UltraSound Transmitter ?

[Stef Mientki]

hi,

I'm thinking of making a simple 3D location circuit, for multiple target
points.
I've the feeling that Ultrasound is the cheepest and a (quiet) reliable
way to perform that task.
I once saw a system, called "graphbar" (almost 15 years ago), that
performed 2D measurements, in a area of 40*40 cm, with a resolution of
about 0.1 mm (I'm not sure about that, but it was quiet remarkable).

One of the problems with ultrasound seems to make a "wideband" pulse, or
in other words creating a puls with a fast rising edge.
The trick the "graphbar" used was to make sparks over electrodes a few
millimetres apart.

Are there any other ways (and don't like sparks) to create fast rising
ultrasound pulses, with enough power ?
Does anyone know some interesting links about this subject ?

thanks,
Stef Mientki

 

[Dr Engelbert Buxbaum]

Stef Mientki wrote:

hi,
Are there any other ways (and don't like sparks) to create fast rising
ultrasound pulses, with enough power ?

For ultrasound motion detectors I would use a square wave oscillator,
with a suitably sized power amplifier. You can make the oscillator from
two NAND or Schmitt-Trigger CMOS gates. One additional gate acts as
buffer, a fourth one as inverter. The ultrasound transmitter is operated
between the outputs of the 3. and 4. gate. This is not a lot of power,
but enough for survailance of an entire room.

However, an accuracy of 0.1 mm would be hard to achieve with ultrasound,
as the wavelength would have to be in that order of magnitude. With
sound velocity of 360 m/s and wavelength 0.1 mm, frequency would have to
be 360000 mm / 0.1 mm s = 3.6 MHz.

For that sort of accuracy you would probably need radar.