Interrogation Techniques and Interface Circuits for Coil-Coupled Passive Sensors

Area of Science:

• Electrical Engineering
• Sensor Technology
• Physics

Background:

• Coil-coupled passive sensors utilize magnetic coupling for contactless interrogation.
• Resonant sensor units, including capacitive and piezoelectric types, provide readout signals like resonant frequency and quality factor.
• Existing interrogation techniques theoretically offer distance independence, but parasitic capacitance poses a challenge.

Purpose of the Study:

• To analyze the impact of parasitic capacitance on coil-coupled resonant sensor readings.
• To develop and validate a compensation circuit for achieving distance-independent sensor measurements.
• To demonstrate the effectiveness of the proposed solution for both capacitive and piezoelectric sensors.

Main Methods:

• Analysis of frequency-domain and time-domain interrogation techniques for resonant sensors.
• Theoretical investigation of parasitic capacitance effects on sensor readings.
• Development and experimental validation of an innovative compensation circuit.
• Testing with coil-coupled capacitance and quartz crystal resonators.

Main Results:

• Parasitic capacitance introduces undesired distance dependence in sensor readings, particularly for capacitive sensors.
• The proposed compensation circuit effectively counteracts parasitic capacitance effects.
• Experimental tests showed minimal deviations (300 ppm for capacitance, 0.5 ppm for quartz) within 18 mm interrogation distances.
• Distance-independent readings were achieved under real operating conditions.

Conclusions:

• The developed compensation circuit successfully enables distance-independent interrogation of coil-coupled resonant sensors.
• This advancement is crucial for reliable proximity sensing applications, especially with capacitive sensors.
• The technique offers high accuracy and minimal error, enhancing the performance of wireless sensor systems.