Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Phased array beamforming methods for powering biomedical ultrasonic
  implants   Millimeter-scale implants using ultrasound for power and communication have
been proposed for a range of deep-tissue applications, including neural
recording and stimulation. However, published implementations have shown high
sensitivity to misalignment with the external ultrasound transducer. Ultrasonic
beamforming using a phased array to these implants can improve tolerance to
misalignment, reduce implant volume, and allow multiple implants to be operated
simultaneously in different locations. This paper details the design of a
custom planar phased array ultrasound system, which is capable of steering and
focusing ultrasound power within a 3D volume. Analysis and simulation is
performed to determine the choice of array element pitch, with special
attention given to maximizing the power available at the implant while meeting
FDA limits for diagnostic ultrasound. Time reversal is proposed as a
computationally simple approach to beamforming that is robust despite
scattering and inhomogeneity of the acoustic medium. This technique is
demonstrated both in active drive and pulse-echo modes, and it is
experimentally compared with other beamforming techniques by measuring energy
transfer efficiency at varying depths and angles. Simultaneous power delivery
to multiple implants is also demonstrated.

24
The categories of this paper are: dg-ga
35
The categories of this paper are: mtrl-th
12
The categories of this paper are: nucl-th
31
The categories of this paper are: ao-sci
28
The categories of this paper are: alg-geom
27
The categories of this paper are: comp-gas
34
The categories of this paper are: chem-ph
30
The categories of this paper are: q-alg
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The categories of this paper are: solv-int
15
The categories of this paper are: nucl-ex
9
The categories of this paper are: nlin
18
The categories of this paper are: econ
21
The categories of this paper are: adap-org
2
The categories of this paper are: math
11
The categories of this paper are: hep-lat
0
The categories of this paper are: hep-ph