This paper reports two new methods that are effective to know the accurate values of the electromechanical coupling factor (kt) and the mechanical Q (Qm) for low Q materials. In order to realize the required sensitivity and bandwidth of an ultrasonic probe, it is necessary to know the accurate values of kt and Q of a material. about twice larger than the exact value when applying the usual resonant-antiresonant method to these materials.The fundamental concept or' the new methods is to derive these constants by comparing certain physical values with measured and calculated values.These methods were applied to several ?iezoelectric materials. It has been found that more reasonable values than those from the conventional method can be obtained.However, the value o? kt becomes

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