Views:6 Author:Site Editor Publish Time: 2020-01-10 Origin:Site
Not only《the properties and detection of nondestructive testing ultrasonic device》 but also 《ultrasonic detection》are not differentiate, or some theses,define them as “pulse width”,de-emphasize their difference and casual relationship,and not explain harm of confusing ,this article puts forward own simple views,if improper,please correct.2 the difference and relationship of two ,the natural frequency of probe fo decided by thickness of wafer t and acoustic speed c,namely fo=c/(2t) , (1) when probe has been stimulated,the quality of sound pulse signal is related to forms and width of incentive electrical impulse.Ultrasonic quality triggered by square wave is the best,and comparing strength and amplitude to ultrasonic triggered by peak electric pulse,it can multiply.The “square wave width ”is the width of incentive electrical impulses td, normally giving followed equation : 2∏fo=3n/td (n=1，2，3，…) (2) in the equation :f0--probe nominal frequency ;td-- incentive electrical impulse width.
N--optional natural number, n=1,2,3,....,normally the n=1 is the best;
∏=3.1416。If makes ∏≈3,then the equation (1) can be changed into 2fo.td≈n (3) choose n=1, 2fo.td≈1 (4),according to equation (4):the rise and fall of square wave side error half cycle, triggered effects can be multiplied.In addition ,from above equation：from incentive circuit design,we should make incentive electrical impulse --square wave width td is inversely proportional to fixed frequency of probe fo.The adjustment of td of Incentive electrical impulse is a method of improving electromechanical coupling mass and probe launches acoustic impulse,and there is no connection with acoustic impulse width generated by probe.Acoustic impulse width generated by probe is just decided by quality of probe damping .
Therefore ,the width of incentive electrical impulse and ultrasonic pulse width sent or received by probe have different concept respectively.Have own measuring method，should not be confused.3. Harm,the result of confusing these will mislead ：acoustic pulse width it is inversely proportional to frequency fo.Because acoustic pulse width t,not electrical impulse width td.The product of 2t and fo doesn’t equal to 1:namely,acoustic impulse width t ，has nothing to do with frequency,and it just decided by quality of probe damping.