Blatek (United States)

Ultrasound imaging with high resolution and large field of depth has been increasingly adopted in medical diagnosis, surgery guidance and treatment assessment because of its relatively low cost, non-invasive and capability of real-time imaging. There is always a tradeoff between the resolution and depth of field in ultrasound imaging. Conventional ultrasound works at a particular frequency, with −6 dB fractional bandwidth of < 100%, limiting the resolution or field of depth in many ultrasound imaging cases. In this paper, a bi-frequency co-linear array covering a frequency range of 5 MHz-20 MHz was investigated to meet the requirements of resolution and depth of field for a broad range of ultrasound imaging applications. As a demonstration, a 31-element bi-frequency co-linear array was designed and fabricated, followed by element characterization and real time sectorial scan (S-scan) phantom imaging using a Verasonics system.

A system is composed of 64 channels of analog front-end pulser/receiver, 64 channels of Time-Gain Compensation (TGC), 64 channels of high-speed digitizer, and DSP-based beamformer implementation. The data are transferred to a PC via an Ethernet card. The system provides 64 channels of excitation pulsers while receiving simultaneously at a 120–200 MHz sampling rate at 12-bit resolution. The digitized data of all channels are first fed through FPGAs, and then stored in memories. Those raw data are then accessed by a DSP where the beamformer is implemented. The open architecture of the system design has the capability of carrying out synthetic aperture algorithms with the combination of single/multiple elements in transmit and single/multiple elements in reception.

PMN-PT single crystal 1-3 composite high frequency phased arrays with center frequency of 35 MHz were fabricated and characterized for silicon carbide (SiC) NDE imaging applications. The 35 MHz 64-element array was successfully prototyped using PMN-PT single crystal and PC-MUT technology. The broad bandwidth > 90% and high sensitivity (echo amplitude > 500 mV from the impulse response with 0 gain) was observed with reasonably high uniformity. These high frequency phased arrays are promising for ceramic NDE imaging.

In this paper, the design, fabrication and characterization of PMN-PT single crystal/epoxy composites are reported for NDT ultrasound transducers. Specifically, 1-3 PMN-PT/epoxy composites with center frequencies of 5 MHz - 40 MHz were designed and fabricated using either the dice-and-fill method or a photolithography based micromachining process. The measured electromechanical coefficients for composites with frequency of 5 MHz - 15 MHz were about 0.78-0.83, and the coupling coefficients for composites with frequencies of 25 MHz- 40 MHz were about 0.71-0.72. The dielectric loss remains low (< 0.05). These properties hold promise for advanced NDT ultrasound applications.

One key parameter in using electroactive materials to harvest electric energy from mechanical sources is the energy conversion efficiency. Recently, it was shown that, in the relaxor ferroelectric PMN-PT single crystals, a very high longitudinal electromechanical coupling factor (>90%) can be obtained. This paper investigates energy harvesting using 1-3 composites of PMN-PT single crystals in a soft epoxy matrix. It is shown that 1-3 composites enable the single crystals operating in the longitudinal mode to achieve high efficiency for energy harvesting, and the soft-polymer, matrix-supported single-crystal rods maintain high mechanical integrity under different external loads. For comparison, 1-3 composites with piezoceramic PZT also are investigated in energy-harvesting applications, and the results show that the high coupling factor of single crystal PMN-PT 1-3 composites leads to much higher electric energy output for similar mechanical energy input. The harvested energy density of 1-3 composite with single crystal (22.1 mW/cm3 under a stress of 40.4 MPa) is about twice of that harvested with PZT ceramic 1-3 composite (12 mW/cm3 under a stress of 39 MPa). At a higher stress level, the harvested-energy density of 1-3 PMN-PT single crystal composite can reach 96 mW/cm3.

The aim of this research is to produce 2-2 PZT/polymer composite using tape casting technology. PZT tapes were printed with a fugitive phase (carbon) to define voids which were then backfilled with epoxy after the carbon was removed by thermal treatment at 1250/spl deg/C. Final dimensions of the 2-2 composite were in the range of 25 /spl mu/m for the ceramic bar and 5 /spl mu/m for the epoxy-filled kerf. Specific emphasis was placed on achieving uniformity and straightness of the ceramic beam and kerf thicknesses. The composites were fabricated into 20 MHz single element pachymeters and benchmarked against commercial devices fabricated by dice-and-fill. The tape cast material compared favorably with high sensitivity and a little lower bandwidth. Fabrication of a 35 MHz linear array transducer is in progress. Electrode patterning to define individual array elements has been successfully completed.