Miniaturized Antenna Design for Wireless and Powerless Surface Acoustic Wave Temperature Sensors

Area of Science:

• Electromagnetics and Sensor Technology
• Wireless Communication Systems

Background:

• Miniaturization of Surface Acoustic Wave (SAW) sensor interrogation systems is crucial for advanced wireless passive sensing applications.
• Optimizing antenna performance at 915 MHz is key for improving the accuracy of SAW-based temperature sensing.

Purpose of the Study:

• To introduce, design, and experimentally validate two novel small helical antennas: the normal-mode cylindrical helical antenna (CHA) and the hemispherical helical antenna (HSHA).
• To integrate these antennas into a 915 MHz SAW sensor interrogation system for enhanced wireless passive temperature sensing.

Main Methods:

• Design and simulation of CHA and HSHA for the Industrial, Scientific, and Medical (ISM) band (902-928 MHz).
• Experimental validation of antenna resonance at 915 MHz, measuring operational bandwidths of 30 MHz for CHA and 22 MHz for HSHA.
• Characterization of a notch within the operating band caused by SAW sensor properties, crucial for temperature measurement.

Main Results:

• Both CHA and HSHA designs achieved resonance at 915 MHz, demonstrating operational bandwidths suitable for the ISM band.
• The presence of a SAW-induced notch in the antenna's operating band was confirmed and utilized for temperature sensing.
• Temperature measurements demonstrated a frequency shift of approximately 66.67 kHz per 10 °C across a 30 °C to 90 °C range.

Conclusions:

• The developed helical antennas are effective components for miniaturized wireless passive SAW temperature sensing systems.
• The unique notch characteristic is vital for accurate temperature readings, enabling frequency shift-based measurements.
• The experimental validation confirms the system's capability to perform precise temperature sensing in the specified range.