Is there any emitter/receiver (passive or active) systems that allow distance estimation in the range of 1~2 meters with an accuracy of few centimetres and don't need to have a direct line of sight as optical systems mostly do?

I was thinking about using such sensors as nodes to put on a suit that a human can wear. As a result, a graph can be obtained where each node represents one of those sensors and each edge describes the distance from this node to the other nodes. Using graph optimization techniques, the graph would converge to the correct joint position of the human. Such a system could replace expensive motion capture methods using calibrated external cameras.

  • $\begingroup$ What do you mean by "don't need to have a direct line of sight"? That seems to be a very tough requirement. $\endgroup$
    – hazzey
    Nov 15, 2015 at 14:33
  • $\begingroup$ What is the engineering problem you are trying to solve? How about an ultrasonic sensor? $\endgroup$ Nov 15, 2015 at 16:30
  • $\begingroup$ @hazzey imagine having the emitters/receivers mounted on your neck, elbow, feet etc. Each one emitting some sort of signal and receiving the signal of the other nodes, which would allow to estimate the relative distance to them. You can't always guarantee that all receivers have a direct line of sight with the emitters. And Mahendra how do you estimate range between the emitter and the receiver with an ultrasonic sensor? $\endgroup$
    – Mehdi
    Nov 15, 2015 at 16:43
  • $\begingroup$ @Mehdi I shared some ideas on the use of Ultrasonic sensor for proximity sensing. I work mostly with TI products, but also look at other semiconductor vendors. Come back and share your experiences? May be I can learn something from you. $\endgroup$ Nov 17, 2015 at 2:04
  • $\begingroup$ Lead markers and a pair of x-ray cameras to produce a 3d map of the marker location. Not very healthy to the human at all, but hey, it works. $\endgroup$
    – SF.
    Nov 17, 2015 at 12:58

2 Answers 2


I think you have approached your problem from the wrong direction. There are currently no sensors that measure distance between each other regardless of material in the path. It would be possible to make a device with optical or ultrasonic time of flight technology, but that would be a project all by itself. These sensors are very expensive and need calibrated for a fixed environment. It would require lots of development to remove all the variables from a biomechanics type application.

I recommend you look at currently available sensing technology and look how you can apply those sensors in new ways. Optical is likely the future in this field. Computer software can be written to splice multiple images and reverse render the position and texture of objects. If this still does not solve the problem, you could look at using wavelengths outside the visible spectrum such as near infrared.

  • $\begingroup$ Thanks this is the answer I needed. So I need to rethink about the whole thing. $\endgroup$
    – Mehdi
    Nov 16, 2015 at 9:24

Ultrasonic sensing is can be used for distance measurement. Ultrasonic proximity sensing technology is commonly used in automotive as part of Advanced Driver Assistance Systems. The basic theory behind this technology is Time-of- Flight (TOF). Below few images to help visualize the idea.

Park Assist-1 Park Assist-2

To achieve this you can use PGA450 Ultrasonic Analog Front End (AFE) from Texas Instruments. As I understand this sensor is capable of distances up to 7M.

The PGA450-Q1 device can measure distances ranging from less than 1 meter up to 7 meters, at a resolution of 1 cm depending on the transducer-transformer sensor pair used in the system.

Below is a diagram describing the concept.


Also you might want to check out TDC1000 Ultrasonic AFE. I am much more familiar with this part. But I have not used this part for proximity sensing. Once again below is a diagram describing the application.


Also TDC1000 has a configuration where the emitter and receiver are seperate that might be interesting.

TDC1000 AFE Separate emitter and receiver

Below are some references that you might find interesting


  • $\begingroup$ Thanks for this well formulated answer but ultrasonic sensors are not suitable for my problem. I need to estimate the distance between an emitter and a receiver directly, and not the distance from the emitter to some obstacle where the emitted signal is reflected back. As eric mentioned, the kind of sensor technology I imagined doesn't exist (yet?). $\endgroup$
    – Mehdi
    Nov 17, 2015 at 12:21
  • $\begingroup$ Take a look at the TDC1000. They have configuration where the emitter and receiver are separate. I have added a image for your reference. I am not to familiar with the applicaiton. $\endgroup$ Nov 17, 2015 at 12:38

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