Ultrasonic Transducer not getting any echo - Page 1
Forum section: electronics / beginners

author: vlaichu
author_rank: Newbie
timestamp: July 23, 2025, 04:49:11 am
content: Actually, the transducer has its own logger. However, it's very expensive, so I decided to create my own driver. The transducer's specification is not available in detail, but from the datasheet of the logger I can confirm this transcuder ran at 1 MHz. The function of this transducer is for measuring waterflow.Here is the logger datasheet:https://www.hispacontrol.com/recursos/pdf/BM_TTFM100_Fijo.pdfThe transducer have 3 terminals +, -, and GND (?). All this time, I connect + to the positive side of my output circuit and connect - to negative side of my push pull circuit. And also connect the third pin to earth in my power supply.My driver transmit side is going like the picture below, I'm using push-pull connection to amplitude the original signal (3.3 V 1 MHz square using function generator) to 12 V. I measured the transducer capacitor using LCR meter and got 4.2 nF at 1 kHz, so I decided to put 6 uH in series to get the resonance circuit.After all setup complete, I measured the echo directly connect the receiver side to oscilloscope like this without any filter like the picture below. But I never get the echo, when I measured it using an oscilloscope.1. Did I make a mistake when I connecting the terminals?2. Do I have to measure the equivalent transducer circuit to create more accurate resonant circuit to get the echo?

author: Poroit
author_rank: Frequent Contributor
timestamp: July 23, 2025, 06:30:32 am
content: G'day vlaichu,Could it be your method of test that is causing the problems?From past experience, I remember that the Mode of positioning the transducers on the pipework was extremely important.Refer attached.

author: vlaichu
author_rank: Newbie
timestamp: July 23, 2025, 06:51:41 am
content: Currently, I'm not using a pipe for testing. I just want to know whether the signal from the transmitter is being received by the receiver using an oscilloscope. So, based on your reference, I need to use proper positioning, like the Z or V method, right? I'm just wondering why the receiver isn't getting any echo with this face-to-face setup. Is there a blind spot in the ultrasonic transducer?

author: Kleinstein
author_rank: Super Contributor
timestamp: July 23, 2025, 08:09:26 am
content: The transducers are made more pipes, not for air. In air they will very ineffcient and thus too little amplitude. For a test connect some metal or glass between the transducers. For good mechanical contact use some petroleum gelee or similar.

author: vlaichu
author_rank: Newbie
timestamp: July 23, 2025, 10:04:00 am
content: Quote from: Kleinstein on July 23, 2025, 08:09:26 amOkay, thanks for the suggestion! I'll come back with the results soon. Do you have any idea why this transducer has three terminals? As far as I know, most transducers on the market only have two.

author: vlaichu
author_rank: Newbie
timestamp: July 24, 2025, 04:43:38 am
content: Hello, after several tests and adjustments, I decided to place the transducers touching each other, and I was able to observe an echo on my oscilloscope. However, I'm not sure which signal is the actual echo, because I see two different echo-like signals (images attached).The yellow trace is the transmitter signal, and the purple trace is the receiver signal.1. Is the signal in the red box the actual echo, or just a coupling? It looks very similar to the transmitter signal but with lower strength.2. If the signal in the blue box is the real echo, how can I suppress or eliminate the signal in the red box?

author: Uunoctium
author_rank: Frequent Contributor
timestamp: July 24, 2025, 07:04:57 am
content: As @Kleinstein said above, your setup won't work in air. At the transition to air total reflections occur, thats why psysicians use ultrasonic contact gel at sonography. You have to couple the energy into the medium on both sides Tx and Rx by applying a thick and bubble-free layer of acoustic couplant onto the transducers windows. See notes from an alternate mfg below

author: vlaichu
author_rank: Newbie
timestamp: July 24, 2025, 07:54:57 am
content: Quote from: Uunoctium on July 24, 2025, 07:04:57 amSo, even if I place the TX and RX transducers touching each other, am I still unable to see a true echo? I'm really confused because based on my last oscilloscope screenshot (on my last reply), I thought those signals were echoes.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 24, 2025, 09:13:51 am
content: We still don't know the details of the transducers. Some of them are resonant transducers an only work well over a relatively narrow frequency range.This is especially bad in th eair transducers, but also the ones for solids / liquids can be narrow band.A first point could be checking how the sending transducer reacts to different frequency the drive signals.With the transducers directly next to each other is there some coupling agent in between ? Even a thin air layer is a pretty poor medium for ultrasonic and most is reflected at the interfaces (transducer to air and back).A medium (preferrible isolating) in between could help in the test tests as it would add delay and this way allow to separate the direct coupling from an acoustic signal.

author: Uunoctium
author_rank: Frequent Contributor
timestamp: July 24, 2025, 04:49:33 pm
content: Found an intresting tutorial from Comsol-Multiphysics. In Fig 3 you may have an impression on the relation of amplitudes between Tx and Rx transducers of a flowmeter setup. Fig 1 shows a typical burst packet with over 100Vpp at transmitter piezo.https://doc.comsol.com/6.0/doc/com.comsol.help.models.aco.flow_meter_piezoelectric_transducers/flow_meter_piezoelectric_transducers.html

author: Niklas
author_rank: Frequent Contributor
timestamp: July 24, 2025, 07:57:48 pm
content: The driver circuit looks very similar to what I have used to drive a 1 MHz piezo transducer with. It would have been nice to see what the signal across the piezo and the square wave output from the driver midpoint look like.You will get several echoes and some of them are related to the mechanical structure itself, for instance the plastic enclosure. The frequency of the echo is typically the primary mode of oscillation and it could be different from the frequency used for excitation. If I remember correct, the excitation burst length is conserved. The transducer has several modes of oscillation based on the physical dimensions (thickness, diameter, diagonal front-back), so you can observe a change in frequency, as can be seen during the ring down, as oscillations at different frequencies have different lower thresholds in energy needed to sustain the oscillation.The first thing I would have done would be to put both transducers into a container with water and approx 10 cm/4 inches distance, which would correspond to approx 50us time of flight. That would make it possible to insert something in between to interrupt the coupling path in the liquid, but it will keep the path through the mechanical structure.There might be additional echoes that appear at multiples of the primary time of flight as some of the excitation burst energy is reflected at the receiver, bouncing back, reflecting again before arriving at the receiver again. This is something that must be characterised in your application to avoid false echoes. Just allow enough time for the echoes to die out before the next excitation begins.

author: CaptDon
author_rank: Super Contributor
timestamp: July 25, 2025, 05:54:38 pm
content: With the transducers against each other there is no sensible time delay so the first burst would be the 'echo'. Most liquid flow sensors are using Doppler phase shift to detect flow rate.

author: vlaichu
author_rank: Newbie
timestamp: July 28, 2025, 10:21:12 am
content: Quote from: Kleinstein on July 24, 2025, 09:13:51 amSadly, it's very hard to find detailed information about the transducers. The only detail I know is that the resonance frequency is 1 MHz.Recently, I tested the transducers on a 4-inch pipe (image attached), but I didn’t use a coupling agent during the test. I didn’t get any echo this time either (image attached #2)—probably because I wasn’t using the coupling agent.Quote from: Uunoctium on July 24, 2025, 04:49:33 pmYour reference is very helpful, sir. I just realized that the receiver voltage is much lower compared to the transmitter. As for the placement, maybe I tested it incorrectly — I thought the transducers should be placed parallel to the pipe (image attached #1). Later, I’ll follow what the tutorial suggests.Quote from: Niklas on July 24, 2025, 07:57:48 pmYes, I am using your driver circuit and have changed several values to match my transducers. Thank you for your circuit reference, sir. Here's a picture of the midpoint (purple) and the signal across piezo (yellow). Can you tell me if this is a good transmitter signal or not? (image attached #3)I already placed the transducers parallel to the 4 inches pipe, but I couldn't see the echo (image attached #2). Maybe I should use a coupling agent as suggested in the tutorial.Quote from: CaptDon on July 25, 2025, 05:54:38 pmI don't think the signal in the red box is the actual signal, because every time I placed one of the transducers far away, the signal in the red box still appeared. However, the signal in the blue box only appeared when I placed the transducers face to face.

author: Poroit
author_rank: Frequent Contributor
timestamp: July 29, 2025, 07:31:00 am
content: Are your transducers TTS100-TS2-NG-20 ?I still think your method of test is incorrect.(see attached)It looks like you have a piece of 100mm pipe filled with water....no flow and the sensors are directly opposite another not V format.Do you have access to a section of pipe that has some flow? Swimming pool plumbing or similar.

author: Niklas
author_rank: Frequent Contributor
timestamp: July 29, 2025, 09:00:04 am
content: I think the driver midpoint signal looks good, but I am not so sure about the signal across the transducer. You can expect some distortion of the sine wave due to mismatch between the excitation and L-C-resonance frequencies, but I am more worried about the envelope. The quick rampup followed by a drop in amplitude over the burst instead of a smoother rampup and sustained amplitude seems to relate to the 10nF capacitor in the driver. The BD1XX transistors have lower gain and possible also need a higher amount of charge in the B-E junction compared to the BC846/856 that I used, but simulation hints that the 10nF could be lowered to 1-2nF. This change could result in some dips on the top and bottom of the driver midpoint square wave, but that could be acceptable if the resulting output sinewave is improved.Another thing that could also be worth to mention is that water bubbles can cause a lot of funny issues, such as dispersion and change in average speed of sound, on the transmitted signal. Fresh tap water takes a couple of hours to outgas and bubbles can stick to the inside of the plastic tube, but they can be removed with a small brush. Another trick is to pour water into a bucket, let it outgas for a day and then use it for your tests. If you need bubbles for testing, go to an aquarium shop to get an aeration stone and feed it with compressed air trough a valve.

author: vlaichu
author_rank: Newbie
timestamp: August 01, 2025, 09:06:53 am
content: Hello, after several tests with different setups, I was finally able to see the echo. Thanks for the guidance! Now it's time for the next step. I'm going to build my own receiver preamp because there's a lot of noise in the receiver, and the echo signal is 1 MHz with only 60 mVpp. So, I need to filter and amplify it. Do you guys have any references or examples for building a preamp using an op-amp or something similar?

author: Niklas
author_rank: Frequent Contributor
timestamp: August 05, 2025, 06:06:47 am
content: We used two stages of multiple feedback filters, either bandpass-bandpass or high pass-low pass, depending on the needed frequency range. In your case I would go with bandpass.This Japanese site has some filter calculators:http://sim.okawa-denshi.jp/en/OPtazyuBakeisan.htmThe capacitors are typically in the pF range and don't skip out small ones, like 5 pF, in the feedback path as they are needed to dampen the system.The op-amps can be 3.3V single supply, rail-rail on at least the output, and look for at least 100 MHz GPBW. TI OPA2354 might be an option. The virtual ground cound be a 10k+10k voltage divider with a 100nF buffering capacitor to begin with. Could also be buffered by a voltage following opamp, but start with just the divider.Don't forget to add a 47-100 ohm series resistor close to the opamp output to decouple wire or trace stray capacitance from the opamp.