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Time of Flight

The phrase “Time of Flight” has come up quite a few times in recent weeks. I think it is important to understand what this relates to and more importantly, what it relates to in today’s latest electronics developments.

Time of flight (TOF) identifies a number of ways that measure the time that it takes for an object, particle or acoustic, electromagnetic or other wave to travel a distance through some medium.

Most recently, this “Time of Flight” phrase has entered into my consciousness with these articles:

Finding the origin of the Universe: Assisted by High speed ADC capability at 12 bits, 4 Gsps where I discuss the CERN neutron time-of-flight (nTOF) facility with regards efforts to answer the ever-lingering question on mankind’s mind—How did we get here and where and how did it all start? See Figure 1.

Figure 1

The 4π calorimeter inside the n_TOF experimental area (Source: The n_TOF collaboration.)

The 4π calorimeter inside the n_TOF experimental area (Source: The n_TOF collaboration.)

The second instance was a paper I came across by the University of California, Berkeley entitled RF Time of Flight Ranging for Wireless Sensor Network Localization, authored by Steven Lanzisera, David T. Lin and Kristofer S.J. Pister. There are many technologies that have been tried for providing localization in Wireless Sensor Networks (WSN). RF time of flight (TOF) ranging is one of those technologies.

The paper discusses two types of RF TOF measurement systems. First there is a method where some number of devices have very accurate and synchronized clocks. A signal is sent from a known location device with an accurate clock to another device with an accurate clock and then the departure time of the signal is compared to the actual time of arrival.

The second method is which has only loose absolute time synchronization. An example is in ad hoc networks. Synchronization in the order of microseconds is possible, but not fine enough for ranging purposes. Pair-wise roundtrip TOF measurements do not need absolute synchronization. If we send a ranging signal and wait for a reply, the individual clock biases are subtracted away.

Figure 2 shows a block diagram using commercially available components on PC boards consisting of a 2.4 GHz transceiver board, and ADC interface board, and an FPGA board. See Figure 2.

Figure 2

Block diagram using commercially available components on PC boards consisting of a 2.4 GHz transceiver board, and ADC interface board, and an FPGA board.

Block diagram using commercially available components on PC boards consisting of a 2.4 GHz transceiver board, and ADC interface board, and an FPGA board.

I also found a really nice tutorial on Time of Flight Fundamentals done by Jordan TOF Products.

Next, I found some very good technical reference articles on Time-of-Flight on IEEE XPlore, one such article addresses TOF for Sensor Fusion which is ultimately relating to the IoT. A Weighted Optimization Approach to Time-of-Flight Sensor Fusion. This article discusses aspects of surveillance, robotics and drones with cameras and computer vision. TOF cameras can provide depth information in real-time as opposed to traditional stereo methods. See Figure 3.

Figure 3

Combined TOF and video capture setup (a) and projective geometry (b). (Image courtesy of IEEE Transactions on Image Processing, Vol. 23, No. 1, January 2014 article entitled A Weighted Optimization Approach to Time-of-Flight Sensor Fusion by Sebastian Schwarz, Graduate Student Member, IEEE , Mårten Sjöström, Member, IEEE, and Roger Olsson, Member, IEEE)

Combined TOF and video capture setup (a) and projective geometry (b). (Image courtesy of IEEE Transactions on Image Processing, Vol. 23, No. 1, January 2014 article entitled A Weighted Optimization Approach to Time-of-Flight Sensor Fusion by Sebastian Schwarz, Graduate Student Member, IEEE , Mårten Sjöström, Member, IEEE, and Roger Olsson, Member, IEEE)

A TOF camera can only produce depth readings, so it is often used in combination with a video camera for (color) texture information. This texture information is then used to colorize a reconstructed 3D object or can be used as guidance information in a depth scaling process as in Figure 2a is showing a Basler acA 1300-30gc machine vision camera on top of a Fotonic B70 TOF camera. The images from both cameras are combined and the two viewing angles are fused into one as shown in Figure 2b and as explained in detail in the IEEE XPlore paper. Indoor positioning and navigation uses TOF cameras as well. And is discussed in this book entitled Indoor Positioning and Navigation Using Time-Of-Flight Cameras .

Texas Instruments has a very good 3D TOF Imaging Solution.

Please share with our audience your experiences with Time of Flight.

8 comments on “Time of Flight

  1. Victor Lorenzo
    February 23, 2015

    @Steve, thanks for pointing us to these interesting subject.

    Similar principle to TOF is used for determining lightnings impact location.

    This technique is commonly known as Time of Arrival (TOA). Very sensitive RF receivers capture the EMI generated by the lightning current impulse and send signatures to one (or more) remote server. Signatures contain the GPS location coordinates combined with the time of detection. All receivers use the same clock source for synchronization (GPS clock signal) so the impact location and altitude can be estimated/calculated using data from several receivers.

    From the same captured signals it is possible to determine if the event was a positive or negative discharge, cloud to cloud, intra-cloud or cloud to ground stroke.

  2. Victor Lorenzo
    February 23, 2015

    @Steve, yet another similar technique is used for detecting failures in long power cable runs.

    A cut cable, or a short circuit, presents an impedance discontinuity at the end where the problem exists. Inyecting a step signal from one cable end and meassuring the time elapsed until the reflections are received is also a method for determining the distance to failure location.

  3. etnapowers
    February 24, 2015

    @Victor,  interesting comment, as usual, could you indicate a place to download some files about this procedure of checking long power cable runs?

  4. Victor Lorenzo
    February 24, 2015

    @etnapowers, Take a look at patent US5754053 A “In service cable failure detector and method”. This (http://omicron-lab.jp/application_notes/coaxial-cable-analysis.pdf) app note gives some usefull hints on the subject too.

    And I think this (http://i4energy.org/downloads/projects/sutardja-dai/4-Underground_Cables.pdf) presentation will attract some interest from You.

  5. Steve Taranovich
    February 24, 2015

    Great insights Victor–thanks!

  6. etnapowers
    February 26, 2015

    Victor, thank you very much for your interesting links: I have read the pdf file and I found that the BODE 100 provides an answer to this question:

     

    Is there a difference between a complete cut and a separate break in screen or the inner conductor?

     

    I find that this system is very interesting , with an high capability of individuating and classifying the damage of the cable. Thank you very much Victor!

  7. Pingback: ADI and Microsoft Allow Time-of-Flight Technology for 3D Imaging - Tech News300

  8. Pingback: ADI and Microsoft Enable Time-of-Flight Technology for 3D Imaging – JWEasyTech

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