In　ultrasonic　testing,　omnidirectional　wave　propagation　presents　challenges　of　nonfocus　energy　loss　and　interface　interference.　Traditional　phased　array　(PA)　methods,　despite　their　focusing　capabilities,　suffer　from　limitations　in　energy　utilization　and　target　detection　accuracy.　Frequency　diverse　array　(FDA)　technology,　initially　developed　for　radar,　has　demonstrated　potential　for　improved　range-angle-dependent　ultrasonic　beampatterns　but　still　exhibits　limitations　due　to　S-shaped　coupling.　This　study　proposes　an　ultrasonic　nonlinear　frequency　diverse　array　(ultrasonic-NFDA)　with　nonuniform　frequency　offsets　to　address　these　issues.　The　ultrasonic-NFDA　employs　modulated　frequency　offsets　by　introducing　nonlinear　carrying　functions　and　incorporating　additional　parameters　to　manipulate　beamforming　and　enhances　energy　concentration　at　focal　points.　Furthermore,　the　multi-objective　differential　evolution　algorithm　is　used　for　parameter　optimization.　The　proposed　method　decouples　the　range-angle　beampattern　and　improves　the　signal-to-interference-plus-noise　ratio.　Numerical　evaluations　and　simulations　demonstrate　that　ultrasonic-NFDA　outperforms　the　ultrasonic　linear　FDA　and　PA　series,　achieving　better　peak　sidelobe　level　and　half-power　beam　width.　Experimental　validations　confirm　the　effectiveness　of　ultrasonic-NFDA　in　practical　ultrasonic　testing　scenarios,　showing　significant　improvements　in　defect　detection　and　imaging　clarity.　The　optimized　beampatterns　effectively　reduce　artifacts　and　enhance　the　precision　of　defect　localization.　The　proposed　integration　of　nonlinear　frequency　offsets　and　parameter　optimization　in　array　testing　offers　a　robust　solution　for　more　accurate　and　efficient　ultrasonic　inspection　methodologies.　©　The　Author(s)　2024.