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Passive Filters

Passive Filters

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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Active filters are electronic circuits that use operational amplifiers (op-amps), resistors, and capacitors to filter out unwanted frequency components from a signal. A first-order low-pass active filter is designed to pass signals with a frequency lower than a certain cutoff frequency and attenuate frequencies higher than that cutoff frequency. The transfer function for a first-order low-pass active filter is:

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A half-wave rectifier is a fundamental circuit in electronics, designed to convert alternating current (AC) voltage into a unidirectional voltage. It utilizes the simplest form of diode rectification, where the circuit comprises a single diode in series with a load resistor and an AC power source.

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Full wave rectifier

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Passive Extraction of Signal Feature Using a Rectifier with a Mechanically Switched Inductor for Low Power Acoustic

Marko Gazivoda¹, Dinko Oletić¹, Carlo Trigona²

¹Faculty of Electrical Engineering and Computing, University of Zagreb, 10000 Zagreb, Croatia.

Sensors (Basel, Switzerland)

|September 25, 2020

Summary

This study introduces a new passive electromechanical device for underwater acoustic event detection. It significantly improves sensitivity and reduces power consumption in low signal-to-noise ratio environments.

Keywords:

acoustic vibrations low SNR passive electromechanical transducer pattern recognition wake-up interface

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Area of Science:

Acoustic Signal Processing
Materials Science
Electrical Engineering

Background:

Analog hardware for acoustic event detection has low sensitivity and poor performance in low signal-to-noise ratio (SNR) undersea environments.
Existing solutions struggle with the challenges of underwater acoustic monitoring.

Purpose of the Study:

To propose and validate a novel passive electromechanical solution for low-frequency acoustic signal feature extraction.
To enhance the performance and efficiency of low-power acoustic event detection systems.

Main Methods:

Development of a passive electromechanical device featuring a piezoelectric vibration transducer and a rectifier with a mechanically switched inductor.
Simulation and experimental characterization of the proof-of-concept device.
Comparison with active electrical solutions.

Main Results:

The passive electromechanical device operates effectively with lower input signals (<20 mV vs. 40 mV).
Demonstrated higher robustness in low SNR conditions, with minimal output voltage loss (-10 dB ≤ SNR < 40 dB).
Achieved over 76% reduction in power consumption per detector channel compared to previous work.

Conclusions:

The novel passive electromechanical feature extractor offers significant advantages for low-power analog wake-up event detectors.
This represents a pioneering solution for passive electromechanical feature extraction in such interfaces.
The technology enables extended operational lifetime and improved detection quality in underwater acoustic monitoring.