Fixed-Frequency Low-Loss Dielectric Material Sensing Transmitter

This article presents an all-in-one system for the detection of the relative permittivity of samples in direct contact with a sensor antenna, based on the frequency variation detection and using a cost- and energy-effective manner. In a specific application, in which the antenna should be in contact with the sensing material, characteristics of the antenna change with respect to the frequency spectrum for different materials. Conventionally, a frequency spectrum monitoring device is required to monitor these changes, and the sensing data should be obtained by postprocessing the observation. The proposed system converts the sensing information in the frequency response of the device to a voltage, which can be utilized further for transmission as well as compensating and frequency retuning the system. The sensor antenna loads the radio frequency oscillator at the transmitter resulting in a change at the operating frequency of the system. A small portion of the signal is sampled and used for recovery in a phase/frequency comparator (PFC). The output of the PFC is a voltage corresponding to the difference between the operating frequency and the reference signal. The proposed sensor system is fabricated at the 915-MHz ultrahigh-frequency radio frequency identification band using on-off keying modulation as an evaluation, and the measured results with some known samples are presented. Since the proposed technique is implemented by utilizing the building blocks of a conventional transmitter, the power consumption and cost of the system are kept intact.