Nanocrystalline powder and fibres of lead zirconate titanate (PZT) were prepared by the sol-gel p... more Nanocrystalline powder and fibres of lead zirconate titanate (PZT) were prepared by the sol-gel process. The structural variation of the PZT powder with annealing temperature was studied by differential thermal analysis, thermogravimetry and x-ray diffraction. The lowest temperature for the formation of single-phase PZT nanocrystals in the powder was found to be 650°C and the average crystallite diameter in the powder annealed at 650°C was 35 nm. By controlling the concentration of the precursor, fibres of diameter 50-100 !Jlll were drawn from the gel. After annealing at 700°C the crystallite size in these fibres was 0.3-0.5 !Jlll.
The performance of transducers operating at high frequencies is greatly influenced by the propert... more The performance of transducers operating at high frequencies is greatly influenced by the properties of the piezoelectric materials used in their fabrication. Selection of an appropriate material for a transducer is based upon many factors, including material properties, transducer area, and frequency of operation. This review article outlines the major developments in the field of piezoelectrics with emphasis on materials suitable for the design of high frequency medical imaging ultrasonic transducers. Recent developments in the areas of fine grain and thin film ceramics, piezo-polymers, single crystal relaxor piezoelectrics, as well as lead-free and composite materials are discussed.
0-3 composites with nanosized lead zirconate titanate (PZT) powder imbedded in a vinylidene fluor... more 0-3 composites with nanosized lead zirconate titanate (PZT) powder imbedded in a vinylidene fluoridetrifluoroethylene copolymer (P(VDF-TrFE)) matrix have been fabricated. Since the piezoelectric coefficients of PZT and P(VDF-TrFE) have opposite signs, the PZT and P(VDF-TrFE) phases in the nanocomposites were poled in opposite directions in order to enhance the piezoelectric activity. The PZT powder, prepared by a sol-gel process, has a tetragonal structure. The ratio of the (002) and (200) X-ray diffraction peaks was used as a measure of the degree of poling in the ceramic phase. The piezoelectric coefficient of the nanocomposite film was measured by a laser interferometry technique. A needle type hydrophone for the calibration of medical ultrasonic transducers was fabricated using the nanocomposite as the sensing element and its performance was evaluated.
A novel fiber-optic hydrophone based on a dual-polarization, short-cavity fiber grating laser as ... more A novel fiber-optic hydrophone based on a dual-polarization, short-cavity fiber grating laser as the sensing element is described. Wet chemical etching was used to fabricate a thinned fiber sensor to extend its frequency response as well as spatial resolution. The lateral beam profile at the focal plane of a 40-MHz lens-focused lithium niobate (LiNbO 3) transducer was measured with the fiber sensor, and a tomographic technique was used to compute the transducer profile, which is compared with that obtained by a PVDF hydrophone. The fiber hydrophone has a sensitivity of approximately −259 dB re 1V/µPa up to 40 MHz, which is higher than that of a commercial PVDF hydrophone. Moreover, it is capable of accurately characterizing the beam generated by high-frequency transducer.
Powder agglomeration is a major problem in the fabrication of calcium and lanthanum modified lead... more Powder agglomeration is a major problem in the fabrication of calcium and lanthanum modified lead titanate/vinylidene fluoride-trifluoroethylene [PCLT/P(VDF-TrFE)] 0–3 nanocomposites. To ensure uniform dispersion of the nanocrystalline PCLT powder in the P(VDF-TrFE) matrix, the powder is often dispersed in a liquid (e.g. methyl-ethyl ketone) placed in a high power ultrasonic bath. In this study, PCLT nanocrystalline powder derived from a sol-gel process was dispersed in various liquids placed in an ultrasonic bath for different periods of time tu. The size and specific surface area of the particles were measured as functions of tu. By choosing a good dispersing agent and an appropriate t, PCLT/P(VDF-TrFE) nanocomposites with a uniform dispersion of nanosized particles can be prepared. The dielectric, piezoelectric and pyroelectric properties of these composites have been investigated.
Nanocrystalline powder and fibres of lead zirconate titanate (PZT) were prepared by the sol-gel p... more Nanocrystalline powder and fibres of lead zirconate titanate (PZT) were prepared by the sol-gel process. The structural variation of the PZT powder with annealing temperature was studied by differential thermal analysis, thermogravimetry and x-ray diffraction. The lowest temperature for the formation of single-phase PZT nanocrystals in the powder was found to be 650°C and the average crystallite diameter in the powder annealed at 650°C was 35 nm. By controlling the concentration of the precursor, fibres of diameter 50-100 !Jlll were drawn from the gel. After annealing at 700°C the crystallite size in these fibres was 0.3-0.5 !Jlll.
The performance of transducers operating at high frequencies is greatly influenced by the propert... more The performance of transducers operating at high frequencies is greatly influenced by the properties of the piezoelectric materials used in their fabrication. Selection of an appropriate material for a transducer is based upon many factors, including material properties, transducer area, and frequency of operation. This review article outlines the major developments in the field of piezoelectrics with emphasis on materials suitable for the design of high frequency medical imaging ultrasonic transducers. Recent developments in the areas of fine grain and thin film ceramics, piezo-polymers, single crystal relaxor piezoelectrics, as well as lead-free and composite materials are discussed.
0-3 composites with nanosized lead zirconate titanate (PZT) powder imbedded in a vinylidene fluor... more 0-3 composites with nanosized lead zirconate titanate (PZT) powder imbedded in a vinylidene fluoridetrifluoroethylene copolymer (P(VDF-TrFE)) matrix have been fabricated. Since the piezoelectric coefficients of PZT and P(VDF-TrFE) have opposite signs, the PZT and P(VDF-TrFE) phases in the nanocomposites were poled in opposite directions in order to enhance the piezoelectric activity. The PZT powder, prepared by a sol-gel process, has a tetragonal structure. The ratio of the (002) and (200) X-ray diffraction peaks was used as a measure of the degree of poling in the ceramic phase. The piezoelectric coefficient of the nanocomposite film was measured by a laser interferometry technique. A needle type hydrophone for the calibration of medical ultrasonic transducers was fabricated using the nanocomposite as the sensing element and its performance was evaluated.
A novel fiber-optic hydrophone based on a dual-polarization, short-cavity fiber grating laser as ... more A novel fiber-optic hydrophone based on a dual-polarization, short-cavity fiber grating laser as the sensing element is described. Wet chemical etching was used to fabricate a thinned fiber sensor to extend its frequency response as well as spatial resolution. The lateral beam profile at the focal plane of a 40-MHz lens-focused lithium niobate (LiNbO 3) transducer was measured with the fiber sensor, and a tomographic technique was used to compute the transducer profile, which is compared with that obtained by a PVDF hydrophone. The fiber hydrophone has a sensitivity of approximately −259 dB re 1V/µPa up to 40 MHz, which is higher than that of a commercial PVDF hydrophone. Moreover, it is capable of accurately characterizing the beam generated by high-frequency transducer.
Powder agglomeration is a major problem in the fabrication of calcium and lanthanum modified lead... more Powder agglomeration is a major problem in the fabrication of calcium and lanthanum modified lead titanate/vinylidene fluoride-trifluoroethylene [PCLT/P(VDF-TrFE)] 0–3 nanocomposites. To ensure uniform dispersion of the nanocrystalline PCLT powder in the P(VDF-TrFE) matrix, the powder is often dispersed in a liquid (e.g. methyl-ethyl ketone) placed in a high power ultrasonic bath. In this study, PCLT nanocrystalline powder derived from a sol-gel process was dispersed in various liquids placed in an ultrasonic bath for different periods of time tu. The size and specific surface area of the particles were measured as functions of tu. By choosing a good dispersing agent and an appropriate t, PCLT/P(VDF-TrFE) nanocomposites with a uniform dispersion of nanosized particles can be prepared. The dielectric, piezoelectric and pyroelectric properties of these composites have been investigated.
Uploads
Papers by Qifa Zhou