共查询到20条相似文献,搜索用时 15 毫秒
1.
Tang SC Clement GT 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2008,55(2):359-367
The aim of this study is to evaluate the feasibility of using harmonic cancellation for a therapeutic ultrasound transducer excited by a switched-mode power converter without an additional output filter. A switching waveform without the third harmonic was created by cascading two switched-mode power inverter modules at which their output waveforms were pi/3 phase shifted from each other. A PSPICE simulation model for the power converter output stage was developed. The simulated results were in good agreement with the measurement. The waveform and harmonic contents of the acoustic pressure generated by a 1-MHz, self-focused piezoelectric transducer with and without harmonic cancellation have been evaluated. Measured results indicated that the acoustic third harmonicto- fundamental ratio at the focus was small (-48 dB) with harmonic cancellation, compared to that without harmonic cancellation (-20 dB). The measured acoustic levels of the fifth harmonic for both cases with and without harmonic cancellation also were small (-46 dB) compared to the fundamental. This study shows that it is viable to drive a piezoelectric ultrasound transducer using a switched-mode power converter without the requirement of an additional output filter in many high-intensity focused ultrasound (HIFU) applications. 相似文献
2.
Determination of the acoustic output of a harmonic scalpel 总被引:1,自引:0,他引:1
Koch C Borys M Fedtke T Richter U Pöhl B 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2002,49(11):1522-1529
The acoustic output of a harmonic scalpel was experimentally determined, and both the airborne ultrasound and the ultrasound transmitted in water were taken into account. The sound pressure level of airborne ultrasound was measured with a microphone and an artificial head, so that the free-field value and the sound level at the entrance at the bottom of the cavum conchae of the ear could be determined. The derived output power in water was obtained from a hydrophone measurement. The results were strongly influenced by cavitation effects, and it is shown that the power values with and without cavitation differ by more than a factor of 5. The measurement of acoustic output parameters forms the basis for describing the performance of the devices and for an assessment of the risk of harmful bioeffects on both the operator and the patient. 相似文献
3.
Jansson T Jurkonis R Mast TD Persson HW Lindström K 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2002,49(6):715-725
Speckle in continuous wave (CW) Doppler has previously been found to cause large variations in detected Doppler power in blood perfusion measurements, where a large number of blood vessels are present in the sample volume. This artifact can be suppressed by using a number of simultaneously transmitted frequencies and averaging the detected signals. To optimize the strategy, statistical properties of speckle in CW ultrasound need to be known. This paper presents analysis of the frequency separation necessary to obtain independent values of the received power for CW ultrasound using a simplified mathematical model for insonation of a static, lossless, statistically homogeneous, weakly scattering medium. Specifically, the autocovariance function for received power is derived, which functionally is the square of the (deterministic) autocorrelation function of the effective sample volumes produced by the transducer pair for varying frequencies, at least if a delta correlated medium is assumed. A marginal broadening of the modeled autocovariance functions is expected for insonation of blood. The theory is applicable to any transducer aperture, but has been experimentally verified here with 5-MHz, 6.35-mm circular transducers using an agar phantom containing small, randomly dispersed glass particles. A similar experimental verification of a transducer used in multiple-frequency blood perfusion measurements shows that the model proposed in this paper is plausible for explaining the decorrelation between different channels in such a measurement 相似文献
4.
Johansson J Martinsson PE Delsing J 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2007,54(10):1977-1983
Equivalent circuits for piezoelectric devices and ultrasonic transmission media can be used to cosimulate electronics and ultrasound parts in simulators originally intended for electronics. To achieve efficient system-level optimization, it is important to simulate correct, absolute amplitude of the ultrasound signal in the system, as this determines the requirements on the electronics regarding dynamic range, circuit noise, and power consumption. This paper presents methods to achieve correct, absolute amplitude of an ultrasound signal in a simulation of a pulse-echo system using equivalent circuits. This is achieved by taking into consideration loss due to diffraction and the effect of the cable that connects the electronics and the piezoelectric transducer. The conductive loss in the transmission line that models the propagation media of the ultrasound pulse is used to model the loss due to diffraction. Results show that the simulated amplitude of the echo follows measured values well in both near and far fields, with an offset of about 10%. The use of a coaxial cable introduces inductance and capacitance that affect the amplitude of a received echo. Amplitude variations of 60% were observed when the cable length was varied between 0.07 m and 2.3 m, with simulations predicting similar variations. The high precision in the achieved results show that electronic design and system optimization can rely on system simulations alone. This will simplify the development of integrated electronics aimed at ultrasound systems. 相似文献
5.
Forward-viewing CMUT arrays for medical imaging 总被引:3,自引:0,他引:3
Demirci U Ergun AS Oralkan O Karaman M Khuri-Yakub BT 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2004,51(7):887-895
This paper reports the design and testing of forward-viewing annular arrays fabricated using capacitive micromachined ultrasonic transducer (CMUT) technology. Recent research studies have shown that CMUTs have broad frequency bandwidth and high-transduction efficiency. One- and two-dimensional CMUT arrays of various sizes already have been fabricated, and their viability for medical imaging applications has been demonstrated. We fabricated 64-element, forward-viewing annular arrays using the standard CMUT fabrication process and carried out experiments to measure the operating frequency, bandwidth, and transmit/receive efficiency of the array elements. The annular array elements, designed for imaging applications in the 20 MHz range, had a resonance frequency of 13.5 MHz in air. The immersion pulse-echo data collected from a plane reflector showed that the devices operate in the 5-26 MHz range with a fractional bandwidth of 135%. The output pressure at the surface of the transducer was measured to be 24 kPa/V. These values translate into a dynamic range of 131.5 dB for 1-V excitation in 1-Hz bandwidth with a commercial low noise receiving circuitry. The designed, forward-viewing annular CMUT array is suitable for mounting on the front surface of a cylindrical catheter probe and can provide Doppler information for measurement of blood flow and guiding information for navigation through blood vessels in intravascular ultrasound imaging. 相似文献
6.
Patton C.A. Harris G.R. Phillips R.A. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1994,41(3):353-359
As part of the section 510(k) requirements of the 1976 Medical Device Amendments to the Federal Food, Drug, and Cosmetic Act, manufacturers of diagnostic ultrasound devices submit acoustic output data to the U.S. Food and Drug Administration. Because this information is pertinent to the assessment of any potential bioeffects due to ultrasound exposure, we have summarized the measurement data processed during 1990 and 1991. Exposure data were summarized for real-time B-mode and M-mode, general pulsed Doppler, peripheral vascular (PV) pulsed Doppler, and color flow Doppler. Exposure quantities included peak rarefactional and compressional pressures, spatial-peak pulse-average and spatial-peak temporal-average intensities (both water and derated values), and power. Also, where data permitted, mechanical and thermal indices were calculated. Ranges, means, medians, and standard deviations were categorized for the exposure quantities and indices. In general the temporal-average values (including indices) were higher in Doppler modes than in B/M imaging modes. Differences among the temporal-peak exposure quantities and indices were less distinct, although values tended to be higher in the PV and color flow Doppler categories. These data, along with comparable results collected by others, provide a means to relate the output of current devices to levels of exposure relevant to ultrasound induced biological effects 相似文献
7.
Corbett SS 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1988,35(2):162-167
Miniature polyvinylidene fluoride (PVDF) hydrophones used in determining the power and intensity output of ultrasonic fields, including those radiated from diagnostic ultrasound equipment, were calibrated under a variety of field conditions using the planar scanning technique. A diagnostic B-scan piston-type transducer was used as a source, and the output intensity (spatial-peak pulse-average, or SPPA) was varied from 2 to 30 W/cm(2) while the total power was kept constant. The higher-intensity waveforms were significantly nonlinear in the focal region of the source. When the lateral beam profiles of the source (as measured by the hydrophone to be calibrated) were determined by positive-peak-detecting the ultrasonic pulse, the calibrated pressure sensitivity of the hydrophone systematically decreased as the field became progressively more nonlinear. When the beam profiles were measured using the pulse intensity integral, no systematic dependence of the calibration on field linearity was noted. These results imply that measured values of power and intensity of ultrasound diagnostic equipment may be dependent on the methodology utilized to map the lateral beam profiles of the transducer being measured, and the extent of nonlinear effects in the field under characterization. 相似文献
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Design and evaluation of a feedback based phased array system for ultrasound surgery 总被引:2,自引:0,他引:2
Daum DR Buchanan MT Fjield T Hynynen K 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1998,45(2):431-438
A driving system has been designed for phased array ultrasound applicators. The system is designed to-operate in the bandwidth 1.2 to 1.8 MHz, with independent channel power control up to 60 W (8 bit resolution) for each array element. To reduce power variation between elements, the system utilizes switching regulators in a feedback loop to automatically adjust the DC supply of a class D/E power converter. This feedback reduces the RF electrical power variation from 20% to 1% into a 16 element array. DC-to-RF efficiencies close to 70% for all power levels eliminates the need for large heat sinks. In addition to power control, each channel may be phase shifted 360 degrees with a minimum of 8 bit resolution. To ensure proper operation while driving ultrasound arrays with varying element sizes, each RF driving channel implements phase feedback such that proper phase of the driving signal is produced either at the amplifier output before the matching circuitry or after the matching circuitry at the transducer face. This feedback has been experimentally shown to increase the focal intensities by 20 to 25% of two tested phased arrays without array calibration using a hydrophone. 相似文献
10.
Zeqiri B Gélat PN Barrie J Bickley CJ 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2007,54(11):2318-2330
This paper describes a new thermally based method of monitoring acoustic output power generated by ultrasonic transducers. Its novelty lies in the exploitation of the pyroelectric properties of a thin membrane of polyvinylidene fluoride (PVDF). The membrane is backed by a thick layer of polyurethane rubber that is extremely attenuating to ultrasound, with the result that the majority of the applied acoustic power is absorbed within a few millimeters of the membrane-backing interface. Through the resultant rapid increase in temperature of the membrane, a voltage is generated across its electrodes whose magnitude is proportional to the rate of change of temperature with respect to time. Changes in the pyroelectric voltage generated by switching the transducer ON and OFF are related to the acoustic power delivered by the transducer. Features of the technique are explored through the development of a simple one-dimensional model. An experimental evaluation of the potential secondary measurement technique is also presented, covering the frequency range 1 to 5 MHz, for delivered powers up to a watt. Predictions of the sensor output signals, as well as the frequency dependent sensitivity, are in good agreement with observation. The potential of the new method as a simple, rapid means of providing traceable ultrasonic power measurements is outlined. 相似文献
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Martin K 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1988,35(2):140-145
Current national and international standards for the measurement of acoustic output parameters of diagnostic medical ultrasound devices rely for their strict implementation on the ability to measure pulse intensity integral or pressure squared integral. A relatively inexpensive measurement system that utilizes a calibrated hydrophone in conjunction with a thermal RMS device is described. It is shown that this system can be used to locate maximum pulse average parameters in static beam devices and true maximum temporal average parameters in complex real-time diagnostic systems. The advantages of the system are discussed and measurement uncertainties are assessed. 相似文献
13.
Gammell PM Harris GR 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2003,50(12):1722-1728
Two high-voltage pulser designs are presented that offer advantages in some ultrasound measurement applications, such as driving thick ultrasonic source transducers used for broadband measurements of attenuation or hydrophone frequency response and directivity. The pulsers use integrated gate bipolar transistors (IGBTs) as the switching devices, and in one design an output voltage pulse is produced that has a peak amplitude nearly twice that of the supply voltage. The pulsers are inexpensive and relatively easy to construct. The power supply need only provide the average current to charge the capacitors, as opposed to the much higher peak pulse current. With a 1200 V supply and a pulse repetition frequency of 200 Hz, the nondoubling and doubling pulsers provided peak voltages of greater than 1100 V and 2200 V, respectively, into loads ranging from 50 /spl Omega/ to 500 /spl Omega/. For a 50 /spl Omega/ load, slewing rates of 38 V/ns and 23 V/ns were measured for the nondoubling and doubling pulsers, respectively. For a 500 /spl Omega/ load these values were 56 V/ns and 36 V/ns. 相似文献
14.
Fuller MI Blalock TN Hossack JA Walker WF 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2007,54(1):79-86
The problem of protecting or isolating extremely sensitive receive circuitry from high-voltage transmit circuitry is commonly addressed through the use of diode bridges, transformers, or high-voltage switches, which prove to be prohibitively expensive, bulky, and power consuming for use in portable, low-cost, battery-powered systems. These approaches also compound the interconnect difficulties associated with two-dimensional (2-D) transducer arrays. In this paper we present a novel transmit protection scheme that allows compact MOSFET shunting devices to be brought on-chip within each receive channel implemented in a standard CMOS integrated circuit process. During transmit, the high voltage transmit pulse is driven onto the common connection of the transducer array and the on-chip MOSFET devices shunt the current to ground. During receive, these devices are turned off, the common connection of the transducer array is shunted to ground, and the received echo can be detected as usual. The transmit protection scheme was experimentally shown to shunt a 16 mA peak current resulting from the equivalent of a 100-V, 25-ns-risetime transmit pulse through a 4 pF transducer element. The scheme was also incorporated into a prototype 1024-channel, low-cost, ultrasound system successfully used to form pulse echo images. 相似文献
15.
Ultrasound has wide applications in medical instruments for both diagnostic and therapeutic purposes. As medical ultrasound is being used on human bodies, it is particularly important that the output power level must be well known for safety reasons. To meet this increasing need, we have realized a medical ultrasound power measurement system based on radiation force balance method. In this paper, we will discuss the system set-up in the National Metrology Centre (NMC), Agency for Science, Technology and Research (A*STAR), Singapore and the uncertainty evaluation of this system. 相似文献
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Park J Hu C Li X Zhou Q Shung KK 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2012,59(4):825-832
Linear power amplifiers are critical components in ultrasonic imaging systems that implement chirp-coded excitation. Bench-top commercial power amplifiers are usually used in academic laboratories for high-frequency ultrasound imaging, and the imaging performance depends greatly on these general-purpose instruments. To achieve a wide dynamic range, a power amplifier consisting of two stages is developed for chirp-coded ultrasound imaging applications through the implementation of custom-designed broadband 1:1 transformers and the optimization of feedback circuits. The amplifier has broad bandwidth (5 to 135 MHz), maintaining a linearity up to the 1-dB gain compression point (P1dB) of 41.5 dBm, allowing 16 dBm input power level at 60 MHz. The mean and the maximum values of output third-order intercept points (OIP3) are 51.8 and 53.5 dBm, respectively, between 20 and 110 MHz. With 12 dBm input power, the gain of the amplifier varies between 24 and 29 dB, offering a uniformity which would allow excitation of a 70-MHz single-element transducer with windowed chirp-coded bursts sweeping from 40 to 100 MHz. The performance in high-frequency ultrasound imaging is evaluated with a wire phantom. Echo signal-to-noise ratio (eSNR) of the designed amplifier is 7 dB better than a commercial amplifier, and spatial resolution is maintained. 相似文献
18.
Chao CY Ashkenazi S Huang SW O'Donnell M Guo LJ 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2007,54(5):957-965
Polymer microring resonators are demonstrated as high-frequency, ultrasound detectors. An optical microring resonator consists of a ring waveguide closely coupled to a straight bus waveguide, serving as light input and output. Acoustic waves irradiating the ring induce strain, deforming the waveguide dimensions and changing the refractive index of the waveguide via the elasto-optic effect. These effects modify the effective refractive index of the guided mode inside the waveguide. The sharp wavelength dependence of the microring resonance can enhance the optical response to acoustic strain. Such polymer microring resonators are experimentally demonstrated in detecting broadband ultrasound pulses from a 50 MHz transducer. Measured frequency response shows that these devices have potential in high-frequency, ultrasound detection. Design guidelines for polymer microring resonators forming an ultrasound detector array are discussed. 相似文献
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DF Lemmerhirt X Cheng R White CA Rich M Zhang JB Fowlkes OD Kripfgans 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2012,59(7):1521-1536
As ultrasound imagers become increasingly portable and lower cost, breakthroughs in transducer technology will be needed to provide high-resolution, real-time 3-D imaging while maintaining the affordability needed for portable systems. This paper presents a 32 x 32 ultrasound array prototype, manufactured using a CMUT-in-CMOS approach whereby ultrasonic transducer elements and readout circuits are integrated on a single chip using a standard integrated circuit manufacturing process in a commercial CMOS foundry. Only blanket wet-etch and sealing steps are added to complete the MEMS devices after the CMOS process. This process typically yields better than 99% working elements per array, with less than ±1.5 dB variation in receive sensitivity among the 1024 individually addressable elements. The CMUT pulseecho frequency response is typically centered at 2.1 MHz with a -6 dB fractional bandwidth of 60%, and elements are arranged on a 250 μm hexagonal grid (less than half-wavelength pitch). Multiplexers and CMOS buffers within the array are used to make on-chip routing manageable, reduce the number of physical output leads, and drive the transducer cable. The array has been interfaced to a commercial imager as well as a set of custom transmit and receive electronics, and volumetric images of nylon fishing line targets have been produced. 相似文献