Thermoacoustic imaging (TAI) is an emerging high-resolution and high-contrast imaging technology. In recent years, metal wires have been used in TAI experiments to quantitatively evaluate the spatial resolution of different systems. However, there is still a lack of analysis of the response characteristics and principles of metal wires in TAI. Through theoretical and simulation analyses, this paper proposes that the response of metal (copper) wires during TAI is equivalent to the response of antennas. More critically, the response of the copper wire is equivalent to the response of a half-wave dipole antenna. When its length is close to half the wavelength of the incident electromagnetic wave, it obtains the best response. In simulation, when the microwave excitation frequencies are 1.3 GHz, 3.0 GHz, and 5.3 GHz, and the lengths of copper wires are separately set to 11 cm, 5 cm, and 2.5 cm, the maximum SAR distribution and energy coupling e±ciency are obtained. This result is connected with the best response of half-wave dipole antennas with lengths of 11 cm, 4.77 cm, and 2.7 cm under the theoretical design, respectively. Regarding the further application, TAI can be used to conduct guided minimally invasive surgery on surgical instrument imaging. Thus, this paper indicated that results can also guide the design of metal surgical instruments utilized in different microwave frequencies.