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Passive Filters

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Passive filters are utilized to shape the frequency spectrum of signals across a diverse array of applications. These filters, using only passive elements like resistors (R), inductors (L), and capacitors (C), are capable of selectively allowing or blocking certain frequency ranges without the need for external power sources.
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Low-pass filters are designed to transmit signals with frequencies lower than the cutoff frequency, ωc, and attenuate those above it. The cutoff frequency...

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Op Amp AC Circuits

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Updated: Jun 19, 2026

Simulation, Fabrication and Characterization of THz Metamaterial Absorbers

Simulation, Fabrication and Characterization of THz Metamaterial Absorbers

Published on: December 27, 2012

A digital-filter model for simulating sound absorption in the air.

Rubén Fraile¹, Juan José Gómez-Alfageme¹, Elena Blanco-Martín¹

¹CEIMM, Universidad Politécnica de Madrid, Campus Sur, Madrid 28031, Spain.

The Journal of the Acoustical Society of America

|June 18, 2026

Summary

This study introduces a new digital filter model for simulating air absorption in acoustics. The model offers low-cost, stable simulations across various atmospheric conditions and distances.

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Area of Science:

Acoustics
Signal Processing
Environmental Engineering

Background:

Acoustic propagation simulations often neglect air absorption due to a lack of efficient modeling techniques.
Accurate modeling of air absorption is crucial for realistic acoustic simulations.

Purpose of the Study:

To propose a low-complexity, valid, and robust digital filter model for simulating air absorption.
To analytically derive filter coefficients based on propagation conditions and sampling frequency.

Main Methods:

Developed a third-order digital filter model for air absorption.
Derived filter coefficients analytically using temperature, pressure, relative humidity, propagation distance, and sampling frequency.
Validated the model against the ISO 9613 standard for acoustic absorption.

Main Results:

The proposed filters closely approximate ISO 9613 air absorption.
Errors are below 50% for 95% of the 20 Hz–20 kHz spectrum up to 25m.
The model maintains accuracy for distances up to 100m at temperatures below 20°C.
Filters are minimum-phase, allowing for stable inverse filtering.

Conclusions:

The developed digital filter provides a computationally efficient and accurate method for simulating air absorption.
This approach enables both low-cost acoustic simulations and stable inverse filtering for de-absorption.