SAW Sensor Cover Wettability for Bubble-Free Sample Flow
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Solution Overview
Problem
Conventional surface acoustic wave sensors face challenges in controlling the flow of liquid samples, leading to propagation loss and air bubble formation due to the presence of a partition wall between the IDT electrodes and the detection part.
Innovation Solution
A surface acoustic wave sensor design featuring a piezoelectric substrate with IDT electrodes sandwiching a detection part, covered by a cover with a lower surface having a first region with a smaller contact angle to the sample than the second regions, allowing for controlled liquid sample flow without a partition wall.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a partition wall is provided between the IDT electrode and the detection part to prevent liquid sample flow onto the IDT electrode, then the liquid sample flow is controlled, but the partition wall becomes a primary factor of propagation loss of the SAW
Solution Approach 1:
The invention removes the partition wall that was previously used to control liquid sample flow. Instead of using a physical barrier, the liquid sample flow is controlled by the channel structure itself, which guides the liquid to flow directly onto the detection part without requiring additional partition walls that would cause SAW propagation loss.
Solution Approach 2:
The invention segments the lower surface of the cover into different regions with different wettability characteristics. The first region (facing the detection part) has higher wettability to attract liquid sample flow, while the second regions (facing the IDT electrodes) have lower wettability to repel liquid sample flow. This segmentation controls liquid flow without physical partition walls.
2Ease of operation
If the channel wall is positioned outside the detection part and IDT electrode to allow liquid sample flow onto the IDT electrode, then the liquid sample can reach the detection part, but air bubbles are liable to form on the detection part
Solution Approach 1:
The invention applies different wettability properties to different local regions of the cover's lower surface. The first region facing the detection part has higher wettability (smaller contact angle) to actively attract and guide liquid sample flow onto the detection part. The second regions facing the IDT electrodes have lower wettability (larger contact angle) to repel liquid sample flow. This local quality differentiation ensures controlled liquid flow paths that prevent air bubble formation.
3Reliability
If a sealing member is provided to form a closed space over the IDT electrode to prevent immersion, then the IDT electrode is protected from liquid sample, but the structure becomes more complex
Solution Approach 1:
The invention merges the sealing function with the cover structure itself. The cover serves dual purposes: it seals the space to protect the IDT electrode from liquid sample immersion, and its lower surface with differentiated wettability regions actively controls liquid sample flow. This integration eliminates the need for separate partition walls or additional sealing components, reducing overall device complexity.
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
This design reduces propagation loss and improves signal-to-noise ratio by ensuring the liquid sample flows preferentially to the detection region, minimizing air bubble formation and enhancing measurement accuracy.
Implementation Method 1
A lower surface of the cover has a first region which faces the detection part and a pair of second regions which are located on the two sides relative to the first region. The first region has a smaller contact angle to the sample than that of the pair of second regions.
Data Source
AI summary
The present invention provides a surface acoustic wave sensor capable of suitably controlling the flow of a liquid sample onto IDT electrodes. A surface acoustic wave sensor has a piezoelectric substrate, a first IDT electrode and a second IDT electrode which are located on the upper surface of the piezoelectric substrate and are separated from each other while sandwiching a detection part on the piezoelectric substrate therebetween, and the cover which forms the space being on the first IDT electrode, second IDT electrode, and the detection part and straddling them. On the lower surface of the cover, the detection part-facing surface facing the detection part has a smaller contact angle to the liquid sample than that of a pair of electrode-facing surfaces facing the first IDT electrode and second IDT electrode.