Pathological changes of human tissues, such as tumors, can cause changes in the dielectric properties of the tissues. Based on this characteristic, we propose an implantable antenna sensor and study its radiation and sensing performance in breast tumor recurrence diagnosis in the 2.45 GHz Industrial, Scientific, and Medical (ISM) band. The antenna sensor shows the advantage of miniaturization with a volume of 13.2mm ³ by employing an S-shape monopole antenna and a closed loop. The simulated results show that the antenna sensor has a good radiation pattern with peak gain values of -8.4 and -17.9dBi in normal and malignant breast tissue, respectively. Furthermore, the antenna sensor exhibits good sensitivity to the dielectric properties of breast tissue. When the permittivity increases by 10, the resonance frequency decreases between 9-18MHz. To verify the simulated results, the sensing properties and the radiation patterns of the implantable antenna sensor were measured in the pork and tissue-mimicking liquid. The measured results are consistent with the simulated ones. Hence, the proposed antenna can be used as a wireless sensor to monitor pathological changes of human tissues, such as breast tumors.

With the popularization of electronic products, more and more people have cervical spine troubles. This paper proposed an antenna sensor for detecting the bending state of the neck in people’s daily life. The antenna works in the 2.45 GHz industrial, scientific, and medical (ISM) band. When the cervical spine drives the antenna sensor to bend, the resonance frequency of the antenna sensor shifts. Based on this characteristic, the antenna sensor can monitor the bending angle of the cervical spine wirelessly. Placing a ${2}\times {2}$ electromagnetic bandgap (EBG) array between the antenna sensor and the neck reduces the specific absorption rate (SAR) of the human body by about 90% and increases the peak gain from 2.46 dBi to 6.75 dBi. Even if the antenna sensor is bent and deformed greatly, the gain of the antenna sensor remains good. The efficiency of the antenna sensor loaded with the EBG array keep at 65%, and the sensitivity to the bending angle reaches 7.5 MHz/1°. The measured results of the fabricated antenna sensor are in good agreement with the simulated ones. The experimental results show that the proposed antenna sensor is suitable for cervical curvature monitoring.

Some special environments, such as closed or harsh spaces, require contactless and real-time humidity monitoring. A flexible 920 MHz antenna sensor with vertical graphene (VG) as a sensitive film is proposed, which can measure humidity and transmit data wirelessly in real time. When the humidity changes, the number of H2O molecules absorbed by the graphene film will vary, which affects the permittivity of the antenna patch, and results in shifts in the resonant frequency. Remote humidity monitoring can be realized by analyzing the frequency response at the receiver. By depositing vertical graphene film on the antenna patch, the sensitivity can be improved from 16.3 to 32.6 kHz/% RH (linear range: 0. 57% RH) and from 145 to 290.5 kHz/% RH (57.90% RH). During humidity change, the radiation direction of the VG-based antenna sensor remains stable, and the maximum wireless transmission distance reaches 100 m. For the first time, the model of the antenna sensor is established. Furthermore, the flexible sensor can conform to various installation shapes. The experimental results show that the wireless VG-based antenna sensor is a good candidate for remote humidity monitoring and the Internet of Things.

When ethanol and water are mixed into gasoline, the dielectric properties of gasoline will change. Based on this characteristic, we propose an antenna sensor and study its radiation and sensing performance in detection of ethanol gasoline in 6-7GHz band. In order to avoid the corrosion of the oil sample on the antenna, the antenna adopts a multilayer dielectric substrate structure. A $2\times 2$ artificial magnetic conductor (AMC) array is loaded on the bottom of the antenna to increase the gain of the sensor and reduce the return loss. The antenna sensor has good radiation pattern with a peak gain of 4 dB and high quality factor(Q) up to 69. Furthermore, the antenna sensor shows the advantages of high sensitivity and wide detection range on the detection of oil-water mixture and ethanol gasoline concentration. In order to verify the simulated results, the radiation and sensing performance of the antenna were measured, and the measured results were basically consistent with the simulated ones. Therefore, the proposed antenna sensor can be used for real-time wireless detection in ethanol gasoline transportation.