Bridges, Synchronous Rectifiers, Fast Amplifiers

By balancing the bridge so that the signal measured by the detector is equal to zero, the unknown admittance Y2 can be calculated using the relation Y1Y4 = Y2Y3. 

The advantage of bridges is their high-resolution capabilities, a feature very important for extending dielectric measurements to low frequencies in tissue (see Section 3.8). 

for instance, has a conductivity of about 1 S/m and of 1500, frequency independent up to 100 kHz. A conduction resolution of about 10 is necessary for a precision of 10% at 1 kHz, (Schwan, 1963). Schwan (1963) discussed both low- and high-frequency bridges, and Schwan and Ferris (1968) discussed high-resolution tetrapolar bridges. Hayakawa et aL (1975) have further increased the precision of bridge instrumentation. 

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