Morgan Kinney, Tanner Hoppman, Jude Franklin

This week we were able to complete the building and testing of our T/R switch. Since we were unsure the cause of our T/R switch malfunctions from before, we re-soldered all of the components, which fixed the issue. The return loss measurements at each port shown in Element 1 were all within expected ranges, indicating our switch was working properly. The image in Element 2 was obtained by injecting a 5 MHz signal into the transducer port and measuring the signal at the receive port. The signal remaining at 5 MHz frequency also indicates that our switch was functioning properly.

Element 1. Return loss measurements at each port of the T/R switch.

Element 2. Image of oscilloscope measuring the 5 MHz signal detected at the receive port of the T/R switch when a 5 MHz signal is generated through the transducer port.

Question: How would you express this (an open circuit) mathematically?

Answer: An open circuit is represented mathematically by an infinite impedance, so that there can be no current flow.

This week, we began making a sinusoidal function generator to test our T/R switch. Below is the pulse-echo sequence flow graph we made that outputs a pulse of 1 microsecond duration separated by a tunable pulse repetition time.

Figure 1: Block diagram of our multiplier

Question: The simplest solution using the above three elements has an upper limit on the pulse repetition time because of the very large delays required. How can you modify it so you only use a 1 microsecond delay?

By inverting any given time varying signal (i.e. multiplying by -1 so as to flip all the values about the time axis) and then summing the inverted and non-inverted signals together, the result will be 0. Using this approach to generate the 1 microsecond delay is more feasible since it does not require a large amount of memory bandwidth. Given a 1 Megahertz signal, the period for a single sample will be 1 microsecond. By delaying an inverted 1 MHz signal one sample we are in essence generating two signals (one inverted one non-inverted) that differ by only 1 microsecond. By summing these two signals together, we generate a pulse of only 1 microsecond. Our block diagram is shown in Figure 1.

Below are images of the progress we made on the ultrasound scanner before Vanderbilt yeeted us out.

Figure 2: Sinusoidal source waveform

Figure 3: Pulse width modulation signal. This scope capture represents our efforts at attempting to generate the 1 microsecond pulse

Figure 4: This picture shown above represents our first attempt at generating the 1 microsecond pulse delay. This approach fails since it requires us to delay the second signal by too many samples which requires too much memory bandwidth.

Figure 5: This waveform shown above represents the 1 microsecond pulse that we successfully generated using the radio blocks in Fig.

Myron Mageswaran, Alex Boyd, and Maggie Ford

During week 3 for this lab, we first tinkered with the GNURadio software in order to create the desired input into the switch using the radio shown in Figure 1.  This task took longer than expected, but we were able to set up an input signal that was pulsed for one microsecond using the schematic shown in Figure 2.

Figure 1:  the software defined radio that is interfaced with the Linux virtual machine

Figure 2: block diagram schematic

After programming the Arduino, we were ready to take our first scan and took out our cast out of the mold and filled our bin with water only to realize that we only had three minutes remaining in class, (and unsuspectingly the rest of the semester) so we did not have time to take any actual readings.

Question: What is the purpose of the quarter wave line?                                                  The quarter wave line is able to change impedance creating either an open or closed circuit to Rx, which creates the switching effect.

Blog Post Week #3: Imaging Instrumentation Ultrasound Lab
Jorie Budzikowski, Stephanie Molitor, and Rachel Welscott

This week we worked on:
I. Making a pulse-echo sequence
II. Programming the Servo to sweep through a range of angles for B-mode imaging
III. Finalized our setup prior to data acquisition

I. Making a pulse-echo sequence
Once we got a basic sinusoidal function generator functioning through the GNU Radio software (Figure 1), we were able to alter the conditions of the signal source to create pulses that are 1 microsecond in duration. We are able to do so by introducing a delay, a multiplier, and an additional function to our square wave source. The pulse is sent to the radio, will be amplified, and then transmitted through the ultrasound probe. We also added a radio source and GUI sink component in order to read what signal is reflected back from the ultrasound transducer. The block diagram for our pulse-echo sequence is shown in Figure 2.

Figure 1. Simple 5 MHz sinusoidal signal from our function generator using the USRP radio.

Figure 2. Block diagram for our pulse-echo sequence.

Figure 3. Oscilloscope readout of our 1 us pulse signal from the URSP radio.

II. Programming the Servo to sweep through a range of angles for B-mode imaging
The arduino was programmed to move to the angle plugged into the serial monitor. The servo object was first created and the serial monitor was initialized. The position variable (pos) was initialized and set equal to the read in value that was entered into the serial monitor. Next we used an if statement to ensure that the value that was inputted into the serial monitor is attainable by the servo motor. Finally, the inputted position was written to the servo motor so that ultrasound probe was pointed at the intended angle. See the attached video of our servo moving the ultrasound transducer.

Figure 4. Arduino code to control the servo arm and have it move to a desired angle.

III. Final Equipment Setup Prior to Data Acquisition
Now that we have programmed our URSP radio to transmit and receive signals, and programmed our servo arm to move the transducer, we are ready to start collecting some ultrasound data!

Figure 5-6. The electronics of the ultrasound probe system and the physical probe-stand tabletop model.

Questions to answer this week:

• Question: How can you do this using a single square wave signal source, a delay, and a signal multiply block?
  • You can send the single pulse as an input into two different operator functions. One of the functions should not do anything to the waveform while the other function adds a delay and a multiplication constant. These 2 new wave forms are then multiplied together to result in a square waveform with a very short pulse width.
• Question: The simplest solution using the above three elements has an upper limit on the pulse repetition time, because of the very large delays required. How can you modify it so that you can use only a 1 us delay?
  • The simplest solution only involves the signal source, a delay, and a multiplier. We originally planned to use a large delay with this setup; however, due to the upper limit we found that we had to modify our design. We instead changed the used a short delay in combination with an addition operation to get a 1 us delay.

Week 8

Javier and Nicholas J. Holden

This week was spent working with the radio in order to try and get the radio to release a pulse for the ultrasound. The beginning of the week was primarily about getting used to the GNUradio by doing the different tutorials given by the software and viewing the results using the oscilloscope. Once these were finished, we attempted to create the pulse wave needed for the ultrasound. We figured out the parts needed in order to create the wave. We did encounter some issues in this process primarily because of getting the pulse duration just right by deciding the timings of the different pieces and amounts.  

Nicholas J. Holden persevered on Thursday due to teammate and hardware specialist, Javier, having to attend to a sensitive matter. The beginnings of the Arduino code was formed in an effort to begin work to move the ultrasound sensor around the artifact. Unfortunately, this did not get too far in the development stage. Nicholas J. Holden then tried to work on the GNUradio with the software associated with the device. Little progress was made, however, much was learned from Grissom who gave a short lecture to two groups about the overall direction he wanted groups to go with the software.

Figure 1 – illustrates the sinusoidal wave achieved with the radio.

Figure 2 – illustrates the software we have working with to generate the appropriate waves.

We are currently trying to survive the Coronavirus and will continue to update this blog and the continuation of our work.

Question: What is the role of the quarter-wave line?

This allows the path to the Rx port to seem like an open or closed circuit by changing the impedance of the line. This wire has to be a quarter of the length of the wavelength of the wave being used.

Week 8 Blog Post: Ultrasound Scanner

Hunter Spivey and Aayush Gupta

This week we began to test the T/R switch using our antenna analyzer but were running into issues with return loss measurements. Our return loss measurements were for the most part as expected, with us getting a return loss of zero when sending signal into the TX in port. However, our return loss when sending signal into the RX port was only about 3 dB whereas we had been expecting about 10 dB. We attempted to solder the components onto the board better, but this made little difference and we were still only getting about 6 dB. After struggling with this, replacing our inductor, and still getting only 6 dB, we recalibrated our antenna analyzer program and were finally able to get the 10 dB return loss we expected. Now with confirmation that our T/R switch was indeed working as we expected, we moved on and began setting up our GNU radio software. Unfortunately we ran out of time before we could get very far with our software though, and were only able to get it started and run through some basic tutorials.

We next hope to finish the GNU radio software provided coronavirus doesn’t do us all in/we even have class anymore?

Return Loss of TX in:

Question: How close can you get to these values (L and C) with the components we have (without, e.g. using multiple components in each position)?

Answer: We can use a 1.5 microHenri inductor and two 680 picoFarad capacitors

Blog Post Week #2: Imaging Instrumentation Ultrasound Lab

Jorie Budzikowski, Stephanie Molitor, and Rachel Welscott

(overheard) QUOTE OF THE WEEK: 

“Everything is a learning experience”

This week we worked on: 

1. Measuring the return loss of our T/R switch
2. Characterizing the signals for different inputs/outputs of our T/R switch
3. Making a 5 MHz function generator on Ubuntu

Measuring the return loss of our T/R switch

After soldering our T/R switch last week, we needed to verify that it is functioning properly. We did this by measuring the return loss at different ports. We injected a low amplitude, 5 MHz, voltage signal into our switch via the AIM radio, which then also read the signal that was reflected back to it. If all of the signal is reflected, we would get a return loss of 0. When we injected the signal into the Transmit port, we saw a very small return, which indicates that no signal was transmitted. This was expected because a low amplitude voltage should not be enough to turn on the diodes and transmit the signal. When we injected the signal into the Probe port (as if we were reading a signal from the US probe), however, we saw a significant return loss, which means that some of our signal was actually being transmitted to the receiver. These return loss measurements are illustrated in figures 1-5 below.

Figure 1. Return loss: antenna connected to TX out, nothing on TX in, 50 ohms on Rx OUT OF BOX

Figure 2. Return loss: antenna connected to Tx out, 50 ohms on Tx in and 50 ohms on Rx OUT OF BOX

Figure 3. Return loss: antenna connected to Tx in, 50 ohms on Tx and Rx, OUT OF BOX

Figure 4. Return loss: antenna connected to Tx out, 50 ohms on Tx in and 50 ohms on Rx IN THE BOX

Figure 5. Return loss: antenna connected to Tx in, 50 ohms on Tx and Rx, IN THE BOX

Characterizing the signals for different inputs/outputs of our T/R switch

Once we were able to verify that our return loss values matched or expectations, we were also able to characterize our signal with different input/output connections. Using the same AIM radio as a low amplitude, 5 MHz voltage generator, we were able to inject a signal into our T/R switch, and then read the output on an oscilloscope. When we injected the signal into the Transmit port, and measured the signal at the Probe port (with the Receive port loaded with 50 Ohms) we saw a negligible signal, with a peak-to-peak amplitude of 10 mV. This was expected because the low amplitude voltage should not be enough to turn on the diodes and transmit the signal. When we injected the signal into the Probe port, and measured the signal at the Receive port (with the Transmit port loaded with 50 Ohms), we got a signal with a 230 mV peak-to-peak amplitude, which indicates that we are able to measure the signal that would come in from the US probe. The signals received on the oscilloscope are captured in figures 6 and 7 below. 

Figure 6. Oscilloscope at Tx out, antenna at Tx in, 50 at Rx, p2p amp =10 mV antenna at Tx out, oscilloscope at Tx in, 50 at Rx, p2p amp = 6 mV

Figure 7. Oscilloscope signal at Rx, antenna at Tx out, 50 at Tx in, p2p amp =230 mV 0 attenuation when device is plugged in.

Creating a 5 MHz function Generator on Ubuntu

Since our AIM radio is limited to only producing low amplitude signals, we needed to create a function generator to transmit a larger signal to the US probe. We were able to create a simple 5 MHz signal using GNU Radio Companion supported by Ubuntu, that we sent through the USRP1 Software Defined Radio and measured with an oscilloscope. The code that was used and the images that were collected can be seen in figures 8-12 below.

Figure 8

Figure 9

Figure 10

Figures 8-10. The top block Python code generated when the function generator was compiled. 

Figure 11

Figure 11. The block diagram of 5MHz function generator with a 500 mV amplitude. 

Questions to answer this week:

• Question: Under what conditions do each pair of crossed diodes turn on? 
  • Both pairs of diodes turn on under large voltage pulses from the transmitter. Neither pair of diodes is turned on in between the large voltage pulses.

Morgan Kinney, Tanner Hoppman, Jude Franklin

This week while finishing our data acquisition for the IR CT scanner we were able to begin working on our next project, the ultrasound machine. Our first step was creating the phantom to be imaged once we build our ultrasound probe. This was done by combining water with agar and graphite, heating it up in a microwave, and then cooling it and inserting a 3-D printed shape part-way through the cooling process. Next, we built our transmit/receive switch using the board shown in Fig. 1 to match the circuit diagram in Fig. 2 with ceramic chip capacitors, a surface mount inductor, SMA connectors, and four Schottky diodes. The last thing we did was enclose our switch in a metal enclosure for storage so that our next step will be to test it to make sure our soldering has been done properly.

Figure 1. Transmit/Receive switch board used to build T/R switch.

Figure 2. Transmit/Receive switch diagram. The quarter-wave line is modeled through a pi network of two identical capacitors and an inductor.

Question: Under what conditions do each pair of crossed diodes turn on? 

Answer: In Fig. 2, the diodes between TX and the probe turn on when the TX amplifier produces large voltages during transmit to induce a loss of power, and the other diodes turn on when the transducer acts as a source producing small voltage signals during receive.

Week 7

Javier and Nicholas J. Holden

This week was spent on trying to make sure that the TR switch was constructed and functioning properly. Figure 1 shows the soldered circuit. Upon testing the circuit for the first time, we discovered that the inductor was not properly soldered onto the board. This in turn created a break in circuit at the inductor. This was incredibly frustrating because they were difficult to replace due to being delicate. After solving this problem, we then tested that the circuit was continuous. Once this was confirmed we resumed testing for return loss. We encountered a problem when we first did the testing, but we discovered that the error wasn’t from the TR switch but rather the antenna analyzer. This was discovered by testing a working TR switch and observing a very low return loss for Tx-Out with a 50 Ohm load on the Rx port. Figure 2 displays the outer shell of the circuit that was attached with the ports labelled. Upon switching out the analyzer, the return loss was then collected for a variety of situations. This includes a -9.14 dB return signal with the analyzer connected to Tx-Out and a 50 Ohm load on the Rx port. The reverse of this situation was also tested and returned -9.27 dB. This was good as it should be symmetric. When the 50 Ohm load is removed, the return loss in both situations are 0.64 and 0.62 dB. Finally the Tx-In port was tested and had a return loss of .02 dB which is what we expected to occur. Next week, we will get started on running the GNURadio and SDR in order to create a pulse signal as well as familiarizing ourselves with the GNURadio.    

Figure 1

Figure 2

Question: How would you express this mathematically?

Answer: You would express this as an infinite amount of impedance preventing the flow of current. This makes the circuit appear as an open circuit.

Week 7 Blog Post: Ultrasound Scanner

Hunter Spivey and Aayush Gupta

This week we continued working on our T/R switch, and began by calculating our element values necessary for the capacitors and inductor on the T/R switch. After calculating these values, we began soldering the elements on, which was tedious work that took us most of the time we had available. We finished soldering on our elements, but unfortunately had soldered the inductor on upside down, and had to remove and resolder it. Finally we tested our T/R switch using the continuity function of the multimeter, and began setting up our antenna analyzer to test it further. We were able to successfully start and calibrate the antenna analyzer before we ran out of time.

Next we plan on finishing our antenna analyzer tests and moving on the the GNU radio.

T/R switch:

Question: What is the role of the quarter-wave line?

Answer: It changes impedance to allow the path to the RX line to be either a short or open circuit

Question: What values do you get for L and C?

Answer: We get 1.59 microHenris and 636 picoFarads