US Patent 7524040 Liquid ejection head and liquid ejection apparatus

The liquid ejection head comprises: an ejection hole which ejects liquid; a pressure chamber which accommodates the liquid to be ejected from the ejection hole; an ejection force generating element which applies an ejection force to the liquid inside the pressure chamber; and a pressure measurement device including a capacitance-type pressure measurement element which measures pressure generated in the pressure chamber, the pressure measurement device having a resistance and a capacitance whereby frequency f and cut-off frequency fC of a measurement signal obtained from the pressure measurement element in accordance with the pressure generated in the pressure chamber satisfy a relationship of f<fC.