Bone ultrasound transducer

Low-intensity pulsed ultrasound (LIPUS) is used on bone-healing. One expected healing mechanism of this technique is the contribution of piezoelectricity. Actually, the piezoelectricity in dry bone at low frequencies has been reported by many investigators. However, the ultrasonic investigation of the piezoelectricity in bone has still remained very few. We have then made original transducers with bovine cortical bone samples, which were fabricated into plates (diameter: 10 mm, thickness: 0.5~1.0 mm). Using a conventional ultrasonic pulse technique in MHz range, we confirmed the observation of ultrasonic wave by the transducer. Here, the bone transducer was set in water at the focal position of a PVDF transmitter, which was excited by a single sinusoidal pulse of 70 Vp-p in the MHz range. The maximum voltage of the received wave was about 200 μVp-p. It was almost 1/2000 of the homemade PVDF transducer, which was made by the same procedure. The observed wave amplitude changed due to the sound wave frequency and bone thickness. Considering the inhomogeneous bone microstructure and the thickness dependence of the bone transducer, the piezoelectricity of bone in the MHz range is discussed.