Acoustic radiation efficiency is defined as the ratio of sound power radiated to the surface vibration power of a piston with equivalent surface area. It has been shown that the radiation efficiency is maximized and may exceed unity when the structural and acoustic wavelengths are approximately equal. The frequency at which this occurs is called the critical frequency and can be shifted with structural modifications. This has proven to be an effective way to reduce noise. The standard radiation efficiency measurement is comprised of an intensity scan for sound power measurement and accelerometer array for spatially averaged vibration determination. This method is difficult to apply to lightweight structures, complicated geometries, and when acoustic sources are in close proximity to one another. Recently, robust particle velocity sensors have been developed. Combined with a small microphone in the same instrument, particle velocity and sound pressure can be measured simultaneously and at the same location. This permits radiation efficiency to be measured using a non-contact approach with a single sensor. A suggested practice for measuring radiation efficiency has been developed and validated with several examples including two flat plates of different thickness, an oil pan, and components on a running small engine.

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This thesis investigates sound transmission loss through flat finite panels using composite materials, which incorporate both carbon and flax fibres. The study wascarried out by performing FEM simulations developed and validated in steps. Thevalidation process was time-consuming but crucial in ensuring the model’s reliability.The analysis demonstrates the relationship between the panels’ mass, stiffness, andsound reduction effectiveness by studying the sound transmission loss for a flat plate.The results show how by adjusting the plate’s stiffness, thickness, and mass one cancontrol its reaction to the incoming sound. This allows resonance frequencies to beshifted away from critical points and avoids coincidence frequencies. By understanding the acoustic behavior of composite panels, this research contributes to improvingsoundproofing properties while preserving their mechanical advantages. In an era ofgrowing demand for better acoustic performance in the automotive industry, exploring innovative methods to optimize the sound transmission loss of composite panelsis essential. / Denna studie undersöker ljudöverföringsförluster genom platta finita paneler sombestår av kompositmaterial, som innehåller både kol- och linfiber. Studien utförFEM-simuleringar som utvecklats och validerats i steg. Valideringsprocessen vartidskrävande men avgörande för att säkerställa modellernas tillförlitlighet. Analysenvisar sambandet mellan panelernas massa, styvhet och ljudreducerande effektivitetgenom att studera ljudtransmissionsförluster för en platt panel. Resultatet visarhur justering av plattans styvhet, tjocklek och massa kan styra dess reaktion på detinkommande ljudet, vilket gör att resonansfrekvenser kan flyttas bort från kritiskapunkter och undvika sammanfallande frekvenser. Genom att förstå det akustiskabeteendet hos kompositpaneler bidrar denna studie till att förbättra ljudisoleringsegenskaperna samtidigt som deras mekaniska fördelar bevaras. I en tid av växande efterfrågan på bättre akustisk prestanda inom bilindustrin, blir det viktigt att utforska innovativa metoder för att optimera ljudöverföringsförlusten hos kompositpaneler.