Optimization of linear permanent magnet synchronous motors for needle-free jet injection

We present a scaling model for linear permanent magnet synchronous motors applied to needle-free jet injection, a drug delivery technique that requires the generation of high fluid pressures. This model shows that either the motor stroke or the motor constant can be increased to reduce the electrical power required to perform an injection. We then present computationally efficient semi-analytical field solutions for a tubular linear synchronous motor, and use them to develop optimized motor designs for minimal jet injection power. A finite-permeability solution is developed and compared to both finite element results and a simplified infinite-permeability solution to validate the model and to establish criteria for choosing the back-iron thickness. We find that optimal jet injector motor configurations favor long stroke lengths, even at the expense of motor constant. However, designs constrained to physically reasonable motor lengths still offer an order of magnitude reduction in input power as compared to existing voice-coil-driven injection systems.