Impedance analysis of ultrasonic probe

We know that normal people can hear the sound frequency range is 20hz~20khz, ultrasound is the sound frequency of more than 20KHz voice signal, avoid the human ear can hear the sound signal, so that the ultrasound has a strong anti-jamming ability.

The easiest way to do this is to use a network analyzer, two port pairs, to give directly | The curve of the z|~f change. But the network analyzer is too expensive. Unless the big company otherwise generally can't afford, there is another way is to take the circuit themselves. Measured with a sine wave signal generator. The following is the measured method of the circuit (this part of the method and test data from the network article "Ultrasonic Measuring Distance module").

Ultrasound

At last, the matching impedance values of two different frequencies are given in the experiment. Ohm's law is also met in nonlinear circuits. Only the resistance is replaced by the impedance. "Ohm's law is a great discovery,"

The transmitting distance of ultrasonic and the energy p=u^2/| of ultrasonic probe Z| about, the distance ultrasonic distance of course hope is: under the same voltage. The smaller the impedance of the ultrasonic probe, the better.

Since 40KHz and 51KHz are two low peaks of impedance matching resonance, the corresponding minimum point of the impedance, which is why the market for ultrasound is generally used 40KHz (40KHz resonant point changes relative to the 51KHz flat. When there is a small deviation in the driving frequency, the effect on the output is less than 50KHz. As can be seen from the above curve, it is assumed that the circuit agrees that the ultrasonic distance from the 51KHz will be farther (lower impedance than 40KHz).

Because of the production of ultrasonic emitter, the resonant frequency is not necessarily accurate 40KHz and 51KHz, there will inevitably be errors. The best approach is to use a vector network analyzer to directly measure | z| _{F-curve, using | The resonant frequency measured by the z|f.}

I purchased the resonant frequency point of the transceiver ultrasonic probe at 51.48KHz.

The correction after testing

Through the design circuit test found that in the vicinity of 51KHz, the signal received by ultrasound is very weak, but the signal received near 40KHz is very strong.

The above analysis concludes-assuming that the circuit agrees, using 51KHz to make the ultrasonic distance farther away-there is a problem.

Make for example the following corrections:

Because the 51KHz only considers the gain of the transmitter side. The overall signal reception situation is Gain (total) =gain (TX) *gain (Reception). When the emission gain is very large at 51KHz. At 51KHz, the gain at the receiving end is very small. Finally, the gain (total) is very small. The joint test is received by transmitting (using the signal generator to adjust the frequency manually). At the end of the 40KHz (in order to obtain a more detailed ultrasonic probe 39.5KHz) time gain (total) maximum.

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Impedance analysis of ultrasonic probe