Thermocouple Shield for RF Field Protection
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Solution Overview
Problem
Conventional thermocouples fail to accurately measure temperatures in RF fields due to arcing and heating caused by the concentration of electrical fields, leading to erroneous readings and device failure.
Innovation Solution
A thermocouple shield comprising an electrically conductive tube with a ceramic sheath is used to shield the thermocouple device, increasing its diameter and reducing RF field perturbation, while the ceramic sheath is electrically insulating and transparent to RF energy, preventing arcing and heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a bare thermocouple or thermocouple probe is used to measure temperature in an RF field, then the thermocouple can directly contact the thermal region of interest, but the thermocouple concentrates electrical fields which causes arcing and heating leading to measurement errors and device failure
Solution Approach 1:
A dielectric bead is introduced as an intermediary element between the thermocouple junction and the RF field. The bead has a diameter of 0.02 to 0.06 inches and serves as a mediator that prevents direct interaction between the thermocouple and concentrated electrical fields, thereby eliminating arcing and heating while maintaining thermal coupling to the measurement region
Solution Approach 2:
The physical configuration of the thermocouple tip is modified by adding a dielectric bead with specific dimensional parameters (diameter 0.02-0.06 inches). This parameter change alters the electrical field distribution around the thermocouple junction, preventing field concentration and the subsequent harmful effects of arcing and RF-induced heating
2Reliability
If the thermocouple diameter is increased to reduce RF field perturbation, then less arcing and heating occurs, but the thermocouple device becomes larger and more intrusive in the thermal region
Solution Approach 1:
The thermocouple assembly is transformed into a composite structure combining the thermocouple junction, lead wires, and a dielectric bead. This composite configuration allows the small-diameter thermocouple to achieve the RF field interaction characteristics of a larger device, reducing arcing and heating without increasing the intrusive size of the measurement probe
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 solution effectively shields the thermocouple from RF energy, preventing arcing and heating, ensuring accurate temperature measurements and extending the device's lifespan in high-energy RF environments.
Implementation Method 1
an electrically conductive tube that has at least minimal structural integrity at the temperature 'T'... The electrically conductive tube has a substantially cylindrically-shaped section... to shield the thermocouple device from a radio frequency (RF) field
Implementation Method 2
where the thermocouple probe has an electrically conductive jacket with a tip end surrounding a thermocouple junction... There is a ceramic sheath disposed within the tube bore... The ceramic sheath is electrically insulating and substantially transparent to a radio frequency field
Implementation Method 3
The ceramic sheath is electrically insulating and substantially transparent to a radio frequency field... preventing arcing and heating
Implementation Method 4
Thermocouples are used to measure temperature by converting thermal energy into a change in electrical resistance at a junction between two specially selected materials
Data Source
AI summary
A thermocouple shield for use in radio frequency fields. In some embodiments the shield includes an electrically conductive tube that houses a standard thermocouple having a thermocouple junction. The electrically conductive tube protects the thermocouple from damage by an RF (including microwave) field and mitigates erroneous temperature readings due to the microwave or RF field. The thermocouple may be surrounded by a ceramic sheath to further protect the thermocouple. The ceramic sheath is generally formed from a material that is transparent to the wavelength of the microwave or RF energy. The microwave transparency property precludes heating of the ceramic sheath due to microwave coupling, which could affect the accuracy of temperature measurements. The ceramic sheath material is typically an electrically insulating material. The electrically insulative properties of the ceramic sheath help avert electrical arcing, which could damage the thermocouple junction. The electrically conductive tube is generally disposed around the thermocouple junction and disposed around at least a portion of the ceramic sheath. The concepts of the thermocouple shield may be incorporated into an integrated shielded thermocouple assembly.