Negative impedance converter (NIC) circuits are very interesting and beneficial building blocks with the capability of generating negative resistance, capacitance and/or inductance elements which do not exist as a singular electrical component in practice. They are commonly used for the impedance matching and parasitic element cancellation in electrically small antennas and amplifier circuits. In this study, a special kind of NIC circuit in HF band up to 30 MHz is analysed, designed and physically realised with a current feedback (CFB) operational amplifier (OPAMP) which is the core active element of the NIC circuit. The non-inverting terminal of CFB OPAMP is used for RF input signal with the elimination of DC offset voltage in the proposed NIC circuit. The negative impedance conversion capability of the circuit is theoretically proved and simulated first. This capability of CFB OPAMP to generate negative impedance is very important in high-frequency applications as they have low distortion and faster switching than that of voltage feedback (VFB) OPAMP. For the physical realizations, printed circuit board (PCB) is designed and manufactured on FR-4 dielectric material. Measurement results obtained from the realized circuit with resistive (100Ω) and capacitive (10pF) loads to be converted negatively showed that the negative impedance conversion performance of the circuit is very close to its theoretical behaviour in the lower HF frequencies generally in 3- 20 MHz band.

Contamination and degradation in the quality of the fresh water under the ground is one of the major problems of our world. Water quality on the other hand, determined by the physical, chemical and biological compounds in the water. TDS (Total Dissolved Solid), salinity, dissolved oxygen, temperature, metabolic wastes, toxic compounds and conductivity are some of the major indicators of the water quality. These items are sometimes correlated and any increase in one factor may decrease/increase other factors as well. The aim of this work is to develop an idea about the contamination due to chemicals dissolved or biological anomalies in the water. Mainly the indicator of this change has been examined by the change in the conductivity parameter, which is a major electrical property that affects the Electromagnetic reflectivity of the surface ground.