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

## TL;DR

This paper introduces two small helical antennae for wireless temperature sensors that operate without power and improve performance at 915 MHz.

## Contribution

The novel contribution is the design and validation of miniaturized antennae for SAW temperature sensors in the ISM band.

## Key findings

- The CHA and HSHA antennae resonate at 915 MHz with operational bandwidths of 30 MHz and 22 MHz, respectively.
- The SAW sensor's resonance frequency decreases by 66.67 kHz per 10 °C, validated across 30 °C to 90 °C.
- A notch in the operating band aids in calculating frequency shifts for accurate temperature measurement.

## Abstract

This paper presents the introduction, design, and experimental validation of two small helical antennae. These antennae are a component of the surface acoustic wave (SAW) sensor interrogation system, which has been miniaturized to operate at 915 MHz and aims to improve the performance of wireless passive SAW temperature-sensing applications. The proposed antenna designs are the normal-mode cylindrical helical antenna (CHA) and the hemispherical helical antenna (HSHA); both designed structures are developed for the ISM band, which ranges from 902 MHz to 928 MHz. The antennae exhibit resonance at 915 MHz with an operational bandwidth of 30 MHz for the CHA and 22 MHz for the HSHA. A notch occurs in the operating band, caused by the characteristics of the SAW sensor. The presence of this notch is crucial for the temperature measurement by aiding in calculating the frequency shifting of that notch. The decrement in the resonance frequency of the SAW sensor is about 66.67 kHz for every 10 °C, which is obtained by conducting the temperature measurement of the system model across temperature environments ranging from 30 °C to 90 °C to validate the variation in system performance.