Modulation Frequency Based RFID Sensor

Abstract

The Internet of Things (IoT) refers to the ever-growing network in which many physical objects,livestock, environment, and even human beings are expected to be equipped with wireless sensorsor other wireless devices. In many cases, these wireless sensors cannot contain batteries, becausethey would limit the operating conditions or the lifetime of the devices, or make them bulky orharmful to the environment. In addition to this, it is also desirable for sensors to be able to respondto an incoming signal by returning a signal towards the reader without prior knowledge of itslocation.

Passive wireless sensors have been proposed to overcome the battery lifetime constraints, butthese sensors typically only support relatively short communication distances. Moreover, they maynot provide a means to identify a certain sensor and to sense of some external parameters, such aspressure, temperature or strain. This dissertation develops a novel type of passive wireless sensor(RFID sensor) based on frequency modulation. This type of passive wireless sensors are potentiallyable to address the formidable challenges of IoT.

The first part of the thesis introduces a novel concept of passive wireless sensor that cansimultaneously provide sensing, identification, memory, anti-collision, and a large read-outdistance. A design strategy and analytical solution for the RFID sensor for a given application areintroduced. In addition to this, a figure of merit for selecting a suitable diode for the rectificationis presented, and the RFID sensor is demonstrated with real sensing elements. The result showsthat a change in the sensing element can be detected across a distance of 15 m with low uncertainty.Furthermore, a generic platform to simultaneously realize multi-sensing also demonstrated withreal sensing elements (humidity and light).

Finally, a novel design concept to obtain a passive retrodirective sensor operation is introducedin this dissertation. The utilized sensor is based on frequency modulation, and the proposedconcept is investigated both theoretically and experimentally. The results of the study show thatthe designed sensor platform can be used to detect a change in sensor capacitance across a distanceof up to 12 m and sensing information can be detected across wider ranges of incident angles (upto ±90°) than with more conventional passive wireless sensors.