Surface Acoustic Wave Proximity Sensor with Air Gap
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Solution Overview
Problem
Conventional proximity sensors using photodiodes are vulnerable to noise and are too large for use in mobile or wearable devices, limiting their effectiveness and applicability.
Innovation Solution
A proximity sensor utilizing a light-receiving element that employs surface acoustic waves, including a substrate with piezo-electric material, IDT electrodes, and a sensing film to measure light and temperature, integrated with a circuit board and IC chip, and featuring a transparent board to form an air gap and reduce noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If photodiodes are used for proximity sensing, then optical detection capability is achieved, but noise vulnerability increases and device size becomes too large
Solution Approach 1:
The patent replaces the photodiode-based optical detection system with a surface acoustic wave (SAW) based mechanical detection system. The SAW sensor detects changes in acoustic wave propagation caused by light-induced heating or mechanical effects, eliminating the need for photodiodes and their associated amplifying circuits, thus reducing noise vulnerability while maintaining detection capability
Solution Approach 2:
The patent changes the detection parameter from direct optical detection by photodiodes to indirect detection via surface acoustic wave propagation characteristics. By measuring changes in acoustic wave speed, attenuation, or frequency caused by light interaction with the piezoelectric substrate, the system achieves optical sensing through mechanical wave parameters, improving noise immunity
2Measurement precision
If photodiodes with amplifying circuits are used, then optical sensing is achieved, but device size increases making it unsuitable for mobile devices
Solution Approach 1:
The patent replaces the bulky photodiode and amplifying circuit assembly with a compact surface acoustic wave sensor structure. The SAW sensor requires only a piezoelectric substrate with interdigitated electrodes, eliminating the need for complex electronic amplification circuits and reducing overall device volume significantly
Solution Approach 2:
The patent extracts and removes the amplifying circuits from the optical sensing system, replacing them with a passive surface acoustic wave detection mechanism. This extraction of unnecessary components directly reduces device size while maintaining sensing functionality through the SAW effect
3Reliability
If surface acoustic wave technology is used, then noise resistance improves, but device size is too big for mobile applications
Solution Approach 1:
The patent scales down the surface acoustic wave sensor dimensions by changing the physical parameters of the piezoelectric substrate and electrode geometry. By optimizing the substrate size, electrode finger width, spacing, and length, the patent achieves miniaturization while preserving the noise-resistant SAW detection mechanism
Solution Approach 2:
The patent applies local quality optimization by concentrating the SAW sensing function in a localized region of the piezoelectric substrate. The interdigitated electrodes are configured to generate and detect acoustic waves in a specific localized area, enabling compact device design while maintaining the inherent noise resistance of SAW 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 sensor achieves reliable noise-resistant measurements of proximity and temperature with high Q values, enabling a compact design suitable for mobile devices while maintaining high measurement accuracy.
Implementation Method 1
a substrate having a light sensing area and a temperature sensing area and including a piezo electric material
Implementation Method 2
a sensing film overlapping the first delay gap and covering at least some portions of the first input electrode and the first output electrode
Data Source
AI summary
A proximity sensor includes a circuit board; a light-emitting element and a light-receiving element on the circuit board; a light barrier; molding portions; and a transparent board disposed on the molding portions and configured to form an air gap with the light-receiving element. The light-receiving element includes: a substrate having a light sensing area and a temperature sensing area; a first input electrode and a first output electrode which are aligned in the light sensing area and apart from each other with a first delay gap therebetween; a sensing film covering at least some portions of the first input electrode and the first output electrode; and a second input electrode and a second output electrode which are aligned in the temperature sensing area and apart from each other with a second delay gap therebetween. The second delay gap is exposed to air.