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Abstract
Harmonic transponder sensors, receiving radio-frequency (RF) signal and converting it to a modulated second harmonic, have been demonstrated to be effective for signal interrogation in environments with strong clutters. Here, we propose a compact dual-resonance microstrip antenna consisting of an elliptical patch loaded with shorting pins. Such an antenna utilizes the TM e 110 resonant mode to intercept the perpendicularly-polarized fundamental tone (2.86 GHz) and uses the TM o 110 resonant mode to retransmits the parallelly-polarized second harmonic (5.72 GHz). Moreover, we have developed a harmonic-based wireless liquid sensor comprising the proposed antenna and a micromachined liquid channel. Our measurement results show that even in the noisy environment, the second harmonic strength can precisely indicate the dielectric property of liquid filled in the microfluidic tank (e.g., acetone-water mixtures with various concentrations). However, a similar setup without frequency and polarization modulations (i.e., linear and passive backscatter tag) fails to provide a sensitive and quantitative measurement of liquid property. The proposed low-profile dual-resonance antenna with sensing capability will pave the way for the development of harmonic sensors and nonlinear radio-frequency identification (RFID) tags.
Highlights
C OMPACT and zero-power wireless sensors have been the subject of intense research in the past few years because of their practical uses in many engineering applications, including Internet-of-Things (IoTs), industrial 4.0, smart cities, wireless healthcare and environmental monitoring, to name a name [1]–[3]
Unlike traditional passive wireless sensor systems, of which reader and sensor working at the same frequency [15]–[17], the passive harmonic sensor system has a nonlinear tag or harmonic transponder that receives a fundamental tone, modulating the received RF signal, and retransmitting a high/sub-harmonic tone to the reader (Fig. 1) [18], [19]
We have proposed a compact, low-profile microstrip antenna for harmonic transponder sensors that demand a dual resonance at the fundamental and second-harmonic frequencies (f 0 and 2f 0)
Summary
C OMPACT and zero-power wireless sensors have been the subject of intense research in the past few years because of their practical uses in many engineering applications, including Internet-of-Things (IoTs), industrial 4.0, smart cities, wireless healthcare and environmental monitoring, to name a name [1]–[3]. These two modes have different polarizations perpendicular to each other, which further reduces one stage of interference. If a fluidic channel is suitably loaded onto the elliptical patch, the resonance frequency of the TMo110 mode can be sensitively tuned, whereas the resonance frequency of the TMe110 remains unchanged In this manner, the sensor/tag always receives the same input fundamental tone, while the output second harmonic received by the reader has a magnitude tuned by the dielectric property or volume of the liquid under test.
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