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.
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.
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.
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.