchannel could delay accumulation on the wall, which can improve extrusion-based 3D printing.

Schematic diagram of experimental setup.

Researchers from NTU recently published a paper on their 3D printing work with acoustics, titled “Cells alignment and accumulation using acoustic nozzle for 3D printing.”

The abstract reads, “Arrangement or patterning of microparticles/cells would enhance the efficiency, performance, and function of the printed construct. This could be utilized in various applications such as fibers reinforced polymer matrix, hydrogel scaffold, and 3D printed biological samples. Magnetic manipulation and dielectrophoresis have some drawbacks, such as time-consuming and only valid for samples with specific physical properties. Here, acoustic manipulation of microparticles in the cylindrical glass nozzle is proposed to produce a structural vibration at the specific resonant frequency. With the acoustic excitation, microparticles were accumulated at the center of the nozzle and consequently printed construct at the fundamental frequency of 871 kHz. The distribution of microparticles fits well with a Gaussian distribution. In addition, C2C12 cells were also patterned by the acoustic waves inside the cylindrical glass tube and in the printed hydrogel construct. Overall, the proposed acoustic approach is able to accumulate the microparticles and biological cells in the printed construct at a low cost, easy configuration, low power, and high biocompatibility.”

Morphology and distribution of the cells in 5% GelMA without the acoustic excitation on (a) day 1, (b) day 4, (c) day 7, and with the acoustic excitation on (d) day 1,(e) day 4, (f) day 7.

The team numerically and experimentally studied the structural vibration of a cylindrical tube, as well as the patterning of the microparticles and cells inside of it.

“Firstly, the resonant frequency was numerically predicted and validated with experiment,” the researchers wrote. “Subsequently, the distribution of microparticles and biological cells inside the cylindrical tube and printed construct was investigated. Lastly, the growth of biological cells undergone the acoustic excitation was monitored for up to 7 days.”

During an acoustic excitation, a mixture of C2C12 cells embedded in 2 ml of 5% GelMA was printed on a 4″ petri dish, with the nozzle perpendicular to the print bed. The researchers discovered that during the excitation, most of the microparticles that were initially suspended in fluid ended up accumulating at the center of the glass tube. There seemed to be a good overall agreement between the experimental results and numerical simulation of the excitation frequency, along with the location of pressure nodes in the glass tube.

The researchers further evaluated their acoustic nozzle’s performance using C2C12 muscle cells, and determined that without the excitation during printing, the distribution of the cells in the tube was very random.

Microparticle distribution in the cylindrical tube (a) without and (b) with the acoustic excitation at 877 kHz.

“Results of simulation and experiment are agreeable with a slight difference in the resonant frequency (< 2%). In the experiment, microparticles were accumulated at the center of the nozzle and consequently printed construct. The distribution of microparticles fits well in a Gaussian curve with a standard deviation of (V = 0.16 mm). Furthermore, the acoustic excitation could also be used for patterning biological cells in the 3D printed construct of GelMA,” the researchers concluded. “Subsequently, the distribution of cells was quite dense at the center of the printed structure, and accumulated C2C12 cells had greater growth and differentiation in comparison to the suspended ones in the control group.”

Co-authors of the paper are Yannapol Sriphutkiat, Surasak Kasetsirikul, Dettachai Ketpun, and Yufeng Zhou.

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Acoustics Play a Role in Determining 3D Print Quality

Metal 3D printing is constantly under study to improve its quality and repeatability. A new research paper focuses on direct metal laser sintering (DMLS), also known as selective laser melting (SLM) and Powder Bed Fusion for Metal. DMLS still has its shortcomings, which include delamination between base plates and inaccuracy among various orientations. The paper, entitled “Characterization of acoustic signals during a direct metal laser sintering process,” points out that sintered parts tend to still be relatively large, soft and porous, hampering their widespread use, so improving part quality and repetability is crucial, especially for industries like aerospace and medicine.

The researchers look at acoustic signal processing as a way to monitor the build quality of a 3D printed part while in progress.

“This paper reports the relationship between acoustic signals, laser power as well as its laser scanning speed,” the researchers state. “The variety of acoustic signal power spectrum density (PSD) is presented and then the mechanism of acoustic signal formation is elaborated. A good mapping between acoustic signals and laser parameters has been found during the DMLS process. This lays a good foundation for monitoring the process and quality by acoustic signal and will enhance the part quality during the powder-based laser sintering and melting processes in the future.”

Several methods of in-process monitoring exist, such as optical, thermal, ultrasound and acoustic signals. Each has its drawbacks, but acoustic signals have been found to be an effective method as long as they are not disrupted by environmental noise. In this study, acoustic signals generated during the DMLS process were sampled and utilized for online monitoring.

Acoustic signals in a DMLS process are generated by several factors, mostly by the vibration from the friction of flow medium with liquid or solid matter, as well as flow motion. The signals in this study were sampled by an electret condenser microphone and processed with MATLAB 2015b.

The results of the experiment showed that there was a good correlation between the laser frequency and laser power as well as the laser scanning speed and acoustic signals.

“Through the investigation of the acoustic signal, information on the laser scanning characteristics can be extracted,” the researchers explain. “The second frequency peak is more promising for detecting the laser scanning attributes.”

The study showed that there was a good mapping between the acoustic signals and laser scanning status as well as the resulting laser sintering quality. These results, according to the researchers, will lead to future monitoring techniques for DMLS and provide a strong foundation for real-time control of metal printing processes.

“Future studies will be carried out on part qualities such as surface roughness, porosity, density and composition of the powder mixture interpreted via acoustic signals,” they conclude. “Defects can be predicted automatically for quality monitoring and feedback control.”

Studies like this one are important steps toward understanding what is happening during the metal 3D printing process, so that defects can be caught and avoided. Metal 3D printing is far from a perfect process, but the more technology is applied to understanding it, the more effective it will be.

Authors of the paper include Dongsen Ye, Yingjie Zhang, Kunpeng Zhu, Geok Soon Hong and Jerry Fuh Ying His.

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Could Your Next Headphones Use 3D Printed Metamaterials?

We’ve often seen 3D printing used to fabricate headphones and earbuds. But a team of researchers from the Department of Electrical and Electronic Engineering in the University of Strathclyde in Glasgow are taking this idea to the next level with acoustic metamaterials. Metamaterials, which can morph according to their environment, make up a new class of finely-engineered surfaces that can perform nature-defying tasks like 3D printing holograms and shaping sound waves. Acoustic metamaterials have the unique ability to attenuate sound by breaking the mass-density law, due to properties such as negative effective density and bulk modulus – no easy feat when it comes to small devices since thin walls are easily penetrated by acoustic waves.

The researchers, who are all affiliated in various capacities with the university’s Centre for Ultrasonic Engineering (CUE), recently published a paper, titled “Enhancing the Sound Absorption of Small-Scale 3D Printed Acoustic Metamaterials Based on Helmholtz Resonators,” detailing how their SLA 3D printed acoustic metametarials, based on Helmholtz resonators, can be used for small-scale sound absorption applications.

The abstract reads, “The directional response due to the position of the acoustic source on the sound attenuation provided by the metamaterial is investigated by controlling the location of a loudspeaker with a robot arm. To enhance and broaden the absorption bands, structural modifications are added such that overtones are tuned to selected frequencies, and membranes are included at the base of the resonators. This design is made possible by innovative 3D printing techniques based on stereolithography and on the use of specific UV-curable resins. These results show that these designs could be used for sound control in small-scale electroacoustic devices and sensors.”

To cut a material’s sound transmission by half, you have to double its acoustic frequency, density, or thickness. When an acoustic metamaterial has negative parameters, stop bands will form where the sound is deeply attenuated at certain frequencies.

“Acoustic metamaterials can break the mass-density law by exploiting the stop bands formed in the proximity of the resonance frequencies of their unit cells,” the researchers explain. “These material structures are often based on Helmholtz resonators and membranes. The frequency band that is attenuated by using these kind of unit cells is nevertheless narrow, hence solutions such as coupling of multiple resonances and leveraging the losses of the materials are generally used to make the attenuation broadband.”

Kuka robotic arm configuration.

The team’s paper presents a basic design of these small-scale, sub-wavelength 3D printed acoustic metamaterials, which use Helmholtz resonators arrays to generate stop bands where sound attenuation increases with the number of unit cells. A loudspeaker, guided by a KUKA robot arm through a quarter-hemisphere trajectory, illustrated that an absorption band forms “for every angle of incidence of the impinging sound wave.” A reference microphone was used to measure sound transmission in the air, while the transmission above the sample was measured by a second microphone.

The paper also explains two methods of enhancing the stop band, the first of which requires the resonators’ overtones to be tuned more closely to the fundamental frequency; this causes the band to grow wider. The second method involves printing membranes at the resonators’ base.

“In this work a novel fabrication technique is used, where thin membranes are fabricated inside Helmholtz resonators, the two units consisting of different materials,” the researchers wrote. “The presented manufacturing technique could result in rapid prototyping of metamaterials and contribute to the advancement of this field into the industrial environment. Simple physical models of the presented metamaterials are included in each section, nevertheless this work is mostly based on experimental results and aims at developing metamaterials that could be included in real devices. Potential applications of this work include noise cancellation for devices such as headphones, hearing aids and other sensors.”

Work is continuing to advance acoustic metamaterials in applications like acoustic cloaking, sound focusing and waveguiding, and imaging and computation, but the results are not often integrated into functional devices. But if studies like this one by the University of Strathclyde researchers can be validated, we could be looking at vastly improved headphones in the near future.

Co-authors of the paper are IEEE Student Member Cecilia Casarini, Benjamin Tiller, Carmelo Mineo, Charles N. MacLeod, IEEE Senior Member Professor James F. C. Windmill, and Joseph C. Jackson.

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