Transducer Excitation Research Articles

Duplex ultrasonic imaging system with repetitive excitation of common transducer in Doppler modality

A duplex imaging system with a common transducer array for both modes of operation satisfies the conflicting bandwidth requirements by single impulse excitation of the transducer in B-scan imaging operation to generate a wide bandwidth ultrasound pulse and multiple impulse excitation at the emission frequency in Doppler mode operation to generate a narrow bandwidth ultrasound phase. The multiple impulse excitation has a variable repetition frequency depending on range to a sample volume and velocity of blood flow. A Doppler modality, in which the frequency shift of echoes caused by flow of blood is measured to derive the flow velocity, is incorporated into a sector scanner with little additional complexity.

Application of air-borne ultrasound to biomedical measurements.

Remote measurement of distance, direction, size, form and volume are common but intricate measurement problems. We have applied the ultrasound pulse echo method, well-known from diagnostic ultrasound, for remote measurement in air. Short ultrasound pulses are emitted in air by electric excitation of an ultrasound transducer. When the ultrasonic wave is incident on a boundary between media of different acoustic impedance, part is reflected back as an echo. The time delay between transmission of the ultrasound pulse and the reception of an echo is a measure of the distance between the transducer and the echo-generating structure. The information obtained can be processed in different ways to produce the three main types of display: A-mode, B-mode and TM-mode. As a consequence most methods from diagnostic ultrasound can be applied also for ultrasound in air. Examples are given of biomedical applications, including a real-time ultrasound scanner for use in air.

FET pulse generator for ultrasonic pulse echo applications

Ultrasonic NDT applications are frequently based on the spike excitation of piezoelectric transducers by means of efficient pulsers which usually include a power switching device (e.g. SCR or MOS-FET) and some rectifier components. In this paper we present an approximate frequency domain electro-acoustic model for pulsed piezoelectric ultrasonic transmitters which, by integrating partial models of the different stages (driving electronics, tuning/matching networks and broadband piezoelectric transducer), allows the computation of the emission transfer function and output force temporal waveform. An approximate frequency domain model is used for the evaluation of the electrical driving pulse from the spike generator. Tuning circuits, interconnecting cable and mechanical impedance matching layers are modeled by means of transmission lines and the classical quadripole approach. The KLM model is used for the piezoelectric transducer. In addition, a PSPICE scheme is used for an alternative simulation of the broadband driving spike, including the accurate evaluation of non-linear driving effects. Several examples illustrate the capabilities of the specifically developed software.

Mobility of high impedance structures

There are a number of ways of measuring mechanical mobility which are commonly used today. These involve differences primarily in transducer instrumentation, excitation signal, and data processing. As part of the author's doctoral research, a number of mechanical mobility measurements were made on a cast iron engine block. The techniques chosen for mobility measurement are strongly influenced by the structures to be studied. The techniques chosen by the author are presented. An unusual technique for measuring the impedance head stiffness is discussed in detail. Examples are given demonstrating reciprocity and reproducibility of data. Some applications of the mobility measurements are presented.

Electric excitation of ultrasound transducers for short pulse generation

A method for the generation of short ultrasound pulses by a piezoelectric transducer is presented. The method uses various combinations of voltage steps which are applied to the transducer as excitation pulses. Compared with conventional excitation used in echo systems this results in an appreciable shortening of the received signal. A qualitative explanation of the results obtained is given.

Analytical representation of transient ultrasonic phased-array near- and far-fields

The present contribution provides a method for the derivation of analytical near- and far-field expressions for the pressure step-function response of nonuniformly excited ultrasonic transducers modeled as pistons of arbitrary shape in an infinite rigid baffle. Explicit inversion of the Laplace transformed ultrasonic field using Cagniard's idea results in elementary functions or definite integrals of elementary functions, depending on the assumed nonuniform aperture distribution. The basic signal distortion is illustrated in terms of three-dimensional space-time plots of the pressure unit step-function response of a rectangular uniform aperture. The corresponding results for a phased-array transducer are also given. In addition, we investigate the pressure profile on the axis perpendicular to a uniform rectangular piston and its horizontal radiation pattern for different bandwidths of the exciting impulse.

Generation characteristics of SAW in the excited IDT

By utilizing the optical diffraction produced by acousto‐optical interaction, the generation characteristics of SAW in the excited interdigital transducer may be observed directly and measured quantitatively. Both the method of dark field imaging and that of simple optical probing have been used. The periodic IDT and LFM IDT deposited on the substrates of YZ‐LiNbO3 have been investigated. For the periodic IDT, the experimental investigations show that the SAW generation characteristic are of symmetric growth in both emission directions of the excited IDT, but in the case of LFM IDT, the experimental results indicate asymmetric. Observations of the latter will be described and discussed in some length. Theoretical calculations have been made and their comparison with experimental data are presented. As concluding remarks, it is pointed out that all the intensities (or power flux) of SAW under investigation are represented both in theory and in experiment by the intensities of the superposition of two‐direc...

Theory for magnetostatic forward volume wave excitation

The present paper reports a theory for the excitation of magnetostatic forward volume waves (MSFVW’s) in YIG films by the most basic of all transducers, viz., an electric line current source, and various ramifications thereof (microstrip, meander-line and grating couplers). Expressions for power in the MSFVW’s excited by these transducers are derived, and computations of the transducer excitation characteristics are presented. It is found that all transducers yield a significant excitation of higher-order MSFVW’s, with the best suppression of these modes provided by the single microstrip coupler.

New method for wideband excitation of interdigital surface-wave transducers

A new method of designing coupled resonator networks for wideband excitation of interdigital surface-wave transducers is described. The elements of the tuning network are chosen, using an optimisation computer program. The insertion loss is minimised over the bandwidth of interest. For interdigital transducers on a monolithic zinc-oxide-on-silicon structure with Δv/v = 0.0036, a fractional bandwidth of 20% can be obtained. For a narrow-acoustic-beam interdigital transducer on a LiNbO3 halfspace with Δv/v = 0.022, a fractional bandwidth of 40% can be obtained. The design of the coupled resonator network takes into consideration the variation of the transducer acoustic impedance with frequency.

Force and electrical Thevenin equivalent circuits and simulations for thickness mode piezoelectric transducers

A simple model is reported for thickness-mode piezoelectric elements used as ultrasonic transducers in measurement systems. The model represents the excitation system and transducer as a Thevenin mechanical equivalent for the transmitting mode and a Thevenin electrical equivalent for the receiving mode. Computer programs based on the model have been developed, and computer simulations to study the effects of backing materials, element areas, and excitation sources are reported. The nature in which the source impedance alters the Thevenin mechanical output impedance and its importance in determining peak transmission frequency and in computing acoustic coating layers for matching was found. A total transfer improvement of 28 dB was shown for epoxy-backed elements radiating into fluid with the transducer used as both transmitter and receiver by using high values of source and load impedances in contrast to low values. The model was found to agree closely with experimental data of a 2.7-MHz transducer. Subject Classification: 85.40; 80.70; 85.52.

Orthogonal excitation of magnetostrictive transducers

A piston-type magnetostrictive transducer consisting of a scroll-wound tube 12 in. long, 1.25 in. in diameter, and of 0.125-in. wall thickness was constructed from 0.008-in. Nickel 200 sheet and fitted with toroid-wound and solenoid-wound drive coils. This prototype device was evaluated using both conventional and orthogonal modes of excitation. Electrical impedance measurements at low drive levels showed an increase in the electromechanical coupling coefficient with orthogonal excitation. Power tests were conducted with output power levels up to 50 W/cm2 of active core area by driving the piston into a tuned ceramic dummy load. Device efficiency in excess of 50% was obtained at 5 W/cm2 output power. As the output power was increased, orthogonal excitation consistently provided higher efficiency and linearity than conventional excitation. Device linearity improved with increasing drive level for the orthogonal tests. Self-biased excitation was obtained by driving the two coils plus a pair of diodes in parallel. For self-biased excitation, device efficiency increased with drive level exceeding 30% at 40 W/cm2 output power. These results confirm the earlier theoretical predictions [J. Acoust. Soc. Am. 55, No. 5 (1974)] for orthogonal excitation.

Pulsed excitation of transducers

Results from field measurements of sound propagation from an approximate point source over grass covered ground are shown. The experimental data are compared with theoretical predictions of the sound pressure levels. The theoretical results are based upon different ground models for which local reaction within the ground is assumed. The ground models used are the one parameter model which was originally suggested by Delany and Bazley [1, 2] and later taken up by Chessell [3], the four parameter porous layer model proposed by Thomcasso [4], and a two parameter porous layer model which is proposed in this paper. The possibility of extended reaction properties in the ground is also touched upon.

Pulsed excitation of transducers: Kanevskii, I.N., Soviet physics—acoustics, vol 15, no 1 (July–September 1969) pp50–53

Pulsed excitation of transducers: Kanevskii, I.N., Soviet physics—acoustics, vol 15, no 1 (July–September 1969) pp50–53

Frequency response of an interdigital transducer for excitation of surface elastic waves: Tseng, C.C. IEEE Transactions on Electron Devices, Vol ED-15, No 8 (August 1968) pp 586–594 (958)

The Multisensor Glucose Monitoring System (MGMS) features non invasive sensors for dielectric characterisation of the skin and underlying tissue in a wide frequency range (1 kHz–100 MHz, 1 and 2 GHz) as well as optical characterisation. In this paper we describe the results of using an MGMS in a miniaturised housing with fully integrated sensors and battery.Six patients with Type I Diabetes Mellitus (age 44 ± 16 y; BMI 24.1 ± 1.3 kg/m2, duration of diabetes 27 ± 12 y; HbA1c 7.3 ± 1.0%) wore a single Multisensor at the upper arm position and performed a total of 45 in-clinic study days with 7 study days per patient on average (min. 5 and max. 10). Glucose changes were induced either orally or by i.v. glucose administration and the blood glucose was measured routinely. Several prospective data evaluation routines were applied to evaluate the data. The results are shown using one of the restrictive data evaluation routines, where measurements from the first 22 study days were used to train a linear regression model. The global model was then prospectively applied to the data of the remaining 23 study days to allow for an external validation of glucose prediction. The model application yielded a Mean Absolute Relative Difference of 40.8%, a Mean Absolute Difference of 51.9 mg dL−1, and a correlation of 0.84 on average per study day. The Clarke error grid analyses showed 89.0% in A + B, 4.5% in C, 4.6% in D and 1.9% in the E region.Prospective application of a global, purely statistical model, demonstrates that glucose variations can be tracked non invasively by the MGMS in most cases under these conditions.

Frequency response of an interdigital transducer for excitation of surface elastic waves

Excitation of elastic waves in a piezoelectric solid by an interdigital transducer, in terms of a simplified model, has been analyzed using Lamb's integral solution. The transducer generates three types of disturbances propagating at the velocities of irrotational, equivoluminal, and Rayleigh waves. While the amplitudes of the former two waves diminish as the three-half power of the distance from the transducer, that of the latter does not decay with distance on the surface. Dependence of particle displacement of the waves on electric fields, number of electrodes, electrode width, and wave numbers has been derived. It has been shown that a conventional interdigital transducer, in which all the electrode widths and all the spacings are respectively equal among themselves, can respond to fundamental and odd harmonic excitations, but not to the even harmonics. Means to improve the insertion loss and the bandwidth of the transducer are discussed. A flat overall frequency response can be synthesized by parallel operation of two or more transducers, the fundamental frequencies of which are properly staggered.

Instrumentation for Ultrasonic Studies at Frequencies from 0.2 to 2.0 GHz

Instrumentation for ultrasonic pulse-echo experiments in the frequency range of 0.2 to 2.0 GHz is described. The apparatus includes a conventional pulsed rf transmitter, superheterodyne receiver, and tunable resonant cavity. Microwave diode switches are employed in single-ended operation of the equipment. A simple technique for the excitation of acoustic transducers with stripline is described. Additionally, a detection system is presented which utilizes correlation techniques for the recording of acoustic signals with an enhanced signal-to-noise ratio.

Pulsing Technique for Studying Cavitation Erosion of Metals

Abstract A technique is described in which materials are exposed to cavitation in an intermittent, periodic manner by applying pulsed excitation of a magnetostrictive transducer. Such pulsed cavitation is proposed as a means to overcome the extremely accelerated nature of the usual laboratory procedure for the study of cavitation damage properties of materials. Specimens under study are subjected to oscillating accelerations in the cavitating liquid, and the oscillation amplitude is modulated so that cavitating interval can be made any desired fraction of total period. Materials tested were mild steel, 4340 steel, Inconel X and 17-7 PH stainless steel. All except mild steel were also tested in a hardened condition. When pulsed and steady cavitation were compared in a chemically inert liquid (toluene) with an inert gas environment (helium), no significant difference in cavitation damage rate was observed. It was concluded that the pulsed cavitation technique provides a significant method for studying cavit...

Maximum Directivity Index and Efficiency of Linear Arrays

The maximum directivity index of a symmetrical, linear array has been calculated as a function of the number and spacing of the elements in the array. Data so obtained make it possible to design an array to yield a specified value of the maximized directivity index. In general, the directional response patterns of such arrays do not have minor lobes of equal, nor of small, amplitude, although the minor lobes are sometimes smaller than for a uniformly excited array. Except for arrays comprising elements spaced an integral number of half-wave-lengths, the maximum directivity index exceeds that for a uniform array. For element spacings exceeding a half-wave-length, the difference is slight, but as the spacing is progressively decreased, the improvement becomes more significant but is finally obtained at the expense of requiring large, out-of-phase excitation. In an effort to evaluate the practicability of using such “super-directive” arrays, expressions have been derived for the sound transmission efficiency of the array, and the electrical power available in sound reception, as a function of the manner of excitation and type of transducers comprising the array.