Silicon Resonant Differential Pressure Sensor

A silicon resonant differential pressure sensor is a type of resonant sensor manufactured using silicon micromachining technology, specifically designed to measure the pressure difference between two pressure inlets. Its core principle is determining the differential pressure value by measuring the change in the natural frequency of a single-crystal silicon resonant beam.

 

It perfectly combines the advantages of three advanced technologies:

1. Differential Pressure Measurement: Suitable for critical applications like flow and level measurement.

2. Resonant Principle: Provides unparalleled accuracy and long-term stability.

3. Silicon MEMS Technology: Enables miniaturization, batch production, and high reliability.

Its core is a complex microstructure fabricated on a silicon wafer using MEMS technology.

Core Structure:

• A Glass-Silicon-Glass triple-layer bonded structure.
• Upper Glass Layer: Contains pressure inlet holes connected to the high-pressure side.
• Lower Glass Layer: Contains pressure inlet holes connected to the low-pressure side.
• Middle Silicon Layer: Micromachined and contains:

Sensing Diaphragm: A thin yet robust silicon diaphragm that senses the pressure difference from both sides.

Resonant Beams: Located above (or integrated within) the sensing diaphragm, these are suspended silicon beam structures. Typically, there are two identical resonant beams inside one sensor, located at the center and the edge of the diaphragm, respectively.

Drive Electrodes and Pick-up Electrodes: Used to excite the resonant beams into vibration and detect their vibration frequency.

Operating Process:

• Apply Differential Pressure: High pressure (P1) and low pressure (P2) act on either side of the sensing diaphragm.
• Diaphragm Deformation: The pressure difference causes the sensing diaphragm to undergo minute bending deformation.
• Stress Generation: This deformation creates a stress distribution on the diaphragm:

The resonant beam at the center of the diaphragm experiences compressive stress.

The resonant beam at the edge of the diaphragm experiences tensile stress.

Frequency Change:

According to the resonant principle, compressive stress causes its resonant frequency to decrease.

Tensile stress causes its resonant frequency to increase.

Differential Measurement: The sensor measures the frequency difference between the two resonant beams (Δf = f₁ - f₂).

The output is the difference between the two resonant frequencies, which offers significant benefits:

Common-Mode Error Rejection:

• Temperature Effects: If the temperature increases, the frequencies of both resonant beams change in the same direction (e.g., both decrease), but their frequency difference remains unchanged.
• Static Pressure Effects: Similar static pressure applied to both sides affects both beams similarly, and their frequency difference likewise remains stable.
• Extremely High Accuracy and Resolution: Frequency can be measured with extreme precision, resulting in very high sensor resolution and repeatability, with accuracy reaching ±0.075% or even higher.
• Inherently Digital: The output is a frequency signal, which offers strong anti-interference capability and is easy for digital systems to process.

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