Question about ultrasonic receiver orientation

[nikosb]

I would like to use an ultrasonic transmitter and three receivers to be able to determine the position of the transmitter relative to the receivers. The distances to be measured are around 3-4 ft. I want to understand how the receivers orientation relative to the transmitter can affect the distance measurement. I attach some simple pictures for illustration, in the first one the receiver is placed directly in front of the transmitter and opposite which is the ideal situation. In the second picture the receiver is placed in front of the transmitter but it is facing away from it. In the third picture the receiver is within the beam angle but is facing almost tangent to the beam. Basically as long as the receiver is within the beam range does its orientation matter?

 

[berkeman]

I would like to use an ultrasonic transmitter and three receivers to be able to determine the position of the transmitter relative to the receivers. The distances to be measured are around 3-4 ft. I want to understand how the receivers orientation relative to the transmitter can affect the distance measurement. I attach some simple pictures for illustration, in the first one the receiver is placed directly in front of the transmitter and opposite which is the ideal situation. In the second picture the receiver is placed in front of the transmitter but it is facing away from it. In the third picture the receiver is within the beam angle but is facing almost tangent to the beam. Basically as long as the receiver is within the beam range does its orientation matter?

It sounds like you are wanting to use an omnidirectional ultrasound transmitter and 3 triangulating receivers to do this. First problem is that there aren't any omnidirectional US transmitters that I know of, at least not simple ones. Second problem is if there can be reflections from any nearby walls or structures, that will confuse any amplitude-centric triangulation algorithms.

Can you say more about what your overall project is? Is it something like robotic location or something? Can you use other techniques for the location function? One variation would be time-of-flight measurements to triangulate with US...

 

[Baluncore]

If this is a 2D positioning system then phase and orientation of the Rx and Tx will be important. To resolve the problem, mount all transducer elements on the same plane with their axis vertical. Place a conical reflector on axis to give phase independent 360° azimuth radiation patterns. The cone profile can be adjusted to a hyperboloid which will give a better horizontal radiation pattern.

To measure position you need to measure the arrival time of pulses from the transmitter. To measure more accurately you might transmit a pseudo random sequence, then correlate the received channels to get the relative delay times. I would also consider transmitting a chirp, then multiplying the RX channels by each other to get the beat frequencies and hence period = differential time.

Depending on the number and position of RXs there may be a position error due to wind speed. It may also be a Doppler anemometer.

 

[Danger]

The reason that I didn't respond to this before is that I think he's still referring to the 3D feet and wrist motion tracking system that he introduced a couple of thread back.