Ultrasonic Sensor Shielding Isolation for Noise Cancellation
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Solution Overview
Problem
Conventional ultrasonic sensors suffer from reduced signal-to-noise ratio due to asymmetrical circuit configurations, which fail to effectively cancel common mode noise, leading to decreased Electromagnetic Compatibility (EMC) and Electrostatic Discharge (ESD) resistance.
Innovation Solution
The ultrasonic sensor features a microphone with a piezoelectric film and a microphone case that includes a shielding portion made of an electrical conductor, electrically isolated from the negative electrode line, providing a symmetrical circuit configuration and connecting the microphone case to ground potential without connecting it to the negative electrode line, thereby suppressing noise and maintaining EMC and ESD resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the microphone case is connected to the negative electrode line for grounding, then the shielding effect is improved, but the circuit configuration becomes asymmetrical leading to reduced noise cancellation capability
Solution Approach 1:
The grounding path is segmented into two separate connections: the microphone case is connected to ground potential through a dedicated ground connection, while the negative electrode line remains electrically isolated from ground. This segmentation allows the shielding function to be maintained independently from the differential signal path, resolving the contradiction between shielding effectiveness and noise cancellation capability.
Solution Approach 2:
A dedicated ground connection serves as an intermediary element that provides the shielding function without directly connecting the microphone case to the negative electrode line. This intermediary grounding path enables electromagnetic shielding while preserving the symmetrical differential circuit configuration needed for effective common mode noise rejection.
2Reliability
If the microphone case is connected to ground potential, then EMC and ESD resistance is improved, but the negative electrode line becomes vulnerable to noise
Solution Approach 1:
The electrical connections are segmented into distinct functional paths: the microphone case connects to ground for EMC/ESD protection, while the negative electrode line maintains electrical isolation from ground to preserve noise immunity. This segmentation allows each component to fulfill its specific function without compromising the other.
Solution Approach 2:
The patent intentionally creates an asymmetrical grounding configuration where the microphone case is grounded but the negative electrode line is not. This controlled asymmetry resolves the contradiction by providing EMC protection through case grounding while maintaining noise susceptibility resistance through differential circuit operation with the ungrounded negative line.
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 configuration enhances noise cancellation, improves the signal-to-noise ratio, and maintains EMC and ESD resistance by isolating the negative electrode line from ground and connecting the microphone case to ground potential, effectively addressing the noise suppression issue in conventional ultrasonic sensors.
Implementation Method 1
a microphone (2) having a piezoelectric film (2a) with positive and negative terminals (2b, 2c) on respective sides thereof, and configured with a piezoelectric vibrating element for converting an electrical signal into vibration and converting a vibration into an electrical signal
Implementation Method 2
a shielding portion (3d) made of an electrical conductor, electrically isolated from the negative electrode line (5f), configured to provide a shielding effect by surrounding the microphone (2)
Data Source
AI summary
In an ultrasonic sensor that is attached to a body component, a negative electrode line connected to a negative terminal is isolated from a shielding portion. The shielding portion is connected to a ground potential point without being connected to the negative electrode line.