Piezoelectric Respiratory Belt Adapter Circuit for PSG Compatibility
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Solution Overview
Problem
Existing polysomnographic (PSG) machines face challenges in accurately measuring respiratory effort due to incompatibility between piezoelectric and inductive respiratory belts, leading to artifacts and poor compatibility with existing PSG machines, which hinders the market acceptance of PVDF-based respiratory belts.
Innovation Solution
An adapter circuit that amplifies the piezo signal from a PVDF film transducer, applies a low-pass filter to remove noise, and emulates the inductance of a RIP belt, allowing the PVDF belt to be used with existing PSG machines by introducing an appropriate inductance or inductive reactance value, effectively mimicking the signal produced by a RIP belt.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a piezoelectric sensor is used to measure belt tension changes, then the measurement is simple and inexpensive, but the method produces trapping artifacts and false signals when the belt tension changes with body position changes
Solution Approach 1:
The patent introduces an intermediary elastic element (spring or elastomeric material) between the piezoelectric sensor and the belt. This intermediary absorbs the trapping artifacts and body position changes, allowing the piezoelectric sensor to measure only the respiratory-related belt tension changes without false signals from belt trapping.
2Ease of operation
If an elastic belt is used to measure chest or abdominal movement, then the measurement is simple, but the belt becomes trapped when the patient turns during sleep, resulting in variable tension and false signals
Solution Approach 1:
The patent introduces an intermediary elastic element (spring or elastomeric material) between the piezoelectric sensor and the belt. This intermediary absorbs the trapping artifacts and body position changes, allowing the piezoelectric sensor to measure only the respiratory-related belt tension changes without false signals from belt trapping.
3Reliability
If PVDF film transducer is used to generate voltage signal, then robust signal output is achieved, but compatibility with existing RIP-based PSG machines is poor
Solution Approach 1:
The patent introduces an adapter circuit as an intermediary between the PVDF film transducer and the RIP-based PSG machine. The adapter circuit converts the high-impedance capacitive voltage output from the PVDF sensor into the low-impedance inductive signal format expected by RIP-based PSG machines, enabling compatibility while preserving the robust signal output of PVDF technology.
Solution Approach 2:
The adapter circuit changes the electrical parameters of the signal from the PVDF transducer. It converts the high-impedance capacitive output characteristics into low-impedance inductive output characteristics that match the expectations of RIP-based PSG machines, thereby enabling interoperability between incompatible technologies.
4Adaptability or versatility
If piezoelectric and inductive technologies are bridged using an adapter, then compatibility with existing PSG machines is improved, but device complexity increases
Solution Approach 1:
The patent introduces an adapter circuit as an intermediary between the PVDF film transducer and the RIP-based PSG machine. The adapter circuit converts the high-impedance capacitive voltage output from the PVDF sensor into the low-impedance inductive signal format expected by RIP-based PSG machines, enabling compatibility while preserving the robust signal output of PVDF technology.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The adapter circuit enhances the accuracy of respiratory effort measurement by reducing artifacts and ensuring compatibility with existing PSG machines, enabling the use of PVDF-based belts in polysomnographic studies while maintaining the robust signal output of PVDF technology.
Implementation Method 1
a piezoelectric sensor, i.e., a crystal that directly generates a voltage when compressed or stretched
Implementation Method 2
An adapter circuit is designed to accept the piezo signal from the PVDF film transducer and amplify the signal
Implementation Method 3
The signal is then applied to a low-pass filter, preferably a third order Butterworth filter having unity gain and a cutoff frequency of approximately 0.5 Hz
Implementation Method 4
An alternating current is passed through the belt, generating a magnetic field. The frequency of the alternating current is set to be much greater than the typical respiratory rate in order to achieve adequate sampling of the respiratory effort waveform and in order to monitor the change in inductance due to breathing reliably
Data Source
AI summary
Circuits for rendering piezo-based respiratory belts compatible with polysomnograph (PSG) machines designed for use with respiratory induction belts (RIPs) comprise an instrumentation amplifier adapted to be connected to a piezoelectric transducer and providing an AC output signal to a low-pass filter. In a first embodiment, the low-pass filter output is applied to an input of a microcontroller's A to D converter and the resulting digitized samples are used to vary the resistance of a digital potentiometer whose wiper terminal is coupled in series with an inductor so as to emulate the presence of a RIP belt to the PSG machine. In a second embodiment, the low-pass filter output is used to drive the primary of a transformer so as to vary the permeability of the transformer's ferrite core in a way that emulates the performance of a RIP belt to the PSG.