Relating the ultrasonic and aerosol filtration properties of filters
Bibliographic record
Abstract
Non-contact methods are useful to improve the quality control of particle filtration media.The purpose of this paper is to investigate the correlation between the filtration efficiency of a porous sheet and its ultrasonic properties obtained using a non-contact technique.An air-coupled ultrasonic technique is used to obtain rapid measurements without affecting the integrity of the material.High frequencies (from 0.1 to 2.5 MHz) are used to improve technique sensitivity, and transmitted waves are measured to probe the internal properties of the material.Measurements of transmission coefficient spectra (amplitude and phase) and the corresponding ultrasound velocity and attenuation coefficient at different frequencies are obtained for a set of filtration media with well-characterized properties.Results show that the ultrasonic properties of filtration media vary as a function of basis weight, and therefore filtration efficiency, for a given charge state.However, the effect of electrostatic charge on ultrasonic propagation is almost negligible, as expected.We conclude that ultrasonic transmission may provide a valuable tool for the continuous online monitoring of material quality during fabrication and as a method to tease apart mechanical and electrostatic contributions to particle filtration. Keywords Filtration efficiency, Air-coupled ultrasound, Air filters testingThe filtration of aerosolized particles is critical to respiratory protection, within the context of both occupational and public health, and to building ventilation systems 1,2 .The demand for better, consistent quality filters requires methods to quickly ensure homogeneity and reproducibility of the materials that make up these products.This may become increasingly important as new filtration materials and new manufacturing methods are developed.Currently, measurements of particle filtration efficiency and pressure resistance require slow, typically offline, and typically destructive approaches to filter testing.Given that, in most cases, these materials can present some degree of intrinsic heterogeneity, testing large portions of the produced filters can become a key issue.This leaves an opportunity for complementing standard testing with non-destructive, online techniques.Acoustic and ultrasonic techniques, encompassing both water and air-coupled approaches, have been used in the past to test different porous media, where ultrasonic and acoustic properties have been correlated with different material properties, including permeability, fluid filtration efficiency, tortuosity, porosity, and pore size.The relationship between permeability or fluid resistance and acoustic propagation in air saturated porous materials at audio frequencies is well understood and has been employed to characterize porous materials in different applications, especially for sound absorbers [3][4][5][6][7][8][9] .At the same time, fluid immersion ultrasonic techniques have also been used to study porous materials for fluid filtration-mainly filtration membranes-to determine membrane fouling during operation 10,11 and particle retention capability 12 .Closer to the application here studied, ultrasonic waves and air-coupled techniques have also been used to study the correlation between permeability, flux resistivity, porosity and tortuosity with ultrasound propagation features for different porous and filtration materials 5,[13][14][15][16][17][18][19] .It has recently been demonstrated that, by using air-coupled ultrasonic transducers [20][21][22] with high sensitivity, high center frequency (> 150 kHz), and large frequency band (fractional bandwidth at -20 dB > 50%), it is possible to transmit ultrasonic signals through a variety of filtration layers used in the fabrication of face masks with sufficient signal-to-noise ratio to extract valuable information 23 .In addition, it was demonstrated that ultrasonic propagation takes place in the air gaps, such that ultrasonic parameters are sensitive to effective pore size, tortuosity, and porosity.In addition, it was shown that the loss in the transmission coefficient increases with the face mask grade, ranging from cloth face masks to respirators.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.004 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 0.003 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.017 | 0.004 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".