Thermally induced ultrasonic emission from porous silicon

Abstract

The most common mechanism 1 for generating ultrasound in air is via a piezoelectric transducer, whereby an electrical signal is converted directly into a mechanical vibration. But the acoustic pressure so generated is usually limited to less than 10 Pa, the frequency bandwidth of most piezoelectric ceramics is narrow, and it is difficult to assemble such transducers into a fine-scale phase array with no crosstalk 2,3 . An alternative strategy using micromachined electrostatic diaphragms is showing some promise 4,5 , but the high voltages required and the mechanical weakness of the diaphragms may prove problematic for applications. Here we show that simple heat conduction from porous silicon to air results in high-intensity ultrasound without the need for any mechanical vibrational system. Our non-optimized device generates an acoustic pressure of 0.1 Pa at a power consumption of 1 W cm −2 , and exhibits a flat frequency response up to at least 100 kHz. We expect that substantial improvements in efficiency should be possible. Moreover, as this material lends itself to integration with conventional electronic circuitry, it should be relatively straightforward to develop finely structured phase arrays of these devices, which would give control over the wavefront of the acoustic emissions.

Solution for acoustic field of thermo-acoustic emission from arbitrary source

“…1,16 So, when using Eq. (9) to calculate TA emission from a small surface area element dΩ of a TA sample with backing, the corrections of both the heat distribution factor at surface due to backing influence and the directivity due to its hemispherical emission should be taken into account.…”

“…1 Many experimental investigations on this phenomenon and its application were carried out, regarding various aspects of TA ultrasound, such as characteristics, intensification, radiation pressure, three-dimensional image sensing, phased array and impulse operation, and sound reproduction, which show that thermo-acoustic ultrasound has lots of advantages over traditional electric-acoustic ultrasound due to its unique nature −− wideband flat frequency response: larger frequency bandwidth and acoustic pressure, lesser reverberation and distortion, higher sensing accuracy and spatial resolution, easily integrated in MEMs and sound signal self-demodulation, and availability and controllability for finely structured phase arrays operation. [2][3][4][5][6][7][8][9][10][11][12][13] However, theoretical investigation of TA emission seriously lags behind the experimental one due to comparatively fewer efforts.…”

“…[2][3][4][5][6][7][8][9][10][11][12][13] However, theoretical investigation of TA emission seriously lags behind the experimental one due to comparatively fewer efforts. Currently, alomast all the formulas for calculating TA emission so far are one-dimensional, 1,[14][15][16][17]19,22 taking advantage of the plane-wave solution based on the pressure-temperature coupled equations in a fluid given by F. A. McDonald and G. C. Wetsel, Jr., 18 and the problems of near-and far-field TA emission need to be dealt with seperately. The multi-dimensional TA emission problems, e.g.…”

Bringing Silicon to Light: Luminescence in Silicon Nanostructures

“…The intensity of research and development on light emission in Si is increasing as a result of these stimulating advances in materials engineering and technology. It is likely that a Si-based injection laser will emerge from this research in the near future, although the actual active laser material could be none of those discussed here, because of the burgeoning diversification (7,9,10,106,121,146,(153)(154)(155)(156)(157)(158) in Si-based materials and their applications.…”

Determining Ultrasonic Vocalization Preferences in Mice using a Two-choice Playback Test

“…This device is unique in that, unlike common sound generators that depend on mechanical vibrations, it can reproduce sound without the need of a diaphragm. The emitter exhibits a flat sound pressure level at frequencies from 20 to 160 kHz (Figure 2), and can reproduce digitally recorded murine USVs very accurately in terms of duration, frequency, and sound pressure level 15,18,19 .…”