Bellows refers to a tubular elastic sensitive element connected by foldable corrugated sheets along the folding and stretching direction. Bellows are widely used in instruments and meters. Their main purpose is to be used as a measuring element of pressure measuring instruments to convert pressure into displacement or force. The wall of the bellows is thinner and the sensitivity is higher. The measuring range is from tens of Pa to tens of MPa. Its open end is fixed, the sealed end is in a free state, and an auxiliary spiral spring or reed is used to increase the elasticity.