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A patch antenna, consisting of a radiation patch, a dielectric substrate, and a ground plane, resonates at distinct fundamental frequencies that depend on the substrate dielectric constant and the dimensions of the radiation patch. Since these parameters change with the applied strain and temperature, this study investigates simultaneous strain and temperature sensing using a single antenna that has two fundamental resonant frequencies. The theoretical relationship between the antenna resonant frequency shifts, the temperature, and the applied strain was first established to guide the selection of the dielectric substrate, based on which an antenna sensor with a rectangular radiation patch was designed and fabricated. A tensile test specimen instrumented with the antenna sensor was subjected to thermo-mechanical tests. Experiment results validated the theoretical predictions that the normalized antenna resonant frequency shifts are linearly proportional to the applied strain and temperature changes. An inverse method was developed to determine the strain and temperature changes from the normalized antenna resonant frequency shifts, yielding measurement uncertainty of 0.4 °C and 17.22 μ for temperature and strain measurement, respectively.

This paper investigates a microstrip patch antenna for measuring the thickness and dielectric constant of the medium above the antenna (i.e. the superstrate) as well as the temperature. The intended application is simultaneous sensing of ash accumulation and temperature inside a boiler, with the aim of enhancing safety, improving efficiency, and reducing downtime associated with maintenance. A patch antenna, consisting of a dielectric substrate, a radiation patch, and a ground plane, functions as an electromagnetic resonator with specific fundamental frequencies. A dielectric medium placed above the patch antenna changes its effective dielectric constant and thus its resonant frequencies. Meanwhile, temperature also influences the antenna frequencies because of the thermal expansion of the conductors (i.e. the radiation patch and ground plane), and the dielectric constant of dielectric materials due to their temperature dependency. Since a rectangular patch antenna has two fundamental frequencies, it enables determining these two parameters simultaneously. Once the temperature and superstrate thickness are determined, the dielectric constant of the superstrate and its temperature dependency can also be extracted. To demonstrate this capability, a dual-frequency patch antenna was designed, fabricated, and characterized with a superstrate of various thicknesses and at different temperatures. By fitting the antenna resonant frequencies as functions of the superstrate thickness and temperature, these two parameters were inversely determined from the measured antenna frequencies. Using ash from charcoal briquettes as a superstrate, the measurement uncertainties were determined to be ±0.58 °C and ±58.05 μm for the temperature and the superstrate thickness respectively. The dielectric constant of the ash was found to be 2.64 at room temperature and its thermal coefficient of dielectric constant (TCDk) was found to be 918 ppm °C−1.

This paper presents a novel interrogation mechanism for an antenna sensor subjected to high temperatures. In sensor node, an Ultra-wide Band (UWB) microstrip antenna was used as a wireless Tx/Rx transceiver to amplify the reflected interrogation signal from the temperature-sensing element, i.e. the patch antenna-sensor. A microstrip delay line was used to connect the Tx/Rx antenna and the antenna-sensor so that the reflected signal from the sensor node is delayed and can be separated from the background clutter using time-domain (T-D) gating technique. In this paper, the principle of operation of the proposed interrogation mechanism is first discussed, followed by the design and simulations of the sensor node circuitry. Finally, a temperature test was conducted to validate the wireless temperature sensing performance of the antenna sensor.

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