Holder for flat, approximately rectangular devices such as tablet computers or smartphones

Apparatus for filtering a flow stream flowing in a flow pipe in a flow direction, comprising:

• opposing acoustic transducers arranged on the flow pipe that include
• a first ultrasonic transmitter configured to respond to control signaling and provide a first acoustic signal at a first frequency F1;
• a second ultrasonic transmitter configured to respond to the control signaling and provide a second acoustic signal at a second frequency F2, the first frequency F1 and the second frequency F2 being two different frequencies F1 and F2;
• and
• an acoustic comb filter module having a controller configured to
• receive signaling containing information about the first frequency F1 and the second frequency F2, and
• provide the control signaling for controlling the operation of the first ultrasonic transmitter and the second ultrasonic transmitter to generate a swept acoustic standing wave that is transverse to the flow direction of the flow stream in the flow pipe and having a selected comb spacing D set up via excitation based at least partly on the two different frequencies F1 and F2 to capture and sweep lower certain particles having a selected size X in a flow stream flowing in a flow pipe, the sweep of the swept acoustic standing wave being based at least partly on a transit time across the flow stream being less than a capture time of the certain particles.

A method for filtering a flow stream flowing in a flow pipe in a flow direction, comprising:

• arranging opposing acoustic transducers on the flow pipe having a first ultrasonic transmitter and a second ultrasonic transmitter;
• responding with the first ultrasonic transmitter to control signaling and providing a first acoustic signal at a first frequency F1;
• responding with the second ultrasonic transmitter to the control signaling and providing a second acoustic signal at a second frequency F2, the first frequency F1 and the second frequency F2 being two different frequencies F1 and F2;
• and
• receiving in an acoustic comb filter module having a controller signaling containing information about the first frequency F1 and the second frequency F2, and providing the control signaling for controlling the operation of the first ultrasonic transmitter and the second ultrasonic transmitter to generate a swept acoustic standing wave that is transverse to the flow direction of the flow stream in the flow pipe and having a selected comb spacing D set up via excitation based at least partly on the two different frequencies F1 and F2 to capture and sweep lower certain particles having a selected size X in a flow stream flowing in a flow pipe, the sweep of the swept acoustic standing wave being based at least partly on a transit time across the flow stream being less than a capture time of the certain particles.