Stand-off device with special fluid

Claim 1

A stand-off device for coupling an acoustic transducer to a human body having tissue with a given acoustic impedance Z B , comprising: means defining a chamber having a pliant diaphragm at a side thereof that conforms to the contours of a patient's body, said diaphragm having inner and outer surfaces and having an acoustic impedance Z D that is between 1.73 and 1.8 megrayls inclusive and a thickness that is within ∓50% of a quarter wavelength of an odd integral number of quarter wavelengths of the central frequency transmitted by a transducer with which the stand-off device is to be used, means for coupling another side of said chamber to said transducer, liquid having a given acoustic impedance Z L that is between 1.89 and 2.02 megrayls inclusive contained in said chamber so as to conduct acoustic waves from said transducer when coupled to said chamber to said diaphragm, the reflection coefficients (Z D -Z L )/(Z D +Z L ) and (Z B -Z D )/(Z B +Z D ) and the thickness of the diaphragm being such that the acoustic waves from said transducer that are reflected at the outer and inner surfaces of said diaphragm cancel each other to such an extent that the energy reflected toward the transducer is within 6 db of the energy reflected from these surfaces when the reflection coefficients are equal and the thickness of the diaphragm is precisely an odd number of quarter-wavelengths of the central frequency of the transducer with which the stand-off device is to be used.