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Images of the suspended wire loudspeaker. (a) Scanning electron microscope image taken near the edge of the wire array. The length of the wires is about , the width is about and the thickness of the Al film is 30 nm. The distance between wires is in this case . The image is taken after measurements and handling outside clean room which is responsible for the impurities seen on the supporting Al. (b) Closeup of the wire supporting crossbar and five Al wires. (c) Photograph of the measurement arrangement inside an anechoic chamber. The round 150 mm wafer is seen in the middle attached to the circuit board.
Principle of operation. [(a) and (b)] Schematic of the time dependence of the applied voltage and resulting temperature and sound pressure variation without (a) and with (b) dc biasing. The black curve is the voltage while the red curve represents temperature or pressure. (c) Schematic instantaneous temperature profiles at the temperature extrema. RT stands for room temperature. (d) Measured frequency dependence of the sound pressure of loudspeaker E (with 233 200 suspended wires). Results measured in two different setups are shown. In the 20 kHz bandwidth data indicated by circles and diamonds the dc powers were 0 and 15.5 W, respectively, while the ac power was 1.9 W in both. The 40 kHz bandwidth data indicated by squares were measured two months later without dc power and with an ac power of 9.8 W. The distance to the microphone in the 40 kHz bandwidth case was 8 cm (enhanced online). Video 1 Video 2. [URL: http://dx.doi.org/10.1063/1.3249770.1] [URL: http://dx.doi.org/10.1063/1.3249770.2]10.1063/1.3249770.110.1063/1.3249770.2
Measured frequency responses for the loudspeakers without dc biasing. (a) Results for speaker B at different values of ac driving. The markers from top to bottom correspond to 2.1, 1.2, and 0.56 W. Least-squares fitting to gives and . The solid lines are drawn using the mean values of these parameters. (b) Similar data for speaker C (twice denser wire array). The electrical powers are from top to bottom 7.0, 2.7, and 0.84 W. For this speaker least-squares fitting gives and .
Harmonic ratio for nonzero dc bias voltage . (a) Sound pressure level of the first harmonic against applied frequency. From top to bottom: speaker E with and ; speaker C with and ; speaker B with and . (b) Ratio of the second harmonic to the first harmonic vs applied frequency (i.e., the first harmonic). Top to bottom: speaker C, speaker E, and speaker B. Solid lines are calculated from with .
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