TUSS4440: How to process strong ultrasonic echo?

Hi Guohong,

Thank you for posting to the Sensors forum!

Could you clarify what you mean when you say that the TUSS4440 goes wrong with higher peak-to-peak voltages? Could you describe the behavior that you are seeing? If possible, do you have waveforms that you can share? Also, are you able to share your current register configuration.

Best,

~Alicia

Dear Alicia,

Thank you for your kind attention.

I use the typical application diagram of TUSS4470, not TUSS4440 as described in  the previous post. Where Rinp=3k, Cinp=330p, driving frequency is 88kHz, pulse number is 16

When I put the ultrasonic transducer int he air, the figure on the oscilloscope is as follow,

Ch1 is the trig pulse from microprocessor, Ch2 is the voltage applied to the transducer, Ch3 is Vout of  TUSS4470.

On this situation, TUSS4470 acts magically, although almost noting can be found on CH2 by eye,  Vout  tells the actual distance.

When I put the  transducer in water, as it is designed for,  the figure on the oscilloscope is as follow, while each channel is defined as before

Ch1 and Ch2 behave almost the same as in the air, except echo can be observed on Ch2 by eye. But no echo pulse can be found on Vout.

The configuration of TUSS4470 are the same for both situation, they are

0x0E, // 0 Filter selecting: use factory trim, use BPF, center frequency is 86.89kHz
0x00, // 1 BPF setting: Q=4
0x37, // 2 Log-amp config: user defined parameter, slop_adj=3.3V, Int_adj=2.738
0xC2, // 3 Log-amp config: disable first stage, enable last stage, voltage_scale=3.3V, LAN_GAIN 20V/V
0x4, // 4 Driving_mode=0, pulse_pattern_error_time=48us
0, // 5
45448, // 6 driving Frequency, 88kHz=8*500MHz/45558
0x12, // 7 enable echo interrupt comparator output, compare threshold=0.48V

0x14, // 8 disable zero crossing compare, compare threshold = 230mV
0, // 9
0x50, // 10 disable half-bridge mode, pre-drive, burst_pulses_number=16 (<38)

Hi Guohong,

Thank you for this detailed information. I will need some time to look into it and will aim to provide an update tomorrow.

Best,

~Alicia

Hi Guohong,

Apologies, but I forgot to ask what is the range of measurement that you are trying to target?

The differing results when in water via air isn't really surprising given how these mediums affect ultrasonic performance. The rate of ultrasonic attenuation tends to increase as the medium becomes denser. Air, being less dense than water, allows low-frequency ultrasound to travel farther, when compared to using the same ultrasonic frequency in water. 

Additionally, the speed of sound is also impacted by the transmission medium. Sound travels nearly five times faster in water than through air, which also has an impact on the rate of ultrasonic attenuation. For this reason, high-frequency ultrasound, usually in the hundreds+ kHz range, is more suitable for liquid transmission.

Best,

~Alicia

Hi, Alicia

My target ranging is 2m.

It's true that the mediums density has great influence on ultrasonic behaviour, including speed, attenuation.

As I want to use the same transducer both in the air and water, so a transducer designed for water application is chosen.

All the experimental phenomenon is within expecting. The echo in air is weak, about 1/100 of that in the water. TUSS4470 can process the signal and recognize the distance correctly. Although the echo under water is so strong that the distance information can be read from the waveform, TUSS4470 can not treat this signal properly. This is the key point that confusing me.

I want to make sure the signal processing range of TUSS4470, and how to pre-process the strong signal if necessary before it  feed to TUSS4470.

If there were no way to use TUSS4470 for under water  ranging, any possible solution would be too sophisticated, because two approach should be used at the meantime for air and water.

Hope to get your advise.

Best,

Guohong

Hi Guohong,

What kind of transducer are you using? Is it rated for water? Sometimes transducers are not meant for water applications which could cause it to behave strangely.

Just to be sure, is the transducer mounted to tank properly? And how big is the tank? Depending on its size, the signal could be bouncing around the tank resulting in strange behavior?

Best

~Alicia

This transducer is designed for water application, and rated for water. It is mounted to a small experimental support which is a little big than the transducer, and the reflective plate is large enough. The echo signal seems to be reasonable. 

Hi Guohong,

From your second plot on CH2, are those fluctuations (circled below) echoes or just noise? I would recommend decreasing the number of pulses and disabling the last stage of the log amp to help reduce any noise that you may be seeing.

Also, for water applications, typically the driving frequency is in the order of MHz, so having a frequency of 88kHz may not be high enough. Given that your target range is 2m, I would recommend increasing your driving frequency to at least 500kHz. 

Best,

~Alicia 

Hi Alicia,

Sorry for delayed response, as I'm trying the solution these days.

I think the fluctuations circled on CH2 are echoes.

I have decreased the  pulse number to 8, and disabled the last stage of the log amp, but the result haven't improved, no applicable information can be seen on TUSS4470's Vout.

Maybe, the reflect  signal is too strong for TUSS4470 to process, as it's LNA minimum gain is 10V/V. 

Perhaps I have to find other approach now.

Thank you.

Guohong

Hi Guohong,

I believe that the driving frequency that you are currently using is impacting the results that you are seeing. As mentioned previously, water applications tend to use driving frequencies in the order of MHz, so using 88kHz is not high enough. If possible, I would highly recommend increasing your driving frequency to at least 500kHz to see if that helps.

Best,

~Alicia