Utilizing Unitransducer Ultrasound

Hello,

In a couple of months I am going to need to make a circuit that utilizes a 50W 200khz underwater ultrasound transducer, and I thought it would be wise to get familiar with a 40khz transducer first. I am trying to utilize a lm358 opamp to amplify the signal from the sensor. I am aware that it is probably not the best choice of an op-amp for this application, but I would try to use it if possible.

The MOSFET will deliver the pulses to the transducer and Q2 will serve to route the 12V signals to ground when it is in transmit mode. Why haven't I seen anyone drive a ultrasonic transducer with an h-bridge? Wouldn't it would be the easiest way to get the element to move 2 times better?

If you could glance over the schematic and let me know if you see any major flaws or possible ways to make it better I would appreciate it. If you can't tell it is my first attempt to use op-amps in any sort of circuit, hence that is why I am asking for advice before I make a PCB.

Thanks!

Edit: the two unlabeled resistors on top will be of equal value. Probably 10K or 100K

hi,
Do you plan to use the 200KHz transducer under water or in air?
You will get very little acoustic energy from a 50W 200KHz transducer if you drive it with only 12Volts.

Do you have a part number for the 200KHz transducer, or a picture?
I maybe able to get some techinfo for you.

Looking at your opa's I would check what gain you are expecting, check the
opa negative feedback connections

Regards
Eric

Also, the transducer is capacitve and therefore requires a push-pull driver, a common source switch won't give you much power.

Also that MOSFET is connected up incorrectly, it will be on all the time as (being p-channel) it needs 12V to turn off.

Your PNP transistor is upside-down. Q1 and Q3 don't do anything so what are they for?

Your opamps have positive feedback causing them to latch, instead of negative feedback so they can amplify.

The very old LM358 has a max frequency response with a 15V p-p output of up to only 6kHz. At 40kHz The output would be a low level triangle-wave if the opamps were connected properly.

I agree that the Mosfet won't turn off.

Q1 and Q3 I thought were hooked up in a totem-pole configuration for driving the mosfet at higher frequencies as this guy did with his flyback driver: https://www.electronics-lab.com/projects/misc/016/index.html Is it not required? Or is it that a PIC pin has a similar sort of configuration internally?

I will use something other than a lm358. Would a tl071 or 741 work or will I have to order one with a better gain at 40khz?

Well anyways, I updated the schematic with the stupid backward transistors problem, and the sensor now has a push-pull driver. This again brings me to the question wouldn't an h-bridge be good for driving a ultrasonic transducer because it is similar to a push-pull driver but would give it twice the voltage between peaks?

@ericgibbs: The 200khz will be used underwater and I will definitely drive it with a much higher voltage. Here is the one I was thinking of using:
**broken link removed**
datasheet:
https://www.electro-tech-online.com/custompdfs/2007/07/PROWAVE-undertx.pdf

If you happen to know of any underwater transducers that are cheaper I would definitely be open to using them instead. I am going to stick them in a AUV. One for forward looking sonar to avoid obstacles and one for short range depth finding. I should only need it detect up to 10m because it will be following the bottom. Sidescan would probably be more useful but I can't afford using a kilowatt of power because I want it to go as far as possible. About how many watts do you think I will need to detect up to ten meters?

Thanks guys for the help!

I am glad you got rid of your Mosfet, made the transistors emitter-followers and used the correct negative feedback for the opamps.
But the first opamp needs to be biased at half the supply voltage.

The old 741 opamp has a max frequency response of only 9kHz at 26V p-p. A TL071 has a max frequency response of 100kHz at 26V p-p. Its minimum recommended supply voltage is 7V.

So the TL071 should work? In that case, I wouldn't need to bias because it needs a dual supply.

freeskier89 said:

So the TL071 should work? In that case, I wouldn't need to bias because it needs a dual supply.

Click to expand...

No it doesn't.
Any opamp can be biased with two or three resistors and powered from a single supply voltage.
The transistor you have that shorts the opamp's input to ground might act strange with a TL071. When its input goes lower than its minimum rated common-mode voltage then its output suddenly inverts.

audioguru said:

I am glad you got rid of your Mosfet, made the transistors emitter-followers and used the correct negative feedback for the opamps.
But the first opamp needs to be biased at half the supply voltage.

The old 741 opamp has a max frequency response of only 9kHz at 26V p-p. A TL071 has a max frequency response of 100kHz at 26V p-p. Its minimum recommended supply voltage is 7V.

Click to expand...

AG, look again. Those aren't emitter followers. Those are push-pull common emitters that will draw huge current spikes on each transition of the input, due to storage time. Emitter followers would certainly be better. The base resistors are unnecessary, in that case. The input needs to swing zero to 12V in either case.
I suspect that the transistor switch (when he gets the bias right) that is intended to block the transmit signal from the amplifier will still allow more signal through than he will get from the transducer in receive mode.

Is there any better way you can think of isolating the opamp and transducer on the transmit mode? I saw one schematic that used a cd4016 to route the signals, but to me that seems a little excessive. Couldn't one just use one transistor or Mosfet or something else to direct the current rather than a clunky IC? I suppose someone could put a npn transistor on the gnd pin of the op amp to eliminate connections to ground during transmit, but I would imagine that would have absolutely horrid performance lol.

Every single Ultrasonic transducer driving circuit I have found online uses a push-pull driver as Hero999 suggested. And I just now found a schematic that uses an h-bridge to drive it as I originally thought would be best.

Your transducer peaks at 200kHz and its response at 40kHz isn't even shown.
It is probably horribly poor at 40kHz.

Sorry about the confusion. I might be utterly confused when it comes to analog stuff but I am not that confused to use a 200khz transducer at 40khz . But I did just realize the sensor I am planning using is actually a 25khz version instead of 40khz. I am first just going to get familiar with ultrasound using a simple 25khz transducer. This is the one I am currently going to be using: **broken link removed**

The el-cheapo 25kHz transducer doesn't have a detailed datasheet.
It doesn't even have a manufacturer's name.

Yeah, the manufacturer is Matsushita but that doesn't help because the part is probably 50 years old and there seems to be no datasheet .

freeskier89 said:

Is there any better way you can think of isolating the opamp and transducer on the transmit mode? I saw one schematic that used a cd4016 to route the signals, but to me that seems a little excessive. Couldn't one just use one transistor or Mosfet or something else to direct the current rather than a clunky IC? I suppose someone could put a npn transistor on the gnd pin of the op amp to eliminate connections to ground during transmit, but I would imagine that would have absolutely horrid performance lol.

Every single Ultrasonic transducer driving circuit I have found online uses a push-pull driver as Hero999 suggested. And I just now found a schematic that uses an h-bridge to drive it as I originally thought would be best.

Click to expand...

Hi,
Although the 25KHz and 200KHz are both acoustic projects and appear to be similar, IMO you will not be able to apply most of the 25KHz [air] circuitry to the 200KHz [water] project. The voltage and power levels in the two systems are different.
Unless you have a requirement for the 25/40KHz system, other than learning, I would suggest that you concentrate on the 200KHz water based project.

Down load a LM1812 datasheet from www.datasheetarchive.com, if you can still get a LM1812, it will be ideal for your 200KHz project.

Can you tell us which country you are posting from?

Eric

Masushita is called Panasonic in the West.
I think the symbol on the el-cheapo transducer is Mitsubishi.

I fear the 200khz water project will falsely trigger when it comes acrross a temperature inversion bewteen hot and cold bodies of water ... Also lower frequency travel better in water then higher frequency, why not use audio signals like the old style submarine Ping unless it is a miltary application ? You could get away with standard speakers and microphone acoutically coupled to the hull then !