A resonant bridge with frequency-dependent negative resistance

Investigations were conducted on the properties of 24 circuits for which the impedance in the ideal case is equal to s² E, where s is the complex frequency and E is a constant. For harmonic excitation each circuit forms a negative resistance-ω²E and is hence called a frequency-dependent negative resistance (FDNR). From these 24 circuits, four that are stable were selected; measurements were made on these, and their equivalent circuit diagrams were determined. A resonant bridge was constructed with one branch containing an FDNR. Using this bridge it is possible to measure inductances with dissipation factors, tan δ, as high as 10⁴