Patent ID: 7819509

Claim:
A liquid ejection head, comprising: a liquid ejection port; a pressure chamber which has a recess part connected to the liquid ejection port; a lower electrode which is arranged on the pressure chamber; a piezoelectric body which has a planar face arranged on the lower electrode; and an upper electrode which is arranged on the piezoelectric body, wherein: a cross section of the recess part of the pressure chamber taken in parallel to the planar face of the piezoelectric body is oblong and has a breadth CWx in a breadthways direction and a length CWy in a lengthwise direction; the piezoelectric body has an active region positioned between the lower and upper electrodes and contributing to displacement of the piezoelectric body, an area of the active region being smaller than an area of the cross section of the recess part of the pressure chamber, the active region having a breadth DWx in the breadthways direction of the cross section of the recess part of the pressure chamber and a length DWy in the lengthwise direction of the cross section of the recess part of the pressure chamber; a ratio CWy/CWx is in a range of 2 through 5; a ratio DWx/CWx is in a range of 0.4 through 0.75; and a ratio DWy/CWy is in a range of ±0.05 of a central value of 0.133×ln(CWy/CWx) +0.7312, where ln(CWy/CWx) is a natural logarithm of the ratio CWy/CWx.