Microwave sensor design for liquids detection

Liquids are important substances that directly or indirectly affect human life and are used for different purposes in various sectors. While liquids have critical effects on human health in the food sector, friction-reducing oils in the machinery industry allow the protection of machine parts and increased efficiency. Especially in the automotive sector, engine oils are vital for the efficient operation of the engine. The chemical properties of engine oils that reduce friction in the components in the engine decrease as the engine is used. Therefore, engine oils must be changed at certain times. In the first of the studies carried out within the scope of this thesis, an antenna-based sensor design is proposed to determine engine oil life and level. In this study, an "Asymmetric Coplanar Strip-Fed Microstrip Sensor Antenna" operating at 2.40 GHz was designed. Measurements were carried out on 0 km and 10.000 km used engine oil samples with the antenna-based sensor. In the measurements made by immersing the proposed sensor antenna 60 mm into the engine oil, a difference of 3.01 dB was observed between clean engine oil and 10.000 km used engine oil. In addition, in measurements made at different length levels, the resonance frequency of the sensor varied between 2.34-1.86 GHz. Thus, measurements were made for both engine oil level and engine oil life determination with the proposed sensor. Milk, which is one of the most used liquids in the food sector, is an important source of nutrition for human health; however, adulteration and counterfeiting in dairy products can lead to serious economic losses and health problems. For this reason, milk analysis studies are carried out to determine the purity and content of milk. While determining the milk fat content helps to determine the nutritional value of milk and dairy products, adulteration analysis allows the detection of fake or low-quality milk components. Another study conducted within the scope of this thesis is the study titled "Milk Fat Content Determination and Adulteration Analysis". Within the scope of this study, a TEE-LC (Complementary Elliptic Electric-LC) Resonator Structured Transmission Line Based Microwave Sensor design operating at 4.96 GHz is proposed. The measurements of homogenized and non-homogenized milks with 8 different fat content were performed with the proposed transmission line based sensor. In the measurements made with homogenized milks, the resonance frequency of the sensor changed from 2.04 GHz to 2.47 GHz with the increase in milk fat content. vi In the measurements made with non-homogenized milks, the resonance frequency of the sensor changed from 2.045 GHz to 2.345 GHz with the increase in milk fat content. In the sensitivity analysis made to determine the performance of the proposed sensor in liquid content analysis, the average sensitivity of the transmission line based sensor to detect fat content of homogenized milks was calculated as 1.065%, while the average sensitivity of the detection of non-homogenized milks was calculated as 1.284%. Within the scope of this study, a "TEE-LC Resonator Structured Branch Line Coupler Based Microwave Sensor" design operating at 7.02 GHz, which has increased sensitivity compared to the transmission line based sensor and can perform both milk fat content detection and adulteration analysis, was proposed. For milk fat ratio determination, homogenized and non-homogenized milks with different fat ratios were measured with a sensor with increased sensitivity. In the measurements made with non-homogenized milks, the resonance frequency of the sensor changed from 2.23 GHz to 2.40 GHz with the increase in milk fat ratio. In the measurements made with homogenized milks, the resonance frequency of the sensor changed from 2.18 GHz to 2.325 GHz with the increase in milk fat ratio. For milk adulteration analysis, water was added to homogenized and non-homogenized milks in 10% increments and measurements were carried out with the recommended sensor. By adding water at the specified rates to buffalo milk, the operating frequency of the sensor changed from 2.40 GHz to 2.105 GHz. In addition, in order to determine the adulteration of jersey milk in buffalo and goat milks, measurements of adulterated buffalo and goat milks were carried out with the recommended sensor. In these measurements, jersey milk added to buffalo milk at 10% ratios changed the sensor's operating frequency from 2.40 GHz to 2.32 GHz. In the sensitivity analysis performed to determine the performance of the liquid content analysis of the proposed sensor, the average sensitivity of the branch line coupler based sensor in detecting the fat content of homogenized milk was calculated as 1.35%, while the average sensitivity of detecting non-homogenized milk was calculated as 1.553%. Within the scope of the thesis, a new measurement system that can be used in field studies for milk fat content and adulteration analysis was developed. This system consists of a TEE-LC Resonator Structured Microwave sensor, a voltage-controlled RF oscillator and a power detector. The voltage-controlled RF oscillator sends a signal to the sensor at a specified frequency, while the power detector converts this signal into a DC signal. In this way, milk fat content and adulteration analysis can be performed with changes in DC voltage values. In the measurements of water ratios added to buffalo milk, DC output values decreased from 1.55 volts to 1.18 volts. It is thought that the proposed system exhibits better performance compared to similar studies in the literature and can provide an important solution to field problems.