PVDF Sensor Mat with Impedance Matching Layer for Breath Sound Detection
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Solution Overview
Problem
Existing sensor systems for recording body movements and breathing sounds are intrusive, uncomfortable for patients, and often fail to reliably detect low-amplitude high-frequency vibrations due to attenuation through multiple layers of material, such as clothing and mattress layers.
Innovation Solution
A sensor system comprising a mat with piezoelectric membranes coated with an impedance matching layer, such as latex, and mounted in an elastomeric envelope within the mat, which compresses against the patient's chest to transmit breath sounds without significant attenuation, allowing for the detection of a wide range of frequencies and amplitudes, including fine breath sounds and pathological vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sensors are placed directly on or under the patient's mattress, then the sensor can detect body movements and breathing, but the sensor fails to reliably pick up breath sounds due to attenuation through multiple layers of material
Solution Approach 1:
A mat with an aperture is introduced as an intermediary component between the sensor and the patient. The mat positions the sensor closer to the patient's body while still allowing compression against the chest wall, serving as a mediator that overcomes the attenuation problem of direct mattress placement while maintaining comfort and reliability.
Solution Approach 2:
The sensor system transitions from a two-dimensional mattress surface to a three-dimensional configuration with a mat that has height and depth. This allows the sensor to be positioned in a hole in the mat, enabling it to compress against the patient's chest wall and capture breath sounds more effectively by adding a vertical dimension to the detection path.
2Reliability
If sensors are attached or pressed directly against the patient's chest wall, then breath sounds can be detected, but the sensor becomes intrusive and disturbs the patient's sleep
Solution Approach 1:
The mat acts as a comfortable intermediary that allows the sensor to achieve effective contact with the patient's chest wall without requiring direct attachment. The mat can be covered with sheets and clothing, making it non-intrusive while still enabling reliable breath sound detection through the compression mechanism.
Solution Approach 2:
The sensor system utilizes the patient's own body weight and the recoil of the mattress to automatically compress the sensor against the chest wall during normal sleeping positions. This self-service mechanism eliminates the need for active compression or intrusive attachment, maintaining patient comfort while ensuring reliable detection.
3Measurement precision
If pressure detectors or accelerometers are used in the mattress, then body movements can be detected, but low-amplitude high-frequency vibrations such as breath sounds are attenuated
Solution Approach 1:
The system changes the operational parameters of the piezoelectric membrane sensor by positioning it in a hole in the mat that allows direct compression against the patient's chest wall. This parameter change enables the sensor to detect low-amplitude high-frequency vibrations effectively by eliminating the attenuation caused by multiple layers of material.
Solution Approach 2:
The patent replaces pressure detectors and accelerometers with a piezoelectric membrane sensor that is specifically suited for detecting acoustic vibrations. This substitution of the sensing mechanism allows for better detection of low-amplitude high-frequency breath sounds while reducing energy loss through the material layers.
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 system effectively detects and records low and high-frequency breath sounds, enabling the monitoring of sleep apnea, asthma, and heart failure by compressing the sensor against the patient's thorax, ensuring comfort and accurate signal transmission without losing fine vibrations, thus improving diagnostic capabilities.
Implementation Method 1
each sensor comprising: a sensor housing, a sound vibration sensing element in the form of a piezoelectric membrane
Implementation Method 2
an elastomeric envelope/container in which the sensor housing is mounted, the envelope/container mounting the sensor in the mat and acting as an independent suspension means that suspends the sensor in the hole and compresses the sensor against a patient overlying the mat
Data Source
Figure 1
Figure 2~3
AI summary
A sensor system comprises a mat (20) for placement over a patient's mattress including a number of sensors (10) located in the mat. The sensors include a sensor housing (12), a sound vibration sensing element in the form of a PVDF membrane (13), and means for amplifying sensed sounds. The PVDF membrane is coated/covered with a typically latex, impedance matching layer (14). The sensor automatically provides for auscultation, in which the patient's own weight, from the patient lying on the bed, compresses their thorax against the membrane, compressing also the patient's clothing, bed sheet and mattress cover material between the two. The recoil in the mattress opposes the body mass, thus compressing the membrane against the thorax. The impedance matching layer on top of the membrane transmits fine breath sounds through to the membrane as the latex does not weaken or attenuate the fine breath sounds but transmits them to the PVDF membrane. However being flexible, it is not uncomfortable to lie on.