Helmholtz resonators (HRs) have been central in many acoustic metamaterial devices. For example, one can use an array of HRs to obtain negative effective bulk modulus or a panel of HRs to achieve total absorption of low-frequency sound. The aforementioned applications are based on the local monopolar resonance of each HR. However, the HR behaves differently in water. The elastic modulus of the resonator wall can become comparable to the modulus of water making the resonant frequency much lower than the rigid wall case. Moreover, considering the wall elasticity and mass leads to large structural asymmetry and induces cross-coupling between pressure and velocity fields. In this talk, we provide a lumped element model in order to predict the resonant frequency of the elastic HR. The model is demonstrated by sound scattering from an elastic HR in the context of acoustic bianisotropy, or Willis behavior, following a recent paper [Li Quan et al., Phys. Rev. Lett., 2018]. It is found that both the pressure and velocity fields can generate monopole and dipole responses from an elastic HR. The explicit example of an elastic HR in a one-dimensional waveguide will be discussed.Helmholtz resonators (HRs) have been central in many acoustic metamaterial devices. For example, one can use an array of HRs to obtain negative effective bulk modulus or a panel of HRs to achieve total absorption of low-frequency sound. The aforementioned applications are based on the local monopolar resonance of each HR. However, the HR behaves differently in water. The elastic modulus of the resonator wall can become comparable to the modulus of water making the resonant frequency much lower than the rigid wall case. Moreover, considering the wall elasticity and mass leads to large structural asymmetry and induces cross-coupling between pressure and velocity fields. In this talk, we provide a lumped element model in order to predict the resonant frequency of the elastic HR. The model is demonstrated by sound scattering from an elastic HR in the context of acoustic bianisotropy, or Willis behavior, following a recent paper [Li Quan et al., Phys. Rev. Lett., 2018]. It is found that both the pressure and v...