The spectral density of magnetic flux noise SΦ1/2(f ) is investigated for high-Tc rf SQUIDs with a pumping frequency of 390–457 MHz, placed inside three-layer Permalloy and superconducting shields. A superconducting interferometer with inner dimensions of the pickup loop of 100×100 μm is prepared by thin-film technology with a YBaCuO–PrBaCuO–YBaCuO Josephson junction of the ramp-edge type. It is shown that with the use of a cooled preamplifier, the energy sensitivity of SQUIDs in the “white” noise region (at frequencies above 1 kHz) is 4×10−30 J/Hz and is mainly determined by the intrinsic noise of the high-Tc superconducting interferometer and the shields. At low frequencies the predominant noise is from external fields penetrating directly into the shields. The addition of a ferromagnetic antenna to the SQUID microscope increases the intrinsic noise of the magnetometer to 8×10−30 J/Hz at frequencies above 1 kHz.

For the first time we have designed, constructed and investigated an UHF high-T c SQUID pumped at 360 MHz at 77 K. The SQUID is based on an one-hole interferometer with a microbridge Josephson contact made of bulk YBaCuO ceramics by the standard technique of mechanical scribing, followed by finishing with a high-voltage discharge electroerrosion. Magnetic flux sensitivity of the UHF SQUID as measured by the output signal of a quadratic detector with a dc amplifier of 40 kHz bandwidth was found to be about 5 × 10−5ϕ0/ Hz 1/2 in the quasiwhite noise region (at a frequency over 700 Hz).

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