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

Abstract

Analog hardware used for signal envelope extraction in low-power interfaces for acoustic event detection, owing to its low complexity and power consumption, suffers from low sensitivity and performs poorly under low signal to noise ratios (SNR) found in undersea environments. To overcome those problems, in this paper, we propose a novel passive electromechanical solution for the signal feature extraction in low frequency acoustic range (200–1000 Hz), in the form of a piezoelectric vibration transducer, and a rectifier with a mechanically switched inductor. A simulation study of the novel solution is presented, and a proof-of-concept device is developed and experimentally characterized. We demonstrate its applicability and show the advantages of the passive electromechanical device in comparison to the active electrical solution in terms of operation with lower input signals (<20 mV compared to 40 mV), and higher robustness in low SNR conditions (output voltage loss for −10 dB ≤ SNR < 40 dB of 1 mV, compared to 10 mV). In addition to the signal processing performance improvements, compared to our previous work, the utilization of the presented novel passive feature extractor would also decrease power consumption of a detector’s channel by over 76%, enabling life-time extension and/or increased quality of detection with larger number of channels. To the best of our knowledge, this is the first solution presented in the literature that demonstrates the possibility of using a passive electromechanical feature extractor in a low-power analog wake-up event detector interface.

Low-Power Sensor Interface with a Switched Inductor Frequency Selective Envelope Detector

“…The passive components of interest are: input capacitor C in , inductor L , Q factor of the input switched inductor filter, and output capacitors, C out 1 and C out 2 , which we analyzed in detail in our previous work [ 17 , 18 ]. The diodes were also chosen based on previous work analyzing their influence on weak-signal rectifier performance [ 14 , 22 ].…”

“…The interface synthesis is performed in a series of steps: Choosing the output capacitors C out 1 and C out 2 to ensure the desired output signal waveform and its key parameters (more details in [ 17 , 18 ]). Determining the wanted frequency characteristic of the interface, by choosing its resonant frequency, f res , (and angular frequency ω res = 2π f res ) and Q factor.…”

“…Choosing the output capacitors C out 1 and C out 2 to ensure the desired output signal waveform and its key parameters (more details in [ 17 , 18 ]).…”

“…In [ 17 ] we studied the impact of the envelope detector on sensitivity and power consumption of the wake-up sensor interface in the lower audio frequency range. Based on the mechanically switched inductor energy harvester [ 16 ], in [ 18 ] we demonstrated that a piezoelectric energy harvester can be used as a vibration sensor utilizing a mechanically switched inductor driven by the sensed vibrations.…”

“…In Section 6 a set of design recommendations for interface synthesis are given. Section 7 presents a comparison of the novel sensor interface and interface presented in [ 9 , 18 ] and Section 8 states the concluding remarks of the paper and presents future work.…”