The authors examined the possibility of using a second harmonic type modulator made of ferroelectric material with an electrometer. It was established that if modulation is carried out at a temperature slightly above the Curie point utilizing the odd symmetry of the relationship between voltage and charge of a ferroelectric capacitor, then the delay in response to a large input signal (memory effect) is eliminated, both zero drift and noise are reduced, and carrier amplitude is diminished largely in contrast to the results obtained at room temperature. In the experiments, triglycine sulfate single crystal (TGS) whose Curie point lay around 50deg;C was used with a carrier frequency of 50 kHz, reducing zero drift to the order of 10 mgr;Vsol;day and realizing low noise as characterized by 6 mgr;V phyphen;p with 1 MOHgr; input resistance and in the bandwidth from dc to 1 Hz. This modulator is solid state, and its input resistance is about 1013OHgr; as determined by the specific resistance of a TGS single crystal. Owing to the absence of any vibrating part, the carrier frequency can be raised and the bandwidth is more than several kilohertz. Compared with the best vibrating capacitor electrometer, this modulator has advantages in bandwidth and lack of vibrating parts, but a disadvantage in input resistance. There remain some practical problems such as the method of keeping the element temperature in the vicinity of the Curie point, and the initial zero drift.
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