Terminals Of Transducer Research Articles

Acousto-optic Modulation of Terahertz Radiation in Liquefied Sulfur Hexafluoride at Room Temperature

Acousto-optic modulation of terahertz free-electron laser radiation was investigated using diffraction on an acoustic wave in liquefied sulfur hexafluoride at room temperature. At the wavelength 130 μ m, the diffraction efficiency in Bragg regime of interaction 1% was obtained at 75 V driving electrical signal applied to the transducer terminals.

Beam diffraction effects in sound transmission of a fluid-embedded viscoelastic plate at normal incidence.

The characteristics of a sound beam transmitted through a fluid-embedded viscoelastic plate at normal incidence can deviate significantly from those of a plane-wave. Phenomena such as frequency shift, signal amplification or reduction, and changed beam properties, are observed for resonance peaks associated with specific leaky Lamb modes. When interpreting measurements using plane-wave theory, such deviations will influence the measurement of material parameters and plate thickness. The finite-element-based models used in this study describe the signal chain from the electrical voltage excitation at the piezoelectric transducer terminals to the sound pressure propagated through the plate and fluid to the position at which it is measured by a hydrophone. The measured phenomena are described at a quantitative level.

Adaptive Stabilization of Electro-Dynamical Transducers

A new control technique for electro-dynamical transducer is presented which stabilizes the voice coil position, compensates for nonlinear distortion and generates a desired transfer response by preprocessing the electrical input signal. The control law is derived from transducer modeling using lumped elements and identifies all free parameters of the model by monitoring the electrical signals at the transducer terminals. The control system stays operative for any stimulus including music and other audio signals. The active stabilization is important for small loudspeakers generating the acoustical output at maximum efficiency.

Design optimization of an out-of-plane gap-closing electrostatic Vibration Energy Harvester (VEH) with a limitation on the output voltage

This paper presents a simple analytical method to optimize the efficiency of an electrostatic out-of-plane gap-closing (OPGC) Vibration Energy Harvesters (VEH). For the first time the electrical and mechanical behaviours of the transducer are addressed simultaneously, while a voltage limitation on the transducer's terminals is set to prevent any damage in the conditioning electronic. The presented work allows to the designer to determine the best strategy depending on whereas the system is passive or able to be self-adapted to the external vibrations parameters. The optimization is performed for a 1 cm² device made of bulk silicon to be fabricated using a batch MEMS process. Up to 15 μW can be obtained at 200 Hz if the output voltage is limited to 60 V. The calculations are validated by VHDL-AMS/ELDO simulations.

Evaluation of Impedance Matching Schemes for Pulse-Echo Ultrasonic Piezoelectric Transducers

In order to optimize the broadband response of a piezoelectric transducer, different impedance matching procedures are used, looking for a compromise between efficiency and bandwidth. In this paper a general methodology for the evaluation of acoustic and electrical matching schemes is presented. Broadband acoustic impedance matching schemes are evaluated in the frequency domain using the transmission line analogy. Electrical matching networks at the reception stage are evaluated using the transmission matrix approach. In practical cases of ultrasonic imaging and NDE, electronic "spike" generators based on capacitive discharges are used. The special topology of such generators (including semiconductor devices) conditions the electrical driving pulse at the transducer terminals. This driving waveform (determined by the interactions among the spike generator, the electrical matching network and the transducer) is approximately evaluated in the frequency domain for the low Megahertz range. Several examples in emission and reception illustrate the methodology, including a comparative study of criteria proposed for the optimum design of quarter-wave transmission line matching layers.

Electroacoustic energy converter for transformation between thermal and electrical energy

Electroacoustic converter for transformation between thermal and electrical energy, comprising working chamber filled with working medium, piezoelectric transducer, acoustic filter and source of gaseous substance to be supplied into working chamber under pressure. Combustion of gaseous substance causes its pulsation accompanied by emitting acoustic waves, which being transmitted via working medium to said transducer are converted into electrical signals. The signals can be released from the electrical terminals of transducer. The same device can function in opposite direction in the sense that it converts the supplied to transducer electrical energy into acoustical waves which being emitted by the transducer are transferred through the working medium to the gaseous stream. This process is accompanied by adiabatic heating and cooling of the stream and thus transferring of electrical energy into heat energy takes place while converter operates as a heat machine.

Measurement of microphone membrane displacement with an optical beam deflection technique

Optical beam deflection is a simple and reliable method for the detection of small displacements. This paper describes its application to the measurement of the displacement of the membrane of a condenser microphone, where the displacement is induced by supplying an alternate voltage to the transducer terminals. A sensitive reconstruction of the dynamic deformation of a microphone membrane in a wide frequency range is obtained.

A frequency-tracking dynamic absorber with and without feedback

A dynamic absorber can be combined with a transducer to shift the antiresonant frequency by inserting an electrical element across the transducer terminals. For a disturbance with a slowly varying frequency, tracking can be effected by means of, e.g., a digital logic circuit that estimates the frequency, assigns it to a certain frequency interval, selects a corresponding interval, and selects a corresponding electrical termination to put across the transducer. At any given frequency setting, the total Q is high to obtain good suppression, thus running the chance of creating an “ear” in the frequency response. This effect can be reduced by suitable filters, shunting all or part of the electrical termination. A means, involving a special “broadband” termination, can extend the range of suppression without sacrificing Q at any frequency in the range. A composite device utilizes both a dynamic absorber (even the frequency-following kind) and a negative feedback velocity control. A brief comparison will be made among the several types indicated, as well as with standard active vibration controls.

Theory of transit time ultrasonic flowmeters

A theory of transit time ultrasonic flowmeters for clean fluids is developed from the equations of fluid mechanics applied simultaneously to the fluid and the sound vibrations. These equations are linearized (weak sound) and use is made of the electroacoustic reciprocity theorem to give a relation between the voltages and currents at the transducer terminals and the fluid velocity. The technique of “reciprocal operation” of a transit time ultrasonic flowmeter is described and the way this technique eliminates zero drift is explained. The theory can be applied to meters with broad sound beams (which provide a better average over velocity profiles) or meters in which the wavelength of sound is not necessarily small compared with the duct diameter. Small modificaition of the sound field (due to flow) is assumed and the resulting phase (or amplitude) shift of the received signal is expressed as an integral throughout the fluid of the dot product of the fluid velocity and a weight vector defined in terms of the sound fields in the stationary fluid. Simple flowmeter designs which approach the ideal of complete immunity to velocity distribution are described.

Transmission of Ultrasound Through Living Human Thorax

Experiments are described demonstrating the passage of one-mc/sec continuous wave ultrasound through the heart and lungs at power levels of 100 mw/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at the transducer terminals (a total of 1.25 watts). When the sound was directed through the region of the heart, the ultrasound was modulated by the moving intra-thoracic structures in synchronism with the heart beat. The records obtained were modified both by exercise and by amyl nitrite administered to the subject, but remained synchronous with the heart rate. Modulation of the ultrasound did not occur in two warm corpses. Sonic energy at the levels used to traverse the thorax did not affect a simultaneously recorded electrocardiogram. No deleterious effects have been observed on a subject whose heart was irradiated at 1 watt/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 3 watts/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (totals of 12.5 and 37.5 watts, respectively) applied to transducer terminals at intervals over a period of one year (Appendix I). When continuous wave ultrasound was directed through a lung field clear of the heart, it was found that the attenuation varied 50 db between full inspiration and a lung emptying of 3400 cubic cm (0 db = full inspiration). In addition to direct transmission, sound is scattered throughout the thorax. The mechanics of the ultrasonic phenomena are described.