Cascaded gapped cantilever for low-frequency vibration sensing
Inventors
Xu, Yong • Hu, Yating • Tu, Hongen
Assignees
Wayne State University • National Science Foundation NSF
Publication Number
US-10724897-B2
Publication Date
2020-07-28
Expiration Date
2036-06-16
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Abstract
This disclosure describes a sensor for detecting vibrations, particularly low-frequency vibrations. The sensor is of a cascaded gapped cantilever construction and may include a single sensing beam extending from a base to a proof mass across the plurality of gaps, a mechanical beam opposite the piezoelectric beam. The sensor may be included in a system including a housing, a support, and electronic components for converting and measuring signal. The sensor may be mounted to an item of furniture, such as a bed or a sofa, and measure physiological data including ballistocardiogram and respiratory data of a subject positioned on the furniture.
Core Innovation
The invention describes a sensor device employing a cascaded gapped cantilever structure specifically designed for low-frequency vibration sensing. The sensor includes a base connected to a proof mass by a mechanical beam, with a piezo beam extending from the base to the proof mass across multiple gaps formed by ridges extending from the mechanical beam's inner surface. This arrangement enables the piezo beam's movement to correspond consistently with the proof mass movement, allowing effective detection of low-frequency vibrations.
The problem addressed arises from the challenge of sensing low-frequency vibrations such as heartbeat and respiration, which are difficult to detect with traditional cantilever sensors having high spring constants or those not physically attached to the subject. Conventional wearable cardiovascular monitoring devices present inconvenience and low patient compliance, creating a need for non-contact, high-sensitivity sensors capable of capturing physiological vibrations without direct body contact.
This cascaded gapped cantilever sensor improves sensitivity by increasing the distance between the piezoelectric sensing layer and the neutral plane through multiple gaps, thereby enhancing strain sensitivity while minimizing undesirable shear bending. Adjustments in gap dimensions and mechanical beam thickness allow for uniform strain distribution and energy efficiency, enabling detection of low-frequency physiological signals. The sensor design also supports integration into systems with housing, support structures, and electronic components for converting and measuring signals, allowing deployment on furniture such as beds and sofas to monitor physiological data including ballistocardiogram and respiration.
Claims Coverage
The patent includes two main independent claims covering the sensor device and a system incorporating the sensor device. The following outlines the main inventive features extracted from these claims.
Sensor device with cascaded gapped cantilever structure
The sensor device comprises a base connected to a support, a movable proof mass, and a mechanical beam with an inner surface connecting them. A piezo beam made of sensing material is directly attached at one end to the base and at the other end to the proof mass. At least one ridge extends from the mechanical beam's inner surface to the piezo beam, forming multiple gaps between the piezo beam and mechanical beam. The mechanical beam and piezo beam are arranged oppositely relative to the ridges such that the piezo beam movement corresponds directly to proof mass movement, enabling vibration detection.
Vibration sensing system including the sensor device and housing
The system includes a support with the sensor device attached, where the sensor device has a gapped cantilever arrangement as described, with the piezo beam and mechanical beam forming gaps via ridges and the movement of the piezo beam consistent with that of the movable proof mass. Additionally, the system includes a housing connected to the support and generally surrounding the sensor device, and may further include a printed circuit board for electrical connection and signal processing.
The independent claims cover the sensor device's cascaded gapped cantilever design enabling low-frequency vibration detection via a piezo beam and mechanical beam with ridges forming multiple gaps, and a system incorporating this sensor device with support structures and housing for practical application. These inventive features focus on the mechanical configuration facilitating enhanced sensitivity and correspondence between piezo beam and proof mass movements.
Stated Advantages
Increased sensitivity for low-frequency vibration detection due to greater distance between the sensing layer and the neutral plane enabled by the gapped cantilever design.
Improved energy efficiency by minimizing undesirable shear bending and concentrating strain in the sensing beam via cascaded gaps and thickness variation.
Ability to detect physiological signals such as heartbeat and respiration without direct contact, facilitating non-wearable monitoring.
Enhanced robustness and/or sensitivity through adjustable gap depths and stage lengths in the cascaded cantilever design.
Documented Applications
Monitoring physiological data such as ballistocardiogram, heart rate, pulse, and respiratory signals through non-contact sensing when mounted on items of furniture like beds, sofas, and chairs.
Sleep quality monitoring by detecting cardiac and respiratory signals without requiring the subject to wear devices.
General vibration sensing applications including energy harvesting, accelerometers, petroleum-detection and harvesting, and earthquake sensing.
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