Backscatter coefficient estimation using array transducers

This paper describes an extension of our broadband method for estimating backscatter coefficients from random media to include data from array transducers. Four different transducer designs have now been considered: oneand two-dimensional linear arrays, annular arrays, and single-element focused pistons commonly used in mechanical sector scanners. The analysis shows that if the backscatter echo spectrum is properly normalized, the shape of the piezoelectric elements affects only the magnitude and not the frequency dependence of the backscatter coefficient estimates. Experimental data were acquired using laboratory and clinical imaging instrumentation to verify the analysis. We compared backscatter coefficients measured as a function of frequency from well-defined scattering media that were obtained using a 1-D linear array and focused piston transducers. Instrument-independent results were found that matched theoretical predictions within the measurement error between 2 and 12 MHz. We conclude from this study that accurate backscatter coefficient estimates may be easily obtained using current clinical imaging instrumentation.     

聚焦换能器离散发射阵列的辐射力计算

为了对医学超声中使用的聚焦换能器离散阵列的辐射力进行估算,文章中应用几何声学的方法,推导了聚焦换能器离散发射阵列超声作用于吸收靶上的辐射力公式,并分别给出了活塞阵元与聚焦阵元的辐射力公式。将该几何声学公式与瑞利积分结果比较显示,当声束倾斜角θi<30°,半孔径角α<15°时,误差不超过4.5%。这种结果说明了这种方法可以用来有效地估算离散阵列聚焦换能器的辐射力。     

Selective detection of hydrogen sulfide using copper oxide-doped tin oxide based thick film sensor array

In this work, copper oxide-doped (1, 3 and 5 wt%) tin oxide powders have been synthesised by sol–gel method and thick film sensor array has been developed by screen printing technique for the detection of H₂S gas. Powder X-ray diffraction pattern shows that the tin oxide (SnO₂) doped with 3 wt% copper oxide (CuO) has smaller crystallite size in comparison to 0, 1 and 5 wt% CuO-doped SnO₂. Furthermore, field emission scanning electron microscopy manifests the formation of porous film consisting of loosely interconnected small crystallites. The effect of various amounts of CuO dopant has been studied on the sensing properties of sensor array with respect to hydrogen sulfide (H₂S) gas. It is found that the SnO₂ doped with 3 wt% CuO is extremely sensitive (82%) to H₂S gas at 150 °C, while it is almost insensitive to many other gases, i.e., hydrogen (H₂), carbon monoxide (CO), sulphur dioxide (SO₂) and liquefied petroleum gas (LPG). Moreover, at low concentration of gas, it shows fast recovery as compared to response time. Such high performance of 3 wt% CuO-doped SnO₂ thick film sensor is probably due to the diminishing of the p–n junction and the smallest crystallite size (11 nm) along with porous structure.     

Multi-layered PZT/polymer composites to increase signal-to-noise ratio and resolution for medical ultrasound transducers part II: thick film technology

For pt.I, see ibid., vol.46, no.4, p.961-71 (1999). Increasing transducer bandwidth and signal-to-noise ratio (SNR) is fundamental to improving the quality of medical ultrasound images. In previous work, we have proposed the use of multi-layer 1-3 PZT/polymer composites to increase both, but have encountered significant fabrication challenges. Thus, we have developed a multi-layer composite hybrid array that will not require post alignment. Starting from a 2-MHz, three-layer PZT-5H, thick film transducer designed for 1.5-D arrays, cuts are made only through the top layer and back-filled with epoxy, forming a composite layer on top of two ceramic layers. Finite element (PZFlex) simulations show that for a 2-MHz phased-array element with a single matching layer, the three-layer hybrid structure increases the pulse echo SNR by 11 dB versus a single layer PZT element and improves -6 dB pulse echo fractional bandwidth by a factor of 1.4. Composite hybrid arrays fabricated in our laboratory showed an improvement in SNR of 6 to 11 dB over a PZT control and an increase in -6 dB bandwidth by a factor of 1.1. Images from a phased-array scanner confirmed these improvements     

Design and development of high voltage high power operational amplifier using thick film technology

Applications of power operational amplifiers (opamps) are increasing day by day in the industry as they are used in audio amplifiers, Piezo transducer systems and the electron deflection systems. Power operational amplifiers have all the features of a general purpose opamp except the additional power handling capability. The power handling feature can be achieved using an external circuitry around a regular opamp. Normally power opamps can deliver current more than 50 mA and can operate on the supply voltage more than ±25 V. This paper gives the details of one of the power opamps developed to drive the Piezo Actuators for Active Vibration Control (AVC) of aircraft/aerospace structures. The designed power opamp will work on ±200 V supply voltage and can deliver 200 mA current.     

Two-dimensional ultrasound receive array using an angle-tuned Fabry-Perot polymer film sensor for transducer field characterization and transmission ultrasound imaging

A 2-D optical ultrasound receive array has been investigated. The transduction mechanism is based upon the detection of acoustically induced changes in the optical thickness of a thin polymer film acting as a Fabry-Perot sensing interferometer (FPI). By illuminating the sensor with a large-area laser beam and mechanically scanning a photodiode across the reflected output beam, while using a novel angle-tuned phase bias control system to optimally set the FPI working point, a notional 2-D ultrasound array was synthesized. To demonstrate the concept, 1-D and 2-D ultrasound field distributions produced by planar 3.5-MHz and focused 5-MHz PZT ultrasound transducers were mapped. The system was also evaluated by performing transmission ultrasound imaging of a spatially calibrated target. The "array" aperture, defined by the dimensions of the incident optical field, was elliptical, of dimensions 16 x 12 mm and spatially sampled in steps of 0.1 mm or 0.2 mm. Element sizes, defined by the photodiode aperture, of 0.8, 0.4, and 0.2 mm were variously used for these experiments. Two types of sensor were evaluated. One was a discrete 75-microm-thick polyethylene terephthalate FPI bonded to a polymer backing stub which had a wideband peak noise-equivalent pressure of 6.5 kPa and an acoustic bandwidth 12 MHz. The other was a 40-microm Parylene film FPI which was directly vacuum-deposited onto a glass backing stub and had an NEP of 8 kPa and an acoustic bandwidth of 17.5 MHz. It is considered that this approach offers an alternative to piezoelectric ultrasound arrays for transducer field characterization, transmission medical and industrial ultrasound imaging, biomedical photoacoustic imaging, and ultrasonic nondestructive testing.     

A sensitive magnetic field sensor using BPSCCO thick film

A highly sensitive magnetic sensor operating at liquid nitrogen temperature and based on BPSCCO screen-printed thick film, is reported. The sensor resistance for an applied magnetic field of 100 ×10⁻⁴ T (100 gauss) exhibits an increase by 360% of its value in zero field at 77.4 K. The performance of the sensor in presence of magnetic field, the hysteretic features and the effect of thermal cycling, has been discussed.     

Multilayer piezoelectric ceramics for two-dimensional array transducers

In medical ultrasound imaging, 2-D array transducers have become essential to implement dynamic focusing and phase-correction in the elevation dimension as well as real-time volumetric scanning. Unfortunately, the small size of a 2-D array element results in a small clamped capacitance and a large electrical impedance near resonance. These elements have poor sensitivity because their impedance is much higher than the electrical impedance of the transmit and receive circuitry. Sensitivity can be improved by using an N layer structure of PZT ceramic with the layers connected acoustically in series and electrically in parallel. For the multilayer ceramic (MLC), the damped capacitance is multiplied by a factor of N(2) and the electrical impedance by 1/N(2) compared to a single layer element of the same dimensions. A 3x43 phased-array transducer has been fabricated using 3 layer PZT-5H material. Each element had a thickness of 0.66 mm and an area of 0.37x3.5 mm. The MLC was manufactured using thick film technology with plated-through vias to electrically interconnect the electrode layers. The completed transducer was compared to a single layer control array of similar dimensions. With a light epoxy backing and a lambda/4 matching layer, the MLC array elements had an impedance of 100 Omega at series resonance of 2.25 MHz, compared to 800 Omega for the control elements. The lower impedance of the MLC elements resulted in a minimum round-trip insertion loss of 24.0 dB, compared to an 34.1 dB for the control array elements. These results were consistent with KLM modeling. B-scan images were made of cysts in a tissue-mimicking phantom and of the left kidney in vivo. The images clearly showed a higher signal-to-noise ratio for the MLC array compared to the control. As a result, 2-D arrays made of multilayer ceramics can be used to form images at a higher frequency and greater range than single layer arrays.     

利用纳米ZnO粉制备厚膜气敏传感器的研究

以ZnO纳米粉(平均粒径30nm)为原料,利用水热热压方法制备了ZnO多孔纳米固体,同时用通常的水热法对ZnO纳米粉进行了预处理(预处理ZnO纳米粉)。然后,分别以ZnO多孔纳米固体和预处理ZnO纳米粉为原料,制备了厚膜气敏传感器。本征电阻的测试结果表明,这两种厚膜气敏传感器的本征电阻比用未经处理的ZnO纳米粉(以下简称“原料ZnO纳米粉”)制备的厚膜气敏传感器大大降低并很快达到稳定状态。有效地改善了器件工作的稳定性。结合对三种传感器的显微结构分析,对出现上述差异的原因进行了讨论。     

Fabrication of a highly sensitive magnetic sensor using an HTS thick film

A highly sensitive magnetic sensor based on Y₁Ba₂Cu₃O_7−x (YBCO) has been fabricated by the spray technique. The value of resistance R_ms in the transitional region ΔT of the thick film, was highly sensitive to the applied magnetic field B_ex. Here, ΔT is the transitional temperature region between the resistance drop temperature T_c^onset and residual resistance temperature T_c^res. The value of residual resistance R_res for an applied magnetic field of 80×10⁻⁴ T (80 G) exhibited an increase of about 580% over the resistance found in a zero magnetic field, and did not display any evidence of hysteresis. The fabrication and magnetic characteristics are discussed.     

Three-dimensional radiochromic film dosimetry of proton clinical beams using a gafchromic EBT2 film array

In this work, three-dimensional (3D) film-based proton beam measurements were used for the first time to verify the patient-specific radiation dose distribution, beam range and compensator shape. Three passively scattered proton beams and one uniform scanning proton beam were directed onto an acrylic phantom with inserted Gafchromic EBT films. The average gamma index for a comparison of the dose distributions was less than one for 97.2 % of all pixels from the passively scattered proton beams and 98.1 % of all pixels for the uniform scanning proton beams, with a 3 % dose and a 3 mm distance-to-dose agreement tolerance limit. The results also showed that the average percentage of points within the acceptance criteria for proton beam ranges was 94.6 % for the passively scattered proton beams. Both the dose distribution and the proton beam range determined by the 3D EBT film measurement agreed well with the planning system values.     

Low cost microwave thick film structures

This paper examines the potential use of low cost materials and processes to produce thick film structures at low microwave frequencies. It examines empirically the upper frequency limits for the use of simple design techniques as a function of substrate thickness. It concludes that satisfactory results can be obtained using low cost methods up to about 12 GHz for 1 mm 96% alumina substrates and 16 GHz for 0.63 mm substrates. These are the most commonly available thick film substrate thicknesses. A low permittivity protective layer is desirable to maintain reliability.     

Infrared absorption in thick film resistors

Infrared absorption in polymer and glass-based thick film resistors has been measured between 400 and 1500 cm^–1. Sample structures are discussed on the basis of X-ray, Fourier transform-infrared and resistance-temperature data. It is shown that in polymer-based thick film resistors, the particulate phase is mostly responsible for the infrared absorption between 400 and 900 cm^–1, whereas the infrared absorption at higher wave numbers is related to the continuous phase. In glass-based thick film resistors, absorption is mostly determined by the highly doped glass. The results indicate that thick film resistors can be used as an absorbent coating in the 400–1500 cm^–1 region by suitable selection of the continuous and particulate phases.     

Stress field forming of sector array transducers for vibro-acoustography

This paper presents a study of the stress field forming of sector array transducers for vibro-acoustography applications. The system point-spread function (PSF) is given in terms of the dynamic radiation stress exerted on a point target by a dual ultrasound beam with slightly different frequencies. The radiation stress is calculated by assuming that the resulting ultrasound beam is a plane wave. The stress is proportional to the product of the velocity potential of each incident ultrasound beam. The beamforming and stress field forming of sector array transducers are analyzed through linear acoustics. An expression for the velocity potential produced by sector array transducers is derived. The vibro-acoustography PSF is evaluated numerically. A comparison between the PSF of a sector array and a confocal transducers is presented. The compared characteristics of the PSF are sidelobe levels, transverse, and in-depth spatial resolution. Indeed, one motivation to study sector transducers is the fact the depth-of-field of these transducers should be smaller than that of same size confocal transducers. An experimental setup was used to validate the theoretical PSF of sector array transducers. Results show that the measured PSF is in good agreement with the theoretical predications. Vibro-acoustography images of a breast-phantom by both transducers are presented and discussed.     

Screen printed nanosized ZnO thick film

Nanosized ZnO was prepared by polyol synthesis. Fluorescence spectrum of the ZnO colloid at varying pump intensities was studied. The powder was extracted and characterized by XRD and BET. The extracted powder was screen printed on glass substrates using ethyl cellulose as binder and turpinol as solvent. Coherent back scattering studies were performed on the screen printed sample which showed evidence of weak localization. The screen printed pattern showed strong UV emission.     

按需滴定法制备掺杂型聚合物微透镜阵列

采用MMA单体与其聚合物PMMA及掺杂剂的混合溶液,以按需滴定法制备了掺杂若丹明6G的微透镜阵列。并对其焦距一致性、成像效果、表面粗糙度、透射光谱和荧光光谱等光学性能进行了测试。焦距不均匀度不超过1．8％,测定数值和理论值相差不到1．7％。表面热处理后表面粗糙度肋小于0．9nm,光学透过率从近紫外到近红外都在90％以上,可以用于光纤放大器和生物化学传感器。