Abstract: Low frequency pulse-echo ultrasonic transducers are provided especially suited for use in downhole cement bond evaluation, but usable for various applications. One frequency pulse-echo ultrasonic transducer comprises a transducer stack having alternating layers of a piezoceramic element and an ultrasonic attenuating element that is preferably acoustic impedance matched to the piezoceramic elements in order to reduce the Q of the transducer stack. Another low frequency pulse-echo ultrasonic transducer comprises an assembly having the present transducer stack disposed on an acoustic attenuating backing and a front face. Yet another low frequency pulse-echo ultrasonic transducer comprises a transducer composite made from a lead metaniobate. Still another frequency pulse-echo ultrasonic transducer comprises a composite stack. A further low frequency pulse-echo ultrasonic transducer comprises a composite stack, wherein multiple drive elements allow driving individual elements at different times.

Abstract: A device for acoustic measuring in a medium in a borehole such as velocity of sound in the medium or velocity of the medium, includes at least a first acoustic array situated in a first, slanted sidewall of a measuring area and operating to emit a series of acoustic waveforms across a measuring area. In one form, the device includes a second acoustic array situated in a second, slanted sidewall of the measuring area and operating to receive an acoustic signal resulting from the emitted series of acoustic waveforms or to receive said acoustic signal and emit a second series of acoustic waveforms.

Abstract: A device for acoustic measuring in a medium in a borehole such as velocity of sound in the medium or velocity of the medium, includes at least a first acoustic array situated in a first, slanted sidewall of a measuring area and operating to emit a series of acoustic waveforms across a measuring area. In one form, the device includes a second acoustic array situated in a second, slanted sidewall of the measuring area and operating to receive an acoustic signal resulting from the emitted series of acoustic waveforms or to receive said acoustic signal and emit a second series of acoustic waveforms.

Abstract: Low frequency pulse-echo ultrasonic transducers are provided especially suited for use in downhole cement bond evaluation, but usable for various applications. One frequency pulse-echo ultrasonic transducer comprises a transducer stack having alternating layers of a piezoceramic element and an ultrasonic attenuating element that is preferably acoustic impedance matched to the piezoceramic elements in order to reduce the Q of the transducer stack. Another low frequency pulse-echo ultrasonic transducer comprises an assembly having the present transducer stack disposed on an acoustic attenuating backing and a front face. Yet another low frequency pulse-echo ultrasonic transducer comprises a transducer composite made from a lead metaniobate. Still another frequency pulse-echo ultrasonic transducer comprises a composite stack. A further low frequency pulse-echo ultrasonic transducer comprises a composite stack, wherein multiple drive elements allow driving individual elements at different times.

Abstract: An apparatus for estimating a property in a borehole penetrating the earth, the apparatus having: a carrier configured for being conveyed through the borehole; a scintillation crystal disposed at the carrier, a first portion of the crystal having a first cross-sectional area; and a photodetector optically coupled to the scintillation crystal and configured to detect photons generated in the crystal by interactions with radiation to estimate the property, the photodetector having a second cross-sectional area configured to couple to the crystal; wherein the crystal at a second portion tapers from the first cross-sectional area to the second cross-sectional area to guide the generated photons to the photodetector.

Abstract: A photodiode whose long-wavelength cutoff is in the short-wavelength range (preferably, between ultraviolet and yellowish-green) having reduced temperature sensitivity is used in downhole applications. It may be matched with scintillation devices having an output matched to the response curve of the photodiode for use with nuclear logging devices. The photodiode may also be used in gyroscopes in which light from an LED matched to the photodiode is reflected from a spinning mass.

Abstract: An acoustic attenuator suppresses acoustic signals traveling along the body of a measurement-while-drilling (MWD) tool, making it possible to obtain acoustic measurements relating to underground formations. Shaped cavities (spherical or cylindrical) filled with a fluid have a resonance frequency that is tuned to be within the band of interest thereby attenuating acoustic signals traveling through the body at these resonance frequencies. The staggered arrangement of the cavities increases the path length for the acoustic signals and provides further attenuation. Attenuation may also be accomplished by use of a composite consisting of cylindrical layers of two different materials with thicknesses that attenuate selected frequencies. Additional attenuation is provided by lengthening the path length of a seismic signal passing through the more competent of the two materials of the composite.