Our device functions in the kHz frequency domain in contrast with the theoretically predicted MHz domain which is characteristic for the generation of SAWs. We therefore precisely analyze the working principle and quality of our embedded-IDTs and define a mechanism for our observed acoustoinjection in the kHz frequency domain on our one chip device. By LDV measurements, we characterize the resonance frequencies and the characteristics of the acoustic fields when operating our acoustofluidic devices in the MHz and kHz frequency ranges with various input amplitudes. In the MHz domain, we observe a precisely focused SAW. However, infrared camera measurements clearly demonstrate that in the MHz frequency domain, much of the energy required for the droplet manipulation is lost as heat. When operating in the kHz frequency domain, our one-chip device transmits an acoustic pressure wave, with minimal thermal loses, causing destabilization of water-in-oil droplet interfaces and therefore enabling controlled injection of water-in-oil droplets on one, integrated chip. We characterize the substrate displacement, or actual mechanical propagation, of the produced acoustic fields to be the most efficient at a frequency of 10 kHz. The comparison of input/output power measurements of several devices on different substrates together with micro-CT images of the quality of the individual IDTs supports that our devices work reproducibly in the kHz frequency domain regardless of the quality of the IDTs. Finally, we use the newly developed device for the injection of water-in-oil droplets in the kHz frequency domain. We evaluate the injection efficiency for different surfactant concentrations, droplet passing speeds, injection rates, applied frequencies and amplitudes. With these experiments, we find perfect conditions in which 100 % of our passing droplets are injected at droplet passing rates up to 160 Hz, with the potential to progress to even higher passing speeds.