How to use mongoose-field-encryption with array type

I can use mongoose-field-encryption with string type putting in 'fields array'.

const messageSchema = new Schema({
  title: String,
  message: String,
  name: String
});

messageSchema.plugin(mongooseFieldEncryption, {
  fields: ["message", "name"],
  secret: "some secret key",
  saltGenerator: function(secret) {
    return "1234567890123456"; // should ideally use the secret to return a string of length 16
  }
});

But when I have array type in Schema, I can't encrypt the specific key in array.
For example,

{
 title: 'hey',
 car: [{
        engine: 'small',
        wheel: 'big'
       },
       {
        engine: 'small',
        wheel: 'big'
       },
 ] 
}

I can encrypt as below only one index.

fields: ["car[0].engine],

But I want to encrypt all engine value with one field.
I think I can't use '$elemMatch' here.
Is there other solution for this?
Thank you for reading it.