The use of conventional sensor nodes requiring an internal power source and complex signal-processing circuits are becoming costly and impractical for widespread deployment. Battery-less UHF RFID sensors, on the other hand, provide real-time continuous sensing measurement with high reliability and without the use of any internal power source or a complex signal-processing circuit, by utilizing the phase variation of the backscattered signal as a sensing parameter. These passive RFID sensing nodes use energy harvesting from the signal sent by the reading device that reduces cost and increases the reliability of the wireless sensor systems. In addition to tracking and identification, RFID technologies are receiving increasing popularity as a wireless sensing system in many industrial applications [2,3,4]. However, the conventional RFID tag design has to be modified for most of the modern sensing applications [5,6,7]. Therefore, a new robust sensing method needs to be established to use the current RFID systems for a reliable passive wireless measurement of liquid level.
The detection of liquid level is divided broadly into few categories such as classification based on the type of measurement, i.e., continuous level measurement  for process monitoring or point level measurement  for marking a single liquid-level height to activate an alarm. These sensors are further classified based on their contact  and non-contact  nature with the sensing medium. The accuracy of contact-type sensors is usually smaller due to their dependence on liquid properties that affect the sensor performance, mostly in the case of conducting type liquids; therefore, non-contact level measurement is widely explored in the literature. Although most of the work is focused on the sensitivity and detection range improvement, much less emphasis has been given to the development of low-power reliable sensing nodes that can be densely deployed for applications such as wireless IOT. Most of the liquid-detection sensors need a wired connection or a built-in battery to operate, which increases the design complexity and cost and requires regular maintenance, making them unsuitable for many modern sensing applications .
My earlier text,* discusses various methods of measuring vector forces andtorques. In general, it is not possible to measure such three-dimensionalquantities directly; rather, we design uniaxial transducers to selectively measure the components of the vectors and then use computation to fi nd the vector magnitudes and directions. This chapter will explore those applicationswhere there is suffi cient space available to use separate force transducers tomeasure each component of the vector. One such area of application of majorimportance to mechanical and aerospace engineers is the measurement ofthe forces and moments produced by aircraft or spacecraft engines, sinceknowledge of these quantities is vital to the prediction of vehicle performance. For air-breathing (jet) engines used in aircraft and missiles, the needoriginally was to measure only the thrust force along the longitudinal axis ofthe engine. As aircraft (such as the British Harrier) that use thrust vectoringas a control method were later developed, knowledge of all the forces andmoments became important. For rocket engines, this need was there fromthe beginning of that technology. 2b1af7f3a8