It passed more than 30 years since the ultra-high vacuum technique was developed. The ultimate pressure available in an ultra-high vacuum system gradually decreased with the advent of sputter ion pumps (SIP), turbomolecular pumps (TMP) and cryopumps (CP), but still remains in the range of 10-9Pa now. Recently there are increasing number of reports for the generation of extremely high vacuum (XHV), which corresponds to the pressure less than 1×10-10Pa. The vacuum pumps used for the generation of XHV are liquid-nitrogen cooled sublimation pumps, liquid-helium and liquid-nitrogen cooled cryopumps, and helium-refrigerator cooled cryopumps. They are closely related with cryogenic engineering. We summarize recent successful works for the generation of XHV. The production technique of XHV is advancing steadily, but total and partial pressure gauges which can measure such low pressure without disturbing vacuum condition have not been developed yet, and they are strongly demanded.
The recent development of SQUID system for biomagnetic study is remarkable. The high sensitive SQUID system makes possible to study the brain function and the research for the application of biomagnetic measurement to the diagnosis is in progress. In this review, the techniques for measuring the weak magnetic fields emanating from active positions in a human body are described and the estimation of source location of the biomagnetic field is described, The SQUID sensor, magnetically shielded room, reduction of magnetic noise and multi-channel SQUID systems are presented.