Modal body touch using ultrasound

1. A method comprising:

identifying, using data from a sensor, a particular state of a limb of a user on which a device is worn that indicates to activate ultrasound sensing;

detecting, by the device that is worn by the user, an ultrasound event that includes receipt of an ultrasound signal that is transdermally propagated on the body of the user and effected by an on-body touch in an area in which the ultrasound signal has propagated; and

selecting, by the device, an input based on the receipt of the ultrasound signal and the state of the limb.

2. The method of claim 1 , further comprising:

transmitting the input to a second device; and

performing an action specified by the input via the second device.

3. The method of claim 1 , further comprising:

detecting, by the sensor, movement of the limb of the user; and

determining, by the device, whether the state of the limb is in a contracted state based on the detecting of the movement of the limb.

4. The method of claim 1 , wherein the input is one of an input that can be made via a mouse, a keyboard, or a touch display.

5. The method of claim 1 , further comprising:

analyzing a characteristic of the ultrasound signal received, wherein the characteristic includes at least one of frequency, amplitude, or propagation speed; and

identifying a type of on-body touch based on the analyzing.

6. The method of claim 1 , wherein the input is application-specific.

7. The method of claim 1 , wherein the on-body touch is a tap or a sliding gesture.

8. A device comprising:

an ultrasound transducer;

an accelerometer;

a memory, wherein the memory stores software; and

a processor, wherein the processor executes the software to:

identify, using data from the accelerometer, a particular state of a limb of a user on which the device is worn that indicates to activate ultrasound sensing;

detect, via the ultrasound transducer, an ultrasound event that includes an ultrasound signal that is transdermally propagated on the body of the user and effected by an on-body touch in an area in which the ultrasound signal has propagated;

detect a state and a degree of contraction of the limb, wherein the state is a contracted state or a relaxed state; and

select an input based on a receipt of the ultrasound signal, the state of the limb, and the degree of contraction.

9. The device of claim 8 , further comprising:

a communication interface, wherein the processor further executes the software to:

transmit, via the communication interface, the input to another device.

10. The device of claim 8 , wherein the accelerometer detects movement of the limb, and wherein the processor further executes the software to:

determine whether the state of the limb is in the contracted state or the relaxed state during a time of the on-body touch based on data received from the accelerometer.

11. The device of claim 8 , wherein the input is one of an input that can be made via a mouse, a keyboard, or a touch display.

12. The device of claim 8 , wherein the processor further executes the software to:

analyze a characteristic of the ultrasound signal received, wherein the characteristic includes at least one of frequency, amplitude, or propagation speed; and

identify a type of on-body touch based on an analysis of the characteristic.

13. The device of claim 8 , wherein the processor further executes the software to:

store a database that includes ultrasound signal profiles, states of the limb, and inputs; and

use the database to select the input.

14. The device of claim 8 , further comprising:

a machine learning module that allows the user to train the device to recognize particular on-body touch events performed by the user and select inputs corresponding to the on-body touch events.

15. A non-transitory storage medium that stores instructions executable by a processor of a computational device worn by a user, which when executed, cause the computational device to:

identify, using data from a sensor, a state of a limb of the user on which the computational device is worn that indicates to activate ultrasound sensing;

detect, via an ultrasound transducer of the computational device, an ultrasound event that includes an ultrasound signal that is transdermally propagated on the body of the user and generated by an on-body touch in an area in which the ultrasound signal has propagated;

and

select an input based on a receipt of the ultrasound signal and the state of the limb.

16. The non-transitory storage medium of claim 15 , wherein the instructions comprise instructions to:

analyze a characteristic of the ultrasound signal received, wherein the characteristic includes at least one of frequency, amplitude, or propagation speed; and

identify a type of on-body touch based on an analysis of the characteristic.

17. The non-transitory storage medium of claim 15 , wherein the instructions comprise instructions to:

store a database that maps ultrasound signal profiles, states of the limb, and inputs; and

use the database to select the input.

18. The non-transitory storage medium of claim 15 , wherein the instructions comprise instructions to:

determine whether the state of the limb is in a contracted state or a relaxed state during a time of the on-body touch based on data received from the sensor.