Experimental observation of piezoelectric effect in cancellous bone generated by ultrasound irradiation

Three-dimensional coupled vibration of the rectangular piezoelectric ceramic stack

The three-dimensional coupled vibration of the rectangular piezoelectric ceramic stack is analyzed by adopting the equivalent elastic method, which is an approximate analytical method. When the shear stress and strain are ignored, the complex coupled vibration of the rectangular piezoelectric ceramic stack is simplified to three one-dimensional coupled vibrations by defining three mechanical coupled coefficients. The three-dimensional electromechanical equivalent circuit is established on the basis of the analysis. The resonance frequency equation which determines the vibration mode of the piezoelectric vibrator is derived and the resonance frequencies of different modes can be calculated. According to the resonance frequency equation of coupled vibration, the effects of the length, width, and thickness of the rectangular piezoelectric ceramic stack on the resonance frequency are analyzed. Three groups of the rectangular piezoelectric ceramic stack of different dimensions are made for experiments and numerical simulations. The results show that the theoretical results are in good agreement with the experimental analysis and simulation results, which provide theoretical support for expanding the application of rectangular piezoelectric vibrators.

Piezoelectric and Inversely Piezoelectric Responses of Bone Tissue Plates in the Megahertz Range

Piezoelectricity in bone is thought to be a mechanism by which ultrasound promotes the healing of bone fractures. However, a few studies have been conducted in the more clinically relevant megahertz range. To understand the piezoelectricity in bone, we fabricated ultrasound transducers using bone samples as piezoelectric materials and identified the longitudinal ultrasound radiation and reception in the megahertz range. The maximum transmitting sensitivity of the bone transducer was 140 mPa/V, which was nearly 1/1000 of a polyvinylidene difluoride (PVDF) transducer that has better electrical properties and piezoelectricity. The resonance frequencies of the transducer depend on the plate thickness and angle between the bone axis (alignment direction of the hydroxyapatite crystallites) and ultrasound propagation direction, reflecting the anisotropic character of the bone. The reception and transmission sensitivities of the bone transducers also depend on the plate thickness and angle, showing maximum values at off-axis angles. These results indicate the existence of both piezoelectricity and inverse piezoelectricity in bone, which may be key factors in understanding the bone healing by low-intensity biophysical (electrical or mechanical) stimulation.

Analysis on the three-dimensional coupled vibration of composite cylindrical piezoelectric transducers

Three-dimensional coupled vibration of the composite cylindrical piezoelectric transducer is analyzed. The composite cylindrical piezoelectric transducer consists of an inner axially polarized piezoelectric ceramic cylinder and an outer metal cylinder with the same height. Coupled vibration of the composite cylindrical piezoelectric transducer is analyzed by equivalent elasticity method, which is an approximate analytical approach. According to this method, coupled vibration of the cylindrical transducer is regarded as an interaction between a plane radial vibration and a longitudinal vibration. The radial and longitudinal electromechanical equivalent circuits of the piezoelectric transducer are acquired. Input impedances as functions of the resonance frequency and the mechanical coupling coefficient are derived to obtain resonance frequency equations. The analytical results are supported by experimental and numerical simulated results of two prototypes of the piezoelectric transducer. The composite cylindrical piezoelectric transducer presented in this paper is superior to single cylindrical piezoelectric transducers, composite ring-type, and tube-type transducers in the field of high output power and efficiency.

Investigation of piezoelectric anisotropy of bovine cortical bone at an ultrasound frequency by coupling an experiment and a simulation

An investigation of the piezoelectric anisotropy of bovine cortical bone at 1 MHz was attempted by coupling data obtained from an experiment and a simulation. In the experiment, a piezoelectric cell (PE-cell) was used as an ultrasound receiver. In the PE-cell, the cortical bone disk, which was cut in the direction perpendicular to the bone axis, was electrically shielded. The directivity of the PE-cell was measured at 0°-22.5° and was compared to four simulated results using the piezoelectric finite-difference time-domain method. It was shown that the piezoelectric signal in the bone could be generated by a transverse ultrasound wave.