Acoustic balance: weighing in ultrasonic non-contact manipulators

An apparatus for a non-contact acoustic determination of a mass of an object, comprising:

• an array of ultrasound transducers configured for generating an ultrasound field;
• and
• a controller configured to generate phase delay signals for the array of ultrasound transducers;
• wherein the ultrasound field is configured for:
• capturing the object within an acoustic trap of an acoustic balance;
• in response to changing at least one acoustic parameter of the acoustic balance, changing an equilibrium position of the object;
• and
• in response to changing the equilibrium position of the object, causing the object to oscillate,
• wherein the controller is configured for:
• determining a resonant frequency of oscillation of the object;
• and
• based on the resonant frequency of oscillation of the object, determining the mass of the object.