Downhole Pressure Gauge Core — Technical Principles and Engineering Applications of Sapphire Pressure Sensors

I. Product Overview

The downhole pressure gauge core is the central sensing unit of a downhole pressure measurement system. Its performance directly determines the reliability and data credibility of the entire measurement system under high-temperature, high-pressure, strongly corrosive, and long-term continuous operating conditions.

Nexisense sapphire series pressure sensors use single-crystal sapphire (Al₂O₃) as the insulating substrate material, combined with silicon-on-sapphire semiconductor sensing technology to form a highly stable pressure sensing structure. Compared with traditional silicon piezoresistive sensors, this structure has no hysteresis, fatigue, or creep issues, and maintains excellent linearity and repeatability under long-term loading and complex operating conditions.

Sapphire material maintains good elasticity and insulation performance at temperatures up to 1000 °C, is insensitive to temperature variation, and exhibits outstanding radiation resistance. This enables the product series to meet the stringent requirements of downhole logging, nuclear power, aerospace, and other high-demand application scenarios.

In addition, silicon-on-sapphire sensing elements do not generate p-n junction drift effects, effectively avoiding zero drift and output instability under high-temperature conditions, thus providing a solid foundation for high-precision pressure measurement in harsh environments.

II. Working Principle and Measurement Mechanism

Nexisense sapphire pressure sensors adopt a dual-diaphragm composite structure design, achieving high-precision pressure measurement through stable mechanical-to-electrical signal conversion.

The core operating process is as follows:

The measured medium pressure first acts on the titanium alloy measuring diaphragm
The titanium alloy diaphragm undergoes slight elastic deformation under pressure
The deformation is transmitted to the sapphire receiving diaphragm through a welded structure
The hetero-epitaxial silicon-on-sapphire strain bridge on the sapphire diaphragm senses the strain change
The bridge imbalance varies with pressure and outputs an electrical signal proportional to pressure

The entire measurement process involves no intermediate transmission components. The mechanical structure is simple and the signal path is short, effectively reducing mechanical hysteresis and energy loss, thereby ensuring highly stable output.

III. Core Structural Analysis

1. Titanium Alloy Measuring Diaphragm

Manufactured from high-strength titanium alloy, offering excellent pressure resistance, fatigue resistance, and corrosion resistance. It is suitable for long-term exposure to high-pressure downhole environments containing sulfur, salts, and other complex media.

2. Sapphire Receiving Diaphragm

Machined from single-crystal sapphire, featuring extremely high elastic modulus and insulation performance, maintaining stable mechanical and electrical characteristics in high-temperature environments.

3. Silicon-on-Sapphire Strain Bridge

A silicon strain-sensitive layer is integrated onto the sapphire substrate surface through hetero-epitaxial technology, forming a highly consistent and stable strain detection bridge structure.

4. Welded Connection Structure

High-reliability welding technology is used to achieve permanent bonding between diaphragms, avoiding adhesive aging issues and enhancing long-term reliability under high-temperature and high-pressure conditions.

IV. Product Features and Technical Advantages

Wide temperature range stable operation
Wide operating temperature range
Strong temperature adaptability
Minimal zero and sensitivity variation under high-temperature conditions

High accuracy and high repeatability
Excellent strain output linearity
Minimal long-term drift
Suitable for metrology and calibration-grade applications

Outstanding environmental adaptability
Strong radiation resistance
Corrosion and high-pressure resistance
Suitable for extreme operating conditions

Compact structure and strong adaptability
Small size and lightweight
Easy integration into various pressure transmitters and downhole measurement systems
Better cost-performance ratio compared with similar high-end sensing solutions

V. Typical Application Scenarios

Nexisense sapphire pressure sensors are widely used in industries with extremely high requirements for reliability and stability:

Downhole pressure gauges and logging systems
Oilfield and gas field pressure monitoring
Industrial process pressure control
High-precision digital pressure calibrators
Aerospace pressure measurement systems
Marine and offshore engineering
Power plants and nuclear power station equipment
Petroleum and chemical installations
Research institute laboratory equipment
Core sensing element selection for pressure transmitters

VI. Technical Parameter Overview (Example)

The following parameters can be customized according to specific models:

Measurement range: covering low pressure to ultra-high pressure ranges
Output signal: mV-level bridge signal
Excitation method: constant voltage / constant current excitation
Accuracy class: high-precision design
Temperature influence: minimal temperature error with excellent compensation performance
Insulation performance: high insulation resistance

(Specific parameters are subject to the Nexisense technical datasheet.)

VII. Comparative Advantages Over Traditional Pressure Sensors

Compared with conventional silicon piezoresistive pressure sensors, sapphire pressure sensors offer superior performance in the following aspects:

No p-n junction drift
Significantly improved high-temperature stability
Superior long-term reliability
Suitable for long-term operation in extreme environments

This makes them a preferred solution for downhole pressure gauges and high-end industrial measurement applications.

VIII. Frequently Asked Questions (FAQ)

Are sapphire pressure sensors suitable for long-term downhole use?
Yes. Their materials and structure are specifically designed for high-temperature, high-pressure, and strongly corrosive environments, enabling long-term stable operation.

Can they be integrated into pressure transmitters?
Yes. These cores are commonly used as the key sensing elements in high-end pressure transmitters.

What are the advantages compared with ceramic pressure sensors?
They perform better in terms of high-temperature stability, radiation resistance, and long-term drift control.

v

Summary

As the core component of pressure measurement systems, downhole pressure gauge cores place extremely high demands on accuracy, stability, and reliability. Based on the silicon-on-sapphire technology route, Nexisense sapphire pressure sensors achieve stable measurement performance under high-temperature, high-pressure, and complex environments through optimized structural design and mature manufacturing processes.