Embedded Resonances for Discrimination of Multiple Passive Nonlinear Targets Applicable to Dort

Abstract

This paper presents a method to distinguish multiple passive nonlinear targets, which can be applied to detection and selective wave focusing based on the decomposition of the time-reversal operator (DORT). A recent demonstration of DORT applied to harmonic scattering has shown that passive nonlinear targets (scatterers) can be detected in the presence of linear scatterers and separated into discrete eigenvalues. While DORT is effective in detecting multiple nonlinear targets, it could be difficult to discriminate these nonlinear scatters as their harmonic responses would look similar to each other. Our proposed approach to overcoming this difficulty is based on simply embedding a unique resonant notch in the second harmonic band for each nonlinear scatter, so as to make the notch appear in the associated eigenvalue, permitting identification and discrimination of the scatterer. We numerically demonstrate the basic feasibility of the proposed idea by considering various configurations in a two-dimensional model. The results show that a uniquely embedded resonant notch in a nonlinear target consistently appears in the corresponding eigenvalue of the time reversal operator, allowing it to be a reliable identifying feature. Further investigation into this technique holds promise towards smart wireless power transfer, biomedical, and IoT applications.

Detection of Electronic Devices Using FMCW Nonlinear Radar

“…Since σ is the apparent RCS as seen by the radar, it has the unit of [m 2 ]. But unlike linear RCS its value depends on the transmit power, gain, and distance, which determines the incident power level at the target as indicated in Equation (9). Depending on the incident power level at the target, the nonlinear response from the target varies.…”

“…For a given target with σ 2 , the apparent RCS can vary depending on the incident power level as indicated in Equation (9). To validate this, we obtain the values of σ at different incident power density levels (P t G t /4πR 2 ) by varying P t for three targets with the largest, middle, and smallest σ 2 .…”

“…Such a relationship can be attributed to two possible reasons: (1) the increase in the physical size of the target generally follows the size of the electronic boards within the target, which in turn increases n tgt G and tgt A of the target, and (2) the increase in the electronic board size should also be roughly proportional to the number of semiconductor devices, which may result in a higher level of excited harmonic response (i.e., increase in the values of n a ). For a given target with 2  , the apparent RCS can vary depending on the incident power level as indicated in Equation (9). To validate this, we obtain the values of   at different incident power density levels  .…”

“…Since natural linear scatterer and responses from other non-electronic objects do not produce nonlinear responses, it is possible to eliminate the linear response and only receive the desired nonlinear response from electronic devices. This allows for the effective detection of small electronic targets that would otherwise be difficult to achieve with linear radars [5][6][7][8][9][10][11][12]. Nonlinear radars can be utilized in various applications.…”

Ultrawideband planar bow‐tie with curved directive strips for gain enhancement

“…11 The initial motivation for obtaining added gain in the bow-tie antenna described here is due to its role as a scattering target in our active investigation of multistatic detection for smart far-field wireless power transmission. [12][13][14] This work employs a multistatic detection technique involving time-reversal and pulse inversion to permit nonlinear targets, formed by connecting a passive rectifier to an antenna (to form a rectenna), to be located and distinguished. Because this technique is based on detection of harmonic responses, the antenna must have an ultrawide bandwidth and enhanced gain will result in increased backscattered energy.…”